1 /*
2 * Copyright (c) 2008, 2025, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.access.SharedSecrets;
29 import jdk.internal.misc.Unsafe;
30 import jdk.internal.misc.VM;
31 import jdk.internal.reflect.CallerSensitive;
32 import jdk.internal.reflect.CallerSensitiveAdapter;
33 import jdk.internal.reflect.Reflection;
34 import jdk.internal.util.ClassFileDumper;
35 import jdk.internal.vm.annotation.ForceInline;
36 import jdk.internal.vm.annotation.Stable;
37 import sun.invoke.util.ValueConversions;
38 import sun.invoke.util.VerifyAccess;
39 import sun.invoke.util.Wrapper;
40
41 import java.lang.classfile.ClassFile;
42 import java.lang.classfile.ClassModel;
43 import java.lang.constant.ClassDesc;
44 import java.lang.constant.ConstantDescs;
45 import java.lang.invoke.LambdaForm.BasicType;
46 import java.lang.invoke.MethodHandleImpl.Intrinsic;
47 import java.lang.reflect.Constructor;
48 import java.lang.reflect.Field;
49 import java.lang.reflect.Member;
50 import java.lang.reflect.Method;
51 import java.lang.reflect.Modifier;
52 import java.nio.ByteOrder;
53 import java.security.ProtectionDomain;
54 import java.util.ArrayList;
55 import java.util.Arrays;
56 import java.util.BitSet;
57 import java.util.Comparator;
58 import java.util.Iterator;
59 import java.util.List;
60 import java.util.Objects;
61 import java.util.Set;
62 import java.util.concurrent.ConcurrentHashMap;
63 import java.util.stream.Stream;
64
65 import static java.lang.classfile.ClassFile.*;
66 import static java.lang.invoke.LambdaForm.BasicType.V_TYPE;
67 import static java.lang.invoke.MethodHandleNatives.Constants.*;
68 import static java.lang.invoke.MethodHandleStatics.*;
69 import static java.lang.invoke.MethodType.methodType;
70
71 /**
72 * This class consists exclusively of static methods that operate on or return
73 * method handles. They fall into several categories:
74 * <ul>
75 * <li>Lookup methods which help create method handles for methods and fields.
76 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
77 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
78 * </ul>
79 * A lookup, combinator, or factory method will fail and throw an
80 * {@code IllegalArgumentException} if the created method handle's type
81 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
82 *
83 * @author John Rose, JSR 292 EG
84 * @since 1.7
85 */
86 public final class MethodHandles {
87
88 private MethodHandles() { } // do not instantiate
89
90 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
91
92 // See IMPL_LOOKUP below.
93
94 //--- Method handle creation from ordinary methods.
95
96 /**
97 * Returns a {@link Lookup lookup object} with
98 * full capabilities to emulate all supported bytecode behaviors of the caller.
99 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller.
100 * Factory methods on the lookup object can create
101 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
102 * for any member that the caller has access to via bytecodes,
103 * including protected and private fields and methods.
104 * This lookup object is created by the original lookup class
105 * and has the {@link Lookup#ORIGINAL ORIGINAL} bit set.
106 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
107 * Do not store it in place where untrusted code can access it.
108 * <p>
109 * This method is caller sensitive, which means that it may return different
110 * values to different callers.
111 * In cases where {@code MethodHandles.lookup} is called from a context where
112 * there is no caller frame on the stack (e.g. when called directly
113 * from a JNI attached thread), {@code IllegalCallerException} is thrown.
114 * To obtain a {@link Lookup lookup object} in such a context, use an auxiliary class that will
115 * implicitly be identified as the caller, or use {@link MethodHandles#publicLookup()}
116 * to obtain a low-privileged lookup instead.
117 * @return a lookup object for the caller of this method, with
118 * {@linkplain Lookup#ORIGINAL original} and
119 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}.
120 * @throws IllegalCallerException if there is no caller frame on the stack.
121 */
122 @CallerSensitive
123 @ForceInline // to ensure Reflection.getCallerClass optimization
124 public static Lookup lookup() {
125 final Class<?> c = Reflection.getCallerClass();
126 if (c == null) {
127 throw new IllegalCallerException("no caller frame");
128 }
129 return new Lookup(c);
130 }
131
132 /**
133 * This lookup method is the alternate implementation of
134 * the lookup method with a leading caller class argument which is
135 * non-caller-sensitive. This method is only invoked by reflection
136 * and method handle.
137 */
138 @CallerSensitiveAdapter
139 private static Lookup lookup(Class<?> caller) {
140 if (caller.getClassLoader() == null) {
141 throw newInternalError("calling lookup() reflectively is not supported: "+caller);
142 }
143 return new Lookup(caller);
144 }
145
146 /**
147 * Returns a {@link Lookup lookup object} which is trusted minimally.
148 * The lookup has the {@code UNCONDITIONAL} mode.
149 * It can only be used to create method handles to public members of
150 * public classes in packages that are exported unconditionally.
151 * <p>
152 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
153 * of this lookup object will be {@link java.lang.Object}.
154 *
155 * @apiNote The use of Object is conventional, and because the lookup modes are
156 * limited, there is no special access provided to the internals of Object, its package
157 * or its module. This public lookup object or other lookup object with
158 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
159 * is not used to determine the lookup context.
160 *
161 * <p style="font-size:smaller;">
162 * <em>Discussion:</em>
163 * The lookup class can be changed to any other class {@code C} using an expression of the form
164 * {@link Lookup#in publicLookup().in(C.class)}.
165 * Also, it cannot access
166 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
167 * @return a lookup object which is trusted minimally
168 */
169 public static Lookup publicLookup() {
170 return Lookup.PUBLIC_LOOKUP;
171 }
172
173 /**
174 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
175 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>.
176 * The returned lookup object can provide access to classes in modules and packages,
177 * and members of those classes, outside the normal rules of Java access control,
178 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
179 * <p>
180 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
181 * allowed to do deep reflection on module {@code M2} and package of the target class
182 * if and only if all of the following conditions are {@code true}:
183 * <ul>
184 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess()
185 * full privilege access}. Specifically:
186 * <ul>
187 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
188 * (This is because otherwise there would be no way to ensure the original lookup
189 * creator was a member of any particular module, and so any subsequent checks
190 * for readability and qualified exports would become ineffective.)
191 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
192 * (This is because an application intending to share intra-module access
193 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
194 * deep reflection to its own module.)
195 * </ul>
196 * <li>The target class must be a proper class, not a primitive or array class.
197 * (Thus, {@code M2} is well-defined.)
198 * <li>If the caller module {@code M1} differs from
199 * the target module {@code M2} then both of the following must be true:
200 * <ul>
201 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
202 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
203 * containing the target class to at least {@code M1}.</li>
204 * </ul>
205 * </ul>
206 * <p>
207 * If any of the above checks is violated, this method fails with an
208 * exception.
209 * <p>
210 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
211 * returns a {@code Lookup} on {@code targetClass} with
212 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}
213 * with {@code null} previous lookup class.
214 * <p>
215 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
216 * returns a {@code Lookup} on {@code targetClass} that records
217 * the lookup class of the caller as the new previous lookup class with
218 * {@code PRIVATE} access but no {@code MODULE} access.
219 * <p>
220 * The resulting {@code Lookup} object has no {@code ORIGINAL} access.
221 *
222 * @apiNote The {@code Lookup} object returned by this method is allowed to
223 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
224 * of {@code targetClass}. Extreme caution should be taken when opening a package
225 * to another module as such defined classes have the same full privilege
226 * access as other members in {@code targetClass}'s module.
227 *
228 * @param targetClass the target class
229 * @param caller the caller lookup object
230 * @return a lookup object for the target class, with private access
231 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class
232 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
233 * @throws IllegalAccessException if any of the other access checks specified above fails
234 * @since 9
235 * @see Lookup#dropLookupMode
236 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
237 */
238 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
239 if (caller.allowedModes == Lookup.TRUSTED) {
240 return new Lookup(targetClass);
241 }
242
243 if (targetClass.isPrimitive())
244 throw new IllegalArgumentException(targetClass + " is a primitive class");
245 if (targetClass.isArray())
246 throw new IllegalArgumentException(targetClass + " is an array class");
247 // Ensure that we can reason accurately about private and module access.
248 int requireAccess = Lookup.PRIVATE|Lookup.MODULE;
249 if ((caller.lookupModes() & requireAccess) != requireAccess)
250 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode");
251
252 // previous lookup class is never set if it has MODULE access
253 assert caller.previousLookupClass() == null;
254
255 Class<?> callerClass = caller.lookupClass();
256 Module callerModule = callerClass.getModule(); // M1
257 Module targetModule = targetClass.getModule(); // M2
258 Class<?> newPreviousClass = null;
259 int newModes = Lookup.FULL_POWER_MODES & ~Lookup.ORIGINAL;
260
261 if (targetModule != callerModule) {
262 if (!callerModule.canRead(targetModule))
263 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
264 if (targetModule.isNamed()) {
265 String pn = targetClass.getPackageName();
266 assert !pn.isEmpty() : "unnamed package cannot be in named module";
267 if (!targetModule.isOpen(pn, callerModule))
268 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
269 }
270
271 // M2 != M1, set previous lookup class to M1 and drop MODULE access
272 newPreviousClass = callerClass;
273 newModes &= ~Lookup.MODULE;
274 }
275 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
276 }
277
278 /**
279 * Returns the <em>class data</em> associated with the lookup class
280 * of the given {@code caller} lookup object, or {@code null}.
281 *
282 * <p> A hidden class with class data can be created by calling
283 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
284 * Lookup::defineHiddenClassWithClassData}.
285 * This method will cause the static class initializer of the lookup
286 * class of the given {@code caller} lookup object be executed if
287 * it has not been initialized.
288 *
289 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
290 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
291 * {@code null} is returned if this method is called on the lookup object
292 * on these classes.
293 *
294 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
295 * must have {@linkplain Lookup#ORIGINAL original access}
296 * in order to retrieve the class data.
297 *
298 * @apiNote
299 * This method can be called as a bootstrap method for a dynamically computed
300 * constant. A framework can create a hidden class with class data, for
301 * example that can be {@code Class} or {@code MethodHandle} object.
302 * The class data is accessible only to the lookup object
303 * created by the original caller but inaccessible to other members
304 * in the same nest. If a framework passes security sensitive objects
305 * to a hidden class via class data, it is recommended to load the value
306 * of class data as a dynamically computed constant instead of storing
307 * the class data in private static field(s) which are accessible to
308 * other nestmates.
309 *
310 * @param <T> the type to cast the class data object to
311 * @param caller the lookup context describing the class performing the
312 * operation (normally stacked by the JVM)
313 * @param name must be {@link ConstantDescs#DEFAULT_NAME}
314 * ({@code "_"})
315 * @param type the type of the class data
316 * @return the value of the class data if present in the lookup class;
317 * otherwise {@code null}
318 * @throws IllegalArgumentException if name is not {@code "_"}
319 * @throws IllegalAccessException if the lookup context does not have
320 * {@linkplain Lookup#ORIGINAL original} access
321 * @throws ClassCastException if the class data cannot be converted to
322 * the given {@code type}
323 * @throws NullPointerException if {@code caller} or {@code type} argument
324 * is {@code null}
325 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
326 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
327 * @since 16
328 * @jvms 5.5 Initialization
329 */
330 public static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException {
331 Objects.requireNonNull(caller);
332 Objects.requireNonNull(type);
333 if (!ConstantDescs.DEFAULT_NAME.equals(name)) {
334 throw new IllegalArgumentException("name must be \"_\": " + name);
335 }
336
337 if ((caller.lookupModes() & Lookup.ORIGINAL) != Lookup.ORIGINAL) {
338 throw new IllegalAccessException(caller + " does not have ORIGINAL access");
339 }
340
341 Object classdata = classData(caller.lookupClass());
342 if (classdata == null) return null;
343
344 try {
345 return BootstrapMethodInvoker.widenAndCast(classdata, type);
346 } catch (RuntimeException|Error e) {
347 throw e; // let CCE and other runtime exceptions through
348 } catch (Throwable e) {
349 throw new InternalError(e);
350 }
351 }
352
353 /*
354 * Returns the class data set by the VM in the Class::classData field.
355 *
356 * This is also invoked by LambdaForms as it cannot use condy via
357 * MethodHandles::classData due to bootstrapping issue.
358 */
359 static Object classData(Class<?> c) {
360 UNSAFE.ensureClassInitialized(c);
361 return SharedSecrets.getJavaLangAccess().classData(c);
362 }
363
364 /**
365 * Returns the element at the specified index in the
366 * {@linkplain #classData(Lookup, String, Class) class data},
367 * if the class data associated with the lookup class
368 * of the given {@code caller} lookup object is a {@code List}.
369 * If the class data is not present in this lookup class, this method
370 * returns {@code null}.
371 *
372 * <p> A hidden class with class data can be created by calling
373 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
374 * Lookup::defineHiddenClassWithClassData}.
375 * This method will cause the static class initializer of the lookup
376 * class of the given {@code caller} lookup object be executed if
377 * it has not been initialized.
378 *
379 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
380 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
381 * {@code null} is returned if this method is called on the lookup object
382 * on these classes.
383 *
384 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
385 * must have {@linkplain Lookup#ORIGINAL original access}
386 * in order to retrieve the class data.
387 *
388 * @apiNote
389 * This method can be called as a bootstrap method for a dynamically computed
390 * constant. A framework can create a hidden class with class data, for
391 * example that can be {@code List.of(o1, o2, o3....)} containing more than
392 * one object and use this method to load one element at a specific index.
393 * The class data is accessible only to the lookup object
394 * created by the original caller but inaccessible to other members
395 * in the same nest. If a framework passes security sensitive objects
396 * to a hidden class via class data, it is recommended to load the value
397 * of class data as a dynamically computed constant instead of storing
398 * the class data in private static field(s) which are accessible to other
399 * nestmates.
400 *
401 * @param <T> the type to cast the result object to
402 * @param caller the lookup context describing the class performing the
403 * operation (normally stacked by the JVM)
404 * @param name must be {@link java.lang.constant.ConstantDescs#DEFAULT_NAME}
405 * ({@code "_"})
406 * @param type the type of the element at the given index in the class data
407 * @param index index of the element in the class data
408 * @return the element at the given index in the class data
409 * if the class data is present; otherwise {@code null}
410 * @throws IllegalArgumentException if name is not {@code "_"}
411 * @throws IllegalAccessException if the lookup context does not have
412 * {@linkplain Lookup#ORIGINAL original} access
413 * @throws ClassCastException if the class data cannot be converted to {@code List}
414 * or the element at the specified index cannot be converted to the given type
415 * @throws IndexOutOfBoundsException if the index is out of range
416 * @throws NullPointerException if {@code caller} or {@code type} argument is
417 * {@code null}; or if unboxing operation fails because
418 * the element at the given index is {@code null}
419 *
420 * @since 16
421 * @see #classData(Lookup, String, Class)
422 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
423 */
424 public static <T> T classDataAt(Lookup caller, String name, Class<T> type, int index)
425 throws IllegalAccessException
426 {
427 @SuppressWarnings("unchecked")
428 List<Object> classdata = (List<Object>)classData(caller, name, List.class);
429 if (classdata == null) return null;
430
431 try {
432 Object element = classdata.get(index);
433 return BootstrapMethodInvoker.widenAndCast(element, type);
434 } catch (RuntimeException|Error e) {
435 throw e; // let specified exceptions and other runtime exceptions/errors through
436 } catch (Throwable e) {
437 throw new InternalError(e);
438 }
439 }
440
441 /**
442 * Performs an unchecked "crack" of a
443 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
444 * The result is as if the user had obtained a lookup object capable enough
445 * to crack the target method handle, called
446 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
447 * on the target to obtain its symbolic reference, and then called
448 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
449 * to resolve the symbolic reference to a member.
450 * @param <T> the desired type of the result, either {@link Member} or a subtype
451 * @param expected a class object representing the desired result type {@code T}
452 * @param target a direct method handle to crack into symbolic reference components
453 * @return a reference to the method, constructor, or field object
454 * @throws NullPointerException if either argument is {@code null}
455 * @throws IllegalArgumentException if the target is not a direct method handle
456 * @throws ClassCastException if the member is not of the expected type
457 * @since 1.8
458 */
459 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) {
460 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
461 return lookup.revealDirect(target).reflectAs(expected, lookup);
462 }
463
464 /**
465 * A <em>lookup object</em> is a factory for creating method handles,
466 * when the creation requires access checking.
467 * Method handles do not perform
468 * access checks when they are called, but rather when they are created.
469 * Therefore, method handle access
470 * restrictions must be enforced when a method handle is created.
471 * The caller class against which those restrictions are enforced
472 * is known as the {@linkplain #lookupClass() lookup class}.
473 * <p>
474 * A lookup class which needs to create method handles will call
475 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
476 * When the {@code Lookup} factory object is created, the identity of the lookup class is
477 * determined, and securely stored in the {@code Lookup} object.
478 * The lookup class (or its delegates) may then use factory methods
479 * on the {@code Lookup} object to create method handles for access-checked members.
480 * This includes all methods, constructors, and fields which are allowed to the lookup class,
481 * even private ones.
482 *
483 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
484 * The factory methods on a {@code Lookup} object correspond to all major
485 * use cases for methods, constructors, and fields.
486 * Each method handle created by a factory method is the functional
487 * equivalent of a particular <em>bytecode behavior</em>.
488 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of
489 * the Java Virtual Machine Specification.)
490 * Here is a summary of the correspondence between these factory methods and
491 * the behavior of the resulting method handles:
492 * <table class="striped">
493 * <caption style="display:none">lookup method behaviors</caption>
494 * <thead>
495 * <tr>
496 * <th scope="col"><a id="equiv"></a>lookup expression</th>
497 * <th scope="col">member</th>
498 * <th scope="col">bytecode behavior</th>
499 * </tr>
500 * </thead>
501 * <tbody>
502 * <tr>
503 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
504 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
505 * </tr>
506 * <tr>
507 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
508 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
509 * </tr>
510 * <tr>
511 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
512 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
513 * </tr>
514 * <tr>
515 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
516 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
517 * </tr>
518 * <tr>
519 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
520 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
521 * </tr>
522 * <tr>
523 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
524 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
525 * </tr>
526 * <tr>
527 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
528 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
529 * </tr>
530 * <tr>
531 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
532 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
533 * </tr>
534 * <tr>
535 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
536 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
537 * </tr>
538 * <tr>
539 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
540 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
541 * </tr>
542 * <tr>
543 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
544 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
545 * </tr>
546 * <tr>
547 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
548 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
549 * </tr>
550 * <tr>
551 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th>
552 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
553 * </tr>
554 * <tr>
555 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
556 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
557 * </tr>
558 * </tbody>
559 * </table>
560 *
561 * Here, the type {@code C} is the class or interface being searched for a member,
562 * documented as a parameter named {@code refc} in the lookup methods.
563 * The method type {@code MT} is composed from the return type {@code T}
564 * and the sequence of argument types {@code A*}.
565 * The constructor also has a sequence of argument types {@code A*} and
566 * is deemed to return the newly-created object of type {@code C}.
567 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
568 * The formal parameter {@code this} stands for the self-reference of type {@code C};
569 * if it is present, it is always the leading argument to the method handle invocation.
570 * (In the case of some {@code protected} members, {@code this} may be
571 * restricted in type to the lookup class; see below.)
572 * The name {@code arg} stands for all the other method handle arguments.
573 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
574 * stands for a null reference if the accessed method or field is static,
575 * and {@code this} otherwise.
576 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
577 * for reflective objects corresponding to the given members declared in type {@code C}.
578 * <p>
579 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
580 * as if by {@code ldc CONSTANT_Class}.
581 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
582 * <p>
583 * In cases where the given member is of variable arity (i.e., a method or constructor)
584 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
585 * In all other cases, the returned method handle will be of fixed arity.
586 * <p style="font-size:smaller;">
587 * <em>Discussion:</em>
588 * The equivalence between looked-up method handles and underlying
589 * class members and bytecode behaviors
590 * can break down in a few ways:
591 * <ul style="font-size:smaller;">
592 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
593 * the lookup can still succeed, even when there is no equivalent
594 * Java expression or bytecoded constant.
595 * <li>Likewise, if {@code T} or {@code MT}
596 * is not symbolically accessible from the lookup class's loader,
597 * the lookup can still succeed.
598 * For example, lookups for {@code MethodHandle.invokeExact} and
599 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
600 * <li>If the looked-up method has a
601 * <a href="MethodHandle.html#maxarity">very large arity</a>,
602 * the method handle creation may fail with an
603 * {@code IllegalArgumentException}, due to the method handle type having
604 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
605 * </ul>
606 *
607 * <h2><a id="access"></a>Access checking</h2>
608 * Access checks are applied in the factory methods of {@code Lookup},
609 * when a method handle is created.
610 * This is a key difference from the Core Reflection API, since
611 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
612 * performs access checking against every caller, on every call.
613 * <p>
614 * All access checks start from a {@code Lookup} object, which
615 * compares its recorded lookup class against all requests to
616 * create method handles.
617 * A single {@code Lookup} object can be used to create any number
618 * of access-checked method handles, all checked against a single
619 * lookup class.
620 * <p>
621 * A {@code Lookup} object can be shared with other trusted code,
622 * such as a metaobject protocol.
623 * A shared {@code Lookup} object delegates the capability
624 * to create method handles on private members of the lookup class.
625 * Even if privileged code uses the {@code Lookup} object,
626 * the access checking is confined to the privileges of the
627 * original lookup class.
628 * <p>
629 * A lookup can fail, because
630 * the containing class is not accessible to the lookup class, or
631 * because the desired class member is missing, or because the
632 * desired class member is not accessible to the lookup class, or
633 * because the lookup object is not trusted enough to access the member.
634 * In the case of a field setter function on a {@code final} field,
635 * finality enforcement is treated as a kind of access control,
636 * and the lookup will fail, except in special cases of
637 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
638 * In any of these cases, a {@code ReflectiveOperationException} will be
639 * thrown from the attempted lookup. The exact class will be one of
640 * the following:
641 * <ul>
642 * <li>NoSuchMethodException — if a method is requested but does not exist
643 * <li>NoSuchFieldException — if a field is requested but does not exist
644 * <li>IllegalAccessException — if the member exists but an access check fails
645 * </ul>
646 * <p>
647 * In general, the conditions under which a method handle may be
648 * looked up for a method {@code M} are no more restrictive than the conditions
649 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
650 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
651 * a method handle lookup will generally raise a corresponding
652 * checked exception, such as {@code NoSuchMethodException}.
653 * And the effect of invoking the method handle resulting from the lookup
654 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
655 * to executing the compiled, verified, and resolved call to {@code M}.
656 * The same point is true of fields and constructors.
657 * <p style="font-size:smaller;">
658 * <em>Discussion:</em>
659 * Access checks only apply to named and reflected methods,
660 * constructors, and fields.
661 * Other method handle creation methods, such as
662 * {@link MethodHandle#asType MethodHandle.asType},
663 * do not require any access checks, and are used
664 * independently of any {@code Lookup} object.
665 * <p>
666 * If the desired member is {@code protected}, the usual JVM rules apply,
667 * including the requirement that the lookup class must either be in the
668 * same package as the desired member, or must inherit that member.
669 * (See the Java Virtual Machine Specification, sections {@jvms
670 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.)
671 * In addition, if the desired member is a non-static field or method
672 * in a different package, the resulting method handle may only be applied
673 * to objects of the lookup class or one of its subclasses.
674 * This requirement is enforced by narrowing the type of the leading
675 * {@code this} parameter from {@code C}
676 * (which will necessarily be a superclass of the lookup class)
677 * to the lookup class itself.
678 * <p>
679 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
680 * that the receiver argument must match both the resolved method <em>and</em>
681 * the current class. Again, this requirement is enforced by narrowing the
682 * type of the leading parameter to the resulting method handle.
683 * (See the Java Virtual Machine Specification, section {@jvms 4.10.1.9}.)
684 * <p>
685 * The JVM represents constructors and static initializer blocks as internal methods
686 * with special names ({@value ConstantDescs#INIT_NAME} and {@value
687 * ConstantDescs#CLASS_INIT_NAME}).
688 * The internal syntax of invocation instructions allows them to refer to such internal
689 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
690 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
691 * <p>
692 * If the relationship between nested types is expressed directly through the
693 * {@code NestHost} and {@code NestMembers} attributes
694 * (see the Java Virtual Machine Specification, sections {@jvms
695 * 4.7.28} and {@jvms 4.7.29}),
696 * then the associated {@code Lookup} object provides direct access to
697 * the lookup class and all of its nestmates
698 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
699 * Otherwise, access between nested classes is obtained by the Java compiler creating
700 * a wrapper method to access a private method of another class in the same nest.
701 * For example, a nested class {@code C.D}
702 * can access private members within other related classes such as
703 * {@code C}, {@code C.D.E}, or {@code C.B},
704 * but the Java compiler may need to generate wrapper methods in
705 * those related classes. In such cases, a {@code Lookup} object on
706 * {@code C.E} would be unable to access those private members.
707 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
708 * which can transform a lookup on {@code C.E} into one on any of those other
709 * classes, without special elevation of privilege.
710 * <p>
711 * The accesses permitted to a given lookup object may be limited,
712 * according to its set of {@link #lookupModes lookupModes},
713 * to a subset of members normally accessible to the lookup class.
714 * For example, the {@link MethodHandles#publicLookup publicLookup}
715 * method produces a lookup object which is only allowed to access
716 * public members in public classes of exported packages.
717 * The caller sensitive method {@link MethodHandles#lookup lookup}
718 * produces a lookup object with full capabilities relative to
719 * its caller class, to emulate all supported bytecode behaviors.
720 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
721 * with fewer access modes than the original lookup object.
722 *
723 * <p style="font-size:smaller;">
724 * <a id="privacc"></a>
725 * <em>Discussion of private and module access:</em>
726 * We say that a lookup has <em>private access</em>
727 * if its {@linkplain #lookupModes lookup modes}
728 * include the possibility of accessing {@code private} members
729 * (which includes the private members of nestmates).
730 * As documented in the relevant methods elsewhere,
731 * only lookups with private access possess the following capabilities:
732 * <ul style="font-size:smaller;">
733 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
734 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
735 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
736 * within the same package member
737 * </ul>
738 * <p style="font-size:smaller;">
739 * Similarly, a lookup with module access ensures that the original lookup creator was
740 * a member in the same module as the lookup class.
741 * <p style="font-size:smaller;">
742 * Private and module access are independently determined modes; a lookup may have
743 * either or both or neither. A lookup which possesses both access modes is said to
744 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}.
745 * <p style="font-size:smaller;">
746 * A lookup with <em>original access</em> ensures that this lookup is created by
747 * the original lookup class and the bootstrap method invoked by the VM.
748 * Such a lookup with original access also has private and module access
749 * which has the following additional capability:
750 * <ul style="font-size:smaller;">
751 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
752 * such as {@code Class.forName}
753 * <li>obtain the {@linkplain MethodHandles#classData(Lookup, String, Class)
754 * class data} associated with the lookup class</li>
755 * </ul>
756 * <p style="font-size:smaller;">
757 * Each of these permissions is a consequence of the fact that a lookup object
758 * with private access can be securely traced back to an originating class,
759 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
760 * can be reliably determined and emulated by method handles.
761 *
762 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
763 * When a lookup class in one module {@code M1} accesses a class in another module
764 * {@code M2}, extra access checking is performed beyond the access mode bits.
765 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
766 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
767 * and when the type is in a package of {@code M2} that is exported to
768 * at least {@code M1}.
769 * <p>
770 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
771 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
772 * MethodHandles.privateLookupIn} methods.
773 * Teleporting across modules will always record the original lookup class as
774 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
775 * and drops {@link Lookup#MODULE MODULE} access.
776 * If the target class is in the same module as the lookup class {@code C},
777 * then the target class becomes the new lookup class
778 * and there is no change to the previous lookup class.
779 * If the target class is in a different module from {@code M1} ({@code C}'s module),
780 * {@code C} becomes the new previous lookup class
781 * and the target class becomes the new lookup class.
782 * In that case, if there was already a previous lookup class in {@code M0},
783 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
784 * drops all privileges.
785 * For example,
786 * {@snippet lang="java" :
787 * Lookup lookup = MethodHandles.lookup(); // in class C
788 * Lookup lookup2 = lookup.in(D.class);
789 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
790 * }
791 * <p>
792 * The {@link #lookup()} factory method produces a {@code Lookup} object
793 * with {@code null} previous lookup class.
794 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
795 * to class {@code D} without elevation of privileges.
796 * If {@code C} and {@code D} are in the same module,
797 * {@code lookup2} records {@code D} as the new lookup class and keeps the
798 * same previous lookup class as the original {@code lookup}, or
799 * {@code null} if not present.
800 * <p>
801 * When a {@code Lookup} teleports from a class
802 * in one nest to another nest, {@code PRIVATE} access is dropped.
803 * When a {@code Lookup} teleports from a class in one package to
804 * another package, {@code PACKAGE} access is dropped.
805 * When a {@code Lookup} teleports from a class in one module to another module,
806 * {@code MODULE} access is dropped.
807 * Teleporting across modules drops the ability to access non-exported classes
808 * in both the module of the new lookup class and the module of the old lookup class
809 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
810 * A {@code Lookup} can teleport back and forth to a class in the module of
811 * the lookup class and the module of the previous class lookup.
812 * Teleporting across modules can only decrease access but cannot increase it.
813 * Teleporting to some third module drops all accesses.
814 * <p>
815 * In the above example, if {@code C} and {@code D} are in different modules,
816 * {@code lookup2} records {@code D} as its lookup class and
817 * {@code C} as its previous lookup class and {@code lookup2} has only
818 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
819 * {@code C}'s module and {@code D}'s module.
820 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
821 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
822 * class {@code D} is recorded as its previous lookup class.
823 * <p>
824 * Teleporting across modules restricts access to the public types that
825 * both the lookup class and the previous lookup class can equally access
826 * (see below).
827 * <p>
828 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
829 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
830 * and produce a new {@code Lookup} with <a href="#privacc">private access</a>
831 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
832 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
833 * to call {@code privateLookupIn}.
834 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
835 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
836 * produces a new {@code Lookup} on {@code T} with full capabilities.
837 * A {@code lookup} on {@code C} is also allowed
838 * to do deep reflection on {@code T} in another module {@code M2} if
839 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
840 * the package containing {@code T} to at least {@code M1}.
841 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
842 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
843 * The resulting {@code Lookup} can be used to do member lookup or teleport
844 * to another lookup class by calling {@link #in Lookup::in}. But
845 * it cannot be used to obtain another private {@code Lookup} by calling
846 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
847 * because it has no {@code MODULE} access.
848 * <p>
849 * The {@code Lookup} object returned by {@code privateLookupIn} is allowed to
850 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
851 * of {@code T}. Extreme caution should be taken when opening a package
852 * to another module as such defined classes have the same full privilege
853 * access as other members in {@code M2}.
854 *
855 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
856 *
857 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
858 * allows cross-module access. The access checking is performed with respect
859 * to both the lookup class and the previous lookup class if present.
860 * <p>
861 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
862 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
863 * exported unconditionally}.
864 * <p>
865 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
866 * the lookup with {@link #PUBLIC} mode can access all public types in modules
867 * that are readable to {@code M1} and the type is in a package that is exported
868 * at least to {@code M1}.
869 * <p>
870 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
871 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
872 * the intersection of all public types that are accessible to {@code M1}
873 * with all public types that are accessible to {@code M0}. {@code M0}
874 * reads {@code M1} and hence the set of accessible types includes:
875 *
876 * <ul>
877 * <li>unconditional-exported packages from {@code M1}</li>
878 * <li>unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</li>
879 * <li>
880 * unconditional-exported packages from a third module {@code M2}if both {@code M0}
881 * and {@code M1} read {@code M2}
882 * </li>
883 * <li>qualified-exported packages from {@code M1} to {@code M0}</li>
884 * <li>qualified-exported packages from {@code M0} to {@code M1} if {@code M1} reads {@code M0}</li>
885 * <li>
886 * qualified-exported packages from a third module {@code M2} to both {@code M0} and
887 * {@code M1} if both {@code M0} and {@code M1} read {@code M2}
888 * </li>
889 * </ul>
890 *
891 * <h2><a id="access-modes"></a>Access modes</h2>
892 *
893 * The table below shows the access modes of a {@code Lookup} produced by
894 * any of the following factory or transformation methods:
895 * <ul>
896 * <li>{@link #lookup() MethodHandles::lookup}</li>
897 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li>
898 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li>
899 * <li>{@link Lookup#in Lookup::in}</li>
900 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li>
901 * </ul>
902 *
903 * <table class="striped">
904 * <caption style="display:none">
905 * Access mode summary
906 * </caption>
907 * <thead>
908 * <tr>
909 * <th scope="col">Lookup object</th>
910 * <th style="text-align:center">original</th>
911 * <th style="text-align:center">protected</th>
912 * <th style="text-align:center">private</th>
913 * <th style="text-align:center">package</th>
914 * <th style="text-align:center">module</th>
915 * <th style="text-align:center">public</th>
916 * </tr>
917 * </thead>
918 * <tbody>
919 * <tr>
920 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
921 * <td style="text-align:center">ORI</td>
922 * <td style="text-align:center">PRO</td>
923 * <td style="text-align:center">PRI</td>
924 * <td style="text-align:center">PAC</td>
925 * <td style="text-align:center">MOD</td>
926 * <td style="text-align:center">1R</td>
927 * </tr>
928 * <tr>
929 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
930 * <td></td>
931 * <td></td>
932 * <td></td>
933 * <td style="text-align:center">PAC</td>
934 * <td style="text-align:center">MOD</td>
935 * <td style="text-align:center">1R</td>
936 * </tr>
937 * <tr>
938 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
939 * <td></td>
940 * <td></td>
941 * <td></td>
942 * <td></td>
943 * <td style="text-align:center">MOD</td>
944 * <td style="text-align:center">1R</td>
945 * </tr>
946 * <tr>
947 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
948 * <td></td>
949 * <td></td>
950 * <td></td>
951 * <td></td>
952 * <td></td>
953 * <td style="text-align:center">2R</td>
954 * </tr>
955 * <tr>
956 * <th scope="row" style="text-align:left">{@code CL.in(D).in(C)} hop back to module</th>
957 * <td></td>
958 * <td></td>
959 * <td></td>
960 * <td></td>
961 * <td></td>
962 * <td style="text-align:center">2R</td>
963 * </tr>
964 * <tr>
965 * <th scope="row" style="text-align:left">{@code PRI1 = privateLookupIn(C1,CL)}</th>
966 * <td></td>
967 * <td style="text-align:center">PRO</td>
968 * <td style="text-align:center">PRI</td>
969 * <td style="text-align:center">PAC</td>
970 * <td style="text-align:center">MOD</td>
971 * <td style="text-align:center">1R</td>
972 * </tr>
973 * <tr>
974 * <th scope="row" style="text-align:left">{@code PRI1a = privateLookupIn(C,PRI1)}</th>
975 * <td></td>
976 * <td style="text-align:center">PRO</td>
977 * <td style="text-align:center">PRI</td>
978 * <td style="text-align:center">PAC</td>
979 * <td style="text-align:center">MOD</td>
980 * <td style="text-align:center">1R</td>
981 * </tr>
982 * <tr>
983 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} same package</th>
984 * <td></td>
985 * <td></td>
986 * <td></td>
987 * <td style="text-align:center">PAC</td>
988 * <td style="text-align:center">MOD</td>
989 * <td style="text-align:center">1R</td>
990 * </tr>
991 * <tr>
992 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} different package</th>
993 * <td></td>
994 * <td></td>
995 * <td></td>
996 * <td></td>
997 * <td style="text-align:center">MOD</td>
998 * <td style="text-align:center">1R</td>
999 * </tr>
1000 * <tr>
1001 * <th scope="row" style="text-align:left">{@code PRI1.in(D)} different module</th>
1002 * <td></td>
1003 * <td></td>
1004 * <td></td>
1005 * <td></td>
1006 * <td></td>
1007 * <td style="text-align:center">2R</td>
1008 * </tr>
1009 * <tr>
1010 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PROTECTED)}</th>
1011 * <td></td>
1012 * <td></td>
1013 * <td style="text-align:center">PRI</td>
1014 * <td style="text-align:center">PAC</td>
1015 * <td style="text-align:center">MOD</td>
1016 * <td style="text-align:center">1R</td>
1017 * </tr>
1018 * <tr>
1019 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PRIVATE)}</th>
1020 * <td></td>
1021 * <td></td>
1022 * <td></td>
1023 * <td style="text-align:center">PAC</td>
1024 * <td style="text-align:center">MOD</td>
1025 * <td style="text-align:center">1R</td>
1026 * </tr>
1027 * <tr>
1028 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PACKAGE)}</th>
1029 * <td></td>
1030 * <td></td>
1031 * <td></td>
1032 * <td></td>
1033 * <td style="text-align:center">MOD</td>
1034 * <td style="text-align:center">1R</td>
1035 * </tr>
1036 * <tr>
1037 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(MODULE)}</th>
1038 * <td></td>
1039 * <td></td>
1040 * <td></td>
1041 * <td></td>
1042 * <td></td>
1043 * <td style="text-align:center">1R</td>
1044 * </tr>
1045 * <tr>
1046 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PUBLIC)}</th>
1047 * <td></td>
1048 * <td></td>
1049 * <td></td>
1050 * <td></td>
1051 * <td></td>
1052 * <td style="text-align:center">none</td>
1053 * <tr>
1054 * <th scope="row" style="text-align:left">{@code PRI2 = privateLookupIn(D,CL)}</th>
1055 * <td></td>
1056 * <td style="text-align:center">PRO</td>
1057 * <td style="text-align:center">PRI</td>
1058 * <td style="text-align:center">PAC</td>
1059 * <td></td>
1060 * <td style="text-align:center">2R</td>
1061 * </tr>
1062 * <tr>
1063 * <th scope="row" style="text-align:left">{@code privateLookupIn(D,PRI1)}</th>
1064 * <td></td>
1065 * <td style="text-align:center">PRO</td>
1066 * <td style="text-align:center">PRI</td>
1067 * <td style="text-align:center">PAC</td>
1068 * <td></td>
1069 * <td style="text-align:center">2R</td>
1070 * </tr>
1071 * <tr>
1072 * <th scope="row" style="text-align:left">{@code privateLookupIn(C,PRI2)} fails</th>
1073 * <td></td>
1074 * <td></td>
1075 * <td></td>
1076 * <td></td>
1077 * <td></td>
1078 * <td style="text-align:center">IAE</td>
1079 * </tr>
1080 * <tr>
1081 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} same package</th>
1082 * <td></td>
1083 * <td></td>
1084 * <td></td>
1085 * <td style="text-align:center">PAC</td>
1086 * <td></td>
1087 * <td style="text-align:center">2R</td>
1088 * </tr>
1089 * <tr>
1090 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} different package</th>
1091 * <td></td>
1092 * <td></td>
1093 * <td></td>
1094 * <td></td>
1095 * <td></td>
1096 * <td style="text-align:center">2R</td>
1097 * </tr>
1098 * <tr>
1099 * <th scope="row" style="text-align:left">{@code PRI2.in(C1)} hop back to module</th>
1100 * <td></td>
1101 * <td></td>
1102 * <td></td>
1103 * <td></td>
1104 * <td></td>
1105 * <td style="text-align:center">2R</td>
1106 * </tr>
1107 * <tr>
1108 * <th scope="row" style="text-align:left">{@code PRI2.in(E)} hop to third module</th>
1109 * <td></td>
1110 * <td></td>
1111 * <td></td>
1112 * <td></td>
1113 * <td></td>
1114 * <td style="text-align:center">none</td>
1115 * </tr>
1116 * <tr>
1117 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PROTECTED)}</th>
1118 * <td></td>
1119 * <td></td>
1120 * <td style="text-align:center">PRI</td>
1121 * <td style="text-align:center">PAC</td>
1122 * <td></td>
1123 * <td style="text-align:center">2R</td>
1124 * </tr>
1125 * <tr>
1126 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PRIVATE)}</th>
1127 * <td></td>
1128 * <td></td>
1129 * <td></td>
1130 * <td style="text-align:center">PAC</td>
1131 * <td></td>
1132 * <td style="text-align:center">2R</td>
1133 * </tr>
1134 * <tr>
1135 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PACKAGE)}</th>
1136 * <td></td>
1137 * <td></td>
1138 * <td></td>
1139 * <td></td>
1140 * <td></td>
1141 * <td style="text-align:center">2R</td>
1142 * </tr>
1143 * <tr>
1144 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(MODULE)}</th>
1145 * <td></td>
1146 * <td></td>
1147 * <td></td>
1148 * <td></td>
1149 * <td></td>
1150 * <td style="text-align:center">2R</td>
1151 * </tr>
1152 * <tr>
1153 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PUBLIC)}</th>
1154 * <td></td>
1155 * <td></td>
1156 * <td></td>
1157 * <td></td>
1158 * <td></td>
1159 * <td style="text-align:center">none</td>
1160 * </tr>
1161 * <tr>
1162 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PROTECTED)}</th>
1163 * <td></td>
1164 * <td></td>
1165 * <td style="text-align:center">PRI</td>
1166 * <td style="text-align:center">PAC</td>
1167 * <td style="text-align:center">MOD</td>
1168 * <td style="text-align:center">1R</td>
1169 * </tr>
1170 * <tr>
1171 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PRIVATE)}</th>
1172 * <td></td>
1173 * <td></td>
1174 * <td></td>
1175 * <td style="text-align:center">PAC</td>
1176 * <td style="text-align:center">MOD</td>
1177 * <td style="text-align:center">1R</td>
1178 * </tr>
1179 * <tr>
1180 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PACKAGE)}</th>
1181 * <td></td>
1182 * <td></td>
1183 * <td></td>
1184 * <td></td>
1185 * <td style="text-align:center">MOD</td>
1186 * <td style="text-align:center">1R</td>
1187 * </tr>
1188 * <tr>
1189 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(MODULE)}</th>
1190 * <td></td>
1191 * <td></td>
1192 * <td></td>
1193 * <td></td>
1194 * <td></td>
1195 * <td style="text-align:center">1R</td>
1196 * </tr>
1197 * <tr>
1198 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PUBLIC)}</th>
1199 * <td></td>
1200 * <td></td>
1201 * <td></td>
1202 * <td></td>
1203 * <td></td>
1204 * <td style="text-align:center">none</td>
1205 * </tr>
1206 * <tr>
1207 * <th scope="row" style="text-align:left">{@code PUB = publicLookup()}</th>
1208 * <td></td>
1209 * <td></td>
1210 * <td></td>
1211 * <td></td>
1212 * <td></td>
1213 * <td style="text-align:center">U</td>
1214 * </tr>
1215 * <tr>
1216 * <th scope="row" style="text-align:left">{@code PUB.in(D)} different module</th>
1217 * <td></td>
1218 * <td></td>
1219 * <td></td>
1220 * <td></td>
1221 * <td></td>
1222 * <td style="text-align:center">U</td>
1223 * </tr>
1224 * <tr>
1225 * <th scope="row" style="text-align:left">{@code PUB.in(D).in(E)} third module</th>
1226 * <td></td>
1227 * <td></td>
1228 * <td></td>
1229 * <td></td>
1230 * <td></td>
1231 * <td style="text-align:center">U</td>
1232 * </tr>
1233 * <tr>
1234 * <th scope="row" style="text-align:left">{@code PUB.dropLookupMode(UNCONDITIONAL)}</th>
1235 * <td></td>
1236 * <td></td>
1237 * <td></td>
1238 * <td></td>
1239 * <td></td>
1240 * <td style="text-align:center">none</td>
1241 * </tr>
1242 * <tr>
1243 * <th scope="row" style="text-align:left">{@code privateLookupIn(C1,PUB)} fails</th>
1244 * <td></td>
1245 * <td></td>
1246 * <td></td>
1247 * <td></td>
1248 * <td></td>
1249 * <td style="text-align:center">IAE</td>
1250 * </tr>
1251 * <tr>
1252 * <th scope="row" style="text-align:left">{@code ANY.in(X)}, for inaccessible {@code X}</th>
1253 * <td></td>
1254 * <td></td>
1255 * <td></td>
1256 * <td></td>
1257 * <td></td>
1258 * <td style="text-align:center">none</td>
1259 * </tr>
1260 * </tbody>
1261 * </table>
1262 *
1263 * <p>
1264 * Notes:
1265 * <ul>
1266 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1267 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1268 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1269 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1270 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set,
1271 * {@code PRO} indicates {@link #PROTECTED} bit set,
1272 * {@code PRI} indicates {@link #PRIVATE} bit set,
1273 * {@code PAC} indicates {@link #PACKAGE} bit set,
1274 * {@code MOD} indicates {@link #MODULE} bit set,
1275 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1276 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1277 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1278 * <li>Public access comes in three kinds:
1279 * <ul>
1280 * <li>unconditional ({@code U}): the lookup assumes readability.
1281 * The lookup has {@code null} previous lookup class.
1282 * <li>one-module-reads ({@code 1R}): the module access checking is
1283 * performed with respect to the lookup class. The lookup has {@code null}
1284 * previous lookup class.
1285 * <li>two-module-reads ({@code 2R}): the module access checking is
1286 * performed with respect to the lookup class and the previous lookup class.
1287 * The lookup has a non-null previous lookup class which is in a
1288 * different module from the current lookup class.
1289 * </ul>
1290 * <li>Any attempt to reach a third module loses all access.</li>
1291 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1292 * all access modes are dropped.</li>
1293 * </ul>
1294 *
1295 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1296 * A small number of Java methods have a special property called caller sensitivity.
1297 * A <em>caller-sensitive</em> method can behave differently depending on the
1298 * identity of its immediate caller.
1299 * <p>
1300 * If a method handle for a caller-sensitive method is requested,
1301 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1302 * but they take account of the lookup class in a special way.
1303 * The resulting method handle behaves as if it were called
1304 * from an instruction contained in the lookup class,
1305 * so that the caller-sensitive method detects the lookup class.
1306 * (By contrast, the invoker of the method handle is disregarded.)
1307 * Thus, in the case of caller-sensitive methods,
1308 * different lookup classes may give rise to
1309 * differently behaving method handles.
1310 * <p>
1311 * In cases where the lookup object is
1312 * {@link MethodHandles#publicLookup() publicLookup()},
1313 * or some other lookup object without the
1314 * {@linkplain #ORIGINAL original access},
1315 * the lookup class is disregarded.
1316 * In such cases, no caller-sensitive method handle can be created,
1317 * access is forbidden, and the lookup fails with an
1318 * {@code IllegalAccessException}.
1319 * <p style="font-size:smaller;">
1320 * <em>Discussion:</em>
1321 * For example, the caller-sensitive method
1322 * {@link java.lang.Class#forName(String) Class.forName(x)}
1323 * can return varying classes or throw varying exceptions,
1324 * depending on the class loader of the class that calls it.
1325 * A public lookup of {@code Class.forName} will fail, because
1326 * there is no reasonable way to determine its bytecode behavior.
1327 * <p style="font-size:smaller;">
1328 * If an application caches method handles for broad sharing,
1329 * it should use {@code publicLookup()} to create them.
1330 * If there is a lookup of {@code Class.forName}, it will fail,
1331 * and the application must take appropriate action in that case.
1332 * It may be that a later lookup, perhaps during the invocation of a
1333 * bootstrap method, can incorporate the specific identity
1334 * of the caller, making the method accessible.
1335 * <p style="font-size:smaller;">
1336 * The function {@code MethodHandles.lookup} is caller sensitive
1337 * so that there can be a secure foundation for lookups.
1338 * Nearly all other methods in the JSR 292 API rely on lookup
1339 * objects to check access requests.
1340 */
1341 public static final
1342 class Lookup {
1343 /** The class on behalf of whom the lookup is being performed. */
1344 private final Class<?> lookupClass;
1345
1346 /** previous lookup class */
1347 private final Class<?> prevLookupClass;
1348
1349 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1350 private final int allowedModes;
1351
1352 static {
1353 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1354 }
1355
1356 /** A single-bit mask representing {@code public} access,
1357 * which may contribute to the result of {@link #lookupModes lookupModes}.
1358 * The value, {@code 0x01}, happens to be the same as the value of the
1359 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1360 * <p>
1361 * A {@code Lookup} with this lookup mode performs cross-module access check
1362 * with respect to the {@linkplain #lookupClass() lookup class} and
1363 * {@linkplain #previousLookupClass() previous lookup class} if present.
1364 */
1365 public static final int PUBLIC = Modifier.PUBLIC;
1366
1367 /** A single-bit mask representing {@code private} access,
1368 * which may contribute to the result of {@link #lookupModes lookupModes}.
1369 * The value, {@code 0x02}, happens to be the same as the value of the
1370 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1371 */
1372 public static final int PRIVATE = Modifier.PRIVATE;
1373
1374 /** A single-bit mask representing {@code protected} access,
1375 * which may contribute to the result of {@link #lookupModes lookupModes}.
1376 * The value, {@code 0x04}, happens to be the same as the value of the
1377 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1378 */
1379 public static final int PROTECTED = Modifier.PROTECTED;
1380
1381 /** A single-bit mask representing {@code package} access (default access),
1382 * which may contribute to the result of {@link #lookupModes lookupModes}.
1383 * The value is {@code 0x08}, which does not correspond meaningfully to
1384 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1385 */
1386 public static final int PACKAGE = Modifier.STATIC;
1387
1388 /** A single-bit mask representing {@code module} access,
1389 * which may contribute to the result of {@link #lookupModes lookupModes}.
1390 * The value is {@code 0x10}, which does not correspond meaningfully to
1391 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1392 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1393 * with this lookup mode can access all public types in the module of the
1394 * lookup class and public types in packages exported by other modules
1395 * to the module of the lookup class.
1396 * <p>
1397 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1398 * previous lookup class} is always {@code null}.
1399 *
1400 * @since 9
1401 */
1402 public static final int MODULE = PACKAGE << 1;
1403
1404 /** A single-bit mask representing {@code unconditional} access
1405 * which may contribute to the result of {@link #lookupModes lookupModes}.
1406 * The value is {@code 0x20}, which does not correspond meaningfully to
1407 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1408 * A {@code Lookup} with this lookup mode assumes {@linkplain
1409 * java.lang.Module#canRead(java.lang.Module) readability}.
1410 * This lookup mode can access all public members of public types
1411 * of all modules when the type is in a package that is {@link
1412 * java.lang.Module#isExported(String) exported unconditionally}.
1413 *
1414 * <p>
1415 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1416 * previous lookup class} is always {@code null}.
1417 *
1418 * @since 9
1419 * @see #publicLookup()
1420 */
1421 public static final int UNCONDITIONAL = PACKAGE << 2;
1422
1423 /** A single-bit mask representing {@code original} access
1424 * which may contribute to the result of {@link #lookupModes lookupModes}.
1425 * The value is {@code 0x40}, which does not correspond meaningfully to
1426 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1427 *
1428 * <p>
1429 * If this lookup mode is set, the {@code Lookup} object must be
1430 * created by the original lookup class by calling
1431 * {@link MethodHandles#lookup()} method or by a bootstrap method
1432 * invoked by the VM. The {@code Lookup} object with this lookup
1433 * mode has {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1434 *
1435 * @since 16
1436 */
1437 public static final int ORIGINAL = PACKAGE << 3;
1438
1439 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL);
1440 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); // with original access
1441 private static final int TRUSTED = -1;
1442
1443 /*
1444 * Adjust PUBLIC => PUBLIC|MODULE|ORIGINAL|UNCONDITIONAL
1445 * Adjust 0 => PACKAGE
1446 */
1447 private static int fixmods(int mods) {
1448 mods &= (ALL_MODES - PACKAGE - MODULE - ORIGINAL - UNCONDITIONAL);
1449 if (Modifier.isPublic(mods))
1450 mods |= UNCONDITIONAL;
1451 return (mods != 0) ? mods : PACKAGE;
1452 }
1453
1454 /** Tells which class is performing the lookup. It is this class against
1455 * which checks are performed for visibility and access permissions.
1456 * <p>
1457 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1458 * access checks are performed against both the lookup class and the previous lookup class.
1459 * <p>
1460 * The class implies a maximum level of access permission,
1461 * but the permissions may be additionally limited by the bitmask
1462 * {@link #lookupModes lookupModes}, which controls whether non-public members
1463 * can be accessed.
1464 * @return the lookup class, on behalf of which this lookup object finds members
1465 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1466 */
1467 public Class<?> lookupClass() {
1468 return lookupClass;
1469 }
1470
1471 /** Reports a lookup class in another module that this lookup object
1472 * was previously teleported from, or {@code null}.
1473 * <p>
1474 * A {@code Lookup} object produced by the factory methods, such as the
1475 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1476 * has {@code null} previous lookup class.
1477 * A {@code Lookup} object has a non-null previous lookup class
1478 * when this lookup was teleported from an old lookup class
1479 * in one module to a new lookup class in another module.
1480 *
1481 * @return the lookup class in another module that this lookup object was
1482 * previously teleported from, or {@code null}
1483 * @since 14
1484 * @see #in(Class)
1485 * @see MethodHandles#privateLookupIn(Class, Lookup)
1486 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1487 */
1488 public Class<?> previousLookupClass() {
1489 return prevLookupClass;
1490 }
1491
1492 // This is just for calling out to MethodHandleImpl.
1493 private Class<?> lookupClassOrNull() {
1494 return (allowedModes == TRUSTED) ? null : lookupClass;
1495 }
1496
1497 /** Tells which access-protection classes of members this lookup object can produce.
1498 * The result is a bit-mask of the bits
1499 * {@linkplain #PUBLIC PUBLIC (0x01)},
1500 * {@linkplain #PRIVATE PRIVATE (0x02)},
1501 * {@linkplain #PROTECTED PROTECTED (0x04)},
1502 * {@linkplain #PACKAGE PACKAGE (0x08)},
1503 * {@linkplain #MODULE MODULE (0x10)},
1504 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)},
1505 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}.
1506 * <p>
1507 * A freshly-created lookup object
1508 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1509 * all possible bits set, except {@code UNCONDITIONAL}.
1510 * A lookup object on a new lookup class
1511 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1512 * may have some mode bits set to zero.
1513 * Mode bits can also be
1514 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1515 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1516 * The purpose of this is to restrict access via the new lookup object,
1517 * so that it can access only names which can be reached by the original
1518 * lookup object, and also by the new lookup class.
1519 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1520 * @see #in
1521 * @see #dropLookupMode
1522 */
1523 public int lookupModes() {
1524 return allowedModes & ALL_MODES;
1525 }
1526
1527 /** Embody the current class (the lookupClass) as a lookup class
1528 * for method handle creation.
1529 * Must be called by from a method in this package,
1530 * which in turn is called by a method not in this package.
1531 */
1532 Lookup(Class<?> lookupClass) {
1533 this(lookupClass, null, FULL_POWER_MODES);
1534 }
1535
1536 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1537 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1538 && prevLookupClass.getModule() != lookupClass.getModule());
1539 assert !lookupClass.isArray() && !lookupClass.isPrimitive();
1540 this.lookupClass = lookupClass;
1541 this.prevLookupClass = prevLookupClass;
1542 this.allowedModes = allowedModes;
1543 }
1544
1545 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1546 // make sure we haven't accidentally picked up a privileged class:
1547 checkUnprivilegedlookupClass(lookupClass);
1548 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1549 }
1550
1551 /**
1552 * Creates a lookup on the specified new lookup class.
1553 * The resulting object will report the specified
1554 * class as its own {@link #lookupClass() lookupClass}.
1555 *
1556 * <p>
1557 * However, the resulting {@code Lookup} object is guaranteed
1558 * to have no more access capabilities than the original.
1559 * In particular, access capabilities can be lost as follows:<ul>
1560 * <li>If the new lookup class is different from the old lookup class,
1561 * i.e. {@link #ORIGINAL ORIGINAL} access is lost.
1562 * <li>If the new lookup class is in a different module from the old one,
1563 * i.e. {@link #MODULE MODULE} access is lost.
1564 * <li>If the new lookup class is in a different package
1565 * than the old one, protected and default (package) members will not be accessible,
1566 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1567 * <li>If the new lookup class is not within the same package member
1568 * as the old one, private members will not be accessible, and protected members
1569 * will not be accessible by virtue of inheritance,
1570 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1571 * (Protected members may continue to be accessible because of package sharing.)
1572 * <li>If the new lookup class is not
1573 * {@linkplain #accessClass(Class) accessible} to this lookup,
1574 * then no members, not even public members, will be accessible
1575 * i.e. all access modes are lost.
1576 * <li>If the new lookup class, the old lookup class and the previous lookup class
1577 * are all in different modules i.e. teleporting to a third module,
1578 * all access modes are lost.
1579 * </ul>
1580 * <p>
1581 * The new previous lookup class is chosen as follows:
1582 * <ul>
1583 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1584 * the new previous lookup class is {@code null}.
1585 * <li>If the new lookup class is in the same module as the old lookup class,
1586 * the new previous lookup class is the old previous lookup class.
1587 * <li>If the new lookup class is in a different module from the old lookup class,
1588 * the new previous lookup class is the old lookup class.
1589 *</ul>
1590 * <p>
1591 * The resulting lookup's capabilities for loading classes
1592 * (used during {@link #findClass} invocations)
1593 * are determined by the lookup class' loader,
1594 * which may change due to this operation.
1595 *
1596 * @param requestedLookupClass the desired lookup class for the new lookup object
1597 * @return a lookup object which reports the desired lookup class, or the same object
1598 * if there is no change
1599 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class
1600 * @throws NullPointerException if the argument is null
1601 *
1602 * @see #accessClass(Class)
1603 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1604 */
1605 public Lookup in(Class<?> requestedLookupClass) {
1606 Objects.requireNonNull(requestedLookupClass);
1607 if (requestedLookupClass.isPrimitive())
1608 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1609 if (requestedLookupClass.isArray())
1610 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1611
1612 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1613 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1614 if (requestedLookupClass == this.lookupClass)
1615 return this; // keep same capabilities
1616 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL;
1617 Module fromModule = this.lookupClass.getModule();
1618 Module targetModule = requestedLookupClass.getModule();
1619 Class<?> plc = this.previousLookupClass();
1620 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1621 assert plc == null;
1622 newModes = UNCONDITIONAL;
1623 } else if (fromModule != targetModule) {
1624 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1625 // allow hopping back and forth between fromModule and plc's module
1626 // but not the third module
1627 newModes = 0;
1628 }
1629 // drop MODULE access
1630 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1631 // teleport from this lookup class
1632 plc = this.lookupClass;
1633 }
1634 if ((newModes & PACKAGE) != 0
1635 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1636 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1637 }
1638 // Allow nestmate lookups to be created without special privilege:
1639 if ((newModes & PRIVATE) != 0
1640 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1641 newModes &= ~(PRIVATE|PROTECTED);
1642 }
1643 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1644 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1645 // The requested class it not accessible from the lookup class.
1646 // No permissions.
1647 newModes = 0;
1648 }
1649 return newLookup(requestedLookupClass, plc, newModes);
1650 }
1651
1652 /**
1653 * Creates a lookup on the same lookup class which this lookup object
1654 * finds members, but with a lookup mode that has lost the given lookup mode.
1655 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1656 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED},
1657 * {@link #PRIVATE PRIVATE}, {@link #ORIGINAL ORIGINAL}, or
1658 * {@link #UNCONDITIONAL UNCONDITIONAL}.
1659 *
1660 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup},
1661 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set.
1662 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting
1663 * lookup has no access.
1664 *
1665 * <p> If this lookup is not a public lookup, then the following applies
1666 * regardless of its {@linkplain #lookupModes() lookup modes}.
1667 * {@link #PROTECTED PROTECTED} and {@link #ORIGINAL ORIGINAL} are always
1668 * dropped and so the resulting lookup mode will never have these access
1669 * capabilities. When dropping {@code PACKAGE}
1670 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE}
1671 * access. When dropping {@code MODULE} then the resulting lookup will not
1672 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access.
1673 * When dropping {@code PUBLIC} then the resulting lookup has no access.
1674 *
1675 * @apiNote
1676 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1677 * delegate non-public access within the package of the lookup class without
1678 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1679 * A lookup with {@code MODULE} but not
1680 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1681 * the module of the lookup class without conferring package access.
1682 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1683 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1684 * to public classes accessible to both the module of the lookup class
1685 * and the module of the previous lookup class.
1686 *
1687 * @param modeToDrop the lookup mode to drop
1688 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1689 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1690 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE}, {@code ORIGINAL}
1691 * or {@code UNCONDITIONAL}
1692 * @see MethodHandles#privateLookupIn
1693 * @since 9
1694 */
1695 public Lookup dropLookupMode(int modeToDrop) {
1696 int oldModes = lookupModes();
1697 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL);
1698 switch (modeToDrop) {
1699 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1700 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1701 case PACKAGE: newModes &= ~(PRIVATE); break;
1702 case PROTECTED:
1703 case PRIVATE:
1704 case ORIGINAL:
1705 case UNCONDITIONAL: break;
1706 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1707 }
1708 if (newModes == oldModes) return this; // return self if no change
1709 return newLookup(lookupClass(), previousLookupClass(), newModes);
1710 }
1711
1712 /**
1713 * Creates and links a class or interface from {@code bytes}
1714 * with the same class loader and in the same runtime package and
1715 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1716 * {@linkplain #lookupClass() lookup class} as if calling
1717 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1718 * ClassLoader::defineClass}.
1719 *
1720 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1721 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1722 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1723 * that the lookup object was created by a caller in the runtime package (or derived
1724 * from a lookup originally created by suitably privileged code to a target class in
1725 * the runtime package). </p>
1726 *
1727 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1728 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1729 * same package as the lookup class. </p>
1730 *
1731 * <p> This method does not run the class initializer. The class initializer may
1732 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1733 * Specification</em>. </p>
1734 *
1735 * @param bytes the class bytes
1736 * @return the {@code Class} object for the class
1737 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1738 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1739 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
1740 * than the lookup class or {@code bytes} is not a class or interface
1741 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
1742 * @throws VerifyError if the newly created class cannot be verified
1743 * @throws LinkageError if the newly created class cannot be linked for any other reason
1744 * @throws NullPointerException if {@code bytes} is {@code null}
1745 * @since 9
1746 * @see MethodHandles#privateLookupIn
1747 * @see Lookup#dropLookupMode
1748 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1749 */
1750 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1751 if ((lookupModes() & PACKAGE) == 0)
1752 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1753 return makeClassDefiner(bytes.clone()).defineClass(false);
1754 }
1755
1756 /**
1757 * The set of class options that specify whether a hidden class created by
1758 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
1759 * Lookup::defineHiddenClass} method is dynamically added as a new member
1760 * to the nest of a lookup class and/or whether a hidden class has
1761 * a strong relationship with the class loader marked as its defining loader.
1762 *
1763 * @since 15
1764 */
1765 public enum ClassOption {
1766 /**
1767 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest}
1768 * of a lookup class as a nestmate.
1769 *
1770 * <p> A hidden nestmate class has access to the private members of all
1771 * classes and interfaces in the same nest.
1772 *
1773 * @see Class#getNestHost()
1774 */
1775 NESTMATE(NESTMATE_CLASS),
1776
1777 /**
1778 * Specifies that a hidden class has a <em>strong</em>
1779 * relationship with the class loader marked as its defining loader,
1780 * as a normal class or interface has with its own defining loader.
1781 * This means that the hidden class may be unloaded if and only if
1782 * its defining loader is not reachable and thus may be reclaimed
1783 * by a garbage collector (JLS {@jls 12.7}).
1784 *
1785 * <p> By default, a hidden class or interface may be unloaded
1786 * even if the class loader that is marked as its defining loader is
1787 * <a href="../ref/package-summary.html#reachability">reachable</a>.
1788
1789 *
1790 * @jls 12.7 Unloading of Classes and Interfaces
1791 */
1792 STRONG(STRONG_LOADER_LINK);
1793
1794 /* the flag value is used by VM at define class time */
1795 private final int flag;
1796 ClassOption(int flag) {
1797 this.flag = flag;
1798 }
1799
1800 static int optionsToFlag(ClassOption[] options) {
1801 int flags = 0;
1802 for (ClassOption cp : options) {
1803 if ((flags & cp.flag) != 0) {
1804 throw new IllegalArgumentException("Duplicate ClassOption " + cp);
1805 }
1806 flags |= cp.flag;
1807 }
1808 return flags;
1809 }
1810 }
1811
1812 /**
1813 * Creates a <em>hidden</em> class or interface from {@code bytes},
1814 * returning a {@code Lookup} on the newly created class or interface.
1815 *
1816 * <p> Ordinarily, a class or interface {@code C} is created by a class loader,
1817 * which either defines {@code C} directly or delegates to another class loader.
1818 * A class loader defines {@code C} directly by invoking
1819 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1820 * ClassLoader::defineClass}, which causes the Java Virtual Machine
1821 * to derive {@code C} from a purported representation in {@code class} file format.
1822 * In situations where use of a class loader is undesirable, a class or interface
1823 * {@code C} can be created by this method instead. This method is capable of
1824 * defining {@code C}, and thereby creating it, without invoking
1825 * {@code ClassLoader::defineClass}.
1826 * Instead, this method defines {@code C} as if by arranging for
1827 * the Java Virtual Machine to derive a nonarray class or interface {@code C}
1828 * from a purported representation in {@code class} file format
1829 * using the following rules:
1830 *
1831 * <ol>
1832 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup}
1833 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access.
1834 * This level of access is needed to create {@code C} in the module
1835 * of the lookup class of this {@code Lookup}.</li>
1836 *
1837 * <li> The purported representation in {@code bytes} must be a {@code ClassFile}
1838 * structure (JVMS {@jvms 4.1}) of a supported major and minor version.
1839 * The major and minor version may differ from the {@code class} file version
1840 * of the lookup class of this {@code Lookup}.</li>
1841 *
1842 * <li> The value of {@code this_class} must be a valid index in the
1843 * {@code constant_pool} table, and the entry at that index must be a valid
1844 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name
1845 * encoded in internal form that is specified by this structure. {@code N} must
1846 * denote a class or interface in the same package as the lookup class.</li>
1847 *
1848 * <li> Let {@code CN} be the string {@code N + "." + <suffix>},
1849 * where {@code <suffix>} is an unqualified name.
1850 *
1851 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by
1852 * {@code bytes} with an additional entry in the {@code constant_pool} table,
1853 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and
1854 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class}
1855 * refers to the new {@code CONSTANT_Utf8_info} structure.
1856 *
1857 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}.
1858 *
1859 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and
1860 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5},
1861 * with the following adjustments:
1862 * <ul>
1863 * <li> The constant indicated by {@code this_class} is permitted to specify a name
1864 * that includes a single {@code "."} character, even though this is not a valid
1865 * binary class or interface name in internal form.</li>
1866 *
1867 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C},
1868 * but no class loader is recorded as an initiating class loader of {@code C}.</li>
1869 *
1870 * <li> {@code C} is considered to have the same runtime
1871 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module}
1872 * and {@linkplain java.security.ProtectionDomain protection domain}
1873 * as the lookup class of this {@code Lookup}.
1874 * <li> Let {@code GN} be the binary name obtained by taking {@code N}
1875 * (a binary name encoded in internal form) and replacing ASCII forward slashes with
1876 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}:
1877 * <ul>
1878 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>},
1879 * even though this is not a valid binary class or interface name.</li>
1880 * <li> {@link Class#descriptorString()} returns the string
1881 * {@code "L" + N + "." + <suffix> + ";"},
1882 * even though this is not a valid type descriptor name.</li>
1883 * <li> {@link Class#describeConstable()} returns an empty optional as {@code C}
1884 * cannot be described in {@linkplain java.lang.constant.ClassDesc nominal form}.</li>
1885 * </ul>
1886 * </ul>
1887 * </li>
1888 * </ol>
1889 *
1890 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine.
1891 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments:
1892 * <ul>
1893 * <li> During verification, whenever it is necessary to load the class named
1894 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is
1895 * made of any class loader.</li>
1896 *
1897 * <li> On any attempt to resolve the entry in the run-time constant pool indicated
1898 * by {@code this_class}, the symbolic reference is considered to be resolved to
1899 * {@code C} and resolution always succeeds immediately.</li>
1900 * </ul>
1901 *
1902 * <p> If the {@code initialize} parameter is {@code true},
1903 * then {@code C} is initialized by the Java Virtual Machine.
1904 *
1905 * <p> The newly created class or interface {@code C} serves as the
1906 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object
1907 * returned by this method. {@code C} is <em>hidden</em> in the sense that
1908 * no other class or interface can refer to {@code C} via a constant pool entry.
1909 * That is, a hidden class or interface cannot be named as a supertype, a field type,
1910 * a method parameter type, or a method return type by any other class.
1911 * This is because a hidden class or interface does not have a binary name, so
1912 * there is no internal form available to record in any class's constant pool.
1913 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)},
1914 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and
1915 * is not {@linkplain java.instrument/java.lang.instrument.Instrumentation#isModifiableClass(Class)
1916 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html">
1917 * JVM Tool Interface</a>.
1918 *
1919 * <p> A class or interface created by
1920 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1921 * a class loader} has a strong relationship with that class loader.
1922 * That is, every {@code Class} object contains a reference to the {@code ClassLoader}
1923 * that {@linkplain Class#getClassLoader() defined it}.
1924 * This means that a class created by a class loader may be unloaded if and
1925 * only if its defining loader is not reachable and thus may be reclaimed
1926 * by a garbage collector (JLS {@jls 12.7}).
1927 *
1928 * By default, however, a hidden class or interface may be unloaded even if
1929 * the class loader that is marked as its defining loader is
1930 * <a href="../ref/package-summary.html#reachability">reachable</a>.
1931 * This behavior is useful when a hidden class or interface serves multiple
1932 * classes defined by arbitrary class loaders. In other cases, a hidden
1933 * class or interface may be linked to a single class (or a small number of classes)
1934 * with the same defining loader as the hidden class or interface.
1935 * In such cases, where the hidden class or interface must be coterminous
1936 * with a normal class or interface, the {@link ClassOption#STRONG STRONG}
1937 * option may be passed in {@code options}.
1938 * This arranges for a hidden class to have the same strong relationship
1939 * with the class loader marked as its defining loader,
1940 * as a normal class or interface has with its own defining loader.
1941 *
1942 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass}
1943 * may still prevent a hidden class or interface from being
1944 * unloaded by ensuring that the {@code Class} object is reachable.
1945 *
1946 * <p> The unloading characteristics are set for each hidden class when it is
1947 * defined, and cannot be changed later. An advantage of allowing hidden classes
1948 * to be unloaded independently of the class loader marked as their defining loader
1949 * is that a very large number of hidden classes may be created by an application.
1950 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory,
1951 * just as if normal classes were created by class loaders.
1952 *
1953 * <p> Classes and interfaces in a nest are allowed to have mutual access to
1954 * their private members. The nest relationship is determined by
1955 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and
1956 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file.
1957 * By default, a hidden class belongs to a nest consisting only of itself
1958 * because a hidden class has no binary name.
1959 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options}
1960 * to create a hidden class or interface {@code C} as a member of a nest.
1961 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute
1962 * in the {@code ClassFile} structure from which {@code C} was derived.
1963 * Instead, the following rules determine the nest host of {@code C}:
1964 * <ul>
1965 * <li>If the nest host of the lookup class of this {@code Lookup} has previously
1966 * been determined, then let {@code H} be the nest host of the lookup class.
1967 * Otherwise, the nest host of the lookup class is determined using the
1968 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li>
1969 * <li>The nest host of {@code C} is determined to be {@code H},
1970 * the nest host of the lookup class.</li>
1971 * </ul>
1972 *
1973 * <p> A hidden class or interface may be serializable, but this requires a custom
1974 * serialization mechanism in order to ensure that instances are properly serialized
1975 * and deserialized. The default serialization mechanism supports only classes and
1976 * interfaces that are discoverable by their class name.
1977 *
1978 * @param bytes the bytes that make up the class data,
1979 * in the format of a valid {@code class} file as defined by
1980 * <cite>The Java Virtual Machine Specification</cite>.
1981 * @param initialize if {@code true} the class will be initialized.
1982 * @param options {@linkplain ClassOption class options}
1983 * @return the {@code Lookup} object on the hidden class,
1984 * with {@linkplain #ORIGINAL original} and
1985 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
1986 *
1987 * @throws IllegalAccessException if this {@code Lookup} does not have
1988 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
1989 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1990 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
1991 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
1992 * than the lookup class or {@code bytes} is not a class or interface
1993 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
1994 * @throws IncompatibleClassChangeError if the class or interface named as
1995 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
1996 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
1997 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
1998 * {@code C} is {@code C} itself
1999 * @throws VerifyError if the newly created class cannot be verified
2000 * @throws LinkageError if the newly created class cannot be linked for any other reason
2001 * @throws NullPointerException if any parameter is {@code null}
2002 *
2003 * @since 15
2004 * @see Class#isHidden()
2005 * @jvms 4.2.1 Binary Class and Interface Names
2006 * @jvms 4.2.2 Unqualified Names
2007 * @jvms 4.7.28 The {@code NestHost} Attribute
2008 * @jvms 4.7.29 The {@code NestMembers} Attribute
2009 * @jvms 5.4.3.1 Class and Interface Resolution
2010 * @jvms 5.4.4 Access Control
2011 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2012 * @jvms 5.4 Linking
2013 * @jvms 5.5 Initialization
2014 * @jls 12.7 Unloading of Classes and Interfaces
2015 */
2016 @SuppressWarnings("doclint:reference") // cross-module links
2017 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options)
2018 throws IllegalAccessException
2019 {
2020 Objects.requireNonNull(bytes);
2021 int flags = ClassOption.optionsToFlag(options);
2022 if (!hasFullPrivilegeAccess()) {
2023 throw new IllegalAccessException(this + " does not have full privilege access");
2024 }
2025
2026 return makeHiddenClassDefiner(bytes.clone(), false, flags).defineClassAsLookup(initialize);
2027 }
2028
2029 /**
2030 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated
2031 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data},
2032 * returning a {@code Lookup} on the newly created class or interface.
2033 *
2034 * <p> This method is equivalent to calling
2035 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)}
2036 * as if the hidden class is injected with a private static final <i>unnamed</i>
2037 * field which is initialized with the given {@code classData} at
2038 * the first instruction of the class initializer.
2039 * The newly created class is linked by the Java Virtual Machine.
2040 *
2041 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData}
2042 * and {@link MethodHandles#classDataAt(Lookup, String, Class, int) MethodHandles::classDataAt}
2043 * methods can be used to retrieve the {@code classData}.
2044 *
2045 * @apiNote
2046 * A framework can create a hidden class with class data with one or more
2047 * objects and load the class data as dynamically-computed constant(s)
2048 * via a bootstrap method. {@link MethodHandles#classData(Lookup, String, Class)
2049 * Class data} is accessible only to the lookup object created by the newly
2050 * defined hidden class but inaccessible to other members in the same nest
2051 * (unlike private static fields that are accessible to nestmates).
2052 * Care should be taken w.r.t. mutability for example when passing
2053 * an array or other mutable structure through the class data.
2054 * Changing any value stored in the class data at runtime may lead to
2055 * unpredictable behavior.
2056 * If the class data is a {@code List}, it is good practice to make it
2057 * unmodifiable for example via {@link List#of List::of}.
2058 *
2059 * @param bytes the class bytes
2060 * @param classData pre-initialized class data
2061 * @param initialize if {@code true} the class will be initialized.
2062 * @param options {@linkplain ClassOption class options}
2063 * @return the {@code Lookup} object on the hidden class,
2064 * with {@linkplain #ORIGINAL original} and
2065 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2066 *
2067 * @throws IllegalAccessException if this {@code Lookup} does not have
2068 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2069 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2070 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2071 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2072 * than the lookup class or {@code bytes} is not a class or interface
2073 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2074 * @throws IncompatibleClassChangeError if the class or interface named as
2075 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2076 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2077 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2078 * {@code C} is {@code C} itself
2079 * @throws VerifyError if the newly created class cannot be verified
2080 * @throws LinkageError if the newly created class cannot be linked for any other reason
2081 * @throws NullPointerException if any parameter is {@code null}
2082 *
2083 * @since 16
2084 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
2085 * @see Class#isHidden()
2086 * @see MethodHandles#classData(Lookup, String, Class)
2087 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
2088 * @jvms 4.2.1 Binary Class and Interface Names
2089 * @jvms 4.2.2 Unqualified Names
2090 * @jvms 4.7.28 The {@code NestHost} Attribute
2091 * @jvms 4.7.29 The {@code NestMembers} Attribute
2092 * @jvms 5.4.3.1 Class and Interface Resolution
2093 * @jvms 5.4.4 Access Control
2094 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2095 * @jvms 5.4 Linking
2096 * @jvms 5.5 Initialization
2097 * @jls 12.7 Unloading of Classes and Interfaces
2098 */
2099 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options)
2100 throws IllegalAccessException
2101 {
2102 Objects.requireNonNull(bytes);
2103 Objects.requireNonNull(classData);
2104
2105 int flags = ClassOption.optionsToFlag(options);
2106
2107 if (!hasFullPrivilegeAccess()) {
2108 throw new IllegalAccessException(this + " does not have full privilege access");
2109 }
2110
2111 return makeHiddenClassDefiner(bytes.clone(), false, flags)
2112 .defineClassAsLookup(initialize, classData);
2113 }
2114
2115 // A default dumper for writing class files passed to Lookup::defineClass
2116 // and Lookup::defineHiddenClass to disk for debugging purposes. To enable,
2117 // set -Djdk.invoke.MethodHandle.dumpHiddenClassFiles or
2118 // -Djdk.invoke.MethodHandle.dumpHiddenClassFiles=true
2119 //
2120 // This default dumper does not dump hidden classes defined by LambdaMetafactory
2121 // and LambdaForms and method handle internals. They are dumped via
2122 // different ClassFileDumpers.
2123 private static ClassFileDumper defaultDumper() {
2124 return DEFAULT_DUMPER;
2125 }
2126
2127 private static final ClassFileDumper DEFAULT_DUMPER = ClassFileDumper.getInstance(
2128 "jdk.invoke.MethodHandle.dumpClassFiles", "DUMP_CLASS_FILES");
2129
2130 /**
2131 * This method checks the class file version and the structure of `this_class`.
2132 * and checks if the bytes is a class or interface (ACC_MODULE flag not set)
2133 * that is in the named package.
2134 *
2135 * @throws IllegalArgumentException if ACC_MODULE flag is set in access flags
2136 * or the class is not in the given package name.
2137 */
2138 static String validateAndFindInternalName(byte[] bytes, String pkgName) {
2139 int magic = readInt(bytes, 0);
2140 if (magic != ClassFile.MAGIC_NUMBER) {
2141 throw new ClassFormatError("Incompatible magic value: " + magic);
2142 }
2143 // We have to read major and minor this way as ClassFile API throws IAE
2144 // yet we want distinct ClassFormatError and UnsupportedClassVersionError
2145 int minor = readUnsignedShort(bytes, 4);
2146 int major = readUnsignedShort(bytes, 6);
2147
2148 if (!VM.isSupportedClassFileVersion(major, minor)) {
2149 throw new UnsupportedClassVersionError("Unsupported class file version " + major + "." + minor);
2150 }
2151
2152 String name;
2153 ClassDesc sym;
2154 int accessFlags;
2155 try {
2156 ClassModel cm = ClassFile.of().parse(bytes);
2157 var thisClass = cm.thisClass();
2158 name = thisClass.asInternalName();
2159 sym = thisClass.asSymbol();
2160 accessFlags = cm.flags().flagsMask();
2161 } catch (IllegalArgumentException e) {
2162 ClassFormatError cfe = new ClassFormatError();
2163 cfe.initCause(e);
2164 throw cfe;
2165 }
2166 // must be a class or interface
2167 if ((accessFlags & ACC_MODULE) != 0) {
2168 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set");
2169 }
2170
2171 String pn = sym.packageName();
2172 if (!pn.equals(pkgName)) {
2173 throw newIllegalArgumentException(name + " not in same package as lookup class");
2174 }
2175
2176 return name;
2177 }
2178
2179 private static int readInt(byte[] bytes, int offset) {
2180 if ((offset + 4) > bytes.length) {
2181 throw new ClassFormatError("Invalid ClassFile structure");
2182 }
2183 return ((bytes[offset] & 0xFF) << 24)
2184 | ((bytes[offset + 1] & 0xFF) << 16)
2185 | ((bytes[offset + 2] & 0xFF) << 8)
2186 | (bytes[offset + 3] & 0xFF);
2187 }
2188
2189 private static int readUnsignedShort(byte[] bytes, int offset) {
2190 if ((offset+2) > bytes.length) {
2191 throw new ClassFormatError("Invalid ClassFile structure");
2192 }
2193 return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF);
2194 }
2195
2196 /*
2197 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2198 * from the given bytes.
2199 *
2200 * Caller should make a defensive copy of the arguments if needed
2201 * before calling this factory method.
2202 *
2203 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2204 * {@code bytes} denotes a class in a different package than the lookup class
2205 */
2206 private ClassDefiner makeClassDefiner(byte[] bytes) {
2207 var internalName = validateAndFindInternalName(bytes, lookupClass().getPackageName());
2208 return new ClassDefiner(this, internalName, bytes, STRONG_LOADER_LINK, defaultDumper());
2209 }
2210
2211 /**
2212 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2213 * from the given bytes. No package name check on the given bytes.
2214 *
2215 * @param internalName internal name
2216 * @param bytes class bytes
2217 * @param dumper dumper to write the given bytes to the dumper's output directory
2218 * @return ClassDefiner that defines a normal class of the given bytes.
2219 */
2220 ClassDefiner makeClassDefiner(String internalName, byte[] bytes, ClassFileDumper dumper) {
2221 // skip package name validation
2222 return new ClassDefiner(this, internalName, bytes, STRONG_LOADER_LINK, dumper);
2223 }
2224
2225 /**
2226 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2227 * from the given bytes. The name must be in the same package as the lookup class.
2228 *
2229 * Caller should make a defensive copy of the arguments if needed
2230 * before calling this factory method.
2231 *
2232 * @param bytes class bytes
2233 * @param dumper dumper to write the given bytes to the dumper's output directory
2234 * @return ClassDefiner that defines a hidden class of the given bytes.
2235 *
2236 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2237 * {@code bytes} denotes a class in a different package than the lookup class
2238 */
2239 ClassDefiner makeHiddenClassDefiner(byte[] bytes, ClassFileDumper dumper) {
2240 var internalName = validateAndFindInternalName(bytes, lookupClass().getPackageName());
2241 return makeHiddenClassDefiner(internalName, bytes, false, dumper, 0);
2242 }
2243
2244 /**
2245 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2246 * from the given bytes and options.
2247 * The name must be in the same package as the lookup class.
2248 *
2249 * Caller should make a defensive copy of the arguments if needed
2250 * before calling this factory method.
2251 *
2252 * @param bytes class bytes
2253 * @param flags class option flag mask
2254 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2255 * @return ClassDefiner that defines a hidden class of the given bytes and options
2256 *
2257 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2258 * {@code bytes} denotes a class in a different package than the lookup class
2259 */
2260 private ClassDefiner makeHiddenClassDefiner(byte[] bytes,
2261 boolean accessVmAnnotations,
2262 int flags) {
2263 var internalName = validateAndFindInternalName(bytes, lookupClass().getPackageName());
2264 return makeHiddenClassDefiner(internalName, bytes, accessVmAnnotations, defaultDumper(), flags);
2265 }
2266
2267 /**
2268 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2269 * from the given bytes and the given options. No package name check on the given bytes.
2270 *
2271 * @param internalName internal name that specifies the prefix of the hidden class
2272 * @param bytes class bytes
2273 * @param dumper dumper to write the given bytes to the dumper's output directory
2274 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2275 */
2276 ClassDefiner makeHiddenClassDefiner(String internalName, byte[] bytes, ClassFileDumper dumper) {
2277 Objects.requireNonNull(dumper);
2278 // skip name and access flags validation
2279 return makeHiddenClassDefiner(internalName, bytes, false, dumper, 0);
2280 }
2281
2282 /**
2283 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2284 * from the given bytes and the given options. No package name check on the given bytes.
2285 *
2286 * @param internalName internal name that specifies the prefix of the hidden class
2287 * @param bytes class bytes
2288 * @param flags class options flag mask
2289 * @param dumper dumper to write the given bytes to the dumper's output directory
2290 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2291 */
2292 ClassDefiner makeHiddenClassDefiner(String internalName, byte[] bytes, ClassFileDumper dumper, int flags) {
2293 Objects.requireNonNull(dumper);
2294 // skip name and access flags validation
2295 return makeHiddenClassDefiner(internalName, bytes, false, dumper, flags);
2296 }
2297
2298 /**
2299 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2300 * from the given class file and options.
2301 *
2302 * @param internalName internal name
2303 * @param bytes Class byte array
2304 * @param flags class option flag mask
2305 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2306 * @param dumper dumper to write the given bytes to the dumper's output directory
2307 */
2308 private ClassDefiner makeHiddenClassDefiner(String internalName,
2309 byte[] bytes,
2310 boolean accessVmAnnotations,
2311 ClassFileDumper dumper,
2312 int flags) {
2313 flags |= HIDDEN_CLASS;
2314 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) {
2315 // jdk.internal.vm.annotations are permitted for classes
2316 // defined to boot loader and platform loader
2317 flags |= ACCESS_VM_ANNOTATIONS;
2318 }
2319
2320 return new ClassDefiner(this, internalName, bytes, flags, dumper);
2321 }
2322
2323 record ClassDefiner(Lookup lookup, String internalName, byte[] bytes, int classFlags, ClassFileDumper dumper) {
2324 ClassDefiner {
2325 assert ((classFlags & HIDDEN_CLASS) != 0 || (classFlags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK);
2326 }
2327
2328 Class<?> defineClass(boolean initialize) {
2329 return defineClass(initialize, null);
2330 }
2331
2332 Lookup defineClassAsLookup(boolean initialize) {
2333 Class<?> c = defineClass(initialize, null);
2334 return new Lookup(c, null, FULL_POWER_MODES);
2335 }
2336
2337 /**
2338 * Defines the class of the given bytes and the given classData.
2339 * If {@code initialize} parameter is true, then the class will be initialized.
2340 *
2341 * @param initialize true if the class to be initialized
2342 * @param classData classData or null
2343 * @return the class
2344 *
2345 * @throws LinkageError linkage error
2346 */
2347 Class<?> defineClass(boolean initialize, Object classData) {
2348 Class<?> lookupClass = lookup.lookupClass();
2349 ClassLoader loader = lookupClass.getClassLoader();
2350 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null;
2351 Class<?> c = null;
2352 try {
2353 c = SharedSecrets.getJavaLangAccess()
2354 .defineClass(loader, lookupClass, internalName, bytes, pd, initialize, classFlags, classData);
2355 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost();
2356 return c;
2357 } finally {
2358 // dump the classfile for debugging
2359 if (dumper.isEnabled()) {
2360 String name = internalName();
2361 if (c != null) {
2362 dumper.dumpClass(name, c, bytes);
2363 } else {
2364 dumper.dumpFailedClass(name, bytes);
2365 }
2366 }
2367 }
2368 }
2369
2370 /**
2371 * Defines the class of the given bytes and the given classData.
2372 * If {@code initialize} parameter is true, then the class will be initialized.
2373 *
2374 * @param initialize true if the class to be initialized
2375 * @param classData classData or null
2376 * @return a Lookup for the defined class
2377 *
2378 * @throws LinkageError linkage error
2379 */
2380 Lookup defineClassAsLookup(boolean initialize, Object classData) {
2381 Class<?> c = defineClass(initialize, classData);
2382 return new Lookup(c, null, FULL_POWER_MODES);
2383 }
2384
2385 private boolean isNestmate() {
2386 return (classFlags & NESTMATE_CLASS) != 0;
2387 }
2388 }
2389
2390 private ProtectionDomain lookupClassProtectionDomain() {
2391 ProtectionDomain pd = cachedProtectionDomain;
2392 if (pd == null) {
2393 cachedProtectionDomain = pd = SharedSecrets.getJavaLangAccess().protectionDomain(lookupClass);
2394 }
2395 return pd;
2396 }
2397
2398 // cached protection domain
2399 private volatile ProtectionDomain cachedProtectionDomain;
2400
2401 // Make sure outer class is initialized first.
2402 static { IMPL_NAMES.getClass(); }
2403
2404 /** Package-private version of lookup which is trusted. */
2405 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
2406
2407 /** Version of lookup which is trusted minimally.
2408 * It can only be used to create method handles to publicly accessible
2409 * members in packages that are exported unconditionally.
2410 */
2411 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
2412
2413 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
2414 String name = lookupClass.getName();
2415 if (name.startsWith("java.lang.invoke."))
2416 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
2417 }
2418
2419 /**
2420 * Displays the name of the class from which lookups are to be made,
2421 * followed by "/" and the name of the {@linkplain #previousLookupClass()
2422 * previous lookup class} if present.
2423 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
2424 * If there are restrictions on the access permitted to this lookup,
2425 * this is indicated by adding a suffix to the class name, consisting
2426 * of a slash and a keyword. The keyword represents the strongest
2427 * allowed access, and is chosen as follows:
2428 * <ul>
2429 * <li>If no access is allowed, the suffix is "/noaccess".
2430 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
2431 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
2432 * <li>If only public and module access are allowed, the suffix is "/module".
2433 * <li>If public and package access are allowed, the suffix is "/package".
2434 * <li>If public, package, and private access are allowed, the suffix is "/private".
2435 * </ul>
2436 * If none of the above cases apply, it is the case that
2437 * {@linkplain #hasFullPrivilegeAccess() full privilege access}
2438 * (public, module, package, private, and protected) is allowed.
2439 * In this case, no suffix is added.
2440 * This is true only of an object obtained originally from
2441 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
2442 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
2443 * always have restricted access, and will display a suffix.
2444 * <p>
2445 * (It may seem strange that protected access should be
2446 * stronger than private access. Viewed independently from
2447 * package access, protected access is the first to be lost,
2448 * because it requires a direct subclass relationship between
2449 * caller and callee.)
2450 * @see #in
2451 */
2452 @Override
2453 public String toString() {
2454 String cname = lookupClass.getName();
2455 if (prevLookupClass != null)
2456 cname += "/" + prevLookupClass.getName();
2457 switch (allowedModes) {
2458 case 0: // no privileges
2459 return cname + "/noaccess";
2460 case UNCONDITIONAL:
2461 return cname + "/publicLookup";
2462 case PUBLIC:
2463 return cname + "/public";
2464 case PUBLIC|MODULE:
2465 return cname + "/module";
2466 case PUBLIC|PACKAGE:
2467 case PUBLIC|MODULE|PACKAGE:
2468 return cname + "/package";
2469 case PUBLIC|PACKAGE|PRIVATE:
2470 case PUBLIC|MODULE|PACKAGE|PRIVATE:
2471 return cname + "/private";
2472 case PUBLIC|PACKAGE|PRIVATE|PROTECTED:
2473 case PUBLIC|MODULE|PACKAGE|PRIVATE|PROTECTED:
2474 case FULL_POWER_MODES:
2475 return cname;
2476 case TRUSTED:
2477 return "/trusted"; // internal only; not exported
2478 default: // Should not happen, but it's a bitfield...
2479 cname = cname + "/" + Integer.toHexString(allowedModes);
2480 assert(false) : cname;
2481 return cname;
2482 }
2483 }
2484
2485 /**
2486 * Produces a method handle for a static method.
2487 * The type of the method handle will be that of the method.
2488 * (Since static methods do not take receivers, there is no
2489 * additional receiver argument inserted into the method handle type,
2490 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
2491 * The method and all its argument types must be accessible to the lookup object.
2492 * <p>
2493 * The returned method handle will have
2494 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2495 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2496 * <p>
2497 * If the returned method handle is invoked, the method's class will
2498 * be initialized, if it has not already been initialized.
2499 * <p><b>Example:</b>
2500 * {@snippet lang="java" :
2501 import static java.lang.invoke.MethodHandles.*;
2502 import static java.lang.invoke.MethodType.*;
2503 ...
2504 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
2505 "asList", methodType(List.class, Object[].class));
2506 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
2507 * }
2508 * @param refc the class from which the method is accessed
2509 * @param name the name of the method
2510 * @param type the type of the method
2511 * @return the desired method handle
2512 * @throws NoSuchMethodException if the method does not exist
2513 * @throws IllegalAccessException if access checking fails,
2514 * or if the method is not {@code static},
2515 * or if the method's variable arity modifier bit
2516 * is set and {@code asVarargsCollector} fails
2517 * @throws NullPointerException if any argument is null
2518 */
2519 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2520 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
2521 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method));
2522 }
2523
2524 /**
2525 * Produces a method handle for a virtual method.
2526 * The type of the method handle will be that of the method,
2527 * with the receiver type (usually {@code refc}) prepended.
2528 * The method and all its argument types must be accessible to the lookup object.
2529 * <p>
2530 * When called, the handle will treat the first argument as a receiver
2531 * and, for non-private methods, dispatch on the receiver's type to determine which method
2532 * implementation to enter.
2533 * For private methods the named method in {@code refc} will be invoked on the receiver.
2534 * (The dispatching action is identical with that performed by an
2535 * {@code invokevirtual} or {@code invokeinterface} instruction.)
2536 * <p>
2537 * The first argument will be of type {@code refc} if the lookup
2538 * class has full privileges to access the member. Otherwise
2539 * the member must be {@code protected} and the first argument
2540 * will be restricted in type to the lookup class.
2541 * <p>
2542 * The returned method handle will have
2543 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2544 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2545 * <p>
2546 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
2547 * instructions and method handles produced by {@code findVirtual},
2548 * if the class is {@code MethodHandle} and the name string is
2549 * {@code invokeExact} or {@code invoke}, the resulting
2550 * method handle is equivalent to one produced by
2551 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
2552 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
2553 * with the same {@code type} argument.
2554 * <p>
2555 * If the class is {@code VarHandle} and the name string corresponds to
2556 * the name of a signature-polymorphic access mode method, the resulting
2557 * method handle is equivalent to one produced by
2558 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
2559 * the access mode corresponding to the name string and with the same
2560 * {@code type} arguments.
2561 * <p>
2562 * <b>Example:</b>
2563 * {@snippet lang="java" :
2564 import static java.lang.invoke.MethodHandles.*;
2565 import static java.lang.invoke.MethodType.*;
2566 ...
2567 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
2568 "concat", methodType(String.class, String.class));
2569 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
2570 "hashCode", methodType(int.class));
2571 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
2572 "hashCode", methodType(int.class));
2573 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
2574 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
2575 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
2576 // interface method:
2577 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
2578 "subSequence", methodType(CharSequence.class, int.class, int.class));
2579 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
2580 // constructor "internal method" must be accessed differently:
2581 MethodType MT_newString = methodType(void.class); //()V for new String()
2582 try { assertEquals("impossible", lookup()
2583 .findVirtual(String.class, "<init>", MT_newString));
2584 } catch (NoSuchMethodException ex) { } // OK
2585 MethodHandle MH_newString = publicLookup()
2586 .findConstructor(String.class, MT_newString);
2587 assertEquals("", (String) MH_newString.invokeExact());
2588 * }
2589 *
2590 * @param refc the class or interface from which the method is accessed
2591 * @param name the name of the method
2592 * @param type the type of the method, with the receiver argument omitted
2593 * @return the desired method handle
2594 * @throws NoSuchMethodException if the method does not exist
2595 * @throws IllegalAccessException if access checking fails,
2596 * or if the method is {@code static},
2597 * or if the method's variable arity modifier bit
2598 * is set and {@code asVarargsCollector} fails
2599 * @throws NullPointerException if any argument is null
2600 */
2601 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2602 if (refc == MethodHandle.class) {
2603 MethodHandle mh = findVirtualForMH(name, type);
2604 if (mh != null) return mh;
2605 } else if (refc == VarHandle.class) {
2606 MethodHandle mh = findVirtualForVH(name, type);
2607 if (mh != null) return mh;
2608 }
2609 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
2610 MemberName method = resolveOrFail(refKind, refc, name, type);
2611 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method));
2612 }
2613 private MethodHandle findVirtualForMH(String name, MethodType type) {
2614 // these names require special lookups because of the implicit MethodType argument
2615 if ("invoke".equals(name))
2616 return invoker(type);
2617 if ("invokeExact".equals(name))
2618 return exactInvoker(type);
2619 assert(!MemberName.isMethodHandleInvokeName(name));
2620 return null;
2621 }
2622 private MethodHandle findVirtualForVH(String name, MethodType type) {
2623 try {
2624 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
2625 } catch (IllegalArgumentException e) {
2626 return null;
2627 }
2628 }
2629
2630 /**
2631 * Produces a method handle which creates an object and initializes it, using
2632 * the constructor of the specified type.
2633 * The parameter types of the method handle will be those of the constructor,
2634 * while the return type will be a reference to the constructor's class.
2635 * The constructor and all its argument types must be accessible to the lookup object.
2636 * <p>
2637 * The requested type must have a return type of {@code void}.
2638 * (This is consistent with the JVM's treatment of constructor type descriptors.)
2639 * <p>
2640 * The returned method handle will have
2641 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2642 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2643 * <p>
2644 * If the returned method handle is invoked, the constructor's class will
2645 * be initialized, if it has not already been initialized.
2646 * <p><b>Example:</b>
2647 * {@snippet lang="java" :
2648 import static java.lang.invoke.MethodHandles.*;
2649 import static java.lang.invoke.MethodType.*;
2650 ...
2651 MethodHandle MH_newArrayList = publicLookup().findConstructor(
2652 ArrayList.class, methodType(void.class, Collection.class));
2653 Collection orig = Arrays.asList("x", "y");
2654 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
2655 assert(orig != copy);
2656 assertEquals(orig, copy);
2657 // a variable-arity constructor:
2658 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
2659 ProcessBuilder.class, methodType(void.class, String[].class));
2660 ProcessBuilder pb = (ProcessBuilder)
2661 MH_newProcessBuilder.invoke("x", "y", "z");
2662 assertEquals("[x, y, z]", pb.command().toString());
2663 * }
2664 * @param refc the class or interface from which the method is accessed
2665 * @param type the type of the method, with the receiver argument omitted, and a void return type
2666 * @return the desired method handle
2667 * @throws NoSuchMethodException if the constructor does not exist
2668 * @throws IllegalAccessException if access checking fails
2669 * or if the method's variable arity modifier bit
2670 * is set and {@code asVarargsCollector} fails
2671 * @throws NullPointerException if any argument is null
2672 */
2673 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2674 if (refc.isArray()) {
2675 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
2676 }
2677 String name = ConstantDescs.INIT_NAME;
2678 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
2679 return getDirectConstructor(refc, ctor);
2680 }
2681
2682 /**
2683 * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
2684 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
2685 * Such a resolution, as specified in JVMS {@jvms 5.4.3.1}, attempts to locate and load the class,
2686 * and then determines whether the class is accessible to this lookup object.
2687 * <p>
2688 * For a class or an interface, the name is the {@linkplain ClassLoader##binary-name binary name}.
2689 * For an array class of {@code n} dimensions, the name begins with {@code n} occurrences
2690 * of {@code '['} and followed by the element type as encoded in the
2691 * {@linkplain Class##nameFormat table} specified in {@link Class#getName}.
2692 * <p>
2693 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
2694 * its class loader, and the {@linkplain #lookupModes() lookup modes}.
2695 *
2696 * @param targetName the {@linkplain ClassLoader##binary-name binary name} of the class
2697 * or the string representing an array class
2698 * @return the requested class.
2699 * @throws LinkageError if the linkage fails
2700 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
2701 * @throws IllegalAccessException if the class is not accessible, using the allowed access
2702 * modes.
2703 * @throws NullPointerException if {@code targetName} is null
2704 * @since 9
2705 * @jvms 5.4.3.1 Class and Interface Resolution
2706 */
2707 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
2708 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
2709 return accessClass(targetClass);
2710 }
2711
2712 /**
2713 * Ensures that {@code targetClass} has been initialized. The class
2714 * to be initialized must be {@linkplain #accessClass accessible}
2715 * to this {@code Lookup} object. This method causes {@code targetClass}
2716 * to be initialized if it has not been already initialized,
2717 * as specified in JVMS {@jvms 5.5}.
2718 *
2719 * <p>
2720 * This method returns when {@code targetClass} is fully initialized, or
2721 * when {@code targetClass} is being initialized by the current thread.
2722 *
2723 * @param <T> the type of the class to be initialized
2724 * @param targetClass the class to be initialized
2725 * @return {@code targetClass} that has been initialized, or that is being
2726 * initialized by the current thread.
2727 *
2728 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or {@code void}
2729 * or array class
2730 * @throws IllegalAccessException if {@code targetClass} is not
2731 * {@linkplain #accessClass accessible} to this lookup
2732 * @throws ExceptionInInitializerError if the class initialization provoked
2733 * by this method fails
2734 * @since 15
2735 * @jvms 5.5 Initialization
2736 */
2737 public <T> Class<T> ensureInitialized(Class<T> targetClass) throws IllegalAccessException {
2738 if (targetClass.isPrimitive())
2739 throw new IllegalArgumentException(targetClass + " is a primitive class");
2740 if (targetClass.isArray())
2741 throw new IllegalArgumentException(targetClass + " is an array class");
2742
2743 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2744 throw makeAccessException(targetClass);
2745 }
2746
2747 // ensure class initialization
2748 Unsafe.getUnsafe().ensureClassInitialized(targetClass);
2749 return targetClass;
2750 }
2751
2752 /*
2753 * Returns IllegalAccessException due to access violation to the given targetClass.
2754 *
2755 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized}
2756 * which verifies access to a class rather a member.
2757 */
2758 private IllegalAccessException makeAccessException(Class<?> targetClass) {
2759 String message = "access violation: "+ targetClass;
2760 if (this == MethodHandles.publicLookup()) {
2761 message += ", from public Lookup";
2762 } else {
2763 Module m = lookupClass().getModule();
2764 message += ", from " + lookupClass() + " (" + m + ")";
2765 if (prevLookupClass != null) {
2766 message += ", previous lookup " +
2767 prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")";
2768 }
2769 }
2770 return new IllegalAccessException(message);
2771 }
2772
2773 /**
2774 * Determines if a class can be accessed from the lookup context defined by
2775 * this {@code Lookup} object. The static initializer of the class is not run.
2776 * If {@code targetClass} is an array class, {@code targetClass} is accessible
2777 * if the element type of the array class is accessible. Otherwise,
2778 * {@code targetClass} is determined as accessible as follows.
2779 *
2780 * <p>
2781 * If {@code targetClass} is in the same module as the lookup class,
2782 * the lookup class is {@code LC} in module {@code M1} and
2783 * the previous lookup class is in module {@code M0} or
2784 * {@code null} if not present,
2785 * {@code targetClass} is accessible if and only if one of the following is true:
2786 * <ul>
2787 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
2788 * {@code LC} or other class in the same nest of {@code LC}.</li>
2789 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
2790 * in the same runtime package of {@code LC}.</li>
2791 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
2792 * a public type in {@code M1}.</li>
2793 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
2794 * a public type in a package exported by {@code M1} to at least {@code M0}
2795 * if the previous lookup class is present; otherwise, {@code targetClass}
2796 * is a public type in a package exported by {@code M1} unconditionally.</li>
2797 * </ul>
2798 *
2799 * <p>
2800 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2801 * can access public types in all modules when the type is in a package
2802 * that is exported unconditionally.
2803 * <p>
2804 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass},
2805 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2806 * is inaccessible.
2807 * <p>
2808 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2809 * {@code M1} is the module containing {@code lookupClass} and
2810 * {@code M2} is the module containing {@code targetClass},
2811 * then {@code targetClass} is accessible if and only if
2812 * <ul>
2813 * <li>{@code M1} reads {@code M2}, and
2814 * <li>{@code targetClass} is public and in a package exported by
2815 * {@code M2} at least to {@code M1}.
2816 * </ul>
2817 * <p>
2818 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2819 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2820 * containing the previous lookup class, then {@code targetClass} is accessible
2821 * if and only if one of the following is true:
2822 * <ul>
2823 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2824 * {@linkplain Module#reads reads} {@code M0} and the type is
2825 * in a package that is exported to at least {@code M1}.
2826 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2827 * {@linkplain Module#reads reads} {@code M1} and the type is
2828 * in a package that is exported to at least {@code M0}.
2829 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2830 * and {@code M1} reads {@code M2} and the type is in a package
2831 * that is exported to at least both {@code M0} and {@code M2}.
2832 * </ul>
2833 * <p>
2834 * Otherwise, {@code targetClass} is not accessible.
2835 *
2836 * @param <T> the type of the class to be access-checked
2837 * @param targetClass the class to be access-checked
2838 * @return {@code targetClass} that has been access-checked
2839 * @throws IllegalAccessException if the class is not accessible from the lookup class
2840 * and previous lookup class, if present, using the allowed access modes.
2841 * @throws NullPointerException if {@code targetClass} is {@code null}
2842 * @since 9
2843 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
2844 */
2845 public <T> Class<T> accessClass(Class<T> targetClass) throws IllegalAccessException {
2846 if (!isClassAccessible(targetClass)) {
2847 throw makeAccessException(targetClass);
2848 }
2849 return targetClass;
2850 }
2851
2852 /**
2853 * Produces an early-bound method handle for a virtual method.
2854 * It will bypass checks for overriding methods on the receiver,
2855 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2856 * instruction from within the explicitly specified {@code specialCaller}.
2857 * The type of the method handle will be that of the method,
2858 * with a suitably restricted receiver type prepended.
2859 * (The receiver type will be {@code specialCaller} or a subtype.)
2860 * The method and all its argument types must be accessible
2861 * to the lookup object.
2862 * <p>
2863 * Before method resolution,
2864 * if the explicitly specified caller class is not identical with the
2865 * lookup class, or if this lookup object does not have
2866 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2867 * privileges, the access fails.
2868 * <p>
2869 * The returned method handle will have
2870 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2871 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2872 * <p style="font-size:smaller;">
2873 * <em>(Note: JVM internal methods named {@value ConstantDescs#INIT_NAME}
2874 * are not visible to this API,
2875 * even though the {@code invokespecial} instruction can refer to them
2876 * in special circumstances. Use {@link #findConstructor findConstructor}
2877 * to access instance initialization methods in a safe manner.)</em>
2878 * <p><b>Example:</b>
2879 * {@snippet lang="java" :
2880 import static java.lang.invoke.MethodHandles.*;
2881 import static java.lang.invoke.MethodType.*;
2882 ...
2883 static class Listie extends ArrayList {
2884 public String toString() { return "[wee Listie]"; }
2885 static Lookup lookup() { return MethodHandles.lookup(); }
2886 }
2887 ...
2888 // no access to constructor via invokeSpecial:
2889 MethodHandle MH_newListie = Listie.lookup()
2890 .findConstructor(Listie.class, methodType(void.class));
2891 Listie l = (Listie) MH_newListie.invokeExact();
2892 try { assertEquals("impossible", Listie.lookup().findSpecial(
2893 Listie.class, "<init>", methodType(void.class), Listie.class));
2894 } catch (NoSuchMethodException ex) { } // OK
2895 // access to super and self methods via invokeSpecial:
2896 MethodHandle MH_super = Listie.lookup().findSpecial(
2897 ArrayList.class, "toString" , methodType(String.class), Listie.class);
2898 MethodHandle MH_this = Listie.lookup().findSpecial(
2899 Listie.class, "toString" , methodType(String.class), Listie.class);
2900 MethodHandle MH_duper = Listie.lookup().findSpecial(
2901 Object.class, "toString" , methodType(String.class), Listie.class);
2902 assertEquals("[]", (String) MH_super.invokeExact(l));
2903 assertEquals(""+l, (String) MH_this.invokeExact(l));
2904 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
2905 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
2906 String.class, "toString", methodType(String.class), Listie.class));
2907 } catch (IllegalAccessException ex) { } // OK
2908 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
2909 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
2910 * }
2911 *
2912 * @param refc the class or interface from which the method is accessed
2913 * @param name the name of the method (which must not be "<init>")
2914 * @param type the type of the method, with the receiver argument omitted
2915 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
2916 * @return the desired method handle
2917 * @throws NoSuchMethodException if the method does not exist
2918 * @throws IllegalAccessException if access checking fails,
2919 * or if the method is {@code static},
2920 * or if the method's variable arity modifier bit
2921 * is set and {@code asVarargsCollector} fails
2922 * @throws NullPointerException if any argument is null
2923 */
2924 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
2925 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
2926 checkSpecialCaller(specialCaller, refc);
2927 Lookup specialLookup = this.in(specialCaller);
2928 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
2929 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method));
2930 }
2931
2932 /**
2933 * Produces a method handle giving read access to a non-static field.
2934 * The type of the method handle will have a return type of the field's
2935 * value type.
2936 * The method handle's single argument will be the instance containing
2937 * the field.
2938 * Access checking is performed immediately on behalf of the lookup class.
2939 * @param refc the class or interface from which the method is accessed
2940 * @param name the field's name
2941 * @param type the field's type
2942 * @return a method handle which can load values from the field
2943 * @throws NoSuchFieldException if the field does not exist
2944 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2945 * @throws NullPointerException if any argument is null
2946 * @see #findVarHandle(Class, String, Class)
2947 */
2948 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2949 MemberName field = resolveOrFail(REF_getField, refc, name, type);
2950 return getDirectField(REF_getField, refc, field);
2951 }
2952
2953 /**
2954 * Produces a method handle giving write access to a non-static field.
2955 * The type of the method handle will have a void return type.
2956 * The method handle will take two arguments, the instance containing
2957 * the field, and the value to be stored.
2958 * The second argument will be of the field's value type.
2959 * Access checking is performed immediately on behalf of the lookup class.
2960 * @param refc the class or interface from which the method is accessed
2961 * @param name the field's name
2962 * @param type the field's type
2963 * @return a method handle which can store values into the field
2964 * @throws NoSuchFieldException if the field does not exist
2965 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2966 * or {@code final}
2967 * @throws NullPointerException if any argument is null
2968 * @see #findVarHandle(Class, String, Class)
2969 */
2970 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2971 MemberName field = resolveOrFail(REF_putField, refc, name, type);
2972 return getDirectField(REF_putField, refc, field);
2973 }
2974
2975 /**
2976 * Produces a VarHandle giving access to a non-static field {@code name}
2977 * of type {@code type} declared in a class of type {@code recv}.
2978 * The VarHandle's variable type is {@code type} and it has one
2979 * coordinate type, {@code recv}.
2980 * <p>
2981 * Access checking is performed immediately on behalf of the lookup
2982 * class.
2983 * <p>
2984 * Certain access modes of the returned VarHandle are unsupported under
2985 * the following conditions:
2986 * <ul>
2987 * <li>if the field is declared {@code final}, then the write, atomic
2988 * update, numeric atomic update, and bitwise atomic update access
2989 * modes are unsupported.
2990 * <li>if the field type is anything other than {@code byte},
2991 * {@code short}, {@code char}, {@code int}, {@code long},
2992 * {@code float}, or {@code double} then numeric atomic update
2993 * access modes are unsupported.
2994 * <li>if the field type is anything other than {@code boolean},
2995 * {@code byte}, {@code short}, {@code char}, {@code int} or
2996 * {@code long} then bitwise atomic update access modes are
2997 * unsupported.
2998 * </ul>
2999 * <p>
3000 * If the field is declared {@code volatile} then the returned VarHandle
3001 * will override access to the field (effectively ignore the
3002 * {@code volatile} declaration) in accordance to its specified
3003 * access modes.
3004 * <p>
3005 * If the field type is {@code float} or {@code double} then numeric
3006 * and atomic update access modes compare values using their bitwise
3007 * representation (see {@link Float#floatToRawIntBits} and
3008 * {@link Double#doubleToRawLongBits}, respectively).
3009 * @apiNote
3010 * Bitwise comparison of {@code float} values or {@code double} values,
3011 * as performed by the numeric and atomic update access modes, differ
3012 * from the primitive {@code ==} operator and the {@link Float#equals}
3013 * and {@link Double#equals} methods, specifically with respect to
3014 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3015 * Care should be taken when performing a compare and set or a compare
3016 * and exchange operation with such values since the operation may
3017 * unexpectedly fail.
3018 * There are many possible NaN values that are considered to be
3019 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3020 * provided by Java can distinguish between them. Operation failure can
3021 * occur if the expected or witness value is a NaN value and it is
3022 * transformed (perhaps in a platform specific manner) into another NaN
3023 * value, and thus has a different bitwise representation (see
3024 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3025 * details).
3026 * The values {@code -0.0} and {@code +0.0} have different bitwise
3027 * representations but are considered equal when using the primitive
3028 * {@code ==} operator. Operation failure can occur if, for example, a
3029 * numeric algorithm computes an expected value to be say {@code -0.0}
3030 * and previously computed the witness value to be say {@code +0.0}.
3031 * @param recv the receiver class, of type {@code R}, that declares the
3032 * non-static field
3033 * @param name the field's name
3034 * @param type the field's type, of type {@code T}
3035 * @return a VarHandle giving access to non-static fields.
3036 * @throws NoSuchFieldException if the field does not exist
3037 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3038 * @throws NullPointerException if any argument is null
3039 * @since 9
3040 */
3041 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3042 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
3043 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
3044 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
3045 }
3046
3047 /**
3048 * Produces a method handle giving read access to a static field.
3049 * The type of the method handle will have a return type of the field's
3050 * value type.
3051 * The method handle will take no arguments.
3052 * Access checking is performed immediately on behalf of the lookup class.
3053 * <p>
3054 * If the returned method handle is invoked, the field's class will
3055 * be initialized, if it has not already been initialized.
3056 * @param refc the class or interface from which the method is accessed
3057 * @param name the field's name
3058 * @param type the field's type
3059 * @return a method handle which can load values from the field
3060 * @throws NoSuchFieldException if the field does not exist
3061 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3062 * @throws NullPointerException if any argument is null
3063 */
3064 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3065 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
3066 return getDirectField(REF_getStatic, refc, field);
3067 }
3068
3069 /**
3070 * Produces a method handle giving write access to a static field.
3071 * The type of the method handle will have a void return type.
3072 * The method handle will take a single
3073 * argument, of the field's value type, the value to be stored.
3074 * Access checking is performed immediately on behalf of the lookup class.
3075 * <p>
3076 * If the returned method handle is invoked, the field's class will
3077 * be initialized, if it has not already been initialized.
3078 * @param refc the class or interface from which the method is accessed
3079 * @param name the field's name
3080 * @param type the field's type
3081 * @return a method handle which can store values into the field
3082 * @throws NoSuchFieldException if the field does not exist
3083 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3084 * or is {@code final}
3085 * @throws NullPointerException if any argument is null
3086 */
3087 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3088 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
3089 return getDirectField(REF_putStatic, refc, field);
3090 }
3091
3092 /**
3093 * Produces a VarHandle giving access to a static field {@code name} of
3094 * type {@code type} declared in a class of type {@code decl}.
3095 * The VarHandle's variable type is {@code type} and it has no
3096 * coordinate types.
3097 * <p>
3098 * Access checking is performed immediately on behalf of the lookup
3099 * class.
3100 * <p>
3101 * If the returned VarHandle is operated on, the declaring class will be
3102 * initialized, if it has not already been initialized.
3103 * <p>
3104 * Certain access modes of the returned VarHandle are unsupported under
3105 * the following conditions:
3106 * <ul>
3107 * <li>if the field is declared {@code final}, then the write, atomic
3108 * update, numeric atomic update, and bitwise atomic update access
3109 * modes are unsupported.
3110 * <li>if the field type is anything other than {@code byte},
3111 * {@code short}, {@code char}, {@code int}, {@code long},
3112 * {@code float}, or {@code double}, then numeric atomic update
3113 * access modes are unsupported.
3114 * <li>if the field type is anything other than {@code boolean},
3115 * {@code byte}, {@code short}, {@code char}, {@code int} or
3116 * {@code long} then bitwise atomic update access modes are
3117 * unsupported.
3118 * </ul>
3119 * <p>
3120 * If the field is declared {@code volatile} then the returned VarHandle
3121 * will override access to the field (effectively ignore the
3122 * {@code volatile} declaration) in accordance to its specified
3123 * access modes.
3124 * <p>
3125 * If the field type is {@code float} or {@code double} then numeric
3126 * and atomic update access modes compare values using their bitwise
3127 * representation (see {@link Float#floatToRawIntBits} and
3128 * {@link Double#doubleToRawLongBits}, respectively).
3129 * @apiNote
3130 * Bitwise comparison of {@code float} values or {@code double} values,
3131 * as performed by the numeric and atomic update access modes, differ
3132 * from the primitive {@code ==} operator and the {@link Float#equals}
3133 * and {@link Double#equals} methods, specifically with respect to
3134 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3135 * Care should be taken when performing a compare and set or a compare
3136 * and exchange operation with such values since the operation may
3137 * unexpectedly fail.
3138 * There are many possible NaN values that are considered to be
3139 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3140 * provided by Java can distinguish between them. Operation failure can
3141 * occur if the expected or witness value is a NaN value and it is
3142 * transformed (perhaps in a platform specific manner) into another NaN
3143 * value, and thus has a different bitwise representation (see
3144 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3145 * details).
3146 * The values {@code -0.0} and {@code +0.0} have different bitwise
3147 * representations but are considered equal when using the primitive
3148 * {@code ==} operator. Operation failure can occur if, for example, a
3149 * numeric algorithm computes an expected value to be say {@code -0.0}
3150 * and previously computed the witness value to be say {@code +0.0}.
3151 * @param decl the class that declares the static field
3152 * @param name the field's name
3153 * @param type the field's type, of type {@code T}
3154 * @return a VarHandle giving access to a static field
3155 * @throws NoSuchFieldException if the field does not exist
3156 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3157 * @throws NullPointerException if any argument is null
3158 * @since 9
3159 */
3160 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3161 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
3162 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
3163 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
3164 }
3165
3166 /**
3167 * Produces an early-bound method handle for a non-static method.
3168 * The receiver must have a supertype {@code defc} in which a method
3169 * of the given name and type is accessible to the lookup class.
3170 * The method and all its argument types must be accessible to the lookup object.
3171 * The type of the method handle will be that of the method,
3172 * without any insertion of an additional receiver parameter.
3173 * The given receiver will be bound into the method handle,
3174 * so that every call to the method handle will invoke the
3175 * requested method on the given receiver.
3176 * <p>
3177 * The returned method handle will have
3178 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3179 * the method's variable arity modifier bit ({@code 0x0080}) is set
3180 * <em>and</em> the trailing array argument is not the only argument.
3181 * (If the trailing array argument is the only argument,
3182 * the given receiver value will be bound to it.)
3183 * <p>
3184 * This is almost equivalent to the following code, with some differences noted below:
3185 * {@snippet lang="java" :
3186 import static java.lang.invoke.MethodHandles.*;
3187 import static java.lang.invoke.MethodType.*;
3188 ...
3189 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
3190 MethodHandle mh1 = mh0.bindTo(receiver);
3191 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
3192 return mh1;
3193 * }
3194 * where {@code defc} is either {@code receiver.getClass()} or a super
3195 * type of that class, in which the requested method is accessible
3196 * to the lookup class.
3197 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
3198 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
3199 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
3200 * the receiver is restricted by {@code findVirtual} to the lookup class.)
3201 * @param receiver the object from which the method is accessed
3202 * @param name the name of the method
3203 * @param type the type of the method, with the receiver argument omitted
3204 * @return the desired method handle
3205 * @throws NoSuchMethodException if the method does not exist
3206 * @throws IllegalAccessException if access checking fails
3207 * or if the method's variable arity modifier bit
3208 * is set and {@code asVarargsCollector} fails
3209 * @throws NullPointerException if any argument is null
3210 * @see MethodHandle#bindTo
3211 * @see #findVirtual
3212 */
3213 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3214 Class<? extends Object> refc = receiver.getClass(); // may get NPE
3215 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
3216 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method));
3217 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
3218 throw new IllegalAccessException("The restricted defining class " +
3219 mh.type().leadingReferenceParameter().getName() +
3220 " is not assignable from receiver class " +
3221 receiver.getClass().getName());
3222 }
3223 return mh.bindArgumentL(0, receiver).setVarargs(method);
3224 }
3225
3226 /**
3227 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3228 * to <i>m</i>, if the lookup class has permission.
3229 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
3230 * If <i>m</i> is virtual, overriding is respected on every call.
3231 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
3232 * The type of the method handle will be that of the method,
3233 * with the receiver type prepended (but only if it is non-static).
3234 * If the method's {@code accessible} flag is not set,
3235 * access checking is performed immediately on behalf of the lookup class.
3236 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
3237 * <p>
3238 * The returned method handle will have
3239 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3240 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3241 * <p>
3242 * If <i>m</i> is static, and
3243 * if the returned method handle is invoked, the method's class will
3244 * be initialized, if it has not already been initialized.
3245 * @param m the reflected method
3246 * @return a method handle which can invoke the reflected method
3247 * @throws IllegalAccessException if access checking fails
3248 * or if the method's variable arity modifier bit
3249 * is set and {@code asVarargsCollector} fails
3250 * @throws NullPointerException if the argument is null
3251 */
3252 public MethodHandle unreflect(Method m) throws IllegalAccessException {
3253 if (m.getDeclaringClass() == MethodHandle.class) {
3254 MethodHandle mh = unreflectForMH(m);
3255 if (mh != null) return mh;
3256 }
3257 if (m.getDeclaringClass() == VarHandle.class) {
3258 MethodHandle mh = unreflectForVH(m);
3259 if (mh != null) return mh;
3260 }
3261 MemberName method = new MemberName(m);
3262 byte refKind = method.getReferenceKind();
3263 if (refKind == REF_invokeSpecial)
3264 refKind = REF_invokeVirtual;
3265 assert(method.isMethod());
3266 @SuppressWarnings("deprecation")
3267 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
3268 return lookup.getDirectMethod(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3269 }
3270 private MethodHandle unreflectForMH(Method m) {
3271 // these names require special lookups because they throw UnsupportedOperationException
3272 if (MemberName.isMethodHandleInvokeName(m.getName()))
3273 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
3274 return null;
3275 }
3276 private MethodHandle unreflectForVH(Method m) {
3277 // these names require special lookups because they throw UnsupportedOperationException
3278 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
3279 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
3280 return null;
3281 }
3282
3283 /**
3284 * Produces a method handle for a reflected method.
3285 * It will bypass checks for overriding methods on the receiver,
3286 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3287 * instruction from within the explicitly specified {@code specialCaller}.
3288 * The type of the method handle will be that of the method,
3289 * with a suitably restricted receiver type prepended.
3290 * (The receiver type will be {@code specialCaller} or a subtype.)
3291 * If the method's {@code accessible} flag is not set,
3292 * access checking is performed immediately on behalf of the lookup class,
3293 * as if {@code invokespecial} instruction were being linked.
3294 * <p>
3295 * Before method resolution,
3296 * if the explicitly specified caller class is not identical with the
3297 * lookup class, or if this lookup object does not have
3298 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3299 * privileges, the access fails.
3300 * <p>
3301 * The returned method handle will have
3302 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3303 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3304 * @param m the reflected method
3305 * @param specialCaller the class nominally calling the method
3306 * @return a method handle which can invoke the reflected method
3307 * @throws IllegalAccessException if access checking fails,
3308 * or if the method is {@code static},
3309 * or if the method's variable arity modifier bit
3310 * is set and {@code asVarargsCollector} fails
3311 * @throws NullPointerException if any argument is null
3312 */
3313 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
3314 checkSpecialCaller(specialCaller, m.getDeclaringClass());
3315 Lookup specialLookup = this.in(specialCaller);
3316 MemberName method = new MemberName(m, true);
3317 assert(method.isMethod());
3318 // ignore m.isAccessible: this is a new kind of access
3319 return specialLookup.getDirectMethod(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3320 }
3321
3322 /**
3323 * Produces a method handle for a reflected constructor.
3324 * The type of the method handle will be that of the constructor,
3325 * with the return type changed to the declaring class.
3326 * The method handle will perform a {@code newInstance} operation,
3327 * creating a new instance of the constructor's class on the
3328 * arguments passed to the method handle.
3329 * <p>
3330 * If the constructor's {@code accessible} flag is not set,
3331 * access checking is performed immediately on behalf of the lookup class.
3332 * <p>
3333 * The returned method handle will have
3334 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3335 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
3336 * <p>
3337 * If the returned method handle is invoked, the constructor's class will
3338 * be initialized, if it has not already been initialized.
3339 * @param c the reflected constructor
3340 * @return a method handle which can invoke the reflected constructor
3341 * @throws IllegalAccessException if access checking fails
3342 * or if the method's variable arity modifier bit
3343 * is set and {@code asVarargsCollector} fails
3344 * @throws NullPointerException if the argument is null
3345 */
3346 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
3347 MemberName ctor = new MemberName(c);
3348 assert(ctor.isConstructor());
3349 @SuppressWarnings("deprecation")
3350 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
3351 return lookup.getDirectConstructor(ctor.getDeclaringClass(), ctor);
3352 }
3353
3354 /*
3355 * Produces a method handle that is capable of creating instances of the given class
3356 * and instantiated by the given constructor.
3357 *
3358 * This method should only be used by ReflectionFactory::newConstructorForSerialization.
3359 */
3360 /* package-private */ MethodHandle serializableConstructor(Class<?> decl, Constructor<?> c) throws IllegalAccessException {
3361 MemberName ctor = new MemberName(c);
3362 assert(ctor.isConstructor() && constructorInSuperclass(decl, c));
3363 checkAccess(REF_newInvokeSpecial, decl, ctor);
3364 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3365 return DirectMethodHandle.makeAllocator(decl, ctor).setVarargs(ctor);
3366 }
3367
3368 private static boolean constructorInSuperclass(Class<?> decl, Constructor<?> ctor) {
3369 if (decl == ctor.getDeclaringClass())
3370 return true;
3371
3372 Class<?> cl = decl;
3373 while ((cl = cl.getSuperclass()) != null) {
3374 if (cl == ctor.getDeclaringClass()) {
3375 return true;
3376 }
3377 }
3378 return false;
3379 }
3380
3381 /**
3382 * Produces a method handle giving read access to a reflected field.
3383 * The type of the method handle will have a return type of the field's
3384 * value type.
3385 * If the field is {@code static}, the method handle will take no arguments.
3386 * Otherwise, its single argument will be the instance containing
3387 * the field.
3388 * If the {@code Field} object's {@code accessible} flag is not set,
3389 * access checking is performed immediately on behalf of the lookup class.
3390 * <p>
3391 * If the field is static, and
3392 * if the returned method handle is invoked, the field's class will
3393 * be initialized, if it has not already been initialized.
3394 * @param f the reflected field
3395 * @return a method handle which can load values from the reflected field
3396 * @throws IllegalAccessException if access checking fails
3397 * @throws NullPointerException if the argument is null
3398 */
3399 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
3400 return unreflectField(f, false);
3401 }
3402
3403 /**
3404 * Produces a method handle giving write access to a reflected field.
3405 * The type of the method handle will have a void return type.
3406 * If the field is {@code static}, the method handle will take a single
3407 * argument, of the field's value type, the value to be stored.
3408 * Otherwise, the two arguments will be the instance containing
3409 * the field, and the value to be stored.
3410 * If the {@code Field} object's {@code accessible} flag is not set,
3411 * access checking is performed immediately on behalf of the lookup class.
3412 * <p>
3413 * If the field is {@code final}, write access will not be
3414 * allowed and access checking will fail, except under certain
3415 * narrow circumstances documented for {@link Field#set Field.set}.
3416 * A method handle is returned only if a corresponding call to
3417 * the {@code Field} object's {@code set} method could return
3418 * normally. In particular, fields which are both {@code static}
3419 * and {@code final} may never be set.
3420 * <p>
3421 * If the field is {@code static}, and
3422 * if the returned method handle is invoked, the field's class will
3423 * be initialized, if it has not already been initialized.
3424 * @param f the reflected field
3425 * @return a method handle which can store values into the reflected field
3426 * @throws IllegalAccessException if access checking fails,
3427 * or if the field is {@code final} and write access
3428 * is not enabled on the {@code Field} object
3429 * @throws NullPointerException if the argument is null
3430 */
3431 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
3432 return unreflectField(f, true);
3433 }
3434
3435 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
3436 MemberName field = new MemberName(f, isSetter);
3437 if (isSetter && field.isFinal()) {
3438 if (field.isTrustedFinalField()) {
3439 String msg = field.isStatic() ? "static final field has no write access"
3440 : "final field has no write access";
3441 throw field.makeAccessException(msg, this);
3442 }
3443 }
3444 assert(isSetter
3445 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
3446 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
3447 @SuppressWarnings("deprecation")
3448 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
3449 return lookup.getDirectField(field.getReferenceKind(), f.getDeclaringClass(), field);
3450 }
3451
3452 /**
3453 * Produces a VarHandle giving access to a reflected field {@code f}
3454 * of type {@code T} declared in a class of type {@code R}.
3455 * The VarHandle's variable type is {@code T}.
3456 * If the field is non-static the VarHandle has one coordinate type,
3457 * {@code R}. Otherwise, the field is static, and the VarHandle has no
3458 * coordinate types.
3459 * <p>
3460 * Access checking is performed immediately on behalf of the lookup
3461 * class, regardless of the value of the field's {@code accessible}
3462 * flag.
3463 * <p>
3464 * If the field is static, and if the returned VarHandle is operated
3465 * on, the field's declaring class will be initialized, if it has not
3466 * already been initialized.
3467 * <p>
3468 * Certain access modes of the returned VarHandle are unsupported under
3469 * the following conditions:
3470 * <ul>
3471 * <li>if the field is declared {@code final}, then the write, atomic
3472 * update, numeric atomic update, and bitwise atomic update access
3473 * modes are unsupported.
3474 * <li>if the field type is anything other than {@code byte},
3475 * {@code short}, {@code char}, {@code int}, {@code long},
3476 * {@code float}, or {@code double} then numeric atomic update
3477 * access modes are unsupported.
3478 * <li>if the field type is anything other than {@code boolean},
3479 * {@code byte}, {@code short}, {@code char}, {@code int} or
3480 * {@code long} then bitwise atomic update access modes are
3481 * unsupported.
3482 * </ul>
3483 * <p>
3484 * If the field is declared {@code volatile} then the returned VarHandle
3485 * will override access to the field (effectively ignore the
3486 * {@code volatile} declaration) in accordance to its specified
3487 * access modes.
3488 * <p>
3489 * If the field type is {@code float} or {@code double} then numeric
3490 * and atomic update access modes compare values using their bitwise
3491 * representation (see {@link Float#floatToRawIntBits} and
3492 * {@link Double#doubleToRawLongBits}, respectively).
3493 * @apiNote
3494 * Bitwise comparison of {@code float} values or {@code double} values,
3495 * as performed by the numeric and atomic update access modes, differ
3496 * from the primitive {@code ==} operator and the {@link Float#equals}
3497 * and {@link Double#equals} methods, specifically with respect to
3498 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3499 * Care should be taken when performing a compare and set or a compare
3500 * and exchange operation with such values since the operation may
3501 * unexpectedly fail.
3502 * There are many possible NaN values that are considered to be
3503 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3504 * provided by Java can distinguish between them. Operation failure can
3505 * occur if the expected or witness value is a NaN value and it is
3506 * transformed (perhaps in a platform specific manner) into another NaN
3507 * value, and thus has a different bitwise representation (see
3508 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3509 * details).
3510 * The values {@code -0.0} and {@code +0.0} have different bitwise
3511 * representations but are considered equal when using the primitive
3512 * {@code ==} operator. Operation failure can occur if, for example, a
3513 * numeric algorithm computes an expected value to be say {@code -0.0}
3514 * and previously computed the witness value to be say {@code +0.0}.
3515 * @param f the reflected field, with a field of type {@code T}, and
3516 * a declaring class of type {@code R}
3517 * @return a VarHandle giving access to non-static fields or a static
3518 * field
3519 * @throws IllegalAccessException if access checking fails
3520 * @throws NullPointerException if the argument is null
3521 * @since 9
3522 */
3523 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
3524 MemberName getField = new MemberName(f, false);
3525 MemberName putField = new MemberName(f, true);
3526 return getFieldVarHandle(getField.getReferenceKind(), putField.getReferenceKind(),
3527 f.getDeclaringClass(), getField, putField);
3528 }
3529
3530 /**
3531 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3532 * created by this lookup object or a similar one.
3533 * Security and access checks are performed to ensure that this lookup object
3534 * is capable of reproducing the target method handle.
3535 * This means that the cracking may fail if target is a direct method handle
3536 * but was created by an unrelated lookup object.
3537 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
3538 * and was created by a lookup object for a different class.
3539 * @param target a direct method handle to crack into symbolic reference components
3540 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
3541 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
3542 * @throws NullPointerException if the target is {@code null}
3543 * @see MethodHandleInfo
3544 * @since 1.8
3545 */
3546 public MethodHandleInfo revealDirect(MethodHandle target) {
3547 if (!target.isCrackable()) {
3548 throw newIllegalArgumentException("not a direct method handle");
3549 }
3550 MemberName member = target.internalMemberName();
3551 Class<?> defc = member.getDeclaringClass();
3552 byte refKind = member.getReferenceKind();
3553 assert(MethodHandleNatives.refKindIsValid(refKind));
3554 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
3555 // Devirtualized method invocation is usually formally virtual.
3556 // To avoid creating extra MemberName objects for this common case,
3557 // we encode this extra degree of freedom using MH.isInvokeSpecial.
3558 refKind = REF_invokeVirtual;
3559 if (refKind == REF_invokeVirtual && defc.isInterface())
3560 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
3561 refKind = REF_invokeInterface;
3562 // Check member access before cracking.
3563 try {
3564 checkAccess(refKind, defc, member);
3565 } catch (IllegalAccessException ex) {
3566 throw new IllegalArgumentException(ex);
3567 }
3568 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
3569 Class<?> callerClass = target.internalCallerClass();
3570 if ((lookupModes() & ORIGINAL) == 0 || callerClass != lookupClass())
3571 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
3572 }
3573 // Produce the handle to the results.
3574 return new InfoFromMemberName(this, member, refKind);
3575 }
3576
3577 //--- Helper methods, all package-private.
3578
3579 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3580 checkSymbolicClass(refc); // do this before attempting to resolve
3581 Objects.requireNonNull(name);
3582 Objects.requireNonNull(type);
3583 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3584 NoSuchFieldException.class);
3585 }
3586
3587 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3588 checkSymbolicClass(refc); // do this before attempting to resolve
3589 Objects.requireNonNull(type);
3590 checkMethodName(refKind, name); // implicit null-check of name
3591 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3592 NoSuchMethodException.class);
3593 }
3594
3595 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
3596 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
3597 Objects.requireNonNull(member.getName());
3598 Objects.requireNonNull(member.getType());
3599 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), allowedModes,
3600 ReflectiveOperationException.class);
3601 }
3602
3603 MemberName resolveOrNull(byte refKind, MemberName member) {
3604 // do this before attempting to resolve
3605 if (!isClassAccessible(member.getDeclaringClass())) {
3606 return null;
3607 }
3608 Objects.requireNonNull(member.getName());
3609 Objects.requireNonNull(member.getType());
3610 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull(), allowedModes);
3611 }
3612
3613 MemberName resolveOrNull(byte refKind, Class<?> refc, String name, MethodType type) {
3614 // do this before attempting to resolve
3615 if (!isClassAccessible(refc)) {
3616 return null;
3617 }
3618 Objects.requireNonNull(type);
3619 // implicit null-check of name
3620 if (name.startsWith("<") && refKind != REF_newInvokeSpecial) {
3621 return null;
3622 }
3623 return IMPL_NAMES.resolveOrNull(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes);
3624 }
3625
3626 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
3627 if (!isClassAccessible(refc)) {
3628 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
3629 }
3630 }
3631
3632 boolean isClassAccessible(Class<?> refc) {
3633 Objects.requireNonNull(refc);
3634 Class<?> caller = lookupClassOrNull();
3635 Class<?> type = refc;
3636 while (type.isArray()) {
3637 type = type.getComponentType();
3638 }
3639 return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes);
3640 }
3641
3642 /** Check name for an illegal leading "<" character. */
3643 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
3644 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
3645 throw new NoSuchMethodException("illegal method name: "+name);
3646 }
3647
3648 /**
3649 * Find my trustable caller class if m is a caller sensitive method.
3650 * If this lookup object has original full privilege access, then the caller class is the lookupClass.
3651 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
3652 */
3653 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException {
3654 if (MethodHandleNatives.isCallerSensitive(m) && (lookupModes() & ORIGINAL) == 0) {
3655 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods
3656 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3657 }
3658 return this;
3659 }
3660
3661 /**
3662 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3663 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3664 *
3665 * @deprecated This method was originally designed to test {@code PRIVATE} access
3666 * that implies full privilege access but {@code MODULE} access has since become
3667 * independent of {@code PRIVATE} access. It is recommended to call
3668 * {@link #hasFullPrivilegeAccess()} instead.
3669 * @since 9
3670 */
3671 @Deprecated(since="14")
3672 public boolean hasPrivateAccess() {
3673 return hasFullPrivilegeAccess();
3674 }
3675
3676 /**
3677 * Returns {@code true} if this lookup has <em>full privilege access</em>,
3678 * i.e. {@code PRIVATE} and {@code MODULE} access.
3679 * A {@code Lookup} object must have full privilege access in order to
3680 * access all members that are allowed to the
3681 * {@linkplain #lookupClass() lookup class}.
3682 *
3683 * @return {@code true} if this lookup has full privilege access.
3684 * @since 14
3685 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a>
3686 */
3687 public boolean hasFullPrivilegeAccess() {
3688 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE);
3689 }
3690
3691 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3692 boolean wantStatic = (refKind == REF_invokeStatic);
3693 String message;
3694 if (m.isConstructor())
3695 message = "expected a method, not a constructor";
3696 else if (!m.isMethod())
3697 message = "expected a method";
3698 else if (wantStatic != m.isStatic())
3699 message = wantStatic ? "expected a static method" : "expected a non-static method";
3700 else
3701 { checkAccess(refKind, refc, m); return; }
3702 throw m.makeAccessException(message, this);
3703 }
3704
3705 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3706 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
3707 String message;
3708 if (wantStatic != m.isStatic())
3709 message = wantStatic ? "expected a static field" : "expected a non-static field";
3710 else
3711 { checkAccess(refKind, refc, m); return; }
3712 throw m.makeAccessException(message, this);
3713 }
3714
3715 private boolean isArrayClone(byte refKind, Class<?> refc, MemberName m) {
3716 return Modifier.isProtected(m.getModifiers()) &&
3717 refKind == REF_invokeVirtual &&
3718 m.getDeclaringClass() == Object.class &&
3719 m.getName().equals("clone") &&
3720 refc.isArray();
3721 }
3722
3723 /** Check public/protected/private bits on the symbolic reference class and its member. */
3724 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3725 assert(m.referenceKindIsConsistentWith(refKind) &&
3726 MethodHandleNatives.refKindIsValid(refKind) &&
3727 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
3728 int allowedModes = this.allowedModes;
3729 if (allowedModes == TRUSTED) return;
3730 int mods = m.getModifiers();
3731 if (isArrayClone(refKind, refc, m)) {
3732 // The JVM does this hack also.
3733 // (See ClassVerifier::verify_invoke_instructions
3734 // and LinkResolver::check_method_accessability.)
3735 // Because the JVM does not allow separate methods on array types,
3736 // there is no separate method for int[].clone.
3737 // All arrays simply inherit Object.clone.
3738 // But for access checking logic, we make Object.clone
3739 // (normally protected) appear to be public.
3740 // Later on, when the DirectMethodHandle is created,
3741 // its leading argument will be restricted to the
3742 // requested array type.
3743 // N.B. The return type is not adjusted, because
3744 // that is *not* the bytecode behavior.
3745 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
3746 }
3747 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
3748 // cannot "new" a protected ctor in a different package
3749 mods ^= Modifier.PROTECTED;
3750 }
3751 if (Modifier.isFinal(mods) &&
3752 MethodHandleNatives.refKindIsSetter(refKind))
3753 throw m.makeAccessException("unexpected set of a final field", this);
3754 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
3755 if ((requestedModes & allowedModes) != 0) {
3756 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
3757 mods, lookupClass(), previousLookupClass(), allowedModes))
3758 return;
3759 } else {
3760 // Protected members can also be checked as if they were package-private.
3761 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
3762 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
3763 return;
3764 }
3765 throw m.makeAccessException(accessFailedMessage(refc, m), this);
3766 }
3767
3768 String accessFailedMessage(Class<?> refc, MemberName m) {
3769 Class<?> defc = m.getDeclaringClass();
3770 int mods = m.getModifiers();
3771 // check the class first:
3772 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
3773 (defc == refc ||
3774 Modifier.isPublic(refc.getModifiers())));
3775 if (!classOK && (allowedModes & PACKAGE) != 0) {
3776 // ignore previous lookup class to check if default package access
3777 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
3778 (defc == refc ||
3779 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
3780 }
3781 if (!classOK)
3782 return "class is not public";
3783 if (Modifier.isPublic(mods))
3784 return "access to public member failed"; // (how?, module not readable?)
3785 if (Modifier.isPrivate(mods))
3786 return "member is private";
3787 if (Modifier.isProtected(mods))
3788 return "member is protected";
3789 return "member is private to package";
3790 }
3791
3792 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
3793 int allowedModes = this.allowedModes;
3794 if (allowedModes == TRUSTED) return;
3795 if ((lookupModes() & PRIVATE) == 0
3796 || (specialCaller != lookupClass()
3797 // ensure non-abstract methods in superinterfaces can be special-invoked
3798 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
3799 throw new MemberName(specialCaller).
3800 makeAccessException("no private access for invokespecial", this);
3801 }
3802
3803 private boolean restrictProtectedReceiver(MemberName method) {
3804 // The accessing class only has the right to use a protected member
3805 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
3806 if (!method.isProtected() || method.isStatic()
3807 || allowedModes == TRUSTED
3808 || method.getDeclaringClass() == lookupClass()
3809 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
3810 return false;
3811 return true;
3812 }
3813 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
3814 assert(!method.isStatic());
3815 // receiver type of mh is too wide; narrow to caller
3816 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
3817 throw method.makeAccessException("caller class must be a subclass below the method", caller);
3818 }
3819 MethodType rawType = mh.type();
3820 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
3821 MethodType narrowType = rawType.changeParameterType(0, caller);
3822 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
3823 assert(mh.viewAsTypeChecks(narrowType, true));
3824 return mh.copyWith(narrowType, mh.form);
3825 }
3826
3827 /** Check access and get the requested method. */
3828 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3829 final boolean doRestrict = true;
3830 return getDirectMethodCommon(refKind, refc, method, doRestrict, callerLookup);
3831 }
3832 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
3833 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3834 final boolean doRestrict = false;
3835 return getDirectMethodCommon(REF_invokeSpecial, refc, method, doRestrict, callerLookup);
3836 }
3837 /** Common code for all methods; do not call directly except from immediately above. */
3838 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
3839 boolean doRestrict,
3840 Lookup boundCaller) throws IllegalAccessException {
3841 checkMethod(refKind, refc, method);
3842 assert(!method.isMethodHandleInvoke());
3843
3844 if (refKind == REF_invokeSpecial &&
3845 refc != lookupClass() &&
3846 !refc.isInterface() && !lookupClass().isInterface() &&
3847 refc != lookupClass().getSuperclass() &&
3848 refc.isAssignableFrom(lookupClass())) {
3849 assert(!method.getName().equals(ConstantDescs.INIT_NAME)); // not this code path
3850
3851 // Per JVMS 6.5, desc. of invokespecial instruction:
3852 // If the method is in a superclass of the LC,
3853 // and if our original search was above LC.super,
3854 // repeat the search (symbolic lookup) from LC.super
3855 // and continue with the direct superclass of that class,
3856 // and so forth, until a match is found or no further superclasses exist.
3857 // FIXME: MemberName.resolve should handle this instead.
3858 Class<?> refcAsSuper = lookupClass();
3859 MemberName m2;
3860 do {
3861 refcAsSuper = refcAsSuper.getSuperclass();
3862 m2 = new MemberName(refcAsSuper,
3863 method.getName(),
3864 method.getMethodType(),
3865 REF_invokeSpecial);
3866 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull(), allowedModes);
3867 } while (m2 == null && // no method is found yet
3868 refc != refcAsSuper); // search up to refc
3869 if (m2 == null) throw new InternalError(method.toString());
3870 method = m2;
3871 refc = refcAsSuper;
3872 // redo basic checks
3873 checkMethod(refKind, refc, method);
3874 }
3875 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
3876 MethodHandle mh = dmh;
3877 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
3878 if ((doRestrict && refKind == REF_invokeSpecial) ||
3879 (MethodHandleNatives.refKindHasReceiver(refKind) &&
3880 restrictProtectedReceiver(method) &&
3881 // All arrays simply inherit the protected Object.clone method.
3882 // The leading argument is already restricted to the requested
3883 // array type (not the lookup class).
3884 !isArrayClone(refKind, refc, method))) {
3885 mh = restrictReceiver(method, dmh, lookupClass());
3886 }
3887 mh = maybeBindCaller(method, mh, boundCaller);
3888 mh = mh.setVarargs(method);
3889 return mh;
3890 }
3891 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller)
3892 throws IllegalAccessException {
3893 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
3894 return mh;
3895
3896 // boundCaller must have full privilege access.
3897 // It should have been checked by findBoundCallerLookup. Safe to check this again.
3898 if ((boundCaller.lookupModes() & ORIGINAL) == 0)
3899 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3900
3901 assert boundCaller.hasFullPrivilegeAccess();
3902
3903 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass);
3904 // Note: caller will apply varargs after this step happens.
3905 return cbmh;
3906 }
3907
3908 /** Check access and get the requested field. */
3909 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3910 return getDirectFieldCommon(refKind, refc, field);
3911 }
3912 /** Common code for all fields; do not call directly except from immediately above. */
3913 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3914 checkField(refKind, refc, field);
3915 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
3916 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
3917 restrictProtectedReceiver(field));
3918 if (doRestrict)
3919 return restrictReceiver(field, dmh, lookupClass());
3920 return dmh;
3921 }
3922 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
3923 Class<?> refc, MemberName getField, MemberName putField)
3924 throws IllegalAccessException {
3925 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField);
3926 }
3927 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
3928 Class<?> refc, MemberName getField,
3929 MemberName putField) throws IllegalAccessException {
3930 assert getField.isStatic() == putField.isStatic();
3931 assert getField.isGetter() && putField.isSetter();
3932 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
3933 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
3934
3935 checkField(getRefKind, refc, getField);
3936
3937 if (!putField.isFinal()) {
3938 // A VarHandle does not support updates to final fields, any
3939 // such VarHandle to a final field will be read-only and
3940 // therefore the following write-based accessibility checks are
3941 // only required for non-final fields
3942 checkField(putRefKind, refc, putField);
3943 }
3944
3945 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
3946 restrictProtectedReceiver(getField));
3947 if (doRestrict) {
3948 assert !getField.isStatic();
3949 // receiver type of VarHandle is too wide; narrow to caller
3950 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
3951 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
3952 }
3953 refc = lookupClass();
3954 }
3955 return VarHandles.makeFieldHandle(getField, refc,
3956 this.allowedModes == TRUSTED && !getField.isTrustedFinalField());
3957 }
3958 /** Check access and get the requested constructor. */
3959 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3960 return getDirectConstructorCommon(refc, ctor);
3961 }
3962 /** Common code for all constructors; do not call directly except from immediately above. */
3963 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3964 assert(ctor.isConstructor());
3965 checkAccess(REF_newInvokeSpecial, refc, ctor);
3966 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3967 return DirectMethodHandle.make(ctor).setVarargs(ctor);
3968 }
3969
3970 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
3971 */
3972 /*non-public*/
3973 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
3974 throws ReflectiveOperationException {
3975 if (!(type instanceof Class || type instanceof MethodType))
3976 throw new InternalError("unresolved MemberName");
3977 MemberName member = new MemberName(refKind, defc, name, type);
3978 MethodHandle mh = LOOKASIDE_TABLE.get(member);
3979 if (mh != null) {
3980 checkSymbolicClass(defc);
3981 return mh;
3982 }
3983 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
3984 // Treat MethodHandle.invoke and invokeExact specially.
3985 mh = findVirtualForMH(member.getName(), member.getMethodType());
3986 if (mh != null) {
3987 return mh;
3988 }
3989 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
3990 // Treat signature-polymorphic methods on VarHandle specially.
3991 mh = findVirtualForVH(member.getName(), member.getMethodType());
3992 if (mh != null) {
3993 return mh;
3994 }
3995 }
3996 MemberName resolved = resolveOrFail(refKind, member);
3997 mh = getDirectMethodForConstant(refKind, defc, resolved);
3998 if (mh instanceof DirectMethodHandle dmh
3999 && canBeCached(refKind, defc, resolved)) {
4000 MemberName key = mh.internalMemberName();
4001 if (key != null) {
4002 key = key.asNormalOriginal();
4003 }
4004 if (member.equals(key)) { // better safe than sorry
4005 LOOKASIDE_TABLE.put(key, dmh);
4006 }
4007 }
4008 return mh;
4009 }
4010 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
4011 if (refKind == REF_invokeSpecial) {
4012 return false;
4013 }
4014 if (!Modifier.isPublic(defc.getModifiers()) ||
4015 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
4016 !member.isPublic() ||
4017 member.isCallerSensitive()) {
4018 return false;
4019 }
4020 ClassLoader loader = defc.getClassLoader();
4021 if (loader != null) {
4022 ClassLoader sysl = ClassLoader.getSystemClassLoader();
4023 boolean found = false;
4024 while (sysl != null) {
4025 if (loader == sysl) { found = true; break; }
4026 sysl = sysl.getParent();
4027 }
4028 if (!found) {
4029 return false;
4030 }
4031 }
4032 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
4033 new MemberName(refKind, defc, member.getName(), member.getType()));
4034 if (resolved2 == null) {
4035 return false;
4036 }
4037 return true;
4038 }
4039 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
4040 throws ReflectiveOperationException {
4041 if (MethodHandleNatives.refKindIsField(refKind)) {
4042 return getDirectField(refKind, defc, member);
4043 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
4044 return getDirectMethod(refKind, defc, member, findBoundCallerLookup(member));
4045 } else if (refKind == REF_newInvokeSpecial) {
4046 return getDirectConstructor(defc, member);
4047 }
4048 // oops
4049 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
4050 }
4051
4052 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
4053 }
4054
4055 /**
4056 * Produces a method handle constructing arrays of a desired type,
4057 * as if by the {@code anewarray} bytecode.
4058 * The return type of the method handle will be the array type.
4059 * The type of its sole argument will be {@code int}, which specifies the size of the array.
4060 *
4061 * <p> If the returned method handle is invoked with a negative
4062 * array size, a {@code NegativeArraySizeException} will be thrown.
4063 *
4064 * @param arrayClass an array type
4065 * @return a method handle which can create arrays of the given type
4066 * @throws NullPointerException if the argument is {@code null}
4067 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
4068 * @see java.lang.reflect.Array#newInstance(Class, int)
4069 * @jvms 6.5 {@code anewarray} Instruction
4070 * @since 9
4071 */
4072 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
4073 if (!arrayClass.isArray()) {
4074 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
4075 }
4076 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
4077 bindTo(arrayClass.getComponentType());
4078 return ani.asType(ani.type().changeReturnType(arrayClass));
4079 }
4080
4081 /**
4082 * Produces a method handle returning the length of an array,
4083 * as if by the {@code arraylength} bytecode.
4084 * The type of the method handle will have {@code int} as return type,
4085 * and its sole argument will be the array type.
4086 *
4087 * <p> If the returned method handle is invoked with a {@code null}
4088 * array reference, a {@code NullPointerException} will be thrown.
4089 *
4090 * @param arrayClass an array type
4091 * @return a method handle which can retrieve the length of an array of the given array type
4092 * @throws NullPointerException if the argument is {@code null}
4093 * @throws IllegalArgumentException if arrayClass is not an array type
4094 * @jvms 6.5 {@code arraylength} Instruction
4095 * @since 9
4096 */
4097 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
4098 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
4099 }
4100
4101 /**
4102 * Produces a method handle giving read access to elements of an array,
4103 * as if by the {@code aaload} bytecode.
4104 * The type of the method handle will have a return type of the array's
4105 * element type. Its first argument will be the array type,
4106 * and the second will be {@code int}.
4107 *
4108 * <p> When the returned method handle is invoked,
4109 * the array reference and array index are checked.
4110 * A {@code NullPointerException} will be thrown if the array reference
4111 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4112 * thrown if the index is negative or if it is greater than or equal to
4113 * the length of the array.
4114 *
4115 * @param arrayClass an array type
4116 * @return a method handle which can load values from the given array type
4117 * @throws NullPointerException if the argument is null
4118 * @throws IllegalArgumentException if arrayClass is not an array type
4119 * @jvms 6.5 {@code aaload} Instruction
4120 */
4121 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
4122 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
4123 }
4124
4125 /**
4126 * Produces a method handle giving write access to elements of an array,
4127 * as if by the {@code astore} bytecode.
4128 * The type of the method handle will have a void return type.
4129 * Its last argument will be the array's element type.
4130 * The first and second arguments will be the array type and int.
4131 *
4132 * <p> When the returned method handle is invoked,
4133 * the array reference and array index are checked.
4134 * A {@code NullPointerException} will be thrown if the array reference
4135 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4136 * thrown if the index is negative or if it is greater than or equal to
4137 * the length of the array.
4138 *
4139 * @param arrayClass the class of an array
4140 * @return a method handle which can store values into the array type
4141 * @throws NullPointerException if the argument is null
4142 * @throws IllegalArgumentException if arrayClass is not an array type
4143 * @jvms 6.5 {@code aastore} Instruction
4144 */
4145 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
4146 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
4147 }
4148
4149 /**
4150 * Produces a VarHandle giving access to elements of an array of type
4151 * {@code arrayClass}. The VarHandle's variable type is the component type
4152 * of {@code arrayClass} and the list of coordinate types is
4153 * {@code (arrayClass, int)}, where the {@code int} coordinate type
4154 * corresponds to an argument that is an index into an array.
4155 * <p>
4156 * Certain access modes of the returned VarHandle are unsupported under
4157 * the following conditions:
4158 * <ul>
4159 * <li>if the component type is anything other than {@code byte},
4160 * {@code short}, {@code char}, {@code int}, {@code long},
4161 * {@code float}, or {@code double} then numeric atomic update access
4162 * modes are unsupported.
4163 * <li>if the component type is anything other than {@code boolean},
4164 * {@code byte}, {@code short}, {@code char}, {@code int} or
4165 * {@code long} then bitwise atomic update access modes are
4166 * unsupported.
4167 * </ul>
4168 * <p>
4169 * If the component type is {@code float} or {@code double} then numeric
4170 * and atomic update access modes compare values using their bitwise
4171 * representation (see {@link Float#floatToRawIntBits} and
4172 * {@link Double#doubleToRawLongBits}, respectively).
4173 *
4174 * <p> When the returned {@code VarHandle} is invoked,
4175 * the array reference and array index are checked.
4176 * A {@code NullPointerException} will be thrown if the array reference
4177 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4178 * thrown if the index is negative or if it is greater than or equal to
4179 * the length of the array.
4180 *
4181 * @apiNote
4182 * Bitwise comparison of {@code float} values or {@code double} values,
4183 * as performed by the numeric and atomic update access modes, differ
4184 * from the primitive {@code ==} operator and the {@link Float#equals}
4185 * and {@link Double#equals} methods, specifically with respect to
4186 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
4187 * Care should be taken when performing a compare and set or a compare
4188 * and exchange operation with such values since the operation may
4189 * unexpectedly fail.
4190 * There are many possible NaN values that are considered to be
4191 * {@code NaN} in Java, although no IEEE 754 floating-point operation
4192 * provided by Java can distinguish between them. Operation failure can
4193 * occur if the expected or witness value is a NaN value and it is
4194 * transformed (perhaps in a platform specific manner) into another NaN
4195 * value, and thus has a different bitwise representation (see
4196 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
4197 * details).
4198 * The values {@code -0.0} and {@code +0.0} have different bitwise
4199 * representations but are considered equal when using the primitive
4200 * {@code ==} operator. Operation failure can occur if, for example, a
4201 * numeric algorithm computes an expected value to be say {@code -0.0}
4202 * and previously computed the witness value to be say {@code +0.0}.
4203 * @param arrayClass the class of an array, of type {@code T[]}
4204 * @return a VarHandle giving access to elements of an array
4205 * @throws NullPointerException if the arrayClass is null
4206 * @throws IllegalArgumentException if arrayClass is not an array type
4207 * @since 9
4208 */
4209 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
4210 return VarHandles.makeArrayElementHandle(arrayClass);
4211 }
4212
4213 /**
4214 * Produces a VarHandle giving access to elements of a {@code byte[]} array
4215 * viewed as if it were a different primitive array type, such as
4216 * {@code int[]} or {@code long[]}.
4217 * The VarHandle's variable type is the component type of
4218 * {@code viewArrayClass} and the list of coordinate types is
4219 * {@code (byte[], int)}, where the {@code int} coordinate type
4220 * corresponds to an argument that is an index into a {@code byte[]} array.
4221 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
4222 * array, composing bytes to or from a value of the component type of
4223 * {@code viewArrayClass} according to the given endianness.
4224 * <p>
4225 * The supported component types (variables types) are {@code short},
4226 * {@code char}, {@code int}, {@code long}, {@code float} and
4227 * {@code double}.
4228 * <p>
4229 * Access of bytes at a given index will result in an
4230 * {@code ArrayIndexOutOfBoundsException} if the index is less than {@code 0}
4231 * or greater than the {@code byte[]} array length minus the size (in bytes)
4232 * of {@code T}.
4233 * <p>
4234 * Only plain {@linkplain VarHandle.AccessMode#GET get} and {@linkplain VarHandle.AccessMode#SET set}
4235 * access modes are supported by the returned var handle. For all other access modes, an
4236 * {@link UnsupportedOperationException} will be thrown.
4237 *
4238 * @apiNote if access modes other than plain access are required, clients should
4239 * consider using off-heap memory through
4240 * {@linkplain java.nio.ByteBuffer#allocateDirect(int) direct byte buffers} or
4241 * off-heap {@linkplain java.lang.foreign.MemorySegment memory segments},
4242 * or memory segments backed by a
4243 * {@linkplain java.lang.foreign.MemorySegment#ofArray(long[]) {@code long[]}},
4244 * for which stronger alignment guarantees can be made.
4245 *
4246 * @param viewArrayClass the view array class, with a component type of
4247 * type {@code T}
4248 * @param byteOrder the endianness of the view array elements, as
4249 * stored in the underlying {@code byte} array
4250 * @return a VarHandle giving access to elements of a {@code byte[]} array
4251 * viewed as if elements corresponding to the components type of the view
4252 * array class
4253 * @throws NullPointerException if viewArrayClass or byteOrder is null
4254 * @throws IllegalArgumentException if viewArrayClass is not an array type
4255 * @throws UnsupportedOperationException if the component type of
4256 * viewArrayClass is not supported as a variable type
4257 * @since 9
4258 */
4259 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
4260 ByteOrder byteOrder) throws IllegalArgumentException {
4261 Objects.requireNonNull(byteOrder);
4262 return VarHandles.byteArrayViewHandle(viewArrayClass,
4263 byteOrder == ByteOrder.BIG_ENDIAN);
4264 }
4265
4266 /**
4267 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
4268 * viewed as if it were an array of elements of a different primitive
4269 * component type to that of {@code byte}, such as {@code int[]} or
4270 * {@code long[]}.
4271 * The VarHandle's variable type is the component type of
4272 * {@code viewArrayClass} and the list of coordinate types is
4273 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
4274 * corresponds to an argument that is an index into a {@code byte[]} array.
4275 * The returned VarHandle accesses bytes at an index in a
4276 * {@code ByteBuffer}, composing bytes to or from a value of the component
4277 * type of {@code viewArrayClass} according to the given endianness.
4278 * <p>
4279 * The supported component types (variables types) are {@code short},
4280 * {@code char}, {@code int}, {@code long}, {@code float} and
4281 * {@code double}.
4282 * <p>
4283 * Access will result in a {@code ReadOnlyBufferException} for anything
4284 * other than the read access modes if the {@code ByteBuffer} is read-only.
4285 * <p>
4286 * Access of bytes at a given index will result in an
4287 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
4288 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
4289 * {@code T}.
4290 * <p>
4291 * For heap byte buffers, access is always unaligned. As a result, only the plain
4292 * {@linkplain VarHandle.AccessMode#GET get}
4293 * and {@linkplain VarHandle.AccessMode#SET set} access modes are supported by the
4294 * returned var handle. For all other access modes, an {@link IllegalStateException}
4295 * will be thrown.
4296 * <p>
4297 * For direct buffers only, access of bytes at an index may be aligned or misaligned for {@code T},
4298 * with respect to the underlying memory address, {@code A} say, associated
4299 * with the {@code ByteBuffer} and index.
4300 * If access is misaligned then access for anything other than the
4301 * {@code get} and {@code set} access modes will result in an
4302 * {@code IllegalStateException}. In such cases atomic access is only
4303 * guaranteed with respect to the largest power of two that divides the GCD
4304 * of {@code A} and the size (in bytes) of {@code T}.
4305 * If access is aligned then following access modes are supported and are
4306 * guaranteed to support atomic access:
4307 * <ul>
4308 * <li>read write access modes for all {@code T}, with the exception of
4309 * access modes {@code get} and {@code set} for {@code long} and
4310 * {@code double} on 32-bit platforms.
4311 * <li>atomic update access modes for {@code int}, {@code long},
4312 * {@code float} or {@code double}.
4313 * (Future major platform releases of the JDK may support additional
4314 * types for certain currently unsupported access modes.)
4315 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4316 * (Future major platform releases of the JDK may support additional
4317 * numeric types for certain currently unsupported access modes.)
4318 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4319 * (Future major platform releases of the JDK may support additional
4320 * numeric types for certain currently unsupported access modes.)
4321 * </ul>
4322 * <p>
4323 * Misaligned access, and therefore atomicity guarantees, may be determined
4324 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
4325 * {@code index}, {@code T} and its corresponding boxed type,
4326 * {@code T_BOX}, as follows:
4327 * <pre>{@code
4328 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4329 * ByteBuffer bb = ...
4330 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
4331 * boolean isMisaligned = misalignedAtIndex != 0;
4332 * }</pre>
4333 * <p>
4334 * If the variable type is {@code float} or {@code double} then atomic
4335 * update access modes compare values using their bitwise representation
4336 * (see {@link Float#floatToRawIntBits} and
4337 * {@link Double#doubleToRawLongBits}, respectively).
4338 * @param viewArrayClass the view array class, with a component type of
4339 * type {@code T}
4340 * @param byteOrder the endianness of the view array elements, as
4341 * stored in the underlying {@code ByteBuffer} (Note this overrides the
4342 * endianness of a {@code ByteBuffer})
4343 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
4344 * viewed as if elements corresponding to the components type of the view
4345 * array class
4346 * @throws NullPointerException if viewArrayClass or byteOrder is null
4347 * @throws IllegalArgumentException if viewArrayClass is not an array type
4348 * @throws UnsupportedOperationException if the component type of
4349 * viewArrayClass is not supported as a variable type
4350 * @since 9
4351 */
4352 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
4353 ByteOrder byteOrder) throws IllegalArgumentException {
4354 Objects.requireNonNull(byteOrder);
4355 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
4356 byteOrder == ByteOrder.BIG_ENDIAN);
4357 }
4358
4359
4360 //--- method handle invocation (reflective style)
4361
4362 /**
4363 * Produces a method handle which will invoke any method handle of the
4364 * given {@code type}, with a given number of trailing arguments replaced by
4365 * a single trailing {@code Object[]} array.
4366 * The resulting invoker will be a method handle with the following
4367 * arguments:
4368 * <ul>
4369 * <li>a single {@code MethodHandle} target
4370 * <li>zero or more leading values (counted by {@code leadingArgCount})
4371 * <li>an {@code Object[]} array containing trailing arguments
4372 * </ul>
4373 * <p>
4374 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
4375 * the indicated {@code type}.
4376 * That is, if the target is exactly of the given {@code type}, it will behave
4377 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
4378 * is used to convert the target to the required {@code type}.
4379 * <p>
4380 * The type of the returned invoker will not be the given {@code type}, but rather
4381 * will have all parameters except the first {@code leadingArgCount}
4382 * replaced by a single array of type {@code Object[]}, which will be
4383 * the final parameter.
4384 * <p>
4385 * Before invoking its target, the invoker will spread the final array, apply
4386 * reference casts as necessary, and unbox and widen primitive arguments.
4387 * If, when the invoker is called, the supplied array argument does
4388 * not have the correct number of elements, the invoker will throw
4389 * an {@link IllegalArgumentException} instead of invoking the target.
4390 * <p>
4391 * This method is equivalent to the following code (though it may be more efficient):
4392 * {@snippet lang="java" :
4393 MethodHandle invoker = MethodHandles.invoker(type);
4394 int spreadArgCount = type.parameterCount() - leadingArgCount;
4395 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
4396 return invoker;
4397 * }
4398 * This method throws no reflective exceptions.
4399 * @param type the desired target type
4400 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
4401 * @return a method handle suitable for invoking any method handle of the given type
4402 * @throws NullPointerException if {@code type} is null
4403 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
4404 * the range from 0 to {@code type.parameterCount()} inclusive,
4405 * or if the resulting method handle's type would have
4406 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4407 */
4408 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
4409 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
4410 throw newIllegalArgumentException("bad argument count", leadingArgCount);
4411 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
4412 return type.invokers().spreadInvoker(leadingArgCount);
4413 }
4414
4415 /**
4416 * Produces a special <em>invoker method handle</em> which can be used to
4417 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
4418 * The resulting invoker will have a type which is
4419 * exactly equal to the desired type, except that it will accept
4420 * an additional leading argument of type {@code MethodHandle}.
4421 * <p>
4422 * This method is equivalent to the following code (though it may be more efficient):
4423 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
4424 *
4425 * <p style="font-size:smaller;">
4426 * <em>Discussion:</em>
4427 * Invoker method handles can be useful when working with variable method handles
4428 * of unknown types.
4429 * For example, to emulate an {@code invokeExact} call to a variable method
4430 * handle {@code M}, extract its type {@code T},
4431 * look up the invoker method {@code X} for {@code T},
4432 * and call the invoker method, as {@code X.invoke(T, A...)}.
4433 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
4434 * is unknown.)
4435 * If spreading, collecting, or other argument transformations are required,
4436 * they can be applied once to the invoker {@code X} and reused on many {@code M}
4437 * method handle values, as long as they are compatible with the type of {@code X}.
4438 * <p style="font-size:smaller;">
4439 * <em>(Note: The invoker method is not available via the Core Reflection API.
4440 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4441 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4442 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4443 * <p>
4444 * This method throws no reflective exceptions.
4445 * @param type the desired target type
4446 * @return a method handle suitable for invoking any method handle of the given type
4447 * @throws IllegalArgumentException if the resulting method handle's type would have
4448 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4449 */
4450 public static MethodHandle exactInvoker(MethodType type) {
4451 return type.invokers().exactInvoker();
4452 }
4453
4454 /**
4455 * Produces a special <em>invoker method handle</em> which can be used to
4456 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
4457 * The resulting invoker will have a type which is
4458 * exactly equal to the desired type, except that it will accept
4459 * an additional leading argument of type {@code MethodHandle}.
4460 * <p>
4461 * Before invoking its target, if the target differs from the expected type,
4462 * the invoker will apply reference casts as
4463 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
4464 * Similarly, the return value will be converted as necessary.
4465 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
4466 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
4467 * <p>
4468 * This method is equivalent to the following code (though it may be more efficient):
4469 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
4470 * <p style="font-size:smaller;">
4471 * <em>Discussion:</em>
4472 * A {@linkplain MethodType#genericMethodType general method type} is one which
4473 * mentions only {@code Object} arguments and return values.
4474 * An invoker for such a type is capable of calling any method handle
4475 * of the same arity as the general type.
4476 * <p style="font-size:smaller;">
4477 * <em>(Note: The invoker method is not available via the Core Reflection API.
4478 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4479 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4480 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4481 * <p>
4482 * This method throws no reflective exceptions.
4483 * @param type the desired target type
4484 * @return a method handle suitable for invoking any method handle convertible to the given type
4485 * @throws IllegalArgumentException if the resulting method handle's type would have
4486 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4487 */
4488 public static MethodHandle invoker(MethodType type) {
4489 return type.invokers().genericInvoker();
4490 }
4491
4492 /**
4493 * Produces a special <em>invoker method handle</em> which can be used to
4494 * invoke a signature-polymorphic access mode method on any VarHandle whose
4495 * associated access mode type is compatible with the given type.
4496 * The resulting invoker will have a type which is exactly equal to the
4497 * desired given type, except that it will accept an additional leading
4498 * argument of type {@code VarHandle}.
4499 *
4500 * @param accessMode the VarHandle access mode
4501 * @param type the desired target type
4502 * @return a method handle suitable for invoking an access mode method of
4503 * any VarHandle whose access mode type is of the given type.
4504 * @since 9
4505 */
4506 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4507 return type.invokers().varHandleMethodExactInvoker(accessMode);
4508 }
4509
4510 /**
4511 * Produces a special <em>invoker method handle</em> which can be used to
4512 * invoke a signature-polymorphic access mode method on any VarHandle whose
4513 * associated access mode type is compatible with the given type.
4514 * The resulting invoker will have a type which is exactly equal to the
4515 * desired given type, except that it will accept an additional leading
4516 * argument of type {@code VarHandle}.
4517 * <p>
4518 * Before invoking its target, if the access mode type differs from the
4519 * desired given type, the invoker will apply reference casts as necessary
4520 * and box, unbox, or widen primitive values, as if by
4521 * {@link MethodHandle#asType asType}. Similarly, the return value will be
4522 * converted as necessary.
4523 * <p>
4524 * This method is equivalent to the following code (though it may be more
4525 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
4526 *
4527 * @param accessMode the VarHandle access mode
4528 * @param type the desired target type
4529 * @return a method handle suitable for invoking an access mode method of
4530 * any VarHandle whose access mode type is convertible to the given
4531 * type.
4532 * @since 9
4533 */
4534 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4535 return type.invokers().varHandleMethodInvoker(accessMode);
4536 }
4537
4538 /*non-public*/
4539 static MethodHandle basicInvoker(MethodType type) {
4540 return type.invokers().basicInvoker();
4541 }
4542
4543 //--- method handle modification (creation from other method handles)
4544
4545 /**
4546 * Produces a method handle which adapts the type of the
4547 * given method handle to a new type by pairwise argument and return type conversion.
4548 * The original type and new type must have the same number of arguments.
4549 * The resulting method handle is guaranteed to report a type
4550 * which is equal to the desired new type.
4551 * <p>
4552 * If the original type and new type are equal, returns target.
4553 * <p>
4554 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
4555 * and some additional conversions are also applied if those conversions fail.
4556 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
4557 * if possible, before or instead of any conversions done by {@code asType}:
4558 * <ul>
4559 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
4560 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
4561 * (This treatment of interfaces follows the usage of the bytecode verifier.)
4562 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
4563 * the boolean is converted to a byte value, 1 for true, 0 for false.
4564 * (This treatment follows the usage of the bytecode verifier.)
4565 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
4566 * <em>T0</em> is converted to byte via Java casting conversion (JLS {@jls 5.5}),
4567 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
4568 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
4569 * then a Java casting conversion (JLS {@jls 5.5}) is applied.
4570 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
4571 * widening and/or narrowing.)
4572 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
4573 * conversion will be applied at runtime, possibly followed
4574 * by a Java casting conversion (JLS {@jls 5.5}) on the primitive value,
4575 * possibly followed by a conversion from byte to boolean by testing
4576 * the low-order bit.
4577 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
4578 * and if the reference is null at runtime, a zero value is introduced.
4579 * </ul>
4580 * @param target the method handle to invoke after arguments are retyped
4581 * @param newType the expected type of the new method handle
4582 * @return a method handle which delegates to the target after performing
4583 * any necessary argument conversions, and arranges for any
4584 * necessary return value conversions
4585 * @throws NullPointerException if either argument is null
4586 * @throws WrongMethodTypeException if the conversion cannot be made
4587 * @see MethodHandle#asType
4588 */
4589 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
4590 explicitCastArgumentsChecks(target, newType);
4591 // use the asTypeCache when possible:
4592 MethodType oldType = target.type();
4593 if (oldType == newType) return target;
4594 if (oldType.explicitCastEquivalentToAsType(newType)) {
4595 return target.asFixedArity().asType(newType);
4596 }
4597 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
4598 }
4599
4600 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
4601 if (target.type().parameterCount() != newType.parameterCount()) {
4602 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
4603 }
4604 }
4605
4606 /**
4607 * Produces a method handle which adapts the calling sequence of the
4608 * given method handle to a new type, by reordering the arguments.
4609 * The resulting method handle is guaranteed to report a type
4610 * which is equal to the desired new type.
4611 * <p>
4612 * The given array controls the reordering.
4613 * Call {@code #I} the number of incoming parameters (the value
4614 * {@code newType.parameterCount()}, and call {@code #O} the number
4615 * of outgoing parameters (the value {@code target.type().parameterCount()}).
4616 * Then the length of the reordering array must be {@code #O},
4617 * and each element must be a non-negative number less than {@code #I}.
4618 * For every {@code N} less than {@code #O}, the {@code N}-th
4619 * outgoing argument will be taken from the {@code I}-th incoming
4620 * argument, where {@code I} is {@code reorder[N]}.
4621 * <p>
4622 * No argument or return value conversions are applied.
4623 * The type of each incoming argument, as determined by {@code newType},
4624 * must be identical to the type of the corresponding outgoing parameter
4625 * or parameters in the target method handle.
4626 * The return type of {@code newType} must be identical to the return
4627 * type of the original target.
4628 * <p>
4629 * The reordering array need not specify an actual permutation.
4630 * An incoming argument will be duplicated if its index appears
4631 * more than once in the array, and an incoming argument will be dropped
4632 * if its index does not appear in the array.
4633 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
4634 * incoming arguments which are not mentioned in the reordering array
4635 * may be of any type, as determined only by {@code newType}.
4636 * {@snippet lang="java" :
4637 import static java.lang.invoke.MethodHandles.*;
4638 import static java.lang.invoke.MethodType.*;
4639 ...
4640 MethodType intfn1 = methodType(int.class, int.class);
4641 MethodType intfn2 = methodType(int.class, int.class, int.class);
4642 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
4643 assert(sub.type().equals(intfn2));
4644 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
4645 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
4646 assert((int)rsub.invokeExact(1, 100) == 99);
4647 MethodHandle add = ... (int x, int y) -> (x+y) ...;
4648 assert(add.type().equals(intfn2));
4649 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
4650 assert(twice.type().equals(intfn1));
4651 assert((int)twice.invokeExact(21) == 42);
4652 * }
4653 * <p>
4654 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4655 * variable-arity method handle}, even if the original target method handle was.
4656 * @param target the method handle to invoke after arguments are reordered
4657 * @param newType the expected type of the new method handle
4658 * @param reorder an index array which controls the reordering
4659 * @return a method handle which delegates to the target after it
4660 * drops unused arguments and moves and/or duplicates the other arguments
4661 * @throws NullPointerException if any argument is null
4662 * @throws IllegalArgumentException if the index array length is not equal to
4663 * the arity of the target, or if any index array element
4664 * not a valid index for a parameter of {@code newType},
4665 * or if two corresponding parameter types in
4666 * {@code target.type()} and {@code newType} are not identical,
4667 */
4668 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
4669 reorder = reorder.clone(); // get a private copy
4670 MethodType oldType = target.type();
4671 permuteArgumentChecks(reorder, newType, oldType);
4672 // first detect dropped arguments and handle them separately
4673 int[] originalReorder = reorder;
4674 BoundMethodHandle result = target.rebind();
4675 LambdaForm form = result.form;
4676 int newArity = newType.parameterCount();
4677 // Normalize the reordering into a real permutation,
4678 // by removing duplicates and adding dropped elements.
4679 // This somewhat improves lambda form caching, as well
4680 // as simplifying the transform by breaking it up into steps.
4681 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
4682 if (ddIdx > 0) {
4683 // We found a duplicated entry at reorder[ddIdx].
4684 // Example: (x,y,z)->asList(x,y,z)
4685 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
4686 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
4687 // The starred element corresponds to the argument
4688 // deleted by the dupArgumentForm transform.
4689 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
4690 boolean killFirst = false;
4691 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
4692 // Set killFirst if the dup is larger than an intervening position.
4693 // This will remove at least one inversion from the permutation.
4694 if (dupVal > val) killFirst = true;
4695 }
4696 if (!killFirst) {
4697 srcPos = dstPos;
4698 dstPos = ddIdx;
4699 }
4700 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
4701 assert (reorder[srcPos] == reorder[dstPos]);
4702 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
4703 // contract the reordering by removing the element at dstPos
4704 int tailPos = dstPos + 1;
4705 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
4706 reorder = Arrays.copyOf(reorder, reorder.length - 1);
4707 } else {
4708 int dropVal = ~ddIdx, insPos = 0;
4709 while (insPos < reorder.length && reorder[insPos] < dropVal) {
4710 // Find first element of reorder larger than dropVal.
4711 // This is where we will insert the dropVal.
4712 insPos += 1;
4713 }
4714 Class<?> ptype = newType.parameterType(dropVal);
4715 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
4716 oldType = oldType.insertParameterTypes(insPos, ptype);
4717 // expand the reordering by inserting an element at insPos
4718 int tailPos = insPos + 1;
4719 reorder = Arrays.copyOf(reorder, reorder.length + 1);
4720 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
4721 reorder[insPos] = dropVal;
4722 }
4723 assert (permuteArgumentChecks(reorder, newType, oldType));
4724 }
4725 assert (reorder.length == newArity); // a perfect permutation
4726 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
4727 form = form.editor().permuteArgumentsForm(1, reorder);
4728 if (newType == result.type() && form == result.internalForm())
4729 return result;
4730 return result.copyWith(newType, form);
4731 }
4732
4733 /**
4734 * Return an indication of any duplicate or omission in reorder.
4735 * If the reorder contains a duplicate entry, return the index of the second occurrence.
4736 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
4737 * Otherwise, return zero.
4738 * If an element not in [0..newArity-1] is encountered, return reorder.length.
4739 */
4740 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
4741 final int BIT_LIMIT = 63; // max number of bits in bit mask
4742 if (newArity < BIT_LIMIT) {
4743 long mask = 0;
4744 for (int i = 0; i < reorder.length; i++) {
4745 int arg = reorder[i];
4746 if (arg >= newArity) {
4747 return reorder.length;
4748 }
4749 long bit = 1L << arg;
4750 if ((mask & bit) != 0) {
4751 return i; // >0 indicates a dup
4752 }
4753 mask |= bit;
4754 }
4755 if (mask == (1L << newArity) - 1) {
4756 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
4757 return 0;
4758 }
4759 // find first zero
4760 long zeroBit = Long.lowestOneBit(~mask);
4761 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
4762 assert(zeroPos <= newArity);
4763 if (zeroPos == newArity) {
4764 return 0;
4765 }
4766 return ~zeroPos;
4767 } else {
4768 // same algorithm, different bit set
4769 BitSet mask = new BitSet(newArity);
4770 for (int i = 0; i < reorder.length; i++) {
4771 int arg = reorder[i];
4772 if (arg >= newArity) {
4773 return reorder.length;
4774 }
4775 if (mask.get(arg)) {
4776 return i; // >0 indicates a dup
4777 }
4778 mask.set(arg);
4779 }
4780 int zeroPos = mask.nextClearBit(0);
4781 assert(zeroPos <= newArity);
4782 if (zeroPos == newArity) {
4783 return 0;
4784 }
4785 return ~zeroPos;
4786 }
4787 }
4788
4789 static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
4790 if (newType.returnType() != oldType.returnType())
4791 throw newIllegalArgumentException("return types do not match",
4792 oldType, newType);
4793 if (reorder.length != oldType.parameterCount())
4794 throw newIllegalArgumentException("old type parameter count and reorder array length do not match",
4795 oldType, Arrays.toString(reorder));
4796
4797 int limit = newType.parameterCount();
4798 for (int j = 0; j < reorder.length; j++) {
4799 int i = reorder[j];
4800 if (i < 0 || i >= limit) {
4801 throw newIllegalArgumentException("index is out of bounds for new type",
4802 i, newType);
4803 }
4804 Class<?> src = newType.parameterType(i);
4805 Class<?> dst = oldType.parameterType(j);
4806 if (src != dst)
4807 throw newIllegalArgumentException("parameter types do not match after reorder",
4808 oldType, newType);
4809 }
4810 return true;
4811 }
4812
4813 /**
4814 * Produces a method handle of the requested return type which returns the given
4815 * constant value every time it is invoked.
4816 * <p>
4817 * Before the method handle is returned, the passed-in value is converted to the requested type.
4818 * If the requested type is primitive, widening primitive conversions are attempted,
4819 * else reference conversions are attempted.
4820 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
4821 * @param type the return type of the desired method handle
4822 * @param value the value to return
4823 * @return a method handle of the given return type and no arguments, which always returns the given value
4824 * @throws NullPointerException if the {@code type} argument is null
4825 * @throws ClassCastException if the value cannot be converted to the required return type
4826 * @throws IllegalArgumentException if the given type is {@code void.class}
4827 */
4828 public static MethodHandle constant(Class<?> type, Object value) {
4829 if (Objects.requireNonNull(type) == void.class)
4830 throw newIllegalArgumentException("void type");
4831 return MethodHandleImpl.makeConstantReturning(type, value);
4832 }
4833
4834 /**
4835 * Produces a method handle which returns its sole argument when invoked.
4836 * @param type the type of the sole parameter and return value of the desired method handle
4837 * @return a unary method handle which accepts and returns the given type
4838 * @throws NullPointerException if the argument is null
4839 * @throws IllegalArgumentException if the given type is {@code void.class}
4840 */
4841 public static MethodHandle identity(Class<?> type) {
4842 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
4843 int pos = btw.ordinal();
4844 MethodHandle ident = IDENTITY_MHS[pos];
4845 if (ident == null) {
4846 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
4847 }
4848 if (ident.type().returnType() == type)
4849 return ident;
4850 // something like identity(Foo.class); do not bother to intern these
4851 assert (btw == Wrapper.OBJECT);
4852 return makeIdentity(type);
4853 }
4854
4855 /**
4856 * Produces a constant method handle of the requested return type which
4857 * returns the default value for that type every time it is invoked.
4858 * The resulting constant method handle will have no side effects.
4859 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
4860 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
4861 * since {@code explicitCastArguments} converts {@code null} to default values.
4862 * @param type the expected return type of the desired method handle
4863 * @return a constant method handle that takes no arguments
4864 * and returns the default value of the given type (or void, if the type is void)
4865 * @throws NullPointerException if the argument is null
4866 * @see MethodHandles#constant
4867 * @see MethodHandles#empty
4868 * @see MethodHandles#explicitCastArguments
4869 * @since 9
4870 */
4871 public static MethodHandle zero(Class<?> type) {
4872 Objects.requireNonNull(type);
4873 return type.isPrimitive() ? primitiveZero(Wrapper.forPrimitiveType(type))
4874 : MethodHandleImpl.makeConstantReturning(type, null);
4875 }
4876
4877 private static MethodHandle identityOrVoid(Class<?> type) {
4878 return type == void.class ? zero(type) : identity(type);
4879 }
4880
4881 /**
4882 * Produces a method handle of the requested type which ignores any arguments, does nothing,
4883 * and returns a suitable default depending on the return type.
4884 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
4885 * <p>The returned method handle is equivalent to
4886 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
4887 *
4888 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
4889 * {@code guardWithTest(pred, target, empty(target.type())}.
4890 * @param type the type of the desired method handle
4891 * @return a constant method handle of the given type, which returns a default value of the given return type
4892 * @throws NullPointerException if the argument is null
4893 * @see MethodHandles#primitiveZero
4894 * @see MethodHandles#constant
4895 * @since 9
4896 */
4897 public static MethodHandle empty(MethodType type) {
4898 Objects.requireNonNull(type);
4899 return dropArgumentsTrusted(zero(type.returnType()), 0, type.ptypes());
4900 }
4901
4902 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
4903 private static MethodHandle makeIdentity(Class<?> ptype) {
4904 MethodType mtype = methodType(ptype, ptype); // throws IAE for void
4905 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
4906 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
4907 }
4908
4909 private static MethodHandle primitiveZero(Wrapper w) {
4910 assert w != Wrapper.OBJECT : w;
4911 int pos = w.ordinal();
4912 MethodHandle mh = PRIMITIVE_ZERO_MHS[pos];
4913 if (mh == null) {
4914 mh = setCachedMethodHandle(PRIMITIVE_ZERO_MHS, pos, makePrimitiveZero(w));
4915 }
4916 assert (mh.type().returnType() == w.primitiveType()) : mh;
4917 return mh;
4918 }
4919
4920 private static MethodHandle makePrimitiveZero(Wrapper w) {
4921 if (w == Wrapper.VOID) {
4922 var lf = LambdaForm.identityForm(V_TYPE); // ensures BMH & SimpleMH are initialized
4923 return SimpleMethodHandle.make(MethodType.methodType(void.class), lf);
4924 } else {
4925 return MethodHandleImpl.makeConstantReturning(w.primitiveType(), w.zero());
4926 }
4927 }
4928
4929 private static final @Stable MethodHandle[] PRIMITIVE_ZERO_MHS = new MethodHandle[Wrapper.COUNT];
4930
4931 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
4932 // Simulate a CAS, to avoid racy duplication of results.
4933 MethodHandle prev = cache[pos];
4934 if (prev != null) return prev;
4935 return cache[pos] = value;
4936 }
4937
4938 /**
4939 * Provides a target method handle with one or more <em>bound arguments</em>
4940 * in advance of the method handle's invocation.
4941 * The formal parameters to the target corresponding to the bound
4942 * arguments are called <em>bound parameters</em>.
4943 * Returns a new method handle which saves away the bound arguments.
4944 * When it is invoked, it receives arguments for any non-bound parameters,
4945 * binds the saved arguments to their corresponding parameters,
4946 * and calls the original target.
4947 * <p>
4948 * The type of the new method handle will drop the types for the bound
4949 * parameters from the original target type, since the new method handle
4950 * will no longer require those arguments to be supplied by its callers.
4951 * <p>
4952 * Each given argument object must match the corresponding bound parameter type.
4953 * If a bound parameter type is a primitive, the argument object
4954 * must be a wrapper, and will be unboxed to produce the primitive value.
4955 * <p>
4956 * The {@code pos} argument selects which parameters are to be bound.
4957 * It may range between zero and <i>N-L</i> (inclusively),
4958 * where <i>N</i> is the arity of the target method handle
4959 * and <i>L</i> is the length of the values array.
4960 * <p>
4961 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4962 * variable-arity method handle}, even if the original target method handle was.
4963 * @param target the method handle to invoke after the argument is inserted
4964 * @param pos where to insert the argument (zero for the first)
4965 * @param values the series of arguments to insert
4966 * @return a method handle which inserts an additional argument,
4967 * before calling the original method handle
4968 * @throws NullPointerException if the target or the {@code values} array is null
4969 * @throws IllegalArgumentException if {@code pos} is less than {@code 0} or greater than
4970 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
4971 * is the length of the values array.
4972 * @throws ClassCastException if an argument does not match the corresponding bound parameter
4973 * type.
4974 * @see MethodHandle#bindTo
4975 */
4976 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
4977 int insCount = values.length;
4978 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
4979 if (insCount == 0) return target;
4980 BoundMethodHandle result = target.rebind();
4981 for (int i = 0; i < insCount; i++) {
4982 Object value = values[i];
4983 Class<?> ptype = ptypes[pos+i];
4984 if (ptype.isPrimitive()) {
4985 result = insertArgumentPrimitive(result, pos, ptype, value);
4986 } else {
4987 value = ptype.cast(value); // throw CCE if needed
4988 result = result.bindArgumentL(pos, value);
4989 }
4990 }
4991 return result;
4992 }
4993
4994 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
4995 Class<?> ptype, Object value) {
4996 Wrapper w = Wrapper.forPrimitiveType(ptype);
4997 // perform unboxing and/or primitive conversion
4998 value = w.convert(value, ptype);
4999 return switch (w) {
5000 case INT -> result.bindArgumentI(pos, (int) value);
5001 case LONG -> result.bindArgumentJ(pos, (long) value);
5002 case FLOAT -> result.bindArgumentF(pos, (float) value);
5003 case DOUBLE -> result.bindArgumentD(pos, (double) value);
5004 default -> result.bindArgumentI(pos, ValueConversions.widenSubword(value));
5005 };
5006 }
5007
5008 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
5009 MethodType oldType = target.type();
5010 int outargs = oldType.parameterCount();
5011 int inargs = outargs - insCount;
5012 if (inargs < 0)
5013 throw newIllegalArgumentException("too many values to insert");
5014 if (pos < 0 || pos > inargs)
5015 throw newIllegalArgumentException("no argument type to append");
5016 return oldType.ptypes();
5017 }
5018
5019 /**
5020 * Produces a method handle which will discard some dummy arguments
5021 * before calling some other specified <i>target</i> method handle.
5022 * The type of the new method handle will be the same as the target's type,
5023 * except it will also include the dummy argument types,
5024 * at some given position.
5025 * <p>
5026 * The {@code pos} argument may range between zero and <i>N</i>,
5027 * where <i>N</i> is the arity of the target.
5028 * If {@code pos} is zero, the dummy arguments will precede
5029 * the target's real arguments; if {@code pos} is <i>N</i>
5030 * they will come after.
5031 * <p>
5032 * <b>Example:</b>
5033 * {@snippet lang="java" :
5034 import static java.lang.invoke.MethodHandles.*;
5035 import static java.lang.invoke.MethodType.*;
5036 ...
5037 MethodHandle cat = lookup().findVirtual(String.class,
5038 "concat", methodType(String.class, String.class));
5039 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5040 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
5041 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
5042 assertEquals(bigType, d0.type());
5043 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
5044 * }
5045 * <p>
5046 * This method is also equivalent to the following code:
5047 * <blockquote><pre>
5048 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
5049 * </pre></blockquote>
5050 * @param target the method handle to invoke after the arguments are dropped
5051 * @param pos position of first argument to drop (zero for the leftmost)
5052 * @param valueTypes the type(s) of the argument(s) to drop
5053 * @return a method handle which drops arguments of the given types,
5054 * before calling the original method handle
5055 * @throws NullPointerException if the target is null,
5056 * or if the {@code valueTypes} list or any of its elements is null
5057 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5058 * or if {@code pos} is negative or greater than the arity of the target,
5059 * or if the new method handle's type would have too many parameters
5060 */
5061 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
5062 return dropArgumentsTrusted(target, pos, valueTypes.toArray(new Class<?>[0]).clone());
5063 }
5064
5065 static MethodHandle dropArgumentsTrusted(MethodHandle target, int pos, Class<?>[] valueTypes) {
5066 MethodType oldType = target.type(); // get NPE
5067 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
5068 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
5069 if (dropped == 0) return target;
5070 BoundMethodHandle result = target.rebind();
5071 LambdaForm lform = result.form;
5072 int insertFormArg = 1 + pos;
5073 for (Class<?> ptype : valueTypes) {
5074 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
5075 }
5076 result = result.copyWith(newType, lform);
5077 return result;
5078 }
5079
5080 private static int dropArgumentChecks(MethodType oldType, int pos, Class<?>[] valueTypes) {
5081 int dropped = valueTypes.length;
5082 MethodType.checkSlotCount(dropped);
5083 int outargs = oldType.parameterCount();
5084 int inargs = outargs + dropped;
5085 if (pos < 0 || pos > outargs)
5086 throw newIllegalArgumentException("no argument type to remove"
5087 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
5088 );
5089 return dropped;
5090 }
5091
5092 /**
5093 * Produces a method handle which will discard some dummy arguments
5094 * before calling some other specified <i>target</i> method handle.
5095 * The type of the new method handle will be the same as the target's type,
5096 * except it will also include the dummy argument types,
5097 * at some given position.
5098 * <p>
5099 * The {@code pos} argument may range between zero and <i>N</i>,
5100 * where <i>N</i> is the arity of the target.
5101 * If {@code pos} is zero, the dummy arguments will precede
5102 * the target's real arguments; if {@code pos} is <i>N</i>
5103 * they will come after.
5104 * @apiNote
5105 * {@snippet lang="java" :
5106 import static java.lang.invoke.MethodHandles.*;
5107 import static java.lang.invoke.MethodType.*;
5108 ...
5109 MethodHandle cat = lookup().findVirtual(String.class,
5110 "concat", methodType(String.class, String.class));
5111 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5112 MethodHandle d0 = dropArguments(cat, 0, String.class);
5113 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
5114 MethodHandle d1 = dropArguments(cat, 1, String.class);
5115 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
5116 MethodHandle d2 = dropArguments(cat, 2, String.class);
5117 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
5118 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
5119 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
5120 * }
5121 * <p>
5122 * This method is also equivalent to the following code:
5123 * <blockquote><pre>
5124 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
5125 * </pre></blockquote>
5126 * @param target the method handle to invoke after the arguments are dropped
5127 * @param pos position of first argument to drop (zero for the leftmost)
5128 * @param valueTypes the type(s) of the argument(s) to drop
5129 * @return a method handle which drops arguments of the given types,
5130 * before calling the original method handle
5131 * @throws NullPointerException if the target is null,
5132 * or if the {@code valueTypes} array or any of its elements is null
5133 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5134 * or if {@code pos} is negative or greater than the arity of the target,
5135 * or if the new method handle's type would have
5136 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5137 */
5138 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
5139 return dropArgumentsTrusted(target, pos, valueTypes.clone());
5140 }
5141
5142 /* Convenience overloads for trusting internal low-arity call-sites */
5143 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1) {
5144 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1 });
5145 }
5146 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1, Class<?> valueType2) {
5147 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1, valueType2 });
5148 }
5149
5150 // private version which allows caller some freedom with error handling
5151 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, Class<?>[] newTypes, int pos,
5152 boolean nullOnFailure) {
5153 Class<?>[] oldTypes = target.type().ptypes();
5154 int match = oldTypes.length;
5155 if (skip != 0) {
5156 if (skip < 0 || skip > match) {
5157 throw newIllegalArgumentException("illegal skip", skip, target);
5158 }
5159 oldTypes = Arrays.copyOfRange(oldTypes, skip, match);
5160 match -= skip;
5161 }
5162 Class<?>[] addTypes = newTypes;
5163 int add = addTypes.length;
5164 if (pos != 0) {
5165 if (pos < 0 || pos > add) {
5166 throw newIllegalArgumentException("illegal pos", pos, Arrays.toString(newTypes));
5167 }
5168 addTypes = Arrays.copyOfRange(addTypes, pos, add);
5169 add -= pos;
5170 assert(addTypes.length == add);
5171 }
5172 // Do not add types which already match the existing arguments.
5173 if (match > add || !Arrays.equals(oldTypes, 0, oldTypes.length, addTypes, 0, match)) {
5174 if (nullOnFailure) {
5175 return null;
5176 }
5177 throw newIllegalArgumentException("argument lists do not match",
5178 Arrays.toString(oldTypes), Arrays.toString(newTypes));
5179 }
5180 addTypes = Arrays.copyOfRange(addTypes, match, add);
5181 add -= match;
5182 assert(addTypes.length == add);
5183 // newTypes: ( P*[pos], M*[match], A*[add] )
5184 // target: ( S*[skip], M*[match] )
5185 MethodHandle adapter = target;
5186 if (add > 0) {
5187 adapter = dropArgumentsTrusted(adapter, skip+ match, addTypes);
5188 }
5189 // adapter: (S*[skip], M*[match], A*[add] )
5190 if (pos > 0) {
5191 adapter = dropArgumentsTrusted(adapter, skip, Arrays.copyOfRange(newTypes, 0, pos));
5192 }
5193 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
5194 return adapter;
5195 }
5196
5197 /**
5198 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
5199 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
5200 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
5201 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
5202 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
5203 * {@link #dropArguments(MethodHandle, int, Class[])}.
5204 * <p>
5205 * The resulting handle will have the same return type as the target handle.
5206 * <p>
5207 * In more formal terms, assume these two type lists:<ul>
5208 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
5209 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
5210 * {@code newTypes}.
5211 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
5212 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
5213 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
5214 * sub-list.
5215 * </ul>
5216 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
5217 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
5218 * {@link #dropArguments(MethodHandle, int, Class[])}.
5219 *
5220 * @apiNote
5221 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
5222 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
5223 * {@snippet lang="java" :
5224 import static java.lang.invoke.MethodHandles.*;
5225 import static java.lang.invoke.MethodType.*;
5226 ...
5227 ...
5228 MethodHandle h0 = constant(boolean.class, true);
5229 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
5230 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
5231 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
5232 if (h1.type().parameterCount() < h2.type().parameterCount())
5233 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
5234 else
5235 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
5236 MethodHandle h3 = guardWithTest(h0, h1, h2);
5237 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
5238 * }
5239 * @param target the method handle to adapt
5240 * @param skip number of targets parameters to disregard (they will be unchanged)
5241 * @param newTypes the list of types to match {@code target}'s parameter type list to
5242 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
5243 * @return a possibly adapted method handle
5244 * @throws NullPointerException if either argument is null
5245 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
5246 * or if {@code skip} is negative or greater than the arity of the target,
5247 * or if {@code pos} is negative or greater than the newTypes list size,
5248 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
5249 * {@code pos}.
5250 * @since 9
5251 */
5252 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
5253 Objects.requireNonNull(target);
5254 Objects.requireNonNull(newTypes);
5255 return dropArgumentsToMatch(target, skip, newTypes.toArray(new Class<?>[0]).clone(), pos, false);
5256 }
5257
5258 /**
5259 * Drop the return value of the target handle (if any).
5260 * The returned method handle will have a {@code void} return type.
5261 *
5262 * @param target the method handle to adapt
5263 * @return a possibly adapted method handle
5264 * @throws NullPointerException if {@code target} is null
5265 * @since 16
5266 */
5267 public static MethodHandle dropReturn(MethodHandle target) {
5268 Objects.requireNonNull(target);
5269 MethodType oldType = target.type();
5270 Class<?> oldReturnType = oldType.returnType();
5271 if (oldReturnType == void.class)
5272 return target;
5273 MethodType newType = oldType.changeReturnType(void.class);
5274 BoundMethodHandle result = target.rebind();
5275 LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true);
5276 result = result.copyWith(newType, lform);
5277 return result;
5278 }
5279
5280 /**
5281 * Adapts a target method handle by pre-processing
5282 * one or more of its arguments, each with its own unary filter function,
5283 * and then calling the target with each pre-processed argument
5284 * replaced by the result of its corresponding filter function.
5285 * <p>
5286 * The pre-processing is performed by one or more method handles,
5287 * specified in the elements of the {@code filters} array.
5288 * The first element of the filter array corresponds to the {@code pos}
5289 * argument of the target, and so on in sequence.
5290 * The filter functions are invoked in left to right order.
5291 * <p>
5292 * Null arguments in the array are treated as identity functions,
5293 * and the corresponding arguments left unchanged.
5294 * (If there are no non-null elements in the array, the original target is returned.)
5295 * Each filter is applied to the corresponding argument of the adapter.
5296 * <p>
5297 * If a filter {@code F} applies to the {@code N}th argument of
5298 * the target, then {@code F} must be a method handle which
5299 * takes exactly one argument. The type of {@code F}'s sole argument
5300 * replaces the corresponding argument type of the target
5301 * in the resulting adapted method handle.
5302 * The return type of {@code F} must be identical to the corresponding
5303 * parameter type of the target.
5304 * <p>
5305 * It is an error if there are elements of {@code filters}
5306 * (null or not)
5307 * which do not correspond to argument positions in the target.
5308 * <p><b>Example:</b>
5309 * {@snippet lang="java" :
5310 import static java.lang.invoke.MethodHandles.*;
5311 import static java.lang.invoke.MethodType.*;
5312 ...
5313 MethodHandle cat = lookup().findVirtual(String.class,
5314 "concat", methodType(String.class, String.class));
5315 MethodHandle upcase = lookup().findVirtual(String.class,
5316 "toUpperCase", methodType(String.class));
5317 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5318 MethodHandle f0 = filterArguments(cat, 0, upcase);
5319 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
5320 MethodHandle f1 = filterArguments(cat, 1, upcase);
5321 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
5322 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
5323 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
5324 * }
5325 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5326 * denotes the return type of both the {@code target} and resulting adapter.
5327 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
5328 * of the parameters and arguments that precede and follow the filter position
5329 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
5330 * values of the filtered parameters and arguments; they also represent the
5331 * return types of the {@code filter[i]} handles. The latter accept arguments
5332 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
5333 * the resulting adapter.
5334 * {@snippet lang="java" :
5335 * T target(P... p, A[i]... a[i], B... b);
5336 * A[i] filter[i](V[i]);
5337 * T adapter(P... p, V[i]... v[i], B... b) {
5338 * return target(p..., filter[i](v[i])..., b...);
5339 * }
5340 * }
5341 * <p>
5342 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5343 * variable-arity method handle}, even if the original target method handle was.
5344 *
5345 * @param target the method handle to invoke after arguments are filtered
5346 * @param pos the position of the first argument to filter
5347 * @param filters method handles to call initially on filtered arguments
5348 * @return method handle which incorporates the specified argument filtering logic
5349 * @throws NullPointerException if the target is null
5350 * or if the {@code filters} array is null
5351 * @throws IllegalArgumentException if a non-null element of {@code filters}
5352 * does not match a corresponding argument type of target as described above,
5353 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
5354 * or if the resulting method handle's type would have
5355 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5356 */
5357 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
5358 // In method types arguments start at index 0, while the LF
5359 // editor have the MH receiver at position 0 - adjust appropriately.
5360 final int MH_RECEIVER_OFFSET = 1;
5361 filterArgumentsCheckArity(target, pos, filters);
5362 MethodHandle adapter = target;
5363
5364 // keep track of currently matched filters, as to optimize repeated filters
5365 int index = 0;
5366 int[] positions = new int[filters.length];
5367 MethodHandle filter = null;
5368
5369 // process filters in reverse order so that the invocation of
5370 // the resulting adapter will invoke the filters in left-to-right order
5371 for (int i = filters.length - 1; i >= 0; --i) {
5372 MethodHandle newFilter = filters[i];
5373 if (newFilter == null) continue; // ignore null elements of filters
5374
5375 // flush changes on update
5376 if (filter != newFilter) {
5377 if (filter != null) {
5378 if (index > 1) {
5379 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5380 } else {
5381 adapter = filterArgument(adapter, positions[0] - 1, filter);
5382 }
5383 }
5384 filter = newFilter;
5385 index = 0;
5386 }
5387
5388 filterArgumentChecks(target, pos + i, newFilter);
5389 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
5390 }
5391 if (index > 1) {
5392 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5393 } else if (index == 1) {
5394 adapter = filterArgument(adapter, positions[0] - 1, filter);
5395 }
5396 return adapter;
5397 }
5398
5399 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
5400 MethodType targetType = adapter.type();
5401 MethodType filterType = filter.type();
5402 BoundMethodHandle result = adapter.rebind();
5403 Class<?> newParamType = filterType.parameterType(0);
5404
5405 Class<?>[] ptypes = targetType.ptypes().clone();
5406 for (int pos : positions) {
5407 ptypes[pos - 1] = newParamType;
5408 }
5409 MethodType newType = MethodType.methodType(targetType.rtype(), ptypes, true);
5410
5411 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
5412 return result.copyWithExtendL(newType, lform, filter);
5413 }
5414
5415 /*non-public*/
5416 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
5417 filterArgumentChecks(target, pos, filter);
5418 MethodType targetType = target.type();
5419 MethodType filterType = filter.type();
5420 BoundMethodHandle result = target.rebind();
5421 Class<?> newParamType = filterType.parameterType(0);
5422 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
5423 MethodType newType = targetType.changeParameterType(pos, newParamType);
5424 result = result.copyWithExtendL(newType, lform, filter);
5425 return result;
5426 }
5427
5428 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
5429 MethodType targetType = target.type();
5430 int maxPos = targetType.parameterCount();
5431 if (pos + filters.length > maxPos)
5432 throw newIllegalArgumentException("too many filters");
5433 }
5434
5435 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5436 MethodType targetType = target.type();
5437 MethodType filterType = filter.type();
5438 if (filterType.parameterCount() != 1
5439 || filterType.returnType() != targetType.parameterType(pos))
5440 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5441 }
5442
5443 /**
5444 * Adapts a target method handle by pre-processing
5445 * a sub-sequence of its arguments with a filter (another method handle).
5446 * The pre-processed arguments are replaced by the result (if any) of the
5447 * filter function.
5448 * The target is then called on the modified (usually shortened) argument list.
5449 * <p>
5450 * If the filter returns a value, the target must accept that value as
5451 * its argument in position {@code pos}, preceded and/or followed by
5452 * any arguments not passed to the filter.
5453 * If the filter returns void, the target must accept all arguments
5454 * not passed to the filter.
5455 * No arguments are reordered, and a result returned from the filter
5456 * replaces (in order) the whole subsequence of arguments originally
5457 * passed to the adapter.
5458 * <p>
5459 * The argument types (if any) of the filter
5460 * replace zero or one argument types of the target, at position {@code pos},
5461 * in the resulting adapted method handle.
5462 * The return type of the filter (if any) must be identical to the
5463 * argument type of the target at position {@code pos}, and that target argument
5464 * is supplied by the return value of the filter.
5465 * <p>
5466 * In all cases, {@code pos} must be greater than or equal to zero, and
5467 * {@code pos} must also be less than or equal to the target's arity.
5468 * <p><b>Example:</b>
5469 * {@snippet lang="java" :
5470 import static java.lang.invoke.MethodHandles.*;
5471 import static java.lang.invoke.MethodType.*;
5472 ...
5473 MethodHandle deepToString = publicLookup()
5474 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
5475
5476 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
5477 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
5478
5479 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
5480 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
5481
5482 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
5483 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
5484 assertEquals("[top, [up, down], strange]",
5485 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
5486
5487 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
5488 assertEquals("[top, [up, down], [strange]]",
5489 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
5490
5491 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
5492 assertEquals("[top, [[up, down, strange], charm], bottom]",
5493 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
5494 * }
5495 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5496 * represents the return type of the {@code target} and resulting adapter.
5497 * {@code V}/{@code v} stand for the return type and value of the
5498 * {@code filter}, which are also found in the signature and arguments of
5499 * the {@code target}, respectively, unless {@code V} is {@code void}.
5500 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
5501 * and values preceding and following the collection position, {@code pos},
5502 * in the {@code target}'s signature. They also turn up in the resulting
5503 * adapter's signature and arguments, where they surround
5504 * {@code B}/{@code b}, which represent the parameter types and arguments
5505 * to the {@code filter} (if any).
5506 * {@snippet lang="java" :
5507 * T target(A...,V,C...);
5508 * V filter(B...);
5509 * T adapter(A... a,B... b,C... c) {
5510 * V v = filter(b...);
5511 * return target(a...,v,c...);
5512 * }
5513 * // and if the filter has no arguments:
5514 * T target2(A...,V,C...);
5515 * V filter2();
5516 * T adapter2(A... a,C... c) {
5517 * V v = filter2();
5518 * return target2(a...,v,c...);
5519 * }
5520 * // and if the filter has a void return:
5521 * T target3(A...,C...);
5522 * void filter3(B...);
5523 * T adapter3(A... a,B... b,C... c) {
5524 * filter3(b...);
5525 * return target3(a...,c...);
5526 * }
5527 * }
5528 * <p>
5529 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
5530 * one which first "folds" the affected arguments, and then drops them, in separate
5531 * steps as follows:
5532 * {@snippet lang="java" :
5533 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
5534 * mh = MethodHandles.foldArguments(mh, coll); //step 1
5535 * }
5536 * If the target method handle consumes no arguments besides than the result
5537 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
5538 * is equivalent to {@code filterReturnValue(coll, mh)}.
5539 * If the filter method handle {@code coll} consumes one argument and produces
5540 * a non-void result, then {@code collectArguments(mh, N, coll)}
5541 * is equivalent to {@code filterArguments(mh, N, coll)}.
5542 * Other equivalences are possible but would require argument permutation.
5543 * <p>
5544 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5545 * variable-arity method handle}, even if the original target method handle was.
5546 *
5547 * @param target the method handle to invoke after filtering the subsequence of arguments
5548 * @param pos the position of the first adapter argument to pass to the filter,
5549 * and/or the target argument which receives the result of the filter
5550 * @param filter method handle to call on the subsequence of arguments
5551 * @return method handle which incorporates the specified argument subsequence filtering logic
5552 * @throws NullPointerException if either argument is null
5553 * @throws IllegalArgumentException if the return type of {@code filter}
5554 * is non-void and is not the same as the {@code pos} argument of the target,
5555 * or if {@code pos} is not between 0 and the target's arity, inclusive,
5556 * or if the resulting method handle's type would have
5557 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5558 * @see MethodHandles#foldArguments
5559 * @see MethodHandles#filterArguments
5560 * @see MethodHandles#filterReturnValue
5561 */
5562 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
5563 MethodType newType = collectArgumentsChecks(target, pos, filter);
5564 MethodType collectorType = filter.type();
5565 BoundMethodHandle result = target.rebind();
5566 LambdaForm lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
5567 return result.copyWithExtendL(newType, lform, filter);
5568 }
5569
5570 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5571 MethodType targetType = target.type();
5572 MethodType filterType = filter.type();
5573 Class<?> rtype = filterType.returnType();
5574 Class<?>[] filterArgs = filterType.ptypes();
5575 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) ||
5576 (rtype != void.class && pos >= targetType.parameterCount())) {
5577 throw newIllegalArgumentException("position is out of range for target", target, pos);
5578 }
5579 if (rtype == void.class) {
5580 return targetType.insertParameterTypes(pos, filterArgs);
5581 }
5582 if (rtype != targetType.parameterType(pos)) {
5583 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5584 }
5585 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs);
5586 }
5587
5588 /**
5589 * Adapts a target method handle by post-processing
5590 * its return value (if any) with a filter (another method handle).
5591 * The result of the filter is returned from the adapter.
5592 * <p>
5593 * If the target returns a value, the filter must accept that value as
5594 * its only argument.
5595 * If the target returns void, the filter must accept no arguments.
5596 * <p>
5597 * The return type of the filter
5598 * replaces the return type of the target
5599 * in the resulting adapted method handle.
5600 * The argument type of the filter (if any) must be identical to the
5601 * return type of the target.
5602 * <p><b>Example:</b>
5603 * {@snippet lang="java" :
5604 import static java.lang.invoke.MethodHandles.*;
5605 import static java.lang.invoke.MethodType.*;
5606 ...
5607 MethodHandle cat = lookup().findVirtual(String.class,
5608 "concat", methodType(String.class, String.class));
5609 MethodHandle length = lookup().findVirtual(String.class,
5610 "length", methodType(int.class));
5611 System.out.println((String) cat.invokeExact("x", "y")); // xy
5612 MethodHandle f0 = filterReturnValue(cat, length);
5613 System.out.println((int) f0.invokeExact("x", "y")); // 2
5614 * }
5615 * <p>Here is pseudocode for the resulting adapter. In the code,
5616 * {@code T}/{@code t} represent the result type and value of the
5617 * {@code target}; {@code V}, the result type of the {@code filter}; and
5618 * {@code A}/{@code a}, the types and values of the parameters and arguments
5619 * of the {@code target} as well as the resulting adapter.
5620 * {@snippet lang="java" :
5621 * T target(A...);
5622 * V filter(T);
5623 * V adapter(A... a) {
5624 * T t = target(a...);
5625 * return filter(t);
5626 * }
5627 * // and if the target has a void return:
5628 * void target2(A...);
5629 * V filter2();
5630 * V adapter2(A... a) {
5631 * target2(a...);
5632 * return filter2();
5633 * }
5634 * // and if the filter has a void return:
5635 * T target3(A...);
5636 * void filter3(V);
5637 * void adapter3(A... a) {
5638 * T t = target3(a...);
5639 * filter3(t);
5640 * }
5641 * }
5642 * <p>
5643 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5644 * variable-arity method handle}, even if the original target method handle was.
5645 * @param target the method handle to invoke before filtering the return value
5646 * @param filter method handle to call on the return value
5647 * @return method handle which incorporates the specified return value filtering logic
5648 * @throws NullPointerException if either argument is null
5649 * @throws IllegalArgumentException if the argument list of {@code filter}
5650 * does not match the return type of target as described above
5651 */
5652 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
5653 MethodType targetType = target.type();
5654 MethodType filterType = filter.type();
5655 filterReturnValueChecks(targetType, filterType);
5656 BoundMethodHandle result = target.rebind();
5657 BasicType rtype = BasicType.basicType(filterType.returnType());
5658 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
5659 MethodType newType = targetType.changeReturnType(filterType.returnType());
5660 result = result.copyWithExtendL(newType, lform, filter);
5661 return result;
5662 }
5663
5664 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
5665 Class<?> rtype = targetType.returnType();
5666 int filterValues = filterType.parameterCount();
5667 if (filterValues == 0
5668 ? (rtype != void.class)
5669 : (rtype != filterType.parameterType(0) || filterValues != 1))
5670 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5671 }
5672
5673 /**
5674 * Filter the return value of a target method handle with a filter function. The filter function is
5675 * applied to the return value of the original handle; if the filter specifies more than one parameters,
5676 * then any remaining parameter is appended to the adapter handle. In other words, the adaptation works
5677 * as follows:
5678 * {@snippet lang="java" :
5679 * T target(A...)
5680 * V filter(B... , T)
5681 * V adapter(A... a, B... b) {
5682 * T t = target(a...);
5683 * return filter(b..., t);
5684 * }
5685 * }
5686 * <p>
5687 * If the filter handle is a unary function, then this method behaves like {@link #filterReturnValue(MethodHandle, MethodHandle)}.
5688 *
5689 * @param target the target method handle
5690 * @param filter the filter method handle
5691 * @return the adapter method handle
5692 */
5693 /* package */ static MethodHandle collectReturnValue(MethodHandle target, MethodHandle filter) {
5694 MethodType targetType = target.type();
5695 MethodType filterType = filter.type();
5696 BoundMethodHandle result = target.rebind();
5697 LambdaForm lform = result.editor().collectReturnValueForm(filterType.basicType());
5698 MethodType newType = targetType.changeReturnType(filterType.returnType());
5699 if (filterType.parameterCount() > 1) {
5700 for (int i = 0 ; i < filterType.parameterCount() - 1 ; i++) {
5701 newType = newType.appendParameterTypes(filterType.parameterType(i));
5702 }
5703 }
5704 result = result.copyWithExtendL(newType, lform, filter);
5705 return result;
5706 }
5707
5708 /**
5709 * Adapts a target method handle by pre-processing
5710 * some of its arguments, and then calling the target with
5711 * the result of the pre-processing, inserted into the original
5712 * sequence of arguments.
5713 * <p>
5714 * The pre-processing is performed by {@code combiner}, a second method handle.
5715 * Of the arguments passed to the adapter, the first {@code N} arguments
5716 * are copied to the combiner, which is then called.
5717 * (Here, {@code N} is defined as the parameter count of the combiner.)
5718 * After this, control passes to the target, with any result
5719 * from the combiner inserted before the original {@code N} incoming
5720 * arguments.
5721 * <p>
5722 * If the combiner returns a value, the first parameter type of the target
5723 * must be identical with the return type of the combiner, and the next
5724 * {@code N} parameter types of the target must exactly match the parameters
5725 * of the combiner.
5726 * <p>
5727 * If the combiner has a void return, no result will be inserted,
5728 * and the first {@code N} parameter types of the target
5729 * must exactly match the parameters of the combiner.
5730 * <p>
5731 * The resulting adapter is the same type as the target, except that the
5732 * first parameter type is dropped,
5733 * if it corresponds to the result of the combiner.
5734 * <p>
5735 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
5736 * that either the combiner or the target does not wish to receive.
5737 * If some of the incoming arguments are destined only for the combiner,
5738 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
5739 * arguments will not need to be live on the stack on entry to the
5740 * target.)
5741 * <p><b>Example:</b>
5742 * {@snippet lang="java" :
5743 import static java.lang.invoke.MethodHandles.*;
5744 import static java.lang.invoke.MethodType.*;
5745 ...
5746 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5747 "println", methodType(void.class, String.class))
5748 .bindTo(System.out);
5749 MethodHandle cat = lookup().findVirtual(String.class,
5750 "concat", methodType(String.class, String.class));
5751 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5752 MethodHandle catTrace = foldArguments(cat, trace);
5753 // also prints "boo":
5754 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5755 * }
5756 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5757 * represents the result type of the {@code target} and resulting adapter.
5758 * {@code V}/{@code v} represent the type and value of the parameter and argument
5759 * of {@code target} that precedes the folding position; {@code V} also is
5760 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
5761 * types and values of the {@code N} parameters and arguments at the folding
5762 * position. {@code B}/{@code b} represent the types and values of the
5763 * {@code target} parameters and arguments that follow the folded parameters
5764 * and arguments.
5765 * {@snippet lang="java" :
5766 * // there are N arguments in A...
5767 * T target(V, A[N]..., B...);
5768 * V combiner(A...);
5769 * T adapter(A... a, B... b) {
5770 * V v = combiner(a...);
5771 * return target(v, a..., b...);
5772 * }
5773 * // and if the combiner has a void return:
5774 * T target2(A[N]..., B...);
5775 * void combiner2(A...);
5776 * T adapter2(A... a, B... b) {
5777 * combiner2(a...);
5778 * return target2(a..., b...);
5779 * }
5780 * }
5781 * <p>
5782 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5783 * variable-arity method handle}, even if the original target method handle was.
5784 * @param target the method handle to invoke after arguments are combined
5785 * @param combiner method handle to call initially on the incoming arguments
5786 * @return method handle which incorporates the specified argument folding logic
5787 * @throws NullPointerException if either argument is null
5788 * @throws IllegalArgumentException if {@code combiner}'s return type
5789 * is non-void and not the same as the first argument type of
5790 * the target, or if the initial {@code N} argument types
5791 * of the target
5792 * (skipping one matching the {@code combiner}'s return type)
5793 * are not identical with the argument types of {@code combiner}
5794 */
5795 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
5796 return foldArguments(target, 0, combiner);
5797 }
5798
5799 /**
5800 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
5801 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
5802 * before the folded arguments.
5803 * <p>
5804 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
5805 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
5806 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
5807 * 0.
5808 *
5809 * @apiNote Example:
5810 * {@snippet lang="java" :
5811 import static java.lang.invoke.MethodHandles.*;
5812 import static java.lang.invoke.MethodType.*;
5813 ...
5814 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5815 "println", methodType(void.class, String.class))
5816 .bindTo(System.out);
5817 MethodHandle cat = lookup().findVirtual(String.class,
5818 "concat", methodType(String.class, String.class));
5819 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5820 MethodHandle catTrace = foldArguments(cat, 1, trace);
5821 // also prints "jum":
5822 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5823 * }
5824 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5825 * represents the result type of the {@code target} and resulting adapter.
5826 * {@code V}/{@code v} represent the type and value of the parameter and argument
5827 * of {@code target} that precedes the folding position; {@code V} also is
5828 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
5829 * types and values of the {@code N} parameters and arguments at the folding
5830 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
5831 * and values of the {@code target} parameters and arguments that precede and
5832 * follow the folded parameters and arguments starting at {@code pos},
5833 * respectively.
5834 * {@snippet lang="java" :
5835 * // there are N arguments in A...
5836 * T target(Z..., V, A[N]..., B...);
5837 * V combiner(A...);
5838 * T adapter(Z... z, A... a, B... b) {
5839 * V v = combiner(a...);
5840 * return target(z..., v, a..., b...);
5841 * }
5842 * // and if the combiner has a void return:
5843 * T target2(Z..., A[N]..., B...);
5844 * void combiner2(A...);
5845 * T adapter2(Z... z, A... a, B... b) {
5846 * combiner2(a...);
5847 * return target2(z..., a..., b...);
5848 * }
5849 * }
5850 * <p>
5851 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5852 * variable-arity method handle}, even if the original target method handle was.
5853 *
5854 * @param target the method handle to invoke after arguments are combined
5855 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
5856 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5857 * @param combiner method handle to call initially on the incoming arguments
5858 * @return method handle which incorporates the specified argument folding logic
5859 * @throws NullPointerException if either argument is null
5860 * @throws IllegalArgumentException if either of the following two conditions holds:
5861 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5862 * {@code pos} of the target signature;
5863 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
5864 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
5865 *
5866 * @see #foldArguments(MethodHandle, MethodHandle)
5867 * @since 9
5868 */
5869 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
5870 MethodType targetType = target.type();
5871 MethodType combinerType = combiner.type();
5872 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
5873 BoundMethodHandle result = target.rebind();
5874 boolean dropResult = rtype == void.class;
5875 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
5876 MethodType newType = targetType;
5877 if (!dropResult) {
5878 newType = newType.dropParameterTypes(pos, pos + 1);
5879 }
5880 result = result.copyWithExtendL(newType, lform, combiner);
5881 return result;
5882 }
5883
5884 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
5885 int foldArgs = combinerType.parameterCount();
5886 Class<?> rtype = combinerType.returnType();
5887 int foldVals = rtype == void.class ? 0 : 1;
5888 int afterInsertPos = foldPos + foldVals;
5889 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
5890 if (ok) {
5891 for (int i = 0; i < foldArgs; i++) {
5892 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
5893 ok = false;
5894 break;
5895 }
5896 }
5897 }
5898 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
5899 ok = false;
5900 if (!ok)
5901 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5902 return rtype;
5903 }
5904
5905 /**
5906 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
5907 * of the pre-processing replacing the argument at the given position.
5908 *
5909 * @param target the method handle to invoke after arguments are combined
5910 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5911 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5912 * @param combiner method handle to call initially on the incoming arguments
5913 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5914 * @return method handle which incorporates the specified argument folding logic
5915 * @throws NullPointerException if either argument is null
5916 * @throws IllegalArgumentException if either of the following two conditions holds:
5917 * (1) {@code combiner}'s return type is not the same as the argument type at position
5918 * {@code pos} of the target signature;
5919 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
5920 * not identical with the argument types of {@code combiner}.
5921 */
5922 /*non-public*/
5923 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5924 return argumentsWithCombiner(true, target, position, combiner, argPositions);
5925 }
5926
5927 /**
5928 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
5929 * the pre-processing inserted into the original sequence of arguments at the given position.
5930 *
5931 * @param target the method handle to invoke after arguments are combined
5932 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5933 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5934 * @param combiner method handle to call initially on the incoming arguments
5935 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5936 * @return method handle which incorporates the specified argument folding logic
5937 * @throws NullPointerException if either argument is null
5938 * @throws IllegalArgumentException if either of the following two conditions holds:
5939 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5940 * {@code pos} of the target signature;
5941 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
5942 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
5943 * with the argument types of {@code combiner}.
5944 */
5945 /*non-public*/
5946 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5947 return argumentsWithCombiner(false, target, position, combiner, argPositions);
5948 }
5949
5950 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5951 MethodType targetType = target.type();
5952 MethodType combinerType = combiner.type();
5953 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
5954 BoundMethodHandle result = target.rebind();
5955
5956 MethodType newType = targetType;
5957 LambdaForm lform;
5958 if (filter) {
5959 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
5960 } else {
5961 boolean dropResult = rtype == void.class;
5962 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
5963 if (!dropResult) {
5964 newType = newType.dropParameterTypes(position, position + 1);
5965 }
5966 }
5967 result = result.copyWithExtendL(newType, lform, combiner);
5968 return result;
5969 }
5970
5971 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
5972 int combinerArgs = combinerType.parameterCount();
5973 if (argPos.length != combinerArgs) {
5974 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
5975 }
5976 Class<?> rtype = combinerType.returnType();
5977
5978 for (int i = 0; i < combinerArgs; i++) {
5979 int arg = argPos[i];
5980 if (arg < 0 || arg > targetType.parameterCount()) {
5981 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
5982 }
5983 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
5984 throw newIllegalArgumentException("target argument type at position " + arg
5985 + " must match combiner argument type at index " + i + ": " + targetType
5986 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
5987 }
5988 }
5989 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
5990 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5991 }
5992 return rtype;
5993 }
5994
5995 /**
5996 * Makes a method handle which adapts a target method handle,
5997 * by guarding it with a test, a boolean-valued method handle.
5998 * If the guard fails, a fallback handle is called instead.
5999 * All three method handles must have the same corresponding
6000 * argument and return types, except that the return type
6001 * of the test must be boolean, and the test is allowed
6002 * to have fewer arguments than the other two method handles.
6003 * <p>
6004 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6005 * represents the uniform result type of the three involved handles;
6006 * {@code A}/{@code a}, the types and values of the {@code target}
6007 * parameters and arguments that are consumed by the {@code test}; and
6008 * {@code B}/{@code b}, those types and values of the {@code target}
6009 * parameters and arguments that are not consumed by the {@code test}.
6010 * {@snippet lang="java" :
6011 * boolean test(A...);
6012 * T target(A...,B...);
6013 * T fallback(A...,B...);
6014 * T adapter(A... a,B... b) {
6015 * if (test(a...))
6016 * return target(a..., b...);
6017 * else
6018 * return fallback(a..., b...);
6019 * }
6020 * }
6021 * Note that the test arguments ({@code a...} in the pseudocode) cannot
6022 * be modified by execution of the test, and so are passed unchanged
6023 * from the caller to the target or fallback as appropriate.
6024 * @param test method handle used for test, must return boolean
6025 * @param target method handle to call if test passes
6026 * @param fallback method handle to call if test fails
6027 * @return method handle which incorporates the specified if/then/else logic
6028 * @throws NullPointerException if any argument is null
6029 * @throws IllegalArgumentException if {@code test} does not return boolean,
6030 * or if all three method types do not match (with the return
6031 * type of {@code test} changed to match that of the target).
6032 */
6033 public static MethodHandle guardWithTest(MethodHandle test,
6034 MethodHandle target,
6035 MethodHandle fallback) {
6036 MethodType gtype = test.type();
6037 MethodType ttype = target.type();
6038 MethodType ftype = fallback.type();
6039 if (!ttype.equals(ftype))
6040 throw misMatchedTypes("target and fallback types", ttype, ftype);
6041 if (gtype.returnType() != boolean.class)
6042 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
6043
6044 test = dropArgumentsToMatch(test, 0, ttype.ptypes(), 0, true);
6045 if (test == null) {
6046 throw misMatchedTypes("target and test types", ttype, gtype);
6047 }
6048 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
6049 }
6050
6051 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
6052 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
6053 }
6054
6055 /**
6056 * Makes a method handle which adapts a target method handle,
6057 * by running it inside an exception handler.
6058 * If the target returns normally, the adapter returns that value.
6059 * If an exception matching the specified type is thrown, the fallback
6060 * handle is called instead on the exception, plus the original arguments.
6061 * <p>
6062 * The target and handler must have the same corresponding
6063 * argument and return types, except that handler may omit trailing arguments
6064 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
6065 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
6066 * <p>
6067 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6068 * represents the return type of the {@code target} and {@code handler},
6069 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
6070 * the types and values of arguments to the resulting handle consumed by
6071 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
6072 * resulting handle discarded by {@code handler}.
6073 * {@snippet lang="java" :
6074 * T target(A..., B...);
6075 * T handler(ExType, A...);
6076 * T adapter(A... a, B... b) {
6077 * try {
6078 * return target(a..., b...);
6079 * } catch (ExType ex) {
6080 * return handler(ex, a...);
6081 * }
6082 * }
6083 * }
6084 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6085 * be modified by execution of the target, and so are passed unchanged
6086 * from the caller to the handler, if the handler is invoked.
6087 * <p>
6088 * The target and handler must return the same type, even if the handler
6089 * always throws. (This might happen, for instance, because the handler
6090 * is simulating a {@code finally} clause).
6091 * To create such a throwing handler, compose the handler creation logic
6092 * with {@link #throwException throwException},
6093 * in order to create a method handle of the correct return type.
6094 * @param target method handle to call
6095 * @param exType the type of exception which the handler will catch
6096 * @param handler method handle to call if a matching exception is thrown
6097 * @return method handle which incorporates the specified try/catch logic
6098 * @throws NullPointerException if any argument is null
6099 * @throws IllegalArgumentException if {@code handler} does not accept
6100 * the given exception type, or if the method handle types do
6101 * not match in their return types and their
6102 * corresponding parameters
6103 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
6104 */
6105 public static MethodHandle catchException(MethodHandle target,
6106 Class<? extends Throwable> exType,
6107 MethodHandle handler) {
6108 MethodType ttype = target.type();
6109 MethodType htype = handler.type();
6110 if (!Throwable.class.isAssignableFrom(exType))
6111 throw new ClassCastException(exType.getName());
6112 if (htype.parameterCount() < 1 ||
6113 !htype.parameterType(0).isAssignableFrom(exType))
6114 throw newIllegalArgumentException("handler does not accept exception type "+exType);
6115 if (htype.returnType() != ttype.returnType())
6116 throw misMatchedTypes("target and handler return types", ttype, htype);
6117 handler = dropArgumentsToMatch(handler, 1, ttype.ptypes(), 0, true);
6118 if (handler == null) {
6119 throw misMatchedTypes("target and handler types", ttype, htype);
6120 }
6121 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
6122 }
6123
6124 /**
6125 * Produces a method handle which will throw exceptions of the given {@code exType}.
6126 * The method handle will accept a single argument of {@code exType},
6127 * and immediately throw it as an exception.
6128 * The method type will nominally specify a return of {@code returnType}.
6129 * The return type may be anything convenient: It doesn't matter to the
6130 * method handle's behavior, since it will never return normally.
6131 * @param returnType the return type of the desired method handle
6132 * @param exType the parameter type of the desired method handle
6133 * @return method handle which can throw the given exceptions
6134 * @throws NullPointerException if either argument is null
6135 */
6136 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
6137 if (!Throwable.class.isAssignableFrom(exType))
6138 throw new ClassCastException(exType.getName());
6139 return MethodHandleImpl.throwException(methodType(returnType, exType));
6140 }
6141
6142 /**
6143 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
6144 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
6145 * delivers the loop's result, which is the return value of the resulting handle.
6146 * <p>
6147 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
6148 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
6149 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
6150 * terms of method handles, each clause will specify up to four independent actions:<ul>
6151 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
6152 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
6153 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
6154 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
6155 * </ul>
6156 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
6157 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
6158 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
6159 * <p>
6160 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
6161 * this case. See below for a detailed description.
6162 * <p>
6163 * <em>Parameters optional everywhere:</em>
6164 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
6165 * As an exception, the init functions cannot take any {@code v} parameters,
6166 * because those values are not yet computed when the init functions are executed.
6167 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
6168 * In fact, any clause function may take no arguments at all.
6169 * <p>
6170 * <em>Loop parameters:</em>
6171 * A clause function may take all the iteration variable values it is entitled to, in which case
6172 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
6173 * with their types and values notated as {@code (A...)} and {@code (a...)}.
6174 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
6175 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
6176 * init function is automatically a loop parameter {@code a}.)
6177 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
6178 * These loop parameters act as loop-invariant values visible across the whole loop.
6179 * <p>
6180 * <em>Parameters visible everywhere:</em>
6181 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
6182 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
6183 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
6184 * Most clause functions will not need all of this information, but they will be formally connected to it
6185 * as if by {@link #dropArguments}.
6186 * <a id="astar"></a>
6187 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
6188 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
6189 * In that notation, the general form of an init function parameter list
6190 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
6191 * <p>
6192 * <em>Checking clause structure:</em>
6193 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
6194 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
6195 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
6196 * met by the inputs to the loop combinator.
6197 * <p>
6198 * <em>Effectively identical sequences:</em>
6199 * <a id="effid"></a>
6200 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
6201 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
6202 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
6203 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
6204 * that longest list.
6205 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
6206 * and the same is true if more sequences of the form {@code (V... A*)} are added.
6207 * <p>
6208 * <em>Step 0: Determine clause structure.</em><ol type="a">
6209 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
6210 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
6211 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
6212 * four. Padding takes place by appending elements to the array.
6213 * <li>Clauses with all {@code null}s are disregarded.
6214 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
6215 * </ol>
6216 * <p>
6217 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
6218 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
6219 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
6220 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
6221 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
6222 * iteration variable type.
6223 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
6224 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
6225 * </ol>
6226 * <p>
6227 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
6228 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
6229 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
6230 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
6231 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
6232 * (These types will be checked in step 2, along with all the clause function types.)
6233 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
6234 * <li>All of the collected parameter lists must be effectively identical.
6235 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
6236 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
6237 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
6238 * the "internal parameter list".
6239 * </ul>
6240 * <p>
6241 * <em>Step 1C: Determine loop return type.</em><ol type="a">
6242 * <li>Examine fini function return types, disregarding omitted fini functions.
6243 * <li>If there are no fini functions, the loop return type is {@code void}.
6244 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
6245 * type.
6246 * </ol>
6247 * <p>
6248 * <em>Step 1D: Check other types.</em><ol type="a">
6249 * <li>There must be at least one non-omitted pred function.
6250 * <li>Every non-omitted pred function must have a {@code boolean} return type.
6251 * </ol>
6252 * <p>
6253 * <em>Step 2: Determine parameter lists.</em><ol type="a">
6254 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
6255 * <li>The parameter list for init functions will be adjusted to the external parameter list.
6256 * (Note that their parameter lists are already effectively identical to this list.)
6257 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
6258 * effectively identical to the internal parameter list {@code (V... A...)}.
6259 * </ol>
6260 * <p>
6261 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
6262 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
6263 * type.
6264 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
6265 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
6266 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
6267 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
6268 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
6269 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
6270 * loop return type.
6271 * </ol>
6272 * <p>
6273 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
6274 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
6275 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
6276 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
6277 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
6278 * pad out the end of the list.
6279 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
6280 * </ol>
6281 * <p>
6282 * <em>Final observations.</em><ol type="a">
6283 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
6284 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
6285 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
6286 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
6287 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
6288 * <li>Each pair of init and step functions agrees in their return type {@code V}.
6289 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
6290 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
6291 * </ol>
6292 * <p>
6293 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
6294 * <ul>
6295 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
6296 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
6297 * (Only one {@code Pn} has to be non-{@code null}.)
6298 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
6299 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
6300 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
6301 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
6302 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
6303 * the resulting loop handle's parameter types {@code (A...)}.
6304 * </ul>
6305 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
6306 * which is natural if most of the loop computation happens in the steps. For some loops,
6307 * the burden of computation might be heaviest in the pred functions, and so the pred functions
6308 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
6309 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
6310 * where the init functions will need the extra parameters. For such reasons, the rules for
6311 * determining these parameters are as symmetric as possible, across all clause parts.
6312 * In general, the loop parameters function as common invariant values across the whole
6313 * loop, while the iteration variables function as common variant values, or (if there is
6314 * no step function) as internal loop invariant temporaries.
6315 * <p>
6316 * <em>Loop execution.</em><ol type="a">
6317 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
6318 * every clause function. These locals are loop invariant.
6319 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
6320 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
6321 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
6322 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
6323 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
6324 * (in argument order).
6325 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
6326 * returns {@code false}.
6327 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
6328 * sequence {@code (v...)} of loop variables.
6329 * The updated value is immediately visible to all subsequent function calls.
6330 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
6331 * (of type {@code R}) is returned from the loop as a whole.
6332 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
6333 * except by throwing an exception.
6334 * </ol>
6335 * <p>
6336 * <em>Usage tips.</em>
6337 * <ul>
6338 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
6339 * sometimes a step function only needs to observe the current value of its own variable.
6340 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
6341 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
6342 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
6343 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
6344 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
6345 * <li>If some of the clause functions are virtual methods on an instance, the instance
6346 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
6347 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
6348 * will be the first iteration variable value, and it will be easy to use virtual
6349 * methods as clause parts, since all of them will take a leading instance reference matching that value.
6350 * </ul>
6351 * <p>
6352 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
6353 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
6354 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
6355 * {@snippet lang="java" :
6356 * V... init...(A...);
6357 * boolean pred...(V..., A...);
6358 * V... step...(V..., A...);
6359 * R fini...(V..., A...);
6360 * R loop(A... a) {
6361 * V... v... = init...(a...);
6362 * for (;;) {
6363 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
6364 * v = s(v..., a...);
6365 * if (!p(v..., a...)) {
6366 * return f(v..., a...);
6367 * }
6368 * }
6369 * }
6370 * }
6371 * }
6372 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
6373 * to their full length, even though individual clause functions may neglect to take them all.
6374 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
6375 *
6376 * @apiNote Example:
6377 * {@snippet lang="java" :
6378 * // iterative implementation of the factorial function as a loop handle
6379 * static int one(int k) { return 1; }
6380 * static int inc(int i, int acc, int k) { return i + 1; }
6381 * static int mult(int i, int acc, int k) { return i * acc; }
6382 * static boolean pred(int i, int acc, int k) { return i < k; }
6383 * static int fin(int i, int acc, int k) { return acc; }
6384 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6385 * // null initializer for counter, should initialize to 0
6386 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6387 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6388 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6389 * assertEquals(120, loop.invoke(5));
6390 * }
6391 * The same example, dropping arguments and using combinators:
6392 * {@snippet lang="java" :
6393 * // simplified implementation of the factorial function as a loop handle
6394 * static int inc(int i) { return i + 1; } // drop acc, k
6395 * static int mult(int i, int acc) { return i * acc; } //drop k
6396 * static boolean cmp(int i, int k) { return i < k; }
6397 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
6398 * // null initializer for counter, should initialize to 0
6399 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6400 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
6401 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
6402 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6403 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6404 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6405 * assertEquals(720, loop.invoke(6));
6406 * }
6407 * A similar example, using a helper object to hold a loop parameter:
6408 * {@snippet lang="java" :
6409 * // instance-based implementation of the factorial function as a loop handle
6410 * static class FacLoop {
6411 * final int k;
6412 * FacLoop(int k) { this.k = k; }
6413 * int inc(int i) { return i + 1; }
6414 * int mult(int i, int acc) { return i * acc; }
6415 * boolean pred(int i) { return i < k; }
6416 * int fin(int i, int acc) { return acc; }
6417 * }
6418 * // assume MH_FacLoop is a handle to the constructor
6419 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6420 * // null initializer for counter, should initialize to 0
6421 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6422 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
6423 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6424 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6425 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
6426 * assertEquals(5040, loop.invoke(7));
6427 * }
6428 *
6429 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
6430 *
6431 * @return a method handle embodying the looping behavior as defined by the arguments.
6432 *
6433 * @throws IllegalArgumentException in case any of the constraints described above is violated.
6434 *
6435 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
6436 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6437 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
6438 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
6439 * @since 9
6440 */
6441 public static MethodHandle loop(MethodHandle[]... clauses) {
6442 // Step 0: determine clause structure.
6443 loopChecks0(clauses);
6444
6445 List<MethodHandle> init = new ArrayList<>();
6446 List<MethodHandle> step = new ArrayList<>();
6447 List<MethodHandle> pred = new ArrayList<>();
6448 List<MethodHandle> fini = new ArrayList<>();
6449
6450 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
6451 init.add(clause[0]); // all clauses have at least length 1
6452 step.add(clause.length <= 1 ? null : clause[1]);
6453 pred.add(clause.length <= 2 ? null : clause[2]);
6454 fini.add(clause.length <= 3 ? null : clause[3]);
6455 });
6456
6457 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
6458 final int nclauses = init.size();
6459
6460 // Step 1A: determine iteration variables (V...).
6461 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
6462 for (int i = 0; i < nclauses; ++i) {
6463 MethodHandle in = init.get(i);
6464 MethodHandle st = step.get(i);
6465 if (in == null && st == null) {
6466 iterationVariableTypes.add(void.class);
6467 } else if (in != null && st != null) {
6468 loopChecks1a(i, in, st);
6469 iterationVariableTypes.add(in.type().returnType());
6470 } else {
6471 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
6472 }
6473 }
6474 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).toList();
6475
6476 // Step 1B: determine loop parameters (A...).
6477 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
6478 loopChecks1b(init, commonSuffix);
6479
6480 // Step 1C: determine loop return type.
6481 // Step 1D: check other types.
6482 // local variable required here; see JDK-8223553
6483 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
6484 .map(MethodType::returnType);
6485 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
6486 loopChecks1cd(pred, fini, loopReturnType);
6487
6488 // Step 2: determine parameter lists.
6489 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
6490 commonParameterSequence.addAll(commonSuffix);
6491 loopChecks2(step, pred, fini, commonParameterSequence);
6492 // Step 3: fill in omitted functions.
6493 for (int i = 0; i < nclauses; ++i) {
6494 Class<?> t = iterationVariableTypes.get(i);
6495 if (init.get(i) == null) {
6496 init.set(i, empty(methodType(t, commonSuffix)));
6497 }
6498 if (step.get(i) == null) {
6499 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
6500 }
6501 if (pred.get(i) == null) {
6502 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence));
6503 }
6504 if (fini.get(i) == null) {
6505 fini.set(i, empty(methodType(t, commonParameterSequence)));
6506 }
6507 }
6508
6509 // Step 4: fill in missing parameter types.
6510 // Also convert all handles to fixed-arity handles.
6511 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
6512 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
6513 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
6514 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
6515
6516 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
6517 allMatch(pl -> pl.equals(commonSuffix));
6518 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
6519 allMatch(pl -> pl.equals(commonParameterSequence));
6520
6521 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
6522 }
6523
6524 private static void loopChecks0(MethodHandle[][] clauses) {
6525 if (clauses == null || clauses.length == 0) {
6526 throw newIllegalArgumentException("null or no clauses passed");
6527 }
6528 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
6529 throw newIllegalArgumentException("null clauses are not allowed");
6530 }
6531 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
6532 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
6533 }
6534 }
6535
6536 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
6537 if (in.type().returnType() != st.type().returnType()) {
6538 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
6539 st.type().returnType());
6540 }
6541 }
6542
6543 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
6544 return mhs.filter(Objects::nonNull)
6545 // take only those that can contribute to a common suffix because they are longer than the prefix
6546 .map(MethodHandle::type)
6547 .filter(t -> t.parameterCount() > skipSize)
6548 .max(Comparator.comparingInt(MethodType::parameterCount))
6549 .map(methodType -> List.of(Arrays.copyOfRange(methodType.ptypes(), skipSize, methodType.parameterCount())))
6550 .orElse(List.of());
6551 }
6552
6553 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
6554 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
6555 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
6556 return longest1.size() >= longest2.size() ? longest1 : longest2;
6557 }
6558
6559 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
6560 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
6561 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
6562 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
6563 " (common suffix: " + commonSuffix + ")");
6564 }
6565 }
6566
6567 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
6568 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6569 anyMatch(t -> t != loopReturnType)) {
6570 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
6571 loopReturnType + ")");
6572 }
6573
6574 if (pred.stream().noneMatch(Objects::nonNull)) {
6575 throw newIllegalArgumentException("no predicate found", pred);
6576 }
6577 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6578 anyMatch(t -> t != boolean.class)) {
6579 throw newIllegalArgumentException("predicates must have boolean return type", pred);
6580 }
6581 }
6582
6583 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
6584 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
6585 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
6586 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
6587 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
6588 }
6589 }
6590
6591 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
6592 return hs.stream().map(h -> {
6593 int pc = h.type().parameterCount();
6594 int tpsize = targetParams.size();
6595 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h;
6596 }).toList();
6597 }
6598
6599 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
6600 return hs.stream().map(MethodHandle::asFixedArity).toList();
6601 }
6602
6603 /**
6604 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
6605 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6606 * <p>
6607 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6608 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
6609 * evaluates to {@code true}).
6610 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
6611 * <p>
6612 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6613 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6614 * and updated with the value returned from its invocation. The result of loop execution will be
6615 * the final value of the additional loop-local variable (if present).
6616 * <p>
6617 * The following rules hold for these argument handles:<ul>
6618 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6619 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6620 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6621 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6622 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6623 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6624 * It will constrain the parameter lists of the other loop parts.
6625 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6626 * list {@code (A...)} is called the <em>external parameter list</em>.
6627 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6628 * additional state variable of the loop.
6629 * The body must both accept and return a value of this type {@code V}.
6630 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6631 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6632 * <a href="MethodHandles.html#effid">effectively identical</a>
6633 * to the external parameter list {@code (A...)}.
6634 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6635 * {@linkplain #empty default value}.
6636 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6637 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6638 * effectively identical to the internal parameter list.
6639 * </ul>
6640 * <p>
6641 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6642 * <li>The loop handle's result type is the result type {@code V} of the body.
6643 * <li>The loop handle's parameter types are the types {@code (A...)},
6644 * from the external parameter list.
6645 * </ul>
6646 * <p>
6647 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6648 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6649 * passed to the loop.
6650 * {@snippet lang="java" :
6651 * V init(A...);
6652 * boolean pred(V, A...);
6653 * V body(V, A...);
6654 * V whileLoop(A... a...) {
6655 * V v = init(a...);
6656 * while (pred(v, a...)) {
6657 * v = body(v, a...);
6658 * }
6659 * return v;
6660 * }
6661 * }
6662 *
6663 * @apiNote Example:
6664 * {@snippet lang="java" :
6665 * // implement the zip function for lists as a loop handle
6666 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
6667 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
6668 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
6669 * zip.add(a.next());
6670 * zip.add(b.next());
6671 * return zip;
6672 * }
6673 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
6674 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
6675 * List<String> a = Arrays.asList("a", "b", "c", "d");
6676 * List<String> b = Arrays.asList("e", "f", "g", "h");
6677 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
6678 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
6679 * }
6680 *
6681 *
6682 * @apiNote The implementation of this method can be expressed as follows:
6683 * {@snippet lang="java" :
6684 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6685 * MethodHandle fini = (body.type().returnType() == void.class
6686 * ? null : identity(body.type().returnType()));
6687 * MethodHandle[]
6688 * checkExit = { null, null, pred, fini },
6689 * varBody = { init, body };
6690 * return loop(checkExit, varBody);
6691 * }
6692 * }
6693 *
6694 * @param init optional initializer, providing the initial value of the loop variable.
6695 * May be {@code null}, implying a default initial value. See above for other constraints.
6696 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6697 * above for other constraints.
6698 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6699 * See above for other constraints.
6700 *
6701 * @return a method handle implementing the {@code while} loop as described by the arguments.
6702 * @throws IllegalArgumentException if the rules for the arguments are violated.
6703 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6704 *
6705 * @see #loop(MethodHandle[][])
6706 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6707 * @since 9
6708 */
6709 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6710 whileLoopChecks(init, pred, body);
6711 MethodHandle fini = identityOrVoid(body.type().returnType());
6712 MethodHandle[] checkExit = { null, null, pred, fini };
6713 MethodHandle[] varBody = { init, body };
6714 return loop(checkExit, varBody);
6715 }
6716
6717 /**
6718 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
6719 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6720 * <p>
6721 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6722 * method will, in each iteration, first execute its body and then evaluate the predicate.
6723 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
6724 * <p>
6725 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6726 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6727 * and updated with the value returned from its invocation. The result of loop execution will be
6728 * the final value of the additional loop-local variable (if present).
6729 * <p>
6730 * The following rules hold for these argument handles:<ul>
6731 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6732 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6733 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6734 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6735 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6736 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6737 * It will constrain the parameter lists of the other loop parts.
6738 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6739 * list {@code (A...)} is called the <em>external parameter list</em>.
6740 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6741 * additional state variable of the loop.
6742 * The body must both accept and return a value of this type {@code V}.
6743 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6744 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6745 * <a href="MethodHandles.html#effid">effectively identical</a>
6746 * to the external parameter list {@code (A...)}.
6747 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6748 * {@linkplain #empty default value}.
6749 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6750 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6751 * effectively identical to the internal parameter list.
6752 * </ul>
6753 * <p>
6754 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6755 * <li>The loop handle's result type is the result type {@code V} of the body.
6756 * <li>The loop handle's parameter types are the types {@code (A...)},
6757 * from the external parameter list.
6758 * </ul>
6759 * <p>
6760 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6761 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6762 * passed to the loop.
6763 * {@snippet lang="java" :
6764 * V init(A...);
6765 * boolean pred(V, A...);
6766 * V body(V, A...);
6767 * V doWhileLoop(A... a...) {
6768 * V v = init(a...);
6769 * do {
6770 * v = body(v, a...);
6771 * } while (pred(v, a...));
6772 * return v;
6773 * }
6774 * }
6775 *
6776 * @apiNote Example:
6777 * {@snippet lang="java" :
6778 * // int i = 0; while (i < limit) { ++i; } return i; => limit
6779 * static int zero(int limit) { return 0; }
6780 * static int step(int i, int limit) { return i + 1; }
6781 * static boolean pred(int i, int limit) { return i < limit; }
6782 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
6783 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
6784 * assertEquals(23, loop.invoke(23));
6785 * }
6786 *
6787 *
6788 * @apiNote The implementation of this method can be expressed as follows:
6789 * {@snippet lang="java" :
6790 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6791 * MethodHandle fini = (body.type().returnType() == void.class
6792 * ? null : identity(body.type().returnType()));
6793 * MethodHandle[] clause = { init, body, pred, fini };
6794 * return loop(clause);
6795 * }
6796 * }
6797 *
6798 * @param init optional initializer, providing the initial value of the loop variable.
6799 * May be {@code null}, implying a default initial value. See above for other constraints.
6800 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6801 * See above for other constraints.
6802 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6803 * above for other constraints.
6804 *
6805 * @return a method handle implementing the {@code while} loop as described by the arguments.
6806 * @throws IllegalArgumentException if the rules for the arguments are violated.
6807 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6808 *
6809 * @see #loop(MethodHandle[][])
6810 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
6811 * @since 9
6812 */
6813 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6814 whileLoopChecks(init, pred, body);
6815 MethodHandle fini = identityOrVoid(body.type().returnType());
6816 MethodHandle[] clause = {init, body, pred, fini };
6817 return loop(clause);
6818 }
6819
6820 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
6821 Objects.requireNonNull(pred);
6822 Objects.requireNonNull(body);
6823 MethodType bodyType = body.type();
6824 Class<?> returnType = bodyType.returnType();
6825 List<Class<?>> innerList = bodyType.parameterList();
6826 List<Class<?>> outerList = innerList;
6827 if (returnType == void.class) {
6828 // OK
6829 } else if (innerList.isEmpty() || innerList.get(0) != returnType) {
6830 // leading V argument missing => error
6831 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6832 throw misMatchedTypes("body function", bodyType, expected);
6833 } else {
6834 outerList = innerList.subList(1, innerList.size());
6835 }
6836 MethodType predType = pred.type();
6837 if (predType.returnType() != boolean.class ||
6838 !predType.effectivelyIdenticalParameters(0, innerList)) {
6839 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
6840 }
6841 if (init != null) {
6842 MethodType initType = init.type();
6843 if (initType.returnType() != returnType ||
6844 !initType.effectivelyIdenticalParameters(0, outerList)) {
6845 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
6846 }
6847 }
6848 }
6849
6850 /**
6851 * Constructs a loop that runs a given number of iterations.
6852 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6853 * <p>
6854 * The number of iterations is determined by the {@code iterations} handle evaluation result.
6855 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
6856 * It will be initialized to 0 and incremented by 1 in each iteration.
6857 * <p>
6858 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6859 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6860 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6861 * <p>
6862 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6863 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6864 * iteration variable.
6865 * The result of the loop handle execution will be the final {@code V} value of that variable
6866 * (or {@code void} if there is no {@code V} variable).
6867 * <p>
6868 * The following rules hold for the argument handles:<ul>
6869 * <li>The {@code iterations} handle must not be {@code null}, and must return
6870 * the type {@code int}, referred to here as {@code I} in parameter type lists.
6871 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6872 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
6873 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6874 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
6875 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
6876 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
6877 * of types called the <em>internal parameter list</em>.
6878 * It will constrain the parameter lists of the other loop parts.
6879 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
6880 * with no additional {@code A} types, then the internal parameter list is extended by
6881 * the argument types {@code A...} of the {@code iterations} handle.
6882 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
6883 * list {@code (A...)} is called the <em>external parameter list</em>.
6884 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6885 * additional state variable of the loop.
6886 * The body must both accept a leading parameter and return a value of this type {@code V}.
6887 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6888 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6889 * <a href="MethodHandles.html#effid">effectively identical</a>
6890 * to the external parameter list {@code (A...)}.
6891 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6892 * {@linkplain #empty default value}.
6893 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
6894 * effectively identical to the external parameter list {@code (A...)}.
6895 * </ul>
6896 * <p>
6897 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6898 * <li>The loop handle's result type is the result type {@code V} of the body.
6899 * <li>The loop handle's parameter types are the types {@code (A...)},
6900 * from the external parameter list.
6901 * </ul>
6902 * <p>
6903 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6904 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
6905 * arguments passed to the loop.
6906 * {@snippet lang="java" :
6907 * int iterations(A...);
6908 * V init(A...);
6909 * V body(V, int, A...);
6910 * V countedLoop(A... a...) {
6911 * int end = iterations(a...);
6912 * V v = init(a...);
6913 * for (int i = 0; i < end; ++i) {
6914 * v = body(v, i, a...);
6915 * }
6916 * return v;
6917 * }
6918 * }
6919 *
6920 * @apiNote Example with a fully conformant body method:
6921 * {@snippet lang="java" :
6922 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6923 * // => a variation on a well known theme
6924 * static String step(String v, int counter, String init) { return "na " + v; }
6925 * // assume MH_step is a handle to the method above
6926 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
6927 * MethodHandle start = MethodHandles.identity(String.class);
6928 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
6929 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
6930 * }
6931 *
6932 * @apiNote Example with the simplest possible body method type,
6933 * and passing the number of iterations to the loop invocation:
6934 * {@snippet lang="java" :
6935 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6936 * // => a variation on a well known theme
6937 * static String step(String v, int counter ) { return "na " + v; }
6938 * // assume MH_step is a handle to the method above
6939 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
6940 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
6941 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
6942 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
6943 * }
6944 *
6945 * @apiNote Example that treats the number of iterations, string to append to, and string to append
6946 * as loop parameters:
6947 * {@snippet lang="java" :
6948 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6949 * // => a variation on a well known theme
6950 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
6951 * // assume MH_step is a handle to the method above
6952 * MethodHandle count = MethodHandles.identity(int.class);
6953 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
6954 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
6955 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
6956 * }
6957 *
6958 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
6959 * to enforce a loop type:
6960 * {@snippet lang="java" :
6961 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6962 * // => a variation on a well known theme
6963 * static String step(String v, int counter, String pre) { return pre + " " + v; }
6964 * // assume MH_step is a handle to the method above
6965 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
6966 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
6967 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
6968 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
6969 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
6970 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
6971 * }
6972 *
6973 * @apiNote The implementation of this method can be expressed as follows:
6974 * {@snippet lang="java" :
6975 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
6976 * return countedLoop(empty(iterations.type()), iterations, init, body);
6977 * }
6978 * }
6979 *
6980 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
6981 * result type must be {@code int}. See above for other constraints.
6982 * @param init optional initializer, providing the initial value of the loop variable.
6983 * May be {@code null}, implying a default initial value. See above for other constraints.
6984 * @param body body of the loop, which may not be {@code null}.
6985 * It controls the loop parameters and result type in the standard case (see above for details).
6986 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
6987 * and may accept any number of additional types.
6988 * See above for other constraints.
6989 *
6990 * @return a method handle representing the loop.
6991 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
6992 * @throws IllegalArgumentException if any argument violates the rules formulated above.
6993 *
6994 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
6995 * @since 9
6996 */
6997 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
6998 return countedLoop(empty(iterations.type()), iterations, init, body);
6999 }
7000
7001 /**
7002 * Constructs a loop that counts over a range of numbers.
7003 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7004 * <p>
7005 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
7006 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
7007 * values of the loop counter.
7008 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
7009 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
7010 * <p>
7011 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7012 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7013 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7014 * <p>
7015 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7016 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7017 * iteration variable.
7018 * The result of the loop handle execution will be the final {@code V} value of that variable
7019 * (or {@code void} if there is no {@code V} variable).
7020 * <p>
7021 * The following rules hold for the argument handles:<ul>
7022 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
7023 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
7024 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7025 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7026 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7027 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7028 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7029 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7030 * of types called the <em>internal parameter list</em>.
7031 * It will constrain the parameter lists of the other loop parts.
7032 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7033 * with no additional {@code A} types, then the internal parameter list is extended by
7034 * the argument types {@code A...} of the {@code end} handle.
7035 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7036 * list {@code (A...)} is called the <em>external parameter list</em>.
7037 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7038 * additional state variable of the loop.
7039 * The body must both accept a leading parameter and return a value of this type {@code V}.
7040 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7041 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7042 * <a href="MethodHandles.html#effid">effectively identical</a>
7043 * to the external parameter list {@code (A...)}.
7044 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7045 * {@linkplain #empty default value}.
7046 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
7047 * effectively identical to the external parameter list {@code (A...)}.
7048 * <li>Likewise, the parameter list of {@code end} must be effectively identical
7049 * to the external parameter list.
7050 * </ul>
7051 * <p>
7052 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7053 * <li>The loop handle's result type is the result type {@code V} of the body.
7054 * <li>The loop handle's parameter types are the types {@code (A...)},
7055 * from the external parameter list.
7056 * </ul>
7057 * <p>
7058 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7059 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7060 * arguments passed to the loop.
7061 * {@snippet lang="java" :
7062 * int start(A...);
7063 * int end(A...);
7064 * V init(A...);
7065 * V body(V, int, A...);
7066 * V countedLoop(A... a...) {
7067 * int e = end(a...);
7068 * int s = start(a...);
7069 * V v = init(a...);
7070 * for (int i = s; i < e; ++i) {
7071 * v = body(v, i, a...);
7072 * }
7073 * return v;
7074 * }
7075 * }
7076 *
7077 * @apiNote The implementation of this method can be expressed as follows:
7078 * {@snippet lang="java" :
7079 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7080 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
7081 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
7082 * // the following semantics:
7083 * // MH_increment: (int limit, int counter) -> counter + 1
7084 * // MH_predicate: (int limit, int counter) -> counter < limit
7085 * Class<?> counterType = start.type().returnType(); // int
7086 * Class<?> returnType = body.type().returnType();
7087 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
7088 * if (returnType != void.class) { // ignore the V variable
7089 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7090 * pred = dropArguments(pred, 1, returnType); // ditto
7091 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
7092 * }
7093 * body = dropArguments(body, 0, counterType); // ignore the limit variable
7094 * MethodHandle[]
7095 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7096 * bodyClause = { init, body }, // v = init(); v = body(v, i)
7097 * indexVar = { start, incr }; // i = start(); i = i + 1
7098 * return loop(loopLimit, bodyClause, indexVar);
7099 * }
7100 * }
7101 *
7102 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
7103 * See above for other constraints.
7104 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
7105 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
7106 * @param init optional initializer, providing the initial value of the loop variable.
7107 * May be {@code null}, implying a default initial value. See above for other constraints.
7108 * @param body body of the loop, which may not be {@code null}.
7109 * It controls the loop parameters and result type in the standard case (see above for details).
7110 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7111 * and may accept any number of additional types.
7112 * See above for other constraints.
7113 *
7114 * @return a method handle representing the loop.
7115 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
7116 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7117 *
7118 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
7119 * @since 9
7120 */
7121 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7122 countedLoopChecks(start, end, init, body);
7123 Class<?> counterType = start.type().returnType(); // int, but who's counting?
7124 Class<?> limitType = end.type().returnType(); // yes, int again
7125 Class<?> returnType = body.type().returnType();
7126 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
7127 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
7128 MethodHandle retv = null;
7129 if (returnType != void.class) {
7130 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7131 pred = dropArguments(pred, 1, returnType); // ditto
7132 retv = dropArguments(identity(returnType), 0, counterType);
7133 }
7134 body = dropArguments(body, 0, counterType); // ignore the limit variable
7135 MethodHandle[]
7136 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7137 bodyClause = { init, body }, // v = init(); v = body(v, i)
7138 indexVar = { start, incr }; // i = start(); i = i + 1
7139 return loop(loopLimit, bodyClause, indexVar);
7140 }
7141
7142 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7143 Objects.requireNonNull(start);
7144 Objects.requireNonNull(end);
7145 Objects.requireNonNull(body);
7146 Class<?> counterType = start.type().returnType();
7147 if (counterType != int.class) {
7148 MethodType expected = start.type().changeReturnType(int.class);
7149 throw misMatchedTypes("start function", start.type(), expected);
7150 } else if (end.type().returnType() != counterType) {
7151 MethodType expected = end.type().changeReturnType(counterType);
7152 throw misMatchedTypes("end function", end.type(), expected);
7153 }
7154 MethodType bodyType = body.type();
7155 Class<?> returnType = bodyType.returnType();
7156 List<Class<?>> innerList = bodyType.parameterList();
7157 // strip leading V value if present
7158 int vsize = (returnType == void.class ? 0 : 1);
7159 if (vsize != 0 && (innerList.isEmpty() || innerList.get(0) != returnType)) {
7160 // argument list has no "V" => error
7161 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7162 throw misMatchedTypes("body function", bodyType, expected);
7163 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
7164 // missing I type => error
7165 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
7166 throw misMatchedTypes("body function", bodyType, expected);
7167 }
7168 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
7169 if (outerList.isEmpty()) {
7170 // special case; take lists from end handle
7171 outerList = end.type().parameterList();
7172 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
7173 }
7174 MethodType expected = methodType(counterType, outerList);
7175 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
7176 throw misMatchedTypes("start parameter types", start.type(), expected);
7177 }
7178 if (end.type() != start.type() &&
7179 !end.type().effectivelyIdenticalParameters(0, outerList)) {
7180 throw misMatchedTypes("end parameter types", end.type(), expected);
7181 }
7182 if (init != null) {
7183 MethodType initType = init.type();
7184 if (initType.returnType() != returnType ||
7185 !initType.effectivelyIdenticalParameters(0, outerList)) {
7186 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7187 }
7188 }
7189 }
7190
7191 /**
7192 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
7193 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7194 * <p>
7195 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
7196 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
7197 * <p>
7198 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7199 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7200 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7201 * <p>
7202 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7203 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7204 * iteration variable.
7205 * The result of the loop handle execution will be the final {@code V} value of that variable
7206 * (or {@code void} if there is no {@code V} variable).
7207 * <p>
7208 * The following rules hold for the argument handles:<ul>
7209 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7210 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
7211 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7212 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
7213 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
7214 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
7215 * of types called the <em>internal parameter list</em>.
7216 * It will constrain the parameter lists of the other loop parts.
7217 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
7218 * with no additional {@code A} types, then the internal parameter list is extended by
7219 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
7220 * single type {@code Iterable} is added and constitutes the {@code A...} list.
7221 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
7222 * list {@code (A...)} is called the <em>external parameter list</em>.
7223 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7224 * additional state variable of the loop.
7225 * The body must both accept a leading parameter and return a value of this type {@code V}.
7226 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7227 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7228 * <a href="MethodHandles.html#effid">effectively identical</a>
7229 * to the external parameter list {@code (A...)}.
7230 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7231 * {@linkplain #empty default value}.
7232 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
7233 * type {@code java.util.Iterator} or a subtype thereof.
7234 * The iterator it produces when the loop is executed will be assumed
7235 * to yield values which can be converted to type {@code T}.
7236 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
7237 * effectively identical to the external parameter list {@code (A...)}.
7238 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
7239 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
7240 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
7241 * handle parameter is adjusted to accept the leading {@code A} type, as if by
7242 * the {@link MethodHandle#asType asType} conversion method.
7243 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
7244 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
7245 * </ul>
7246 * <p>
7247 * The type {@code T} may be either a primitive or reference.
7248 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
7249 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
7250 * as if by the {@link MethodHandle#asType asType} conversion method.
7251 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
7252 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
7253 * <p>
7254 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7255 * <li>The loop handle's result type is the result type {@code V} of the body.
7256 * <li>The loop handle's parameter types are the types {@code (A...)},
7257 * from the external parameter list.
7258 * </ul>
7259 * <p>
7260 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7261 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
7262 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
7263 * {@snippet lang="java" :
7264 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
7265 * V init(A...);
7266 * V body(V,T,A...);
7267 * V iteratedLoop(A... a...) {
7268 * Iterator<T> it = iterator(a...);
7269 * V v = init(a...);
7270 * while (it.hasNext()) {
7271 * T t = it.next();
7272 * v = body(v, t, a...);
7273 * }
7274 * return v;
7275 * }
7276 * }
7277 *
7278 * @apiNote Example:
7279 * {@snippet lang="java" :
7280 * // get an iterator from a list
7281 * static List<String> reverseStep(List<String> r, String e) {
7282 * r.add(0, e);
7283 * return r;
7284 * }
7285 * static List<String> newArrayList() { return new ArrayList<>(); }
7286 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
7287 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
7288 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
7289 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
7290 * assertEquals(reversedList, (List<String>) loop.invoke(list));
7291 * }
7292 *
7293 * @apiNote The implementation of this method can be expressed approximately as follows:
7294 * {@snippet lang="java" :
7295 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7296 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
7297 * Class<?> returnType = body.type().returnType();
7298 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7299 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
7300 * MethodHandle retv = null, step = body, startIter = iterator;
7301 * if (returnType != void.class) {
7302 * // the simple thing first: in (I V A...), drop the I to get V
7303 * retv = dropArguments(identity(returnType), 0, Iterator.class);
7304 * // body type signature (V T A...), internal loop types (I V A...)
7305 * step = swapArguments(body, 0, 1); // swap V <-> T
7306 * }
7307 * if (startIter == null) startIter = MH_getIter;
7308 * MethodHandle[]
7309 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
7310 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
7311 * return loop(iterVar, bodyClause);
7312 * }
7313 * }
7314 *
7315 * @param iterator an optional handle to return the iterator to start the loop.
7316 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
7317 * See above for other constraints.
7318 * @param init optional initializer, providing the initial value of the loop variable.
7319 * May be {@code null}, implying a default initial value. See above for other constraints.
7320 * @param body body of the loop, which may not be {@code null}.
7321 * It controls the loop parameters and result type in the standard case (see above for details).
7322 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
7323 * and may accept any number of additional types.
7324 * See above for other constraints.
7325 *
7326 * @return a method handle embodying the iteration loop functionality.
7327 * @throws NullPointerException if the {@code body} handle is {@code null}.
7328 * @throws IllegalArgumentException if any argument violates the above requirements.
7329 *
7330 * @since 9
7331 */
7332 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7333 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
7334 Class<?> returnType = body.type().returnType();
7335 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
7336 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
7337 MethodHandle startIter;
7338 MethodHandle nextVal;
7339 {
7340 MethodType iteratorType;
7341 if (iterator == null) {
7342 // derive argument type from body, if available, else use Iterable
7343 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
7344 iteratorType = startIter.type().changeParameterType(0, iterableType);
7345 } else {
7346 // force return type to the internal iterator class
7347 iteratorType = iterator.type().changeReturnType(Iterator.class);
7348 startIter = iterator;
7349 }
7350 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7351 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
7352
7353 // perform the asType transforms under an exception transformer, as per spec.:
7354 try {
7355 startIter = startIter.asType(iteratorType);
7356 nextVal = nextRaw.asType(nextValType);
7357 } catch (WrongMethodTypeException ex) {
7358 throw new IllegalArgumentException(ex);
7359 }
7360 }
7361
7362 MethodHandle retv = null, step = body;
7363 if (returnType != void.class) {
7364 // the simple thing first: in (I V A...), drop the I to get V
7365 retv = dropArguments(identity(returnType), 0, Iterator.class);
7366 // body type signature (V T A...), internal loop types (I V A...)
7367 step = swapArguments(body, 0, 1); // swap V <-> T
7368 }
7369
7370 MethodHandle[]
7371 iterVar = { startIter, null, hasNext, retv },
7372 bodyClause = { init, filterArgument(step, 0, nextVal) };
7373 return loop(iterVar, bodyClause);
7374 }
7375
7376 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7377 Objects.requireNonNull(body);
7378 MethodType bodyType = body.type();
7379 Class<?> returnType = bodyType.returnType();
7380 List<Class<?>> internalParamList = bodyType.parameterList();
7381 // strip leading V value if present
7382 int vsize = (returnType == void.class ? 0 : 1);
7383 if (vsize != 0 && (internalParamList.isEmpty() || internalParamList.get(0) != returnType)) {
7384 // argument list has no "V" => error
7385 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7386 throw misMatchedTypes("body function", bodyType, expected);
7387 } else if (internalParamList.size() <= vsize) {
7388 // missing T type => error
7389 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
7390 throw misMatchedTypes("body function", bodyType, expected);
7391 }
7392 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
7393 Class<?> iterableType = null;
7394 if (iterator != null) {
7395 // special case; if the body handle only declares V and T then
7396 // the external parameter list is obtained from iterator handle
7397 if (externalParamList.isEmpty()) {
7398 externalParamList = iterator.type().parameterList();
7399 }
7400 MethodType itype = iterator.type();
7401 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
7402 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
7403 }
7404 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
7405 MethodType expected = methodType(itype.returnType(), externalParamList);
7406 throw misMatchedTypes("iterator parameters", itype, expected);
7407 }
7408 } else {
7409 if (externalParamList.isEmpty()) {
7410 // special case; if the iterator handle is null and the body handle
7411 // only declares V and T then the external parameter list consists
7412 // of Iterable
7413 externalParamList = List.of(Iterable.class);
7414 iterableType = Iterable.class;
7415 } else {
7416 // special case; if the iterator handle is null and the external
7417 // parameter list is not empty then the first parameter must be
7418 // assignable to Iterable
7419 iterableType = externalParamList.get(0);
7420 if (!Iterable.class.isAssignableFrom(iterableType)) {
7421 throw newIllegalArgumentException(
7422 "inferred first loop argument must inherit from Iterable: " + iterableType);
7423 }
7424 }
7425 }
7426 if (init != null) {
7427 MethodType initType = init.type();
7428 if (initType.returnType() != returnType ||
7429 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
7430 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
7431 }
7432 }
7433 return iterableType; // help the caller a bit
7434 }
7435
7436 /*non-public*/
7437 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
7438 // there should be a better way to uncross my wires
7439 int arity = mh.type().parameterCount();
7440 int[] order = new int[arity];
7441 for (int k = 0; k < arity; k++) order[k] = k;
7442 order[i] = j; order[j] = i;
7443 Class<?>[] types = mh.type().parameterArray();
7444 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
7445 MethodType swapType = methodType(mh.type().returnType(), types);
7446 return permuteArguments(mh, swapType, order);
7447 }
7448
7449 /**
7450 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
7451 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
7452 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
7453 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
7454 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
7455 * {@code try-finally} handle.
7456 * <p>
7457 * The {@code cleanup} handle will be passed one or two additional leading arguments.
7458 * The first is the exception thrown during the
7459 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
7460 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
7461 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
7462 * The second argument is not present if the {@code target} handle has a {@code void} return type.
7463 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
7464 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
7465 * <p>
7466 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
7467 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
7468 * two extra leading parameters:<ul>
7469 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
7470 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
7471 * the result from the execution of the {@code target} handle.
7472 * This parameter is not present if the {@code target} returns {@code void}.
7473 * </ul>
7474 * <p>
7475 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
7476 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
7477 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
7478 * the cleanup.
7479 * {@snippet lang="java" :
7480 * V target(A..., B...);
7481 * V cleanup(Throwable, V, A...);
7482 * V adapter(A... a, B... b) {
7483 * V result = (zero value for V);
7484 * Throwable throwable = null;
7485 * try {
7486 * result = target(a..., b...);
7487 * } catch (Throwable t) {
7488 * throwable = t;
7489 * throw t;
7490 * } finally {
7491 * result = cleanup(throwable, result, a...);
7492 * }
7493 * return result;
7494 * }
7495 * }
7496 * <p>
7497 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
7498 * be modified by execution of the target, and so are passed unchanged
7499 * from the caller to the cleanup, if it is invoked.
7500 * <p>
7501 * The target and cleanup must return the same type, even if the cleanup
7502 * always throws.
7503 * To create such a throwing cleanup, compose the cleanup logic
7504 * with {@link #throwException throwException},
7505 * in order to create a method handle of the correct return type.
7506 * <p>
7507 * Note that {@code tryFinally} never converts exceptions into normal returns.
7508 * In rare cases where exceptions must be converted in that way, first wrap
7509 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
7510 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
7511 * <p>
7512 * It is recommended that the first parameter type of {@code cleanup} be
7513 * declared {@code Throwable} rather than a narrower subtype. This ensures
7514 * {@code cleanup} will always be invoked with whatever exception that
7515 * {@code target} throws. Declaring a narrower type may result in a
7516 * {@code ClassCastException} being thrown by the {@code try-finally}
7517 * handle if the type of the exception thrown by {@code target} is not
7518 * assignable to the first parameter type of {@code cleanup}. Note that
7519 * various exception types of {@code VirtualMachineError},
7520 * {@code LinkageError}, and {@code RuntimeException} can in principle be
7521 * thrown by almost any kind of Java code, and a finally clause that
7522 * catches (say) only {@code IOException} would mask any of the others
7523 * behind a {@code ClassCastException}.
7524 *
7525 * @param target the handle whose execution is to be wrapped in a {@code try} block.
7526 * @param cleanup the handle that is invoked in the finally block.
7527 *
7528 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
7529 * @throws NullPointerException if any argument is null
7530 * @throws IllegalArgumentException if {@code cleanup} does not accept
7531 * the required leading arguments, or if the method handle types do
7532 * not match in their return types and their
7533 * corresponding trailing parameters
7534 *
7535 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
7536 * @since 9
7537 */
7538 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
7539 Class<?>[] targetParamTypes = target.type().ptypes();
7540 Class<?> rtype = target.type().returnType();
7541
7542 tryFinallyChecks(target, cleanup);
7543
7544 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
7545 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7546 // target parameter list.
7547 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0, false);
7548
7549 // Ensure that the intrinsic type checks the instance thrown by the
7550 // target against the first parameter of cleanup
7551 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
7552
7553 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
7554 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
7555 }
7556
7557 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
7558 Class<?> rtype = target.type().returnType();
7559 if (rtype != cleanup.type().returnType()) {
7560 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
7561 }
7562 MethodType cleanupType = cleanup.type();
7563 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
7564 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
7565 }
7566 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
7567 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
7568 }
7569 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7570 // target parameter list.
7571 int cleanupArgIndex = rtype == void.class ? 1 : 2;
7572 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
7573 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
7574 cleanup.type(), target.type());
7575 }
7576 }
7577
7578 /**
7579 * Creates a table switch method handle, which can be used to switch over a set of target
7580 * method handles, based on a given target index, called selector.
7581 * <p>
7582 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)},
7583 * and where {@code N} is the number of target method handles, the table switch method
7584 * handle will invoke the n-th target method handle from the list of target method handles.
7585 * <p>
7586 * For a selector value that does not fall in the range {@code [0, N)}, the table switch
7587 * method handle will invoke the given fallback method handle.
7588 * <p>
7589 * All method handles passed to this method must have the same type, with the additional
7590 * requirement that the leading parameter be of type {@code int}. The leading parameter
7591 * represents the selector.
7592 * <p>
7593 * Any trailing parameters present in the type will appear on the returned table switch
7594 * method handle as well. Any arguments assigned to these parameters will be forwarded,
7595 * together with the selector value, to the selected method handle when invoking it.
7596 *
7597 * @apiNote Example:
7598 * The cases each drop the {@code selector} value they are given, and take an additional
7599 * {@code String} argument, which is concatenated (using {@link String#concat(String)})
7600 * to a specific constant label string for each case:
7601 * {@snippet lang="java" :
7602 * MethodHandles.Lookup lookup = MethodHandles.lookup();
7603 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat",
7604 * MethodType.methodType(String.class, String.class));
7605 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class);
7606 *
7607 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: ");
7608 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: ");
7609 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: ");
7610 *
7611 * MethodHandle mhSwitch = MethodHandles.tableSwitch(
7612 * caseDefault,
7613 * case0,
7614 * case1
7615 * );
7616 *
7617 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data"));
7618 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data"));
7619 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data"));
7620 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data"));
7621 * }
7622 *
7623 * @param fallback the fallback method handle that is called when the selector is not
7624 * within the range {@code [0, N)}.
7625 * @param targets array of target method handles.
7626 * @return the table switch method handle.
7627 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any
7628 * any of the elements of the {@code targets} array are
7629 * {@code null}.
7630 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading
7631 * parameter of the fallback handle or any of the target
7632 * handles is not {@code int}, or if the types of
7633 * the fallback handle and all of target handles are
7634 * not the same.
7635 *
7636 * @since 17
7637 */
7638 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) {
7639 Objects.requireNonNull(fallback);
7640 Objects.requireNonNull(targets);
7641 targets = targets.clone();
7642 MethodType type = tableSwitchChecks(fallback, targets);
7643 return MethodHandleImpl.makeTableSwitch(type, fallback, targets);
7644 }
7645
7646 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) {
7647 if (caseActions.length == 0)
7648 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions));
7649
7650 MethodType expectedType = defaultCase.type();
7651
7652 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class)
7653 throw new IllegalArgumentException(
7654 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions));
7655
7656 for (MethodHandle mh : caseActions) {
7657 Objects.requireNonNull(mh);
7658 if (mh.type() != expectedType)
7659 throw new IllegalArgumentException(
7660 "Case actions must have the same type: " + Arrays.toString(caseActions));
7661 }
7662
7663 return expectedType;
7664 }
7665
7666 /**
7667 * Adapts a target var handle by pre-processing incoming and outgoing values using a pair of filter functions.
7668 * <p>
7669 * When calling e.g. {@link VarHandle#set(Object...)} on the resulting var handle, the incoming value (of type {@code T}, where
7670 * {@code T} is the <em>last</em> parameter type of the first filter function) is processed using the first filter and then passed
7671 * to the target var handle.
7672 * Conversely, when calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the return value obtained from
7673 * the target var handle (of type {@code T}, where {@code T} is the <em>last</em> parameter type of the second filter function)
7674 * is processed using the second filter and returned to the caller. More advanced access mode types, such as
7675 * {@link VarHandle.AccessMode#COMPARE_AND_EXCHANGE} might apply both filters at the same time.
7676 * <p>
7677 * For the boxing and unboxing filters to be well-formed, their types must be of the form {@code (A... , S) -> T} and
7678 * {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle. If this is the case,
7679 * the resulting var handle will have type {@code S} and will feature the additional coordinates {@code A...} (which
7680 * will be appended to the coordinates of the target var handle).
7681 * <p>
7682 * If the boxing and unboxing filters throw any checked exceptions when invoked, the resulting var handle will
7683 * throw an {@link IllegalStateException}.
7684 * <p>
7685 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7686 * atomic access guarantees as those featured by the target var handle.
7687 *
7688 * @param target the target var handle
7689 * @param filterToTarget a filter to convert some type {@code S} into the type of {@code target}
7690 * @param filterFromTarget a filter to convert the type of {@code target} to some type {@code S}
7691 * @return an adapter var handle which accepts a new type, performing the provided boxing/unboxing conversions.
7692 * @throws IllegalArgumentException if {@code filterFromTarget} and {@code filterToTarget} are not well-formed, that is, they have types
7693 * other than {@code (A... , S) -> T} and {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle,
7694 * or if it's determined that either {@code filterFromTarget} or {@code filterToTarget} throws any checked exceptions.
7695 * @throws NullPointerException if any of the arguments is {@code null}.
7696 * @since 22
7697 */
7698 public static VarHandle filterValue(VarHandle target, MethodHandle filterToTarget, MethodHandle filterFromTarget) {
7699 return VarHandles.filterValue(target, filterToTarget, filterFromTarget);
7700 }
7701
7702 /**
7703 * Adapts a target var handle by pre-processing incoming coordinate values using unary filter functions.
7704 * <p>
7705 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the incoming coordinate values
7706 * starting at position {@code pos} (of type {@code C1, C2 ... Cn}, where {@code C1, C2 ... Cn} are the return types
7707 * of the unary filter functions) are transformed into new values (of type {@code S1, S2 ... Sn}, where {@code S1, S2 ... Sn} are the
7708 * parameter types of the unary filter functions), and then passed (along with any coordinate that was left unaltered
7709 * by the adaptation) to the target var handle.
7710 * <p>
7711 * For the coordinate filters to be well-formed, their types must be of the form {@code S1 -> T1, S2 -> T1 ... Sn -> Tn},
7712 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
7713 * <p>
7714 * If any of the filters throws a checked exception when invoked, the resulting var handle will
7715 * throw an {@link IllegalStateException}.
7716 * <p>
7717 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7718 * atomic access guarantees as those featured by the target var handle.
7719 *
7720 * @param target the target var handle
7721 * @param pos the position of the first coordinate to be transformed
7722 * @param filters the unary functions which are used to transform coordinates starting at position {@code pos}
7723 * @return an adapter var handle which accepts new coordinate types, applying the provided transformation
7724 * to the new coordinate values.
7725 * @throws IllegalArgumentException if the handles in {@code filters} are not well-formed, that is, they have types
7726 * other than {@code S1 -> T1, S2 -> T2, ... Sn -> Tn} where {@code T1, T2 ... Tn} are the coordinate types starting
7727 * at position {@code pos} of the target var handle, if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
7728 * or if more filters are provided than the actual number of coordinate types available starting at {@code pos},
7729 * or if it's determined that any of the filters throws any checked exceptions.
7730 * @throws NullPointerException if any of the arguments is {@code null} or {@code filters} contains {@code null}.
7731 * @since 22
7732 */
7733 public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) {
7734 return VarHandles.filterCoordinates(target, pos, filters);
7735 }
7736
7737 /**
7738 * Provides a target var handle with one or more <em>bound coordinates</em>
7739 * in advance of the var handle's invocation. As a consequence, the resulting var handle will feature less
7740 * coordinate types than the target var handle.
7741 * <p>
7742 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, incoming coordinate values
7743 * are joined with bound coordinate values, and then passed to the target var handle.
7744 * <p>
7745 * For the bound coordinates to be well-formed, their types must be {@code T1, T2 ... Tn },
7746 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
7747 * <p>
7748 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7749 * atomic access guarantees as those featured by the target var handle.
7750 *
7751 * @param target the var handle to invoke after the bound coordinates are inserted
7752 * @param pos the position of the first coordinate to be inserted
7753 * @param values the series of bound coordinates to insert
7754 * @return an adapter var handle which inserts additional coordinates,
7755 * before calling the target var handle
7756 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
7757 * or if more values are provided than the actual number of coordinate types available starting at {@code pos}.
7758 * @throws ClassCastException if the bound coordinates in {@code values} are not well-formed, that is, they have types
7759 * other than {@code T1, T2 ... Tn }, where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos}
7760 * of the target var handle.
7761 * @throws NullPointerException if any of the arguments is {@code null} or {@code values} contains {@code null}.
7762 * @since 22
7763 */
7764 public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) {
7765 return VarHandles.insertCoordinates(target, pos, values);
7766 }
7767
7768 /**
7769 * Provides a var handle which adapts the coordinate values of the target var handle, by re-arranging them
7770 * so that the new coordinates match the provided ones.
7771 * <p>
7772 * The given array controls the reordering.
7773 * Call {@code #I} the number of incoming coordinates (the value
7774 * {@code newCoordinates.size()}), and call {@code #O} the number
7775 * of outgoing coordinates (the number of coordinates associated with the target var handle).
7776 * Then the length of the reordering array must be {@code #O},
7777 * and each element must be a non-negative number less than {@code #I}.
7778 * For every {@code N} less than {@code #O}, the {@code N}-th
7779 * outgoing coordinate will be taken from the {@code I}-th incoming
7780 * coordinate, where {@code I} is {@code reorder[N]}.
7781 * <p>
7782 * No coordinate value conversions are applied.
7783 * The type of each incoming coordinate, as determined by {@code newCoordinates},
7784 * must be identical to the type of the corresponding outgoing coordinate
7785 * in the target var handle.
7786 * <p>
7787 * The reordering array need not specify an actual permutation.
7788 * An incoming coordinate will be duplicated if its index appears
7789 * more than once in the array, and an incoming coordinate will be dropped
7790 * if its index does not appear in the array.
7791 * <p>
7792 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7793 * atomic access guarantees as those featured by the target var handle.
7794 * @param target the var handle to invoke after the coordinates have been reordered
7795 * @param newCoordinates the new coordinate types
7796 * @param reorder an index array which controls the reordering
7797 * @return an adapter var handle which re-arranges the incoming coordinate values,
7798 * before calling the target var handle
7799 * @throws IllegalArgumentException if the index array length is not equal to
7800 * the number of coordinates of the target var handle, or if any index array element is not a valid index for
7801 * a coordinate of {@code newCoordinates}, or if two corresponding coordinate types in
7802 * the target var handle and in {@code newCoordinates} are not identical.
7803 * @throws NullPointerException if any of the arguments is {@code null} or {@code newCoordinates} contains {@code null}.
7804 * @since 22
7805 */
7806 public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) {
7807 return VarHandles.permuteCoordinates(target, newCoordinates, reorder);
7808 }
7809
7810 /**
7811 * Adapts a target var handle by pre-processing
7812 * a sub-sequence of its coordinate values with a filter (a method handle).
7813 * The pre-processed coordinates are replaced by the result (if any) of the
7814 * filter function and the target var handle is then called on the modified (usually shortened)
7815 * coordinate list.
7816 * <p>
7817 * If {@code R} is the return type of the filter, then:
7818 * <ul>
7819 * <li>if {@code R} <em>is not</em> {@code void}, the target var handle must have a coordinate of type {@code R} in
7820 * position {@code pos}. The parameter types of the filter will replace the coordinate type at position {@code pos}
7821 * of the target var handle. When the returned var handle is invoked, it will be as if the filter is invoked first,
7822 * and its result is passed in place of the coordinate at position {@code pos} in a downstream invocation of the
7823 * target var handle.</li>
7824 * <li> if {@code R} <em>is</em> {@code void}, the parameter types (if any) of the filter will be inserted in the
7825 * coordinate type list of the target var handle at position {@code pos}. In this case, when the returned var handle
7826 * is invoked, the filter essentially acts as a side effect, consuming some of the coordinate values, before a
7827 * downstream invocation of the target var handle.</li>
7828 * </ul>
7829 * <p>
7830 * If any of the filters throws a checked exception when invoked, the resulting var handle will
7831 * throw an {@link IllegalStateException}.
7832 * <p>
7833 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7834 * atomic access guarantees as those featured by the target var handle.
7835 *
7836 * @param target the var handle to invoke after the coordinates have been filtered
7837 * @param pos the position in the coordinate list of the target var handle where the filter is to be inserted
7838 * @param filter the filter method handle
7839 * @return an adapter var handle which filters the incoming coordinate values,
7840 * before calling the target var handle
7841 * @throws IllegalArgumentException if the return type of {@code filter}
7842 * is not void, and it is not the same as the {@code pos} coordinate of the target var handle,
7843 * if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
7844 * if the resulting var handle's type would have <a href="MethodHandle.html#maxarity">too many coordinates</a>,
7845 * or if it's determined that {@code filter} throws any checked exceptions.
7846 * @throws NullPointerException if any of the arguments is {@code null}.
7847 * @since 22
7848 */
7849 public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle filter) {
7850 return VarHandles.collectCoordinates(target, pos, filter);
7851 }
7852
7853 /**
7854 * Returns a var handle which will discard some dummy coordinates before delegating to the
7855 * target var handle. As a consequence, the resulting var handle will feature more
7856 * coordinate types than the target var handle.
7857 * <p>
7858 * The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is the arity of the
7859 * target var handle's coordinate types. If {@code pos} is zero, the dummy coordinates will precede
7860 * the target's real arguments; if {@code pos} is <i>N</i> they will come after.
7861 * <p>
7862 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7863 * atomic access guarantees as those featured by the target var handle.
7864 *
7865 * @param target the var handle to invoke after the dummy coordinates are dropped
7866 * @param pos position of the first coordinate to drop (zero for the leftmost)
7867 * @param valueTypes the type(s) of the coordinate(s) to drop
7868 * @return an adapter var handle which drops some dummy coordinates,
7869 * before calling the target var handle
7870 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive.
7871 * @throws NullPointerException if any of the arguments is {@code null} or {@code valueTypes} contains {@code null}.
7872 * @since 22
7873 */
7874 public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) {
7875 return VarHandles.dropCoordinates(target, pos, valueTypes);
7876 }
7877 }