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 sun.invoke.util.ValueConversions;
37 import sun.invoke.util.VerifyAccess;
38 import sun.invoke.util.Wrapper;
39
40 import java.lang.classfile.ClassFile;
41 import java.lang.classfile.ClassModel;
42 import java.lang.constant.ClassDesc;
43 import java.lang.constant.ConstantDescs;
44 import java.lang.invoke.LambdaForm.BasicType;
45 import java.lang.invoke.MethodHandleImpl.Intrinsic;
46 import java.lang.reflect.Constructor;
47 import java.lang.reflect.Field;
48 import java.lang.reflect.Member;
49 import java.lang.reflect.Method;
50 import java.lang.reflect.Modifier;
51 import java.nio.ByteOrder;
52 import java.security.ProtectionDomain;
53 import java.util.ArrayList;
54 import java.util.Arrays;
55 import java.util.BitSet;
56 import java.util.Comparator;
57 import java.util.Iterator;
58 import java.util.List;
59 import java.util.Objects;
60 import java.util.Set;
61 import java.util.concurrent.ConcurrentHashMap;
62 import java.util.stream.Stream;
63
64 import static java.lang.classfile.ClassFile.*;
65 import static java.lang.invoke.LambdaForm.BasicType.V_TYPE;
66 import static java.lang.invoke.MethodHandleNatives.Constants.*;
67 import static java.lang.invoke.MethodHandleStatics.UNSAFE;
68 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
69 import static java.lang.invoke.MethodHandleStatics.newInternalError;
70 import static java.lang.invoke.MethodType.methodType;
71
72 /**
73 * This class consists exclusively of static methods that operate on or return
74 * method handles. They fall into several categories:
75 * <ul>
76 * <li>Lookup methods which help create method handles for methods and fields.
77 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
78 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
79 * </ul>
80 * A lookup, combinator, or factory method will fail and throw an
81 * {@code IllegalArgumentException} if the created method handle's type
82 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
83 *
84 * @author John Rose, JSR 292 EG
85 * @since 1.7
86 */
87 public final class MethodHandles {
88
89 private MethodHandles() { } // do not instantiate
90
91 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
92
93 // See IMPL_LOOKUP below.
94
95 //--- Method handle creation from ordinary methods.
96
97 /**
98 * Returns a {@link Lookup lookup object} with
99 * full capabilities to emulate all supported bytecode behaviors of the caller.
100 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller.
101 * Factory methods on the lookup object can create
102 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
103 * for any member that the caller has access to via bytecodes,
104 * including protected and private fields and methods.
105 * This lookup object is created by the original lookup class
106 * and has the {@link Lookup#ORIGINAL ORIGINAL} bit set.
107 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
108 * Do not store it in place where untrusted code can access it.
109 * <p>
110 * This method is caller sensitive, which means that it may return different
111 * values to different callers.
112 * In cases where {@code MethodHandles.lookup} is called from a context where
113 * there is no caller frame on the stack (e.g. when called directly
114 * from a JNI attached thread), {@code IllegalCallerException} is thrown.
115 * To obtain a {@link Lookup lookup object} in such a context, use an auxiliary class that will
116 * implicitly be identified as the caller, or use {@link MethodHandles#publicLookup()}
117 * to obtain a low-privileged lookup instead.
118 * @return a lookup object for the caller of this method, with
119 * {@linkplain Lookup#ORIGINAL original} and
120 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}.
121 * @throws IllegalCallerException if there is no caller frame on the stack.
122 */
123 @CallerSensitive
124 @ForceInline // to ensure Reflection.getCallerClass optimization
125 public static Lookup lookup() {
126 final Class<?> c = Reflection.getCallerClass();
127 if (c == null) {
128 throw new IllegalCallerException("no caller frame");
129 }
130 return new Lookup(c);
131 }
132
133 /**
134 * This lookup method is the alternate implementation of
135 * the lookup method with a leading caller class argument which is
136 * non-caller-sensitive. This method is only invoked by reflection
137 * and method handle.
138 */
139 @CallerSensitiveAdapter
140 private static Lookup lookup(Class<?> caller) {
141 if (caller.getClassLoader() == null) {
142 throw newInternalError("calling lookup() reflectively is not supported: "+caller);
143 }
144 return new Lookup(caller);
145 }
146
147 /**
148 * Returns a {@link Lookup lookup object} which is trusted minimally.
149 * The lookup has the {@code UNCONDITIONAL} mode.
150 * It can only be used to create method handles to public members of
151 * public classes in packages that are exported unconditionally.
152 * <p>
153 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
154 * of this lookup object will be {@link java.lang.Object}.
155 *
156 * @apiNote The use of Object is conventional, and because the lookup modes are
157 * limited, there is no special access provided to the internals of Object, its package
158 * or its module. This public lookup object or other lookup object with
159 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
160 * is not used to determine the lookup context.
161 *
162 * <p style="font-size:smaller;">
163 * <em>Discussion:</em>
164 * The lookup class can be changed to any other class {@code C} using an expression of the form
165 * {@link Lookup#in publicLookup().in(C.class)}.
166 * Also, it cannot access
167 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
168 * @return a lookup object which is trusted minimally
169 */
170 public static Lookup publicLookup() {
171 return Lookup.PUBLIC_LOOKUP;
172 }
173
174 /**
175 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
176 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>.
177 * The returned lookup object can provide access to classes in modules and packages,
178 * and members of those classes, outside the normal rules of Java access control,
179 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
180 * <p>
181 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
182 * allowed to do deep reflection on module {@code M2} and package of the target class
183 * if and only if all of the following conditions are {@code true}:
184 * <ul>
185 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess()
186 * full privilege access}. Specifically:
187 * <ul>
188 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
189 * (This is because otherwise there would be no way to ensure the original lookup
190 * creator was a member of any particular module, and so any subsequent checks
191 * for readability and qualified exports would become ineffective.)
192 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
193 * (This is because an application intending to share intra-module access
194 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
195 * deep reflection to its own module.)
196 * </ul>
197 * <li>The target class must be a proper class, not a primitive or array class.
198 * (Thus, {@code M2} is well-defined.)
199 * <li>If the caller module {@code M1} differs from
200 * the target module {@code M2} then both of the following must be true:
201 * <ul>
202 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
203 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
204 * containing the target class to at least {@code M1}.</li>
205 * </ul>
206 * </ul>
207 * <p>
208 * If any of the above checks is violated, this method fails with an
209 * exception.
210 * <p>
211 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
212 * returns a {@code Lookup} on {@code targetClass} with
213 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}
214 * with {@code null} previous lookup class.
215 * <p>
216 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
217 * returns a {@code Lookup} on {@code targetClass} that records
218 * the lookup class of the caller as the new previous lookup class with
219 * {@code PRIVATE} access but no {@code MODULE} access.
220 * <p>
221 * The resulting {@code Lookup} object has no {@code ORIGINAL} access.
222 *
223 * @apiNote The {@code Lookup} object returned by this method is allowed to
224 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
225 * of {@code targetClass}. Extreme caution should be taken when opening a package
226 * to another module as such defined classes have the same full privilege
227 * access as other members in {@code targetClass}'s module.
228 *
229 * @param targetClass the target class
230 * @param caller the caller lookup object
231 * @return a lookup object for the target class, with private access
232 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class
233 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
234 * @throws IllegalAccessException if any of the other access checks specified above fails
235 * @since 9
236 * @see Lookup#dropLookupMode
237 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
238 */
239 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
240 if (caller.allowedModes == Lookup.TRUSTED) {
241 return new Lookup(targetClass);
242 }
243
244 if (targetClass.isPrimitive())
245 throw new IllegalArgumentException(targetClass + " is a primitive class");
246 if (targetClass.isArray())
247 throw new IllegalArgumentException(targetClass + " is an array class");
248 // Ensure that we can reason accurately about private and module access.
249 int requireAccess = Lookup.PRIVATE|Lookup.MODULE;
250 if ((caller.lookupModes() & requireAccess) != requireAccess)
251 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode");
252
253 // previous lookup class is never set if it has MODULE access
254 assert caller.previousLookupClass() == null;
255
256 Class<?> callerClass = caller.lookupClass();
257 Module callerModule = callerClass.getModule(); // M1
258 Module targetModule = targetClass.getModule(); // M2
259 Class<?> newPreviousClass = null;
260 int newModes = Lookup.FULL_POWER_MODES & ~Lookup.ORIGINAL;
261
262 if (targetModule != callerModule) {
263 if (!callerModule.canRead(targetModule))
264 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
265 if (targetModule.isNamed()) {
266 String pn = targetClass.getPackageName();
267 assert !pn.isEmpty() : "unnamed package cannot be in named module";
268 if (!targetModule.isOpen(pn, callerModule))
269 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
270 }
271
272 // M2 != M1, set previous lookup class to M1 and drop MODULE access
273 newPreviousClass = callerClass;
274 newModes &= ~Lookup.MODULE;
275 }
276 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
277 }
278
279 /**
280 * Returns the <em>class data</em> associated with the lookup class
281 * of the given {@code caller} lookup object, or {@code null}.
282 *
283 * <p> A hidden class with class data can be created by calling
284 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
285 * Lookup::defineHiddenClassWithClassData}.
286 * This method will cause the static class initializer of the lookup
287 * class of the given {@code caller} lookup object be executed if
288 * it has not been initialized.
289 *
290 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
291 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
292 * {@code null} is returned if this method is called on the lookup object
293 * on these classes.
294 *
295 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
296 * must have {@linkplain Lookup#ORIGINAL original access}
297 * in order to retrieve the class data.
298 *
299 * @apiNote
300 * This method can be called as a bootstrap method for a dynamically computed
301 * constant. A framework can create a hidden class with class data, for
302 * example that can be {@code Class} or {@code MethodHandle} object.
303 * The class data is accessible only to the lookup object
304 * created by the original caller but inaccessible to other members
305 * in the same nest. If a framework passes security sensitive objects
306 * to a hidden class via class data, it is recommended to load the value
307 * of class data as a dynamically computed constant instead of storing
308 * the class data in private static field(s) which are accessible to
309 * other nestmates.
310 *
311 * @param <T> the type to cast the class data object to
312 * @param caller the lookup context describing the class performing the
313 * operation (normally stacked by the JVM)
314 * @param name must be {@link ConstantDescs#DEFAULT_NAME}
315 * ({@code "_"})
316 * @param type the type of the class data
317 * @return the value of the class data if present in the lookup class;
318 * otherwise {@code null}
319 * @throws IllegalArgumentException if name is not {@code "_"}
320 * @throws IllegalAccessException if the lookup context does not have
321 * {@linkplain Lookup#ORIGINAL original} access
322 * @throws ClassCastException if the class data cannot be converted to
323 * the given {@code type}
324 * @throws NullPointerException if {@code caller} or {@code type} argument
325 * is {@code null}
326 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
327 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
328 * @since 16
329 * @jvms 5.5 Initialization
330 */
331 public static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException {
332 Objects.requireNonNull(caller);
333 Objects.requireNonNull(type);
334 if (!ConstantDescs.DEFAULT_NAME.equals(name)) {
335 throw new IllegalArgumentException("name must be \"_\": " + name);
336 }
337
338 if ((caller.lookupModes() & Lookup.ORIGINAL) != Lookup.ORIGINAL) {
339 throw new IllegalAccessException(caller + " does not have ORIGINAL access");
340 }
341
342 Object classdata = classData(caller.lookupClass());
343 if (classdata == null) return null;
344
345 try {
346 return BootstrapMethodInvoker.widenAndCast(classdata, type);
347 } catch (RuntimeException|Error e) {
348 throw e; // let CCE and other runtime exceptions through
349 } catch (Throwable e) {
350 throw new InternalError(e);
351 }
352 }
353
354 /*
355 * Returns the class data set by the VM in the Class::classData field.
356 *
357 * This is also invoked by LambdaForms as it cannot use condy via
358 * MethodHandles::classData due to bootstrapping issue.
359 */
360 static Object classData(Class<?> c) {
361 UNSAFE.ensureClassInitialized(c);
362 return SharedSecrets.getJavaLangAccess().classData(c);
363 }
364
365 /**
366 * Returns the element at the specified index in the
367 * {@linkplain #classData(Lookup, String, Class) class data},
368 * if the class data associated with the lookup class
369 * of the given {@code caller} lookup object is a {@code List}.
370 * If the class data is not present in this lookup class, this method
371 * returns {@code null}.
372 *
373 * <p> A hidden class with class data can be created by calling
374 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
375 * Lookup::defineHiddenClassWithClassData}.
376 * This method will cause the static class initializer of the lookup
377 * class of the given {@code caller} lookup object be executed if
378 * it has not been initialized.
379 *
380 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
381 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
382 * {@code null} is returned if this method is called on the lookup object
383 * on these classes.
384 *
385 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
386 * must have {@linkplain Lookup#ORIGINAL original access}
387 * in order to retrieve the class data.
388 *
389 * @apiNote
390 * This method can be called as a bootstrap method for a dynamically computed
391 * constant. A framework can create a hidden class with class data, for
392 * example that can be {@code List.of(o1, o2, o3....)} containing more than
393 * one object and use this method to load one element at a specific index.
394 * The class data is accessible only to the lookup object
395 * created by the original caller but inaccessible to other members
396 * in the same nest. If a framework passes security sensitive objects
397 * to a hidden class via class data, it is recommended to load the value
398 * of class data as a dynamically computed constant instead of storing
399 * the class data in private static field(s) which are accessible to other
400 * nestmates.
401 *
402 * @param <T> the type to cast the result object to
403 * @param caller the lookup context describing the class performing the
404 * operation (normally stacked by the JVM)
405 * @param name must be {@link java.lang.constant.ConstantDescs#DEFAULT_NAME}
406 * ({@code "_"})
407 * @param type the type of the element at the given index in the class data
408 * @param index index of the element in the class data
409 * @return the element at the given index in the class data
410 * if the class data is present; otherwise {@code null}
411 * @throws IllegalArgumentException if name is not {@code "_"}
412 * @throws IllegalAccessException if the lookup context does not have
413 * {@linkplain Lookup#ORIGINAL original} access
414 * @throws ClassCastException if the class data cannot be converted to {@code List}
415 * or the element at the specified index cannot be converted to the given type
416 * @throws IndexOutOfBoundsException if the index is out of range
417 * @throws NullPointerException if {@code caller} or {@code type} argument is
418 * {@code null}; or if unboxing operation fails because
419 * the element at the given index is {@code null}
420 *
421 * @since 16
422 * @see #classData(Lookup, String, Class)
423 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
424 */
425 public static <T> T classDataAt(Lookup caller, String name, Class<T> type, int index)
426 throws IllegalAccessException
427 {
428 @SuppressWarnings("unchecked")
429 List<Object> classdata = (List<Object>)classData(caller, name, List.class);
430 if (classdata == null) return null;
431
432 try {
433 Object element = classdata.get(index);
434 return BootstrapMethodInvoker.widenAndCast(element, type);
435 } catch (RuntimeException|Error e) {
436 throw e; // let specified exceptions and other runtime exceptions/errors through
437 } catch (Throwable e) {
438 throw new InternalError(e);
439 }
440 }
441
442 /**
443 * Performs an unchecked "crack" of a
444 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
445 * The result is as if the user had obtained a lookup object capable enough
446 * to crack the target method handle, called
447 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
448 * on the target to obtain its symbolic reference, and then called
449 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
450 * to resolve the symbolic reference to a member.
451 * @param <T> the desired type of the result, either {@link Member} or a subtype
452 * @param expected a class object representing the desired result type {@code T}
453 * @param target a direct method handle to crack into symbolic reference components
454 * @return a reference to the method, constructor, or field object
455 * @throws NullPointerException if either argument is {@code null}
456 * @throws IllegalArgumentException if the target is not a direct method handle
457 * @throws ClassCastException if the member is not of the expected type
458 * @since 1.8
459 */
460 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) {
461 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
462 return lookup.revealDirect(target).reflectAs(expected, lookup);
463 }
464
465 /**
466 * A <em>lookup object</em> is a factory for creating method handles,
467 * when the creation requires access checking.
468 * Method handles do not perform
469 * access checks when they are called, but rather when they are created.
470 * Therefore, method handle access
471 * restrictions must be enforced when a method handle is created.
472 * The caller class against which those restrictions are enforced
473 * is known as the {@linkplain #lookupClass() lookup class}.
474 * <p>
475 * A lookup class which needs to create method handles will call
476 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
477 * When the {@code Lookup} factory object is created, the identity of the lookup class is
478 * determined, and securely stored in the {@code Lookup} object.
479 * The lookup class (or its delegates) may then use factory methods
480 * on the {@code Lookup} object to create method handles for access-checked members.
481 * This includes all methods, constructors, and fields which are allowed to the lookup class,
482 * even private ones.
483 *
484 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
485 * The factory methods on a {@code Lookup} object correspond to all major
486 * use cases for methods, constructors, and fields.
487 * Each method handle created by a factory method is the functional
488 * equivalent of a particular <em>bytecode behavior</em>.
489 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of
490 * the Java Virtual Machine Specification.)
491 * Here is a summary of the correspondence between these factory methods and
492 * the behavior of the resulting method handles:
493 * <table class="striped">
494 * <caption style="display:none">lookup method behaviors</caption>
495 * <thead>
496 * <tr>
497 * <th scope="col"><a id="equiv"></a>lookup expression</th>
498 * <th scope="col">member</th>
499 * <th scope="col">bytecode behavior</th>
500 * </tr>
501 * </thead>
502 * <tbody>
503 * <tr>
504 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
505 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
506 * </tr>
507 * <tr>
508 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
509 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
510 * </tr>
511 * <tr>
512 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
513 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
514 * </tr>
515 * <tr>
516 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
517 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
518 * </tr>
519 * <tr>
520 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
521 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
522 * </tr>
523 * <tr>
524 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
525 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
526 * </tr>
527 * <tr>
528 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
529 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
530 * </tr>
531 * <tr>
532 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
533 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
534 * </tr>
535 * <tr>
536 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
537 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
538 * </tr>
539 * <tr>
540 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
541 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
542 * </tr>
543 * <tr>
544 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
545 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
546 * </tr>
547 * <tr>
548 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
549 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
550 * </tr>
551 * <tr>
552 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th>
553 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
554 * </tr>
555 * <tr>
556 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
557 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
558 * </tr>
559 * </tbody>
560 * </table>
561 *
562 * Here, the type {@code C} is the class or interface being searched for a member,
563 * documented as a parameter named {@code refc} in the lookup methods.
564 * The method type {@code MT} is composed from the return type {@code T}
565 * and the sequence of argument types {@code A*}.
566 * The constructor also has a sequence of argument types {@code A*} and
567 * is deemed to return the newly-created object of type {@code C}.
568 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
569 * The formal parameter {@code this} stands for the self-reference of type {@code C};
570 * if it is present, it is always the leading argument to the method handle invocation.
571 * (In the case of some {@code protected} members, {@code this} may be
572 * restricted in type to the lookup class; see below.)
573 * The name {@code arg} stands for all the other method handle arguments.
574 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
575 * stands for a null reference if the accessed method or field is static,
576 * and {@code this} otherwise.
577 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
578 * for reflective objects corresponding to the given members declared in type {@code C}.
579 * <p>
580 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
581 * as if by {@code ldc CONSTANT_Class}.
582 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
583 * <p>
584 * In cases where the given member is of variable arity (i.e., a method or constructor)
585 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
586 * In all other cases, the returned method handle will be of fixed arity.
587 * <p style="font-size:smaller;">
588 * <em>Discussion:</em>
589 * The equivalence between looked-up method handles and underlying
590 * class members and bytecode behaviors
591 * can break down in a few ways:
592 * <ul style="font-size:smaller;">
593 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
594 * the lookup can still succeed, even when there is no equivalent
595 * Java expression or bytecoded constant.
596 * <li>Likewise, if {@code T} or {@code MT}
597 * is not symbolically accessible from the lookup class's loader,
598 * the lookup can still succeed.
599 * For example, lookups for {@code MethodHandle.invokeExact} and
600 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
601 * <li>If the looked-up method has a
602 * <a href="MethodHandle.html#maxarity">very large arity</a>,
603 * the method handle creation may fail with an
604 * {@code IllegalArgumentException}, due to the method handle type having
605 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
606 * </ul>
607 *
608 * <h2><a id="access"></a>Access checking</h2>
609 * Access checks are applied in the factory methods of {@code Lookup},
610 * when a method handle is created.
611 * This is a key difference from the Core Reflection API, since
612 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
613 * performs access checking against every caller, on every call.
614 * <p>
615 * All access checks start from a {@code Lookup} object, which
616 * compares its recorded lookup class against all requests to
617 * create method handles.
618 * A single {@code Lookup} object can be used to create any number
619 * of access-checked method handles, all checked against a single
620 * lookup class.
621 * <p>
622 * A {@code Lookup} object can be shared with other trusted code,
623 * such as a metaobject protocol.
624 * A shared {@code Lookup} object delegates the capability
625 * to create method handles on private members of the lookup class.
626 * Even if privileged code uses the {@code Lookup} object,
627 * the access checking is confined to the privileges of the
628 * original lookup class.
629 * <p>
630 * A lookup can fail, because
631 * the containing class is not accessible to the lookup class, or
632 * because the desired class member is missing, or because the
633 * desired class member is not accessible to the lookup class, or
634 * because the lookup object is not trusted enough to access the member.
635 * In the case of a field setter function on a {@code final} field,
636 * finality enforcement is treated as a kind of access control,
637 * and the lookup will fail, except in special cases of
638 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
639 * In any of these cases, a {@code ReflectiveOperationException} will be
640 * thrown from the attempted lookup. The exact class will be one of
641 * the following:
642 * <ul>
643 * <li>NoSuchMethodException — if a method is requested but does not exist
644 * <li>NoSuchFieldException — if a field is requested but does not exist
645 * <li>IllegalAccessException — if the member exists but an access check fails
646 * </ul>
647 * <p>
648 * In general, the conditions under which a method handle may be
649 * looked up for a method {@code M} are no more restrictive than the conditions
650 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
651 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
652 * a method handle lookup will generally raise a corresponding
653 * checked exception, such as {@code NoSuchMethodException}.
654 * And the effect of invoking the method handle resulting from the lookup
655 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
656 * to executing the compiled, verified, and resolved call to {@code M}.
657 * The same point is true of fields and constructors.
658 * <p style="font-size:smaller;">
659 * <em>Discussion:</em>
660 * Access checks only apply to named and reflected methods,
661 * constructors, and fields.
662 * Other method handle creation methods, such as
663 * {@link MethodHandle#asType MethodHandle.asType},
664 * do not require any access checks, and are used
665 * independently of any {@code Lookup} object.
666 * <p>
667 * If the desired member is {@code protected}, the usual JVM rules apply,
668 * including the requirement that the lookup class must either be in the
669 * same package as the desired member, or must inherit that member.
670 * (See the Java Virtual Machine Specification, sections {@jvms
671 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.)
672 * In addition, if the desired member is a non-static field or method
673 * in a different package, the resulting method handle may only be applied
674 * to objects of the lookup class or one of its subclasses.
675 * This requirement is enforced by narrowing the type of the leading
676 * {@code this} parameter from {@code C}
677 * (which will necessarily be a superclass of the lookup class)
678 * to the lookup class itself.
679 * <p>
680 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
681 * that the receiver argument must match both the resolved method <em>and</em>
682 * the current class. Again, this requirement is enforced by narrowing the
683 * type of the leading parameter to the resulting method handle.
684 * (See the Java Virtual Machine Specification, section {@jvms 4.10.1.9}.)
685 * <p>
686 * The JVM represents constructors and static initializer blocks as internal methods
687 * with special names ({@value ConstantDescs#INIT_NAME} and {@value
688 * ConstantDescs#CLASS_INIT_NAME}).
689 * The internal syntax of invocation instructions allows them to refer to such internal
690 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
691 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
692 * <p>
693 * If the relationship between nested types is expressed directly through the
694 * {@code NestHost} and {@code NestMembers} attributes
695 * (see the Java Virtual Machine Specification, sections {@jvms
696 * 4.7.28} and {@jvms 4.7.29}),
697 * then the associated {@code Lookup} object provides direct access to
698 * the lookup class and all of its nestmates
699 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
700 * Otherwise, access between nested classes is obtained by the Java compiler creating
701 * a wrapper method to access a private method of another class in the same nest.
702 * For example, a nested class {@code C.D}
703 * can access private members within other related classes such as
704 * {@code C}, {@code C.D.E}, or {@code C.B},
705 * but the Java compiler may need to generate wrapper methods in
706 * those related classes. In such cases, a {@code Lookup} object on
707 * {@code C.E} would be unable to access those private members.
708 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
709 * which can transform a lookup on {@code C.E} into one on any of those other
710 * classes, without special elevation of privilege.
711 * <p>
712 * The accesses permitted to a given lookup object may be limited,
713 * according to its set of {@link #lookupModes lookupModes},
714 * to a subset of members normally accessible to the lookup class.
715 * For example, the {@link MethodHandles#publicLookup publicLookup}
716 * method produces a lookup object which is only allowed to access
717 * public members in public classes of exported packages.
718 * The caller sensitive method {@link MethodHandles#lookup lookup}
719 * produces a lookup object with full capabilities relative to
720 * its caller class, to emulate all supported bytecode behaviors.
721 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
722 * with fewer access modes than the original lookup object.
723 *
724 * <p style="font-size:smaller;">
725 * <a id="privacc"></a>
726 * <em>Discussion of private and module access:</em>
727 * We say that a lookup has <em>private access</em>
728 * if its {@linkplain #lookupModes lookup modes}
729 * include the possibility of accessing {@code private} members
730 * (which includes the private members of nestmates).
731 * As documented in the relevant methods elsewhere,
732 * only lookups with private access possess the following capabilities:
733 * <ul style="font-size:smaller;">
734 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
735 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
736 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
737 * within the same package member
738 * </ul>
739 * <p style="font-size:smaller;">
740 * Similarly, a lookup with module access ensures that the original lookup creator was
741 * a member in the same module as the lookup class.
742 * <p style="font-size:smaller;">
743 * Private and module access are independently determined modes; a lookup may have
744 * either or both or neither. A lookup which possesses both access modes is said to
745 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}.
746 * <p style="font-size:smaller;">
747 * A lookup with <em>original access</em> ensures that this lookup is created by
748 * the original lookup class and the bootstrap method invoked by the VM.
749 * Such a lookup with original access also has private and module access
750 * which has the following additional capability:
751 * <ul style="font-size:smaller;">
752 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
753 * such as {@code Class.forName}
754 * <li>obtain the {@linkplain MethodHandles#classData(Lookup, String, Class)
755 * class data} associated with the lookup class</li>
756 * </ul>
757 * <p style="font-size:smaller;">
758 * Each of these permissions is a consequence of the fact that a lookup object
759 * with private access can be securely traced back to an originating class,
760 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
761 * can be reliably determined and emulated by method handles.
762 *
763 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
764 * When a lookup class in one module {@code M1} accesses a class in another module
765 * {@code M2}, extra access checking is performed beyond the access mode bits.
766 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
767 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
768 * and when the type is in a package of {@code M2} that is exported to
769 * at least {@code M1}.
770 * <p>
771 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
772 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
773 * MethodHandles.privateLookupIn} methods.
774 * Teleporting across modules will always record the original lookup class as
775 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
776 * and drops {@link Lookup#MODULE MODULE} access.
777 * If the target class is in the same module as the lookup class {@code C},
778 * then the target class becomes the new lookup class
779 * and there is no change to the previous lookup class.
780 * If the target class is in a different module from {@code M1} ({@code C}'s module),
781 * {@code C} becomes the new previous lookup class
782 * and the target class becomes the new lookup class.
783 * In that case, if there was already a previous lookup class in {@code M0},
784 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
785 * drops all privileges.
786 * For example,
787 * {@snippet lang="java" :
788 * Lookup lookup = MethodHandles.lookup(); // in class C
789 * Lookup lookup2 = lookup.in(D.class);
790 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
791 * }
792 * <p>
793 * The {@link #lookup()} factory method produces a {@code Lookup} object
794 * with {@code null} previous lookup class.
795 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
796 * to class {@code D} without elevation of privileges.
797 * If {@code C} and {@code D} are in the same module,
798 * {@code lookup2} records {@code D} as the new lookup class and keeps the
799 * same previous lookup class as the original {@code lookup}, or
800 * {@code null} if not present.
801 * <p>
802 * When a {@code Lookup} teleports from a class
803 * in one nest to another nest, {@code PRIVATE} access is dropped.
804 * When a {@code Lookup} teleports from a class in one package to
805 * another package, {@code PACKAGE} access is dropped.
806 * When a {@code Lookup} teleports from a class in one module to another module,
807 * {@code MODULE} access is dropped.
808 * Teleporting across modules drops the ability to access non-exported classes
809 * in both the module of the new lookup class and the module of the old lookup class
810 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
811 * A {@code Lookup} can teleport back and forth to a class in the module of
812 * the lookup class and the module of the previous class lookup.
813 * Teleporting across modules can only decrease access but cannot increase it.
814 * Teleporting to some third module drops all accesses.
815 * <p>
816 * In the above example, if {@code C} and {@code D} are in different modules,
817 * {@code lookup2} records {@code D} as its lookup class and
818 * {@code C} as its previous lookup class and {@code lookup2} has only
819 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
820 * {@code C}'s module and {@code D}'s module.
821 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
822 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
823 * class {@code D} is recorded as its previous lookup class.
824 * <p>
825 * Teleporting across modules restricts access to the public types that
826 * both the lookup class and the previous lookup class can equally access
827 * (see below).
828 * <p>
829 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
830 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
831 * and produce a new {@code Lookup} with <a href="#privacc">private access</a>
832 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
833 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
834 * to call {@code privateLookupIn}.
835 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
836 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
837 * produces a new {@code Lookup} on {@code T} with full capabilities.
838 * A {@code lookup} on {@code C} is also allowed
839 * to do deep reflection on {@code T} in another module {@code M2} if
840 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
841 * the package containing {@code T} to at least {@code M1}.
842 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
843 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
844 * The resulting {@code Lookup} can be used to do member lookup or teleport
845 * to another lookup class by calling {@link #in Lookup::in}. But
846 * it cannot be used to obtain another private {@code Lookup} by calling
847 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
848 * because it has no {@code MODULE} access.
849 * <p>
850 * The {@code Lookup} object returned by {@code privateLookupIn} is allowed to
851 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
852 * of {@code T}. Extreme caution should be taken when opening a package
853 * to another module as such defined classes have the same full privilege
854 * access as other members in {@code M2}.
855 *
856 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
857 *
858 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
859 * allows cross-module access. The access checking is performed with respect
860 * to both the lookup class and the previous lookup class if present.
861 * <p>
862 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
863 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
864 * exported unconditionally}.
865 * <p>
866 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
867 * the lookup with {@link #PUBLIC} mode can access all public types in modules
868 * that are readable to {@code M1} and the type is in a package that is exported
869 * at least to {@code M1}.
870 * <p>
871 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
872 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
873 * the intersection of all public types that are accessible to {@code M1}
874 * with all public types that are accessible to {@code M0}. {@code M0}
875 * reads {@code M1} and hence the set of accessible types includes:
876 *
877 * <ul>
878 * <li>unconditional-exported packages from {@code M1}</li>
879 * <li>unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</li>
880 * <li>
881 * unconditional-exported packages from a third module {@code M2}if both {@code M0}
882 * and {@code M1} read {@code M2}
883 * </li>
884 * <li>qualified-exported packages from {@code M1} to {@code M0}</li>
885 * <li>qualified-exported packages from {@code M0} to {@code M1} if {@code M1} reads {@code M0}</li>
886 * <li>
887 * qualified-exported packages from a third module {@code M2} to both {@code M0} and
888 * {@code M1} if both {@code M0} and {@code M1} read {@code M2}
889 * </li>
890 * </ul>
891 *
892 * <h2><a id="access-modes"></a>Access modes</h2>
893 *
894 * The table below shows the access modes of a {@code Lookup} produced by
895 * any of the following factory or transformation methods:
896 * <ul>
897 * <li>{@link #lookup() MethodHandles::lookup}</li>
898 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li>
899 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li>
900 * <li>{@link Lookup#in Lookup::in}</li>
901 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li>
902 * </ul>
903 *
904 * <table class="striped">
905 * <caption style="display:none">
906 * Access mode summary
907 * </caption>
908 * <thead>
909 * <tr>
910 * <th scope="col">Lookup object</th>
911 * <th style="text-align:center">original</th>
912 * <th style="text-align:center">protected</th>
913 * <th style="text-align:center">private</th>
914 * <th style="text-align:center">package</th>
915 * <th style="text-align:center">module</th>
916 * <th style="text-align:center">public</th>
917 * </tr>
918 * </thead>
919 * <tbody>
920 * <tr>
921 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
922 * <td style="text-align:center">ORI</td>
923 * <td style="text-align:center">PRO</td>
924 * <td style="text-align:center">PRI</td>
925 * <td style="text-align:center">PAC</td>
926 * <td style="text-align:center">MOD</td>
927 * <td style="text-align:center">1R</td>
928 * </tr>
929 * <tr>
930 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
931 * <td></td>
932 * <td></td>
933 * <td></td>
934 * <td style="text-align:center">PAC</td>
935 * <td style="text-align:center">MOD</td>
936 * <td style="text-align:center">1R</td>
937 * </tr>
938 * <tr>
939 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
940 * <td></td>
941 * <td></td>
942 * <td></td>
943 * <td></td>
944 * <td style="text-align:center">MOD</td>
945 * <td style="text-align:center">1R</td>
946 * </tr>
947 * <tr>
948 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
949 * <td></td>
950 * <td></td>
951 * <td></td>
952 * <td></td>
953 * <td></td>
954 * <td style="text-align:center">2R</td>
955 * </tr>
956 * <tr>
957 * <th scope="row" style="text-align:left">{@code CL.in(D).in(C)} hop back to module</th>
958 * <td></td>
959 * <td></td>
960 * <td></td>
961 * <td></td>
962 * <td></td>
963 * <td style="text-align:center">2R</td>
964 * </tr>
965 * <tr>
966 * <th scope="row" style="text-align:left">{@code PRI1 = privateLookupIn(C1,CL)}</th>
967 * <td></td>
968 * <td style="text-align:center">PRO</td>
969 * <td style="text-align:center">PRI</td>
970 * <td style="text-align:center">PAC</td>
971 * <td style="text-align:center">MOD</td>
972 * <td style="text-align:center">1R</td>
973 * </tr>
974 * <tr>
975 * <th scope="row" style="text-align:left">{@code PRI1a = privateLookupIn(C,PRI1)}</th>
976 * <td></td>
977 * <td style="text-align:center">PRO</td>
978 * <td style="text-align:center">PRI</td>
979 * <td style="text-align:center">PAC</td>
980 * <td style="text-align:center">MOD</td>
981 * <td style="text-align:center">1R</td>
982 * </tr>
983 * <tr>
984 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} same package</th>
985 * <td></td>
986 * <td></td>
987 * <td></td>
988 * <td style="text-align:center">PAC</td>
989 * <td style="text-align:center">MOD</td>
990 * <td style="text-align:center">1R</td>
991 * </tr>
992 * <tr>
993 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} different package</th>
994 * <td></td>
995 * <td></td>
996 * <td></td>
997 * <td></td>
998 * <td style="text-align:center">MOD</td>
999 * <td style="text-align:center">1R</td>
1000 * </tr>
1001 * <tr>
1002 * <th scope="row" style="text-align:left">{@code PRI1.in(D)} different module</th>
1003 * <td></td>
1004 * <td></td>
1005 * <td></td>
1006 * <td></td>
1007 * <td></td>
1008 * <td style="text-align:center">2R</td>
1009 * </tr>
1010 * <tr>
1011 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PROTECTED)}</th>
1012 * <td></td>
1013 * <td></td>
1014 * <td style="text-align:center">PRI</td>
1015 * <td style="text-align:center">PAC</td>
1016 * <td style="text-align:center">MOD</td>
1017 * <td style="text-align:center">1R</td>
1018 * </tr>
1019 * <tr>
1020 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PRIVATE)}</th>
1021 * <td></td>
1022 * <td></td>
1023 * <td></td>
1024 * <td style="text-align:center">PAC</td>
1025 * <td style="text-align:center">MOD</td>
1026 * <td style="text-align:center">1R</td>
1027 * </tr>
1028 * <tr>
1029 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PACKAGE)}</th>
1030 * <td></td>
1031 * <td></td>
1032 * <td></td>
1033 * <td></td>
1034 * <td style="text-align:center">MOD</td>
1035 * <td style="text-align:center">1R</td>
1036 * </tr>
1037 * <tr>
1038 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(MODULE)}</th>
1039 * <td></td>
1040 * <td></td>
1041 * <td></td>
1042 * <td></td>
1043 * <td></td>
1044 * <td style="text-align:center">1R</td>
1045 * </tr>
1046 * <tr>
1047 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PUBLIC)}</th>
1048 * <td></td>
1049 * <td></td>
1050 * <td></td>
1051 * <td></td>
1052 * <td></td>
1053 * <td style="text-align:center">none</td>
1054 * <tr>
1055 * <th scope="row" style="text-align:left">{@code PRI2 = privateLookupIn(D,CL)}</th>
1056 * <td></td>
1057 * <td style="text-align:center">PRO</td>
1058 * <td style="text-align:center">PRI</td>
1059 * <td style="text-align:center">PAC</td>
1060 * <td></td>
1061 * <td style="text-align:center">2R</td>
1062 * </tr>
1063 * <tr>
1064 * <th scope="row" style="text-align:left">{@code privateLookupIn(D,PRI1)}</th>
1065 * <td></td>
1066 * <td style="text-align:center">PRO</td>
1067 * <td style="text-align:center">PRI</td>
1068 * <td style="text-align:center">PAC</td>
1069 * <td></td>
1070 * <td style="text-align:center">2R</td>
1071 * </tr>
1072 * <tr>
1073 * <th scope="row" style="text-align:left">{@code privateLookupIn(C,PRI2)} fails</th>
1074 * <td></td>
1075 * <td></td>
1076 * <td></td>
1077 * <td></td>
1078 * <td></td>
1079 * <td style="text-align:center">IAE</td>
1080 * </tr>
1081 * <tr>
1082 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} same package</th>
1083 * <td></td>
1084 * <td></td>
1085 * <td></td>
1086 * <td style="text-align:center">PAC</td>
1087 * <td></td>
1088 * <td style="text-align:center">2R</td>
1089 * </tr>
1090 * <tr>
1091 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} different package</th>
1092 * <td></td>
1093 * <td></td>
1094 * <td></td>
1095 * <td></td>
1096 * <td></td>
1097 * <td style="text-align:center">2R</td>
1098 * </tr>
1099 * <tr>
1100 * <th scope="row" style="text-align:left">{@code PRI2.in(C1)} hop back to module</th>
1101 * <td></td>
1102 * <td></td>
1103 * <td></td>
1104 * <td></td>
1105 * <td></td>
1106 * <td style="text-align:center">2R</td>
1107 * </tr>
1108 * <tr>
1109 * <th scope="row" style="text-align:left">{@code PRI2.in(E)} hop to third module</th>
1110 * <td></td>
1111 * <td></td>
1112 * <td></td>
1113 * <td></td>
1114 * <td></td>
1115 * <td style="text-align:center">none</td>
1116 * </tr>
1117 * <tr>
1118 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PROTECTED)}</th>
1119 * <td></td>
1120 * <td></td>
1121 * <td style="text-align:center">PRI</td>
1122 * <td style="text-align:center">PAC</td>
1123 * <td></td>
1124 * <td style="text-align:center">2R</td>
1125 * </tr>
1126 * <tr>
1127 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PRIVATE)}</th>
1128 * <td></td>
1129 * <td></td>
1130 * <td></td>
1131 * <td style="text-align:center">PAC</td>
1132 * <td></td>
1133 * <td style="text-align:center">2R</td>
1134 * </tr>
1135 * <tr>
1136 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PACKAGE)}</th>
1137 * <td></td>
1138 * <td></td>
1139 * <td></td>
1140 * <td></td>
1141 * <td></td>
1142 * <td style="text-align:center">2R</td>
1143 * </tr>
1144 * <tr>
1145 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(MODULE)}</th>
1146 * <td></td>
1147 * <td></td>
1148 * <td></td>
1149 * <td></td>
1150 * <td></td>
1151 * <td style="text-align:center">2R</td>
1152 * </tr>
1153 * <tr>
1154 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PUBLIC)}</th>
1155 * <td></td>
1156 * <td></td>
1157 * <td></td>
1158 * <td></td>
1159 * <td></td>
1160 * <td style="text-align:center">none</td>
1161 * </tr>
1162 * <tr>
1163 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PROTECTED)}</th>
1164 * <td></td>
1165 * <td></td>
1166 * <td style="text-align:center">PRI</td>
1167 * <td style="text-align:center">PAC</td>
1168 * <td style="text-align:center">MOD</td>
1169 * <td style="text-align:center">1R</td>
1170 * </tr>
1171 * <tr>
1172 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PRIVATE)}</th>
1173 * <td></td>
1174 * <td></td>
1175 * <td></td>
1176 * <td style="text-align:center">PAC</td>
1177 * <td style="text-align:center">MOD</td>
1178 * <td style="text-align:center">1R</td>
1179 * </tr>
1180 * <tr>
1181 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PACKAGE)}</th>
1182 * <td></td>
1183 * <td></td>
1184 * <td></td>
1185 * <td></td>
1186 * <td style="text-align:center">MOD</td>
1187 * <td style="text-align:center">1R</td>
1188 * </tr>
1189 * <tr>
1190 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(MODULE)}</th>
1191 * <td></td>
1192 * <td></td>
1193 * <td></td>
1194 * <td></td>
1195 * <td></td>
1196 * <td style="text-align:center">1R</td>
1197 * </tr>
1198 * <tr>
1199 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PUBLIC)}</th>
1200 * <td></td>
1201 * <td></td>
1202 * <td></td>
1203 * <td></td>
1204 * <td></td>
1205 * <td style="text-align:center">none</td>
1206 * </tr>
1207 * <tr>
1208 * <th scope="row" style="text-align:left">{@code PUB = publicLookup()}</th>
1209 * <td></td>
1210 * <td></td>
1211 * <td></td>
1212 * <td></td>
1213 * <td></td>
1214 * <td style="text-align:center">U</td>
1215 * </tr>
1216 * <tr>
1217 * <th scope="row" style="text-align:left">{@code PUB.in(D)} different module</th>
1218 * <td></td>
1219 * <td></td>
1220 * <td></td>
1221 * <td></td>
1222 * <td></td>
1223 * <td style="text-align:center">U</td>
1224 * </tr>
1225 * <tr>
1226 * <th scope="row" style="text-align:left">{@code PUB.in(D).in(E)} third module</th>
1227 * <td></td>
1228 * <td></td>
1229 * <td></td>
1230 * <td></td>
1231 * <td></td>
1232 * <td style="text-align:center">U</td>
1233 * </tr>
1234 * <tr>
1235 * <th scope="row" style="text-align:left">{@code PUB.dropLookupMode(UNCONDITIONAL)}</th>
1236 * <td></td>
1237 * <td></td>
1238 * <td></td>
1239 * <td></td>
1240 * <td></td>
1241 * <td style="text-align:center">none</td>
1242 * </tr>
1243 * <tr>
1244 * <th scope="row" style="text-align:left">{@code privateLookupIn(C1,PUB)} fails</th>
1245 * <td></td>
1246 * <td></td>
1247 * <td></td>
1248 * <td></td>
1249 * <td></td>
1250 * <td style="text-align:center">IAE</td>
1251 * </tr>
1252 * <tr>
1253 * <th scope="row" style="text-align:left">{@code ANY.in(X)}, for inaccessible {@code X}</th>
1254 * <td></td>
1255 * <td></td>
1256 * <td></td>
1257 * <td></td>
1258 * <td></td>
1259 * <td style="text-align:center">none</td>
1260 * </tr>
1261 * </tbody>
1262 * </table>
1263 *
1264 * <p>
1265 * Notes:
1266 * <ul>
1267 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1268 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1269 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1270 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1271 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set,
1272 * {@code PRO} indicates {@link #PROTECTED} bit set,
1273 * {@code PRI} indicates {@link #PRIVATE} bit set,
1274 * {@code PAC} indicates {@link #PACKAGE} bit set,
1275 * {@code MOD} indicates {@link #MODULE} bit set,
1276 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1277 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1278 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1279 * <li>Public access comes in three kinds:
1280 * <ul>
1281 * <li>unconditional ({@code U}): the lookup assumes readability.
1282 * The lookup has {@code null} previous lookup class.
1283 * <li>one-module-reads ({@code 1R}): the module access checking is
1284 * performed with respect to the lookup class. The lookup has {@code null}
1285 * previous lookup class.
1286 * <li>two-module-reads ({@code 2R}): the module access checking is
1287 * performed with respect to the lookup class and the previous lookup class.
1288 * The lookup has a non-null previous lookup class which is in a
1289 * different module from the current lookup class.
1290 * </ul>
1291 * <li>Any attempt to reach a third module loses all access.</li>
1292 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1293 * all access modes are dropped.</li>
1294 * </ul>
1295 *
1296 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1297 * A small number of Java methods have a special property called caller sensitivity.
1298 * A <em>caller-sensitive</em> method can behave differently depending on the
1299 * identity of its immediate caller.
1300 * <p>
1301 * If a method handle for a caller-sensitive method is requested,
1302 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1303 * but they take account of the lookup class in a special way.
1304 * The resulting method handle behaves as if it were called
1305 * from an instruction contained in the lookup class,
1306 * so that the caller-sensitive method detects the lookup class.
1307 * (By contrast, the invoker of the method handle is disregarded.)
1308 * Thus, in the case of caller-sensitive methods,
1309 * different lookup classes may give rise to
1310 * differently behaving method handles.
1311 * <p>
1312 * In cases where the lookup object is
1313 * {@link MethodHandles#publicLookup() publicLookup()},
1314 * or some other lookup object without the
1315 * {@linkplain #ORIGINAL original access},
1316 * the lookup class is disregarded.
1317 * In such cases, no caller-sensitive method handle can be created,
1318 * access is forbidden, and the lookup fails with an
1319 * {@code IllegalAccessException}.
1320 * <p style="font-size:smaller;">
1321 * <em>Discussion:</em>
1322 * For example, the caller-sensitive method
1323 * {@link java.lang.Class#forName(String) Class.forName(x)}
1324 * can return varying classes or throw varying exceptions,
1325 * depending on the class loader of the class that calls it.
1326 * A public lookup of {@code Class.forName} will fail, because
1327 * there is no reasonable way to determine its bytecode behavior.
1328 * <p style="font-size:smaller;">
1329 * If an application caches method handles for broad sharing,
1330 * it should use {@code publicLookup()} to create them.
1331 * If there is a lookup of {@code Class.forName}, it will fail,
1332 * and the application must take appropriate action in that case.
1333 * It may be that a later lookup, perhaps during the invocation of a
1334 * bootstrap method, can incorporate the specific identity
1335 * of the caller, making the method accessible.
1336 * <p style="font-size:smaller;">
1337 * The function {@code MethodHandles.lookup} is caller sensitive
1338 * so that there can be a secure foundation for lookups.
1339 * Nearly all other methods in the JSR 292 API rely on lookup
1340 * objects to check access requests.
1341 */
1342 public static final
1343 class Lookup {
1344 /** The class on behalf of whom the lookup is being performed. */
1345 private final Class<?> lookupClass;
1346
1347 /** previous lookup class */
1348 private final Class<?> prevLookupClass;
1349
1350 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1351 private final int allowedModes;
1352
1353 static {
1354 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1355 }
1356
1357 /** A single-bit mask representing {@code public} access,
1358 * which may contribute to the result of {@link #lookupModes lookupModes}.
1359 * The value, {@code 0x01}, happens to be the same as the value of the
1360 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1361 * <p>
1362 * A {@code Lookup} with this lookup mode performs cross-module access check
1363 * with respect to the {@linkplain #lookupClass() lookup class} and
1364 * {@linkplain #previousLookupClass() previous lookup class} if present.
1365 */
1366 public static final int PUBLIC = Modifier.PUBLIC;
1367
1368 /** A single-bit mask representing {@code private} access,
1369 * which may contribute to the result of {@link #lookupModes lookupModes}.
1370 * The value, {@code 0x02}, happens to be the same as the value of the
1371 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1372 */
1373 public static final int PRIVATE = Modifier.PRIVATE;
1374
1375 /** A single-bit mask representing {@code protected} access,
1376 * which may contribute to the result of {@link #lookupModes lookupModes}.
1377 * The value, {@code 0x04}, happens to be the same as the value of the
1378 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1379 */
1380 public static final int PROTECTED = Modifier.PROTECTED;
1381
1382 /** A single-bit mask representing {@code package} access (default access),
1383 * which may contribute to the result of {@link #lookupModes lookupModes}.
1384 * The value is {@code 0x08}, which does not correspond meaningfully to
1385 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1386 */
1387 public static final int PACKAGE = Modifier.STATIC;
1388
1389 /** A single-bit mask representing {@code module} access,
1390 * which may contribute to the result of {@link #lookupModes lookupModes}.
1391 * The value is {@code 0x10}, which does not correspond meaningfully to
1392 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1393 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1394 * with this lookup mode can access all public types in the module of the
1395 * lookup class and public types in packages exported by other modules
1396 * to the module of the lookup class.
1397 * <p>
1398 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1399 * previous lookup class} is always {@code null}.
1400 *
1401 * @since 9
1402 */
1403 public static final int MODULE = PACKAGE << 1;
1404
1405 /** A single-bit mask representing {@code unconditional} access
1406 * which may contribute to the result of {@link #lookupModes lookupModes}.
1407 * The value is {@code 0x20}, which does not correspond meaningfully to
1408 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1409 * A {@code Lookup} with this lookup mode assumes {@linkplain
1410 * java.lang.Module#canRead(java.lang.Module) readability}.
1411 * This lookup mode can access all public members of public types
1412 * of all modules when the type is in a package that is {@link
1413 * java.lang.Module#isExported(String) exported unconditionally}.
1414 *
1415 * <p>
1416 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1417 * previous lookup class} is always {@code null}.
1418 *
1419 * @since 9
1420 * @see #publicLookup()
1421 */
1422 public static final int UNCONDITIONAL = PACKAGE << 2;
1423
1424 /** A single-bit mask representing {@code original} access
1425 * which may contribute to the result of {@link #lookupModes lookupModes}.
1426 * The value is {@code 0x40}, which does not correspond meaningfully to
1427 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1428 *
1429 * <p>
1430 * If this lookup mode is set, the {@code Lookup} object must be
1431 * created by the original lookup class by calling
1432 * {@link MethodHandles#lookup()} method or by a bootstrap method
1433 * invoked by the VM. The {@code Lookup} object with this lookup
1434 * mode has {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1435 *
1436 * @since 16
1437 */
1438 public static final int ORIGINAL = PACKAGE << 3;
1439
1440 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL);
1441 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); // with original access
1442 private static final int TRUSTED = -1;
1443
1444 /*
1445 * Adjust PUBLIC => PUBLIC|MODULE|ORIGINAL|UNCONDITIONAL
1446 * Adjust 0 => PACKAGE
1447 */
1448 private static int fixmods(int mods) {
1449 mods &= (ALL_MODES - PACKAGE - MODULE - ORIGINAL - UNCONDITIONAL);
1450 if (Modifier.isPublic(mods))
1451 mods |= UNCONDITIONAL;
1452 return (mods != 0) ? mods : PACKAGE;
1453 }
1454
1455 /** Tells which class is performing the lookup. It is this class against
1456 * which checks are performed for visibility and access permissions.
1457 * <p>
1458 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1459 * access checks are performed against both the lookup class and the previous lookup class.
1460 * <p>
1461 * The class implies a maximum level of access permission,
1462 * but the permissions may be additionally limited by the bitmask
1463 * {@link #lookupModes lookupModes}, which controls whether non-public members
1464 * can be accessed.
1465 * @return the lookup class, on behalf of which this lookup object finds members
1466 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1467 */
1468 public Class<?> lookupClass() {
1469 return lookupClass;
1470 }
1471
1472 /** Reports a lookup class in another module that this lookup object
1473 * was previously teleported from, or {@code null}.
1474 * <p>
1475 * A {@code Lookup} object produced by the factory methods, such as the
1476 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1477 * has {@code null} previous lookup class.
1478 * A {@code Lookup} object has a non-null previous lookup class
1479 * when this lookup was teleported from an old lookup class
1480 * in one module to a new lookup class in another module.
1481 *
1482 * @return the lookup class in another module that this lookup object was
1483 * previously teleported from, or {@code null}
1484 * @since 14
1485 * @see #in(Class)
1486 * @see MethodHandles#privateLookupIn(Class, Lookup)
1487 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1488 */
1489 public Class<?> previousLookupClass() {
1490 return prevLookupClass;
1491 }
1492
1493 // This is just for calling out to MethodHandleImpl.
1494 private Class<?> lookupClassOrNull() {
1495 return (allowedModes == TRUSTED) ? null : lookupClass;
1496 }
1497
1498 /** Tells which access-protection classes of members this lookup object can produce.
1499 * The result is a bit-mask of the bits
1500 * {@linkplain #PUBLIC PUBLIC (0x01)},
1501 * {@linkplain #PRIVATE PRIVATE (0x02)},
1502 * {@linkplain #PROTECTED PROTECTED (0x04)},
1503 * {@linkplain #PACKAGE PACKAGE (0x08)},
1504 * {@linkplain #MODULE MODULE (0x10)},
1505 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)},
1506 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}.
1507 * <p>
1508 * A freshly-created lookup object
1509 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1510 * all possible bits set, except {@code UNCONDITIONAL}.
1511 * A lookup object on a new lookup class
1512 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1513 * may have some mode bits set to zero.
1514 * Mode bits can also be
1515 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1516 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1517 * The purpose of this is to restrict access via the new lookup object,
1518 * so that it can access only names which can be reached by the original
1519 * lookup object, and also by the new lookup class.
1520 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1521 * @see #in
1522 * @see #dropLookupMode
1523 */
1524 public int lookupModes() {
1525 return allowedModes & ALL_MODES;
1526 }
1527
1528 /** Embody the current class (the lookupClass) as a lookup class
1529 * for method handle creation.
1530 * Must be called by from a method in this package,
1531 * which in turn is called by a method not in this package.
1532 */
1533 Lookup(Class<?> lookupClass) {
1534 this(lookupClass, null, FULL_POWER_MODES);
1535 }
1536
1537 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1538 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1539 && prevLookupClass.getModule() != lookupClass.getModule());
1540 assert !lookupClass.isArray() && !lookupClass.isPrimitive();
1541 this.lookupClass = lookupClass;
1542 this.prevLookupClass = prevLookupClass;
1543 this.allowedModes = allowedModes;
1544 }
1545
1546 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1547 // make sure we haven't accidentally picked up a privileged class:
1548 checkUnprivilegedlookupClass(lookupClass);
1549 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1550 }
1551
1552 /**
1553 * Creates a lookup on the specified new lookup class.
1554 * The resulting object will report the specified
1555 * class as its own {@link #lookupClass() lookupClass}.
1556 *
1557 * <p>
1558 * However, the resulting {@code Lookup} object is guaranteed
1559 * to have no more access capabilities than the original.
1560 * In particular, access capabilities can be lost as follows:<ul>
1561 * <li>If the new lookup class is different from the old lookup class,
1562 * i.e. {@link #ORIGINAL ORIGINAL} access is lost.
1563 * <li>If the new lookup class is in a different module from the old one,
1564 * i.e. {@link #MODULE MODULE} access is lost.
1565 * <li>If the new lookup class is in a different package
1566 * than the old one, protected and default (package) members will not be accessible,
1567 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1568 * <li>If the new lookup class is not within the same package member
1569 * as the old one, private members will not be accessible, and protected members
1570 * will not be accessible by virtue of inheritance,
1571 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1572 * (Protected members may continue to be accessible because of package sharing.)
1573 * <li>If the new lookup class is not
1574 * {@linkplain #accessClass(Class) accessible} to this lookup,
1575 * then no members, not even public members, will be accessible
1576 * i.e. all access modes are lost.
1577 * <li>If the new lookup class, the old lookup class and the previous lookup class
1578 * are all in different modules i.e. teleporting to a third module,
1579 * all access modes are lost.
1580 * </ul>
1581 * <p>
1582 * The new previous lookup class is chosen as follows:
1583 * <ul>
1584 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1585 * the new previous lookup class is {@code null}.
1586 * <li>If the new lookup class is in the same module as the old lookup class,
1587 * the new previous lookup class is the old previous lookup class.
1588 * <li>If the new lookup class is in a different module from the old lookup class,
1589 * the new previous lookup class is the old lookup class.
1590 *</ul>
1591 * <p>
1592 * The resulting lookup's capabilities for loading classes
1593 * (used during {@link #findClass} invocations)
1594 * are determined by the lookup class' loader,
1595 * which may change due to this operation.
1596 *
1597 * @param requestedLookupClass the desired lookup class for the new lookup object
1598 * @return a lookup object which reports the desired lookup class, or the same object
1599 * if there is no change
1600 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class
1601 * @throws NullPointerException if the argument is null
1602 *
1603 * @see #accessClass(Class)
1604 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1605 */
1606 public Lookup in(Class<?> requestedLookupClass) {
1607 Objects.requireNonNull(requestedLookupClass);
1608 if (requestedLookupClass.isPrimitive())
1609 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1610 if (requestedLookupClass.isArray())
1611 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1612
1613 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1614 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1615 if (requestedLookupClass == this.lookupClass)
1616 return this; // keep same capabilities
1617 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL;
1618 Module fromModule = this.lookupClass.getModule();
1619 Module targetModule = requestedLookupClass.getModule();
1620 Class<?> plc = this.previousLookupClass();
1621 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1622 assert plc == null;
1623 newModes = UNCONDITIONAL;
1624 } else if (fromModule != targetModule) {
1625 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1626 // allow hopping back and forth between fromModule and plc's module
1627 // but not the third module
1628 newModes = 0;
1629 }
1630 // drop MODULE access
1631 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1632 // teleport from this lookup class
1633 plc = this.lookupClass;
1634 }
1635 if ((newModes & PACKAGE) != 0
1636 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1637 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1638 }
1639 // Allow nestmate lookups to be created without special privilege:
1640 if ((newModes & PRIVATE) != 0
1641 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1642 newModes &= ~(PRIVATE|PROTECTED);
1643 }
1644 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1645 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1646 // The requested class it not accessible from the lookup class.
1647 // No permissions.
1648 newModes = 0;
1649 }
1650 return newLookup(requestedLookupClass, plc, newModes);
1651 }
1652
1653 /**
1654 * Creates a lookup on the same lookup class which this lookup object
1655 * finds members, but with a lookup mode that has lost the given lookup mode.
1656 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1657 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED},
1658 * {@link #PRIVATE PRIVATE}, {@link #ORIGINAL ORIGINAL}, or
1659 * {@link #UNCONDITIONAL UNCONDITIONAL}.
1660 *
1661 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup},
1662 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set.
1663 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting
1664 * lookup has no access.
1665 *
1666 * <p> If this lookup is not a public lookup, then the following applies
1667 * regardless of its {@linkplain #lookupModes() lookup modes}.
1668 * {@link #PROTECTED PROTECTED} and {@link #ORIGINAL ORIGINAL} are always
1669 * dropped and so the resulting lookup mode will never have these access
1670 * capabilities. When dropping {@code PACKAGE}
1671 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE}
1672 * access. When dropping {@code MODULE} then the resulting lookup will not
1673 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access.
1674 * When dropping {@code PUBLIC} then the resulting lookup has no access.
1675 *
1676 * @apiNote
1677 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1678 * delegate non-public access within the package of the lookup class without
1679 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1680 * A lookup with {@code MODULE} but not
1681 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1682 * the module of the lookup class without conferring package access.
1683 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1684 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1685 * to public classes accessible to both the module of the lookup class
1686 * and the module of the previous lookup class.
1687 *
1688 * @param modeToDrop the lookup mode to drop
1689 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1690 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1691 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE}, {@code ORIGINAL}
1692 * or {@code UNCONDITIONAL}
1693 * @see MethodHandles#privateLookupIn
1694 * @since 9
1695 */
1696 public Lookup dropLookupMode(int modeToDrop) {
1697 int oldModes = lookupModes();
1698 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL);
1699 switch (modeToDrop) {
1700 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1701 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1702 case PACKAGE: newModes &= ~(PRIVATE); break;
1703 case PROTECTED:
1704 case PRIVATE:
1705 case ORIGINAL:
1706 case UNCONDITIONAL: break;
1707 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1708 }
1709 if (newModes == oldModes) return this; // return self if no change
1710 return newLookup(lookupClass(), previousLookupClass(), newModes);
1711 }
1712
1713 /**
1714 * Creates and links a class or interface from {@code bytes}
1715 * with the same class loader and in the same runtime package and
1716 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1717 * {@linkplain #lookupClass() lookup class} as if calling
1718 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1719 * ClassLoader::defineClass}.
1720 *
1721 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1722 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1723 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1724 * that the lookup object was created by a caller in the runtime package (or derived
1725 * from a lookup originally created by suitably privileged code to a target class in
1726 * the runtime package). </p>
1727 *
1728 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1729 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1730 * same package as the lookup class. </p>
1731 *
1732 * <p> This method does not run the class initializer. The class initializer may
1733 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1734 * Specification</em>. </p>
1735 *
1736 * @param bytes the class bytes
1737 * @return the {@code Class} object for the class
1738 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1739 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1740 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
1741 * than the lookup class or {@code bytes} is not a class or interface
1742 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
1743 * @throws VerifyError if the newly created class cannot be verified
1744 * @throws LinkageError if the newly created class cannot be linked for any other reason
1745 * @throws NullPointerException if {@code bytes} is {@code null}
1746 * @since 9
1747 * @see MethodHandles#privateLookupIn
1748 * @see Lookup#dropLookupMode
1749 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1750 */
1751 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1752 if ((lookupModes() & PACKAGE) == 0)
1753 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1754 return makeClassDefiner(bytes.clone()).defineClass(false);
1755 }
1756
1757 /**
1758 * The set of class options that specify whether a hidden class created by
1759 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
1760 * Lookup::defineHiddenClass} method is dynamically added as a new member
1761 * to the nest of a lookup class and/or whether a hidden class has
1762 * a strong relationship with the class loader marked as its defining loader.
1763 *
1764 * @since 15
1765 */
1766 public enum ClassOption {
1767 /**
1768 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest}
1769 * of a lookup class as a nestmate.
1770 *
1771 * <p> A hidden nestmate class has access to the private members of all
1772 * classes and interfaces in the same nest.
1773 *
1774 * @see Class#getNestHost()
1775 */
1776 NESTMATE(NESTMATE_CLASS),
1777
1778 /**
1779 * Specifies that a hidden class has a <em>strong</em>
1780 * relationship with the class loader marked as its defining loader,
1781 * as a normal class or interface has with its own defining loader.
1782 * This means that the hidden class may be unloaded if and only if
1783 * its defining loader is not reachable and thus may be reclaimed
1784 * by a garbage collector (JLS {@jls 12.7}).
1785 *
1786 * <p> By default, a hidden class or interface may be unloaded
1787 * even if the class loader that is marked as its defining loader is
1788 * <a href="../ref/package-summary.html#reachability">reachable</a>.
1789
1790 *
1791 * @jls 12.7 Unloading of Classes and Interfaces
1792 */
1793 STRONG(STRONG_LOADER_LINK);
1794
1795 /* the flag value is used by VM at define class time */
1796 private final int flag;
1797 ClassOption(int flag) {
1798 this.flag = flag;
1799 }
1800
1801 static int optionsToFlag(ClassOption[] options) {
1802 int flags = 0;
1803 for (ClassOption cp : options) {
1804 if ((flags & cp.flag) != 0) {
1805 throw new IllegalArgumentException("Duplicate ClassOption " + cp);
1806 }
1807 flags |= cp.flag;
1808 }
1809 return flags;
1810 }
1811 }
1812
1813 /**
1814 * Creates a <em>hidden</em> class or interface from {@code bytes},
1815 * returning a {@code Lookup} on the newly created class or interface.
1816 *
1817 * <p> Ordinarily, a class or interface {@code C} is created by a class loader,
1818 * which either defines {@code C} directly or delegates to another class loader.
1819 * A class loader defines {@code C} directly by invoking
1820 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1821 * ClassLoader::defineClass}, which causes the Java Virtual Machine
1822 * to derive {@code C} from a purported representation in {@code class} file format.
1823 * In situations where use of a class loader is undesirable, a class or interface
1824 * {@code C} can be created by this method instead. This method is capable of
1825 * defining {@code C}, and thereby creating it, without invoking
1826 * {@code ClassLoader::defineClass}.
1827 * Instead, this method defines {@code C} as if by arranging for
1828 * the Java Virtual Machine to derive a nonarray class or interface {@code C}
1829 * from a purported representation in {@code class} file format
1830 * using the following rules:
1831 *
1832 * <ol>
1833 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup}
1834 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access.
1835 * This level of access is needed to create {@code C} in the module
1836 * of the lookup class of this {@code Lookup}.</li>
1837 *
1838 * <li> The purported representation in {@code bytes} must be a {@code ClassFile}
1839 * structure (JVMS {@jvms 4.1}) of a supported major and minor version.
1840 * The major and minor version may differ from the {@code class} file version
1841 * of the lookup class of this {@code Lookup}.</li>
1842 *
1843 * <li> The value of {@code this_class} must be a valid index in the
1844 * {@code constant_pool} table, and the entry at that index must be a valid
1845 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name
1846 * encoded in internal form that is specified by this structure. {@code N} must
1847 * denote a class or interface in the same package as the lookup class.</li>
1848 *
1849 * <li> Let {@code CN} be the string {@code N + "." + <suffix>},
1850 * where {@code <suffix>} is an unqualified name.
1851 *
1852 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by
1853 * {@code bytes} with an additional entry in the {@code constant_pool} table,
1854 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and
1855 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class}
1856 * refers to the new {@code CONSTANT_Utf8_info} structure.
1857 *
1858 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}.
1859 *
1860 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and
1861 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5},
1862 * with the following adjustments:
1863 * <ul>
1864 * <li> The constant indicated by {@code this_class} is permitted to specify a name
1865 * that includes a single {@code "."} character, even though this is not a valid
1866 * binary class or interface name in internal form.</li>
1867 *
1868 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C},
1869 * but no class loader is recorded as an initiating class loader of {@code C}.</li>
1870 *
1871 * <li> {@code C} is considered to have the same runtime
1872 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module}
1873 * and {@linkplain java.security.ProtectionDomain protection domain}
1874 * as the lookup class of this {@code Lookup}.
1875 * <li> Let {@code GN} be the binary name obtained by taking {@code N}
1876 * (a binary name encoded in internal form) and replacing ASCII forward slashes with
1877 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}:
1878 * <ul>
1879 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>},
1880 * even though this is not a valid binary class or interface name.</li>
1881 * <li> {@link Class#descriptorString()} returns the string
1882 * {@code "L" + N + "." + <suffix> + ";"},
1883 * even though this is not a valid type descriptor name.</li>
1884 * <li> {@link Class#describeConstable()} returns an empty optional as {@code C}
1885 * cannot be described in {@linkplain java.lang.constant.ClassDesc nominal form}.</li>
1886 * </ul>
1887 * </ul>
1888 * </li>
1889 * </ol>
1890 *
1891 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine.
1892 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments:
1893 * <ul>
1894 * <li> During verification, whenever it is necessary to load the class named
1895 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is
1896 * made of any class loader.</li>
1897 *
1898 * <li> On any attempt to resolve the entry in the run-time constant pool indicated
1899 * by {@code this_class}, the symbolic reference is considered to be resolved to
1900 * {@code C} and resolution always succeeds immediately.</li>
1901 * </ul>
1902 *
1903 * <p> If the {@code initialize} parameter is {@code true},
1904 * then {@code C} is initialized by the Java Virtual Machine.
1905 *
1906 * <p> The newly created class or interface {@code C} serves as the
1907 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object
1908 * returned by this method. {@code C} is <em>hidden</em> in the sense that
1909 * no other class or interface can refer to {@code C} via a constant pool entry.
1910 * That is, a hidden class or interface cannot be named as a supertype, a field type,
1911 * a method parameter type, or a method return type by any other class.
1912 * This is because a hidden class or interface does not have a binary name, so
1913 * there is no internal form available to record in any class's constant pool.
1914 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)},
1915 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and
1916 * is not {@linkplain java.instrument/java.lang.instrument.Instrumentation#isModifiableClass(Class)
1917 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html">
1918 * JVM Tool Interface</a>.
1919 *
1920 * <p> A class or interface created by
1921 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1922 * a class loader} has a strong relationship with that class loader.
1923 * That is, every {@code Class} object contains a reference to the {@code ClassLoader}
1924 * that {@linkplain Class#getClassLoader() defined it}.
1925 * This means that a class created by a class loader may be unloaded if and
1926 * only if its defining loader is not reachable and thus may be reclaimed
1927 * by a garbage collector (JLS {@jls 12.7}).
1928 *
1929 * By default, however, a hidden class or interface may be unloaded even if
1930 * the class loader that is marked as its defining loader is
1931 * <a href="../ref/package-summary.html#reachability">reachable</a>.
1932 * This behavior is useful when a hidden class or interface serves multiple
1933 * classes defined by arbitrary class loaders. In other cases, a hidden
1934 * class or interface may be linked to a single class (or a small number of classes)
1935 * with the same defining loader as the hidden class or interface.
1936 * In such cases, where the hidden class or interface must be coterminous
1937 * with a normal class or interface, the {@link ClassOption#STRONG STRONG}
1938 * option may be passed in {@code options}.
1939 * This arranges for a hidden class to have the same strong relationship
1940 * with the class loader marked as its defining loader,
1941 * as a normal class or interface has with its own defining loader.
1942 *
1943 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass}
1944 * may still prevent a hidden class or interface from being
1945 * unloaded by ensuring that the {@code Class} object is reachable.
1946 *
1947 * <p> The unloading characteristics are set for each hidden class when it is
1948 * defined, and cannot be changed later. An advantage of allowing hidden classes
1949 * to be unloaded independently of the class loader marked as their defining loader
1950 * is that a very large number of hidden classes may be created by an application.
1951 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory,
1952 * just as if normal classes were created by class loaders.
1953 *
1954 * <p> Classes and interfaces in a nest are allowed to have mutual access to
1955 * their private members. The nest relationship is determined by
1956 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and
1957 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file.
1958 * By default, a hidden class belongs to a nest consisting only of itself
1959 * because a hidden class has no binary name.
1960 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options}
1961 * to create a hidden class or interface {@code C} as a member of a nest.
1962 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute
1963 * in the {@code ClassFile} structure from which {@code C} was derived.
1964 * Instead, the following rules determine the nest host of {@code C}:
1965 * <ul>
1966 * <li>If the nest host of the lookup class of this {@code Lookup} has previously
1967 * been determined, then let {@code H} be the nest host of the lookup class.
1968 * Otherwise, the nest host of the lookup class is determined using the
1969 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li>
1970 * <li>The nest host of {@code C} is determined to be {@code H},
1971 * the nest host of the lookup class.</li>
1972 * </ul>
1973 *
1974 * <p> A hidden class or interface may be serializable, but this requires a custom
1975 * serialization mechanism in order to ensure that instances are properly serialized
1976 * and deserialized. The default serialization mechanism supports only classes and
1977 * interfaces that are discoverable by their class name.
1978 *
1979 * @param bytes the bytes that make up the class data,
1980 * in the format of a valid {@code class} file as defined by
1981 * <cite>The Java Virtual Machine Specification</cite>.
1982 * @param initialize if {@code true} the class will be initialized.
1983 * @param options {@linkplain ClassOption class options}
1984 * @return the {@code Lookup} object on the hidden class,
1985 * with {@linkplain #ORIGINAL original} and
1986 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
1987 *
1988 * @throws IllegalAccessException if this {@code Lookup} does not have
1989 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
1990 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1991 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
1992 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
1993 * than the lookup class or {@code bytes} is not a class or interface
1994 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
1995 * @throws IncompatibleClassChangeError if the class or interface named as
1996 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
1997 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
1998 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
1999 * {@code C} is {@code C} itself
2000 * @throws VerifyError if the newly created class cannot be verified
2001 * @throws LinkageError if the newly created class cannot be linked for any other reason
2002 * @throws NullPointerException if any parameter is {@code null}
2003 *
2004 * @since 15
2005 * @see Class#isHidden()
2006 * @jvms 4.2.1 Binary Class and Interface Names
2007 * @jvms 4.2.2 Unqualified Names
2008 * @jvms 4.7.28 The {@code NestHost} Attribute
2009 * @jvms 4.7.29 The {@code NestMembers} Attribute
2010 * @jvms 5.4.3.1 Class and Interface Resolution
2011 * @jvms 5.4.4 Access Control
2012 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2013 * @jvms 5.4 Linking
2014 * @jvms 5.5 Initialization
2015 * @jls 12.7 Unloading of Classes and Interfaces
2016 */
2017 @SuppressWarnings("doclint:reference") // cross-module links
2018 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options)
2019 throws IllegalAccessException
2020 {
2021 Objects.requireNonNull(bytes);
2022 int flags = ClassOption.optionsToFlag(options);
2023 if (!hasFullPrivilegeAccess()) {
2024 throw new IllegalAccessException(this + " does not have full privilege access");
2025 }
2026
2027 return makeHiddenClassDefiner(bytes.clone(), false, flags).defineClassAsLookup(initialize);
2028 }
2029
2030 /**
2031 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated
2032 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data},
2033 * returning a {@code Lookup} on the newly created class or interface.
2034 *
2035 * <p> This method is equivalent to calling
2036 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)}
2037 * as if the hidden class is injected with a private static final <i>unnamed</i>
2038 * field which is initialized with the given {@code classData} at
2039 * the first instruction of the class initializer.
2040 * The newly created class is linked by the Java Virtual Machine.
2041 *
2042 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData}
2043 * and {@link MethodHandles#classDataAt(Lookup, String, Class, int) MethodHandles::classDataAt}
2044 * methods can be used to retrieve the {@code classData}.
2045 *
2046 * @apiNote
2047 * A framework can create a hidden class with class data with one or more
2048 * objects and load the class data as dynamically-computed constant(s)
2049 * via a bootstrap method. {@link MethodHandles#classData(Lookup, String, Class)
2050 * Class data} is accessible only to the lookup object created by the newly
2051 * defined hidden class but inaccessible to other members in the same nest
2052 * (unlike private static fields that are accessible to nestmates).
2053 * Care should be taken w.r.t. mutability for example when passing
2054 * an array or other mutable structure through the class data.
2055 * Changing any value stored in the class data at runtime may lead to
2056 * unpredictable behavior.
2057 * If the class data is a {@code List}, it is good practice to make it
2058 * unmodifiable for example via {@link List#of List::of}.
2059 *
2060 * @param bytes the class bytes
2061 * @param classData pre-initialized class data
2062 * @param initialize if {@code true} the class will be initialized.
2063 * @param options {@linkplain ClassOption class options}
2064 * @return the {@code Lookup} object on the hidden class,
2065 * with {@linkplain #ORIGINAL original} and
2066 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2067 *
2068 * @throws IllegalAccessException if this {@code Lookup} does not have
2069 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2070 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2071 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2072 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2073 * than the lookup class or {@code bytes} is not a class or interface
2074 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2075 * @throws IncompatibleClassChangeError if the class or interface named as
2076 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2077 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2078 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2079 * {@code C} is {@code C} itself
2080 * @throws VerifyError if the newly created class cannot be verified
2081 * @throws LinkageError if the newly created class cannot be linked for any other reason
2082 * @throws NullPointerException if any parameter is {@code null}
2083 *
2084 * @since 16
2085 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
2086 * @see Class#isHidden()
2087 * @see MethodHandles#classData(Lookup, String, Class)
2088 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
2089 * @jvms 4.2.1 Binary Class and Interface Names
2090 * @jvms 4.2.2 Unqualified Names
2091 * @jvms 4.7.28 The {@code NestHost} Attribute
2092 * @jvms 4.7.29 The {@code NestMembers} Attribute
2093 * @jvms 5.4.3.1 Class and Interface Resolution
2094 * @jvms 5.4.4 Access Control
2095 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2096 * @jvms 5.4 Linking
2097 * @jvms 5.5 Initialization
2098 * @jls 12.7 Unloading of Classes and Interfaces
2099 */
2100 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options)
2101 throws IllegalAccessException
2102 {
2103 Objects.requireNonNull(bytes);
2104 Objects.requireNonNull(classData);
2105
2106 int flags = ClassOption.optionsToFlag(options);
2107
2108 if (!hasFullPrivilegeAccess()) {
2109 throw new IllegalAccessException(this + " does not have full privilege access");
2110 }
2111
2112 return makeHiddenClassDefiner(bytes.clone(), false, flags)
2113 .defineClassAsLookup(initialize, classData);
2114 }
2115
2116 // A default dumper for writing class files passed to Lookup::defineClass
2117 // and Lookup::defineHiddenClass to disk for debugging purposes. To enable,
2118 // set -Djdk.invoke.MethodHandle.dumpHiddenClassFiles or
2119 // -Djdk.invoke.MethodHandle.dumpHiddenClassFiles=true
2120 //
2121 // This default dumper does not dump hidden classes defined by LambdaMetafactory
2122 // and LambdaForms and method handle internals. They are dumped via
2123 // different ClassFileDumpers.
2124 private static ClassFileDumper defaultDumper() {
2125 return DEFAULT_DUMPER;
2126 }
2127
2128 private static final ClassFileDumper DEFAULT_DUMPER = ClassFileDumper.getInstance(
2129 "jdk.invoke.MethodHandle.dumpClassFiles", "DUMP_CLASS_FILES");
2130
2131 /**
2132 * This method checks the class file version and the structure of `this_class`.
2133 * and checks if the bytes is a class or interface (ACC_MODULE flag not set)
2134 * that is in the named package.
2135 *
2136 * @throws IllegalArgumentException if ACC_MODULE flag is set in access flags
2137 * or the class is not in the given package name.
2138 */
2139 static String validateAndFindInternalName(byte[] bytes, String pkgName) {
2140 int magic = readInt(bytes, 0);
2141 if (magic != ClassFile.MAGIC_NUMBER) {
2142 throw new ClassFormatError("Incompatible magic value: " + magic);
2143 }
2144 // We have to read major and minor this way as ClassFile API throws IAE
2145 // yet we want distinct ClassFormatError and UnsupportedClassVersionError
2146 int minor = readUnsignedShort(bytes, 4);
2147 int major = readUnsignedShort(bytes, 6);
2148
2149 if (!VM.isSupportedClassFileVersion(major, minor)) {
2150 throw new UnsupportedClassVersionError("Unsupported class file version " + major + "." + minor);
2151 }
2152
2153 String name;
2154 ClassDesc sym;
2155 int accessFlags;
2156 try {
2157 ClassModel cm = ClassFile.of().parse(bytes);
2158 var thisClass = cm.thisClass();
2159 name = thisClass.asInternalName();
2160 sym = thisClass.asSymbol();
2161 accessFlags = cm.flags().flagsMask();
2162 } catch (IllegalArgumentException e) {
2163 ClassFormatError cfe = new ClassFormatError();
2164 cfe.initCause(e);
2165 throw cfe;
2166 }
2167 // must be a class or interface
2168 if ((accessFlags & ACC_MODULE) != 0) {
2169 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set");
2170 }
2171
2172 String pn = sym.packageName();
2173 if (!pn.equals(pkgName)) {
2174 throw newIllegalArgumentException(name + " not in same package as lookup class");
2175 }
2176
2177 return name;
2178 }
2179
2180 private static int readInt(byte[] bytes, int offset) {
2181 if ((offset + 4) > bytes.length) {
2182 throw new ClassFormatError("Invalid ClassFile structure");
2183 }
2184 return ((bytes[offset] & 0xFF) << 24)
2185 | ((bytes[offset + 1] & 0xFF) << 16)
2186 | ((bytes[offset + 2] & 0xFF) << 8)
2187 | (bytes[offset + 3] & 0xFF);
2188 }
2189
2190 private static int readUnsignedShort(byte[] bytes, int offset) {
2191 if ((offset+2) > bytes.length) {
2192 throw new ClassFormatError("Invalid ClassFile structure");
2193 }
2194 return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF);
2195 }
2196
2197 /*
2198 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2199 * from the given bytes.
2200 *
2201 * Caller should make a defensive copy of the arguments if needed
2202 * before calling this factory method.
2203 *
2204 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2205 * {@code bytes} denotes a class in a different package than the lookup class
2206 */
2207 private ClassDefiner makeClassDefiner(byte[] bytes) {
2208 var internalName = validateAndFindInternalName(bytes, lookupClass().getPackageName());
2209 return new ClassDefiner(this, internalName, bytes, STRONG_LOADER_LINK, defaultDumper());
2210 }
2211
2212 /**
2213 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2214 * from the given bytes. No package name check on the given bytes.
2215 *
2216 * @param internalName internal name
2217 * @param bytes class bytes
2218 * @param dumper dumper to write the given bytes to the dumper's output directory
2219 * @return ClassDefiner that defines a normal class of the given bytes.
2220 */
2221 ClassDefiner makeClassDefiner(String internalName, byte[] bytes, ClassFileDumper dumper) {
2222 // skip package name validation
2223 return new ClassDefiner(this, internalName, bytes, STRONG_LOADER_LINK, dumper);
2224 }
2225
2226 /**
2227 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2228 * from the given bytes. The name must be in the same package as the lookup class.
2229 *
2230 * Caller should make a defensive copy of the arguments if needed
2231 * before calling this factory method.
2232 *
2233 * @param bytes class bytes
2234 * @param dumper dumper to write the given bytes to the dumper's output directory
2235 * @return ClassDefiner that defines a hidden class of the given bytes.
2236 *
2237 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2238 * {@code bytes} denotes a class in a different package than the lookup class
2239 */
2240 ClassDefiner makeHiddenClassDefiner(byte[] bytes, ClassFileDumper dumper) {
2241 var internalName = validateAndFindInternalName(bytes, lookupClass().getPackageName());
2242 return makeHiddenClassDefiner(internalName, bytes, false, dumper, 0);
2243 }
2244
2245 /**
2246 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2247 * from the given bytes and options.
2248 * The name must be in the same package as the lookup class.
2249 *
2250 * Caller should make a defensive copy of the arguments if needed
2251 * before calling this factory method.
2252 *
2253 * @param bytes class bytes
2254 * @param flags class option flag mask
2255 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2256 * @return ClassDefiner that defines a hidden class of the given bytes and options
2257 *
2258 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2259 * {@code bytes} denotes a class in a different package than the lookup class
2260 */
2261 private ClassDefiner makeHiddenClassDefiner(byte[] bytes,
2262 boolean accessVmAnnotations,
2263 int flags) {
2264 var internalName = validateAndFindInternalName(bytes, lookupClass().getPackageName());
2265 return makeHiddenClassDefiner(internalName, bytes, accessVmAnnotations, defaultDumper(), flags);
2266 }
2267
2268 /**
2269 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2270 * from the given bytes and the given options. No package name check on the given bytes.
2271 *
2272 * @param internalName internal name that specifies the prefix of the hidden class
2273 * @param bytes class bytes
2274 * @param dumper dumper to write the given bytes to the dumper's output directory
2275 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2276 */
2277 ClassDefiner makeHiddenClassDefiner(String internalName, byte[] bytes, ClassFileDumper dumper) {
2278 Objects.requireNonNull(dumper);
2279 // skip name and access flags validation
2280 return makeHiddenClassDefiner(internalName, bytes, false, dumper, 0);
2281 }
2282
2283 /**
2284 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2285 * from the given bytes and the given options. No package name check on the given bytes.
2286 *
2287 * @param internalName internal name that specifies the prefix of the hidden class
2288 * @param bytes class bytes
2289 * @param flags class options flag mask
2290 * @param dumper dumper to write the given bytes to the dumper's output directory
2291 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2292 */
2293 ClassDefiner makeHiddenClassDefiner(String internalName, byte[] bytes, ClassFileDumper dumper, int flags) {
2294 Objects.requireNonNull(dumper);
2295 // skip name and access flags validation
2296 return makeHiddenClassDefiner(internalName, bytes, false, dumper, flags);
2297 }
2298
2299 /**
2300 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2301 * from the given class file and options.
2302 *
2303 * @param internalName internal name
2304 * @param bytes Class byte array
2305 * @param flags class option flag mask
2306 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2307 * @param dumper dumper to write the given bytes to the dumper's output directory
2308 */
2309 private ClassDefiner makeHiddenClassDefiner(String internalName,
2310 byte[] bytes,
2311 boolean accessVmAnnotations,
2312 ClassFileDumper dumper,
2313 int flags) {
2314 flags |= HIDDEN_CLASS;
2315 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) {
2316 // jdk.internal.vm.annotations are permitted for classes
2317 // defined to boot loader and platform loader
2318 flags |= ACCESS_VM_ANNOTATIONS;
2319 }
2320
2321 return new ClassDefiner(this, internalName, bytes, flags, dumper);
2322 }
2323
2324 record ClassDefiner(Lookup lookup, String internalName, byte[] bytes, int classFlags, ClassFileDumper dumper) {
2325 ClassDefiner {
2326 assert ((classFlags & HIDDEN_CLASS) != 0 || (classFlags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK);
2327 }
2328
2329 Class<?> defineClass(boolean initialize) {
2330 return defineClass(initialize, null);
2331 }
2332
2333 Lookup defineClassAsLookup(boolean initialize) {
2334 Class<?> c = defineClass(initialize, null);
2335 return new Lookup(c, null, FULL_POWER_MODES);
2336 }
2337
2338 /**
2339 * Defines the class of the given bytes and the given classData.
2340 * If {@code initialize} parameter is true, then the class will be initialized.
2341 *
2342 * @param initialize true if the class to be initialized
2343 * @param classData classData or null
2344 * @return the class
2345 *
2346 * @throws LinkageError linkage error
2347 */
2348 Class<?> defineClass(boolean initialize, Object classData) {
2349 Class<?> lookupClass = lookup.lookupClass();
2350 ClassLoader loader = lookupClass.getClassLoader();
2351 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null;
2352 Class<?> c = null;
2353 try {
2354 c = SharedSecrets.getJavaLangAccess()
2355 .defineClass(loader, lookupClass, internalName, bytes, pd, initialize, classFlags, classData);
2356 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost();
2357 return c;
2358 } finally {
2359 // dump the classfile for debugging
2360 if (dumper.isEnabled()) {
2361 String name = internalName();
2362 if (c != null) {
2363 dumper.dumpClass(name, c, bytes);
2364 } else {
2365 dumper.dumpFailedClass(name, bytes);
2366 }
2367 }
2368 }
2369 }
2370
2371 /**
2372 * Defines the class of the given bytes and the given classData.
2373 * If {@code initialize} parameter is true, then the class will be initialized.
2374 *
2375 * @param initialize true if the class to be initialized
2376 * @param classData classData or null
2377 * @return a Lookup for the defined class
2378 *
2379 * @throws LinkageError linkage error
2380 */
2381 Lookup defineClassAsLookup(boolean initialize, Object classData) {
2382 Class<?> c = defineClass(initialize, classData);
2383 return new Lookup(c, null, FULL_POWER_MODES);
2384 }
2385
2386 private boolean isNestmate() {
2387 return (classFlags & NESTMATE_CLASS) != 0;
2388 }
2389 }
2390
2391 private ProtectionDomain lookupClassProtectionDomain() {
2392 ProtectionDomain pd = cachedProtectionDomain;
2393 if (pd == null) {
2394 cachedProtectionDomain = pd = SharedSecrets.getJavaLangAccess().protectionDomain(lookupClass);
2395 }
2396 return pd;
2397 }
2398
2399 // cached protection domain
2400 private volatile ProtectionDomain cachedProtectionDomain;
2401
2402 // Make sure outer class is initialized first.
2403 static { IMPL_NAMES.getClass(); }
2404
2405 /** Package-private version of lookup which is trusted. */
2406 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
2407
2408 /** Version of lookup which is trusted minimally.
2409 * It can only be used to create method handles to publicly accessible
2410 * members in packages that are exported unconditionally.
2411 */
2412 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
2413
2414 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
2415 String name = lookupClass.getName();
2416 if (name.startsWith("java.lang.invoke."))
2417 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
2418 }
2419
2420 /**
2421 * Displays the name of the class from which lookups are to be made,
2422 * followed by "/" and the name of the {@linkplain #previousLookupClass()
2423 * previous lookup class} if present.
2424 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
2425 * If there are restrictions on the access permitted to this lookup,
2426 * this is indicated by adding a suffix to the class name, consisting
2427 * of a slash and a keyword. The keyword represents the strongest
2428 * allowed access, and is chosen as follows:
2429 * <ul>
2430 * <li>If no access is allowed, the suffix is "/noaccess".
2431 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
2432 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
2433 * <li>If only public and module access are allowed, the suffix is "/module".
2434 * <li>If public and package access are allowed, the suffix is "/package".
2435 * <li>If public, package, and private access are allowed, the suffix is "/private".
2436 * </ul>
2437 * If none of the above cases apply, it is the case that
2438 * {@linkplain #hasFullPrivilegeAccess() full privilege access}
2439 * (public, module, package, private, and protected) is allowed.
2440 * In this case, no suffix is added.
2441 * This is true only of an object obtained originally from
2442 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
2443 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
2444 * always have restricted access, and will display a suffix.
2445 * <p>
2446 * (It may seem strange that protected access should be
2447 * stronger than private access. Viewed independently from
2448 * package access, protected access is the first to be lost,
2449 * because it requires a direct subclass relationship between
2450 * caller and callee.)
2451 * @see #in
2452 */
2453 @Override
2454 public String toString() {
2455 String cname = lookupClass.getName();
2456 if (prevLookupClass != null)
2457 cname += "/" + prevLookupClass.getName();
2458 switch (allowedModes) {
2459 case 0: // no privileges
2460 return cname + "/noaccess";
2461 case UNCONDITIONAL:
2462 return cname + "/publicLookup";
2463 case PUBLIC:
2464 return cname + "/public";
2465 case PUBLIC|MODULE:
2466 return cname + "/module";
2467 case PUBLIC|PACKAGE:
2468 case PUBLIC|MODULE|PACKAGE:
2469 return cname + "/package";
2470 case PUBLIC|PACKAGE|PRIVATE:
2471 case PUBLIC|MODULE|PACKAGE|PRIVATE:
2472 return cname + "/private";
2473 case PUBLIC|PACKAGE|PRIVATE|PROTECTED:
2474 case PUBLIC|MODULE|PACKAGE|PRIVATE|PROTECTED:
2475 case FULL_POWER_MODES:
2476 return cname;
2477 case TRUSTED:
2478 return "/trusted"; // internal only; not exported
2479 default: // Should not happen, but it's a bitfield...
2480 cname = cname + "/" + Integer.toHexString(allowedModes);
2481 assert(false) : cname;
2482 return cname;
2483 }
2484 }
2485
2486 /**
2487 * Produces a method handle for a static method.
2488 * The type of the method handle will be that of the method.
2489 * (Since static methods do not take receivers, there is no
2490 * additional receiver argument inserted into the method handle type,
2491 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
2492 * The method and all its argument types must be accessible to the lookup object.
2493 * <p>
2494 * The returned method handle will have
2495 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2496 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2497 * <p>
2498 * If the returned method handle is invoked, the method's class will
2499 * be initialized, if it has not already been initialized.
2500 * <p><b>Example:</b>
2501 * {@snippet lang="java" :
2502 import static java.lang.invoke.MethodHandles.*;
2503 import static java.lang.invoke.MethodType.*;
2504 ...
2505 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
2506 "asList", methodType(List.class, Object[].class));
2507 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
2508 * }
2509 * @param refc the class from which the method is accessed
2510 * @param name the name of the method
2511 * @param type the type of the method
2512 * @return the desired method handle
2513 * @throws NoSuchMethodException if the method does not exist
2514 * @throws IllegalAccessException if access checking fails,
2515 * or if the method is not {@code static},
2516 * or if the method's variable arity modifier bit
2517 * is set and {@code asVarargsCollector} fails
2518 * @throws NullPointerException if any argument is null
2519 */
2520 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2521 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
2522 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method));
2523 }
2524
2525 /**
2526 * Produces a method handle for a virtual method.
2527 * The type of the method handle will be that of the method,
2528 * with the receiver type (usually {@code refc}) prepended.
2529 * The method and all its argument types must be accessible to the lookup object.
2530 * <p>
2531 * When called, the handle will treat the first argument as a receiver
2532 * and, for non-private methods, dispatch on the receiver's type to determine which method
2533 * implementation to enter.
2534 * For private methods the named method in {@code refc} will be invoked on the receiver.
2535 * (The dispatching action is identical with that performed by an
2536 * {@code invokevirtual} or {@code invokeinterface} instruction.)
2537 * <p>
2538 * The first argument will be of type {@code refc} if the lookup
2539 * class has full privileges to access the member. Otherwise
2540 * the member must be {@code protected} and the first argument
2541 * will be restricted in type to the lookup class.
2542 * <p>
2543 * The returned method handle will have
2544 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2545 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2546 * <p>
2547 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
2548 * instructions and method handles produced by {@code findVirtual},
2549 * if the class is {@code MethodHandle} and the name string is
2550 * {@code invokeExact} or {@code invoke}, the resulting
2551 * method handle is equivalent to one produced by
2552 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
2553 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
2554 * with the same {@code type} argument.
2555 * <p>
2556 * If the class is {@code VarHandle} and the name string corresponds to
2557 * the name of a signature-polymorphic access mode method, the resulting
2558 * method handle is equivalent to one produced by
2559 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
2560 * the access mode corresponding to the name string and with the same
2561 * {@code type} arguments.
2562 * <p>
2563 * <b>Example:</b>
2564 * {@snippet lang="java" :
2565 import static java.lang.invoke.MethodHandles.*;
2566 import static java.lang.invoke.MethodType.*;
2567 ...
2568 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
2569 "concat", methodType(String.class, String.class));
2570 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
2571 "hashCode", methodType(int.class));
2572 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
2573 "hashCode", methodType(int.class));
2574 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
2575 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
2576 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
2577 // interface method:
2578 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
2579 "subSequence", methodType(CharSequence.class, int.class, int.class));
2580 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
2581 // constructor "internal method" must be accessed differently:
2582 MethodType MT_newString = methodType(void.class); //()V for new String()
2583 try { assertEquals("impossible", lookup()
2584 .findVirtual(String.class, "<init>", MT_newString));
2585 } catch (NoSuchMethodException ex) { } // OK
2586 MethodHandle MH_newString = publicLookup()
2587 .findConstructor(String.class, MT_newString);
2588 assertEquals("", (String) MH_newString.invokeExact());
2589 * }
2590 *
2591 * @param refc the class or interface from which the method is accessed
2592 * @param name the name of the method
2593 * @param type the type of the method, with the receiver argument omitted
2594 * @return the desired method handle
2595 * @throws NoSuchMethodException if the method does not exist
2596 * @throws IllegalAccessException if access checking fails,
2597 * or if the method is {@code static},
2598 * or if the method's variable arity modifier bit
2599 * is set and {@code asVarargsCollector} fails
2600 * @throws NullPointerException if any argument is null
2601 */
2602 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2603 if (refc == MethodHandle.class) {
2604 MethodHandle mh = findVirtualForMH(name, type);
2605 if (mh != null) return mh;
2606 } else if (refc == VarHandle.class) {
2607 MethodHandle mh = findVirtualForVH(name, type);
2608 if (mh != null) return mh;
2609 }
2610 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
2611 MemberName method = resolveOrFail(refKind, refc, name, type);
2612 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method));
2613 }
2614 private MethodHandle findVirtualForMH(String name, MethodType type) {
2615 // these names require special lookups because of the implicit MethodType argument
2616 if ("invoke".equals(name))
2617 return invoker(type);
2618 if ("invokeExact".equals(name))
2619 return exactInvoker(type);
2620 assert(!MemberName.isMethodHandleInvokeName(name));
2621 return null;
2622 }
2623 private MethodHandle findVirtualForVH(String name, MethodType type) {
2624 try {
2625 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
2626 } catch (IllegalArgumentException e) {
2627 return null;
2628 }
2629 }
2630
2631 /**
2632 * Produces a method handle which creates an object and initializes it, using
2633 * the constructor of the specified type.
2634 * The parameter types of the method handle will be those of the constructor,
2635 * while the return type will be a reference to the constructor's class.
2636 * The constructor and all its argument types must be accessible to the lookup object.
2637 * <p>
2638 * The requested type must have a return type of {@code void}.
2639 * (This is consistent with the JVM's treatment of constructor type descriptors.)
2640 * <p>
2641 * The returned method handle will have
2642 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2643 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2644 * <p>
2645 * If the returned method handle is invoked, the constructor's class will
2646 * be initialized, if it has not already been initialized.
2647 * <p><b>Example:</b>
2648 * {@snippet lang="java" :
2649 import static java.lang.invoke.MethodHandles.*;
2650 import static java.lang.invoke.MethodType.*;
2651 ...
2652 MethodHandle MH_newArrayList = publicLookup().findConstructor(
2653 ArrayList.class, methodType(void.class, Collection.class));
2654 Collection orig = Arrays.asList("x", "y");
2655 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
2656 assert(orig != copy);
2657 assertEquals(orig, copy);
2658 // a variable-arity constructor:
2659 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
2660 ProcessBuilder.class, methodType(void.class, String[].class));
2661 ProcessBuilder pb = (ProcessBuilder)
2662 MH_newProcessBuilder.invoke("x", "y", "z");
2663 assertEquals("[x, y, z]", pb.command().toString());
2664 * }
2665 * @param refc the class or interface from which the method is accessed
2666 * @param type the type of the method, with the receiver argument omitted, and a void return type
2667 * @return the desired method handle
2668 * @throws NoSuchMethodException if the constructor does not exist
2669 * @throws IllegalAccessException if access checking fails
2670 * or if the method's variable arity modifier bit
2671 * is set and {@code asVarargsCollector} fails
2672 * @throws NullPointerException if any argument is null
2673 */
2674 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2675 if (refc.isArray()) {
2676 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
2677 }
2678 String name = ConstantDescs.INIT_NAME;
2679 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
2680 return getDirectConstructor(refc, ctor);
2681 }
2682
2683 /**
2684 * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
2685 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
2686 * Such a resolution, as specified in JVMS {@jvms 5.4.3.1}, attempts to locate and load the class,
2687 * and then determines whether the class is accessible to this lookup object.
2688 * <p>
2689 * For a class or an interface, the name is the {@linkplain ClassLoader##binary-name binary name}.
2690 * For an array class of {@code n} dimensions, the name begins with {@code n} occurrences
2691 * of {@code '['} and followed by the element type as encoded in the
2692 * {@linkplain Class##nameFormat table} specified in {@link Class#getName}.
2693 * <p>
2694 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
2695 * its class loader, and the {@linkplain #lookupModes() lookup modes}.
2696 *
2697 * @param targetName the {@linkplain ClassLoader##binary-name binary name} of the class
2698 * or the string representing an array class
2699 * @return the requested class.
2700 * @throws LinkageError if the linkage fails
2701 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
2702 * @throws IllegalAccessException if the class is not accessible, using the allowed access
2703 * modes.
2704 * @throws NullPointerException if {@code targetName} is null
2705 * @since 9
2706 * @jvms 5.4.3.1 Class and Interface Resolution
2707 */
2708 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
2709 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
2710 return accessClass(targetClass);
2711 }
2712
2713 /**
2714 * Ensures that {@code targetClass} has been initialized. The class
2715 * to be initialized must be {@linkplain #accessClass accessible}
2716 * to this {@code Lookup} object. This method causes {@code targetClass}
2717 * to be initialized if it has not been already initialized,
2718 * as specified in JVMS {@jvms 5.5}.
2719 *
2720 * <p>
2721 * This method returns when {@code targetClass} is fully initialized, or
2722 * when {@code targetClass} is being initialized by the current thread.
2723 *
2724 * @param <T> the type of the class to be initialized
2725 * @param targetClass the class to be initialized
2726 * @return {@code targetClass} that has been initialized, or that is being
2727 * initialized by the current thread.
2728 *
2729 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or {@code void}
2730 * or array class
2731 * @throws IllegalAccessException if {@code targetClass} is not
2732 * {@linkplain #accessClass accessible} to this lookup
2733 * @throws ExceptionInInitializerError if the class initialization provoked
2734 * by this method fails
2735 * @since 15
2736 * @jvms 5.5 Initialization
2737 */
2738 public <T> Class<T> ensureInitialized(Class<T> targetClass) throws IllegalAccessException {
2739 if (targetClass.isPrimitive())
2740 throw new IllegalArgumentException(targetClass + " is a primitive class");
2741 if (targetClass.isArray())
2742 throw new IllegalArgumentException(targetClass + " is an array class");
2743
2744 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2745 throw makeAccessException(targetClass);
2746 }
2747
2748 // ensure class initialization
2749 Unsafe.getUnsafe().ensureClassInitialized(targetClass);
2750 return targetClass;
2751 }
2752
2753 /*
2754 * Returns IllegalAccessException due to access violation to the given targetClass.
2755 *
2756 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized}
2757 * which verifies access to a class rather a member.
2758 */
2759 private IllegalAccessException makeAccessException(Class<?> targetClass) {
2760 String message = "access violation: "+ targetClass;
2761 if (this == MethodHandles.publicLookup()) {
2762 message += ", from public Lookup";
2763 } else {
2764 Module m = lookupClass().getModule();
2765 message += ", from " + lookupClass() + " (" + m + ")";
2766 if (prevLookupClass != null) {
2767 message += ", previous lookup " +
2768 prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")";
2769 }
2770 }
2771 return new IllegalAccessException(message);
2772 }
2773
2774 /**
2775 * Determines if a class can be accessed from the lookup context defined by
2776 * this {@code Lookup} object. The static initializer of the class is not run.
2777 * If {@code targetClass} is an array class, {@code targetClass} is accessible
2778 * if the element type of the array class is accessible. Otherwise,
2779 * {@code targetClass} is determined as accessible as follows.
2780 *
2781 * <p>
2782 * If {@code targetClass} is in the same module as the lookup class,
2783 * the lookup class is {@code LC} in module {@code M1} and
2784 * the previous lookup class is in module {@code M0} or
2785 * {@code null} if not present,
2786 * {@code targetClass} is accessible if and only if one of the following is true:
2787 * <ul>
2788 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
2789 * {@code LC} or other class in the same nest of {@code LC}.</li>
2790 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
2791 * in the same runtime package of {@code LC}.</li>
2792 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
2793 * a public type in {@code M1}.</li>
2794 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
2795 * a public type in a package exported by {@code M1} to at least {@code M0}
2796 * if the previous lookup class is present; otherwise, {@code targetClass}
2797 * is a public type in a package exported by {@code M1} unconditionally.</li>
2798 * </ul>
2799 *
2800 * <p>
2801 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2802 * can access public types in all modules when the type is in a package
2803 * that is exported unconditionally.
2804 * <p>
2805 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass},
2806 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2807 * is inaccessible.
2808 * <p>
2809 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2810 * {@code M1} is the module containing {@code lookupClass} and
2811 * {@code M2} is the module containing {@code targetClass},
2812 * then {@code targetClass} is accessible if and only if
2813 * <ul>
2814 * <li>{@code M1} reads {@code M2}, and
2815 * <li>{@code targetClass} is public and in a package exported by
2816 * {@code M2} at least to {@code M1}.
2817 * </ul>
2818 * <p>
2819 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2820 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2821 * containing the previous lookup class, then {@code targetClass} is accessible
2822 * if and only if one of the following is true:
2823 * <ul>
2824 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2825 * {@linkplain Module#reads reads} {@code M0} and the type is
2826 * in a package that is exported to at least {@code M1}.
2827 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2828 * {@linkplain Module#reads reads} {@code M1} and the type is
2829 * in a package that is exported to at least {@code M0}.
2830 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2831 * and {@code M1} reads {@code M2} and the type is in a package
2832 * that is exported to at least both {@code M0} and {@code M2}.
2833 * </ul>
2834 * <p>
2835 * Otherwise, {@code targetClass} is not accessible.
2836 *
2837 * @param <T> the type of the class to be access-checked
2838 * @param targetClass the class to be access-checked
2839 * @return {@code targetClass} that has been access-checked
2840 * @throws IllegalAccessException if the class is not accessible from the lookup class
2841 * and previous lookup class, if present, using the allowed access modes.
2842 * @throws NullPointerException if {@code targetClass} is {@code null}
2843 * @since 9
2844 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
2845 */
2846 public <T> Class<T> accessClass(Class<T> targetClass) throws IllegalAccessException {
2847 if (!isClassAccessible(targetClass)) {
2848 throw makeAccessException(targetClass);
2849 }
2850 return targetClass;
2851 }
2852
2853 /**
2854 * Produces an early-bound method handle for a virtual method.
2855 * It will bypass checks for overriding methods on the receiver,
2856 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2857 * instruction from within the explicitly specified {@code specialCaller}.
2858 * The type of the method handle will be that of the method,
2859 * with a suitably restricted receiver type prepended.
2860 * (The receiver type will be {@code specialCaller} or a subtype.)
2861 * The method and all its argument types must be accessible
2862 * to the lookup object.
2863 * <p>
2864 * Before method resolution,
2865 * if the explicitly specified caller class is not identical with the
2866 * lookup class, or if this lookup object does not have
2867 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2868 * privileges, the access fails.
2869 * <p>
2870 * The returned method handle will have
2871 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2872 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2873 * <p style="font-size:smaller;">
2874 * <em>(Note: JVM internal methods named {@value ConstantDescs#INIT_NAME}
2875 * are not visible to this API,
2876 * even though the {@code invokespecial} instruction can refer to them
2877 * in special circumstances. Use {@link #findConstructor findConstructor}
2878 * to access instance initialization methods in a safe manner.)</em>
2879 * <p><b>Example:</b>
2880 * {@snippet lang="java" :
2881 import static java.lang.invoke.MethodHandles.*;
2882 import static java.lang.invoke.MethodType.*;
2883 ...
2884 static class Listie extends ArrayList {
2885 public String toString() { return "[wee Listie]"; }
2886 static Lookup lookup() { return MethodHandles.lookup(); }
2887 }
2888 ...
2889 // no access to constructor via invokeSpecial:
2890 MethodHandle MH_newListie = Listie.lookup()
2891 .findConstructor(Listie.class, methodType(void.class));
2892 Listie l = (Listie) MH_newListie.invokeExact();
2893 try { assertEquals("impossible", Listie.lookup().findSpecial(
2894 Listie.class, "<init>", methodType(void.class), Listie.class));
2895 } catch (NoSuchMethodException ex) { } // OK
2896 // access to super and self methods via invokeSpecial:
2897 MethodHandle MH_super = Listie.lookup().findSpecial(
2898 ArrayList.class, "toString" , methodType(String.class), Listie.class);
2899 MethodHandle MH_this = Listie.lookup().findSpecial(
2900 Listie.class, "toString" , methodType(String.class), Listie.class);
2901 MethodHandle MH_duper = Listie.lookup().findSpecial(
2902 Object.class, "toString" , methodType(String.class), Listie.class);
2903 assertEquals("[]", (String) MH_super.invokeExact(l));
2904 assertEquals(""+l, (String) MH_this.invokeExact(l));
2905 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
2906 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
2907 String.class, "toString", methodType(String.class), Listie.class));
2908 } catch (IllegalAccessException ex) { } // OK
2909 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
2910 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
2911 * }
2912 *
2913 * @param refc the class or interface from which the method is accessed
2914 * @param name the name of the method (which must not be "<init>")
2915 * @param type the type of the method, with the receiver argument omitted
2916 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
2917 * @return the desired method handle
2918 * @throws NoSuchMethodException if the method does not exist
2919 * @throws IllegalAccessException if access checking fails,
2920 * or if the method is {@code static},
2921 * or if the method's variable arity modifier bit
2922 * is set and {@code asVarargsCollector} fails
2923 * @throws NullPointerException if any argument is null
2924 */
2925 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
2926 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
2927 checkSpecialCaller(specialCaller, refc);
2928 Lookup specialLookup = this.in(specialCaller);
2929 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
2930 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method));
2931 }
2932
2933 /**
2934 * Produces a method handle giving read access to a non-static field.
2935 * The type of the method handle will have a return type of the field's
2936 * value type.
2937 * The method handle's single argument will be the instance containing
2938 * the field.
2939 * Access checking is performed immediately on behalf of the lookup class.
2940 * @param refc the class or interface from which the method is accessed
2941 * @param name the field's name
2942 * @param type the field's type
2943 * @return a method handle which can load values from the field
2944 * @throws NoSuchFieldException if the field does not exist
2945 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2946 * @throws NullPointerException if any argument is null
2947 * @see #findVarHandle(Class, String, Class)
2948 */
2949 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2950 MemberName field = resolveOrFail(REF_getField, refc, name, type);
2951 return getDirectField(REF_getField, refc, field);
2952 }
2953
2954 /**
2955 * Produces a method handle giving write access to a non-static field.
2956 * The type of the method handle will have a void return type.
2957 * The method handle will take two arguments, the instance containing
2958 * the field, and the value to be stored.
2959 * The second argument will be of the field's value type.
2960 * Access checking is performed immediately on behalf of the lookup class.
2961 * @param refc the class or interface from which the method is accessed
2962 * @param name the field's name
2963 * @param type the field's type
2964 * @return a method handle which can store values into the field
2965 * @throws NoSuchFieldException if the field does not exist
2966 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2967 * or {@code final}
2968 * @throws NullPointerException if any argument is null
2969 * @see #findVarHandle(Class, String, Class)
2970 */
2971 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2972 MemberName field = resolveOrFail(REF_putField, refc, name, type);
2973 return getDirectField(REF_putField, refc, field);
2974 }
2975
2976 /**
2977 * Produces a VarHandle giving access to a non-static field {@code name}
2978 * of type {@code type} declared in a class of type {@code recv}.
2979 * The VarHandle's variable type is {@code type} and it has one
2980 * coordinate type, {@code recv}.
2981 * <p>
2982 * Access checking is performed immediately on behalf of the lookup
2983 * class.
2984 * <p>
2985 * Certain access modes of the returned VarHandle are unsupported under
2986 * the following conditions:
2987 * <ul>
2988 * <li>if the field is declared {@code final}, then the write, atomic
2989 * update, numeric atomic update, and bitwise atomic update access
2990 * modes are unsupported.
2991 * <li>if the field type is anything other than {@code byte},
2992 * {@code short}, {@code char}, {@code int}, {@code long},
2993 * {@code float}, or {@code double} then numeric atomic update
2994 * access modes are unsupported.
2995 * <li>if the field type is anything other than {@code boolean},
2996 * {@code byte}, {@code short}, {@code char}, {@code int} or
2997 * {@code long} then bitwise atomic update access modes are
2998 * unsupported.
2999 * </ul>
3000 * <p>
3001 * If the field is declared {@code volatile} then the returned VarHandle
3002 * will override access to the field (effectively ignore the
3003 * {@code volatile} declaration) in accordance to its specified
3004 * access modes.
3005 * <p>
3006 * If the field type is {@code float} or {@code double} then numeric
3007 * and atomic update access modes compare values using their bitwise
3008 * representation (see {@link Float#floatToRawIntBits} and
3009 * {@link Double#doubleToRawLongBits}, respectively).
3010 * @apiNote
3011 * Bitwise comparison of {@code float} values or {@code double} values,
3012 * as performed by the numeric and atomic update access modes, differ
3013 * from the primitive {@code ==} operator and the {@link Float#equals}
3014 * and {@link Double#equals} methods, specifically with respect to
3015 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3016 * Care should be taken when performing a compare and set or a compare
3017 * and exchange operation with such values since the operation may
3018 * unexpectedly fail.
3019 * There are many possible NaN values that are considered to be
3020 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3021 * provided by Java can distinguish between them. Operation failure can
3022 * occur if the expected or witness value is a NaN value and it is
3023 * transformed (perhaps in a platform specific manner) into another NaN
3024 * value, and thus has a different bitwise representation (see
3025 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3026 * details).
3027 * The values {@code -0.0} and {@code +0.0} have different bitwise
3028 * representations but are considered equal when using the primitive
3029 * {@code ==} operator. Operation failure can occur if, for example, a
3030 * numeric algorithm computes an expected value to be say {@code -0.0}
3031 * and previously computed the witness value to be say {@code +0.0}.
3032 * @param recv the receiver class, of type {@code R}, that declares the
3033 * non-static field
3034 * @param name the field's name
3035 * @param type the field's type, of type {@code T}
3036 * @return a VarHandle giving access to non-static fields.
3037 * @throws NoSuchFieldException if the field does not exist
3038 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3039 * @throws NullPointerException if any argument is null
3040 * @since 9
3041 */
3042 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3043 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
3044 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
3045 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
3046 }
3047
3048 /**
3049 * Produces a method handle giving read access to a static field.
3050 * The type of the method handle will have a return type of the field's
3051 * value type.
3052 * The method handle will take no arguments.
3053 * Access checking is performed immediately on behalf of the lookup class.
3054 * <p>
3055 * If the returned method handle is invoked, the field's class will
3056 * be initialized, if it has not already been initialized.
3057 * @param refc the class or interface from which the method is accessed
3058 * @param name the field's name
3059 * @param type the field's type
3060 * @return a method handle which can load values from the field
3061 * @throws NoSuchFieldException if the field does not exist
3062 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3063 * @throws NullPointerException if any argument is null
3064 */
3065 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3066 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
3067 return getDirectField(REF_getStatic, refc, field);
3068 }
3069
3070 /**
3071 * Produces a method handle giving write access to a static field.
3072 * The type of the method handle will have a void return type.
3073 * The method handle will take a single
3074 * argument, of the field's value type, the value to be stored.
3075 * Access checking is performed immediately on behalf of the lookup class.
3076 * <p>
3077 * If the returned method handle is invoked, the field's class will
3078 * be initialized, if it has not already been initialized.
3079 * @param refc the class or interface from which the method is accessed
3080 * @param name the field's name
3081 * @param type the field's type
3082 * @return a method handle which can store values into the field
3083 * @throws NoSuchFieldException if the field does not exist
3084 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3085 * or is {@code final}
3086 * @throws NullPointerException if any argument is null
3087 */
3088 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3089 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
3090 return getDirectField(REF_putStatic, refc, field);
3091 }
3092
3093 /**
3094 * Produces a VarHandle giving access to a static field {@code name} of
3095 * type {@code type} declared in a class of type {@code decl}.
3096 * The VarHandle's variable type is {@code type} and it has no
3097 * coordinate types.
3098 * <p>
3099 * Access checking is performed immediately on behalf of the lookup
3100 * class.
3101 * <p>
3102 * If the returned VarHandle is operated on, the declaring class will be
3103 * initialized, if it has not already been initialized.
3104 * <p>
3105 * Certain access modes of the returned VarHandle are unsupported under
3106 * the following conditions:
3107 * <ul>
3108 * <li>if the field is declared {@code final}, then the write, atomic
3109 * update, numeric atomic update, and bitwise atomic update access
3110 * modes are unsupported.
3111 * <li>if the field type is anything other than {@code byte},
3112 * {@code short}, {@code char}, {@code int}, {@code long},
3113 * {@code float}, or {@code double}, then numeric atomic update
3114 * access modes are unsupported.
3115 * <li>if the field type is anything other than {@code boolean},
3116 * {@code byte}, {@code short}, {@code char}, {@code int} or
3117 * {@code long} then bitwise atomic update access modes are
3118 * unsupported.
3119 * </ul>
3120 * <p>
3121 * If the field is declared {@code volatile} then the returned VarHandle
3122 * will override access to the field (effectively ignore the
3123 * {@code volatile} declaration) in accordance to its specified
3124 * access modes.
3125 * <p>
3126 * If the field type is {@code float} or {@code double} then numeric
3127 * and atomic update access modes compare values using their bitwise
3128 * representation (see {@link Float#floatToRawIntBits} and
3129 * {@link Double#doubleToRawLongBits}, respectively).
3130 * @apiNote
3131 * Bitwise comparison of {@code float} values or {@code double} values,
3132 * as performed by the numeric and atomic update access modes, differ
3133 * from the primitive {@code ==} operator and the {@link Float#equals}
3134 * and {@link Double#equals} methods, specifically with respect to
3135 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3136 * Care should be taken when performing a compare and set or a compare
3137 * and exchange operation with such values since the operation may
3138 * unexpectedly fail.
3139 * There are many possible NaN values that are considered to be
3140 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3141 * provided by Java can distinguish between them. Operation failure can
3142 * occur if the expected or witness value is a NaN value and it is
3143 * transformed (perhaps in a platform specific manner) into another NaN
3144 * value, and thus has a different bitwise representation (see
3145 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3146 * details).
3147 * The values {@code -0.0} and {@code +0.0} have different bitwise
3148 * representations but are considered equal when using the primitive
3149 * {@code ==} operator. Operation failure can occur if, for example, a
3150 * numeric algorithm computes an expected value to be say {@code -0.0}
3151 * and previously computed the witness value to be say {@code +0.0}.
3152 * @param decl the class that declares the static field
3153 * @param name the field's name
3154 * @param type the field's type, of type {@code T}
3155 * @return a VarHandle giving access to a static field
3156 * @throws NoSuchFieldException if the field does not exist
3157 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3158 * @throws NullPointerException if any argument is null
3159 * @since 9
3160 */
3161 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3162 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
3163 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
3164 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
3165 }
3166
3167 /**
3168 * Produces an early-bound method handle for a non-static method.
3169 * The receiver must have a supertype {@code defc} in which a method
3170 * of the given name and type is accessible to the lookup class.
3171 * The method and all its argument types must be accessible to the lookup object.
3172 * The type of the method handle will be that of the method,
3173 * without any insertion of an additional receiver parameter.
3174 * The given receiver will be bound into the method handle,
3175 * so that every call to the method handle will invoke the
3176 * requested method on the given receiver.
3177 * <p>
3178 * The returned method handle will have
3179 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3180 * the method's variable arity modifier bit ({@code 0x0080}) is set
3181 * <em>and</em> the trailing array argument is not the only argument.
3182 * (If the trailing array argument is the only argument,
3183 * the given receiver value will be bound to it.)
3184 * <p>
3185 * This is almost equivalent to the following code, with some differences noted below:
3186 * {@snippet lang="java" :
3187 import static java.lang.invoke.MethodHandles.*;
3188 import static java.lang.invoke.MethodType.*;
3189 ...
3190 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
3191 MethodHandle mh1 = mh0.bindTo(receiver);
3192 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
3193 return mh1;
3194 * }
3195 * where {@code defc} is either {@code receiver.getClass()} or a super
3196 * type of that class, in which the requested method is accessible
3197 * to the lookup class.
3198 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
3199 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
3200 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
3201 * the receiver is restricted by {@code findVirtual} to the lookup class.)
3202 * @param receiver the object from which the method is accessed
3203 * @param name the name of the method
3204 * @param type the type of the method, with the receiver argument omitted
3205 * @return the desired method handle
3206 * @throws NoSuchMethodException if the method does not exist
3207 * @throws IllegalAccessException if access checking fails
3208 * or if the method's variable arity modifier bit
3209 * is set and {@code asVarargsCollector} fails
3210 * @throws NullPointerException if any argument is null
3211 * @see MethodHandle#bindTo
3212 * @see #findVirtual
3213 */
3214 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3215 Class<? extends Object> refc = receiver.getClass(); // may get NPE
3216 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
3217 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method));
3218 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
3219 throw new IllegalAccessException("The restricted defining class " +
3220 mh.type().leadingReferenceParameter().getName() +
3221 " is not assignable from receiver class " +
3222 receiver.getClass().getName());
3223 }
3224 return mh.bindArgumentL(0, receiver).setVarargs(method);
3225 }
3226
3227 /**
3228 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3229 * to <i>m</i>, if the lookup class has permission.
3230 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
3231 * If <i>m</i> is virtual, overriding is respected on every call.
3232 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
3233 * The type of the method handle will be that of the method,
3234 * with the receiver type prepended (but only if it is non-static).
3235 * If the method's {@code accessible} flag is not set,
3236 * access checking is performed immediately on behalf of the lookup class.
3237 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
3238 * <p>
3239 * The returned method handle will have
3240 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3241 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3242 * <p>
3243 * If <i>m</i> is static, and
3244 * if the returned method handle is invoked, the method's class will
3245 * be initialized, if it has not already been initialized.
3246 * @param m the reflected method
3247 * @return a method handle which can invoke the reflected method
3248 * @throws IllegalAccessException if access checking fails
3249 * or if the method's variable arity modifier bit
3250 * is set and {@code asVarargsCollector} fails
3251 * @throws NullPointerException if the argument is null
3252 */
3253 public MethodHandle unreflect(Method m) throws IllegalAccessException {
3254 if (m.getDeclaringClass() == MethodHandle.class) {
3255 MethodHandle mh = unreflectForMH(m);
3256 if (mh != null) return mh;
3257 }
3258 if (m.getDeclaringClass() == VarHandle.class) {
3259 MethodHandle mh = unreflectForVH(m);
3260 if (mh != null) return mh;
3261 }
3262 MemberName method = new MemberName(m);
3263 byte refKind = method.getReferenceKind();
3264 if (refKind == REF_invokeSpecial)
3265 refKind = REF_invokeVirtual;
3266 assert(method.isMethod());
3267 @SuppressWarnings("deprecation")
3268 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
3269 return lookup.getDirectMethod(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3270 }
3271 private MethodHandle unreflectForMH(Method m) {
3272 // these names require special lookups because they throw UnsupportedOperationException
3273 if (MemberName.isMethodHandleInvokeName(m.getName()))
3274 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
3275 return null;
3276 }
3277 private MethodHandle unreflectForVH(Method m) {
3278 // these names require special lookups because they throw UnsupportedOperationException
3279 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
3280 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
3281 return null;
3282 }
3283
3284 /**
3285 * Produces a method handle for a reflected method.
3286 * It will bypass checks for overriding methods on the receiver,
3287 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3288 * instruction from within the explicitly specified {@code specialCaller}.
3289 * The type of the method handle will be that of the method,
3290 * with a suitably restricted receiver type prepended.
3291 * (The receiver type will be {@code specialCaller} or a subtype.)
3292 * If the method's {@code accessible} flag is not set,
3293 * access checking is performed immediately on behalf of the lookup class,
3294 * as if {@code invokespecial} instruction were being linked.
3295 * <p>
3296 * Before method resolution,
3297 * if the explicitly specified caller class is not identical with the
3298 * lookup class, or if this lookup object does not have
3299 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3300 * privileges, the access fails.
3301 * <p>
3302 * The returned method handle will have
3303 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3304 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3305 * @param m the reflected method
3306 * @param specialCaller the class nominally calling the method
3307 * @return a method handle which can invoke the reflected method
3308 * @throws IllegalAccessException if access checking fails,
3309 * or if the method is {@code static},
3310 * or if the method's variable arity modifier bit
3311 * is set and {@code asVarargsCollector} fails
3312 * @throws NullPointerException if any argument is null
3313 */
3314 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
3315 checkSpecialCaller(specialCaller, m.getDeclaringClass());
3316 Lookup specialLookup = this.in(specialCaller);
3317 MemberName method = new MemberName(m, true);
3318 assert(method.isMethod());
3319 // ignore m.isAccessible: this is a new kind of access
3320 return specialLookup.getDirectMethod(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3321 }
3322
3323 /**
3324 * Produces a method handle for a reflected constructor.
3325 * The type of the method handle will be that of the constructor,
3326 * with the return type changed to the declaring class.
3327 * The method handle will perform a {@code newInstance} operation,
3328 * creating a new instance of the constructor's class on the
3329 * arguments passed to the method handle.
3330 * <p>
3331 * If the constructor's {@code accessible} flag is not set,
3332 * access checking is performed immediately on behalf of the lookup class.
3333 * <p>
3334 * The returned method handle will have
3335 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3336 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
3337 * <p>
3338 * If the returned method handle is invoked, the constructor's class will
3339 * be initialized, if it has not already been initialized.
3340 * @param c the reflected constructor
3341 * @return a method handle which can invoke the reflected constructor
3342 * @throws IllegalAccessException if access checking fails
3343 * or if the method's variable arity modifier bit
3344 * is set and {@code asVarargsCollector} fails
3345 * @throws NullPointerException if the argument is null
3346 */
3347 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
3348 MemberName ctor = new MemberName(c);
3349 assert(ctor.isConstructor());
3350 @SuppressWarnings("deprecation")
3351 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
3352 return lookup.getDirectConstructor(ctor.getDeclaringClass(), ctor);
3353 }
3354
3355 /*
3356 * Produces a method handle that is capable of creating instances of the given class
3357 * and instantiated by the given constructor.
3358 *
3359 * This method should only be used by ReflectionFactory::newConstructorForSerialization.
3360 */
3361 /* package-private */ MethodHandle serializableConstructor(Class<?> decl, Constructor<?> c) throws IllegalAccessException {
3362 MemberName ctor = new MemberName(c);
3363 assert(ctor.isConstructor() && constructorInSuperclass(decl, c));
3364 checkAccess(REF_newInvokeSpecial, decl, ctor);
3365 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3366 return DirectMethodHandle.makeAllocator(decl, ctor).setVarargs(ctor);
3367 }
3368
3369 private static boolean constructorInSuperclass(Class<?> decl, Constructor<?> ctor) {
3370 if (decl == ctor.getDeclaringClass())
3371 return true;
3372
3373 Class<?> cl = decl;
3374 while ((cl = cl.getSuperclass()) != null) {
3375 if (cl == ctor.getDeclaringClass()) {
3376 return true;
3377 }
3378 }
3379 return false;
3380 }
3381
3382 /**
3383 * Produces a method handle giving read access to a reflected field.
3384 * The type of the method handle will have a return type of the field's
3385 * value type.
3386 * If the field is {@code static}, the method handle will take no arguments.
3387 * Otherwise, its single argument will be the instance containing
3388 * the field.
3389 * If the {@code Field} object's {@code accessible} flag is not set,
3390 * access checking is performed immediately on behalf of the lookup class.
3391 * <p>
3392 * If the field is static, and
3393 * if the returned method handle is invoked, the field's class will
3394 * be initialized, if it has not already been initialized.
3395 * @param f the reflected field
3396 * @return a method handle which can load values from the reflected field
3397 * @throws IllegalAccessException if access checking fails
3398 * @throws NullPointerException if the argument is null
3399 */
3400 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
3401 return unreflectField(f, false);
3402 }
3403
3404 /**
3405 * Produces a method handle giving write access to a reflected field.
3406 * The type of the method handle will have a void return type.
3407 * If the field is {@code static}, the method handle will take a single
3408 * argument, of the field's value type, the value to be stored.
3409 * Otherwise, the two arguments will be the instance containing
3410 * the field, and the value to be stored.
3411 * If the {@code Field} object's {@code accessible} flag is not set,
3412 * access checking is performed immediately on behalf of the lookup class.
3413 * <p>
3414 * If the field is {@code final}, write access will not be
3415 * allowed and access checking will fail, except under certain
3416 * narrow circumstances documented for {@link Field#set Field.set}.
3417 * A method handle is returned only if a corresponding call to
3418 * the {@code Field} object's {@code set} method could return
3419 * normally. In particular, fields which are both {@code static}
3420 * and {@code final} may never be set.
3421 * <p>
3422 * If the field is {@code static}, and
3423 * if the returned method handle is invoked, the field's class will
3424 * be initialized, if it has not already been initialized.
3425 * @param f the reflected field
3426 * @return a method handle which can store values into the reflected field
3427 * @throws IllegalAccessException if access checking fails,
3428 * or if the field is {@code final} and write access
3429 * is not enabled on the {@code Field} object
3430 * @throws NullPointerException if the argument is null
3431 */
3432 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
3433 return unreflectField(f, true);
3434 }
3435
3436 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
3437 MemberName field = new MemberName(f, isSetter);
3438 if (isSetter && field.isFinal()) {
3439 if (field.isTrustedFinalField()) {
3440 String msg = field.isStatic() ? "static final field has no write access"
3441 : "final field has no write access";
3442 throw field.makeAccessException(msg, this);
3443 }
3444 }
3445 assert(isSetter
3446 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
3447 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
3448 @SuppressWarnings("deprecation")
3449 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
3450 return lookup.getDirectField(field.getReferenceKind(), f.getDeclaringClass(), field);
3451 }
3452
3453 /**
3454 * Produces a VarHandle giving access to a reflected field {@code f}
3455 * of type {@code T} declared in a class of type {@code R}.
3456 * The VarHandle's variable type is {@code T}.
3457 * If the field is non-static the VarHandle has one coordinate type,
3458 * {@code R}. Otherwise, the field is static, and the VarHandle has no
3459 * coordinate types.
3460 * <p>
3461 * Access checking is performed immediately on behalf of the lookup
3462 * class, regardless of the value of the field's {@code accessible}
3463 * flag.
3464 * <p>
3465 * If the field is static, and if the returned VarHandle is operated
3466 * on, the field's declaring class will be initialized, if it has not
3467 * already been initialized.
3468 * <p>
3469 * Certain access modes of the returned VarHandle are unsupported under
3470 * the following conditions:
3471 * <ul>
3472 * <li>if the field is declared {@code final}, then the write, atomic
3473 * update, numeric atomic update, and bitwise atomic update access
3474 * modes are unsupported.
3475 * <li>if the field type is anything other than {@code byte},
3476 * {@code short}, {@code char}, {@code int}, {@code long},
3477 * {@code float}, or {@code double} then numeric atomic update
3478 * access modes are unsupported.
3479 * <li>if the field type is anything other than {@code boolean},
3480 * {@code byte}, {@code short}, {@code char}, {@code int} or
3481 * {@code long} then bitwise atomic update access modes are
3482 * unsupported.
3483 * </ul>
3484 * <p>
3485 * If the field is declared {@code volatile} then the returned VarHandle
3486 * will override access to the field (effectively ignore the
3487 * {@code volatile} declaration) in accordance to its specified
3488 * access modes.
3489 * <p>
3490 * If the field type is {@code float} or {@code double} then numeric
3491 * and atomic update access modes compare values using their bitwise
3492 * representation (see {@link Float#floatToRawIntBits} and
3493 * {@link Double#doubleToRawLongBits}, respectively).
3494 * @apiNote
3495 * Bitwise comparison of {@code float} values or {@code double} values,
3496 * as performed by the numeric and atomic update access modes, differ
3497 * from the primitive {@code ==} operator and the {@link Float#equals}
3498 * and {@link Double#equals} methods, specifically with respect to
3499 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3500 * Care should be taken when performing a compare and set or a compare
3501 * and exchange operation with such values since the operation may
3502 * unexpectedly fail.
3503 * There are many possible NaN values that are considered to be
3504 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3505 * provided by Java can distinguish between them. Operation failure can
3506 * occur if the expected or witness value is a NaN value and it is
3507 * transformed (perhaps in a platform specific manner) into another NaN
3508 * value, and thus has a different bitwise representation (see
3509 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3510 * details).
3511 * The values {@code -0.0} and {@code +0.0} have different bitwise
3512 * representations but are considered equal when using the primitive
3513 * {@code ==} operator. Operation failure can occur if, for example, a
3514 * numeric algorithm computes an expected value to be say {@code -0.0}
3515 * and previously computed the witness value to be say {@code +0.0}.
3516 * @param f the reflected field, with a field of type {@code T}, and
3517 * a declaring class of type {@code R}
3518 * @return a VarHandle giving access to non-static fields or a static
3519 * field
3520 * @throws IllegalAccessException if access checking fails
3521 * @throws NullPointerException if the argument is null
3522 * @since 9
3523 */
3524 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
3525 MemberName getField = new MemberName(f, false);
3526 MemberName putField = new MemberName(f, true);
3527 return getFieldVarHandle(getField.getReferenceKind(), putField.getReferenceKind(),
3528 f.getDeclaringClass(), getField, putField);
3529 }
3530
3531 /**
3532 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3533 * created by this lookup object or a similar one.
3534 * Security and access checks are performed to ensure that this lookup object
3535 * is capable of reproducing the target method handle.
3536 * This means that the cracking may fail if target is a direct method handle
3537 * but was created by an unrelated lookup object.
3538 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
3539 * and was created by a lookup object for a different class.
3540 * @param target a direct method handle to crack into symbolic reference components
3541 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
3542 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
3543 * @throws NullPointerException if the target is {@code null}
3544 * @see MethodHandleInfo
3545 * @since 1.8
3546 */
3547 public MethodHandleInfo revealDirect(MethodHandle target) {
3548 if (!target.isCrackable()) {
3549 throw newIllegalArgumentException("not a direct method handle");
3550 }
3551 MemberName member = target.internalMemberName();
3552 Class<?> defc = member.getDeclaringClass();
3553 byte refKind = member.getReferenceKind();
3554 assert(MethodHandleNatives.refKindIsValid(refKind));
3555 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
3556 // Devirtualized method invocation is usually formally virtual.
3557 // To avoid creating extra MemberName objects for this common case,
3558 // we encode this extra degree of freedom using MH.isInvokeSpecial.
3559 refKind = REF_invokeVirtual;
3560 if (refKind == REF_invokeVirtual && defc.isInterface())
3561 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
3562 refKind = REF_invokeInterface;
3563 // Check member access before cracking.
3564 try {
3565 checkAccess(refKind, defc, member);
3566 } catch (IllegalAccessException ex) {
3567 throw new IllegalArgumentException(ex);
3568 }
3569 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
3570 Class<?> callerClass = target.internalCallerClass();
3571 if ((lookupModes() & ORIGINAL) == 0 || callerClass != lookupClass())
3572 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
3573 }
3574 // Produce the handle to the results.
3575 return new InfoFromMemberName(this, member, refKind);
3576 }
3577
3578 //--- Helper methods, all package-private.
3579
3580 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3581 checkSymbolicClass(refc); // do this before attempting to resolve
3582 Objects.requireNonNull(name);
3583 Objects.requireNonNull(type);
3584 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3585 NoSuchFieldException.class);
3586 }
3587
3588 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3589 checkSymbolicClass(refc); // do this before attempting to resolve
3590 Objects.requireNonNull(type);
3591 checkMethodName(refKind, name); // implicit null-check of name
3592 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3593 NoSuchMethodException.class);
3594 }
3595
3596 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
3597 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
3598 Objects.requireNonNull(member.getName());
3599 Objects.requireNonNull(member.getType());
3600 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), allowedModes,
3601 ReflectiveOperationException.class);
3602 }
3603
3604 MemberName resolveOrNull(byte refKind, MemberName member) {
3605 // do this before attempting to resolve
3606 if (!isClassAccessible(member.getDeclaringClass())) {
3607 return null;
3608 }
3609 Objects.requireNonNull(member.getName());
3610 Objects.requireNonNull(member.getType());
3611 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull(), allowedModes);
3612 }
3613
3614 MemberName resolveOrNull(byte refKind, Class<?> refc, String name, MethodType type) {
3615 // do this before attempting to resolve
3616 if (!isClassAccessible(refc)) {
3617 return null;
3618 }
3619 Objects.requireNonNull(type);
3620 // implicit null-check of name
3621 if (name.startsWith("<") && refKind != REF_newInvokeSpecial) {
3622 return null;
3623 }
3624 return IMPL_NAMES.resolveOrNull(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes);
3625 }
3626
3627 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
3628 if (!isClassAccessible(refc)) {
3629 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
3630 }
3631 }
3632
3633 boolean isClassAccessible(Class<?> refc) {
3634 Objects.requireNonNull(refc);
3635 Class<?> caller = lookupClassOrNull();
3636 Class<?> type = refc;
3637 while (type.isArray()) {
3638 type = type.getComponentType();
3639 }
3640 return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes);
3641 }
3642
3643 /** Check name for an illegal leading "<" character. */
3644 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
3645 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
3646 throw new NoSuchMethodException("illegal method name: "+name);
3647 }
3648
3649 /**
3650 * Find my trustable caller class if m is a caller sensitive method.
3651 * If this lookup object has original full privilege access, then the caller class is the lookupClass.
3652 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
3653 */
3654 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException {
3655 if (MethodHandleNatives.isCallerSensitive(m) && (lookupModes() & ORIGINAL) == 0) {
3656 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods
3657 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3658 }
3659 return this;
3660 }
3661
3662 /**
3663 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3664 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3665 *
3666 * @deprecated This method was originally designed to test {@code PRIVATE} access
3667 * that implies full privilege access but {@code MODULE} access has since become
3668 * independent of {@code PRIVATE} access. It is recommended to call
3669 * {@link #hasFullPrivilegeAccess()} instead.
3670 * @since 9
3671 */
3672 @Deprecated(since="14")
3673 public boolean hasPrivateAccess() {
3674 return hasFullPrivilegeAccess();
3675 }
3676
3677 /**
3678 * Returns {@code true} if this lookup has <em>full privilege access</em>,
3679 * i.e. {@code PRIVATE} and {@code MODULE} access.
3680 * A {@code Lookup} object must have full privilege access in order to
3681 * access all members that are allowed to the
3682 * {@linkplain #lookupClass() lookup class}.
3683 *
3684 * @return {@code true} if this lookup has full privilege access.
3685 * @since 14
3686 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a>
3687 */
3688 public boolean hasFullPrivilegeAccess() {
3689 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE);
3690 }
3691
3692 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3693 boolean wantStatic = (refKind == REF_invokeStatic);
3694 String message;
3695 if (m.isConstructor())
3696 message = "expected a method, not a constructor";
3697 else if (!m.isMethod())
3698 message = "expected a method";
3699 else if (wantStatic != m.isStatic())
3700 message = wantStatic ? "expected a static method" : "expected a non-static method";
3701 else
3702 { checkAccess(refKind, refc, m); return; }
3703 throw m.makeAccessException(message, this);
3704 }
3705
3706 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3707 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
3708 String message;
3709 if (wantStatic != m.isStatic())
3710 message = wantStatic ? "expected a static field" : "expected a non-static field";
3711 else
3712 { checkAccess(refKind, refc, m); return; }
3713 throw m.makeAccessException(message, this);
3714 }
3715
3716 private boolean isArrayClone(byte refKind, Class<?> refc, MemberName m) {
3717 return Modifier.isProtected(m.getModifiers()) &&
3718 refKind == REF_invokeVirtual &&
3719 m.getDeclaringClass() == Object.class &&
3720 m.getName().equals("clone") &&
3721 refc.isArray();
3722 }
3723
3724 /** Check public/protected/private bits on the symbolic reference class and its member. */
3725 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3726 assert(m.referenceKindIsConsistentWith(refKind) &&
3727 MethodHandleNatives.refKindIsValid(refKind) &&
3728 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
3729 int allowedModes = this.allowedModes;
3730 if (allowedModes == TRUSTED) return;
3731 int mods = m.getModifiers();
3732 if (isArrayClone(refKind, refc, m)) {
3733 // The JVM does this hack also.
3734 // (See ClassVerifier::verify_invoke_instructions
3735 // and LinkResolver::check_method_accessability.)
3736 // Because the JVM does not allow separate methods on array types,
3737 // there is no separate method for int[].clone.
3738 // All arrays simply inherit Object.clone.
3739 // But for access checking logic, we make Object.clone
3740 // (normally protected) appear to be public.
3741 // Later on, when the DirectMethodHandle is created,
3742 // its leading argument will be restricted to the
3743 // requested array type.
3744 // N.B. The return type is not adjusted, because
3745 // that is *not* the bytecode behavior.
3746 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
3747 }
3748 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
3749 // cannot "new" a protected ctor in a different package
3750 mods ^= Modifier.PROTECTED;
3751 }
3752 if (Modifier.isFinal(mods) &&
3753 MethodHandleNatives.refKindIsSetter(refKind))
3754 throw m.makeAccessException("unexpected set of a final field", this);
3755 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
3756 if ((requestedModes & allowedModes) != 0) {
3757 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
3758 mods, lookupClass(), previousLookupClass(), allowedModes))
3759 return;
3760 } else {
3761 // Protected members can also be checked as if they were package-private.
3762 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
3763 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
3764 return;
3765 }
3766 throw m.makeAccessException(accessFailedMessage(refc, m), this);
3767 }
3768
3769 String accessFailedMessage(Class<?> refc, MemberName m) {
3770 Class<?> defc = m.getDeclaringClass();
3771 int mods = m.getModifiers();
3772 // check the class first:
3773 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
3774 (defc == refc ||
3775 Modifier.isPublic(refc.getModifiers())));
3776 if (!classOK && (allowedModes & PACKAGE) != 0) {
3777 // ignore previous lookup class to check if default package access
3778 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
3779 (defc == refc ||
3780 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
3781 }
3782 if (!classOK)
3783 return "class is not public";
3784 if (Modifier.isPublic(mods))
3785 return "access to public member failed"; // (how?, module not readable?)
3786 if (Modifier.isPrivate(mods))
3787 return "member is private";
3788 if (Modifier.isProtected(mods))
3789 return "member is protected";
3790 return "member is private to package";
3791 }
3792
3793 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
3794 int allowedModes = this.allowedModes;
3795 if (allowedModes == TRUSTED) return;
3796 if ((lookupModes() & PRIVATE) == 0
3797 || (specialCaller != lookupClass()
3798 // ensure non-abstract methods in superinterfaces can be special-invoked
3799 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
3800 throw new MemberName(specialCaller).
3801 makeAccessException("no private access for invokespecial", this);
3802 }
3803
3804 private boolean restrictProtectedReceiver(MemberName method) {
3805 // The accessing class only has the right to use a protected member
3806 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
3807 if (!method.isProtected() || method.isStatic()
3808 || allowedModes == TRUSTED
3809 || method.getDeclaringClass() == lookupClass()
3810 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
3811 return false;
3812 return true;
3813 }
3814 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
3815 assert(!method.isStatic());
3816 // receiver type of mh is too wide; narrow to caller
3817 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
3818 throw method.makeAccessException("caller class must be a subclass below the method", caller);
3819 }
3820 MethodType rawType = mh.type();
3821 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
3822 MethodType narrowType = rawType.changeParameterType(0, caller);
3823 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
3824 assert(mh.viewAsTypeChecks(narrowType, true));
3825 return mh.copyWith(narrowType, mh.form);
3826 }
3827
3828 /** Check access and get the requested method. */
3829 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3830 final boolean doRestrict = true;
3831 return getDirectMethodCommon(refKind, refc, method, doRestrict, callerLookup);
3832 }
3833 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
3834 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3835 final boolean doRestrict = false;
3836 return getDirectMethodCommon(REF_invokeSpecial, refc, method, doRestrict, callerLookup);
3837 }
3838 /** Common code for all methods; do not call directly except from immediately above. */
3839 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
3840 boolean doRestrict,
3841 Lookup boundCaller) throws IllegalAccessException {
3842 checkMethod(refKind, refc, method);
3843 assert(!method.isMethodHandleInvoke());
3844
3845 if (refKind == REF_invokeSpecial &&
3846 refc != lookupClass() &&
3847 !refc.isInterface() && !lookupClass().isInterface() &&
3848 refc != lookupClass().getSuperclass() &&
3849 refc.isAssignableFrom(lookupClass())) {
3850 assert(!method.getName().equals(ConstantDescs.INIT_NAME)); // not this code path
3851
3852 // Per JVMS 6.5, desc. of invokespecial instruction:
3853 // If the method is in a superclass of the LC,
3854 // and if our original search was above LC.super,
3855 // repeat the search (symbolic lookup) from LC.super
3856 // and continue with the direct superclass of that class,
3857 // and so forth, until a match is found or no further superclasses exist.
3858 // FIXME: MemberName.resolve should handle this instead.
3859 Class<?> refcAsSuper = lookupClass();
3860 MemberName m2;
3861 do {
3862 refcAsSuper = refcAsSuper.getSuperclass();
3863 m2 = new MemberName(refcAsSuper,
3864 method.getName(),
3865 method.getMethodType(),
3866 REF_invokeSpecial);
3867 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull(), allowedModes);
3868 } while (m2 == null && // no method is found yet
3869 refc != refcAsSuper); // search up to refc
3870 if (m2 == null) throw new InternalError(method.toString());
3871 method = m2;
3872 refc = refcAsSuper;
3873 // redo basic checks
3874 checkMethod(refKind, refc, method);
3875 }
3876 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
3877 MethodHandle mh = dmh;
3878 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
3879 if ((doRestrict && refKind == REF_invokeSpecial) ||
3880 (MethodHandleNatives.refKindHasReceiver(refKind) &&
3881 restrictProtectedReceiver(method) &&
3882 // All arrays simply inherit the protected Object.clone method.
3883 // The leading argument is already restricted to the requested
3884 // array type (not the lookup class).
3885 !isArrayClone(refKind, refc, method))) {
3886 mh = restrictReceiver(method, dmh, lookupClass());
3887 }
3888 mh = maybeBindCaller(method, mh, boundCaller);
3889 mh = mh.setVarargs(method);
3890 return mh;
3891 }
3892 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller)
3893 throws IllegalAccessException {
3894 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
3895 return mh;
3896
3897 // boundCaller must have full privilege access.
3898 // It should have been checked by findBoundCallerLookup. Safe to check this again.
3899 if ((boundCaller.lookupModes() & ORIGINAL) == 0)
3900 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3901
3902 assert boundCaller.hasFullPrivilegeAccess();
3903
3904 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass);
3905 // Note: caller will apply varargs after this step happens.
3906 return cbmh;
3907 }
3908
3909 /** Check access and get the requested field. */
3910 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3911 return getDirectFieldCommon(refKind, refc, field);
3912 }
3913 /** Common code for all fields; do not call directly except from immediately above. */
3914 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3915 checkField(refKind, refc, field);
3916 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
3917 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
3918 restrictProtectedReceiver(field));
3919 if (doRestrict)
3920 return restrictReceiver(field, dmh, lookupClass());
3921 return dmh;
3922 }
3923 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
3924 Class<?> refc, MemberName getField, MemberName putField)
3925 throws IllegalAccessException {
3926 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField);
3927 }
3928 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
3929 Class<?> refc, MemberName getField,
3930 MemberName putField) throws IllegalAccessException {
3931 assert getField.isStatic() == putField.isStatic();
3932 assert getField.isGetter() && putField.isSetter();
3933 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
3934 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
3935
3936 checkField(getRefKind, refc, getField);
3937
3938 if (!putField.isFinal()) {
3939 // A VarHandle does not support updates to final fields, any
3940 // such VarHandle to a final field will be read-only and
3941 // therefore the following write-based accessibility checks are
3942 // only required for non-final fields
3943 checkField(putRefKind, refc, putField);
3944 }
3945
3946 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
3947 restrictProtectedReceiver(getField));
3948 if (doRestrict) {
3949 assert !getField.isStatic();
3950 // receiver type of VarHandle is too wide; narrow to caller
3951 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
3952 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
3953 }
3954 refc = lookupClass();
3955 }
3956 return VarHandles.makeFieldHandle(getField, refc,
3957 this.allowedModes == TRUSTED && !getField.isTrustedFinalField());
3958 }
3959 /** Check access and get the requested constructor. */
3960 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3961 return getDirectConstructorCommon(refc, ctor);
3962 }
3963 /** Common code for all constructors; do not call directly except from immediately above. */
3964 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3965 assert(ctor.isConstructor());
3966 checkAccess(REF_newInvokeSpecial, refc, ctor);
3967 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3968 return DirectMethodHandle.make(ctor).setVarargs(ctor);
3969 }
3970
3971 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
3972 */
3973 /*non-public*/
3974 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
3975 throws ReflectiveOperationException {
3976 if (!(type instanceof Class || type instanceof MethodType))
3977 throw new InternalError("unresolved MemberName");
3978 MemberName member = new MemberName(refKind, defc, name, type);
3979 MethodHandle mh = LOOKASIDE_TABLE.get(member);
3980 if (mh != null) {
3981 checkSymbolicClass(defc);
3982 return mh;
3983 }
3984 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
3985 // Treat MethodHandle.invoke and invokeExact specially.
3986 mh = findVirtualForMH(member.getName(), member.getMethodType());
3987 if (mh != null) {
3988 return mh;
3989 }
3990 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
3991 // Treat signature-polymorphic methods on VarHandle specially.
3992 mh = findVirtualForVH(member.getName(), member.getMethodType());
3993 if (mh != null) {
3994 return mh;
3995 }
3996 }
3997 MemberName resolved = resolveOrFail(refKind, member);
3998 mh = getDirectMethodForConstant(refKind, defc, resolved);
3999 if (mh instanceof DirectMethodHandle dmh
4000 && canBeCached(refKind, defc, resolved)) {
4001 MemberName key = mh.internalMemberName();
4002 if (key != null) {
4003 key = key.asNormalOriginal();
4004 }
4005 if (member.equals(key)) { // better safe than sorry
4006 LOOKASIDE_TABLE.put(key, dmh);
4007 }
4008 }
4009 return mh;
4010 }
4011 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
4012 if (refKind == REF_invokeSpecial) {
4013 return false;
4014 }
4015 if (!Modifier.isPublic(defc.getModifiers()) ||
4016 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
4017 !member.isPublic() ||
4018 member.isCallerSensitive()) {
4019 return false;
4020 }
4021 ClassLoader loader = defc.getClassLoader();
4022 if (loader != null) {
4023 ClassLoader sysl = ClassLoader.getSystemClassLoader();
4024 boolean found = false;
4025 while (sysl != null) {
4026 if (loader == sysl) { found = true; break; }
4027 sysl = sysl.getParent();
4028 }
4029 if (!found) {
4030 return false;
4031 }
4032 }
4033 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
4034 new MemberName(refKind, defc, member.getName(), member.getType()));
4035 if (resolved2 == null) {
4036 return false;
4037 }
4038 return true;
4039 }
4040 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
4041 throws ReflectiveOperationException {
4042 if (MethodHandleNatives.refKindIsField(refKind)) {
4043 return getDirectField(refKind, defc, member);
4044 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
4045 return getDirectMethod(refKind, defc, member, findBoundCallerLookup(member));
4046 } else if (refKind == REF_newInvokeSpecial) {
4047 return getDirectConstructor(defc, member);
4048 }
4049 // oops
4050 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
4051 }
4052
4053 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
4054 }
4055
4056 /**
4057 * Produces a method handle constructing arrays of a desired type,
4058 * as if by the {@code anewarray} bytecode.
4059 * The return type of the method handle will be the array type.
4060 * The type of its sole argument will be {@code int}, which specifies the size of the array.
4061 *
4062 * <p> If the returned method handle is invoked with a negative
4063 * array size, a {@code NegativeArraySizeException} will be thrown.
4064 *
4065 * @param arrayClass an array type
4066 * @return a method handle which can create arrays of the given type
4067 * @throws NullPointerException if the argument is {@code null}
4068 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
4069 * @see java.lang.reflect.Array#newInstance(Class, int)
4070 * @jvms 6.5 {@code anewarray} Instruction
4071 * @since 9
4072 */
4073 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
4074 if (!arrayClass.isArray()) {
4075 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
4076 }
4077 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
4078 bindTo(arrayClass.getComponentType());
4079 return ani.asType(ani.type().changeReturnType(arrayClass));
4080 }
4081
4082 /**
4083 * Produces a method handle returning the length of an array,
4084 * as if by the {@code arraylength} bytecode.
4085 * The type of the method handle will have {@code int} as return type,
4086 * and its sole argument will be the array type.
4087 *
4088 * <p> If the returned method handle is invoked with a {@code null}
4089 * array reference, a {@code NullPointerException} will be thrown.
4090 *
4091 * @param arrayClass an array type
4092 * @return a method handle which can retrieve the length of an array of the given array type
4093 * @throws NullPointerException if the argument is {@code null}
4094 * @throws IllegalArgumentException if arrayClass is not an array type
4095 * @jvms 6.5 {@code arraylength} Instruction
4096 * @since 9
4097 */
4098 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
4099 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
4100 }
4101
4102 /**
4103 * Produces a method handle giving read access to elements of an array,
4104 * as if by the {@code aaload} bytecode.
4105 * The type of the method handle will have a return type of the array's
4106 * element type. Its first argument will be the array type,
4107 * and the second will be {@code int}.
4108 *
4109 * <p> When the returned method handle is invoked,
4110 * the array reference and array index are checked.
4111 * A {@code NullPointerException} will be thrown if the array reference
4112 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4113 * thrown if the index is negative or if it is greater than or equal to
4114 * the length of the array.
4115 *
4116 * @param arrayClass an array type
4117 * @return a method handle which can load values from the given array type
4118 * @throws NullPointerException if the argument is null
4119 * @throws IllegalArgumentException if arrayClass is not an array type
4120 * @jvms 6.5 {@code aaload} Instruction
4121 */
4122 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
4123 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
4124 }
4125
4126 /**
4127 * Produces a method handle giving write access to elements of an array,
4128 * as if by the {@code astore} bytecode.
4129 * The type of the method handle will have a void return type.
4130 * Its last argument will be the array's element type.
4131 * The first and second arguments will be the array type and int.
4132 *
4133 * <p> When the returned method handle is invoked,
4134 * the array reference and array index are checked.
4135 * A {@code NullPointerException} will be thrown if the array reference
4136 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4137 * thrown if the index is negative or if it is greater than or equal to
4138 * the length of the array.
4139 *
4140 * @param arrayClass the class of an array
4141 * @return a method handle which can store values into the array type
4142 * @throws NullPointerException if the argument is null
4143 * @throws IllegalArgumentException if arrayClass is not an array type
4144 * @jvms 6.5 {@code aastore} Instruction
4145 */
4146 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
4147 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
4148 }
4149
4150 /**
4151 * Produces a VarHandle giving access to elements of an array of type
4152 * {@code arrayClass}. The VarHandle's variable type is the component type
4153 * of {@code arrayClass} and the list of coordinate types is
4154 * {@code (arrayClass, int)}, where the {@code int} coordinate type
4155 * corresponds to an argument that is an index into an array.
4156 * <p>
4157 * Certain access modes of the returned VarHandle are unsupported under
4158 * the following conditions:
4159 * <ul>
4160 * <li>if the component type is anything other than {@code byte},
4161 * {@code short}, {@code char}, {@code int}, {@code long},
4162 * {@code float}, or {@code double} then numeric atomic update access
4163 * modes are unsupported.
4164 * <li>if the component type is anything other than {@code boolean},
4165 * {@code byte}, {@code short}, {@code char}, {@code int} or
4166 * {@code long} then bitwise atomic update access modes are
4167 * unsupported.
4168 * </ul>
4169 * <p>
4170 * If the component type is {@code float} or {@code double} then numeric
4171 * and atomic update access modes compare values using their bitwise
4172 * representation (see {@link Float#floatToRawIntBits} and
4173 * {@link Double#doubleToRawLongBits}, respectively).
4174 *
4175 * <p> When the returned {@code VarHandle} is invoked,
4176 * the array reference and array index are checked.
4177 * A {@code NullPointerException} will be thrown if the array reference
4178 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4179 * thrown if the index is negative or if it is greater than or equal to
4180 * the length of the array.
4181 *
4182 * @apiNote
4183 * Bitwise comparison of {@code float} values or {@code double} values,
4184 * as performed by the numeric and atomic update access modes, differ
4185 * from the primitive {@code ==} operator and the {@link Float#equals}
4186 * and {@link Double#equals} methods, specifically with respect to
4187 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
4188 * Care should be taken when performing a compare and set or a compare
4189 * and exchange operation with such values since the operation may
4190 * unexpectedly fail.
4191 * There are many possible NaN values that are considered to be
4192 * {@code NaN} in Java, although no IEEE 754 floating-point operation
4193 * provided by Java can distinguish between them. Operation failure can
4194 * occur if the expected or witness value is a NaN value and it is
4195 * transformed (perhaps in a platform specific manner) into another NaN
4196 * value, and thus has a different bitwise representation (see
4197 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
4198 * details).
4199 * The values {@code -0.0} and {@code +0.0} have different bitwise
4200 * representations but are considered equal when using the primitive
4201 * {@code ==} operator. Operation failure can occur if, for example, a
4202 * numeric algorithm computes an expected value to be say {@code -0.0}
4203 * and previously computed the witness value to be say {@code +0.0}.
4204 * @param arrayClass the class of an array, of type {@code T[]}
4205 * @return a VarHandle giving access to elements of an array
4206 * @throws NullPointerException if the arrayClass is null
4207 * @throws IllegalArgumentException if arrayClass is not an array type
4208 * @since 9
4209 */
4210 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
4211 return VarHandles.makeArrayElementHandle(arrayClass);
4212 }
4213
4214 /**
4215 * Produces a VarHandle giving access to elements of a {@code byte[]} array
4216 * viewed as if it were a different primitive array type, such as
4217 * {@code int[]} or {@code long[]}.
4218 * The VarHandle's variable type is the component type of
4219 * {@code viewArrayClass} and the list of coordinate types is
4220 * {@code (byte[], int)}, where the {@code int} coordinate type
4221 * corresponds to an argument that is an index into a {@code byte[]} array.
4222 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
4223 * array, composing bytes to or from a value of the component type of
4224 * {@code viewArrayClass} according to the given endianness.
4225 * <p>
4226 * The supported component types (variables types) are {@code short},
4227 * {@code char}, {@code int}, {@code long}, {@code float} and
4228 * {@code double}.
4229 * <p>
4230 * Access of bytes at a given index will result in an
4231 * {@code ArrayIndexOutOfBoundsException} if the index is less than {@code 0}
4232 * or greater than the {@code byte[]} array length minus the size (in bytes)
4233 * of {@code T}.
4234 * <p>
4235 * Only plain {@linkplain VarHandle.AccessMode#GET get} and {@linkplain VarHandle.AccessMode#SET set}
4236 * access modes are supported by the returned var handle. For all other access modes, an
4237 * {@link UnsupportedOperationException} will be thrown.
4238 *
4239 * @apiNote if access modes other than plain access are required, clients should
4240 * consider using off-heap memory through
4241 * {@linkplain java.nio.ByteBuffer#allocateDirect(int) direct byte buffers} or
4242 * off-heap {@linkplain java.lang.foreign.MemorySegment memory segments},
4243 * or memory segments backed by a
4244 * {@linkplain java.lang.foreign.MemorySegment#ofArray(long[]) {@code long[]}},
4245 * for which stronger alignment guarantees can be made.
4246 *
4247 * @param viewArrayClass the view array class, with a component type of
4248 * type {@code T}
4249 * @param byteOrder the endianness of the view array elements, as
4250 * stored in the underlying {@code byte} array
4251 * @return a VarHandle giving access to elements of a {@code byte[]} array
4252 * viewed as if elements corresponding to the components type of the view
4253 * array class
4254 * @throws NullPointerException if viewArrayClass or byteOrder is null
4255 * @throws IllegalArgumentException if viewArrayClass is not an array type
4256 * @throws UnsupportedOperationException if the component type of
4257 * viewArrayClass is not supported as a variable type
4258 * @since 9
4259 */
4260 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
4261 ByteOrder byteOrder) throws IllegalArgumentException {
4262 Objects.requireNonNull(byteOrder);
4263 return VarHandles.byteArrayViewHandle(viewArrayClass,
4264 byteOrder == ByteOrder.BIG_ENDIAN);
4265 }
4266
4267 /**
4268 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
4269 * viewed as if it were an array of elements of a different primitive
4270 * component type to that of {@code byte}, such as {@code int[]} or
4271 * {@code long[]}.
4272 * The VarHandle's variable type is the component type of
4273 * {@code viewArrayClass} and the list of coordinate types is
4274 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
4275 * corresponds to an argument that is an index into a {@code byte[]} array.
4276 * The returned VarHandle accesses bytes at an index in a
4277 * {@code ByteBuffer}, composing bytes to or from a value of the component
4278 * type of {@code viewArrayClass} according to the given endianness.
4279 * <p>
4280 * The supported component types (variables types) are {@code short},
4281 * {@code char}, {@code int}, {@code long}, {@code float} and
4282 * {@code double}.
4283 * <p>
4284 * Access will result in a {@code ReadOnlyBufferException} for anything
4285 * other than the read access modes if the {@code ByteBuffer} is read-only.
4286 * <p>
4287 * Access of bytes at a given index will result in an
4288 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
4289 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
4290 * {@code T}.
4291 * <p>
4292 * For heap byte buffers, access is always unaligned. As a result, only the plain
4293 * {@linkplain VarHandle.AccessMode#GET get}
4294 * and {@linkplain VarHandle.AccessMode#SET set} access modes are supported by the
4295 * returned var handle. For all other access modes, an {@link IllegalStateException}
4296 * will be thrown.
4297 * <p>
4298 * For direct buffers only, access of bytes at an index may be aligned or misaligned for {@code T},
4299 * with respect to the underlying memory address, {@code A} say, associated
4300 * with the {@code ByteBuffer} and index.
4301 * If access is misaligned then access for anything other than the
4302 * {@code get} and {@code set} access modes will result in an
4303 * {@code IllegalStateException}. In such cases atomic access is only
4304 * guaranteed with respect to the largest power of two that divides the GCD
4305 * of {@code A} and the size (in bytes) of {@code T}.
4306 * If access is aligned then following access modes are supported and are
4307 * guaranteed to support atomic access:
4308 * <ul>
4309 * <li>read write access modes for all {@code T}, with the exception of
4310 * access modes {@code get} and {@code set} for {@code long} and
4311 * {@code double} on 32-bit platforms.
4312 * <li>atomic update access modes for {@code int}, {@code long},
4313 * {@code float} or {@code double}.
4314 * (Future major platform releases of the JDK may support additional
4315 * types for certain currently unsupported access modes.)
4316 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4317 * (Future major platform releases of the JDK may support additional
4318 * numeric types for certain currently unsupported access modes.)
4319 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4320 * (Future major platform releases of the JDK may support additional
4321 * numeric types for certain currently unsupported access modes.)
4322 * </ul>
4323 * <p>
4324 * Misaligned access, and therefore atomicity guarantees, may be determined
4325 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
4326 * {@code index}, {@code T} and its corresponding boxed type,
4327 * {@code T_BOX}, as follows:
4328 * <pre>{@code
4329 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4330 * ByteBuffer bb = ...
4331 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
4332 * boolean isMisaligned = misalignedAtIndex != 0;
4333 * }</pre>
4334 * <p>
4335 * If the variable type is {@code float} or {@code double} then atomic
4336 * update access modes compare values using their bitwise representation
4337 * (see {@link Float#floatToRawIntBits} and
4338 * {@link Double#doubleToRawLongBits}, respectively).
4339 * @param viewArrayClass the view array class, with a component type of
4340 * type {@code T}
4341 * @param byteOrder the endianness of the view array elements, as
4342 * stored in the underlying {@code ByteBuffer} (Note this overrides the
4343 * endianness of a {@code ByteBuffer})
4344 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
4345 * viewed as if elements corresponding to the components type of the view
4346 * array class
4347 * @throws NullPointerException if viewArrayClass or byteOrder is null
4348 * @throws IllegalArgumentException if viewArrayClass is not an array type
4349 * @throws UnsupportedOperationException if the component type of
4350 * viewArrayClass is not supported as a variable type
4351 * @since 9
4352 */
4353 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
4354 ByteOrder byteOrder) throws IllegalArgumentException {
4355 Objects.requireNonNull(byteOrder);
4356 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
4357 byteOrder == ByteOrder.BIG_ENDIAN);
4358 }
4359
4360
4361 //--- method handle invocation (reflective style)
4362
4363 /**
4364 * Produces a method handle which will invoke any method handle of the
4365 * given {@code type}, with a given number of trailing arguments replaced by
4366 * a single trailing {@code Object[]} array.
4367 * The resulting invoker will be a method handle with the following
4368 * arguments:
4369 * <ul>
4370 * <li>a single {@code MethodHandle} target
4371 * <li>zero or more leading values (counted by {@code leadingArgCount})
4372 * <li>an {@code Object[]} array containing trailing arguments
4373 * </ul>
4374 * <p>
4375 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
4376 * the indicated {@code type}.
4377 * That is, if the target is exactly of the given {@code type}, it will behave
4378 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
4379 * is used to convert the target to the required {@code type}.
4380 * <p>
4381 * The type of the returned invoker will not be the given {@code type}, but rather
4382 * will have all parameters except the first {@code leadingArgCount}
4383 * replaced by a single array of type {@code Object[]}, which will be
4384 * the final parameter.
4385 * <p>
4386 * Before invoking its target, the invoker will spread the final array, apply
4387 * reference casts as necessary, and unbox and widen primitive arguments.
4388 * If, when the invoker is called, the supplied array argument does
4389 * not have the correct number of elements, the invoker will throw
4390 * an {@link IllegalArgumentException} instead of invoking the target.
4391 * <p>
4392 * This method is equivalent to the following code (though it may be more efficient):
4393 * {@snippet lang="java" :
4394 MethodHandle invoker = MethodHandles.invoker(type);
4395 int spreadArgCount = type.parameterCount() - leadingArgCount;
4396 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
4397 return invoker;
4398 * }
4399 * This method throws no reflective exceptions.
4400 * @param type the desired target type
4401 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
4402 * @return a method handle suitable for invoking any method handle of the given type
4403 * @throws NullPointerException if {@code type} is null
4404 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
4405 * the range from 0 to {@code type.parameterCount()} inclusive,
4406 * or if the resulting method handle's type would have
4407 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4408 */
4409 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
4410 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
4411 throw newIllegalArgumentException("bad argument count", leadingArgCount);
4412 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
4413 return type.invokers().spreadInvoker(leadingArgCount);
4414 }
4415
4416 /**
4417 * Produces a special <em>invoker method handle</em> which can be used to
4418 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
4419 * The resulting invoker will have a type which is
4420 * exactly equal to the desired type, except that it will accept
4421 * an additional leading argument of type {@code MethodHandle}.
4422 * <p>
4423 * This method is equivalent to the following code (though it may be more efficient):
4424 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
4425 *
4426 * <p style="font-size:smaller;">
4427 * <em>Discussion:</em>
4428 * Invoker method handles can be useful when working with variable method handles
4429 * of unknown types.
4430 * For example, to emulate an {@code invokeExact} call to a variable method
4431 * handle {@code M}, extract its type {@code T},
4432 * look up the invoker method {@code X} for {@code T},
4433 * and call the invoker method, as {@code X.invoke(T, A...)}.
4434 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
4435 * is unknown.)
4436 * If spreading, collecting, or other argument transformations are required,
4437 * they can be applied once to the invoker {@code X} and reused on many {@code M}
4438 * method handle values, as long as they are compatible with the type of {@code X}.
4439 * <p style="font-size:smaller;">
4440 * <em>(Note: The invoker method is not available via the Core Reflection API.
4441 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4442 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4443 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4444 * <p>
4445 * This method throws no reflective exceptions.
4446 * @param type the desired target type
4447 * @return a method handle suitable for invoking any method handle of the given type
4448 * @throws IllegalArgumentException if the resulting method handle's type would have
4449 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4450 */
4451 public static MethodHandle exactInvoker(MethodType type) {
4452 return type.invokers().exactInvoker();
4453 }
4454
4455 /**
4456 * Produces a special <em>invoker method handle</em> which can be used to
4457 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
4458 * The resulting invoker will have a type which is
4459 * exactly equal to the desired type, except that it will accept
4460 * an additional leading argument of type {@code MethodHandle}.
4461 * <p>
4462 * Before invoking its target, if the target differs from the expected type,
4463 * the invoker will apply reference casts as
4464 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
4465 * Similarly, the return value will be converted as necessary.
4466 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
4467 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
4468 * <p>
4469 * This method is equivalent to the following code (though it may be more efficient):
4470 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
4471 * <p style="font-size:smaller;">
4472 * <em>Discussion:</em>
4473 * A {@linkplain MethodType#genericMethodType general method type} is one which
4474 * mentions only {@code Object} arguments and return values.
4475 * An invoker for such a type is capable of calling any method handle
4476 * of the same arity as the general type.
4477 * <p style="font-size:smaller;">
4478 * <em>(Note: The invoker method is not available via the Core Reflection API.
4479 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4480 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4481 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4482 * <p>
4483 * This method throws no reflective exceptions.
4484 * @param type the desired target type
4485 * @return a method handle suitable for invoking any method handle convertible to the given type
4486 * @throws IllegalArgumentException if the resulting method handle's type would have
4487 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4488 */
4489 public static MethodHandle invoker(MethodType type) {
4490 return type.invokers().genericInvoker();
4491 }
4492
4493 /**
4494 * Produces a special <em>invoker method handle</em> which can be used to
4495 * invoke a signature-polymorphic access mode method on any VarHandle whose
4496 * associated access mode type is compatible with the given type.
4497 * The resulting invoker will have a type which is exactly equal to the
4498 * desired given type, except that it will accept an additional leading
4499 * argument of type {@code VarHandle}.
4500 *
4501 * @param accessMode the VarHandle access mode
4502 * @param type the desired target type
4503 * @return a method handle suitable for invoking an access mode method of
4504 * any VarHandle whose access mode type is of the given type.
4505 * @since 9
4506 */
4507 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4508 return type.invokers().varHandleMethodExactInvoker(accessMode);
4509 }
4510
4511 /**
4512 * Produces a special <em>invoker method handle</em> which can be used to
4513 * invoke a signature-polymorphic access mode method on any VarHandle whose
4514 * associated access mode type is compatible with the given type.
4515 * The resulting invoker will have a type which is exactly equal to the
4516 * desired given type, except that it will accept an additional leading
4517 * argument of type {@code VarHandle}.
4518 * <p>
4519 * Before invoking its target, if the access mode type differs from the
4520 * desired given type, the invoker will apply reference casts as necessary
4521 * and box, unbox, or widen primitive values, as if by
4522 * {@link MethodHandle#asType asType}. Similarly, the return value will be
4523 * converted as necessary.
4524 * <p>
4525 * This method is equivalent to the following code (though it may be more
4526 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
4527 *
4528 * @param accessMode the VarHandle access mode
4529 * @param type the desired target type
4530 * @return a method handle suitable for invoking an access mode method of
4531 * any VarHandle whose access mode type is convertible to the given
4532 * type.
4533 * @since 9
4534 */
4535 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4536 return type.invokers().varHandleMethodInvoker(accessMode);
4537 }
4538
4539 /*non-public*/
4540 static MethodHandle basicInvoker(MethodType type) {
4541 return type.invokers().basicInvoker();
4542 }
4543
4544 //--- method handle modification (creation from other method handles)
4545
4546 /**
4547 * Produces a method handle which adapts the type of the
4548 * given method handle to a new type by pairwise argument and return type conversion.
4549 * The original type and new type must have the same number of arguments.
4550 * The resulting method handle is guaranteed to report a type
4551 * which is equal to the desired new type.
4552 * <p>
4553 * If the original type and new type are equal, returns target.
4554 * <p>
4555 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
4556 * and some additional conversions are also applied if those conversions fail.
4557 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
4558 * if possible, before or instead of any conversions done by {@code asType}:
4559 * <ul>
4560 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
4561 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
4562 * (This treatment of interfaces follows the usage of the bytecode verifier.)
4563 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
4564 * the boolean is converted to a byte value, 1 for true, 0 for false.
4565 * (This treatment follows the usage of the bytecode verifier.)
4566 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
4567 * <em>T0</em> is converted to byte via Java casting conversion (JLS {@jls 5.5}),
4568 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
4569 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
4570 * then a Java casting conversion (JLS {@jls 5.5}) is applied.
4571 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
4572 * widening and/or narrowing.)
4573 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
4574 * conversion will be applied at runtime, possibly followed
4575 * by a Java casting conversion (JLS {@jls 5.5}) on the primitive value,
4576 * possibly followed by a conversion from byte to boolean by testing
4577 * the low-order bit.
4578 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
4579 * and if the reference is null at runtime, a zero value is introduced.
4580 * </ul>
4581 * @param target the method handle to invoke after arguments are retyped
4582 * @param newType the expected type of the new method handle
4583 * @return a method handle which delegates to the target after performing
4584 * any necessary argument conversions, and arranges for any
4585 * necessary return value conversions
4586 * @throws NullPointerException if either argument is null
4587 * @throws WrongMethodTypeException if the conversion cannot be made
4588 * @see MethodHandle#asType
4589 */
4590 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
4591 explicitCastArgumentsChecks(target, newType);
4592 // use the asTypeCache when possible:
4593 MethodType oldType = target.type();
4594 if (oldType == newType) return target;
4595 if (oldType.explicitCastEquivalentToAsType(newType)) {
4596 return target.asFixedArity().asType(newType);
4597 }
4598 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
4599 }
4600
4601 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
4602 if (target.type().parameterCount() != newType.parameterCount()) {
4603 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
4604 }
4605 }
4606
4607 /**
4608 * Produces a method handle which adapts the calling sequence of the
4609 * given method handle to a new type, by reordering the arguments.
4610 * The resulting method handle is guaranteed to report a type
4611 * which is equal to the desired new type.
4612 * <p>
4613 * The given array controls the reordering.
4614 * Call {@code #I} the number of incoming parameters (the value
4615 * {@code newType.parameterCount()}, and call {@code #O} the number
4616 * of outgoing parameters (the value {@code target.type().parameterCount()}).
4617 * Then the length of the reordering array must be {@code #O},
4618 * and each element must be a non-negative number less than {@code #I}.
4619 * For every {@code N} less than {@code #O}, the {@code N}-th
4620 * outgoing argument will be taken from the {@code I}-th incoming
4621 * argument, where {@code I} is {@code reorder[N]}.
4622 * <p>
4623 * No argument or return value conversions are applied.
4624 * The type of each incoming argument, as determined by {@code newType},
4625 * must be identical to the type of the corresponding outgoing parameter
4626 * or parameters in the target method handle.
4627 * The return type of {@code newType} must be identical to the return
4628 * type of the original target.
4629 * <p>
4630 * The reordering array need not specify an actual permutation.
4631 * An incoming argument will be duplicated if its index appears
4632 * more than once in the array, and an incoming argument will be dropped
4633 * if its index does not appear in the array.
4634 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
4635 * incoming arguments which are not mentioned in the reordering array
4636 * may be of any type, as determined only by {@code newType}.
4637 * {@snippet lang="java" :
4638 import static java.lang.invoke.MethodHandles.*;
4639 import static java.lang.invoke.MethodType.*;
4640 ...
4641 MethodType intfn1 = methodType(int.class, int.class);
4642 MethodType intfn2 = methodType(int.class, int.class, int.class);
4643 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
4644 assert(sub.type().equals(intfn2));
4645 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
4646 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
4647 assert((int)rsub.invokeExact(1, 100) == 99);
4648 MethodHandle add = ... (int x, int y) -> (x+y) ...;
4649 assert(add.type().equals(intfn2));
4650 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
4651 assert(twice.type().equals(intfn1));
4652 assert((int)twice.invokeExact(21) == 42);
4653 * }
4654 * <p>
4655 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4656 * variable-arity method handle}, even if the original target method handle was.
4657 * @param target the method handle to invoke after arguments are reordered
4658 * @param newType the expected type of the new method handle
4659 * @param reorder an index array which controls the reordering
4660 * @return a method handle which delegates to the target after it
4661 * drops unused arguments and moves and/or duplicates the other arguments
4662 * @throws NullPointerException if any argument is null
4663 * @throws IllegalArgumentException if the index array length is not equal to
4664 * the arity of the target, or if any index array element
4665 * not a valid index for a parameter of {@code newType},
4666 * or if two corresponding parameter types in
4667 * {@code target.type()} and {@code newType} are not identical,
4668 */
4669 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
4670 reorder = reorder.clone(); // get a private copy
4671 MethodType oldType = target.type();
4672 permuteArgumentChecks(reorder, newType, oldType);
4673 // first detect dropped arguments and handle them separately
4674 int[] originalReorder = reorder;
4675 BoundMethodHandle result = target.rebind();
4676 LambdaForm form = result.form;
4677 int newArity = newType.parameterCount();
4678 // Normalize the reordering into a real permutation,
4679 // by removing duplicates and adding dropped elements.
4680 // This somewhat improves lambda form caching, as well
4681 // as simplifying the transform by breaking it up into steps.
4682 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
4683 if (ddIdx > 0) {
4684 // We found a duplicated entry at reorder[ddIdx].
4685 // Example: (x,y,z)->asList(x,y,z)
4686 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
4687 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
4688 // The starred element corresponds to the argument
4689 // deleted by the dupArgumentForm transform.
4690 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
4691 boolean killFirst = false;
4692 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
4693 // Set killFirst if the dup is larger than an intervening position.
4694 // This will remove at least one inversion from the permutation.
4695 if (dupVal > val) killFirst = true;
4696 }
4697 if (!killFirst) {
4698 srcPos = dstPos;
4699 dstPos = ddIdx;
4700 }
4701 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
4702 assert (reorder[srcPos] == reorder[dstPos]);
4703 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
4704 // contract the reordering by removing the element at dstPos
4705 int tailPos = dstPos + 1;
4706 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
4707 reorder = Arrays.copyOf(reorder, reorder.length - 1);
4708 } else {
4709 int dropVal = ~ddIdx, insPos = 0;
4710 while (insPos < reorder.length && reorder[insPos] < dropVal) {
4711 // Find first element of reorder larger than dropVal.
4712 // This is where we will insert the dropVal.
4713 insPos += 1;
4714 }
4715 Class<?> ptype = newType.parameterType(dropVal);
4716 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
4717 oldType = oldType.insertParameterTypes(insPos, ptype);
4718 // expand the reordering by inserting an element at insPos
4719 int tailPos = insPos + 1;
4720 reorder = Arrays.copyOf(reorder, reorder.length + 1);
4721 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
4722 reorder[insPos] = dropVal;
4723 }
4724 assert (permuteArgumentChecks(reorder, newType, oldType));
4725 }
4726 assert (reorder.length == newArity); // a perfect permutation
4727 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
4728 form = form.editor().permuteArgumentsForm(1, reorder);
4729 if (newType == result.type() && form == result.internalForm())
4730 return result;
4731 return result.copyWith(newType, form);
4732 }
4733
4734 /**
4735 * Return an indication of any duplicate or omission in reorder.
4736 * If the reorder contains a duplicate entry, return the index of the second occurrence.
4737 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
4738 * Otherwise, return zero.
4739 * If an element not in [0..newArity-1] is encountered, return reorder.length.
4740 */
4741 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
4742 final int BIT_LIMIT = 63; // max number of bits in bit mask
4743 if (newArity < BIT_LIMIT) {
4744 long mask = 0;
4745 for (int i = 0; i < reorder.length; i++) {
4746 int arg = reorder[i];
4747 if (arg >= newArity) {
4748 return reorder.length;
4749 }
4750 long bit = 1L << arg;
4751 if ((mask & bit) != 0) {
4752 return i; // >0 indicates a dup
4753 }
4754 mask |= bit;
4755 }
4756 if (mask == (1L << newArity) - 1) {
4757 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
4758 return 0;
4759 }
4760 // find first zero
4761 long zeroBit = Long.lowestOneBit(~mask);
4762 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
4763 assert(zeroPos <= newArity);
4764 if (zeroPos == newArity) {
4765 return 0;
4766 }
4767 return ~zeroPos;
4768 } else {
4769 // same algorithm, different bit set
4770 BitSet mask = new BitSet(newArity);
4771 for (int i = 0; i < reorder.length; i++) {
4772 int arg = reorder[i];
4773 if (arg >= newArity) {
4774 return reorder.length;
4775 }
4776 if (mask.get(arg)) {
4777 return i; // >0 indicates a dup
4778 }
4779 mask.set(arg);
4780 }
4781 int zeroPos = mask.nextClearBit(0);
4782 assert(zeroPos <= newArity);
4783 if (zeroPos == newArity) {
4784 return 0;
4785 }
4786 return ~zeroPos;
4787 }
4788 }
4789
4790 static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
4791 if (newType.returnType() != oldType.returnType())
4792 throw newIllegalArgumentException("return types do not match",
4793 oldType, newType);
4794 if (reorder.length != oldType.parameterCount())
4795 throw newIllegalArgumentException("old type parameter count and reorder array length do not match",
4796 oldType, Arrays.toString(reorder));
4797
4798 int limit = newType.parameterCount();
4799 for (int j = 0; j < reorder.length; j++) {
4800 int i = reorder[j];
4801 if (i < 0 || i >= limit) {
4802 throw newIllegalArgumentException("index is out of bounds for new type",
4803 i, newType);
4804 }
4805 Class<?> src = newType.parameterType(i);
4806 Class<?> dst = oldType.parameterType(j);
4807 if (src != dst)
4808 throw newIllegalArgumentException("parameter types do not match after reorder",
4809 oldType, newType);
4810 }
4811 return true;
4812 }
4813
4814 /**
4815 * Produces a method handle of the requested return type which returns the given
4816 * constant value every time it is invoked.
4817 * <p>
4818 * Before the method handle is returned, the passed-in value is converted to the requested type.
4819 * If the requested type is primitive, widening primitive conversions are attempted,
4820 * else reference conversions are attempted.
4821 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
4822 * @param type the return type of the desired method handle
4823 * @param value the value to return
4824 * @return a method handle of the given return type and no arguments, which always returns the given value
4825 * @throws NullPointerException if the {@code type} argument is null
4826 * @throws ClassCastException if the value cannot be converted to the required return type
4827 * @throws IllegalArgumentException if the given type is {@code void.class}
4828 */
4829 public static MethodHandle constant(Class<?> type, Object value) {
4830 if (type.isPrimitive()) {
4831 if (type == void.class)
4832 throw newIllegalArgumentException("void type");
4833 Wrapper w = Wrapper.forPrimitiveType(type);
4834 value = w.convert(value, type);
4835 if (w.zero().equals(value))
4836 return zero(w, type);
4837 return insertArguments(identity(type), 0, value);
4838 } else {
4839 if (value == null)
4840 return zero(Wrapper.OBJECT, type);
4841 return identity(type).bindTo(value);
4842 }
4843 }
4844
4845 /**
4846 * Produces a method handle which returns its sole argument when invoked.
4847 * @param type the type of the sole parameter and return value of the desired method handle
4848 * @return a unary method handle which accepts and returns the given type
4849 * @throws NullPointerException if the argument is null
4850 * @throws IllegalArgumentException if the given type is {@code void.class}
4851 */
4852 public static MethodHandle identity(Class<?> type) {
4853 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
4854 int pos = btw.ordinal();
4855 MethodHandle ident = IDENTITY_MHS[pos];
4856 if (ident == null) {
4857 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
4858 }
4859 if (ident.type().returnType() == type)
4860 return ident;
4861 // something like identity(Foo.class); do not bother to intern these
4862 assert (btw == Wrapper.OBJECT);
4863 return makeIdentity(type);
4864 }
4865
4866 /**
4867 * Produces a constant method handle of the requested return type which
4868 * returns the default value for that type every time it is invoked.
4869 * The resulting constant method handle will have no side effects.
4870 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
4871 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
4872 * since {@code explicitCastArguments} converts {@code null} to default values.
4873 * @param type the expected return type of the desired method handle
4874 * @return a constant method handle that takes no arguments
4875 * and returns the default value of the given type (or void, if the type is void)
4876 * @throws NullPointerException if the argument is null
4877 * @see MethodHandles#constant
4878 * @see MethodHandles#empty
4879 * @see MethodHandles#explicitCastArguments
4880 * @since 9
4881 */
4882 public static MethodHandle zero(Class<?> type) {
4883 Objects.requireNonNull(type);
4884 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
4885 }
4886
4887 private static MethodHandle identityOrVoid(Class<?> type) {
4888 return type == void.class ? zero(type) : identity(type);
4889 }
4890
4891 /**
4892 * Produces a method handle of the requested type which ignores any arguments, does nothing,
4893 * and returns a suitable default depending on the return type.
4894 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
4895 * <p>The returned method handle is equivalent to
4896 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
4897 *
4898 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
4899 * {@code guardWithTest(pred, target, empty(target.type())}.
4900 * @param type the type of the desired method handle
4901 * @return a constant method handle of the given type, which returns a default value of the given return type
4902 * @throws NullPointerException if the argument is null
4903 * @see MethodHandles#zero
4904 * @see MethodHandles#constant
4905 * @since 9
4906 */
4907 public static MethodHandle empty(MethodType type) {
4908 Objects.requireNonNull(type);
4909 return dropArgumentsTrusted(zero(type.returnType()), 0, type.ptypes());
4910 }
4911
4912 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
4913 private static MethodHandle makeIdentity(Class<?> ptype) {
4914 MethodType mtype = methodType(ptype, ptype);
4915 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
4916 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
4917 }
4918
4919 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
4920 int pos = btw.ordinal();
4921 MethodHandle zero = ZERO_MHS[pos];
4922 if (zero == null) {
4923 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
4924 }
4925 if (zero.type().returnType() == rtype)
4926 return zero;
4927 assert(btw == Wrapper.OBJECT);
4928 return makeZero(rtype);
4929 }
4930 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
4931 private static MethodHandle makeZero(Class<?> rtype) {
4932 MethodType mtype = methodType(rtype);
4933 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
4934 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
4935 }
4936
4937 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
4938 // Simulate a CAS, to avoid racy duplication of results.
4939 MethodHandle prev = cache[pos];
4940 if (prev != null) return prev;
4941 return cache[pos] = value;
4942 }
4943
4944 /**
4945 * Provides a target method handle with one or more <em>bound arguments</em>
4946 * in advance of the method handle's invocation.
4947 * The formal parameters to the target corresponding to the bound
4948 * arguments are called <em>bound parameters</em>.
4949 * Returns a new method handle which saves away the bound arguments.
4950 * When it is invoked, it receives arguments for any non-bound parameters,
4951 * binds the saved arguments to their corresponding parameters,
4952 * and calls the original target.
4953 * <p>
4954 * The type of the new method handle will drop the types for the bound
4955 * parameters from the original target type, since the new method handle
4956 * will no longer require those arguments to be supplied by its callers.
4957 * <p>
4958 * Each given argument object must match the corresponding bound parameter type.
4959 * If a bound parameter type is a primitive, the argument object
4960 * must be a wrapper, and will be unboxed to produce the primitive value.
4961 * <p>
4962 * The {@code pos} argument selects which parameters are to be bound.
4963 * It may range between zero and <i>N-L</i> (inclusively),
4964 * where <i>N</i> is the arity of the target method handle
4965 * and <i>L</i> is the length of the values array.
4966 * <p>
4967 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4968 * variable-arity method handle}, even if the original target method handle was.
4969 * @param target the method handle to invoke after the argument is inserted
4970 * @param pos where to insert the argument (zero for the first)
4971 * @param values the series of arguments to insert
4972 * @return a method handle which inserts an additional argument,
4973 * before calling the original method handle
4974 * @throws NullPointerException if the target or the {@code values} array is null
4975 * @throws IllegalArgumentException if {@code pos} is less than {@code 0} or greater than
4976 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
4977 * is the length of the values array.
4978 * @throws ClassCastException if an argument does not match the corresponding bound parameter
4979 * type.
4980 * @see MethodHandle#bindTo
4981 */
4982 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
4983 int insCount = values.length;
4984 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
4985 if (insCount == 0) return target;
4986 BoundMethodHandle result = target.rebind();
4987 for (int i = 0; i < insCount; i++) {
4988 Object value = values[i];
4989 Class<?> ptype = ptypes[pos+i];
4990 if (ptype.isPrimitive()) {
4991 result = insertArgumentPrimitive(result, pos, ptype, value);
4992 } else {
4993 value = ptype.cast(value); // throw CCE if needed
4994 result = result.bindArgumentL(pos, value);
4995 }
4996 }
4997 return result;
4998 }
4999
5000 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
5001 Class<?> ptype, Object value) {
5002 Wrapper w = Wrapper.forPrimitiveType(ptype);
5003 // perform unboxing and/or primitive conversion
5004 value = w.convert(value, ptype);
5005 return switch (w) {
5006 case INT -> result.bindArgumentI(pos, (int) value);
5007 case LONG -> result.bindArgumentJ(pos, (long) value);
5008 case FLOAT -> result.bindArgumentF(pos, (float) value);
5009 case DOUBLE -> result.bindArgumentD(pos, (double) value);
5010 default -> result.bindArgumentI(pos, ValueConversions.widenSubword(value));
5011 };
5012 }
5013
5014 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
5015 MethodType oldType = target.type();
5016 int outargs = oldType.parameterCount();
5017 int inargs = outargs - insCount;
5018 if (inargs < 0)
5019 throw newIllegalArgumentException("too many values to insert");
5020 if (pos < 0 || pos > inargs)
5021 throw newIllegalArgumentException("no argument type to append");
5022 return oldType.ptypes();
5023 }
5024
5025 /**
5026 * Produces a method handle which will discard some dummy arguments
5027 * before calling some other specified <i>target</i> method handle.
5028 * The type of the new method handle will be the same as the target's type,
5029 * except it will also include the dummy argument types,
5030 * at some given position.
5031 * <p>
5032 * The {@code pos} argument may range between zero and <i>N</i>,
5033 * where <i>N</i> is the arity of the target.
5034 * If {@code pos} is zero, the dummy arguments will precede
5035 * the target's real arguments; if {@code pos} is <i>N</i>
5036 * they will come after.
5037 * <p>
5038 * <b>Example:</b>
5039 * {@snippet lang="java" :
5040 import static java.lang.invoke.MethodHandles.*;
5041 import static java.lang.invoke.MethodType.*;
5042 ...
5043 MethodHandle cat = lookup().findVirtual(String.class,
5044 "concat", methodType(String.class, String.class));
5045 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5046 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
5047 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
5048 assertEquals(bigType, d0.type());
5049 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
5050 * }
5051 * <p>
5052 * This method is also equivalent to the following code:
5053 * <blockquote><pre>
5054 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
5055 * </pre></blockquote>
5056 * @param target the method handle to invoke after the arguments are dropped
5057 * @param pos position of first argument to drop (zero for the leftmost)
5058 * @param valueTypes the type(s) of the argument(s) to drop
5059 * @return a method handle which drops arguments of the given types,
5060 * before calling the original method handle
5061 * @throws NullPointerException if the target is null,
5062 * or if the {@code valueTypes} list or any of its elements is null
5063 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5064 * or if {@code pos} is negative or greater than the arity of the target,
5065 * or if the new method handle's type would have too many parameters
5066 */
5067 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
5068 return dropArgumentsTrusted(target, pos, valueTypes.toArray(new Class<?>[0]).clone());
5069 }
5070
5071 static MethodHandle dropArgumentsTrusted(MethodHandle target, int pos, Class<?>[] valueTypes) {
5072 MethodType oldType = target.type(); // get NPE
5073 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
5074 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
5075 if (dropped == 0) return target;
5076 BoundMethodHandle result = target.rebind();
5077 LambdaForm lform = result.form;
5078 int insertFormArg = 1 + pos;
5079 for (Class<?> ptype : valueTypes) {
5080 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
5081 }
5082 result = result.copyWith(newType, lform);
5083 return result;
5084 }
5085
5086 private static int dropArgumentChecks(MethodType oldType, int pos, Class<?>[] valueTypes) {
5087 int dropped = valueTypes.length;
5088 MethodType.checkSlotCount(dropped);
5089 int outargs = oldType.parameterCount();
5090 int inargs = outargs + dropped;
5091 if (pos < 0 || pos > outargs)
5092 throw newIllegalArgumentException("no argument type to remove"
5093 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
5094 );
5095 return dropped;
5096 }
5097
5098 /**
5099 * Produces a method handle which will discard some dummy arguments
5100 * before calling some other specified <i>target</i> method handle.
5101 * The type of the new method handle will be the same as the target's type,
5102 * except it will also include the dummy argument types,
5103 * at some given position.
5104 * <p>
5105 * The {@code pos} argument may range between zero and <i>N</i>,
5106 * where <i>N</i> is the arity of the target.
5107 * If {@code pos} is zero, the dummy arguments will precede
5108 * the target's real arguments; if {@code pos} is <i>N</i>
5109 * they will come after.
5110 * @apiNote
5111 * {@snippet lang="java" :
5112 import static java.lang.invoke.MethodHandles.*;
5113 import static java.lang.invoke.MethodType.*;
5114 ...
5115 MethodHandle cat = lookup().findVirtual(String.class,
5116 "concat", methodType(String.class, String.class));
5117 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5118 MethodHandle d0 = dropArguments(cat, 0, String.class);
5119 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
5120 MethodHandle d1 = dropArguments(cat, 1, String.class);
5121 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
5122 MethodHandle d2 = dropArguments(cat, 2, String.class);
5123 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
5124 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
5125 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
5126 * }
5127 * <p>
5128 * This method is also equivalent to the following code:
5129 * <blockquote><pre>
5130 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
5131 * </pre></blockquote>
5132 * @param target the method handle to invoke after the arguments are dropped
5133 * @param pos position of first argument to drop (zero for the leftmost)
5134 * @param valueTypes the type(s) of the argument(s) to drop
5135 * @return a method handle which drops arguments of the given types,
5136 * before calling the original method handle
5137 * @throws NullPointerException if the target is null,
5138 * or if the {@code valueTypes} array or any of its elements is null
5139 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5140 * or if {@code pos} is negative or greater than the arity of the target,
5141 * or if the new method handle's type would have
5142 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5143 */
5144 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
5145 return dropArgumentsTrusted(target, pos, valueTypes.clone());
5146 }
5147
5148 /* Convenience overloads for trusting internal low-arity call-sites */
5149 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1) {
5150 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1 });
5151 }
5152 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1, Class<?> valueType2) {
5153 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1, valueType2 });
5154 }
5155
5156 // private version which allows caller some freedom with error handling
5157 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, Class<?>[] newTypes, int pos,
5158 boolean nullOnFailure) {
5159 Class<?>[] oldTypes = target.type().ptypes();
5160 int match = oldTypes.length;
5161 if (skip != 0) {
5162 if (skip < 0 || skip > match) {
5163 throw newIllegalArgumentException("illegal skip", skip, target);
5164 }
5165 oldTypes = Arrays.copyOfRange(oldTypes, skip, match);
5166 match -= skip;
5167 }
5168 Class<?>[] addTypes = newTypes;
5169 int add = addTypes.length;
5170 if (pos != 0) {
5171 if (pos < 0 || pos > add) {
5172 throw newIllegalArgumentException("illegal pos", pos, Arrays.toString(newTypes));
5173 }
5174 addTypes = Arrays.copyOfRange(addTypes, pos, add);
5175 add -= pos;
5176 assert(addTypes.length == add);
5177 }
5178 // Do not add types which already match the existing arguments.
5179 if (match > add || !Arrays.equals(oldTypes, 0, oldTypes.length, addTypes, 0, match)) {
5180 if (nullOnFailure) {
5181 return null;
5182 }
5183 throw newIllegalArgumentException("argument lists do not match",
5184 Arrays.toString(oldTypes), Arrays.toString(newTypes));
5185 }
5186 addTypes = Arrays.copyOfRange(addTypes, match, add);
5187 add -= match;
5188 assert(addTypes.length == add);
5189 // newTypes: ( P*[pos], M*[match], A*[add] )
5190 // target: ( S*[skip], M*[match] )
5191 MethodHandle adapter = target;
5192 if (add > 0) {
5193 adapter = dropArgumentsTrusted(adapter, skip+ match, addTypes);
5194 }
5195 // adapter: (S*[skip], M*[match], A*[add] )
5196 if (pos > 0) {
5197 adapter = dropArgumentsTrusted(adapter, skip, Arrays.copyOfRange(newTypes, 0, pos));
5198 }
5199 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
5200 return adapter;
5201 }
5202
5203 /**
5204 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
5205 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
5206 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
5207 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
5208 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
5209 * {@link #dropArguments(MethodHandle, int, Class[])}.
5210 * <p>
5211 * The resulting handle will have the same return type as the target handle.
5212 * <p>
5213 * In more formal terms, assume these two type lists:<ul>
5214 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
5215 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
5216 * {@code newTypes}.
5217 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
5218 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
5219 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
5220 * sub-list.
5221 * </ul>
5222 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
5223 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
5224 * {@link #dropArguments(MethodHandle, int, Class[])}.
5225 *
5226 * @apiNote
5227 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
5228 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
5229 * {@snippet lang="java" :
5230 import static java.lang.invoke.MethodHandles.*;
5231 import static java.lang.invoke.MethodType.*;
5232 ...
5233 ...
5234 MethodHandle h0 = constant(boolean.class, true);
5235 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
5236 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
5237 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
5238 if (h1.type().parameterCount() < h2.type().parameterCount())
5239 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
5240 else
5241 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
5242 MethodHandle h3 = guardWithTest(h0, h1, h2);
5243 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
5244 * }
5245 * @param target the method handle to adapt
5246 * @param skip number of targets parameters to disregard (they will be unchanged)
5247 * @param newTypes the list of types to match {@code target}'s parameter type list to
5248 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
5249 * @return a possibly adapted method handle
5250 * @throws NullPointerException if either argument is null
5251 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
5252 * or if {@code skip} is negative or greater than the arity of the target,
5253 * or if {@code pos} is negative or greater than the newTypes list size,
5254 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
5255 * {@code pos}.
5256 * @since 9
5257 */
5258 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
5259 Objects.requireNonNull(target);
5260 Objects.requireNonNull(newTypes);
5261 return dropArgumentsToMatch(target, skip, newTypes.toArray(new Class<?>[0]).clone(), pos, false);
5262 }
5263
5264 /**
5265 * Drop the return value of the target handle (if any).
5266 * The returned method handle will have a {@code void} return type.
5267 *
5268 * @param target the method handle to adapt
5269 * @return a possibly adapted method handle
5270 * @throws NullPointerException if {@code target} is null
5271 * @since 16
5272 */
5273 public static MethodHandle dropReturn(MethodHandle target) {
5274 Objects.requireNonNull(target);
5275 MethodType oldType = target.type();
5276 Class<?> oldReturnType = oldType.returnType();
5277 if (oldReturnType == void.class)
5278 return target;
5279 MethodType newType = oldType.changeReturnType(void.class);
5280 BoundMethodHandle result = target.rebind();
5281 LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true);
5282 result = result.copyWith(newType, lform);
5283 return result;
5284 }
5285
5286 /**
5287 * Adapts a target method handle by pre-processing
5288 * one or more of its arguments, each with its own unary filter function,
5289 * and then calling the target with each pre-processed argument
5290 * replaced by the result of its corresponding filter function.
5291 * <p>
5292 * The pre-processing is performed by one or more method handles,
5293 * specified in the elements of the {@code filters} array.
5294 * The first element of the filter array corresponds to the {@code pos}
5295 * argument of the target, and so on in sequence.
5296 * The filter functions are invoked in left to right order.
5297 * <p>
5298 * Null arguments in the array are treated as identity functions,
5299 * and the corresponding arguments left unchanged.
5300 * (If there are no non-null elements in the array, the original target is returned.)
5301 * Each filter is applied to the corresponding argument of the adapter.
5302 * <p>
5303 * If a filter {@code F} applies to the {@code N}th argument of
5304 * the target, then {@code F} must be a method handle which
5305 * takes exactly one argument. The type of {@code F}'s sole argument
5306 * replaces the corresponding argument type of the target
5307 * in the resulting adapted method handle.
5308 * The return type of {@code F} must be identical to the corresponding
5309 * parameter type of the target.
5310 * <p>
5311 * It is an error if there are elements of {@code filters}
5312 * (null or not)
5313 * which do not correspond to argument positions in the target.
5314 * <p><b>Example:</b>
5315 * {@snippet lang="java" :
5316 import static java.lang.invoke.MethodHandles.*;
5317 import static java.lang.invoke.MethodType.*;
5318 ...
5319 MethodHandle cat = lookup().findVirtual(String.class,
5320 "concat", methodType(String.class, String.class));
5321 MethodHandle upcase = lookup().findVirtual(String.class,
5322 "toUpperCase", methodType(String.class));
5323 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5324 MethodHandle f0 = filterArguments(cat, 0, upcase);
5325 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
5326 MethodHandle f1 = filterArguments(cat, 1, upcase);
5327 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
5328 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
5329 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
5330 * }
5331 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5332 * denotes the return type of both the {@code target} and resulting adapter.
5333 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
5334 * of the parameters and arguments that precede and follow the filter position
5335 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
5336 * values of the filtered parameters and arguments; they also represent the
5337 * return types of the {@code filter[i]} handles. The latter accept arguments
5338 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
5339 * the resulting adapter.
5340 * {@snippet lang="java" :
5341 * T target(P... p, A[i]... a[i], B... b);
5342 * A[i] filter[i](V[i]);
5343 * T adapter(P... p, V[i]... v[i], B... b) {
5344 * return target(p..., filter[i](v[i])..., b...);
5345 * }
5346 * }
5347 * <p>
5348 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5349 * variable-arity method handle}, even if the original target method handle was.
5350 *
5351 * @param target the method handle to invoke after arguments are filtered
5352 * @param pos the position of the first argument to filter
5353 * @param filters method handles to call initially on filtered arguments
5354 * @return method handle which incorporates the specified argument filtering logic
5355 * @throws NullPointerException if the target is null
5356 * or if the {@code filters} array is null
5357 * @throws IllegalArgumentException if a non-null element of {@code filters}
5358 * does not match a corresponding argument type of target as described above,
5359 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
5360 * or if the resulting method handle's type would have
5361 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5362 */
5363 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
5364 // In method types arguments start at index 0, while the LF
5365 // editor have the MH receiver at position 0 - adjust appropriately.
5366 final int MH_RECEIVER_OFFSET = 1;
5367 filterArgumentsCheckArity(target, pos, filters);
5368 MethodHandle adapter = target;
5369
5370 // keep track of currently matched filters, as to optimize repeated filters
5371 int index = 0;
5372 int[] positions = new int[filters.length];
5373 MethodHandle filter = null;
5374
5375 // process filters in reverse order so that the invocation of
5376 // the resulting adapter will invoke the filters in left-to-right order
5377 for (int i = filters.length - 1; i >= 0; --i) {
5378 MethodHandle newFilter = filters[i];
5379 if (newFilter == null) continue; // ignore null elements of filters
5380
5381 // flush changes on update
5382 if (filter != newFilter) {
5383 if (filter != null) {
5384 if (index > 1) {
5385 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5386 } else {
5387 adapter = filterArgument(adapter, positions[0] - 1, filter);
5388 }
5389 }
5390 filter = newFilter;
5391 index = 0;
5392 }
5393
5394 filterArgumentChecks(target, pos + i, newFilter);
5395 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
5396 }
5397 if (index > 1) {
5398 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5399 } else if (index == 1) {
5400 adapter = filterArgument(adapter, positions[0] - 1, filter);
5401 }
5402 return adapter;
5403 }
5404
5405 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
5406 MethodType targetType = adapter.type();
5407 MethodType filterType = filter.type();
5408 BoundMethodHandle result = adapter.rebind();
5409 Class<?> newParamType = filterType.parameterType(0);
5410
5411 Class<?>[] ptypes = targetType.ptypes().clone();
5412 for (int pos : positions) {
5413 ptypes[pos - 1] = newParamType;
5414 }
5415 MethodType newType = MethodType.methodType(targetType.rtype(), ptypes, true);
5416
5417 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
5418 return result.copyWithExtendL(newType, lform, filter);
5419 }
5420
5421 /*non-public*/
5422 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
5423 filterArgumentChecks(target, pos, filter);
5424 MethodType targetType = target.type();
5425 MethodType filterType = filter.type();
5426 BoundMethodHandle result = target.rebind();
5427 Class<?> newParamType = filterType.parameterType(0);
5428 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
5429 MethodType newType = targetType.changeParameterType(pos, newParamType);
5430 result = result.copyWithExtendL(newType, lform, filter);
5431 return result;
5432 }
5433
5434 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
5435 MethodType targetType = target.type();
5436 int maxPos = targetType.parameterCount();
5437 if (pos + filters.length > maxPos)
5438 throw newIllegalArgumentException("too many filters");
5439 }
5440
5441 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5442 MethodType targetType = target.type();
5443 MethodType filterType = filter.type();
5444 if (filterType.parameterCount() != 1
5445 || filterType.returnType() != targetType.parameterType(pos))
5446 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5447 }
5448
5449 /**
5450 * Adapts a target method handle by pre-processing
5451 * a sub-sequence of its arguments with a filter (another method handle).
5452 * The pre-processed arguments are replaced by the result (if any) of the
5453 * filter function.
5454 * The target is then called on the modified (usually shortened) argument list.
5455 * <p>
5456 * If the filter returns a value, the target must accept that value as
5457 * its argument in position {@code pos}, preceded and/or followed by
5458 * any arguments not passed to the filter.
5459 * If the filter returns void, the target must accept all arguments
5460 * not passed to the filter.
5461 * No arguments are reordered, and a result returned from the filter
5462 * replaces (in order) the whole subsequence of arguments originally
5463 * passed to the adapter.
5464 * <p>
5465 * The argument types (if any) of the filter
5466 * replace zero or one argument types of the target, at position {@code pos},
5467 * in the resulting adapted method handle.
5468 * The return type of the filter (if any) must be identical to the
5469 * argument type of the target at position {@code pos}, and that target argument
5470 * is supplied by the return value of the filter.
5471 * <p>
5472 * In all cases, {@code pos} must be greater than or equal to zero, and
5473 * {@code pos} must also be less than or equal to the target's arity.
5474 * <p><b>Example:</b>
5475 * {@snippet lang="java" :
5476 import static java.lang.invoke.MethodHandles.*;
5477 import static java.lang.invoke.MethodType.*;
5478 ...
5479 MethodHandle deepToString = publicLookup()
5480 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
5481
5482 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
5483 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
5484
5485 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
5486 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
5487
5488 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
5489 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
5490 assertEquals("[top, [up, down], strange]",
5491 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
5492
5493 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
5494 assertEquals("[top, [up, down], [strange]]",
5495 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
5496
5497 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
5498 assertEquals("[top, [[up, down, strange], charm], bottom]",
5499 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
5500 * }
5501 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5502 * represents the return type of the {@code target} and resulting adapter.
5503 * {@code V}/{@code v} stand for the return type and value of the
5504 * {@code filter}, which are also found in the signature and arguments of
5505 * the {@code target}, respectively, unless {@code V} is {@code void}.
5506 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
5507 * and values preceding and following the collection position, {@code pos},
5508 * in the {@code target}'s signature. They also turn up in the resulting
5509 * adapter's signature and arguments, where they surround
5510 * {@code B}/{@code b}, which represent the parameter types and arguments
5511 * to the {@code filter} (if any).
5512 * {@snippet lang="java" :
5513 * T target(A...,V,C...);
5514 * V filter(B...);
5515 * T adapter(A... a,B... b,C... c) {
5516 * V v = filter(b...);
5517 * return target(a...,v,c...);
5518 * }
5519 * // and if the filter has no arguments:
5520 * T target2(A...,V,C...);
5521 * V filter2();
5522 * T adapter2(A... a,C... c) {
5523 * V v = filter2();
5524 * return target2(a...,v,c...);
5525 * }
5526 * // and if the filter has a void return:
5527 * T target3(A...,C...);
5528 * void filter3(B...);
5529 * T adapter3(A... a,B... b,C... c) {
5530 * filter3(b...);
5531 * return target3(a...,c...);
5532 * }
5533 * }
5534 * <p>
5535 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
5536 * one which first "folds" the affected arguments, and then drops them, in separate
5537 * steps as follows:
5538 * {@snippet lang="java" :
5539 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
5540 * mh = MethodHandles.foldArguments(mh, coll); //step 1
5541 * }
5542 * If the target method handle consumes no arguments besides than the result
5543 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
5544 * is equivalent to {@code filterReturnValue(coll, mh)}.
5545 * If the filter method handle {@code coll} consumes one argument and produces
5546 * a non-void result, then {@code collectArguments(mh, N, coll)}
5547 * is equivalent to {@code filterArguments(mh, N, coll)}.
5548 * Other equivalences are possible but would require argument permutation.
5549 * <p>
5550 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5551 * variable-arity method handle}, even if the original target method handle was.
5552 *
5553 * @param target the method handle to invoke after filtering the subsequence of arguments
5554 * @param pos the position of the first adapter argument to pass to the filter,
5555 * and/or the target argument which receives the result of the filter
5556 * @param filter method handle to call on the subsequence of arguments
5557 * @return method handle which incorporates the specified argument subsequence filtering logic
5558 * @throws NullPointerException if either argument is null
5559 * @throws IllegalArgumentException if the return type of {@code filter}
5560 * is non-void and is not the same as the {@code pos} argument of the target,
5561 * or if {@code pos} is not between 0 and the target's arity, inclusive,
5562 * or if the resulting method handle's type would have
5563 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5564 * @see MethodHandles#foldArguments
5565 * @see MethodHandles#filterArguments
5566 * @see MethodHandles#filterReturnValue
5567 */
5568 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
5569 MethodType newType = collectArgumentsChecks(target, pos, filter);
5570 MethodType collectorType = filter.type();
5571 BoundMethodHandle result = target.rebind();
5572 LambdaForm lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
5573 return result.copyWithExtendL(newType, lform, filter);
5574 }
5575
5576 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5577 MethodType targetType = target.type();
5578 MethodType filterType = filter.type();
5579 Class<?> rtype = filterType.returnType();
5580 Class<?>[] filterArgs = filterType.ptypes();
5581 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) ||
5582 (rtype != void.class && pos >= targetType.parameterCount())) {
5583 throw newIllegalArgumentException("position is out of range for target", target, pos);
5584 }
5585 if (rtype == void.class) {
5586 return targetType.insertParameterTypes(pos, filterArgs);
5587 }
5588 if (rtype != targetType.parameterType(pos)) {
5589 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5590 }
5591 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs);
5592 }
5593
5594 /**
5595 * Adapts a target method handle by post-processing
5596 * its return value (if any) with a filter (another method handle).
5597 * The result of the filter is returned from the adapter.
5598 * <p>
5599 * If the target returns a value, the filter must accept that value as
5600 * its only argument.
5601 * If the target returns void, the filter must accept no arguments.
5602 * <p>
5603 * The return type of the filter
5604 * replaces the return type of the target
5605 * in the resulting adapted method handle.
5606 * The argument type of the filter (if any) must be identical to the
5607 * return type of the target.
5608 * <p><b>Example:</b>
5609 * {@snippet lang="java" :
5610 import static java.lang.invoke.MethodHandles.*;
5611 import static java.lang.invoke.MethodType.*;
5612 ...
5613 MethodHandle cat = lookup().findVirtual(String.class,
5614 "concat", methodType(String.class, String.class));
5615 MethodHandle length = lookup().findVirtual(String.class,
5616 "length", methodType(int.class));
5617 System.out.println((String) cat.invokeExact("x", "y")); // xy
5618 MethodHandle f0 = filterReturnValue(cat, length);
5619 System.out.println((int) f0.invokeExact("x", "y")); // 2
5620 * }
5621 * <p>Here is pseudocode for the resulting adapter. In the code,
5622 * {@code T}/{@code t} represent the result type and value of the
5623 * {@code target}; {@code V}, the result type of the {@code filter}; and
5624 * {@code A}/{@code a}, the types and values of the parameters and arguments
5625 * of the {@code target} as well as the resulting adapter.
5626 * {@snippet lang="java" :
5627 * T target(A...);
5628 * V filter(T);
5629 * V adapter(A... a) {
5630 * T t = target(a...);
5631 * return filter(t);
5632 * }
5633 * // and if the target has a void return:
5634 * void target2(A...);
5635 * V filter2();
5636 * V adapter2(A... a) {
5637 * target2(a...);
5638 * return filter2();
5639 * }
5640 * // and if the filter has a void return:
5641 * T target3(A...);
5642 * void filter3(V);
5643 * void adapter3(A... a) {
5644 * T t = target3(a...);
5645 * filter3(t);
5646 * }
5647 * }
5648 * <p>
5649 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5650 * variable-arity method handle}, even if the original target method handle was.
5651 * @param target the method handle to invoke before filtering the return value
5652 * @param filter method handle to call on the return value
5653 * @return method handle which incorporates the specified return value filtering logic
5654 * @throws NullPointerException if either argument is null
5655 * @throws IllegalArgumentException if the argument list of {@code filter}
5656 * does not match the return type of target as described above
5657 */
5658 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
5659 MethodType targetType = target.type();
5660 MethodType filterType = filter.type();
5661 filterReturnValueChecks(targetType, filterType);
5662 BoundMethodHandle result = target.rebind();
5663 BasicType rtype = BasicType.basicType(filterType.returnType());
5664 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
5665 MethodType newType = targetType.changeReturnType(filterType.returnType());
5666 result = result.copyWithExtendL(newType, lform, filter);
5667 return result;
5668 }
5669
5670 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
5671 Class<?> rtype = targetType.returnType();
5672 int filterValues = filterType.parameterCount();
5673 if (filterValues == 0
5674 ? (rtype != void.class)
5675 : (rtype != filterType.parameterType(0) || filterValues != 1))
5676 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5677 }
5678
5679 /**
5680 * Filter the return value of a target method handle with a filter function. The filter function is
5681 * applied to the return value of the original handle; if the filter specifies more than one parameters,
5682 * then any remaining parameter is appended to the adapter handle. In other words, the adaptation works
5683 * as follows:
5684 * {@snippet lang="java" :
5685 * T target(A...)
5686 * V filter(B... , T)
5687 * V adapter(A... a, B... b) {
5688 * T t = target(a...);
5689 * return filter(b..., t);
5690 * }
5691 * }
5692 * <p>
5693 * If the filter handle is a unary function, then this method behaves like {@link #filterReturnValue(MethodHandle, MethodHandle)}.
5694 *
5695 * @param target the target method handle
5696 * @param filter the filter method handle
5697 * @return the adapter method handle
5698 */
5699 /* package */ static MethodHandle collectReturnValue(MethodHandle target, MethodHandle filter) {
5700 MethodType targetType = target.type();
5701 MethodType filterType = filter.type();
5702 BoundMethodHandle result = target.rebind();
5703 LambdaForm lform = result.editor().collectReturnValueForm(filterType.basicType());
5704 MethodType newType = targetType.changeReturnType(filterType.returnType());
5705 if (filterType.parameterCount() > 1) {
5706 for (int i = 0 ; i < filterType.parameterCount() - 1 ; i++) {
5707 newType = newType.appendParameterTypes(filterType.parameterType(i));
5708 }
5709 }
5710 result = result.copyWithExtendL(newType, lform, filter);
5711 return result;
5712 }
5713
5714 /**
5715 * Adapts a target method handle by pre-processing
5716 * some of its arguments, and then calling the target with
5717 * the result of the pre-processing, inserted into the original
5718 * sequence of arguments.
5719 * <p>
5720 * The pre-processing is performed by {@code combiner}, a second method handle.
5721 * Of the arguments passed to the adapter, the first {@code N} arguments
5722 * are copied to the combiner, which is then called.
5723 * (Here, {@code N} is defined as the parameter count of the combiner.)
5724 * After this, control passes to the target, with any result
5725 * from the combiner inserted before the original {@code N} incoming
5726 * arguments.
5727 * <p>
5728 * If the combiner returns a value, the first parameter type of the target
5729 * must be identical with the return type of the combiner, and the next
5730 * {@code N} parameter types of the target must exactly match the parameters
5731 * of the combiner.
5732 * <p>
5733 * If the combiner has a void return, no result will be inserted,
5734 * and the first {@code N} parameter types of the target
5735 * must exactly match the parameters of the combiner.
5736 * <p>
5737 * The resulting adapter is the same type as the target, except that the
5738 * first parameter type is dropped,
5739 * if it corresponds to the result of the combiner.
5740 * <p>
5741 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
5742 * that either the combiner or the target does not wish to receive.
5743 * If some of the incoming arguments are destined only for the combiner,
5744 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
5745 * arguments will not need to be live on the stack on entry to the
5746 * target.)
5747 * <p><b>Example:</b>
5748 * {@snippet lang="java" :
5749 import static java.lang.invoke.MethodHandles.*;
5750 import static java.lang.invoke.MethodType.*;
5751 ...
5752 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5753 "println", methodType(void.class, String.class))
5754 .bindTo(System.out);
5755 MethodHandle cat = lookup().findVirtual(String.class,
5756 "concat", methodType(String.class, String.class));
5757 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5758 MethodHandle catTrace = foldArguments(cat, trace);
5759 // also prints "boo":
5760 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5761 * }
5762 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5763 * represents the result type of the {@code target} and resulting adapter.
5764 * {@code V}/{@code v} represent the type and value of the parameter and argument
5765 * of {@code target} that precedes the folding position; {@code V} also is
5766 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
5767 * types and values of the {@code N} parameters and arguments at the folding
5768 * position. {@code B}/{@code b} represent the types and values of the
5769 * {@code target} parameters and arguments that follow the folded parameters
5770 * and arguments.
5771 * {@snippet lang="java" :
5772 * // there are N arguments in A...
5773 * T target(V, A[N]..., B...);
5774 * V combiner(A...);
5775 * T adapter(A... a, B... b) {
5776 * V v = combiner(a...);
5777 * return target(v, a..., b...);
5778 * }
5779 * // and if the combiner has a void return:
5780 * T target2(A[N]..., B...);
5781 * void combiner2(A...);
5782 * T adapter2(A... a, B... b) {
5783 * combiner2(a...);
5784 * return target2(a..., b...);
5785 * }
5786 * }
5787 * <p>
5788 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5789 * variable-arity method handle}, even if the original target method handle was.
5790 * @param target the method handle to invoke after arguments are combined
5791 * @param combiner method handle to call initially on the incoming arguments
5792 * @return method handle which incorporates the specified argument folding logic
5793 * @throws NullPointerException if either argument is null
5794 * @throws IllegalArgumentException if {@code combiner}'s return type
5795 * is non-void and not the same as the first argument type of
5796 * the target, or if the initial {@code N} argument types
5797 * of the target
5798 * (skipping one matching the {@code combiner}'s return type)
5799 * are not identical with the argument types of {@code combiner}
5800 */
5801 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
5802 return foldArguments(target, 0, combiner);
5803 }
5804
5805 /**
5806 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
5807 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
5808 * before the folded arguments.
5809 * <p>
5810 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
5811 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
5812 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
5813 * 0.
5814 *
5815 * @apiNote Example:
5816 * {@snippet lang="java" :
5817 import static java.lang.invoke.MethodHandles.*;
5818 import static java.lang.invoke.MethodType.*;
5819 ...
5820 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5821 "println", methodType(void.class, String.class))
5822 .bindTo(System.out);
5823 MethodHandle cat = lookup().findVirtual(String.class,
5824 "concat", methodType(String.class, String.class));
5825 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5826 MethodHandle catTrace = foldArguments(cat, 1, trace);
5827 // also prints "jum":
5828 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5829 * }
5830 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5831 * represents the result type of the {@code target} and resulting adapter.
5832 * {@code V}/{@code v} represent the type and value of the parameter and argument
5833 * of {@code target} that precedes the folding position; {@code V} also is
5834 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
5835 * types and values of the {@code N} parameters and arguments at the folding
5836 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
5837 * and values of the {@code target} parameters and arguments that precede and
5838 * follow the folded parameters and arguments starting at {@code pos},
5839 * respectively.
5840 * {@snippet lang="java" :
5841 * // there are N arguments in A...
5842 * T target(Z..., V, A[N]..., B...);
5843 * V combiner(A...);
5844 * T adapter(Z... z, A... a, B... b) {
5845 * V v = combiner(a...);
5846 * return target(z..., v, a..., b...);
5847 * }
5848 * // and if the combiner has a void return:
5849 * T target2(Z..., A[N]..., B...);
5850 * void combiner2(A...);
5851 * T adapter2(Z... z, A... a, B... b) {
5852 * combiner2(a...);
5853 * return target2(z..., a..., b...);
5854 * }
5855 * }
5856 * <p>
5857 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5858 * variable-arity method handle}, even if the original target method handle was.
5859 *
5860 * @param target the method handle to invoke after arguments are combined
5861 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
5862 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5863 * @param combiner method handle to call initially on the incoming arguments
5864 * @return method handle which incorporates the specified argument folding logic
5865 * @throws NullPointerException if either argument is null
5866 * @throws IllegalArgumentException if either of the following two conditions holds:
5867 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5868 * {@code pos} of the target signature;
5869 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
5870 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
5871 *
5872 * @see #foldArguments(MethodHandle, MethodHandle)
5873 * @since 9
5874 */
5875 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
5876 MethodType targetType = target.type();
5877 MethodType combinerType = combiner.type();
5878 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
5879 BoundMethodHandle result = target.rebind();
5880 boolean dropResult = rtype == void.class;
5881 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
5882 MethodType newType = targetType;
5883 if (!dropResult) {
5884 newType = newType.dropParameterTypes(pos, pos + 1);
5885 }
5886 result = result.copyWithExtendL(newType, lform, combiner);
5887 return result;
5888 }
5889
5890 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
5891 int foldArgs = combinerType.parameterCount();
5892 Class<?> rtype = combinerType.returnType();
5893 int foldVals = rtype == void.class ? 0 : 1;
5894 int afterInsertPos = foldPos + foldVals;
5895 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
5896 if (ok) {
5897 for (int i = 0; i < foldArgs; i++) {
5898 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
5899 ok = false;
5900 break;
5901 }
5902 }
5903 }
5904 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
5905 ok = false;
5906 if (!ok)
5907 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5908 return rtype;
5909 }
5910
5911 /**
5912 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
5913 * of the pre-processing replacing the argument at the given position.
5914 *
5915 * @param target the method handle to invoke after arguments are combined
5916 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5917 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5918 * @param combiner method handle to call initially on the incoming arguments
5919 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5920 * @return method handle which incorporates the specified argument folding logic
5921 * @throws NullPointerException if either argument is null
5922 * @throws IllegalArgumentException if either of the following two conditions holds:
5923 * (1) {@code combiner}'s return type is not the same as the argument type at position
5924 * {@code pos} of the target signature;
5925 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
5926 * not identical with the argument types of {@code combiner}.
5927 */
5928 /*non-public*/
5929 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5930 return argumentsWithCombiner(true, target, position, combiner, argPositions);
5931 }
5932
5933 /**
5934 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
5935 * the pre-processing inserted into the original sequence of arguments at the given position.
5936 *
5937 * @param target the method handle to invoke after arguments are combined
5938 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5939 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5940 * @param combiner method handle to call initially on the incoming arguments
5941 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5942 * @return method handle which incorporates the specified argument folding logic
5943 * @throws NullPointerException if either argument is null
5944 * @throws IllegalArgumentException if either of the following two conditions holds:
5945 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5946 * {@code pos} of the target signature;
5947 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
5948 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
5949 * with the argument types of {@code combiner}.
5950 */
5951 /*non-public*/
5952 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5953 return argumentsWithCombiner(false, target, position, combiner, argPositions);
5954 }
5955
5956 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5957 MethodType targetType = target.type();
5958 MethodType combinerType = combiner.type();
5959 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
5960 BoundMethodHandle result = target.rebind();
5961
5962 MethodType newType = targetType;
5963 LambdaForm lform;
5964 if (filter) {
5965 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
5966 } else {
5967 boolean dropResult = rtype == void.class;
5968 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
5969 if (!dropResult) {
5970 newType = newType.dropParameterTypes(position, position + 1);
5971 }
5972 }
5973 result = result.copyWithExtendL(newType, lform, combiner);
5974 return result;
5975 }
5976
5977 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
5978 int combinerArgs = combinerType.parameterCount();
5979 if (argPos.length != combinerArgs) {
5980 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
5981 }
5982 Class<?> rtype = combinerType.returnType();
5983
5984 for (int i = 0; i < combinerArgs; i++) {
5985 int arg = argPos[i];
5986 if (arg < 0 || arg > targetType.parameterCount()) {
5987 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
5988 }
5989 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
5990 throw newIllegalArgumentException("target argument type at position " + arg
5991 + " must match combiner argument type at index " + i + ": " + targetType
5992 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
5993 }
5994 }
5995 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
5996 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5997 }
5998 return rtype;
5999 }
6000
6001 /**
6002 * Makes a method handle which adapts a target method handle,
6003 * by guarding it with a test, a boolean-valued method handle.
6004 * If the guard fails, a fallback handle is called instead.
6005 * All three method handles must have the same corresponding
6006 * argument and return types, except that the return type
6007 * of the test must be boolean, and the test is allowed
6008 * to have fewer arguments than the other two method handles.
6009 * <p>
6010 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6011 * represents the uniform result type of the three involved handles;
6012 * {@code A}/{@code a}, the types and values of the {@code target}
6013 * parameters and arguments that are consumed by the {@code test}; and
6014 * {@code B}/{@code b}, those types and values of the {@code target}
6015 * parameters and arguments that are not consumed by the {@code test}.
6016 * {@snippet lang="java" :
6017 * boolean test(A...);
6018 * T target(A...,B...);
6019 * T fallback(A...,B...);
6020 * T adapter(A... a,B... b) {
6021 * if (test(a...))
6022 * return target(a..., b...);
6023 * else
6024 * return fallback(a..., b...);
6025 * }
6026 * }
6027 * Note that the test arguments ({@code a...} in the pseudocode) cannot
6028 * be modified by execution of the test, and so are passed unchanged
6029 * from the caller to the target or fallback as appropriate.
6030 * @param test method handle used for test, must return boolean
6031 * @param target method handle to call if test passes
6032 * @param fallback method handle to call if test fails
6033 * @return method handle which incorporates the specified if/then/else logic
6034 * @throws NullPointerException if any argument is null
6035 * @throws IllegalArgumentException if {@code test} does not return boolean,
6036 * or if all three method types do not match (with the return
6037 * type of {@code test} changed to match that of the target).
6038 */
6039 public static MethodHandle guardWithTest(MethodHandle test,
6040 MethodHandle target,
6041 MethodHandle fallback) {
6042 MethodType gtype = test.type();
6043 MethodType ttype = target.type();
6044 MethodType ftype = fallback.type();
6045 if (!ttype.equals(ftype))
6046 throw misMatchedTypes("target and fallback types", ttype, ftype);
6047 if (gtype.returnType() != boolean.class)
6048 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
6049
6050 test = dropArgumentsToMatch(test, 0, ttype.ptypes(), 0, true);
6051 if (test == null) {
6052 throw misMatchedTypes("target and test types", ttype, gtype);
6053 }
6054 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
6055 }
6056
6057 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
6058 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
6059 }
6060
6061 /**
6062 * Makes a method handle which adapts a target method handle,
6063 * by running it inside an exception handler.
6064 * If the target returns normally, the adapter returns that value.
6065 * If an exception matching the specified type is thrown, the fallback
6066 * handle is called instead on the exception, plus the original arguments.
6067 * <p>
6068 * The target and handler must have the same corresponding
6069 * argument and return types, except that handler may omit trailing arguments
6070 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
6071 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
6072 * <p>
6073 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6074 * represents the return type of the {@code target} and {@code handler},
6075 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
6076 * the types and values of arguments to the resulting handle consumed by
6077 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
6078 * resulting handle discarded by {@code handler}.
6079 * {@snippet lang="java" :
6080 * T target(A..., B...);
6081 * T handler(ExType, A...);
6082 * T adapter(A... a, B... b) {
6083 * try {
6084 * return target(a..., b...);
6085 * } catch (ExType ex) {
6086 * return handler(ex, a...);
6087 * }
6088 * }
6089 * }
6090 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6091 * be modified by execution of the target, and so are passed unchanged
6092 * from the caller to the handler, if the handler is invoked.
6093 * <p>
6094 * The target and handler must return the same type, even if the handler
6095 * always throws. (This might happen, for instance, because the handler
6096 * is simulating a {@code finally} clause).
6097 * To create such a throwing handler, compose the handler creation logic
6098 * with {@link #throwException throwException},
6099 * in order to create a method handle of the correct return type.
6100 * @param target method handle to call
6101 * @param exType the type of exception which the handler will catch
6102 * @param handler method handle to call if a matching exception is thrown
6103 * @return method handle which incorporates the specified try/catch logic
6104 * @throws NullPointerException if any argument is null
6105 * @throws IllegalArgumentException if {@code handler} does not accept
6106 * the given exception type, or if the method handle types do
6107 * not match in their return types and their
6108 * corresponding parameters
6109 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
6110 */
6111 public static MethodHandle catchException(MethodHandle target,
6112 Class<? extends Throwable> exType,
6113 MethodHandle handler) {
6114 MethodType ttype = target.type();
6115 MethodType htype = handler.type();
6116 if (!Throwable.class.isAssignableFrom(exType))
6117 throw new ClassCastException(exType.getName());
6118 if (htype.parameterCount() < 1 ||
6119 !htype.parameterType(0).isAssignableFrom(exType))
6120 throw newIllegalArgumentException("handler does not accept exception type "+exType);
6121 if (htype.returnType() != ttype.returnType())
6122 throw misMatchedTypes("target and handler return types", ttype, htype);
6123 handler = dropArgumentsToMatch(handler, 1, ttype.ptypes(), 0, true);
6124 if (handler == null) {
6125 throw misMatchedTypes("target and handler types", ttype, htype);
6126 }
6127 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
6128 }
6129
6130 /**
6131 * Produces a method handle which will throw exceptions of the given {@code exType}.
6132 * The method handle will accept a single argument of {@code exType},
6133 * and immediately throw it as an exception.
6134 * The method type will nominally specify a return of {@code returnType}.
6135 * The return type may be anything convenient: It doesn't matter to the
6136 * method handle's behavior, since it will never return normally.
6137 * @param returnType the return type of the desired method handle
6138 * @param exType the parameter type of the desired method handle
6139 * @return method handle which can throw the given exceptions
6140 * @throws NullPointerException if either argument is null
6141 */
6142 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
6143 if (!Throwable.class.isAssignableFrom(exType))
6144 throw new ClassCastException(exType.getName());
6145 return MethodHandleImpl.throwException(methodType(returnType, exType));
6146 }
6147
6148 /**
6149 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
6150 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
6151 * delivers the loop's result, which is the return value of the resulting handle.
6152 * <p>
6153 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
6154 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
6155 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
6156 * terms of method handles, each clause will specify up to four independent actions:<ul>
6157 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
6158 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
6159 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
6160 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
6161 * </ul>
6162 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
6163 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
6164 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
6165 * <p>
6166 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
6167 * this case. See below for a detailed description.
6168 * <p>
6169 * <em>Parameters optional everywhere:</em>
6170 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
6171 * As an exception, the init functions cannot take any {@code v} parameters,
6172 * because those values are not yet computed when the init functions are executed.
6173 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
6174 * In fact, any clause function may take no arguments at all.
6175 * <p>
6176 * <em>Loop parameters:</em>
6177 * A clause function may take all the iteration variable values it is entitled to, in which case
6178 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
6179 * with their types and values notated as {@code (A...)} and {@code (a...)}.
6180 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
6181 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
6182 * init function is automatically a loop parameter {@code a}.)
6183 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
6184 * These loop parameters act as loop-invariant values visible across the whole loop.
6185 * <p>
6186 * <em>Parameters visible everywhere:</em>
6187 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
6188 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
6189 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
6190 * Most clause functions will not need all of this information, but they will be formally connected to it
6191 * as if by {@link #dropArguments}.
6192 * <a id="astar"></a>
6193 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
6194 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
6195 * In that notation, the general form of an init function parameter list
6196 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
6197 * <p>
6198 * <em>Checking clause structure:</em>
6199 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
6200 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
6201 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
6202 * met by the inputs to the loop combinator.
6203 * <p>
6204 * <em>Effectively identical sequences:</em>
6205 * <a id="effid"></a>
6206 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
6207 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
6208 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
6209 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
6210 * that longest list.
6211 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
6212 * and the same is true if more sequences of the form {@code (V... A*)} are added.
6213 * <p>
6214 * <em>Step 0: Determine clause structure.</em><ol type="a">
6215 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
6216 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
6217 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
6218 * four. Padding takes place by appending elements to the array.
6219 * <li>Clauses with all {@code null}s are disregarded.
6220 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
6221 * </ol>
6222 * <p>
6223 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
6224 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
6225 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
6226 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
6227 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
6228 * iteration variable type.
6229 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
6230 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
6231 * </ol>
6232 * <p>
6233 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
6234 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
6235 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
6236 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
6237 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
6238 * (These types will be checked in step 2, along with all the clause function types.)
6239 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
6240 * <li>All of the collected parameter lists must be effectively identical.
6241 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
6242 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
6243 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
6244 * the "internal parameter list".
6245 * </ul>
6246 * <p>
6247 * <em>Step 1C: Determine loop return type.</em><ol type="a">
6248 * <li>Examine fini function return types, disregarding omitted fini functions.
6249 * <li>If there are no fini functions, the loop return type is {@code void}.
6250 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
6251 * type.
6252 * </ol>
6253 * <p>
6254 * <em>Step 1D: Check other types.</em><ol type="a">
6255 * <li>There must be at least one non-omitted pred function.
6256 * <li>Every non-omitted pred function must have a {@code boolean} return type.
6257 * </ol>
6258 * <p>
6259 * <em>Step 2: Determine parameter lists.</em><ol type="a">
6260 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
6261 * <li>The parameter list for init functions will be adjusted to the external parameter list.
6262 * (Note that their parameter lists are already effectively identical to this list.)
6263 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
6264 * effectively identical to the internal parameter list {@code (V... A...)}.
6265 * </ol>
6266 * <p>
6267 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
6268 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
6269 * type.
6270 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
6271 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
6272 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
6273 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
6274 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
6275 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
6276 * loop return type.
6277 * </ol>
6278 * <p>
6279 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
6280 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
6281 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
6282 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
6283 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
6284 * pad out the end of the list.
6285 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
6286 * </ol>
6287 * <p>
6288 * <em>Final observations.</em><ol type="a">
6289 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
6290 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
6291 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
6292 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
6293 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
6294 * <li>Each pair of init and step functions agrees in their return type {@code V}.
6295 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
6296 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
6297 * </ol>
6298 * <p>
6299 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
6300 * <ul>
6301 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
6302 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
6303 * (Only one {@code Pn} has to be non-{@code null}.)
6304 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
6305 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
6306 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
6307 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
6308 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
6309 * the resulting loop handle's parameter types {@code (A...)}.
6310 * </ul>
6311 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
6312 * which is natural if most of the loop computation happens in the steps. For some loops,
6313 * the burden of computation might be heaviest in the pred functions, and so the pred functions
6314 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
6315 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
6316 * where the init functions will need the extra parameters. For such reasons, the rules for
6317 * determining these parameters are as symmetric as possible, across all clause parts.
6318 * In general, the loop parameters function as common invariant values across the whole
6319 * loop, while the iteration variables function as common variant values, or (if there is
6320 * no step function) as internal loop invariant temporaries.
6321 * <p>
6322 * <em>Loop execution.</em><ol type="a">
6323 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
6324 * every clause function. These locals are loop invariant.
6325 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
6326 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
6327 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
6328 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
6329 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
6330 * (in argument order).
6331 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
6332 * returns {@code false}.
6333 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
6334 * sequence {@code (v...)} of loop variables.
6335 * The updated value is immediately visible to all subsequent function calls.
6336 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
6337 * (of type {@code R}) is returned from the loop as a whole.
6338 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
6339 * except by throwing an exception.
6340 * </ol>
6341 * <p>
6342 * <em>Usage tips.</em>
6343 * <ul>
6344 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
6345 * sometimes a step function only needs to observe the current value of its own variable.
6346 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
6347 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
6348 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
6349 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
6350 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
6351 * <li>If some of the clause functions are virtual methods on an instance, the instance
6352 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
6353 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
6354 * will be the first iteration variable value, and it will be easy to use virtual
6355 * methods as clause parts, since all of them will take a leading instance reference matching that value.
6356 * </ul>
6357 * <p>
6358 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
6359 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
6360 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
6361 * {@snippet lang="java" :
6362 * V... init...(A...);
6363 * boolean pred...(V..., A...);
6364 * V... step...(V..., A...);
6365 * R fini...(V..., A...);
6366 * R loop(A... a) {
6367 * V... v... = init...(a...);
6368 * for (;;) {
6369 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
6370 * v = s(v..., a...);
6371 * if (!p(v..., a...)) {
6372 * return f(v..., a...);
6373 * }
6374 * }
6375 * }
6376 * }
6377 * }
6378 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
6379 * to their full length, even though individual clause functions may neglect to take them all.
6380 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
6381 *
6382 * @apiNote Example:
6383 * {@snippet lang="java" :
6384 * // iterative implementation of the factorial function as a loop handle
6385 * static int one(int k) { return 1; }
6386 * static int inc(int i, int acc, int k) { return i + 1; }
6387 * static int mult(int i, int acc, int k) { return i * acc; }
6388 * static boolean pred(int i, int acc, int k) { return i < k; }
6389 * static int fin(int i, int acc, int k) { return acc; }
6390 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6391 * // null initializer for counter, should initialize to 0
6392 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6393 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6394 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6395 * assertEquals(120, loop.invoke(5));
6396 * }
6397 * The same example, dropping arguments and using combinators:
6398 * {@snippet lang="java" :
6399 * // simplified implementation of the factorial function as a loop handle
6400 * static int inc(int i) { return i + 1; } // drop acc, k
6401 * static int mult(int i, int acc) { return i * acc; } //drop k
6402 * static boolean cmp(int i, int k) { return i < k; }
6403 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
6404 * // null initializer for counter, should initialize to 0
6405 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6406 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
6407 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
6408 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6409 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6410 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6411 * assertEquals(720, loop.invoke(6));
6412 * }
6413 * A similar example, using a helper object to hold a loop parameter:
6414 * {@snippet lang="java" :
6415 * // instance-based implementation of the factorial function as a loop handle
6416 * static class FacLoop {
6417 * final int k;
6418 * FacLoop(int k) { this.k = k; }
6419 * int inc(int i) { return i + 1; }
6420 * int mult(int i, int acc) { return i * acc; }
6421 * boolean pred(int i) { return i < k; }
6422 * int fin(int i, int acc) { return acc; }
6423 * }
6424 * // assume MH_FacLoop is a handle to the constructor
6425 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6426 * // null initializer for counter, should initialize to 0
6427 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6428 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
6429 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6430 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6431 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
6432 * assertEquals(5040, loop.invoke(7));
6433 * }
6434 *
6435 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
6436 *
6437 * @return a method handle embodying the looping behavior as defined by the arguments.
6438 *
6439 * @throws IllegalArgumentException in case any of the constraints described above is violated.
6440 *
6441 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
6442 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6443 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
6444 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
6445 * @since 9
6446 */
6447 public static MethodHandle loop(MethodHandle[]... clauses) {
6448 // Step 0: determine clause structure.
6449 loopChecks0(clauses);
6450
6451 List<MethodHandle> init = new ArrayList<>();
6452 List<MethodHandle> step = new ArrayList<>();
6453 List<MethodHandle> pred = new ArrayList<>();
6454 List<MethodHandle> fini = new ArrayList<>();
6455
6456 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
6457 init.add(clause[0]); // all clauses have at least length 1
6458 step.add(clause.length <= 1 ? null : clause[1]);
6459 pred.add(clause.length <= 2 ? null : clause[2]);
6460 fini.add(clause.length <= 3 ? null : clause[3]);
6461 });
6462
6463 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
6464 final int nclauses = init.size();
6465
6466 // Step 1A: determine iteration variables (V...).
6467 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
6468 for (int i = 0; i < nclauses; ++i) {
6469 MethodHandle in = init.get(i);
6470 MethodHandle st = step.get(i);
6471 if (in == null && st == null) {
6472 iterationVariableTypes.add(void.class);
6473 } else if (in != null && st != null) {
6474 loopChecks1a(i, in, st);
6475 iterationVariableTypes.add(in.type().returnType());
6476 } else {
6477 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
6478 }
6479 }
6480 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).toList();
6481
6482 // Step 1B: determine loop parameters (A...).
6483 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
6484 loopChecks1b(init, commonSuffix);
6485
6486 // Step 1C: determine loop return type.
6487 // Step 1D: check other types.
6488 // local variable required here; see JDK-8223553
6489 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
6490 .map(MethodType::returnType);
6491 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
6492 loopChecks1cd(pred, fini, loopReturnType);
6493
6494 // Step 2: determine parameter lists.
6495 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
6496 commonParameterSequence.addAll(commonSuffix);
6497 loopChecks2(step, pred, fini, commonParameterSequence);
6498 // Step 3: fill in omitted functions.
6499 for (int i = 0; i < nclauses; ++i) {
6500 Class<?> t = iterationVariableTypes.get(i);
6501 if (init.get(i) == null) {
6502 init.set(i, empty(methodType(t, commonSuffix)));
6503 }
6504 if (step.get(i) == null) {
6505 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
6506 }
6507 if (pred.get(i) == null) {
6508 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence));
6509 }
6510 if (fini.get(i) == null) {
6511 fini.set(i, empty(methodType(t, commonParameterSequence)));
6512 }
6513 }
6514
6515 // Step 4: fill in missing parameter types.
6516 // Also convert all handles to fixed-arity handles.
6517 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
6518 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
6519 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
6520 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
6521
6522 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
6523 allMatch(pl -> pl.equals(commonSuffix));
6524 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
6525 allMatch(pl -> pl.equals(commonParameterSequence));
6526
6527 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
6528 }
6529
6530 private static void loopChecks0(MethodHandle[][] clauses) {
6531 if (clauses == null || clauses.length == 0) {
6532 throw newIllegalArgumentException("null or no clauses passed");
6533 }
6534 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
6535 throw newIllegalArgumentException("null clauses are not allowed");
6536 }
6537 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
6538 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
6539 }
6540 }
6541
6542 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
6543 if (in.type().returnType() != st.type().returnType()) {
6544 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
6545 st.type().returnType());
6546 }
6547 }
6548
6549 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
6550 return mhs.filter(Objects::nonNull)
6551 // take only those that can contribute to a common suffix because they are longer than the prefix
6552 .map(MethodHandle::type)
6553 .filter(t -> t.parameterCount() > skipSize)
6554 .max(Comparator.comparingInt(MethodType::parameterCount))
6555 .map(methodType -> List.of(Arrays.copyOfRange(methodType.ptypes(), skipSize, methodType.parameterCount())))
6556 .orElse(List.of());
6557 }
6558
6559 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
6560 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
6561 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
6562 return longest1.size() >= longest2.size() ? longest1 : longest2;
6563 }
6564
6565 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
6566 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
6567 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
6568 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
6569 " (common suffix: " + commonSuffix + ")");
6570 }
6571 }
6572
6573 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
6574 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6575 anyMatch(t -> t != loopReturnType)) {
6576 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
6577 loopReturnType + ")");
6578 }
6579
6580 if (pred.stream().noneMatch(Objects::nonNull)) {
6581 throw newIllegalArgumentException("no predicate found", pred);
6582 }
6583 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6584 anyMatch(t -> t != boolean.class)) {
6585 throw newIllegalArgumentException("predicates must have boolean return type", pred);
6586 }
6587 }
6588
6589 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
6590 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
6591 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
6592 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
6593 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
6594 }
6595 }
6596
6597 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
6598 return hs.stream().map(h -> {
6599 int pc = h.type().parameterCount();
6600 int tpsize = targetParams.size();
6601 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h;
6602 }).toList();
6603 }
6604
6605 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
6606 return hs.stream().map(MethodHandle::asFixedArity).toList();
6607 }
6608
6609 /**
6610 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
6611 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6612 * <p>
6613 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6614 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
6615 * evaluates to {@code true}).
6616 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
6617 * <p>
6618 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6619 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6620 * and updated with the value returned from its invocation. The result of loop execution will be
6621 * the final value of the additional loop-local variable (if present).
6622 * <p>
6623 * The following rules hold for these argument handles:<ul>
6624 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6625 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6626 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6627 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6628 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6629 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6630 * It will constrain the parameter lists of the other loop parts.
6631 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6632 * list {@code (A...)} is called the <em>external parameter list</em>.
6633 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6634 * additional state variable of the loop.
6635 * The body must both accept and return a value of this type {@code V}.
6636 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6637 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6638 * <a href="MethodHandles.html#effid">effectively identical</a>
6639 * to the external parameter list {@code (A...)}.
6640 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6641 * {@linkplain #empty default value}.
6642 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6643 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6644 * effectively identical to the internal parameter list.
6645 * </ul>
6646 * <p>
6647 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6648 * <li>The loop handle's result type is the result type {@code V} of the body.
6649 * <li>The loop handle's parameter types are the types {@code (A...)},
6650 * from the external parameter list.
6651 * </ul>
6652 * <p>
6653 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6654 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6655 * passed to the loop.
6656 * {@snippet lang="java" :
6657 * V init(A...);
6658 * boolean pred(V, A...);
6659 * V body(V, A...);
6660 * V whileLoop(A... a...) {
6661 * V v = init(a...);
6662 * while (pred(v, a...)) {
6663 * v = body(v, a...);
6664 * }
6665 * return v;
6666 * }
6667 * }
6668 *
6669 * @apiNote Example:
6670 * {@snippet lang="java" :
6671 * // implement the zip function for lists as a loop handle
6672 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
6673 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
6674 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
6675 * zip.add(a.next());
6676 * zip.add(b.next());
6677 * return zip;
6678 * }
6679 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
6680 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
6681 * List<String> a = Arrays.asList("a", "b", "c", "d");
6682 * List<String> b = Arrays.asList("e", "f", "g", "h");
6683 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
6684 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
6685 * }
6686 *
6687 *
6688 * @apiNote The implementation of this method can be expressed as follows:
6689 * {@snippet lang="java" :
6690 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6691 * MethodHandle fini = (body.type().returnType() == void.class
6692 * ? null : identity(body.type().returnType()));
6693 * MethodHandle[]
6694 * checkExit = { null, null, pred, fini },
6695 * varBody = { init, body };
6696 * return loop(checkExit, varBody);
6697 * }
6698 * }
6699 *
6700 * @param init optional initializer, providing the initial value of the loop variable.
6701 * May be {@code null}, implying a default initial value. See above for other constraints.
6702 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6703 * above for other constraints.
6704 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6705 * See above for other constraints.
6706 *
6707 * @return a method handle implementing the {@code while} loop as described by the arguments.
6708 * @throws IllegalArgumentException if the rules for the arguments are violated.
6709 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6710 *
6711 * @see #loop(MethodHandle[][])
6712 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6713 * @since 9
6714 */
6715 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6716 whileLoopChecks(init, pred, body);
6717 MethodHandle fini = identityOrVoid(body.type().returnType());
6718 MethodHandle[] checkExit = { null, null, pred, fini };
6719 MethodHandle[] varBody = { init, body };
6720 return loop(checkExit, varBody);
6721 }
6722
6723 /**
6724 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
6725 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6726 * <p>
6727 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6728 * method will, in each iteration, first execute its body and then evaluate the predicate.
6729 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
6730 * <p>
6731 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6732 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6733 * and updated with the value returned from its invocation. The result of loop execution will be
6734 * the final value of the additional loop-local variable (if present).
6735 * <p>
6736 * The following rules hold for these argument handles:<ul>
6737 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6738 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6739 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6740 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6741 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6742 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6743 * It will constrain the parameter lists of the other loop parts.
6744 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6745 * list {@code (A...)} is called the <em>external parameter list</em>.
6746 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6747 * additional state variable of the loop.
6748 * The body must both accept and return a value of this type {@code V}.
6749 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6750 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6751 * <a href="MethodHandles.html#effid">effectively identical</a>
6752 * to the external parameter list {@code (A...)}.
6753 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6754 * {@linkplain #empty default value}.
6755 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6756 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6757 * effectively identical to the internal parameter list.
6758 * </ul>
6759 * <p>
6760 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6761 * <li>The loop handle's result type is the result type {@code V} of the body.
6762 * <li>The loop handle's parameter types are the types {@code (A...)},
6763 * from the external parameter list.
6764 * </ul>
6765 * <p>
6766 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6767 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6768 * passed to the loop.
6769 * {@snippet lang="java" :
6770 * V init(A...);
6771 * boolean pred(V, A...);
6772 * V body(V, A...);
6773 * V doWhileLoop(A... a...) {
6774 * V v = init(a...);
6775 * do {
6776 * v = body(v, a...);
6777 * } while (pred(v, a...));
6778 * return v;
6779 * }
6780 * }
6781 *
6782 * @apiNote Example:
6783 * {@snippet lang="java" :
6784 * // int i = 0; while (i < limit) { ++i; } return i; => limit
6785 * static int zero(int limit) { return 0; }
6786 * static int step(int i, int limit) { return i + 1; }
6787 * static boolean pred(int i, int limit) { return i < limit; }
6788 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
6789 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
6790 * assertEquals(23, loop.invoke(23));
6791 * }
6792 *
6793 *
6794 * @apiNote The implementation of this method can be expressed as follows:
6795 * {@snippet lang="java" :
6796 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6797 * MethodHandle fini = (body.type().returnType() == void.class
6798 * ? null : identity(body.type().returnType()));
6799 * MethodHandle[] clause = { init, body, pred, fini };
6800 * return loop(clause);
6801 * }
6802 * }
6803 *
6804 * @param init optional initializer, providing the initial value of the loop variable.
6805 * May be {@code null}, implying a default initial value. See above for other constraints.
6806 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6807 * See above for other constraints.
6808 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6809 * above for other constraints.
6810 *
6811 * @return a method handle implementing the {@code while} loop as described by the arguments.
6812 * @throws IllegalArgumentException if the rules for the arguments are violated.
6813 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6814 *
6815 * @see #loop(MethodHandle[][])
6816 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
6817 * @since 9
6818 */
6819 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6820 whileLoopChecks(init, pred, body);
6821 MethodHandle fini = identityOrVoid(body.type().returnType());
6822 MethodHandle[] clause = {init, body, pred, fini };
6823 return loop(clause);
6824 }
6825
6826 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
6827 Objects.requireNonNull(pred);
6828 Objects.requireNonNull(body);
6829 MethodType bodyType = body.type();
6830 Class<?> returnType = bodyType.returnType();
6831 List<Class<?>> innerList = bodyType.parameterList();
6832 List<Class<?>> outerList = innerList;
6833 if (returnType == void.class) {
6834 // OK
6835 } else if (innerList.isEmpty() || innerList.get(0) != returnType) {
6836 // leading V argument missing => error
6837 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6838 throw misMatchedTypes("body function", bodyType, expected);
6839 } else {
6840 outerList = innerList.subList(1, innerList.size());
6841 }
6842 MethodType predType = pred.type();
6843 if (predType.returnType() != boolean.class ||
6844 !predType.effectivelyIdenticalParameters(0, innerList)) {
6845 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
6846 }
6847 if (init != null) {
6848 MethodType initType = init.type();
6849 if (initType.returnType() != returnType ||
6850 !initType.effectivelyIdenticalParameters(0, outerList)) {
6851 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
6852 }
6853 }
6854 }
6855
6856 /**
6857 * Constructs a loop that runs a given number of iterations.
6858 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6859 * <p>
6860 * The number of iterations is determined by the {@code iterations} handle evaluation result.
6861 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
6862 * It will be initialized to 0 and incremented by 1 in each iteration.
6863 * <p>
6864 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6865 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6866 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6867 * <p>
6868 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6869 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6870 * iteration variable.
6871 * The result of the loop handle execution will be the final {@code V} value of that variable
6872 * (or {@code void} if there is no {@code V} variable).
6873 * <p>
6874 * The following rules hold for the argument handles:<ul>
6875 * <li>The {@code iterations} handle must not be {@code null}, and must return
6876 * the type {@code int}, referred to here as {@code I} in parameter type lists.
6877 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6878 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
6879 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6880 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
6881 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
6882 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
6883 * of types called the <em>internal parameter list</em>.
6884 * It will constrain the parameter lists of the other loop parts.
6885 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
6886 * with no additional {@code A} types, then the internal parameter list is extended by
6887 * the argument types {@code A...} of the {@code iterations} handle.
6888 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
6889 * list {@code (A...)} is called the <em>external parameter list</em>.
6890 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6891 * additional state variable of the loop.
6892 * The body must both accept a leading parameter and return a value of this type {@code V}.
6893 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6894 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6895 * <a href="MethodHandles.html#effid">effectively identical</a>
6896 * to the external parameter list {@code (A...)}.
6897 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6898 * {@linkplain #empty default value}.
6899 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
6900 * effectively identical to the external parameter list {@code (A...)}.
6901 * </ul>
6902 * <p>
6903 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6904 * <li>The loop handle's result type is the result type {@code V} of the body.
6905 * <li>The loop handle's parameter types are the types {@code (A...)},
6906 * from the external parameter list.
6907 * </ul>
6908 * <p>
6909 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6910 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
6911 * arguments passed to the loop.
6912 * {@snippet lang="java" :
6913 * int iterations(A...);
6914 * V init(A...);
6915 * V body(V, int, A...);
6916 * V countedLoop(A... a...) {
6917 * int end = iterations(a...);
6918 * V v = init(a...);
6919 * for (int i = 0; i < end; ++i) {
6920 * v = body(v, i, a...);
6921 * }
6922 * return v;
6923 * }
6924 * }
6925 *
6926 * @apiNote Example with a fully conformant body method:
6927 * {@snippet lang="java" :
6928 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6929 * // => a variation on a well known theme
6930 * static String step(String v, int counter, String init) { return "na " + v; }
6931 * // assume MH_step is a handle to the method above
6932 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
6933 * MethodHandle start = MethodHandles.identity(String.class);
6934 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
6935 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
6936 * }
6937 *
6938 * @apiNote Example with the simplest possible body method type,
6939 * and passing the number of iterations to the loop invocation:
6940 * {@snippet lang="java" :
6941 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6942 * // => a variation on a well known theme
6943 * static String step(String v, int counter ) { return "na " + v; }
6944 * // assume MH_step is a handle to the method above
6945 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
6946 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
6947 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
6948 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
6949 * }
6950 *
6951 * @apiNote Example that treats the number of iterations, string to append to, and string to append
6952 * as loop parameters:
6953 * {@snippet lang="java" :
6954 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6955 * // => a variation on a well known theme
6956 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
6957 * // assume MH_step is a handle to the method above
6958 * MethodHandle count = MethodHandles.identity(int.class);
6959 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
6960 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
6961 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
6962 * }
6963 *
6964 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
6965 * to enforce a loop type:
6966 * {@snippet lang="java" :
6967 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6968 * // => a variation on a well known theme
6969 * static String step(String v, int counter, String pre) { return pre + " " + v; }
6970 * // assume MH_step is a handle to the method above
6971 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
6972 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
6973 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
6974 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
6975 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
6976 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
6977 * }
6978 *
6979 * @apiNote The implementation of this method can be expressed as follows:
6980 * {@snippet lang="java" :
6981 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
6982 * return countedLoop(empty(iterations.type()), iterations, init, body);
6983 * }
6984 * }
6985 *
6986 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
6987 * result type must be {@code int}. See above for other constraints.
6988 * @param init optional initializer, providing the initial value of the loop variable.
6989 * May be {@code null}, implying a default initial value. See above for other constraints.
6990 * @param body body of the loop, which may not be {@code null}.
6991 * It controls the loop parameters and result type in the standard case (see above for details).
6992 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
6993 * and may accept any number of additional types.
6994 * See above for other constraints.
6995 *
6996 * @return a method handle representing the loop.
6997 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
6998 * @throws IllegalArgumentException if any argument violates the rules formulated above.
6999 *
7000 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
7001 * @since 9
7002 */
7003 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7004 return countedLoop(empty(iterations.type()), iterations, init, body);
7005 }
7006
7007 /**
7008 * Constructs a loop that counts over a range of numbers.
7009 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7010 * <p>
7011 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
7012 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
7013 * values of the loop counter.
7014 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
7015 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
7016 * <p>
7017 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7018 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7019 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7020 * <p>
7021 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7022 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7023 * iteration variable.
7024 * The result of the loop handle execution will be the final {@code V} value of that variable
7025 * (or {@code void} if there is no {@code V} variable).
7026 * <p>
7027 * The following rules hold for the argument handles:<ul>
7028 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
7029 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
7030 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7031 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7032 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7033 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7034 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7035 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7036 * of types called the <em>internal parameter list</em>.
7037 * It will constrain the parameter lists of the other loop parts.
7038 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7039 * with no additional {@code A} types, then the internal parameter list is extended by
7040 * the argument types {@code A...} of the {@code end} handle.
7041 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7042 * list {@code (A...)} is called the <em>external parameter list</em>.
7043 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7044 * additional state variable of the loop.
7045 * The body must both accept a leading parameter and return a value of this type {@code V}.
7046 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7047 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7048 * <a href="MethodHandles.html#effid">effectively identical</a>
7049 * to the external parameter list {@code (A...)}.
7050 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7051 * {@linkplain #empty default value}.
7052 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
7053 * effectively identical to the external parameter list {@code (A...)}.
7054 * <li>Likewise, the parameter list of {@code end} must be effectively identical
7055 * to the external parameter list.
7056 * </ul>
7057 * <p>
7058 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7059 * <li>The loop handle's result type is the result type {@code V} of the body.
7060 * <li>The loop handle's parameter types are the types {@code (A...)},
7061 * from the external parameter list.
7062 * </ul>
7063 * <p>
7064 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7065 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7066 * arguments passed to the loop.
7067 * {@snippet lang="java" :
7068 * int start(A...);
7069 * int end(A...);
7070 * V init(A...);
7071 * V body(V, int, A...);
7072 * V countedLoop(A... a...) {
7073 * int e = end(a...);
7074 * int s = start(a...);
7075 * V v = init(a...);
7076 * for (int i = s; i < e; ++i) {
7077 * v = body(v, i, a...);
7078 * }
7079 * return v;
7080 * }
7081 * }
7082 *
7083 * @apiNote The implementation of this method can be expressed as follows:
7084 * {@snippet lang="java" :
7085 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7086 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
7087 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
7088 * // the following semantics:
7089 * // MH_increment: (int limit, int counter) -> counter + 1
7090 * // MH_predicate: (int limit, int counter) -> counter < limit
7091 * Class<?> counterType = start.type().returnType(); // int
7092 * Class<?> returnType = body.type().returnType();
7093 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
7094 * if (returnType != void.class) { // ignore the V variable
7095 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7096 * pred = dropArguments(pred, 1, returnType); // ditto
7097 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
7098 * }
7099 * body = dropArguments(body, 0, counterType); // ignore the limit variable
7100 * MethodHandle[]
7101 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7102 * bodyClause = { init, body }, // v = init(); v = body(v, i)
7103 * indexVar = { start, incr }; // i = start(); i = i + 1
7104 * return loop(loopLimit, bodyClause, indexVar);
7105 * }
7106 * }
7107 *
7108 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
7109 * See above for other constraints.
7110 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
7111 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
7112 * @param init optional initializer, providing the initial value of the loop variable.
7113 * May be {@code null}, implying a default initial value. See above for other constraints.
7114 * @param body body of the loop, which may not be {@code null}.
7115 * It controls the loop parameters and result type in the standard case (see above for details).
7116 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7117 * and may accept any number of additional types.
7118 * See above for other constraints.
7119 *
7120 * @return a method handle representing the loop.
7121 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
7122 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7123 *
7124 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
7125 * @since 9
7126 */
7127 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7128 countedLoopChecks(start, end, init, body);
7129 Class<?> counterType = start.type().returnType(); // int, but who's counting?
7130 Class<?> limitType = end.type().returnType(); // yes, int again
7131 Class<?> returnType = body.type().returnType();
7132 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
7133 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
7134 MethodHandle retv = null;
7135 if (returnType != void.class) {
7136 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7137 pred = dropArguments(pred, 1, returnType); // ditto
7138 retv = dropArguments(identity(returnType), 0, counterType);
7139 }
7140 body = dropArguments(body, 0, counterType); // ignore the limit variable
7141 MethodHandle[]
7142 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7143 bodyClause = { init, body }, // v = init(); v = body(v, i)
7144 indexVar = { start, incr }; // i = start(); i = i + 1
7145 return loop(loopLimit, bodyClause, indexVar);
7146 }
7147
7148 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7149 Objects.requireNonNull(start);
7150 Objects.requireNonNull(end);
7151 Objects.requireNonNull(body);
7152 Class<?> counterType = start.type().returnType();
7153 if (counterType != int.class) {
7154 MethodType expected = start.type().changeReturnType(int.class);
7155 throw misMatchedTypes("start function", start.type(), expected);
7156 } else if (end.type().returnType() != counterType) {
7157 MethodType expected = end.type().changeReturnType(counterType);
7158 throw misMatchedTypes("end function", end.type(), expected);
7159 }
7160 MethodType bodyType = body.type();
7161 Class<?> returnType = bodyType.returnType();
7162 List<Class<?>> innerList = bodyType.parameterList();
7163 // strip leading V value if present
7164 int vsize = (returnType == void.class ? 0 : 1);
7165 if (vsize != 0 && (innerList.isEmpty() || innerList.get(0) != returnType)) {
7166 // argument list has no "V" => error
7167 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7168 throw misMatchedTypes("body function", bodyType, expected);
7169 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
7170 // missing I type => error
7171 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
7172 throw misMatchedTypes("body function", bodyType, expected);
7173 }
7174 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
7175 if (outerList.isEmpty()) {
7176 // special case; take lists from end handle
7177 outerList = end.type().parameterList();
7178 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
7179 }
7180 MethodType expected = methodType(counterType, outerList);
7181 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
7182 throw misMatchedTypes("start parameter types", start.type(), expected);
7183 }
7184 if (end.type() != start.type() &&
7185 !end.type().effectivelyIdenticalParameters(0, outerList)) {
7186 throw misMatchedTypes("end parameter types", end.type(), expected);
7187 }
7188 if (init != null) {
7189 MethodType initType = init.type();
7190 if (initType.returnType() != returnType ||
7191 !initType.effectivelyIdenticalParameters(0, outerList)) {
7192 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7193 }
7194 }
7195 }
7196
7197 /**
7198 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
7199 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7200 * <p>
7201 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
7202 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
7203 * <p>
7204 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7205 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7206 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7207 * <p>
7208 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7209 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7210 * iteration variable.
7211 * The result of the loop handle execution will be the final {@code V} value of that variable
7212 * (or {@code void} if there is no {@code V} variable).
7213 * <p>
7214 * The following rules hold for the argument handles:<ul>
7215 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7216 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
7217 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7218 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
7219 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
7220 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
7221 * of types called the <em>internal parameter list</em>.
7222 * It will constrain the parameter lists of the other loop parts.
7223 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
7224 * with no additional {@code A} types, then the internal parameter list is extended by
7225 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
7226 * single type {@code Iterable} is added and constitutes the {@code A...} list.
7227 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
7228 * list {@code (A...)} is called the <em>external parameter list</em>.
7229 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7230 * additional state variable of the loop.
7231 * The body must both accept a leading parameter and return a value of this type {@code V}.
7232 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7233 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7234 * <a href="MethodHandles.html#effid">effectively identical</a>
7235 * to the external parameter list {@code (A...)}.
7236 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7237 * {@linkplain #empty default value}.
7238 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
7239 * type {@code java.util.Iterator} or a subtype thereof.
7240 * The iterator it produces when the loop is executed will be assumed
7241 * to yield values which can be converted to type {@code T}.
7242 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
7243 * effectively identical to the external parameter list {@code (A...)}.
7244 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
7245 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
7246 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
7247 * handle parameter is adjusted to accept the leading {@code A} type, as if by
7248 * the {@link MethodHandle#asType asType} conversion method.
7249 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
7250 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
7251 * </ul>
7252 * <p>
7253 * The type {@code T} may be either a primitive or reference.
7254 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
7255 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
7256 * as if by the {@link MethodHandle#asType asType} conversion method.
7257 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
7258 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
7259 * <p>
7260 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7261 * <li>The loop handle's result type is the result type {@code V} of the body.
7262 * <li>The loop handle's parameter types are the types {@code (A...)},
7263 * from the external parameter list.
7264 * </ul>
7265 * <p>
7266 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7267 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
7268 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
7269 * {@snippet lang="java" :
7270 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
7271 * V init(A...);
7272 * V body(V,T,A...);
7273 * V iteratedLoop(A... a...) {
7274 * Iterator<T> it = iterator(a...);
7275 * V v = init(a...);
7276 * while (it.hasNext()) {
7277 * T t = it.next();
7278 * v = body(v, t, a...);
7279 * }
7280 * return v;
7281 * }
7282 * }
7283 *
7284 * @apiNote Example:
7285 * {@snippet lang="java" :
7286 * // get an iterator from a list
7287 * static List<String> reverseStep(List<String> r, String e) {
7288 * r.add(0, e);
7289 * return r;
7290 * }
7291 * static List<String> newArrayList() { return new ArrayList<>(); }
7292 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
7293 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
7294 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
7295 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
7296 * assertEquals(reversedList, (List<String>) loop.invoke(list));
7297 * }
7298 *
7299 * @apiNote The implementation of this method can be expressed approximately as follows:
7300 * {@snippet lang="java" :
7301 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7302 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
7303 * Class<?> returnType = body.type().returnType();
7304 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7305 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
7306 * MethodHandle retv = null, step = body, startIter = iterator;
7307 * if (returnType != void.class) {
7308 * // the simple thing first: in (I V A...), drop the I to get V
7309 * retv = dropArguments(identity(returnType), 0, Iterator.class);
7310 * // body type signature (V T A...), internal loop types (I V A...)
7311 * step = swapArguments(body, 0, 1); // swap V <-> T
7312 * }
7313 * if (startIter == null) startIter = MH_getIter;
7314 * MethodHandle[]
7315 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
7316 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
7317 * return loop(iterVar, bodyClause);
7318 * }
7319 * }
7320 *
7321 * @param iterator an optional handle to return the iterator to start the loop.
7322 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
7323 * See above for other constraints.
7324 * @param init optional initializer, providing the initial value of the loop variable.
7325 * May be {@code null}, implying a default initial value. See above for other constraints.
7326 * @param body body of the loop, which may not be {@code null}.
7327 * It controls the loop parameters and result type in the standard case (see above for details).
7328 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
7329 * and may accept any number of additional types.
7330 * See above for other constraints.
7331 *
7332 * @return a method handle embodying the iteration loop functionality.
7333 * @throws NullPointerException if the {@code body} handle is {@code null}.
7334 * @throws IllegalArgumentException if any argument violates the above requirements.
7335 *
7336 * @since 9
7337 */
7338 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7339 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
7340 Class<?> returnType = body.type().returnType();
7341 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
7342 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
7343 MethodHandle startIter;
7344 MethodHandle nextVal;
7345 {
7346 MethodType iteratorType;
7347 if (iterator == null) {
7348 // derive argument type from body, if available, else use Iterable
7349 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
7350 iteratorType = startIter.type().changeParameterType(0, iterableType);
7351 } else {
7352 // force return type to the internal iterator class
7353 iteratorType = iterator.type().changeReturnType(Iterator.class);
7354 startIter = iterator;
7355 }
7356 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7357 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
7358
7359 // perform the asType transforms under an exception transformer, as per spec.:
7360 try {
7361 startIter = startIter.asType(iteratorType);
7362 nextVal = nextRaw.asType(nextValType);
7363 } catch (WrongMethodTypeException ex) {
7364 throw new IllegalArgumentException(ex);
7365 }
7366 }
7367
7368 MethodHandle retv = null, step = body;
7369 if (returnType != void.class) {
7370 // the simple thing first: in (I V A...), drop the I to get V
7371 retv = dropArguments(identity(returnType), 0, Iterator.class);
7372 // body type signature (V T A...), internal loop types (I V A...)
7373 step = swapArguments(body, 0, 1); // swap V <-> T
7374 }
7375
7376 MethodHandle[]
7377 iterVar = { startIter, null, hasNext, retv },
7378 bodyClause = { init, filterArgument(step, 0, nextVal) };
7379 return loop(iterVar, bodyClause);
7380 }
7381
7382 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7383 Objects.requireNonNull(body);
7384 MethodType bodyType = body.type();
7385 Class<?> returnType = bodyType.returnType();
7386 List<Class<?>> internalParamList = bodyType.parameterList();
7387 // strip leading V value if present
7388 int vsize = (returnType == void.class ? 0 : 1);
7389 if (vsize != 0 && (internalParamList.isEmpty() || internalParamList.get(0) != returnType)) {
7390 // argument list has no "V" => error
7391 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7392 throw misMatchedTypes("body function", bodyType, expected);
7393 } else if (internalParamList.size() <= vsize) {
7394 // missing T type => error
7395 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
7396 throw misMatchedTypes("body function", bodyType, expected);
7397 }
7398 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
7399 Class<?> iterableType = null;
7400 if (iterator != null) {
7401 // special case; if the body handle only declares V and T then
7402 // the external parameter list is obtained from iterator handle
7403 if (externalParamList.isEmpty()) {
7404 externalParamList = iterator.type().parameterList();
7405 }
7406 MethodType itype = iterator.type();
7407 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
7408 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
7409 }
7410 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
7411 MethodType expected = methodType(itype.returnType(), externalParamList);
7412 throw misMatchedTypes("iterator parameters", itype, expected);
7413 }
7414 } else {
7415 if (externalParamList.isEmpty()) {
7416 // special case; if the iterator handle is null and the body handle
7417 // only declares V and T then the external parameter list consists
7418 // of Iterable
7419 externalParamList = List.of(Iterable.class);
7420 iterableType = Iterable.class;
7421 } else {
7422 // special case; if the iterator handle is null and the external
7423 // parameter list is not empty then the first parameter must be
7424 // assignable to Iterable
7425 iterableType = externalParamList.get(0);
7426 if (!Iterable.class.isAssignableFrom(iterableType)) {
7427 throw newIllegalArgumentException(
7428 "inferred first loop argument must inherit from Iterable: " + iterableType);
7429 }
7430 }
7431 }
7432 if (init != null) {
7433 MethodType initType = init.type();
7434 if (initType.returnType() != returnType ||
7435 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
7436 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
7437 }
7438 }
7439 return iterableType; // help the caller a bit
7440 }
7441
7442 /*non-public*/
7443 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
7444 // there should be a better way to uncross my wires
7445 int arity = mh.type().parameterCount();
7446 int[] order = new int[arity];
7447 for (int k = 0; k < arity; k++) order[k] = k;
7448 order[i] = j; order[j] = i;
7449 Class<?>[] types = mh.type().parameterArray();
7450 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
7451 MethodType swapType = methodType(mh.type().returnType(), types);
7452 return permuteArguments(mh, swapType, order);
7453 }
7454
7455 /**
7456 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
7457 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
7458 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
7459 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
7460 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
7461 * {@code try-finally} handle.
7462 * <p>
7463 * The {@code cleanup} handle will be passed one or two additional leading arguments.
7464 * The first is the exception thrown during the
7465 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
7466 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
7467 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
7468 * The second argument is not present if the {@code target} handle has a {@code void} return type.
7469 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
7470 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
7471 * <p>
7472 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
7473 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
7474 * two extra leading parameters:<ul>
7475 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
7476 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
7477 * the result from the execution of the {@code target} handle.
7478 * This parameter is not present if the {@code target} returns {@code void}.
7479 * </ul>
7480 * <p>
7481 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
7482 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
7483 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
7484 * the cleanup.
7485 * {@snippet lang="java" :
7486 * V target(A..., B...);
7487 * V cleanup(Throwable, V, A...);
7488 * V adapter(A... a, B... b) {
7489 * V result = (zero value for V);
7490 * Throwable throwable = null;
7491 * try {
7492 * result = target(a..., b...);
7493 * } catch (Throwable t) {
7494 * throwable = t;
7495 * throw t;
7496 * } finally {
7497 * result = cleanup(throwable, result, a...);
7498 * }
7499 * return result;
7500 * }
7501 * }
7502 * <p>
7503 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
7504 * be modified by execution of the target, and so are passed unchanged
7505 * from the caller to the cleanup, if it is invoked.
7506 * <p>
7507 * The target and cleanup must return the same type, even if the cleanup
7508 * always throws.
7509 * To create such a throwing cleanup, compose the cleanup logic
7510 * with {@link #throwException throwException},
7511 * in order to create a method handle of the correct return type.
7512 * <p>
7513 * Note that {@code tryFinally} never converts exceptions into normal returns.
7514 * In rare cases where exceptions must be converted in that way, first wrap
7515 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
7516 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
7517 * <p>
7518 * It is recommended that the first parameter type of {@code cleanup} be
7519 * declared {@code Throwable} rather than a narrower subtype. This ensures
7520 * {@code cleanup} will always be invoked with whatever exception that
7521 * {@code target} throws. Declaring a narrower type may result in a
7522 * {@code ClassCastException} being thrown by the {@code try-finally}
7523 * handle if the type of the exception thrown by {@code target} is not
7524 * assignable to the first parameter type of {@code cleanup}. Note that
7525 * various exception types of {@code VirtualMachineError},
7526 * {@code LinkageError}, and {@code RuntimeException} can in principle be
7527 * thrown by almost any kind of Java code, and a finally clause that
7528 * catches (say) only {@code IOException} would mask any of the others
7529 * behind a {@code ClassCastException}.
7530 *
7531 * @param target the handle whose execution is to be wrapped in a {@code try} block.
7532 * @param cleanup the handle that is invoked in the finally block.
7533 *
7534 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
7535 * @throws NullPointerException if any argument is null
7536 * @throws IllegalArgumentException if {@code cleanup} does not accept
7537 * the required leading arguments, or if the method handle types do
7538 * not match in their return types and their
7539 * corresponding trailing parameters
7540 *
7541 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
7542 * @since 9
7543 */
7544 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
7545 Class<?>[] targetParamTypes = target.type().ptypes();
7546 Class<?> rtype = target.type().returnType();
7547
7548 tryFinallyChecks(target, cleanup);
7549
7550 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
7551 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7552 // target parameter list.
7553 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0, false);
7554
7555 // Ensure that the intrinsic type checks the instance thrown by the
7556 // target against the first parameter of cleanup
7557 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
7558
7559 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
7560 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
7561 }
7562
7563 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
7564 Class<?> rtype = target.type().returnType();
7565 if (rtype != cleanup.type().returnType()) {
7566 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
7567 }
7568 MethodType cleanupType = cleanup.type();
7569 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
7570 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
7571 }
7572 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
7573 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
7574 }
7575 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7576 // target parameter list.
7577 int cleanupArgIndex = rtype == void.class ? 1 : 2;
7578 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
7579 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
7580 cleanup.type(), target.type());
7581 }
7582 }
7583
7584 /**
7585 * Creates a table switch method handle, which can be used to switch over a set of target
7586 * method handles, based on a given target index, called selector.
7587 * <p>
7588 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)},
7589 * and where {@code N} is the number of target method handles, the table switch method
7590 * handle will invoke the n-th target method handle from the list of target method handles.
7591 * <p>
7592 * For a selector value that does not fall in the range {@code [0, N)}, the table switch
7593 * method handle will invoke the given fallback method handle.
7594 * <p>
7595 * All method handles passed to this method must have the same type, with the additional
7596 * requirement that the leading parameter be of type {@code int}. The leading parameter
7597 * represents the selector.
7598 * <p>
7599 * Any trailing parameters present in the type will appear on the returned table switch
7600 * method handle as well. Any arguments assigned to these parameters will be forwarded,
7601 * together with the selector value, to the selected method handle when invoking it.
7602 *
7603 * @apiNote Example:
7604 * The cases each drop the {@code selector} value they are given, and take an additional
7605 * {@code String} argument, which is concatenated (using {@link String#concat(String)})
7606 * to a specific constant label string for each case:
7607 * {@snippet lang="java" :
7608 * MethodHandles.Lookup lookup = MethodHandles.lookup();
7609 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat",
7610 * MethodType.methodType(String.class, String.class));
7611 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class);
7612 *
7613 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: ");
7614 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: ");
7615 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: ");
7616 *
7617 * MethodHandle mhSwitch = MethodHandles.tableSwitch(
7618 * caseDefault,
7619 * case0,
7620 * case1
7621 * );
7622 *
7623 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data"));
7624 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data"));
7625 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data"));
7626 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data"));
7627 * }
7628 *
7629 * @param fallback the fallback method handle that is called when the selector is not
7630 * within the range {@code [0, N)}.
7631 * @param targets array of target method handles.
7632 * @return the table switch method handle.
7633 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any
7634 * any of the elements of the {@code targets} array are
7635 * {@code null}.
7636 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading
7637 * parameter of the fallback handle or any of the target
7638 * handles is not {@code int}, or if the types of
7639 * the fallback handle and all of target handles are
7640 * not the same.
7641 *
7642 * @since 17
7643 */
7644 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) {
7645 Objects.requireNonNull(fallback);
7646 Objects.requireNonNull(targets);
7647 targets = targets.clone();
7648 MethodType type = tableSwitchChecks(fallback, targets);
7649 return MethodHandleImpl.makeTableSwitch(type, fallback, targets);
7650 }
7651
7652 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) {
7653 if (caseActions.length == 0)
7654 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions));
7655
7656 MethodType expectedType = defaultCase.type();
7657
7658 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class)
7659 throw new IllegalArgumentException(
7660 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions));
7661
7662 for (MethodHandle mh : caseActions) {
7663 Objects.requireNonNull(mh);
7664 if (mh.type() != expectedType)
7665 throw new IllegalArgumentException(
7666 "Case actions must have the same type: " + Arrays.toString(caseActions));
7667 }
7668
7669 return expectedType;
7670 }
7671
7672 /**
7673 * Adapts a target var handle by pre-processing incoming and outgoing values using a pair of filter functions.
7674 * <p>
7675 * When calling e.g. {@link VarHandle#set(Object...)} on the resulting var handle, the incoming value (of type {@code T}, where
7676 * {@code T} is the <em>last</em> parameter type of the first filter function) is processed using the first filter and then passed
7677 * to the target var handle.
7678 * Conversely, when calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the return value obtained from
7679 * the target var handle (of type {@code T}, where {@code T} is the <em>last</em> parameter type of the second filter function)
7680 * is processed using the second filter and returned to the caller. More advanced access mode types, such as
7681 * {@link VarHandle.AccessMode#COMPARE_AND_EXCHANGE} might apply both filters at the same time.
7682 * <p>
7683 * For the boxing and unboxing filters to be well-formed, their types must be of the form {@code (A... , S) -> T} and
7684 * {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle. If this is the case,
7685 * the resulting var handle will have type {@code S} and will feature the additional coordinates {@code A...} (which
7686 * will be appended to the coordinates of the target var handle).
7687 * <p>
7688 * If the boxing and unboxing filters throw any checked exceptions when invoked, the resulting var handle will
7689 * throw an {@link IllegalStateException}.
7690 * <p>
7691 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7692 * atomic access guarantees as those featured by the target var handle.
7693 *
7694 * @param target the target var handle
7695 * @param filterToTarget a filter to convert some type {@code S} into the type of {@code target}
7696 * @param filterFromTarget a filter to convert the type of {@code target} to some type {@code S}
7697 * @return an adapter var handle which accepts a new type, performing the provided boxing/unboxing conversions.
7698 * @throws IllegalArgumentException if {@code filterFromTarget} and {@code filterToTarget} are not well-formed, that is, they have types
7699 * other than {@code (A... , S) -> T} and {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle,
7700 * or if it's determined that either {@code filterFromTarget} or {@code filterToTarget} throws any checked exceptions.
7701 * @throws NullPointerException if any of the arguments is {@code null}.
7702 * @since 22
7703 */
7704 public static VarHandle filterValue(VarHandle target, MethodHandle filterToTarget, MethodHandle filterFromTarget) {
7705 return VarHandles.filterValue(target, filterToTarget, filterFromTarget);
7706 }
7707
7708 /**
7709 * Adapts a target var handle by pre-processing incoming coordinate values using unary filter functions.
7710 * <p>
7711 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the incoming coordinate values
7712 * starting at position {@code pos} (of type {@code C1, C2 ... Cn}, where {@code C1, C2 ... Cn} are the return types
7713 * of the unary filter functions) are transformed into new values (of type {@code S1, S2 ... Sn}, where {@code S1, S2 ... Sn} are the
7714 * parameter types of the unary filter functions), and then passed (along with any coordinate that was left unaltered
7715 * by the adaptation) to the target var handle.
7716 * <p>
7717 * For the coordinate filters to be well-formed, their types must be of the form {@code S1 -> T1, S2 -> T1 ... Sn -> Tn},
7718 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
7719 * <p>
7720 * If any of the filters throws a checked exception when invoked, the resulting var handle will
7721 * throw an {@link IllegalStateException}.
7722 * <p>
7723 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7724 * atomic access guarantees as those featured by the target var handle.
7725 *
7726 * @param target the target var handle
7727 * @param pos the position of the first coordinate to be transformed
7728 * @param filters the unary functions which are used to transform coordinates starting at position {@code pos}
7729 * @return an adapter var handle which accepts new coordinate types, applying the provided transformation
7730 * to the new coordinate values.
7731 * @throws IllegalArgumentException if the handles in {@code filters} are not well-formed, that is, they have types
7732 * other than {@code S1 -> T1, S2 -> T2, ... Sn -> Tn} where {@code T1, T2 ... Tn} are the coordinate types starting
7733 * at position {@code pos} of the target var handle, if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
7734 * or if more filters are provided than the actual number of coordinate types available starting at {@code pos},
7735 * or if it's determined that any of the filters throws any checked exceptions.
7736 * @throws NullPointerException if any of the arguments is {@code null} or {@code filters} contains {@code null}.
7737 * @since 22
7738 */
7739 public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) {
7740 return VarHandles.filterCoordinates(target, pos, filters);
7741 }
7742
7743 /**
7744 * Provides a target var handle with one or more <em>bound coordinates</em>
7745 * in advance of the var handle's invocation. As a consequence, the resulting var handle will feature less
7746 * coordinate types than the target var handle.
7747 * <p>
7748 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, incoming coordinate values
7749 * are joined with bound coordinate values, and then passed to the target var handle.
7750 * <p>
7751 * For the bound coordinates to be well-formed, their types must be {@code T1, T2 ... Tn },
7752 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
7753 * <p>
7754 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7755 * atomic access guarantees as those featured by the target var handle.
7756 *
7757 * @param target the var handle to invoke after the bound coordinates are inserted
7758 * @param pos the position of the first coordinate to be inserted
7759 * @param values the series of bound coordinates to insert
7760 * @return an adapter var handle which inserts additional coordinates,
7761 * before calling the target var handle
7762 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
7763 * or if more values are provided than the actual number of coordinate types available starting at {@code pos}.
7764 * @throws ClassCastException if the bound coordinates in {@code values} are not well-formed, that is, they have types
7765 * other than {@code T1, T2 ... Tn }, where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos}
7766 * of the target var handle.
7767 * @throws NullPointerException if any of the arguments is {@code null} or {@code values} contains {@code null}.
7768 * @since 22
7769 */
7770 public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) {
7771 return VarHandles.insertCoordinates(target, pos, values);
7772 }
7773
7774 /**
7775 * Provides a var handle which adapts the coordinate values of the target var handle, by re-arranging them
7776 * so that the new coordinates match the provided ones.
7777 * <p>
7778 * The given array controls the reordering.
7779 * Call {@code #I} the number of incoming coordinates (the value
7780 * {@code newCoordinates.size()}), and call {@code #O} the number
7781 * of outgoing coordinates (the number of coordinates associated with the target var handle).
7782 * Then the length of the reordering array must be {@code #O},
7783 * and each element must be a non-negative number less than {@code #I}.
7784 * For every {@code N} less than {@code #O}, the {@code N}-th
7785 * outgoing coordinate will be taken from the {@code I}-th incoming
7786 * coordinate, where {@code I} is {@code reorder[N]}.
7787 * <p>
7788 * No coordinate value conversions are applied.
7789 * The type of each incoming coordinate, as determined by {@code newCoordinates},
7790 * must be identical to the type of the corresponding outgoing coordinate
7791 * in the target var handle.
7792 * <p>
7793 * The reordering array need not specify an actual permutation.
7794 * An incoming coordinate will be duplicated if its index appears
7795 * more than once in the array, and an incoming coordinate will be dropped
7796 * if its index does not appear in the array.
7797 * <p>
7798 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7799 * atomic access guarantees as those featured by the target var handle.
7800 * @param target the var handle to invoke after the coordinates have been reordered
7801 * @param newCoordinates the new coordinate types
7802 * @param reorder an index array which controls the reordering
7803 * @return an adapter var handle which re-arranges the incoming coordinate values,
7804 * before calling the target var handle
7805 * @throws IllegalArgumentException if the index array length is not equal to
7806 * the number of coordinates of the target var handle, or if any index array element is not a valid index for
7807 * a coordinate of {@code newCoordinates}, or if two corresponding coordinate types in
7808 * the target var handle and in {@code newCoordinates} are not identical.
7809 * @throws NullPointerException if any of the arguments is {@code null} or {@code newCoordinates} contains {@code null}.
7810 * @since 22
7811 */
7812 public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) {
7813 return VarHandles.permuteCoordinates(target, newCoordinates, reorder);
7814 }
7815
7816 /**
7817 * Adapts a target var handle by pre-processing
7818 * a sub-sequence of its coordinate values with a filter (a method handle).
7819 * The pre-processed coordinates are replaced by the result (if any) of the
7820 * filter function and the target var handle is then called on the modified (usually shortened)
7821 * coordinate list.
7822 * <p>
7823 * If {@code R} is the return type of the filter, then:
7824 * <ul>
7825 * <li>if {@code R} <em>is not</em> {@code void}, the target var handle must have a coordinate of type {@code R} in
7826 * position {@code pos}. The parameter types of the filter will replace the coordinate type at position {@code pos}
7827 * of the target var handle. When the returned var handle is invoked, it will be as if the filter is invoked first,
7828 * and its result is passed in place of the coordinate at position {@code pos} in a downstream invocation of the
7829 * target var handle.</li>
7830 * <li> if {@code R} <em>is</em> {@code void}, the parameter types (if any) of the filter will be inserted in the
7831 * coordinate type list of the target var handle at position {@code pos}. In this case, when the returned var handle
7832 * is invoked, the filter essentially acts as a side effect, consuming some of the coordinate values, before a
7833 * downstream invocation of the target var handle.</li>
7834 * </ul>
7835 * <p>
7836 * If any of the filters throws a checked exception when invoked, the resulting var handle will
7837 * throw an {@link IllegalStateException}.
7838 * <p>
7839 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7840 * atomic access guarantees as those featured by the target var handle.
7841 *
7842 * @param target the var handle to invoke after the coordinates have been filtered
7843 * @param pos the position in the coordinate list of the target var handle where the filter is to be inserted
7844 * @param filter the filter method handle
7845 * @return an adapter var handle which filters the incoming coordinate values,
7846 * before calling the target var handle
7847 * @throws IllegalArgumentException if the return type of {@code filter}
7848 * is not void, and it is not the same as the {@code pos} coordinate of the target var handle,
7849 * if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
7850 * if the resulting var handle's type would have <a href="MethodHandle.html#maxarity">too many coordinates</a>,
7851 * or if it's determined that {@code filter} throws any checked exceptions.
7852 * @throws NullPointerException if any of the arguments is {@code null}.
7853 * @since 22
7854 */
7855 public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle filter) {
7856 return VarHandles.collectCoordinates(target, pos, filter);
7857 }
7858
7859 /**
7860 * Returns a var handle which will discard some dummy coordinates before delegating to the
7861 * target var handle. As a consequence, the resulting var handle will feature more
7862 * coordinate types than the target var handle.
7863 * <p>
7864 * The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is the arity of the
7865 * target var handle's coordinate types. If {@code pos} is zero, the dummy coordinates will precede
7866 * the target's real arguments; if {@code pos} is <i>N</i> they will come after.
7867 * <p>
7868 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7869 * atomic access guarantees as those featured by the target var handle.
7870 *
7871 * @param target the var handle to invoke after the dummy coordinates are dropped
7872 * @param pos position of the first coordinate to drop (zero for the leftmost)
7873 * @param valueTypes the type(s) of the coordinate(s) to drop
7874 * @return an adapter var handle which drops some dummy coordinates,
7875 * before calling the target var handle
7876 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive.
7877 * @throws NullPointerException if any of the arguments is {@code null} or {@code valueTypes} contains {@code null}.
7878 * @since 22
7879 */
7880 public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) {
7881 return VarHandles.dropCoordinates(target, pos, valueTypes);
7882 }
7883 }