1 /*
2 * Copyright (c) 2008, 2022, 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.value.PrimitiveClass;
30 import jdk.internal.foreign.Utils;
31 import jdk.internal.javac.PreviewFeature;
32 import jdk.internal.misc.Unsafe;
33 import jdk.internal.misc.VM;
34 import jdk.internal.org.objectweb.asm.ClassReader;
35 import jdk.internal.org.objectweb.asm.Opcodes;
36 import jdk.internal.org.objectweb.asm.Type;
37 import jdk.internal.reflect.CallerSensitive;
38 import jdk.internal.reflect.CallerSensitiveAdapter;
39 import jdk.internal.reflect.Reflection;
40 import jdk.internal.vm.annotation.ForceInline;
41 import sun.invoke.util.ValueConversions;
42 import sun.invoke.util.VerifyAccess;
43 import sun.invoke.util.Wrapper;
44 import sun.reflect.misc.ReflectUtil;
45 import sun.security.util.SecurityConstants;
46
47 import java.lang.constant.ConstantDescs;
48 import java.lang.foreign.GroupLayout;
49 import java.lang.foreign.MemoryLayout;
50 import java.lang.foreign.MemorySegment;
51 import java.lang.foreign.ValueLayout;
52 import java.lang.invoke.LambdaForm.BasicType;
53 import java.lang.reflect.Constructor;
54 import java.lang.reflect.Field;
55 import java.lang.reflect.Member;
56 import java.lang.reflect.Method;
57 import java.lang.reflect.Modifier;
58 import java.nio.ByteOrder;
59 import java.security.ProtectionDomain;
60 import java.util.ArrayList;
61 import java.util.Arrays;
62 import java.util.BitSet;
63 import java.util.Iterator;
64 import java.util.List;
65 import java.util.Objects;
66 import java.util.Set;
67 import java.util.concurrent.ConcurrentHashMap;
68 import java.util.stream.Stream;
69
70 import static java.lang.invoke.LambdaForm.BasicType.V_TYPE;
71 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
72 import static java.lang.invoke.MethodHandleNatives.Constants.*;
73 import static java.lang.invoke.MethodHandleStatics.UNSAFE;
74 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
75 import static java.lang.invoke.MethodHandleStatics.newInternalError;
76 import static java.lang.invoke.MethodType.methodType;
77
78 /**
79 * This class consists exclusively of static methods that operate on or return
80 * method handles. They fall into several categories:
81 * <ul>
82 * <li>Lookup methods which help create method handles for methods and fields.
83 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
84 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
85 * </ul>
86 * A lookup, combinator, or factory method will fail and throw an
87 * {@code IllegalArgumentException} if the created method handle's type
88 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
89 *
90 * @author John Rose, JSR 292 EG
91 * @since 1.7
92 */
93 public class MethodHandles {
94
95 private MethodHandles() { } // do not instantiate
96
97 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
98
99 // See IMPL_LOOKUP below.
100
101 //// Method handle creation from ordinary methods.
102
103 /**
104 * Returns a {@link Lookup lookup object} with
105 * full capabilities to emulate all supported bytecode behaviors of the caller.
106 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller.
107 * Factory methods on the lookup object can create
108 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
109 * for any member that the caller has access to via bytecodes,
110 * including protected and private fields and methods.
111 * This lookup object is created by the original lookup class
112 * and has the {@link Lookup#ORIGINAL ORIGINAL} bit set.
113 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
114 * Do not store it in place where untrusted code can access it.
115 * <p>
116 * This method is caller sensitive, which means that it may return different
117 * values to different callers.
118 * In cases where {@code MethodHandles.lookup} is called from a context where
119 * there is no caller frame on the stack (e.g. when called directly
120 * from a JNI attached thread), {@code IllegalCallerException} is thrown.
121 * To obtain a {@link Lookup lookup object} in such a context, use an auxiliary class that will
122 * implicitly be identified as the caller, or use {@link MethodHandles#publicLookup()}
123 * to obtain a low-privileged lookup instead.
124 * @return a lookup object for the caller of this method, with
125 * {@linkplain Lookup#ORIGINAL original} and
126 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}.
127 * @throws IllegalCallerException if there is no caller frame on the stack.
128 */
129 @CallerSensitive
130 @ForceInline // to ensure Reflection.getCallerClass optimization
131 public static Lookup lookup() {
132 final Class<?> c = Reflection.getCallerClass();
133 if (c == null) {
134 throw new IllegalCallerException("no caller frame");
135 }
136 return new Lookup(c);
137 }
138
139 /**
140 * This lookup method is the alternate implementation of
141 * the lookup method with a leading caller class argument which is
142 * non-caller-sensitive. This method is only invoked by reflection
143 * and method handle.
144 */
145 @CallerSensitiveAdapter
146 private static Lookup lookup(Class<?> caller) {
147 if (caller.getClassLoader() == null) {
148 throw newInternalError("calling lookup() reflectively is not supported: "+caller);
149 }
150 return new Lookup(caller);
151 }
152
153 /**
154 * Returns a {@link Lookup lookup object} which is trusted minimally.
155 * The lookup has the {@code UNCONDITIONAL} mode.
156 * It can only be used to create method handles to public members of
157 * public classes in packages that are exported unconditionally.
158 * <p>
159 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
160 * of this lookup object will be {@link java.lang.Object}.
161 *
162 * @apiNote The use of Object is conventional, and because the lookup modes are
163 * limited, there is no special access provided to the internals of Object, its package
164 * or its module. This public lookup object or other lookup object with
165 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
166 * is not used to determine the lookup context.
167 *
168 * <p style="font-size:smaller;">
169 * <em>Discussion:</em>
170 * The lookup class can be changed to any other class {@code C} using an expression of the form
171 * {@link Lookup#in publicLookup().in(C.class)}.
172 * A public lookup object is always subject to
173 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
174 * Also, it cannot access
175 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
176 * @return a lookup object which is trusted minimally
177 *
178 * @revised 9
179 */
180 public static Lookup publicLookup() {
181 return Lookup.PUBLIC_LOOKUP;
182 }
183
184 /**
185 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
186 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>.
187 * The returned lookup object can provide access to classes in modules and packages,
188 * and members of those classes, outside the normal rules of Java access control,
189 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
190 * <p>
191 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
192 * allowed to do deep reflection on module {@code M2} and package of the target class
193 * if and only if all of the following conditions are {@code true}:
194 * <ul>
195 * <li>If there is a security manager, its {@code checkPermission} method is
196 * called to check {@code ReflectPermission("suppressAccessChecks")} and
197 * that must return normally.
198 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess()
199 * full privilege access}. Specifically:
200 * <ul>
201 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
202 * (This is because otherwise there would be no way to ensure the original lookup
203 * creator was a member of any particular module, and so any subsequent checks
204 * for readability and qualified exports would become ineffective.)
205 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
206 * (This is because an application intending to share intra-module access
207 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
208 * deep reflection to its own module.)
209 * </ul>
210 * <li>The target class must be a proper class, not a primitive or array class.
211 * (Thus, {@code M2} is well-defined.)
212 * <li>If the caller module {@code M1} differs from
213 * the target module {@code M2} then both of the following must be true:
214 * <ul>
215 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
216 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
217 * containing the target class to at least {@code M1}.</li>
218 * </ul>
219 * </ul>
220 * <p>
221 * If any of the above checks is violated, this method fails with an
222 * exception.
223 * <p>
224 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
225 * returns a {@code Lookup} on {@code targetClass} with
226 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}
227 * with {@code null} previous lookup class.
228 * <p>
229 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
230 * returns a {@code Lookup} on {@code targetClass} that records
231 * the lookup class of the caller as the new previous lookup class with
232 * {@code PRIVATE} access but no {@code MODULE} access.
233 * <p>
234 * The resulting {@code Lookup} object has no {@code ORIGINAL} access.
235 *
236 * @param targetClass the target class
237 * @param caller the caller lookup object
238 * @return a lookup object for the target class, with private access
239 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class
240 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
241 * @throws SecurityException if denied by the security manager
242 * @throws IllegalAccessException if any of the other access checks specified above fails
243 * @since 9
244 * @see Lookup#dropLookupMode
245 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
246 */
247 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
248 if (caller.allowedModes == Lookup.TRUSTED) {
249 return new Lookup(targetClass);
250 }
251
252 @SuppressWarnings("removal")
253 SecurityManager sm = System.getSecurityManager();
254 if (sm != null) sm.checkPermission(SecurityConstants.ACCESS_PERMISSION);
255 if (targetClass.isPrimitive())
256 throw new IllegalArgumentException(targetClass + " is a primitive class");
257 if (targetClass.isArray())
258 throw new IllegalArgumentException(targetClass + " is an array class");
259 // Ensure that we can reason accurately about private and module access.
260 int requireAccess = Lookup.PRIVATE|Lookup.MODULE;
261 if ((caller.lookupModes() & requireAccess) != requireAccess)
262 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode");
263
264 // previous lookup class is never set if it has MODULE access
265 assert caller.previousLookupClass() == null;
266
267 Class<?> callerClass = caller.lookupClass();
268 Module callerModule = callerClass.getModule(); // M1
269 Module targetModule = targetClass.getModule(); // M2
270 Class<?> newPreviousClass = null;
271 int newModes = Lookup.FULL_POWER_MODES & ~Lookup.ORIGINAL;
272
273 if (targetModule != callerModule) {
274 if (!callerModule.canRead(targetModule))
275 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
276 if (targetModule.isNamed()) {
277 String pn = targetClass.getPackageName();
278 assert !pn.isEmpty() : "unnamed package cannot be in named module";
279 if (!targetModule.isOpen(pn, callerModule))
280 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
281 }
282
283 // M2 != M1, set previous lookup class to M1 and drop MODULE access
284 newPreviousClass = callerClass;
285 newModes &= ~Lookup.MODULE;
286 }
287 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
288 }
289
290 /**
291 * Returns the <em>class data</em> associated with the lookup class
292 * of the given {@code caller} lookup object, or {@code null}.
293 *
294 * <p> A hidden class with class data can be created by calling
295 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
296 * Lookup::defineHiddenClassWithClassData}.
297 * This method will cause the static class initializer of the lookup
298 * class of the given {@code caller} lookup object be executed if
299 * it has not been initialized.
300 *
301 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
302 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
303 * {@code null} is returned if this method is called on the lookup object
304 * on these classes.
305 *
306 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
307 * must have {@linkplain Lookup#ORIGINAL original access}
308 * in order to retrieve the class data.
309 *
310 * @apiNote
311 * This method can be called as a bootstrap method for a dynamically computed
312 * constant. A framework can create a hidden class with class data, for
313 * example that can be {@code Class} or {@code MethodHandle} object.
314 * The class data is accessible only to the lookup object
315 * created by the original caller but inaccessible to other members
316 * in the same nest. If a framework passes security sensitive objects
317 * to a hidden class via class data, it is recommended to load the value
318 * of class data as a dynamically computed constant instead of storing
319 * the class data in private static field(s) which are accessible to
320 * other nestmates.
321 *
322 * @param <T> the type to cast the class data object to
323 * @param caller the lookup context describing the class performing the
324 * operation (normally stacked by the JVM)
325 * @param name must be {@link ConstantDescs#DEFAULT_NAME}
326 * ({@code "_"})
327 * @param type the type of the class data
328 * @return the value of the class data if present in the lookup class;
329 * otherwise {@code null}
330 * @throws IllegalArgumentException if name is not {@code "_"}
331 * @throws IllegalAccessException if the lookup context does not have
332 * {@linkplain Lookup#ORIGINAL original} access
333 * @throws ClassCastException if the class data cannot be converted to
334 * the given {@code type}
335 * @throws NullPointerException if {@code caller} or {@code type} argument
336 * is {@code null}
337 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
338 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
339 * @since 16
340 * @jvms 5.5 Initialization
341 */
342 public static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException {
343 Objects.requireNonNull(caller);
344 Objects.requireNonNull(type);
345 if (!ConstantDescs.DEFAULT_NAME.equals(name)) {
346 throw new IllegalArgumentException("name must be \"_\": " + name);
347 }
348
349 if ((caller.lookupModes() & Lookup.ORIGINAL) != Lookup.ORIGINAL) {
350 throw new IllegalAccessException(caller + " does not have ORIGINAL access");
351 }
352
353 Object classdata = classData(caller.lookupClass());
354 if (classdata == null) return null;
355
356 try {
357 return BootstrapMethodInvoker.widenAndCast(classdata, type);
358 } catch (RuntimeException|Error e) {
359 throw e; // let CCE and other runtime exceptions through
360 } catch (Throwable e) {
361 throw new InternalError(e);
362 }
363 }
364
365 /*
366 * Returns the class data set by the VM in the Class::classData field.
367 *
368 * This is also invoked by LambdaForms as it cannot use condy via
369 * MethodHandles::classData due to bootstrapping issue.
370 */
371 static Object classData(Class<?> c) {
372 UNSAFE.ensureClassInitialized(c);
373 return SharedSecrets.getJavaLangAccess().classData(c);
374 }
375
376 /**
377 * Returns the element at the specified index in the
378 * {@linkplain #classData(Lookup, String, Class) class data},
379 * if the class data associated with the lookup class
380 * of the given {@code caller} lookup object is a {@code List}.
381 * If the class data is not present in this lookup class, this method
382 * returns {@code null}.
383 *
384 * <p> A hidden class with class data can be created by calling
385 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
386 * Lookup::defineHiddenClassWithClassData}.
387 * This method will cause the static class initializer of the lookup
388 * class of the given {@code caller} lookup object be executed if
389 * it has not been initialized.
390 *
391 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
392 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
393 * {@code null} is returned if this method is called on the lookup object
394 * on these classes.
395 *
396 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
397 * must have {@linkplain Lookup#ORIGINAL original access}
398 * in order to retrieve the class data.
399 *
400 * @apiNote
401 * This method can be called as a bootstrap method for a dynamically computed
402 * constant. A framework can create a hidden class with class data, for
403 * example that can be {@code List.of(o1, o2, o3....)} containing more than
404 * one object and use this method to load one element at a specific index.
405 * The class data is accessible only to the lookup object
406 * created by the original caller but inaccessible to other members
407 * in the same nest. If a framework passes security sensitive objects
408 * to a hidden class via class data, it is recommended to load the value
409 * of class data as a dynamically computed constant instead of storing
410 * the class data in private static field(s) which are accessible to other
411 * nestmates.
412 *
413 * @param <T> the type to cast the result object to
414 * @param caller the lookup context describing the class performing the
415 * operation (normally stacked by the JVM)
416 * @param name must be {@link java.lang.constant.ConstantDescs#DEFAULT_NAME}
417 * ({@code "_"})
418 * @param type the type of the element at the given index in the class data
419 * @param index index of the element in the class data
420 * @return the element at the given index in the class data
421 * if the class data is present; otherwise {@code null}
422 * @throws IllegalArgumentException if name is not {@code "_"}
423 * @throws IllegalAccessException if the lookup context does not have
424 * {@linkplain Lookup#ORIGINAL original} access
425 * @throws ClassCastException if the class data cannot be converted to {@code List}
426 * or the element at the specified index cannot be converted to the given type
427 * @throws IndexOutOfBoundsException if the index is out of range
428 * @throws NullPointerException if {@code caller} or {@code type} argument is
429 * {@code null}; or if unboxing operation fails because
430 * the element at the given index is {@code null}
431 *
432 * @since 16
433 * @see #classData(Lookup, String, Class)
434 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
435 */
436 public static <T> T classDataAt(Lookup caller, String name, Class<T> type, int index)
437 throws IllegalAccessException
438 {
439 @SuppressWarnings("unchecked")
440 List<Object> classdata = (List<Object>)classData(caller, name, List.class);
441 if (classdata == null) return null;
442
443 try {
444 Object element = classdata.get(index);
445 return BootstrapMethodInvoker.widenAndCast(element, type);
446 } catch (RuntimeException|Error e) {
447 throw e; // let specified exceptions and other runtime exceptions/errors through
448 } catch (Throwable e) {
449 throw new InternalError(e);
450 }
451 }
452
453 /**
454 * Performs an unchecked "crack" of a
455 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
456 * The result is as if the user had obtained a lookup object capable enough
457 * to crack the target method handle, called
458 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
459 * on the target to obtain its symbolic reference, and then called
460 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
461 * to resolve the symbolic reference to a member.
462 * <p>
463 * If there is a security manager, its {@code checkPermission} method
464 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
465 * @param <T> the desired type of the result, either {@link Member} or a subtype
466 * @param target a direct method handle to crack into symbolic reference components
467 * @param expected a class object representing the desired result type {@code T}
468 * @return a reference to the method, constructor, or field object
469 * @throws SecurityException if the caller is not privileged to call {@code setAccessible}
470 * @throws NullPointerException if either argument is {@code null}
471 * @throws IllegalArgumentException if the target is not a direct method handle
472 * @throws ClassCastException if the member is not of the expected type
473 * @since 1.8
474 */
475 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) {
476 @SuppressWarnings("removal")
477 SecurityManager smgr = System.getSecurityManager();
478 if (smgr != null) smgr.checkPermission(SecurityConstants.ACCESS_PERMISSION);
479 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
480 return lookup.revealDirect(target).reflectAs(expected, lookup);
481 }
482
483 /**
484 * A <em>lookup object</em> is a factory for creating method handles,
485 * when the creation requires access checking.
486 * Method handles do not perform
487 * access checks when they are called, but rather when they are created.
488 * Therefore, method handle access
489 * restrictions must be enforced when a method handle is created.
490 * The caller class against which those restrictions are enforced
491 * is known as the {@linkplain #lookupClass() lookup class}.
492 * <p>
493 * A lookup class which needs to create method handles will call
494 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
495 * When the {@code Lookup} factory object is created, the identity of the lookup class is
496 * determined, and securely stored in the {@code Lookup} object.
497 * The lookup class (or its delegates) may then use factory methods
498 * on the {@code Lookup} object to create method handles for access-checked members.
499 * This includes all methods, constructors, and fields which are allowed to the lookup class,
500 * even private ones.
501 *
502 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
503 * The factory methods on a {@code Lookup} object correspond to all major
504 * use cases for methods, constructors, and fields.
505 * Each method handle created by a factory method is the functional
506 * equivalent of a particular <em>bytecode behavior</em>.
507 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of
508 * the Java Virtual Machine Specification.)
509 * Here is a summary of the correspondence between these factory methods and
510 * the behavior of the resulting method handles:
511 * <table class="striped">
512 * <caption style="display:none">lookup method behaviors</caption>
513 * <thead>
514 * <tr>
515 * <th scope="col"><a id="equiv"></a>lookup expression</th>
516 * <th scope="col">member</th>
517 * <th scope="col">bytecode behavior</th>
518 * </tr>
519 * </thead>
520 * <tbody>
521 * <tr>
522 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
523 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
524 * </tr>
525 * <tr>
526 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
527 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
528 * </tr>
529 * <tr>
530 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
531 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
532 * </tr>
533 * <tr>
534 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
535 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
536 * </tr>
537 * <tr>
538 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
539 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
540 * </tr>
541 * <tr>
542 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
543 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
544 * </tr>
545 * <tr>
546 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
547 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
548 * </tr>
549 * <tr>
550 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
551 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
552 * </tr>
553 * <tr>
554 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
555 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
556 * </tr>
557 * <tr>
558 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
559 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
560 * </tr>
561 * <tr>
562 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
563 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
564 * </tr>
565 * <tr>
566 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
567 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
568 * </tr>
569 * <tr>
570 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th>
571 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
572 * </tr>
573 * <tr>
574 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
575 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
576 * </tr>
577 * </tbody>
578 * </table>
579 *
580 * Here, the type {@code C} is the class or interface being searched for a member,
581 * documented as a parameter named {@code refc} in the lookup methods.
582 * The method type {@code MT} is composed from the return type {@code T}
583 * and the sequence of argument types {@code A*}.
584 * The constructor also has a sequence of argument types {@code A*} and
585 * is deemed to return the newly-created object of type {@code C}.
586 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
587 * The formal parameter {@code this} stands for the self-reference of type {@code C};
588 * if it is present, it is always the leading argument to the method handle invocation.
589 * (In the case of some {@code protected} members, {@code this} may be
590 * restricted in type to the lookup class; see below.)
591 * The name {@code arg} stands for all the other method handle arguments.
592 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
593 * stands for a null reference if the accessed method or field is static,
594 * and {@code this} otherwise.
595 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
596 * for reflective objects corresponding to the given members declared in type {@code C}.
597 * <p>
598 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
599 * as if by {@code ldc CONSTANT_Class}.
600 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
601 * <p>
602 * In cases where the given member is of variable arity (i.e., a method or constructor)
603 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
604 * In all other cases, the returned method handle will be of fixed arity.
605 * <p style="font-size:smaller;">
606 * <em>Discussion:</em>
607 * The equivalence between looked-up method handles and underlying
608 * class members and bytecode behaviors
609 * can break down in a few ways:
610 * <ul style="font-size:smaller;">
611 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
612 * the lookup can still succeed, even when there is no equivalent
613 * Java expression or bytecoded constant.
614 * <li>Likewise, if {@code T} or {@code MT}
615 * is not symbolically accessible from the lookup class's loader,
616 * the lookup can still succeed.
617 * For example, lookups for {@code MethodHandle.invokeExact} and
618 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
619 * <li>If there is a security manager installed, it can forbid the lookup
620 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
621 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
622 * constant is not subject to security manager checks.
623 * <li>If the looked-up method has a
624 * <a href="MethodHandle.html#maxarity">very large arity</a>,
625 * the method handle creation may fail with an
626 * {@code IllegalArgumentException}, due to the method handle type having
627 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
628 * </ul>
629 *
630 * <h2><a id="access"></a>Access checking</h2>
631 * Access checks are applied in the factory methods of {@code Lookup},
632 * when a method handle is created.
633 * This is a key difference from the Core Reflection API, since
634 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
635 * performs access checking against every caller, on every call.
636 * <p>
637 * All access checks start from a {@code Lookup} object, which
638 * compares its recorded lookup class against all requests to
639 * create method handles.
640 * A single {@code Lookup} object can be used to create any number
641 * of access-checked method handles, all checked against a single
642 * lookup class.
643 * <p>
644 * A {@code Lookup} object can be shared with other trusted code,
645 * such as a metaobject protocol.
646 * A shared {@code Lookup} object delegates the capability
647 * to create method handles on private members of the lookup class.
648 * Even if privileged code uses the {@code Lookup} object,
649 * the access checking is confined to the privileges of the
650 * original lookup class.
651 * <p>
652 * A lookup can fail, because
653 * the containing class is not accessible to the lookup class, or
654 * because the desired class member is missing, or because the
655 * desired class member is not accessible to the lookup class, or
656 * because the lookup object is not trusted enough to access the member.
657 * In the case of a field setter function on a {@code final} field,
658 * finality enforcement is treated as a kind of access control,
659 * and the lookup will fail, except in special cases of
660 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
661 * In any of these cases, a {@code ReflectiveOperationException} will be
662 * thrown from the attempted lookup. The exact class will be one of
663 * the following:
664 * <ul>
665 * <li>NoSuchMethodException — if a method is requested but does not exist
666 * <li>NoSuchFieldException — if a field is requested but does not exist
667 * <li>IllegalAccessException — if the member exists but an access check fails
668 * </ul>
669 * <p>
670 * In general, the conditions under which a method handle may be
671 * looked up for a method {@code M} are no more restrictive than the conditions
672 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
673 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
674 * a method handle lookup will generally raise a corresponding
675 * checked exception, such as {@code NoSuchMethodException}.
676 * And the effect of invoking the method handle resulting from the lookup
677 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
678 * to executing the compiled, verified, and resolved call to {@code M}.
679 * The same point is true of fields and constructors.
680 * <p style="font-size:smaller;">
681 * <em>Discussion:</em>
682 * Access checks only apply to named and reflected methods,
683 * constructors, and fields.
684 * Other method handle creation methods, such as
685 * {@link MethodHandle#asType MethodHandle.asType},
686 * do not require any access checks, and are used
687 * independently of any {@code Lookup} object.
688 * <p>
689 * If the desired member is {@code protected}, the usual JVM rules apply,
690 * including the requirement that the lookup class must either be in the
691 * same package as the desired member, or must inherit that member.
692 * (See the Java Virtual Machine Specification, sections {@jvms
693 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.)
694 * In addition, if the desired member is a non-static field or method
695 * in a different package, the resulting method handle may only be applied
696 * to objects of the lookup class or one of its subclasses.
697 * This requirement is enforced by narrowing the type of the leading
698 * {@code this} parameter from {@code C}
699 * (which will necessarily be a superclass of the lookup class)
700 * to the lookup class itself.
701 * <p>
702 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
703 * that the receiver argument must match both the resolved method <em>and</em>
704 * the current class. Again, this requirement is enforced by narrowing the
705 * type of the leading parameter to the resulting method handle.
706 * (See the Java Virtual Machine Specification, section {@jvms 4.10.1.9}.)
707 * <p>
708 * The JVM represents constructors and static initializer blocks as internal methods
709 * with special names ({@code "<init>"}, {@code "<vnew>"} and {@code "<clinit>"}).
710 * The internal syntax of invocation instructions allows them to refer to such internal
711 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
712 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
713 * <p>
714 * If the relationship between nested types is expressed directly through the
715 * {@code NestHost} and {@code NestMembers} attributes
716 * (see the Java Virtual Machine Specification, sections {@jvms
717 * 4.7.28} and {@jvms 4.7.29}),
718 * then the associated {@code Lookup} object provides direct access to
719 * the lookup class and all of its nestmates
720 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
721 * Otherwise, access between nested classes is obtained by the Java compiler creating
722 * a wrapper method to access a private method of another class in the same nest.
723 * For example, a nested class {@code C.D}
724 * can access private members within other related classes such as
725 * {@code C}, {@code C.D.E}, or {@code C.B},
726 * but the Java compiler may need to generate wrapper methods in
727 * those related classes. In such cases, a {@code Lookup} object on
728 * {@code C.E} would be unable to access those private members.
729 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
730 * which can transform a lookup on {@code C.E} into one on any of those other
731 * classes, without special elevation of privilege.
732 * <p>
733 * The accesses permitted to a given lookup object may be limited,
734 * according to its set of {@link #lookupModes lookupModes},
735 * to a subset of members normally accessible to the lookup class.
736 * For example, the {@link MethodHandles#publicLookup publicLookup}
737 * method produces a lookup object which is only allowed to access
738 * public members in public classes of exported packages.
739 * The caller sensitive method {@link MethodHandles#lookup lookup}
740 * produces a lookup object with full capabilities relative to
741 * its caller class, to emulate all supported bytecode behaviors.
742 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
743 * with fewer access modes than the original lookup object.
744 *
745 * <p style="font-size:smaller;">
746 * <a id="privacc"></a>
747 * <em>Discussion of private and module access:</em>
748 * We say that a lookup has <em>private access</em>
749 * if its {@linkplain #lookupModes lookup modes}
750 * include the possibility of accessing {@code private} members
751 * (which includes the private members of nestmates).
752 * As documented in the relevant methods elsewhere,
753 * only lookups with private access possess the following capabilities:
754 * <ul style="font-size:smaller;">
755 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
756 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
757 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
758 * for classes accessible to the lookup class
759 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
760 * within the same package member
761 * </ul>
762 * <p style="font-size:smaller;">
763 * Similarly, a lookup with module access ensures that the original lookup creator was
764 * a member in the same module as the lookup class.
765 * <p style="font-size:smaller;">
766 * Private and module access are independently determined modes; a lookup may have
767 * either or both or neither. A lookup which possesses both access modes is said to
768 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}.
769 * <p style="font-size:smaller;">
770 * A lookup with <em>original access</em> ensures that this lookup is created by
771 * the original lookup class and the bootstrap method invoked by the VM.
772 * Such a lookup with original access also has private and module access
773 * which has the following additional capability:
774 * <ul style="font-size:smaller;">
775 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
776 * such as {@code Class.forName}
777 * <li>obtain the {@linkplain MethodHandles#classData(Lookup, String, Class)
778 * class data} associated with the lookup class</li>
779 * </ul>
780 * <p style="font-size:smaller;">
781 * Each of these permissions is a consequence of the fact that a lookup object
782 * with private access can be securely traced back to an originating class,
783 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
784 * can be reliably determined and emulated by method handles.
785 *
786 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
787 * When a lookup class in one module {@code M1} accesses a class in another module
788 * {@code M2}, extra access checking is performed beyond the access mode bits.
789 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
790 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
791 * and when the type is in a package of {@code M2} that is exported to
792 * at least {@code M1}.
793 * <p>
794 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
795 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
796 * MethodHandles.privateLookupIn} methods.
797 * Teleporting across modules will always record the original lookup class as
798 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
799 * and drops {@link Lookup#MODULE MODULE} access.
800 * If the target class is in the same module as the lookup class {@code C},
801 * then the target class becomes the new lookup class
802 * and there is no change to the previous lookup class.
803 * If the target class is in a different module from {@code M1} ({@code C}'s module),
804 * {@code C} becomes the new previous lookup class
805 * and the target class becomes the new lookup class.
806 * In that case, if there was already a previous lookup class in {@code M0},
807 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
808 * drops all privileges.
809 * For example,
810 * {@snippet lang="java" :
811 * Lookup lookup = MethodHandles.lookup(); // in class C
812 * Lookup lookup2 = lookup.in(D.class);
813 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
814 * }
815 * <p>
816 * The {@link #lookup()} factory method produces a {@code Lookup} object
817 * with {@code null} previous lookup class.
818 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
819 * to class {@code D} without elevation of privileges.
820 * If {@code C} and {@code D} are in the same module,
821 * {@code lookup2} records {@code D} as the new lookup class and keeps the
822 * same previous lookup class as the original {@code lookup}, or
823 * {@code null} if not present.
824 * <p>
825 * When a {@code Lookup} teleports from a class
826 * in one nest to another nest, {@code PRIVATE} access is dropped.
827 * When a {@code Lookup} teleports from a class in one package to
828 * another package, {@code PACKAGE} access is dropped.
829 * When a {@code Lookup} teleports from a class in one module to another module,
830 * {@code MODULE} access is dropped.
831 * Teleporting across modules drops the ability to access non-exported classes
832 * in both the module of the new lookup class and the module of the old lookup class
833 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
834 * A {@code Lookup} can teleport back and forth to a class in the module of
835 * the lookup class and the module of the previous class lookup.
836 * Teleporting across modules can only decrease access but cannot increase it.
837 * Teleporting to some third module drops all accesses.
838 * <p>
839 * In the above example, if {@code C} and {@code D} are in different modules,
840 * {@code lookup2} records {@code D} as its lookup class and
841 * {@code C} as its previous lookup class and {@code lookup2} has only
842 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
843 * {@code C}'s module and {@code D}'s module.
844 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
845 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
846 * class {@code D} is recorded as its previous lookup class.
847 * <p>
848 * Teleporting across modules restricts access to the public types that
849 * both the lookup class and the previous lookup class can equally access
850 * (see below).
851 * <p>
852 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
853 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
854 * and create a new {@code Lookup} with <a href="#privacc">private access</a>
855 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
856 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
857 * to call {@code privateLookupIn}.
858 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
859 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
860 * produces a new {@code Lookup} on {@code T} with full capabilities.
861 * A {@code lookup} on {@code C} is also allowed
862 * to do deep reflection on {@code T} in another module {@code M2} if
863 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
864 * the package containing {@code T} to at least {@code M1}.
865 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
866 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
867 * The resulting {@code Lookup} can be used to do member lookup or teleport
868 * to another lookup class by calling {@link #in Lookup::in}. But
869 * it cannot be used to obtain another private {@code Lookup} by calling
870 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
871 * because it has no {@code MODULE} access.
872 *
873 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
874 *
875 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
876 * allows cross-module access. The access checking is performed with respect
877 * to both the lookup class and the previous lookup class if present.
878 * <p>
879 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
880 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
881 * exported unconditionally}.
882 * <p>
883 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
884 * the lookup with {@link #PUBLIC} mode can access all public types in modules
885 * that are readable to {@code M1} and the type is in a package that is exported
886 * at least to {@code M1}.
887 * <p>
888 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
889 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
890 * the intersection of all public types that are accessible to {@code M1}
891 * with all public types that are accessible to {@code M0}. {@code M0}
892 * reads {@code M1} and hence the set of accessible types includes:
893 *
894 * <ul>
895 * <li>unconditional-exported packages from {@code M1}</li>
896 * <li>unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</li>
897 * <li>
898 * unconditional-exported packages from a third module {@code M2}if both {@code M0}
899 * and {@code M1} read {@code M2}
900 * </li>
901 * <li>qualified-exported packages from {@code M1} to {@code M0}</li>
902 * <li>qualified-exported packages from {@code M0} to {@code M1} if {@code M1} reads {@code M0}</li>
903 * <li>
904 * qualified-exported packages from a third module {@code M2} to both {@code M0} and
905 * {@code M1} if both {@code M0} and {@code M1} read {@code M2}
906 * </li>
907 * </ul>
908 *
909 * <h2><a id="access-modes"></a>Access modes</h2>
910 *
911 * The table below shows the access modes of a {@code Lookup} produced by
912 * any of the following factory or transformation methods:
913 * <ul>
914 * <li>{@link #lookup() MethodHandles::lookup}</li>
915 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li>
916 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li>
917 * <li>{@link Lookup#in Lookup::in}</li>
918 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li>
919 * </ul>
920 *
921 * <table class="striped">
922 * <caption style="display:none">
923 * Access mode summary
924 * </caption>
925 * <thead>
926 * <tr>
927 * <th scope="col">Lookup object</th>
928 * <th style="text-align:center">original</th>
929 * <th style="text-align:center">protected</th>
930 * <th style="text-align:center">private</th>
931 * <th style="text-align:center">package</th>
932 * <th style="text-align:center">module</th>
933 * <th style="text-align:center">public</th>
934 * </tr>
935 * </thead>
936 * <tbody>
937 * <tr>
938 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
939 * <td style="text-align:center">ORI</td>
940 * <td style="text-align:center">PRO</td>
941 * <td style="text-align:center">PRI</td>
942 * <td style="text-align:center">PAC</td>
943 * <td style="text-align:center">MOD</td>
944 * <td style="text-align:center">1R</td>
945 * </tr>
946 * <tr>
947 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
948 * <td></td>
949 * <td></td>
950 * <td></td>
951 * <td style="text-align:center">PAC</td>
952 * <td style="text-align:center">MOD</td>
953 * <td style="text-align:center">1R</td>
954 * </tr>
955 * <tr>
956 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
957 * <td></td>
958 * <td></td>
959 * <td></td>
960 * <td></td>
961 * <td style="text-align:center">MOD</td>
962 * <td style="text-align:center">1R</td>
963 * </tr>
964 * <tr>
965 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
966 * <td></td>
967 * <td></td>
968 * <td></td>
969 * <td></td>
970 * <td></td>
971 * <td style="text-align:center">2R</td>
972 * </tr>
973 * <tr>
974 * <th scope="row" style="text-align:left">{@code CL.in(D).in(C)} hop back to module</th>
975 * <td></td>
976 * <td></td>
977 * <td></td>
978 * <td></td>
979 * <td></td>
980 * <td style="text-align:center">2R</td>
981 * </tr>
982 * <tr>
983 * <th scope="row" style="text-align:left">{@code PRI1 = privateLookupIn(C1,CL)}</th>
984 * <td></td>
985 * <td style="text-align:center">PRO</td>
986 * <td style="text-align:center">PRI</td>
987 * <td style="text-align:center">PAC</td>
988 * <td style="text-align:center">MOD</td>
989 * <td style="text-align:center">1R</td>
990 * </tr>
991 * <tr>
992 * <th scope="row" style="text-align:left">{@code PRI1a = privateLookupIn(C,PRI1)}</th>
993 * <td></td>
994 * <td style="text-align:center">PRO</td>
995 * <td style="text-align:center">PRI</td>
996 * <td style="text-align:center">PAC</td>
997 * <td style="text-align:center">MOD</td>
998 * <td style="text-align:center">1R</td>
999 * </tr>
1000 * <tr>
1001 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} same package</th>
1002 * <td></td>
1003 * <td></td>
1004 * <td></td>
1005 * <td style="text-align:center">PAC</td>
1006 * <td style="text-align:center">MOD</td>
1007 * <td style="text-align:center">1R</td>
1008 * </tr>
1009 * <tr>
1010 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} different package</th>
1011 * <td></td>
1012 * <td></td>
1013 * <td></td>
1014 * <td></td>
1015 * <td style="text-align:center">MOD</td>
1016 * <td style="text-align:center">1R</td>
1017 * </tr>
1018 * <tr>
1019 * <th scope="row" style="text-align:left">{@code PRI1.in(D)} different module</th>
1020 * <td></td>
1021 * <td></td>
1022 * <td></td>
1023 * <td></td>
1024 * <td></td>
1025 * <td style="text-align:center">2R</td>
1026 * </tr>
1027 * <tr>
1028 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PROTECTED)}</th>
1029 * <td></td>
1030 * <td></td>
1031 * <td style="text-align:center">PRI</td>
1032 * <td style="text-align:center">PAC</td>
1033 * <td style="text-align:center">MOD</td>
1034 * <td style="text-align:center">1R</td>
1035 * </tr>
1036 * <tr>
1037 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PRIVATE)}</th>
1038 * <td></td>
1039 * <td></td>
1040 * <td></td>
1041 * <td style="text-align:center">PAC</td>
1042 * <td style="text-align:center">MOD</td>
1043 * <td style="text-align:center">1R</td>
1044 * </tr>
1045 * <tr>
1046 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PACKAGE)}</th>
1047 * <td></td>
1048 * <td></td>
1049 * <td></td>
1050 * <td></td>
1051 * <td style="text-align:center">MOD</td>
1052 * <td style="text-align:center">1R</td>
1053 * </tr>
1054 * <tr>
1055 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(MODULE)}</th>
1056 * <td></td>
1057 * <td></td>
1058 * <td></td>
1059 * <td></td>
1060 * <td></td>
1061 * <td style="text-align:center">1R</td>
1062 * </tr>
1063 * <tr>
1064 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PUBLIC)}</th>
1065 * <td></td>
1066 * <td></td>
1067 * <td></td>
1068 * <td></td>
1069 * <td></td>
1070 * <td style="text-align:center">none</td>
1071 * <tr>
1072 * <th scope="row" style="text-align:left">{@code PRI2 = privateLookupIn(D,CL)}</th>
1073 * <td></td>
1074 * <td style="text-align:center">PRO</td>
1075 * <td style="text-align:center">PRI</td>
1076 * <td style="text-align:center">PAC</td>
1077 * <td></td>
1078 * <td style="text-align:center">2R</td>
1079 * </tr>
1080 * <tr>
1081 * <th scope="row" style="text-align:left">{@code privateLookupIn(D,PRI1)}</th>
1082 * <td></td>
1083 * <td style="text-align:center">PRO</td>
1084 * <td style="text-align:center">PRI</td>
1085 * <td style="text-align:center">PAC</td>
1086 * <td></td>
1087 * <td style="text-align:center">2R</td>
1088 * </tr>
1089 * <tr>
1090 * <th scope="row" style="text-align:left">{@code privateLookupIn(C,PRI2)} fails</th>
1091 * <td></td>
1092 * <td></td>
1093 * <td></td>
1094 * <td></td>
1095 * <td></td>
1096 * <td style="text-align:center">IAE</td>
1097 * </tr>
1098 * <tr>
1099 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} same package</th>
1100 * <td></td>
1101 * <td></td>
1102 * <td></td>
1103 * <td style="text-align:center">PAC</td>
1104 * <td></td>
1105 * <td style="text-align:center">2R</td>
1106 * </tr>
1107 * <tr>
1108 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} different package</th>
1109 * <td></td>
1110 * <td></td>
1111 * <td></td>
1112 * <td></td>
1113 * <td></td>
1114 * <td style="text-align:center">2R</td>
1115 * </tr>
1116 * <tr>
1117 * <th scope="row" style="text-align:left">{@code PRI2.in(C1)} hop back to module</th>
1118 * <td></td>
1119 * <td></td>
1120 * <td></td>
1121 * <td></td>
1122 * <td></td>
1123 * <td style="text-align:center">2R</td>
1124 * </tr>
1125 * <tr>
1126 * <th scope="row" style="text-align:left">{@code PRI2.in(E)} hop to third module</th>
1127 * <td></td>
1128 * <td></td>
1129 * <td></td>
1130 * <td></td>
1131 * <td></td>
1132 * <td style="text-align:center">none</td>
1133 * </tr>
1134 * <tr>
1135 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PROTECTED)}</th>
1136 * <td></td>
1137 * <td></td>
1138 * <td style="text-align:center">PRI</td>
1139 * <td style="text-align:center">PAC</td>
1140 * <td></td>
1141 * <td style="text-align:center">2R</td>
1142 * </tr>
1143 * <tr>
1144 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PRIVATE)}</th>
1145 * <td></td>
1146 * <td></td>
1147 * <td></td>
1148 * <td style="text-align:center">PAC</td>
1149 * <td></td>
1150 * <td style="text-align:center">2R</td>
1151 * </tr>
1152 * <tr>
1153 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PACKAGE)}</th>
1154 * <td></td>
1155 * <td></td>
1156 * <td></td>
1157 * <td></td>
1158 * <td></td>
1159 * <td style="text-align:center">2R</td>
1160 * </tr>
1161 * <tr>
1162 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(MODULE)}</th>
1163 * <td></td>
1164 * <td></td>
1165 * <td></td>
1166 * <td></td>
1167 * <td></td>
1168 * <td style="text-align:center">2R</td>
1169 * </tr>
1170 * <tr>
1171 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PUBLIC)}</th>
1172 * <td></td>
1173 * <td></td>
1174 * <td></td>
1175 * <td></td>
1176 * <td></td>
1177 * <td style="text-align:center">none</td>
1178 * </tr>
1179 * <tr>
1180 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PROTECTED)}</th>
1181 * <td></td>
1182 * <td></td>
1183 * <td style="text-align:center">PRI</td>
1184 * <td style="text-align:center">PAC</td>
1185 * <td style="text-align:center">MOD</td>
1186 * <td style="text-align:center">1R</td>
1187 * </tr>
1188 * <tr>
1189 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PRIVATE)}</th>
1190 * <td></td>
1191 * <td></td>
1192 * <td></td>
1193 * <td style="text-align:center">PAC</td>
1194 * <td style="text-align:center">MOD</td>
1195 * <td style="text-align:center">1R</td>
1196 * </tr>
1197 * <tr>
1198 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PACKAGE)}</th>
1199 * <td></td>
1200 * <td></td>
1201 * <td></td>
1202 * <td></td>
1203 * <td style="text-align:center">MOD</td>
1204 * <td style="text-align:center">1R</td>
1205 * </tr>
1206 * <tr>
1207 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(MODULE)}</th>
1208 * <td></td>
1209 * <td></td>
1210 * <td></td>
1211 * <td></td>
1212 * <td></td>
1213 * <td style="text-align:center">1R</td>
1214 * </tr>
1215 * <tr>
1216 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PUBLIC)}</th>
1217 * <td></td>
1218 * <td></td>
1219 * <td></td>
1220 * <td></td>
1221 * <td></td>
1222 * <td style="text-align:center">none</td>
1223 * </tr>
1224 * <tr>
1225 * <th scope="row" style="text-align:left">{@code PUB = publicLookup()}</th>
1226 * <td></td>
1227 * <td></td>
1228 * <td></td>
1229 * <td></td>
1230 * <td></td>
1231 * <td style="text-align:center">U</td>
1232 * </tr>
1233 * <tr>
1234 * <th scope="row" style="text-align:left">{@code PUB.in(D)} different module</th>
1235 * <td></td>
1236 * <td></td>
1237 * <td></td>
1238 * <td></td>
1239 * <td></td>
1240 * <td style="text-align:center">U</td>
1241 * </tr>
1242 * <tr>
1243 * <th scope="row" style="text-align:left">{@code PUB.in(D).in(E)} third module</th>
1244 * <td></td>
1245 * <td></td>
1246 * <td></td>
1247 * <td></td>
1248 * <td></td>
1249 * <td style="text-align:center">U</td>
1250 * </tr>
1251 * <tr>
1252 * <th scope="row" style="text-align:left">{@code PUB.dropLookupMode(UNCONDITIONAL)}</th>
1253 * <td></td>
1254 * <td></td>
1255 * <td></td>
1256 * <td></td>
1257 * <td></td>
1258 * <td style="text-align:center">none</td>
1259 * </tr>
1260 * <tr>
1261 * <th scope="row" style="text-align:left">{@code privateLookupIn(C1,PUB)} fails</th>
1262 * <td></td>
1263 * <td></td>
1264 * <td></td>
1265 * <td></td>
1266 * <td></td>
1267 * <td style="text-align:center">IAE</td>
1268 * </tr>
1269 * <tr>
1270 * <th scope="row" style="text-align:left">{@code ANY.in(X)}, for inaccessible {@code X}</th>
1271 * <td></td>
1272 * <td></td>
1273 * <td></td>
1274 * <td></td>
1275 * <td></td>
1276 * <td style="text-align:center">none</td>
1277 * </tr>
1278 * </tbody>
1279 * </table>
1280 *
1281 * <p>
1282 * Notes:
1283 * <ul>
1284 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1285 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1286 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1287 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1288 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set,
1289 * {@code PRO} indicates {@link #PROTECTED} bit set,
1290 * {@code PRI} indicates {@link #PRIVATE} bit set,
1291 * {@code PAC} indicates {@link #PACKAGE} bit set,
1292 * {@code MOD} indicates {@link #MODULE} bit set,
1293 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1294 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1295 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1296 * <li>Public access comes in three kinds:
1297 * <ul>
1298 * <li>unconditional ({@code U}): the lookup assumes readability.
1299 * The lookup has {@code null} previous lookup class.
1300 * <li>one-module-reads ({@code 1R}): the module access checking is
1301 * performed with respect to the lookup class. The lookup has {@code null}
1302 * previous lookup class.
1303 * <li>two-module-reads ({@code 2R}): the module access checking is
1304 * performed with respect to the lookup class and the previous lookup class.
1305 * The lookup has a non-null previous lookup class which is in a
1306 * different module from the current lookup class.
1307 * </ul>
1308 * <li>Any attempt to reach a third module loses all access.</li>
1309 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1310 * all access modes are dropped.</li>
1311 * </ul>
1312 *
1313 * <h2><a id="secmgr"></a>Security manager interactions</h2>
1314 * Although bytecode instructions can only refer to classes in
1315 * a related class loader, this API can search for methods in any
1316 * class, as long as a reference to its {@code Class} object is
1317 * available. Such cross-loader references are also possible with the
1318 * Core Reflection API, and are impossible to bytecode instructions
1319 * such as {@code invokestatic} or {@code getfield}.
1320 * There is a {@linkplain java.lang.SecurityManager security manager API}
1321 * to allow applications to check such cross-loader references.
1322 * These checks apply to both the {@code MethodHandles.Lookup} API
1323 * and the Core Reflection API
1324 * (as found on {@link java.lang.Class Class}).
1325 * <p>
1326 * If a security manager is present, member and class lookups are subject to
1327 * additional checks.
1328 * From one to three calls are made to the security manager.
1329 * Any of these calls can refuse access by throwing a
1330 * {@link java.lang.SecurityException SecurityException}.
1331 * Define {@code smgr} as the security manager,
1332 * {@code lookc} as the lookup class of the current lookup object,
1333 * {@code refc} as the containing class in which the member
1334 * is being sought, and {@code defc} as the class in which the
1335 * member is actually defined.
1336 * (If a class or other type is being accessed,
1337 * the {@code refc} and {@code defc} values are the class itself.)
1338 * The value {@code lookc} is defined as <em>not present</em>
1339 * if the current lookup object does not have
1340 * {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1341 * The calls are made according to the following rules:
1342 * <ul>
1343 * <li><b>Step 1:</b>
1344 * If {@code lookc} is not present, or if its class loader is not
1345 * the same as or an ancestor of the class loader of {@code refc},
1346 * then {@link SecurityManager#checkPackageAccess
1347 * smgr.checkPackageAccess(refcPkg)} is called,
1348 * where {@code refcPkg} is the package of {@code refc}.
1349 * <li><b>Step 2a:</b>
1350 * If the retrieved member is not public and
1351 * {@code lookc} is not present, then
1352 * {@link SecurityManager#checkPermission smgr.checkPermission}
1353 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
1354 * <li><b>Step 2b:</b>
1355 * If the retrieved class has a {@code null} class loader,
1356 * and {@code lookc} is not present, then
1357 * {@link SecurityManager#checkPermission smgr.checkPermission}
1358 * with {@code RuntimePermission("getClassLoader")} is called.
1359 * <li><b>Step 3:</b>
1360 * If the retrieved member is not public,
1361 * and if {@code lookc} is not present,
1362 * and if {@code defc} and {@code refc} are different,
1363 * then {@link SecurityManager#checkPackageAccess
1364 * smgr.checkPackageAccess(defcPkg)} is called,
1365 * where {@code defcPkg} is the package of {@code defc}.
1366 * </ul>
1367 * Security checks are performed after other access checks have passed.
1368 * Therefore, the above rules presuppose a member or class that is public,
1369 * or else that is being accessed from a lookup class that has
1370 * rights to access the member or class.
1371 * <p>
1372 * If a security manager is present and the current lookup object does not have
1373 * {@linkplain #hasFullPrivilegeAccess() full privilege access}, then
1374 * {@link #defineClass(byte[]) defineClass},
1375 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass},
1376 * {@link #defineHiddenClassWithClassData(byte[], Object, boolean, ClassOption...)
1377 * defineHiddenClassWithClassData}
1378 * calls {@link SecurityManager#checkPermission smgr.checkPermission}
1379 * with {@code RuntimePermission("defineClass")}.
1380 *
1381 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1382 * A small number of Java methods have a special property called caller sensitivity.
1383 * A <em>caller-sensitive</em> method can behave differently depending on the
1384 * identity of its immediate caller.
1385 * <p>
1386 * If a method handle for a caller-sensitive method is requested,
1387 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1388 * but they take account of the lookup class in a special way.
1389 * The resulting method handle behaves as if it were called
1390 * from an instruction contained in the lookup class,
1391 * so that the caller-sensitive method detects the lookup class.
1392 * (By contrast, the invoker of the method handle is disregarded.)
1393 * Thus, in the case of caller-sensitive methods,
1394 * different lookup classes may give rise to
1395 * differently behaving method handles.
1396 * <p>
1397 * In cases where the lookup object is
1398 * {@link MethodHandles#publicLookup() publicLookup()},
1399 * or some other lookup object without the
1400 * {@linkplain #ORIGINAL original access},
1401 * the lookup class is disregarded.
1402 * In such cases, no caller-sensitive method handle can be created,
1403 * access is forbidden, and the lookup fails with an
1404 * {@code IllegalAccessException}.
1405 * <p style="font-size:smaller;">
1406 * <em>Discussion:</em>
1407 * For example, the caller-sensitive method
1408 * {@link java.lang.Class#forName(String) Class.forName(x)}
1409 * can return varying classes or throw varying exceptions,
1410 * depending on the class loader of the class that calls it.
1411 * A public lookup of {@code Class.forName} will fail, because
1412 * there is no reasonable way to determine its bytecode behavior.
1413 * <p style="font-size:smaller;">
1414 * If an application caches method handles for broad sharing,
1415 * it should use {@code publicLookup()} to create them.
1416 * If there is a lookup of {@code Class.forName}, it will fail,
1417 * and the application must take appropriate action in that case.
1418 * It may be that a later lookup, perhaps during the invocation of a
1419 * bootstrap method, can incorporate the specific identity
1420 * of the caller, making the method accessible.
1421 * <p style="font-size:smaller;">
1422 * The function {@code MethodHandles.lookup} is caller sensitive
1423 * so that there can be a secure foundation for lookups.
1424 * Nearly all other methods in the JSR 292 API rely on lookup
1425 * objects to check access requests.
1426 *
1427 * @revised 9
1428 */
1429 public static final
1430 class Lookup {
1431 /** The class on behalf of whom the lookup is being performed. */
1432 private final Class<?> lookupClass;
1433
1434 /** previous lookup class */
1435 private final Class<?> prevLookupClass;
1436
1437 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1438 private final int allowedModes;
1439
1440 static {
1441 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1442 }
1443
1444 /** A single-bit mask representing {@code public} access,
1445 * which may contribute to the result of {@link #lookupModes lookupModes}.
1446 * The value, {@code 0x01}, happens to be the same as the value of the
1447 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1448 * <p>
1449 * A {@code Lookup} with this lookup mode performs cross-module access check
1450 * with respect to the {@linkplain #lookupClass() lookup class} and
1451 * {@linkplain #previousLookupClass() previous lookup class} if present.
1452 */
1453 public static final int PUBLIC = Modifier.PUBLIC;
1454
1455 /** A single-bit mask representing {@code private} access,
1456 * which may contribute to the result of {@link #lookupModes lookupModes}.
1457 * The value, {@code 0x02}, happens to be the same as the value of the
1458 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1459 */
1460 public static final int PRIVATE = Modifier.PRIVATE;
1461
1462 /** A single-bit mask representing {@code protected} access,
1463 * which may contribute to the result of {@link #lookupModes lookupModes}.
1464 * The value, {@code 0x04}, happens to be the same as the value of the
1465 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1466 */
1467 public static final int PROTECTED = Modifier.PROTECTED;
1468
1469 /** A single-bit mask representing {@code package} access (default access),
1470 * which may contribute to the result of {@link #lookupModes lookupModes}.
1471 * The value is {@code 0x08}, which does not correspond meaningfully to
1472 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1473 */
1474 public static final int PACKAGE = Modifier.STATIC;
1475
1476 /** A single-bit mask representing {@code module} access,
1477 * which may contribute to the result of {@link #lookupModes lookupModes}.
1478 * The value is {@code 0x10}, which does not correspond meaningfully to
1479 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1480 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1481 * with this lookup mode can access all public types in the module of the
1482 * lookup class and public types in packages exported by other modules
1483 * to the module of the lookup class.
1484 * <p>
1485 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1486 * previous lookup class} is always {@code null}.
1487 *
1488 * @since 9
1489 */
1490 public static final int MODULE = PACKAGE << 1;
1491
1492 /** A single-bit mask representing {@code unconditional} access
1493 * which may contribute to the result of {@link #lookupModes lookupModes}.
1494 * The value is {@code 0x20}, which does not correspond meaningfully to
1495 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1496 * A {@code Lookup} with this lookup mode assumes {@linkplain
1497 * java.lang.Module#canRead(java.lang.Module) readability}.
1498 * This lookup mode can access all public members of public types
1499 * of all modules when the type is in a package that is {@link
1500 * java.lang.Module#isExported(String) exported unconditionally}.
1501 *
1502 * <p>
1503 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1504 * previous lookup class} is always {@code null}.
1505 *
1506 * @since 9
1507 * @see #publicLookup()
1508 */
1509 public static final int UNCONDITIONAL = PACKAGE << 2;
1510
1511 /** A single-bit mask representing {@code original} access
1512 * which may contribute to the result of {@link #lookupModes lookupModes}.
1513 * The value is {@code 0x40}, which does not correspond meaningfully to
1514 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1515 *
1516 * <p>
1517 * If this lookup mode is set, the {@code Lookup} object must be
1518 * created by the original lookup class by calling
1519 * {@link MethodHandles#lookup()} method or by a bootstrap method
1520 * invoked by the VM. The {@code Lookup} object with this lookup
1521 * mode has {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1522 *
1523 * @since 16
1524 */
1525 public static final int ORIGINAL = PACKAGE << 3;
1526
1527 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL);
1528 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); // with original access
1529 private static final int TRUSTED = -1;
1530
1531 /*
1532 * Adjust PUBLIC => PUBLIC|MODULE|ORIGINAL|UNCONDITIONAL
1533 * Adjust 0 => PACKAGE
1534 */
1535 private static int fixmods(int mods) {
1536 mods &= (ALL_MODES - PACKAGE - MODULE - ORIGINAL - UNCONDITIONAL);
1537 if (Modifier.isPublic(mods))
1538 mods |= UNCONDITIONAL;
1539 return (mods != 0) ? mods : PACKAGE;
1540 }
1541
1542 /** Tells which class is performing the lookup. It is this class against
1543 * which checks are performed for visibility and access permissions.
1544 * <p>
1545 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1546 * access checks are performed against both the lookup class and the previous lookup class.
1547 * <p>
1548 * The class implies a maximum level of access permission,
1549 * but the permissions may be additionally limited by the bitmask
1550 * {@link #lookupModes lookupModes}, which controls whether non-public members
1551 * can be accessed.
1552 * @return the lookup class, on behalf of which this lookup object finds members
1553 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1554 */
1555 public Class<?> lookupClass() {
1556 return lookupClass;
1557 }
1558
1559 /** Reports a lookup class in another module that this lookup object
1560 * was previously teleported from, or {@code null}.
1561 * <p>
1562 * A {@code Lookup} object produced by the factory methods, such as the
1563 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1564 * has {@code null} previous lookup class.
1565 * A {@code Lookup} object has a non-null previous lookup class
1566 * when this lookup was teleported from an old lookup class
1567 * in one module to a new lookup class in another module.
1568 *
1569 * @return the lookup class in another module that this lookup object was
1570 * previously teleported from, or {@code null}
1571 * @since 14
1572 * @see #in(Class)
1573 * @see MethodHandles#privateLookupIn(Class, Lookup)
1574 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1575 */
1576 public Class<?> previousLookupClass() {
1577 return prevLookupClass;
1578 }
1579
1580 // This is just for calling out to MethodHandleImpl.
1581 private Class<?> lookupClassOrNull() {
1582 return (allowedModes == TRUSTED) ? null : lookupClass;
1583 }
1584
1585 /** Tells which access-protection classes of members this lookup object can produce.
1586 * The result is a bit-mask of the bits
1587 * {@linkplain #PUBLIC PUBLIC (0x01)},
1588 * {@linkplain #PRIVATE PRIVATE (0x02)},
1589 * {@linkplain #PROTECTED PROTECTED (0x04)},
1590 * {@linkplain #PACKAGE PACKAGE (0x08)},
1591 * {@linkplain #MODULE MODULE (0x10)},
1592 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)},
1593 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}.
1594 * <p>
1595 * A freshly-created lookup object
1596 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1597 * all possible bits set, except {@code UNCONDITIONAL}.
1598 * A lookup object on a new lookup class
1599 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1600 * may have some mode bits set to zero.
1601 * Mode bits can also be
1602 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1603 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1604 * The purpose of this is to restrict access via the new lookup object,
1605 * so that it can access only names which can be reached by the original
1606 * lookup object, and also by the new lookup class.
1607 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1608 * @see #in
1609 * @see #dropLookupMode
1610 *
1611 * @revised 9
1612 */
1613 public int lookupModes() {
1614 return allowedModes & ALL_MODES;
1615 }
1616
1617 /** Embody the current class (the lookupClass) as a lookup class
1618 * for method handle creation.
1619 * Must be called by from a method in this package,
1620 * which in turn is called by a method not in this package.
1621 */
1622 Lookup(Class<?> lookupClass) {
1623 this(lookupClass, null, FULL_POWER_MODES);
1624 }
1625
1626 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1627 assert PrimitiveClass.isPrimaryType(lookupClass);
1628 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1629 && prevLookupClass.getModule() != lookupClass.getModule());
1630 assert !lookupClass.isArray() && !lookupClass.isPrimitive();
1631 this.lookupClass = lookupClass;
1632 this.prevLookupClass = prevLookupClass;
1633 this.allowedModes = allowedModes;
1634 }
1635
1636 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1637 // make sure we haven't accidentally picked up a privileged class:
1638 checkUnprivilegedlookupClass(lookupClass);
1639 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1640 }
1641
1642 /**
1643 * Creates a lookup on the specified new lookup class.
1644 * The resulting object will report the specified
1645 * class as its own {@link #lookupClass() lookupClass}.
1646 *
1647 * <p>
1648 * However, the resulting {@code Lookup} object is guaranteed
1649 * to have no more access capabilities than the original.
1650 * In particular, access capabilities can be lost as follows:<ul>
1651 * <li>If the new lookup class is different from the old lookup class,
1652 * i.e. {@link #ORIGINAL ORIGINAL} access is lost.
1653 * <li>If the new lookup class is in a different module from the old one,
1654 * i.e. {@link #MODULE MODULE} access is lost.
1655 * <li>If the new lookup class is in a different package
1656 * than the old one, protected and default (package) members will not be accessible,
1657 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1658 * <li>If the new lookup class is not within the same package member
1659 * as the old one, private members will not be accessible, and protected members
1660 * will not be accessible by virtue of inheritance,
1661 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1662 * (Protected members may continue to be accessible because of package sharing.)
1663 * <li>If the new lookup class is not
1664 * {@linkplain #accessClass(Class) accessible} to this lookup,
1665 * then no members, not even public members, will be accessible
1666 * i.e. all access modes are lost.
1667 * <li>If the new lookup class, the old lookup class and the previous lookup class
1668 * are all in different modules i.e. teleporting to a third module,
1669 * all access modes are lost.
1670 * </ul>
1671 * <p>
1672 * The new previous lookup class is chosen as follows:
1673 * <ul>
1674 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1675 * the new previous lookup class is {@code null}.
1676 * <li>If the new lookup class is in the same module as the old lookup class,
1677 * the new previous lookup class is the old previous lookup class.
1678 * <li>If the new lookup class is in a different module from the old lookup class,
1679 * the new previous lookup class is the old lookup class.
1680 *</ul>
1681 * <p>
1682 * The resulting lookup's capabilities for loading classes
1683 * (used during {@link #findClass} invocations)
1684 * are determined by the lookup class' loader,
1685 * which may change due to this operation.
1686 *
1687 * @param requestedLookupClass the desired lookup class for the new lookup object
1688 * @return a lookup object which reports the desired lookup class, or the same object
1689 * if there is no change
1690 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class
1691 * @throws NullPointerException if the argument is null
1692 *
1693 * @revised 9
1694 * @see #accessClass(Class)
1695 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1696 */
1697 public Lookup in(Class<?> requestedLookupClass) {
1698 Objects.requireNonNull(requestedLookupClass);
1699 if (requestedLookupClass.isPrimitive())
1700 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1701 if (requestedLookupClass.isArray())
1702 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1703
1704 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1705 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1706 if (requestedLookupClass == this.lookupClass)
1707 return this; // keep same capabilities
1708 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL;
1709 Module fromModule = this.lookupClass.getModule();
1710 Module targetModule = requestedLookupClass.getModule();
1711 Class<?> plc = this.previousLookupClass();
1712 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1713 assert plc == null;
1714 newModes = UNCONDITIONAL;
1715 } else if (fromModule != targetModule) {
1716 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1717 // allow hopping back and forth between fromModule and plc's module
1718 // but not the third module
1719 newModes = 0;
1720 }
1721 // drop MODULE access
1722 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1723 // teleport from this lookup class
1724 plc = this.lookupClass;
1725 }
1726 if ((newModes & PACKAGE) != 0
1727 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1728 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1729 }
1730 // Allow nestmate lookups to be created without special privilege:
1731 if ((newModes & PRIVATE) != 0
1732 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1733 newModes &= ~(PRIVATE|PROTECTED);
1734 }
1735 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1736 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1737 // The requested class it not accessible from the lookup class.
1738 // No permissions.
1739 newModes = 0;
1740 }
1741 return newLookup(requestedLookupClass, plc, newModes);
1742 }
1743
1744 /**
1745 * Creates a lookup on the same lookup class which this lookup object
1746 * finds members, but with a lookup mode that has lost the given lookup mode.
1747 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1748 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED},
1749 * {@link #PRIVATE PRIVATE}, {@link #ORIGINAL ORIGINAL}, or
1750 * {@link #UNCONDITIONAL UNCONDITIONAL}.
1751 *
1752 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup},
1753 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set.
1754 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting
1755 * lookup has no access.
1756 *
1757 * <p> If this lookup is not a public lookup, then the following applies
1758 * regardless of its {@linkplain #lookupModes() lookup modes}.
1759 * {@link #PROTECTED PROTECTED} and {@link #ORIGINAL ORIGINAL} are always
1760 * dropped and so the resulting lookup mode will never have these access
1761 * capabilities. When dropping {@code PACKAGE}
1762 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE}
1763 * access. When dropping {@code MODULE} then the resulting lookup will not
1764 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access.
1765 * When dropping {@code PUBLIC} then the resulting lookup has no access.
1766 *
1767 * @apiNote
1768 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1769 * delegate non-public access within the package of the lookup class without
1770 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1771 * A lookup with {@code MODULE} but not
1772 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1773 * the module of the lookup class without conferring package access.
1774 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1775 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1776 * to public classes accessible to both the module of the lookup class
1777 * and the module of the previous lookup class.
1778 *
1779 * @param modeToDrop the lookup mode to drop
1780 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1781 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1782 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE}, {@code ORIGINAL}
1783 * or {@code UNCONDITIONAL}
1784 * @see MethodHandles#privateLookupIn
1785 * @since 9
1786 */
1787 public Lookup dropLookupMode(int modeToDrop) {
1788 int oldModes = lookupModes();
1789 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL);
1790 switch (modeToDrop) {
1791 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1792 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1793 case PACKAGE: newModes &= ~(PRIVATE); break;
1794 case PROTECTED:
1795 case PRIVATE:
1796 case ORIGINAL:
1797 case UNCONDITIONAL: break;
1798 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1799 }
1800 if (newModes == oldModes) return this; // return self if no change
1801 return newLookup(lookupClass(), previousLookupClass(), newModes);
1802 }
1803
1804 /**
1805 * Creates and links a class or interface from {@code bytes}
1806 * with the same class loader and in the same runtime package and
1807 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1808 * {@linkplain #lookupClass() lookup class} as if calling
1809 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1810 * ClassLoader::defineClass}.
1811 *
1812 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1813 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1814 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1815 * that the lookup object was created by a caller in the runtime package (or derived
1816 * from a lookup originally created by suitably privileged code to a target class in
1817 * the runtime package). </p>
1818 *
1819 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1820 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1821 * same package as the lookup class. </p>
1822 *
1823 * <p> This method does not run the class initializer. The class initializer may
1824 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1825 * Specification</em>. </p>
1826 *
1827 * <p> If there is a security manager and this lookup does not have {@linkplain
1828 * #hasFullPrivilegeAccess() full privilege access}, its {@code checkPermission} method
1829 * is first called to check {@code RuntimePermission("defineClass")}. </p>
1830 *
1831 * @param bytes the class bytes
1832 * @return the {@code Class} object for the class
1833 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1834 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1835 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
1836 * than the lookup class or {@code bytes} is not a class or interface
1837 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
1838 * @throws VerifyError if the newly created class cannot be verified
1839 * @throws LinkageError if the newly created class cannot be linked for any other reason
1840 * @throws SecurityException if a security manager is present and it
1841 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1842 * @throws NullPointerException if {@code bytes} is {@code null}
1843 * @since 9
1844 * @see Lookup#privateLookupIn
1845 * @see Lookup#dropLookupMode
1846 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1847 */
1848 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1849 ensureDefineClassPermission();
1850 if ((lookupModes() & PACKAGE) == 0)
1851 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1852 return makeClassDefiner(bytes.clone()).defineClass(false);
1853 }
1854
1855 private void ensureDefineClassPermission() {
1856 if (allowedModes == TRUSTED) return;
1857
1858 if (!hasFullPrivilegeAccess()) {
1859 @SuppressWarnings("removal")
1860 SecurityManager sm = System.getSecurityManager();
1861 if (sm != null)
1862 sm.checkPermission(new RuntimePermission("defineClass"));
1863 }
1864 }
1865
1866 /**
1867 * The set of class options that specify whether a hidden class created by
1868 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
1869 * Lookup::defineHiddenClass} method is dynamically added as a new member
1870 * to the nest of a lookup class and/or whether a hidden class has
1871 * a strong relationship with the class loader marked as its defining loader.
1872 *
1873 * @since 15
1874 */
1875 public enum ClassOption {
1876 /**
1877 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest}
1878 * of a lookup class as a nestmate.
1879 *
1880 * <p> A hidden nestmate class has access to the private members of all
1881 * classes and interfaces in the same nest.
1882 *
1883 * @see Class#getNestHost()
1884 */
1885 NESTMATE(NESTMATE_CLASS),
1886
1887 /**
1888 * Specifies that a hidden class has a <em>strong</em>
1889 * relationship with the class loader marked as its defining loader,
1890 * as a normal class or interface has with its own defining loader.
1891 * This means that the hidden class may be unloaded if and only if
1892 * its defining loader is not reachable and thus may be reclaimed
1893 * by a garbage collector (JLS {@jls 12.7}).
1894 *
1895 * <p> By default, a hidden class or interface may be unloaded
1896 * even if the class loader that is marked as its defining loader is
1897 * <a href="../ref/package-summary.html#reachability">reachable</a>.
1898
1899 *
1900 * @jls 12.7 Unloading of Classes and Interfaces
1901 */
1902 STRONG(STRONG_LOADER_LINK);
1903
1904 /* the flag value is used by VM at define class time */
1905 private final int flag;
1906 ClassOption(int flag) {
1907 this.flag = flag;
1908 }
1909
1910 static int optionsToFlag(Set<ClassOption> options) {
1911 int flags = 0;
1912 for (ClassOption cp : options) {
1913 flags |= cp.flag;
1914 }
1915 return flags;
1916 }
1917 }
1918
1919 /**
1920 * Creates a <em>hidden</em> class or interface from {@code bytes},
1921 * returning a {@code Lookup} on the newly created class or interface.
1922 *
1923 * <p> Ordinarily, a class or interface {@code C} is created by a class loader,
1924 * which either defines {@code C} directly or delegates to another class loader.
1925 * A class loader defines {@code C} directly by invoking
1926 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1927 * ClassLoader::defineClass}, which causes the Java Virtual Machine
1928 * to derive {@code C} from a purported representation in {@code class} file format.
1929 * In situations where use of a class loader is undesirable, a class or interface
1930 * {@code C} can be created by this method instead. This method is capable of
1931 * defining {@code C}, and thereby creating it, without invoking
1932 * {@code ClassLoader::defineClass}.
1933 * Instead, this method defines {@code C} as if by arranging for
1934 * the Java Virtual Machine to derive a nonarray class or interface {@code C}
1935 * from a purported representation in {@code class} file format
1936 * using the following rules:
1937 *
1938 * <ol>
1939 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup}
1940 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access.
1941 * This level of access is needed to create {@code C} in the module
1942 * of the lookup class of this {@code Lookup}.</li>
1943 *
1944 * <li> The purported representation in {@code bytes} must be a {@code ClassFile}
1945 * structure (JVMS {@jvms 4.1}) of a supported major and minor version.
1946 * The major and minor version may differ from the {@code class} file version
1947 * of the lookup class of this {@code Lookup}.</li>
1948 *
1949 * <li> The value of {@code this_class} must be a valid index in the
1950 * {@code constant_pool} table, and the entry at that index must be a valid
1951 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name
1952 * encoded in internal form that is specified by this structure. {@code N} must
1953 * denote a class or interface in the same package as the lookup class.</li>
1954 *
1955 * <li> Let {@code CN} be the string {@code N + "." + <suffix>},
1956 * where {@code <suffix>} is an unqualified name.
1957 *
1958 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by
1959 * {@code bytes} with an additional entry in the {@code constant_pool} table,
1960 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and
1961 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class}
1962 * refers to the new {@code CONSTANT_Utf8_info} structure.
1963 *
1964 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}.
1965 *
1966 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and
1967 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5},
1968 * with the following adjustments:
1969 * <ul>
1970 * <li> The constant indicated by {@code this_class} is permitted to specify a name
1971 * that includes a single {@code "."} character, even though this is not a valid
1972 * binary class or interface name in internal form.</li>
1973 *
1974 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C},
1975 * but no class loader is recorded as an initiating class loader of {@code C}.</li>
1976 *
1977 * <li> {@code C} is considered to have the same runtime
1978 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module}
1979 * and {@linkplain java.security.ProtectionDomain protection domain}
1980 * as the lookup class of this {@code Lookup}.
1981 * <li> Let {@code GN} be the binary name obtained by taking {@code N}
1982 * (a binary name encoded in internal form) and replacing ASCII forward slashes with
1983 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}:
1984 * <ul>
1985 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>},
1986 * even though this is not a valid binary class or interface name.</li>
1987 * <li> {@link Class#descriptorString()} returns the string
1988 * {@code "L" + N + "." + <suffix> + ";"},
1989 * even though this is not a valid type descriptor name.</li>
1990 * <li> {@link Class#describeConstable()} returns an empty optional as {@code C}
1991 * cannot be described in {@linkplain java.lang.constant.ClassDesc nominal form}.</li>
1992 * </ul>
1993 * </ul>
1994 * </li>
1995 * </ol>
1996 *
1997 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine.
1998 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments:
1999 * <ul>
2000 * <li> During verification, whenever it is necessary to load the class named
2001 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is
2002 * made of any class loader.</li>
2003 *
2004 * <li> On any attempt to resolve the entry in the run-time constant pool indicated
2005 * by {@code this_class}, the symbolic reference is considered to be resolved to
2006 * {@code C} and resolution always succeeds immediately.</li>
2007 * </ul>
2008 *
2009 * <p> If the {@code initialize} parameter is {@code true},
2010 * then {@code C} is initialized by the Java Virtual Machine.
2011 *
2012 * <p> The newly created class or interface {@code C} serves as the
2013 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object
2014 * returned by this method. {@code C} is <em>hidden</em> in the sense that
2015 * no other class or interface can refer to {@code C} via a constant pool entry.
2016 * That is, a hidden class or interface cannot be named as a supertype, a field type,
2017 * a method parameter type, or a method return type by any other class.
2018 * This is because a hidden class or interface does not have a binary name, so
2019 * there is no internal form available to record in any class's constant pool.
2020 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)},
2021 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and
2022 * is not {@linkplain java.instrument/java.lang.instrument.Instrumentation#isModifiableClass(Class)
2023 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html">
2024 * JVM Tool Interface</a>.
2025 *
2026 * <p> A class or interface created by
2027 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
2028 * a class loader} has a strong relationship with that class loader.
2029 * That is, every {@code Class} object contains a reference to the {@code ClassLoader}
2030 * that {@linkplain Class#getClassLoader() defined it}.
2031 * This means that a class created by a class loader may be unloaded if and
2032 * only if its defining loader is not reachable and thus may be reclaimed
2033 * by a garbage collector (JLS {@jls 12.7}).
2034 *
2035 * By default, however, a hidden class or interface may be unloaded even if
2036 * the class loader that is marked as its defining loader is
2037 * <a href="../ref/package-summary.html#reachability">reachable</a>.
2038 * This behavior is useful when a hidden class or interface serves multiple
2039 * classes defined by arbitrary class loaders. In other cases, a hidden
2040 * class or interface may be linked to a single class (or a small number of classes)
2041 * with the same defining loader as the hidden class or interface.
2042 * In such cases, where the hidden class or interface must be coterminous
2043 * with a normal class or interface, the {@link ClassOption#STRONG STRONG}
2044 * option may be passed in {@code options}.
2045 * This arranges for a hidden class to have the same strong relationship
2046 * with the class loader marked as its defining loader,
2047 * as a normal class or interface has with its own defining loader.
2048 *
2049 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass}
2050 * may still prevent a hidden class or interface from being
2051 * unloaded by ensuring that the {@code Class} object is reachable.
2052 *
2053 * <p> The unloading characteristics are set for each hidden class when it is
2054 * defined, and cannot be changed later. An advantage of allowing hidden classes
2055 * to be unloaded independently of the class loader marked as their defining loader
2056 * is that a very large number of hidden classes may be created by an application.
2057 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory,
2058 * just as if normal classes were created by class loaders.
2059 *
2060 * <p> Classes and interfaces in a nest are allowed to have mutual access to
2061 * their private members. The nest relationship is determined by
2062 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and
2063 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file.
2064 * By default, a hidden class belongs to a nest consisting only of itself
2065 * because a hidden class has no binary name.
2066 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options}
2067 * to create a hidden class or interface {@code C} as a member of a nest.
2068 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute
2069 * in the {@code ClassFile} structure from which {@code C} was derived.
2070 * Instead, the following rules determine the nest host of {@code C}:
2071 * <ul>
2072 * <li>If the nest host of the lookup class of this {@code Lookup} has previously
2073 * been determined, then let {@code H} be the nest host of the lookup class.
2074 * Otherwise, the nest host of the lookup class is determined using the
2075 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li>
2076 * <li>The nest host of {@code C} is determined to be {@code H},
2077 * the nest host of the lookup class.</li>
2078 * </ul>
2079 *
2080 * <p> A hidden class or interface may be serializable, but this requires a custom
2081 * serialization mechanism in order to ensure that instances are properly serialized
2082 * and deserialized. The default serialization mechanism supports only classes and
2083 * interfaces that are discoverable by their class name.
2084 *
2085 * @param bytes the bytes that make up the class data,
2086 * in the format of a valid {@code class} file as defined by
2087 * <cite>The Java Virtual Machine Specification</cite>.
2088 * @param initialize if {@code true} the class will be initialized.
2089 * @param options {@linkplain ClassOption class options}
2090 * @return the {@code Lookup} object on the hidden class,
2091 * with {@linkplain #ORIGINAL original} and
2092 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2093 *
2094 * @throws IllegalAccessException if this {@code Lookup} does not have
2095 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2096 * @throws SecurityException if a security manager is present and it
2097 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2098 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2099 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2100 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2101 * than the lookup class or {@code bytes} is not a class or interface
2102 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2103 * @throws IncompatibleClassChangeError if the class or interface named as
2104 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2105 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2106 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2107 * {@code C} is {@code C} itself
2108 * @throws VerifyError if the newly created class cannot be verified
2109 * @throws LinkageError if the newly created class cannot be linked for any other reason
2110 * @throws NullPointerException if any parameter is {@code null}
2111 *
2112 * @since 15
2113 * @see Class#isHidden()
2114 * @jvms 4.2.1 Binary Class and Interface Names
2115 * @jvms 4.2.2 Unqualified Names
2116 * @jvms 4.7.28 The {@code NestHost} Attribute
2117 * @jvms 4.7.29 The {@code NestMembers} Attribute
2118 * @jvms 5.4.3.1 Class and Interface Resolution
2119 * @jvms 5.4.4 Access Control
2120 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2121 * @jvms 5.4 Linking
2122 * @jvms 5.5 Initialization
2123 * @jls 12.7 Unloading of Classes and Interfaces
2124 */
2125 @SuppressWarnings("doclint:reference") // cross-module links
2126 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options)
2127 throws IllegalAccessException
2128 {
2129 Objects.requireNonNull(bytes);
2130 Objects.requireNonNull(options);
2131
2132 ensureDefineClassPermission();
2133 if (!hasFullPrivilegeAccess()) {
2134 throw new IllegalAccessException(this + " does not have full privilege access");
2135 }
2136
2137 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false).defineClassAsLookup(initialize);
2138 }
2139
2140 /**
2141 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated
2142 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data},
2143 * returning a {@code Lookup} on the newly created class or interface.
2144 *
2145 * <p> This method is equivalent to calling
2146 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)}
2147 * as if the hidden class is injected with a private static final <i>unnamed</i>
2148 * field which is initialized with the given {@code classData} at
2149 * the first instruction of the class initializer.
2150 * The newly created class is linked by the Java Virtual Machine.
2151 *
2152 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData}
2153 * and {@link MethodHandles#classDataAt(Lookup, String, Class, int) MethodHandles::classDataAt}
2154 * methods can be used to retrieve the {@code classData}.
2155 *
2156 * @apiNote
2157 * A framework can create a hidden class with class data with one or more
2158 * objects and load the class data as dynamically-computed constant(s)
2159 * via a bootstrap method. {@link MethodHandles#classData(Lookup, String, Class)
2160 * Class data} is accessible only to the lookup object created by the newly
2161 * defined hidden class but inaccessible to other members in the same nest
2162 * (unlike private static fields that are accessible to nestmates).
2163 * Care should be taken w.r.t. mutability for example when passing
2164 * an array or other mutable structure through the class data.
2165 * Changing any value stored in the class data at runtime may lead to
2166 * unpredictable behavior.
2167 * If the class data is a {@code List}, it is good practice to make it
2168 * unmodifiable for example via {@link List#of List::of}.
2169 *
2170 * @param bytes the class bytes
2171 * @param classData pre-initialized class data
2172 * @param initialize if {@code true} the class will be initialized.
2173 * @param options {@linkplain ClassOption class options}
2174 * @return the {@code Lookup} object on the hidden class,
2175 * with {@linkplain #ORIGINAL original} and
2176 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2177 *
2178 * @throws IllegalAccessException if this {@code Lookup} does not have
2179 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2180 * @throws SecurityException if a security manager is present and it
2181 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2182 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2183 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2184 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2185 * than the lookup class or {@code bytes} is not a class or interface
2186 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2187 * @throws IncompatibleClassChangeError if the class or interface named as
2188 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2189 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2190 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2191 * {@code C} is {@code C} itself
2192 * @throws VerifyError if the newly created class cannot be verified
2193 * @throws LinkageError if the newly created class cannot be linked for any other reason
2194 * @throws NullPointerException if any parameter is {@code null}
2195 *
2196 * @since 16
2197 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
2198 * @see Class#isHidden()
2199 * @see MethodHandles#classData(Lookup, String, Class)
2200 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
2201 * @jvms 4.2.1 Binary Class and Interface Names
2202 * @jvms 4.2.2 Unqualified Names
2203 * @jvms 4.7.28 The {@code NestHost} Attribute
2204 * @jvms 4.7.29 The {@code NestMembers} Attribute
2205 * @jvms 5.4.3.1 Class and Interface Resolution
2206 * @jvms 5.4.4 Access Control
2207 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2208 * @jvms 5.4 Linking
2209 * @jvms 5.5 Initialization
2210 * @jls 12.7 Unloading of Classes and Interface
2211 */
2212 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options)
2213 throws IllegalAccessException
2214 {
2215 Objects.requireNonNull(bytes);
2216 Objects.requireNonNull(classData);
2217 Objects.requireNonNull(options);
2218
2219 ensureDefineClassPermission();
2220 if (!hasFullPrivilegeAccess()) {
2221 throw new IllegalAccessException(this + " does not have full privilege access");
2222 }
2223
2224 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false)
2225 .defineClassAsLookup(initialize, classData);
2226 }
2227
2228 static class ClassFile {
2229 final String name;
2230 final int accessFlags;
2231 final byte[] bytes;
2232 ClassFile(String name, int accessFlags, byte[] bytes) {
2233 this.name = name;
2234 this.accessFlags = accessFlags;
2235 this.bytes = bytes;
2236 }
2237
2238 static ClassFile newInstanceNoCheck(String name, byte[] bytes) {
2239 return new ClassFile(name, 0, bytes);
2240 }
2241
2242 /**
2243 * This method checks the class file version and the structure of `this_class`.
2244 * and checks if the bytes is a class or interface (ACC_MODULE flag not set)
2245 * that is in the named package.
2246 *
2247 * @throws IllegalArgumentException if ACC_MODULE flag is set in access flags
2248 * or the class is not in the given package name.
2249 */
2250 static ClassFile newInstance(byte[] bytes, String pkgName) {
2251 int magic = readInt(bytes, 0);
2252 if (magic != 0xCAFEBABE) {
2253 throw new ClassFormatError("Incompatible magic value: " + magic);
2254 }
2255 int minor = readUnsignedShort(bytes, 4);
2256 int major = readUnsignedShort(bytes, 6);
2257 if (!VM.isSupportedClassFileVersion(major, minor)) {
2258 throw new UnsupportedClassVersionError("Unsupported class file version " + major + "." + minor);
2259 }
2260
2261 String name;
2262 int accessFlags;
2263 try {
2264 ClassReader reader = new ClassReader(bytes);
2265 // ClassReader::getClassName does not check if `this_class` is CONSTANT_Class_info
2266 // workaround to read `this_class` using readConst and validate the value
2267 int thisClass = reader.readUnsignedShort(reader.header + 2);
2268 Object constant = reader.readConst(thisClass, new char[reader.getMaxStringLength()]);
2269 if (!(constant instanceof Type type)) {
2270 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info");
2271 }
2272 if (!type.getDescriptor().startsWith("L")) {
2273 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info");
2274 }
2275 name = type.getClassName();
2276 accessFlags = reader.readUnsignedShort(reader.header);
2277 } catch (RuntimeException e) {
2278 // ASM exceptions are poorly specified
2279 ClassFormatError cfe = new ClassFormatError();
2280 cfe.initCause(e);
2281 throw cfe;
2282 }
2283
2284 // must be a class or interface
2285 if ((accessFlags & Opcodes.ACC_MODULE) != 0) {
2286 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set");
2287 }
2288
2289 // check if it's in the named package
2290 int index = name.lastIndexOf('.');
2291 String pn = (index == -1) ? "" : name.substring(0, index);
2292 if (!pn.equals(pkgName)) {
2293 throw newIllegalArgumentException(name + " not in same package as lookup class");
2294 }
2295
2296 return new ClassFile(name, accessFlags, bytes);
2297 }
2298
2299 private static int readInt(byte[] bytes, int offset) {
2300 if ((offset+4) > bytes.length) {
2301 throw new ClassFormatError("Invalid ClassFile structure");
2302 }
2303 return ((bytes[offset] & 0xFF) << 24)
2304 | ((bytes[offset + 1] & 0xFF) << 16)
2305 | ((bytes[offset + 2] & 0xFF) << 8)
2306 | (bytes[offset + 3] & 0xFF);
2307 }
2308
2309 private static int readUnsignedShort(byte[] bytes, int offset) {
2310 if ((offset+2) > bytes.length) {
2311 throw new ClassFormatError("Invalid ClassFile structure");
2312 }
2313 return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF);
2314 }
2315 }
2316
2317 /*
2318 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2319 * from the given bytes.
2320 *
2321 * Caller should make a defensive copy of the arguments if needed
2322 * before calling this factory method.
2323 *
2324 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2325 * {@bytes} denotes a class in a different package than the lookup class
2326 */
2327 private ClassDefiner makeClassDefiner(byte[] bytes) {
2328 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2329 return new ClassDefiner(this, cf, STRONG_LOADER_LINK);
2330 }
2331
2332 /**
2333 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2334 * from the given bytes. The name must be in the same package as the lookup class.
2335 *
2336 * Caller should make a defensive copy of the arguments if needed
2337 * before calling this factory method.
2338 *
2339 * @param bytes class bytes
2340 * @return ClassDefiner that defines a hidden class of the given bytes.
2341 *
2342 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2343 * {@bytes} denotes a class in a different package than the lookup class
2344 */
2345 ClassDefiner makeHiddenClassDefiner(byte[] bytes) {
2346 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2347 return makeHiddenClassDefiner(cf, Set.of(), false);
2348 }
2349
2350 /**
2351 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2352 * from the given bytes and options.
2353 * The name must be in the same package as the lookup class.
2354 *
2355 * Caller should make a defensive copy of the arguments if needed
2356 * before calling this factory method.
2357 *
2358 * @param bytes class bytes
2359 * @param options class options
2360 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2361 * @return ClassDefiner that defines a hidden class of the given bytes and options
2362 *
2363 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2364 * {@bytes} denotes a class in a different package than the lookup class
2365 */
2366 ClassDefiner makeHiddenClassDefiner(byte[] bytes,
2367 Set<ClassOption> options,
2368 boolean accessVmAnnotations) {
2369 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2370 return makeHiddenClassDefiner(cf, options, accessVmAnnotations);
2371 }
2372
2373 /**
2374 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2375 * from the given bytes and the given options. No package name check on the given name.
2376 *
2377 * @param name fully-qualified name that specifies the prefix of the hidden class
2378 * @param bytes class bytes
2379 * @param options class options
2380 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2381 */
2382 ClassDefiner makeHiddenClassDefiner(String name, byte[] bytes, Set<ClassOption> options) {
2383 // skip name and access flags validation
2384 return makeHiddenClassDefiner(ClassFile.newInstanceNoCheck(name, bytes), options, false);
2385 }
2386
2387 /**
2388 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2389 * from the given class file and options.
2390 *
2391 * @param cf ClassFile
2392 * @param options class options
2393 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2394 */
2395 private ClassDefiner makeHiddenClassDefiner(ClassFile cf,
2396 Set<ClassOption> options,
2397 boolean accessVmAnnotations) {
2398 int flags = HIDDEN_CLASS | ClassOption.optionsToFlag(options);
2399 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) {
2400 // jdk.internal.vm.annotations are permitted for classes
2401 // defined to boot loader and platform loader
2402 flags |= ACCESS_VM_ANNOTATIONS;
2403 }
2404
2405 return new ClassDefiner(this, cf, flags);
2406 }
2407
2408 static class ClassDefiner {
2409 private final Lookup lookup;
2410 private final String name;
2411 private final byte[] bytes;
2412 private final int classFlags;
2413
2414 private ClassDefiner(Lookup lookup, ClassFile cf, int flags) {
2415 assert ((flags & HIDDEN_CLASS) != 0 || (flags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK);
2416 this.lookup = lookup;
2417 this.bytes = cf.bytes;
2418 this.name = cf.name;
2419 this.classFlags = flags;
2420 }
2421
2422 String className() {
2423 return name;
2424 }
2425
2426 Class<?> defineClass(boolean initialize) {
2427 return defineClass(initialize, null);
2428 }
2429
2430 Lookup defineClassAsLookup(boolean initialize) {
2431 Class<?> c = defineClass(initialize, null);
2432 return new Lookup(c, null, FULL_POWER_MODES);
2433 }
2434
2435 /**
2436 * Defines the class of the given bytes and the given classData.
2437 * If {@code initialize} parameter is true, then the class will be initialized.
2438 *
2439 * @param initialize true if the class to be initialized
2440 * @param classData classData or null
2441 * @return the class
2442 *
2443 * @throws LinkageError linkage error
2444 */
2445 Class<?> defineClass(boolean initialize, Object classData) {
2446 Class<?> lookupClass = lookup.lookupClass();
2447 ClassLoader loader = lookupClass.getClassLoader();
2448 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null;
2449 Class<?> c = SharedSecrets.getJavaLangAccess()
2450 .defineClass(loader, lookupClass, name, bytes, pd, initialize, classFlags, classData);
2451 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost();
2452 return c;
2453 }
2454
2455 Lookup defineClassAsLookup(boolean initialize, Object classData) {
2456 Class<?> c = defineClass(initialize, classData);
2457 return new Lookup(c, null, FULL_POWER_MODES);
2458 }
2459
2460 private boolean isNestmate() {
2461 return (classFlags & NESTMATE_CLASS) != 0;
2462 }
2463 }
2464
2465 private ProtectionDomain lookupClassProtectionDomain() {
2466 ProtectionDomain pd = cachedProtectionDomain;
2467 if (pd == null) {
2468 cachedProtectionDomain = pd = SharedSecrets.getJavaLangAccess().protectionDomain(lookupClass);
2469 }
2470 return pd;
2471 }
2472
2473 // cached protection domain
2474 private volatile ProtectionDomain cachedProtectionDomain;
2475
2476 // Make sure outer class is initialized first.
2477 static { IMPL_NAMES.getClass(); }
2478
2479 /** Package-private version of lookup which is trusted. */
2480 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
2481
2482 /** Version of lookup which is trusted minimally.
2483 * It can only be used to create method handles to publicly accessible
2484 * members in packages that are exported unconditionally.
2485 */
2486 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
2487
2488 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
2489 String name = lookupClass.getName();
2490 if (name.startsWith("java.lang.invoke."))
2491 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
2492 }
2493
2494 /**
2495 * Displays the name of the class from which lookups are to be made,
2496 * followed by "/" and the name of the {@linkplain #previousLookupClass()
2497 * previous lookup class} if present.
2498 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
2499 * If there are restrictions on the access permitted to this lookup,
2500 * this is indicated by adding a suffix to the class name, consisting
2501 * of a slash and a keyword. The keyword represents the strongest
2502 * allowed access, and is chosen as follows:
2503 * <ul>
2504 * <li>If no access is allowed, the suffix is "/noaccess".
2505 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
2506 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
2507 * <li>If only public and module access are allowed, the suffix is "/module".
2508 * <li>If public and package access are allowed, the suffix is "/package".
2509 * <li>If public, package, and private access are allowed, the suffix is "/private".
2510 * </ul>
2511 * If none of the above cases apply, it is the case that
2512 * {@linkplain #hasFullPrivilegeAccess() full privilege access}
2513 * (public, module, package, private, and protected) is allowed.
2514 * In this case, no suffix is added.
2515 * This is true only of an object obtained originally from
2516 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
2517 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
2518 * always have restricted access, and will display a suffix.
2519 * <p>
2520 * (It may seem strange that protected access should be
2521 * stronger than private access. Viewed independently from
2522 * package access, protected access is the first to be lost,
2523 * because it requires a direct subclass relationship between
2524 * caller and callee.)
2525 * @see #in
2526 *
2527 * @revised 9
2528 */
2529 @Override
2530 public String toString() {
2531 String cname = lookupClass.getName();
2532 if (prevLookupClass != null)
2533 cname += "/" + prevLookupClass.getName();
2534 switch (allowedModes) {
2535 case 0: // no privileges
2536 return cname + "/noaccess";
2537 case UNCONDITIONAL:
2538 return cname + "/publicLookup";
2539 case PUBLIC:
2540 return cname + "/public";
2541 case PUBLIC|MODULE:
2542 return cname + "/module";
2543 case PUBLIC|PACKAGE:
2544 case PUBLIC|MODULE|PACKAGE:
2545 return cname + "/package";
2546 case PUBLIC|PACKAGE|PRIVATE:
2547 case PUBLIC|MODULE|PACKAGE|PRIVATE:
2548 return cname + "/private";
2549 case PUBLIC|PACKAGE|PRIVATE|PROTECTED:
2550 case PUBLIC|MODULE|PACKAGE|PRIVATE|PROTECTED:
2551 case FULL_POWER_MODES:
2552 return cname;
2553 case TRUSTED:
2554 return "/trusted"; // internal only; not exported
2555 default: // Should not happen, but it's a bitfield...
2556 cname = cname + "/" + Integer.toHexString(allowedModes);
2557 assert(false) : cname;
2558 return cname;
2559 }
2560 }
2561
2562 /**
2563 * Produces a method handle for a static method.
2564 * The type of the method handle will be that of the method.
2565 * (Since static methods do not take receivers, there is no
2566 * additional receiver argument inserted into the method handle type,
2567 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
2568 * The method and all its argument types must be accessible to the lookup object.
2569 * <p>
2570 * The returned method handle will have
2571 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2572 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2573 * <p>
2574 * If the returned method handle is invoked, the method's class will
2575 * be initialized, if it has not already been initialized.
2576 * <p><b>Example:</b>
2577 * {@snippet lang="java" :
2578 import static java.lang.invoke.MethodHandles.*;
2579 import static java.lang.invoke.MethodType.*;
2580 ...
2581 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
2582 "asList", methodType(List.class, Object[].class));
2583 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
2584 * }
2585 * @param refc the class from which the method is accessed
2586 * @param name the name of the method
2587 * @param type the type of the method
2588 * @return the desired method handle
2589 * @throws NoSuchMethodException if the method does not exist
2590 * @throws IllegalAccessException if access checking fails,
2591 * or if the method is not {@code static},
2592 * or if the method's variable arity modifier bit
2593 * is set and {@code asVarargsCollector} fails
2594 * @throws SecurityException if a security manager is present and it
2595 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2596 * @throws NullPointerException if any argument is null
2597 */
2598 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2599 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
2600 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method));
2601 }
2602
2603 /**
2604 * Produces a method handle for a virtual method.
2605 * The type of the method handle will be that of the method,
2606 * with the receiver type (usually {@code refc}) prepended.
2607 * The method and all its argument types must be accessible to the lookup object.
2608 * <p>
2609 * When called, the handle will treat the first argument as a receiver
2610 * and, for non-private methods, dispatch on the receiver's type to determine which method
2611 * implementation to enter.
2612 * For private methods the named method in {@code refc} will be invoked on the receiver.
2613 * (The dispatching action is identical with that performed by an
2614 * {@code invokevirtual} or {@code invokeinterface} instruction.)
2615 * <p>
2616 * The first argument will be of type {@code refc} if the lookup
2617 * class has full privileges to access the member. Otherwise
2618 * the member must be {@code protected} and the first argument
2619 * will be restricted in type to the lookup class.
2620 * <p>
2621 * The returned method handle will have
2622 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2623 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2624 * <p>
2625 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
2626 * instructions and method handles produced by {@code findVirtual},
2627 * if the class is {@code MethodHandle} and the name string is
2628 * {@code invokeExact} or {@code invoke}, the resulting
2629 * method handle is equivalent to one produced by
2630 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
2631 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
2632 * with the same {@code type} argument.
2633 * <p>
2634 * If the class is {@code VarHandle} and the name string corresponds to
2635 * the name of a signature-polymorphic access mode method, the resulting
2636 * method handle is equivalent to one produced by
2637 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
2638 * the access mode corresponding to the name string and with the same
2639 * {@code type} arguments.
2640 * <p>
2641 * <b>Example:</b>
2642 * {@snippet lang="java" :
2643 import static java.lang.invoke.MethodHandles.*;
2644 import static java.lang.invoke.MethodType.*;
2645 ...
2646 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
2647 "concat", methodType(String.class, String.class));
2648 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
2649 "hashCode", methodType(int.class));
2650 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
2651 "hashCode", methodType(int.class));
2652 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
2653 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
2654 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
2655 // interface method:
2656 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
2657 "subSequence", methodType(CharSequence.class, int.class, int.class));
2658 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
2659 // constructor "internal method" must be accessed differently:
2660 MethodType MT_newString = methodType(void.class); //()V for new String()
2661 try { assertEquals("impossible", lookup()
2662 .findVirtual(String.class, "<init>", MT_newString));
2663 } catch (NoSuchMethodException ex) { } // OK
2664 MethodHandle MH_newString = publicLookup()
2665 .findConstructor(String.class, MT_newString);
2666 assertEquals("", (String) MH_newString.invokeExact());
2667 * }
2668 *
2669 * @param refc the class or interface from which the method is accessed
2670 * @param name the name of the method
2671 * @param type the type of the method, with the receiver argument omitted
2672 * @return the desired method handle
2673 * @throws NoSuchMethodException if the method does not exist
2674 * @throws IllegalAccessException if access checking fails,
2675 * or if the method is {@code static},
2676 * or if the method's variable arity modifier bit
2677 * is set and {@code asVarargsCollector} fails
2678 * @throws SecurityException if a security manager is present and it
2679 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2680 * @throws NullPointerException if any argument is null
2681 */
2682 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2683 if (refc == MethodHandle.class) {
2684 MethodHandle mh = findVirtualForMH(name, type);
2685 if (mh != null) return mh;
2686 } else if (refc == VarHandle.class) {
2687 MethodHandle mh = findVirtualForVH(name, type);
2688 if (mh != null) return mh;
2689 }
2690 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
2691 MemberName method = resolveOrFail(refKind, refc, name, type);
2692 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method));
2693 }
2694 private MethodHandle findVirtualForMH(String name, MethodType type) {
2695 // these names require special lookups because of the implicit MethodType argument
2696 if ("invoke".equals(name))
2697 return invoker(type);
2698 if ("invokeExact".equals(name))
2699 return exactInvoker(type);
2700 assert(!MemberName.isMethodHandleInvokeName(name));
2701 return null;
2702 }
2703 private MethodHandle findVirtualForVH(String name, MethodType type) {
2704 try {
2705 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
2706 } catch (IllegalArgumentException e) {
2707 return null;
2708 }
2709 }
2710
2711 /**
2712 * Produces a method handle which creates an object and initializes it, using
2713 * the constructor of the specified type.
2714 * The parameter types of the method handle will be those of the constructor,
2715 * while the return type will be a reference to the constructor's class.
2716 * The constructor and all its argument types must be accessible to the lookup object.
2717 * <p>
2718 * The requested type must have a return type of {@code void}.
2719 * (This is consistent with the JVM's treatment of constructor type descriptors.)
2720 * <p>
2721 * The returned method handle will have
2722 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2723 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2724 * <p>
2725 * If the returned method handle is invoked, the constructor's class will
2726 * be initialized, if it has not already been initialized.
2727 * <p><b>Example:</b>
2728 * {@snippet lang="java" :
2729 import static java.lang.invoke.MethodHandles.*;
2730 import static java.lang.invoke.MethodType.*;
2731 ...
2732 MethodHandle MH_newArrayList = publicLookup().findConstructor(
2733 ArrayList.class, methodType(void.class, Collection.class));
2734 Collection orig = Arrays.asList("x", "y");
2735 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
2736 assert(orig != copy);
2737 assertEquals(orig, copy);
2738 // a variable-arity constructor:
2739 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
2740 ProcessBuilder.class, methodType(void.class, String[].class));
2741 ProcessBuilder pb = (ProcessBuilder)
2742 MH_newProcessBuilder.invoke("x", "y", "z");
2743 assertEquals("[x, y, z]", pb.command().toString());
2744 * }
2745 *
2746 *
2747 * @param refc the class or interface from which the method is accessed
2748 * @param type the type of the method, with the receiver argument omitted, and a void return type
2749 * @return the desired method handle
2750 * @throws NoSuchMethodException if the constructor does not exist
2751 * @throws IllegalAccessException if access checking fails
2752 * or if the method's variable arity modifier bit
2753 * is set and {@code asVarargsCollector} fails
2754 * @throws SecurityException if a security manager is present and it
2755 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2756 * @throws NullPointerException if any argument is null
2757 */
2758 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2759 if (refc.isArray()) {
2760 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
2761 }
2762 if (type.returnType() != void.class) {
2763 throw new NoSuchMethodException("Constructors must have void return type: " + refc.getName());
2764 }
2765 String name = "<init>";
2766 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
2767 return getDirectConstructor(refc, ctor);
2768 }
2769
2770 /**
2771 * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
2772 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
2773 * Such a resolution, as specified in JVMS {@jvms 5.4.3.1}, attempts to locate and load the class,
2774 * and then determines whether the class is accessible to this lookup object.
2775 * <p>
2776 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
2777 * its class loader, and the {@linkplain #lookupModes() lookup modes}.
2778 *
2779 * @param targetName the fully qualified name of the class to be looked up.
2780 * @return the requested class.
2781 * @throws SecurityException if a security manager is present and it
2782 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2783 * @throws LinkageError if the linkage fails
2784 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
2785 * @throws IllegalAccessException if the class is not accessible, using the allowed access
2786 * modes.
2787 * @throws NullPointerException if {@code targetName} is null
2788 * @since 9
2789 * @jvms 5.4.3.1 Class and Interface Resolution
2790 */
2791 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
2792 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
2793 return accessClass(targetClass);
2794 }
2795
2796 /**
2797 * Ensures that {@code targetClass} has been initialized. The class
2798 * to be initialized must be {@linkplain #accessClass accessible}
2799 * to this {@code Lookup} object. This method causes {@code targetClass}
2800 * to be initialized if it has not been already initialized,
2801 * as specified in JVMS {@jvms 5.5}.
2802 *
2803 * <p>
2804 * This method returns when {@code targetClass} is fully initialized, or
2805 * when {@code targetClass} is being initialized by the current thread.
2806 *
2807 * @param targetClass the class to be initialized
2808 * @return {@code targetClass} that has been initialized, or that is being
2809 * initialized by the current thread.
2810 *
2811 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or {@code void}
2812 * or array class
2813 * @throws IllegalAccessException if {@code targetClass} is not
2814 * {@linkplain #accessClass accessible} to this lookup
2815 * @throws ExceptionInInitializerError if the class initialization provoked
2816 * by this method fails
2817 * @throws SecurityException if a security manager is present and it
2818 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2819 * @since 15
2820 * @jvms 5.5 Initialization
2821 */
2822 public Class<?> ensureInitialized(Class<?> targetClass) throws IllegalAccessException {
2823 if (targetClass.isPrimitive())
2824 throw new IllegalArgumentException(targetClass + " is a primitive class");
2825 if (targetClass.isArray())
2826 throw new IllegalArgumentException(targetClass + " is an array class");
2827
2828 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2829 throw makeAccessException(targetClass);
2830 }
2831 checkSecurityManager(targetClass);
2832
2833 // ensure class initialization
2834 Unsafe.getUnsafe().ensureClassInitialized(targetClass);
2835 return targetClass;
2836 }
2837
2838 /*
2839 * Returns IllegalAccessException due to access violation to the given targetClass.
2840 *
2841 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized}
2842 * which verifies access to a class rather a member.
2843 */
2844 private IllegalAccessException makeAccessException(Class<?> targetClass) {
2845 String message = "access violation: "+ targetClass;
2846 if (this == MethodHandles.publicLookup()) {
2847 message += ", from public Lookup";
2848 } else {
2849 Module m = lookupClass().getModule();
2850 message += ", from " + lookupClass() + " (" + m + ")";
2851 if (prevLookupClass != null) {
2852 message += ", previous lookup " +
2853 prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")";
2854 }
2855 }
2856 return new IllegalAccessException(message);
2857 }
2858
2859 /**
2860 * Determines if a class can be accessed from the lookup context defined by
2861 * this {@code Lookup} object. The static initializer of the class is not run.
2862 * If {@code targetClass} is an array class, {@code targetClass} is accessible
2863 * if the element type of the array class is accessible. Otherwise,
2864 * {@code targetClass} is determined as accessible as follows.
2865 *
2866 * <p>
2867 * If {@code targetClass} is in the same module as the lookup class,
2868 * the lookup class is {@code LC} in module {@code M1} and
2869 * the previous lookup class is in module {@code M0} or
2870 * {@code null} if not present,
2871 * {@code targetClass} is accessible if and only if one of the following is true:
2872 * <ul>
2873 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
2874 * {@code LC} or other class in the same nest of {@code LC}.</li>
2875 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
2876 * in the same runtime package of {@code LC}.</li>
2877 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
2878 * a public type in {@code M1}.</li>
2879 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
2880 * a public type in a package exported by {@code M1} to at least {@code M0}
2881 * if the previous lookup class is present; otherwise, {@code targetClass}
2882 * is a public type in a package exported by {@code M1} unconditionally.</li>
2883 * </ul>
2884 *
2885 * <p>
2886 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2887 * can access public types in all modules when the type is in a package
2888 * that is exported unconditionally.
2889 * <p>
2890 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass},
2891 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2892 * is inaccessible.
2893 * <p>
2894 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2895 * {@code M1} is the module containing {@code lookupClass} and
2896 * {@code M2} is the module containing {@code targetClass},
2897 * then {@code targetClass} is accessible if and only if
2898 * <ul>
2899 * <li>{@code M1} reads {@code M2}, and
2900 * <li>{@code targetClass} is public and in a package exported by
2901 * {@code M2} at least to {@code M1}.
2902 * </ul>
2903 * <p>
2904 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2905 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2906 * containing the previous lookup class, then {@code targetClass} is accessible
2907 * if and only if one of the following is true:
2908 * <ul>
2909 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2910 * {@linkplain Module#reads reads} {@code M0} and the type is
2911 * in a package that is exported to at least {@code M1}.
2912 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2913 * {@linkplain Module#reads reads} {@code M1} and the type is
2914 * in a package that is exported to at least {@code M0}.
2915 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2916 * and {@code M1} reads {@code M2} and the type is in a package
2917 * that is exported to at least both {@code M0} and {@code M2}.
2918 * </ul>
2919 * <p>
2920 * Otherwise, {@code targetClass} is not accessible.
2921 *
2922 * @param targetClass the class to be access-checked
2923 * @return the class that has been access-checked
2924 * @throws IllegalAccessException if the class is not accessible from the lookup class
2925 * and previous lookup class, if present, using the allowed access modes.
2926 * @throws SecurityException if a security manager is present and it
2927 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2928 * @throws NullPointerException if {@code targetClass} is {@code null}
2929 * @since 9
2930 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
2931 */
2932 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
2933 if (!isClassAccessible(targetClass)) {
2934 throw makeAccessException(targetClass);
2935 }
2936 checkSecurityManager(targetClass);
2937 return targetClass;
2938 }
2939
2940 /**
2941 * Produces an early-bound method handle for a virtual method.
2942 * It will bypass checks for overriding methods on the receiver,
2943 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2944 * instruction from within the explicitly specified {@code specialCaller}.
2945 * The type of the method handle will be that of the method,
2946 * with a suitably restricted receiver type prepended.
2947 * (The receiver type will be {@code specialCaller} or a subtype.)
2948 * The method and all its argument types must be accessible
2949 * to the lookup object.
2950 * <p>
2951 * Before method resolution,
2952 * if the explicitly specified caller class is not identical with the
2953 * lookup class, or if this lookup object does not have
2954 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2955 * privileges, the access fails.
2956 * <p>
2957 * The returned method handle will have
2958 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2959 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2960 * <p style="font-size:smaller;">
2961 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
2962 * even though the {@code invokespecial} instruction can refer to them
2963 * in special circumstances. Use {@link #findConstructor findConstructor}
2964 * to access instance initialization methods in a safe manner.)</em>
2965 * <p><b>Example:</b>
2966 * {@snippet lang="java" :
2967 import static java.lang.invoke.MethodHandles.*;
2968 import static java.lang.invoke.MethodType.*;
2969 ...
2970 static class Listie extends ArrayList {
2971 public String toString() { return "[wee Listie]"; }
2972 static Lookup lookup() { return MethodHandles.lookup(); }
2973 }
2974 ...
2975 // no access to constructor via invokeSpecial:
2976 MethodHandle MH_newListie = Listie.lookup()
2977 .findConstructor(Listie.class, methodType(void.class));
2978 Listie l = (Listie) MH_newListie.invokeExact();
2979 try { assertEquals("impossible", Listie.lookup().findSpecial(
2980 Listie.class, "<init>", methodType(void.class), Listie.class));
2981 } catch (NoSuchMethodException ex) { } // OK
2982 // access to super and self methods via invokeSpecial:
2983 MethodHandle MH_super = Listie.lookup().findSpecial(
2984 ArrayList.class, "toString" , methodType(String.class), Listie.class);
2985 MethodHandle MH_this = Listie.lookup().findSpecial(
2986 Listie.class, "toString" , methodType(String.class), Listie.class);
2987 MethodHandle MH_duper = Listie.lookup().findSpecial(
2988 Object.class, "toString" , methodType(String.class), Listie.class);
2989 assertEquals("[]", (String) MH_super.invokeExact(l));
2990 assertEquals(""+l, (String) MH_this.invokeExact(l));
2991 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
2992 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
2993 String.class, "toString", methodType(String.class), Listie.class));
2994 } catch (IllegalAccessException ex) { } // OK
2995 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
2996 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
2997 * }
2998 *
2999 * @param refc the class or interface from which the method is accessed
3000 * @param name the name of the method (which must not be "<init>")
3001 * @param type the type of the method, with the receiver argument omitted
3002 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
3003 * @return the desired method handle
3004 * @throws NoSuchMethodException if the method does not exist
3005 * @throws IllegalAccessException if access checking fails,
3006 * or if the method is {@code static},
3007 * or if the method's variable arity modifier bit
3008 * is set and {@code asVarargsCollector} fails
3009 * @throws SecurityException if a security manager is present and it
3010 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3011 * @throws NullPointerException if any argument is null
3012 */
3013 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
3014 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
3015 checkSpecialCaller(specialCaller, refc);
3016 Lookup specialLookup = this.in(specialCaller);
3017 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
3018 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method));
3019 }
3020
3021 /**
3022 * Produces a method handle giving read access to a non-static field.
3023 * The type of the method handle will have a return type of the field's
3024 * value type.
3025 * The method handle's single argument will be the instance containing
3026 * the field.
3027 * Access checking is performed immediately on behalf of the lookup class.
3028 * @param refc the class or interface from which the method is accessed
3029 * @param name the field's name
3030 * @param type the field's type
3031 * @return a method handle which can load values from the field
3032 * @throws NoSuchFieldException if the field does not exist
3033 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3034 * @throws SecurityException if a security manager is present and it
3035 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3036 * @throws NullPointerException if any argument is null
3037 * @see #findVarHandle(Class, String, Class)
3038 */
3039 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3040 MemberName field = resolveOrFail(REF_getField, refc, name, type);
3041 return getDirectField(REF_getField, refc, field);
3042 }
3043
3044 /**
3045 * Produces a method handle giving write access to a non-static field.
3046 * The type of the method handle will have a void return type.
3047 * The method handle will take two arguments, the instance containing
3048 * the field, and the value to be stored.
3049 * The second argument will be of the field's value type.
3050 * Access checking is performed immediately on behalf of the lookup class.
3051 * @param refc the class or interface from which the method is accessed
3052 * @param name the field's name
3053 * @param type the field's type
3054 * @return a method handle which can store values into the field
3055 * @throws NoSuchFieldException if the field does not exist
3056 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3057 * or {@code final}
3058 * @throws SecurityException if a security manager is present and it
3059 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3060 * @throws NullPointerException if any argument is null
3061 * @see #findVarHandle(Class, String, Class)
3062 */
3063 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3064 MemberName field = resolveOrFail(REF_putField, refc, name, type);
3065 return getDirectField(REF_putField, refc, field);
3066 }
3067
3068 /**
3069 * Produces a VarHandle giving access to a non-static field {@code name}
3070 * of type {@code type} declared in a class of type {@code recv}.
3071 * The VarHandle's variable type is {@code type} and it has one
3072 * coordinate type, {@code recv}.
3073 * <p>
3074 * Access checking is performed immediately on behalf of the lookup
3075 * class.
3076 * <p>
3077 * Certain access modes of the returned VarHandle are unsupported under
3078 * the following conditions:
3079 * <ul>
3080 * <li>if the field is declared {@code final}, then the write, atomic
3081 * update, numeric atomic update, and bitwise atomic update access
3082 * modes are unsupported.
3083 * <li>if the field type is anything other than {@code byte},
3084 * {@code short}, {@code char}, {@code int}, {@code long},
3085 * {@code float}, or {@code double} then numeric atomic update
3086 * access modes are unsupported.
3087 * <li>if the field type is anything other than {@code boolean},
3088 * {@code byte}, {@code short}, {@code char}, {@code int} or
3089 * {@code long} then bitwise atomic update access modes are
3090 * unsupported.
3091 * </ul>
3092 * <p>
3093 * If the field is declared {@code volatile} then the returned VarHandle
3094 * will override access to the field (effectively ignore the
3095 * {@code volatile} declaration) in accordance to its specified
3096 * access modes.
3097 * <p>
3098 * If the field type is {@code float} or {@code double} then numeric
3099 * and atomic update access modes compare values using their bitwise
3100 * representation (see {@link Float#floatToRawIntBits} and
3101 * {@link Double#doubleToRawLongBits}, respectively).
3102 * @apiNote
3103 * Bitwise comparison of {@code float} values or {@code double} values,
3104 * as performed by the numeric and atomic update access modes, differ
3105 * from the primitive {@code ==} operator and the {@link Float#equals}
3106 * and {@link Double#equals} methods, specifically with respect to
3107 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3108 * Care should be taken when performing a compare and set or a compare
3109 * and exchange operation with such values since the operation may
3110 * unexpectedly fail.
3111 * There are many possible NaN values that are considered to be
3112 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3113 * provided by Java can distinguish between them. Operation failure can
3114 * occur if the expected or witness value is a NaN value and it is
3115 * transformed (perhaps in a platform specific manner) into another NaN
3116 * value, and thus has a different bitwise representation (see
3117 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3118 * details).
3119 * The values {@code -0.0} and {@code +0.0} have different bitwise
3120 * representations but are considered equal when using the primitive
3121 * {@code ==} operator. Operation failure can occur if, for example, a
3122 * numeric algorithm computes an expected value to be say {@code -0.0}
3123 * and previously computed the witness value to be say {@code +0.0}.
3124 * @param recv the receiver class, of type {@code R}, that declares the
3125 * non-static field
3126 * @param name the field's name
3127 * @param type the field's type, of type {@code T}
3128 * @return a VarHandle giving access to non-static fields.
3129 * @throws NoSuchFieldException if the field does not exist
3130 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3131 * @throws SecurityException if a security manager is present and it
3132 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3133 * @throws NullPointerException if any argument is null
3134 * @since 9
3135 */
3136 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3137 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
3138 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
3139 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
3140 }
3141
3142 /**
3143 * Produces a method handle giving read access to a static field.
3144 * The type of the method handle will have a return type of the field's
3145 * value type.
3146 * The method handle will take no arguments.
3147 * Access checking is performed immediately on behalf of the lookup class.
3148 * <p>
3149 * If the returned method handle is invoked, the field's class will
3150 * be initialized, if it has not already been initialized.
3151 * @param refc the class or interface from which the method is accessed
3152 * @param name the field's name
3153 * @param type the field's type
3154 * @return a method handle which can load values from the field
3155 * @throws NoSuchFieldException if the field does not exist
3156 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3157 * @throws SecurityException if a security manager is present and it
3158 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3159 * @throws NullPointerException if any argument is null
3160 */
3161 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3162 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
3163 return getDirectField(REF_getStatic, refc, field);
3164 }
3165
3166 /**
3167 * Produces a method handle giving write access to a static field.
3168 * The type of the method handle will have a void return type.
3169 * The method handle will take a single
3170 * argument, of the field's value type, the value to be stored.
3171 * Access checking is performed immediately on behalf of the lookup class.
3172 * <p>
3173 * If the returned method handle is invoked, the field's class will
3174 * be initialized, if it has not already been initialized.
3175 * @param refc the class or interface from which the method is accessed
3176 * @param name the field's name
3177 * @param type the field's type
3178 * @return a method handle which can store values into the field
3179 * @throws NoSuchFieldException if the field does not exist
3180 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3181 * or is {@code final}
3182 * @throws SecurityException if a security manager is present and it
3183 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3184 * @throws NullPointerException if any argument is null
3185 */
3186 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3187 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
3188 return getDirectField(REF_putStatic, refc, field);
3189 }
3190
3191 /**
3192 * Produces a VarHandle giving access to a static field {@code name} of
3193 * type {@code type} declared in a class of type {@code decl}.
3194 * The VarHandle's variable type is {@code type} and it has no
3195 * coordinate types.
3196 * <p>
3197 * Access checking is performed immediately on behalf of the lookup
3198 * class.
3199 * <p>
3200 * If the returned VarHandle is operated on, the declaring class will be
3201 * initialized, if it has not already been initialized.
3202 * <p>
3203 * Certain access modes of the returned VarHandle are unsupported under
3204 * the following conditions:
3205 * <ul>
3206 * <li>if the field is declared {@code final}, then the write, atomic
3207 * update, numeric atomic update, and bitwise atomic update access
3208 * modes are unsupported.
3209 * <li>if the field type is anything other than {@code byte},
3210 * {@code short}, {@code char}, {@code int}, {@code long},
3211 * {@code float}, or {@code double}, then numeric atomic update
3212 * access modes are unsupported.
3213 * <li>if the field type is anything other than {@code boolean},
3214 * {@code byte}, {@code short}, {@code char}, {@code int} or
3215 * {@code long} then bitwise atomic update access modes are
3216 * unsupported.
3217 * </ul>
3218 * <p>
3219 * If the field is declared {@code volatile} then the returned VarHandle
3220 * will override access to the field (effectively ignore the
3221 * {@code volatile} declaration) in accordance to its specified
3222 * access modes.
3223 * <p>
3224 * If the field type is {@code float} or {@code double} then numeric
3225 * and atomic update access modes compare values using their bitwise
3226 * representation (see {@link Float#floatToRawIntBits} and
3227 * {@link Double#doubleToRawLongBits}, respectively).
3228 * @apiNote
3229 * Bitwise comparison of {@code float} values or {@code double} values,
3230 * as performed by the numeric and atomic update access modes, differ
3231 * from the primitive {@code ==} operator and the {@link Float#equals}
3232 * and {@link Double#equals} methods, specifically with respect to
3233 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3234 * Care should be taken when performing a compare and set or a compare
3235 * and exchange operation with such values since the operation may
3236 * unexpectedly fail.
3237 * There are many possible NaN values that are considered to be
3238 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3239 * provided by Java can distinguish between them. Operation failure can
3240 * occur if the expected or witness value is a NaN value and it is
3241 * transformed (perhaps in a platform specific manner) into another NaN
3242 * value, and thus has a different bitwise representation (see
3243 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3244 * details).
3245 * The values {@code -0.0} and {@code +0.0} have different bitwise
3246 * representations but are considered equal when using the primitive
3247 * {@code ==} operator. Operation failure can occur if, for example, a
3248 * numeric algorithm computes an expected value to be say {@code -0.0}
3249 * and previously computed the witness value to be say {@code +0.0}.
3250 * @param decl the class that declares the static field
3251 * @param name the field's name
3252 * @param type the field's type, of type {@code T}
3253 * @return a VarHandle giving access to a static field
3254 * @throws NoSuchFieldException if the field does not exist
3255 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3256 * @throws SecurityException if a security manager is present and it
3257 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3258 * @throws NullPointerException if any argument is null
3259 * @since 9
3260 */
3261 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3262 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
3263 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
3264 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
3265 }
3266
3267 /**
3268 * Produces an early-bound method handle for a non-static method.
3269 * The receiver must have a supertype {@code defc} in which a method
3270 * of the given name and type is accessible to the lookup class.
3271 * The method and all its argument types must be accessible to the lookup object.
3272 * The type of the method handle will be that of the method,
3273 * without any insertion of an additional receiver parameter.
3274 * The given receiver will be bound into the method handle,
3275 * so that every call to the method handle will invoke the
3276 * requested method on the given receiver.
3277 * <p>
3278 * The returned method handle will have
3279 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3280 * the method's variable arity modifier bit ({@code 0x0080}) is set
3281 * <em>and</em> the trailing array argument is not the only argument.
3282 * (If the trailing array argument is the only argument,
3283 * the given receiver value will be bound to it.)
3284 * <p>
3285 * This is almost equivalent to the following code, with some differences noted below:
3286 * {@snippet lang="java" :
3287 import static java.lang.invoke.MethodHandles.*;
3288 import static java.lang.invoke.MethodType.*;
3289 ...
3290 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
3291 MethodHandle mh1 = mh0.bindTo(receiver);
3292 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
3293 return mh1;
3294 * }
3295 * where {@code defc} is either {@code receiver.getClass()} or a super
3296 * type of that class, in which the requested method is accessible
3297 * to the lookup class.
3298 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
3299 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
3300 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
3301 * the receiver is restricted by {@code findVirtual} to the lookup class.)
3302 * @param receiver the object from which the method is accessed
3303 * @param name the name of the method
3304 * @param type the type of the method, with the receiver argument omitted
3305 * @return the desired method handle
3306 * @throws NoSuchMethodException if the method does not exist
3307 * @throws IllegalAccessException if access checking fails
3308 * or if the method's variable arity modifier bit
3309 * is set and {@code asVarargsCollector} fails
3310 * @throws SecurityException if a security manager is present and it
3311 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3312 * @throws NullPointerException if any argument is null
3313 * @see MethodHandle#bindTo
3314 * @see #findVirtual
3315 */
3316 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3317 Class<? extends Object> refc = receiver.getClass(); // may get NPE
3318 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
3319 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method));
3320 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
3321 throw new IllegalAccessException("The restricted defining class " +
3322 mh.type().leadingReferenceParameter().getName() +
3323 " is not assignable from receiver class " +
3324 receiver.getClass().getName());
3325 }
3326 return mh.bindArgumentL(0, receiver).setVarargs(method);
3327 }
3328
3329 /**
3330 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3331 * to <i>m</i>, if the lookup class has permission.
3332 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
3333 * If <i>m</i> is virtual, overriding is respected on every call.
3334 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
3335 * The type of the method handle will be that of the method,
3336 * with the receiver type prepended (but only if it is non-static).
3337 * If the method's {@code accessible} flag is not set,
3338 * access checking is performed immediately on behalf of the lookup class.
3339 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
3340 * <p>
3341 * The returned method handle will have
3342 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3343 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3344 * <p>
3345 * If <i>m</i> is static, and
3346 * if the returned method handle is invoked, the method's class will
3347 * be initialized, if it has not already been initialized.
3348 * @param m the reflected method
3349 * @return a method handle which can invoke the reflected method
3350 * @throws IllegalAccessException if access checking fails
3351 * or if the method's variable arity modifier bit
3352 * is set and {@code asVarargsCollector} fails
3353 * @throws NullPointerException if the argument is null
3354 */
3355 public MethodHandle unreflect(Method m) throws IllegalAccessException {
3356 if (m.getDeclaringClass() == MethodHandle.class) {
3357 MethodHandle mh = unreflectForMH(m);
3358 if (mh != null) return mh;
3359 }
3360 if (m.getDeclaringClass() == VarHandle.class) {
3361 MethodHandle mh = unreflectForVH(m);
3362 if (mh != null) return mh;
3363 }
3364 MemberName method = new MemberName(m);
3365 byte refKind = method.getReferenceKind();
3366 if (refKind == REF_invokeSpecial)
3367 refKind = REF_invokeVirtual;
3368 assert(method.isMethod());
3369 @SuppressWarnings("deprecation")
3370 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
3371 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3372 }
3373 private MethodHandle unreflectForMH(Method m) {
3374 // these names require special lookups because they throw UnsupportedOperationException
3375 if (MemberName.isMethodHandleInvokeName(m.getName()))
3376 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
3377 return null;
3378 }
3379 private MethodHandle unreflectForVH(Method m) {
3380 // these names require special lookups because they throw UnsupportedOperationException
3381 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
3382 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
3383 return null;
3384 }
3385
3386 /**
3387 * Produces a method handle for a reflected method.
3388 * It will bypass checks for overriding methods on the receiver,
3389 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3390 * instruction from within the explicitly specified {@code specialCaller}.
3391 * The type of the method handle will be that of the method,
3392 * with a suitably restricted receiver type prepended.
3393 * (The receiver type will be {@code specialCaller} or a subtype.)
3394 * If the method's {@code accessible} flag is not set,
3395 * access checking is performed immediately on behalf of the lookup class,
3396 * as if {@code invokespecial} instruction were being linked.
3397 * <p>
3398 * Before method resolution,
3399 * if the explicitly specified caller class is not identical with the
3400 * lookup class, or if this lookup object does not have
3401 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3402 * privileges, the access fails.
3403 * <p>
3404 * The returned method handle will have
3405 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3406 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3407 * @param m the reflected method
3408 * @param specialCaller the class nominally calling the method
3409 * @return a method handle which can invoke the reflected method
3410 * @throws IllegalAccessException if access checking fails,
3411 * or if the method is {@code static},
3412 * or if the method's variable arity modifier bit
3413 * is set and {@code asVarargsCollector} fails
3414 * @throws NullPointerException if any argument is null
3415 */
3416 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
3417 checkSpecialCaller(specialCaller, m.getDeclaringClass());
3418 Lookup specialLookup = this.in(specialCaller);
3419 MemberName method = new MemberName(m, true);
3420 assert(method.isMethod());
3421 // ignore m.isAccessible: this is a new kind of access
3422 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3423 }
3424
3425 /**
3426 * Produces a method handle for a reflected constructor.
3427 * The type of the method handle will be that of the constructor,
3428 * with the return type changed to the declaring class.
3429 * The method handle will perform a {@code newInstance} operation,
3430 * creating a new instance of the constructor's class on the
3431 * arguments passed to the method handle.
3432 * <p>
3433 * If the constructor's {@code accessible} flag is not set,
3434 * access checking is performed immediately on behalf of the lookup class.
3435 * <p>
3436 * The returned method handle will have
3437 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3438 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
3439 * <p>
3440 * If the returned method handle is invoked, the constructor's class will
3441 * be initialized, if it has not already been initialized.
3442 * @param c the reflected constructor
3443 * @return a method handle which can invoke the reflected constructor
3444 * @throws IllegalAccessException if access checking fails
3445 * or if the method's variable arity modifier bit
3446 * is set and {@code asVarargsCollector} fails
3447 * @throws NullPointerException if the argument is null
3448 */
3449 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
3450 MemberName ctor = new MemberName(c);
3451 assert(ctor.isObjectConstructor() || ctor.isStaticValueFactoryMethod());
3452 @SuppressWarnings("deprecation")
3453 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
3454 Class<?> defc = c.getDeclaringClass();
3455 if (ctor.isObjectConstructor()) {
3456 assert(ctor.getMethodType().returnType() == void.class);
3457 return lookup.getDirectConstructorNoSecurityManager(defc, ctor);
3458 } else {
3459 // static init factory is a static method
3460 assert(ctor.isMethod() && ctor.getMethodType().returnType() == defc && ctor.getReferenceKind() == REF_invokeStatic) : ctor.toString();
3461 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // must not be caller-sensitive
3462 return lookup.getDirectMethodNoSecurityManager(ctor.getReferenceKind(), defc, ctor, lookup);
3463 }
3464 }
3465
3466 /**
3467 * Produces a method handle giving read access to a reflected field.
3468 * The type of the method handle will have a return type of the field's
3469 * value type.
3470 * If the field is {@code static}, the method handle will take no arguments.
3471 * Otherwise, its single argument will be the instance containing
3472 * the field.
3473 * If the {@code Field} object's {@code accessible} flag is not set,
3474 * access checking is performed immediately on behalf of the lookup class.
3475 * <p>
3476 * If the field is static, and
3477 * if the returned method handle is invoked, the field's class will
3478 * be initialized, if it has not already been initialized.
3479 * @param f the reflected field
3480 * @return a method handle which can load values from the reflected field
3481 * @throws IllegalAccessException if access checking fails
3482 * @throws NullPointerException if the argument is null
3483 */
3484 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
3485 return unreflectField(f, false);
3486 }
3487
3488 /**
3489 * Produces a method handle giving write access to a reflected field.
3490 * The type of the method handle will have a void return type.
3491 * If the field is {@code static}, the method handle will take a single
3492 * argument, of the field's value type, the value to be stored.
3493 * Otherwise, the two arguments will be the instance containing
3494 * the field, and the value to be stored.
3495 * If the {@code Field} object's {@code accessible} flag is not set,
3496 * access checking is performed immediately on behalf of the lookup class.
3497 * <p>
3498 * If the field is {@code final}, write access will not be
3499 * allowed and access checking will fail, except under certain
3500 * narrow circumstances documented for {@link Field#set Field.set}.
3501 * A method handle is returned only if a corresponding call to
3502 * the {@code Field} object's {@code set} method could return
3503 * normally. In particular, fields which are both {@code static}
3504 * and {@code final} may never be set.
3505 * <p>
3506 * If the field is {@code static}, and
3507 * if the returned method handle is invoked, the field's class will
3508 * be initialized, if it has not already been initialized.
3509 * @param f the reflected field
3510 * @return a method handle which can store values into the reflected field
3511 * @throws IllegalAccessException if access checking fails,
3512 * or if the field is {@code final} and write access
3513 * is not enabled on the {@code Field} object
3514 * @throws NullPointerException if the argument is null
3515 */
3516 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
3517 return unreflectField(f, true);
3518 }
3519
3520 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
3521 MemberName field = new MemberName(f, isSetter);
3522 if (isSetter && field.isFinal()) {
3523 if (field.isTrustedFinalField()) {
3524 String msg = field.isStatic() ? "static final field has no write access"
3525 : "final field has no write access";
3526 throw field.makeAccessException(msg, this);
3527 }
3528 }
3529 assert(isSetter
3530 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
3531 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
3532 @SuppressWarnings("deprecation")
3533 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
3534 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
3535 }
3536
3537 /**
3538 * Produces a VarHandle giving access to a reflected field {@code f}
3539 * of type {@code T} declared in a class of type {@code R}.
3540 * The VarHandle's variable type is {@code T}.
3541 * If the field is non-static the VarHandle has one coordinate type,
3542 * {@code R}. Otherwise, the field is static, and the VarHandle has no
3543 * coordinate types.
3544 * <p>
3545 * Access checking is performed immediately on behalf of the lookup
3546 * class, regardless of the value of the field's {@code accessible}
3547 * flag.
3548 * <p>
3549 * If the field is static, and if the returned VarHandle is operated
3550 * on, the field's declaring class will be initialized, if it has not
3551 * already been initialized.
3552 * <p>
3553 * Certain access modes of the returned VarHandle are unsupported under
3554 * the following conditions:
3555 * <ul>
3556 * <li>if the field is declared {@code final}, then the write, atomic
3557 * update, numeric atomic update, and bitwise atomic update access
3558 * modes are unsupported.
3559 * <li>if the field type is anything other than {@code byte},
3560 * {@code short}, {@code char}, {@code int}, {@code long},
3561 * {@code float}, or {@code double} then numeric atomic update
3562 * access modes are unsupported.
3563 * <li>if the field type is anything other than {@code boolean},
3564 * {@code byte}, {@code short}, {@code char}, {@code int} or
3565 * {@code long} then bitwise atomic update access modes are
3566 * unsupported.
3567 * </ul>
3568 * <p>
3569 * If the field is declared {@code volatile} then the returned VarHandle
3570 * will override access to the field (effectively ignore the
3571 * {@code volatile} declaration) in accordance to its specified
3572 * access modes.
3573 * <p>
3574 * If the field type is {@code float} or {@code double} then numeric
3575 * and atomic update access modes compare values using their bitwise
3576 * representation (see {@link Float#floatToRawIntBits} and
3577 * {@link Double#doubleToRawLongBits}, respectively).
3578 * @apiNote
3579 * Bitwise comparison of {@code float} values or {@code double} values,
3580 * as performed by the numeric and atomic update access modes, differ
3581 * from the primitive {@code ==} operator and the {@link Float#equals}
3582 * and {@link Double#equals} methods, specifically with respect to
3583 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3584 * Care should be taken when performing a compare and set or a compare
3585 * and exchange operation with such values since the operation may
3586 * unexpectedly fail.
3587 * There are many possible NaN values that are considered to be
3588 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3589 * provided by Java can distinguish between them. Operation failure can
3590 * occur if the expected or witness value is a NaN value and it is
3591 * transformed (perhaps in a platform specific manner) into another NaN
3592 * value, and thus has a different bitwise representation (see
3593 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3594 * details).
3595 * The values {@code -0.0} and {@code +0.0} have different bitwise
3596 * representations but are considered equal when using the primitive
3597 * {@code ==} operator. Operation failure can occur if, for example, a
3598 * numeric algorithm computes an expected value to be say {@code -0.0}
3599 * and previously computed the witness value to be say {@code +0.0}.
3600 * @param f the reflected field, with a field of type {@code T}, and
3601 * a declaring class of type {@code R}
3602 * @return a VarHandle giving access to non-static fields or a static
3603 * field
3604 * @throws IllegalAccessException if access checking fails
3605 * @throws NullPointerException if the argument is null
3606 * @since 9
3607 */
3608 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
3609 MemberName getField = new MemberName(f, false);
3610 MemberName putField = new MemberName(f, true);
3611 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
3612 f.getDeclaringClass(), getField, putField);
3613 }
3614
3615 /**
3616 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3617 * created by this lookup object or a similar one.
3618 * Security and access checks are performed to ensure that this lookup object
3619 * is capable of reproducing the target method handle.
3620 * This means that the cracking may fail if target is a direct method handle
3621 * but was created by an unrelated lookup object.
3622 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
3623 * and was created by a lookup object for a different class.
3624 * @param target a direct method handle to crack into symbolic reference components
3625 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
3626 * @throws SecurityException if a security manager is present and it
3627 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3628 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
3629 * @throws NullPointerException if the target is {@code null}
3630 * @see MethodHandleInfo
3631 * @since 1.8
3632 */
3633 public MethodHandleInfo revealDirect(MethodHandle target) {
3634 if (!target.isCrackable()) {
3635 throw newIllegalArgumentException("not a direct method handle");
3636 }
3637 MemberName member = target.internalMemberName();
3638 Class<?> defc = member.getDeclaringClass();
3639 byte refKind = member.getReferenceKind();
3640 assert(MethodHandleNatives.refKindIsValid(refKind));
3641 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
3642 // Devirtualized method invocation is usually formally virtual.
3643 // To avoid creating extra MemberName objects for this common case,
3644 // we encode this extra degree of freedom using MH.isInvokeSpecial.
3645 refKind = REF_invokeVirtual;
3646 if (refKind == REF_invokeVirtual && defc.isInterface())
3647 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
3648 refKind = REF_invokeInterface;
3649 // Check SM permissions and member access before cracking.
3650 try {
3651 checkAccess(refKind, defc, member);
3652 checkSecurityManager(defc, member);
3653 } catch (IllegalAccessException ex) {
3654 throw new IllegalArgumentException(ex);
3655 }
3656 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
3657 Class<?> callerClass = target.internalCallerClass();
3658 if ((lookupModes() & ORIGINAL) == 0 || callerClass != lookupClass())
3659 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
3660 }
3661 // Produce the handle to the results.
3662 return new InfoFromMemberName(this, member, refKind);
3663 }
3664
3665 /// Helper methods, all package-private.
3666
3667 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3668 checkSymbolicClass(refc); // do this before attempting to resolve
3669 Objects.requireNonNull(name);
3670 Objects.requireNonNull(type);
3671 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3672 NoSuchFieldException.class);
3673 }
3674
3675 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3676 checkSymbolicClass(refc); // do this before attempting to resolve
3677 Objects.requireNonNull(type);
3678 checkMethodName(refKind, name); // implicit null-check of name
3679 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3680 NoSuchMethodException.class);
3681 }
3682
3683 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
3684 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
3685 Objects.requireNonNull(member.getName());
3686 Objects.requireNonNull(member.getType());
3687 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), allowedModes,
3688 ReflectiveOperationException.class);
3689 }
3690
3691 MemberName resolveOrNull(byte refKind, MemberName member) {
3692 // do this before attempting to resolve
3693 if (!isClassAccessible(member.getDeclaringClass())) {
3694 return null;
3695 }
3696 Objects.requireNonNull(member.getName());
3697 Objects.requireNonNull(member.getType());
3698 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull(), allowedModes);
3699 }
3700
3701 MemberName resolveOrNull(byte refKind, Class<?> refc, String name, MethodType type) {
3702 // do this before attempting to resolve
3703 if (!isClassAccessible(refc)) {
3704 return null;
3705 }
3706 Objects.requireNonNull(type);
3707 // implicit null-check of name
3708 if (isIllegalMethodName(refKind, name)) {
3709 return null;
3710 }
3711
3712 return IMPL_NAMES.resolveOrNull(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes);
3713 }
3714
3715 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
3716 if (!isClassAccessible(refc)) {
3717 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
3718 }
3719 }
3720
3721 boolean isClassAccessible(Class<?> refc) {
3722 Objects.requireNonNull(refc);
3723 Class<?> caller = lookupClassOrNull();
3724 Class<?> type = refc;
3725 while (type.isArray()) {
3726 type = type.getComponentType();
3727 }
3728 return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes);
3729 }
3730
3731 /*
3732 * "<init>" can only be invoked via invokespecial
3733 * "<vnew>" factory can only invoked via invokestatic
3734 */
3735 boolean isIllegalMethodName(byte refKind, String name) {
3736 if (name.startsWith("<")) {
3737 return MemberName.VALUE_FACTORY_NAME.equals(name) ? refKind != REF_invokeStatic
3738 : refKind != REF_newInvokeSpecial;
3739 }
3740 return false;
3741 }
3742
3743 /** Check name for an illegal leading "<" character. */
3744 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
3745 if (isIllegalMethodName(refKind, name)) {
3746 throw new NoSuchMethodException("illegal method name: " + name + " " + refKind);
3747 }
3748 }
3749
3750 /**
3751 * Find my trustable caller class if m is a caller sensitive method.
3752 * If this lookup object has original full privilege access, then the caller class is the lookupClass.
3753 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
3754 */
3755 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException {
3756 if (MethodHandleNatives.isCallerSensitive(m) && (lookupModes() & ORIGINAL) == 0) {
3757 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods
3758 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3759 }
3760 return this;
3761 }
3762
3763 /**
3764 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3765 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3766 *
3767 * @deprecated This method was originally designed to test {@code PRIVATE} access
3768 * that implies full privilege access but {@code MODULE} access has since become
3769 * independent of {@code PRIVATE} access. It is recommended to call
3770 * {@link #hasFullPrivilegeAccess()} instead.
3771 * @since 9
3772 */
3773 @Deprecated(since="14")
3774 public boolean hasPrivateAccess() {
3775 return hasFullPrivilegeAccess();
3776 }
3777
3778 /**
3779 * Returns {@code true} if this lookup has <em>full privilege access</em>,
3780 * i.e. {@code PRIVATE} and {@code MODULE} access.
3781 * A {@code Lookup} object must have full privilege access in order to
3782 * access all members that are allowed to the
3783 * {@linkplain #lookupClass() lookup class}.
3784 *
3785 * @return {@code true} if this lookup has full privilege access.
3786 * @since 14
3787 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a>
3788 */
3789 public boolean hasFullPrivilegeAccess() {
3790 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE);
3791 }
3792
3793 /**
3794 * Perform steps 1 and 2b <a href="MethodHandles.Lookup.html#secmgr">access checks</a>
3795 * for ensureInitialzed, findClass or accessClass.
3796 */
3797 void checkSecurityManager(Class<?> refc) {
3798 if (allowedModes == TRUSTED) return;
3799
3800 @SuppressWarnings("removal")
3801 SecurityManager smgr = System.getSecurityManager();
3802 if (smgr == null) return;
3803
3804 // Step 1:
3805 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3806 if (!fullPrivilegeLookup ||
3807 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3808 ReflectUtil.checkPackageAccess(refc);
3809 }
3810
3811 // Step 2b:
3812 if (!fullPrivilegeLookup) {
3813 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
3814 }
3815 }
3816
3817 /**
3818 * Perform steps 1, 2a and 3 <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
3819 * Determines a trustable caller class to compare with refc, the symbolic reference class.
3820 * If this lookup object has full privilege access except original access,
3821 * then the caller class is the lookupClass.
3822 *
3823 * Lookup object created by {@link MethodHandles#privateLookupIn(Class, Lookup)}
3824 * from the same module skips the security permission check.
3825 */
3826 void checkSecurityManager(Class<?> refc, MemberName m) {
3827 Objects.requireNonNull(refc);
3828 Objects.requireNonNull(m);
3829
3830 if (allowedModes == TRUSTED) return;
3831
3832 @SuppressWarnings("removal")
3833 SecurityManager smgr = System.getSecurityManager();
3834 if (smgr == null) return;
3835
3836 // Step 1:
3837 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3838 if (!fullPrivilegeLookup ||
3839 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3840 ReflectUtil.checkPackageAccess(refc);
3841 }
3842
3843 // Step 2a:
3844 if (m.isPublic()) return;
3845 if (!fullPrivilegeLookup) {
3846 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
3847 }
3848
3849 // Step 3:
3850 Class<?> defc = m.getDeclaringClass();
3851 if (!fullPrivilegeLookup && PrimitiveClass.asPrimaryType(defc) != PrimitiveClass.asPrimaryType(refc)) {
3852 ReflectUtil.checkPackageAccess(defc);
3853 }
3854 }
3855
3856 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3857 boolean wantStatic = (refKind == REF_invokeStatic);
3858 String message;
3859 if (m.isObjectConstructor())
3860 message = "expected a method, not a constructor";
3861 else if (!m.isMethod())
3862 message = "expected a method";
3863 else if (wantStatic != m.isStatic())
3864 message = wantStatic ? "expected a static method" : "expected a non-static method";
3865 else
3866 { checkAccess(refKind, refc, m); return; }
3867 throw m.makeAccessException(message, this);
3868 }
3869
3870 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3871 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
3872 String message;
3873 if (wantStatic != m.isStatic())
3874 message = wantStatic ? "expected a static field" : "expected a non-static field";
3875 else
3876 { checkAccess(refKind, refc, m); return; }
3877 throw m.makeAccessException(message, this);
3878 }
3879
3880 /** Check public/protected/private bits on the symbolic reference class and its member. */
3881 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3882 assert(m.referenceKindIsConsistentWith(refKind) &&
3883 MethodHandleNatives.refKindIsValid(refKind) &&
3884 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
3885 int allowedModes = this.allowedModes;
3886 if (allowedModes == TRUSTED) return;
3887 int mods = m.getModifiers();
3888 if (Modifier.isProtected(mods) &&
3889 refKind == REF_invokeVirtual &&
3890 m.getDeclaringClass() == Object.class &&
3891 m.getName().equals("clone") &&
3892 refc.isArray()) {
3893 // The JVM does this hack also.
3894 // (See ClassVerifier::verify_invoke_instructions
3895 // and LinkResolver::check_method_accessability.)
3896 // Because the JVM does not allow separate methods on array types,
3897 // there is no separate method for int[].clone.
3898 // All arrays simply inherit Object.clone.
3899 // But for access checking logic, we make Object.clone
3900 // (normally protected) appear to be public.
3901 // Later on, when the DirectMethodHandle is created,
3902 // its leading argument will be restricted to the
3903 // requested array type.
3904 // N.B. The return type is not adjusted, because
3905 // that is *not* the bytecode behavior.
3906 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
3907 }
3908 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
3909 // cannot "new" a protected ctor in a different package
3910 mods ^= Modifier.PROTECTED;
3911 }
3912 if (Modifier.isFinal(mods) &&
3913 MethodHandleNatives.refKindIsSetter(refKind))
3914 throw m.makeAccessException("unexpected set of a final field", this);
3915 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
3916 if ((requestedModes & allowedModes) != 0) {
3917 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
3918 mods, lookupClass(), previousLookupClass(), allowedModes))
3919 return;
3920 } else {
3921 // Protected members can also be checked as if they were package-private.
3922 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
3923 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
3924 return;
3925 }
3926 throw m.makeAccessException(accessFailedMessage(refc, m), this);
3927 }
3928
3929 String accessFailedMessage(Class<?> refc, MemberName m) {
3930 Class<?> defc = m.getDeclaringClass();
3931 int mods = m.getModifiers();
3932 // check the class first:
3933 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
3934 (PrimitiveClass.asPrimaryType(defc) == PrimitiveClass.asPrimaryType(refc) ||
3935 Modifier.isPublic(refc.getModifiers())));
3936 if (!classOK && (allowedModes & PACKAGE) != 0) {
3937 // ignore previous lookup class to check if default package access
3938 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
3939 (PrimitiveClass.asPrimaryType(defc) == PrimitiveClass.asPrimaryType(refc) ||
3940 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
3941 }
3942 if (!classOK)
3943 return "class is not public";
3944 if (Modifier.isPublic(mods))
3945 return "access to public member failed"; // (how?, module not readable?)
3946 if (Modifier.isPrivate(mods))
3947 return "member is private";
3948 if (Modifier.isProtected(mods))
3949 return "member is protected";
3950 return "member is private to package";
3951 }
3952
3953 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
3954 int allowedModes = this.allowedModes;
3955 if (allowedModes == TRUSTED) return;
3956 if ((lookupModes() & PRIVATE) == 0
3957 || (specialCaller != lookupClass()
3958 // ensure non-abstract methods in superinterfaces can be special-invoked
3959 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
3960 throw new MemberName(specialCaller).
3961 makeAccessException("no private access for invokespecial", this);
3962 }
3963
3964 private boolean restrictProtectedReceiver(MemberName method) {
3965 // The accessing class only has the right to use a protected member
3966 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
3967 if (!method.isProtected() || method.isStatic()
3968 || allowedModes == TRUSTED
3969 || method.getDeclaringClass() == lookupClass()
3970 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
3971 return false;
3972 return true;
3973 }
3974 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
3975 assert(!method.isStatic());
3976 // receiver type of mh is too wide; narrow to caller
3977 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
3978 throw method.makeAccessException("caller class must be a subclass below the method", caller);
3979 }
3980 MethodType rawType = mh.type();
3981 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
3982 MethodType narrowType = rawType.changeParameterType(0, caller);
3983 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
3984 assert(mh.viewAsTypeChecks(narrowType, true));
3985 return mh.copyWith(narrowType, mh.form);
3986 }
3987
3988 /** Check access and get the requested method. */
3989 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3990 final boolean doRestrict = true;
3991 final boolean checkSecurity = true;
3992 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
3993 }
3994 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
3995 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3996 final boolean doRestrict = false;
3997 final boolean checkSecurity = true;
3998 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerLookup);
3999 }
4000 /** Check access and get the requested method, eliding security manager checks. */
4001 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4002 final boolean doRestrict = true;
4003 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4004 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4005 }
4006 /** Common code for all methods; do not call directly except from immediately above. */
4007 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
4008 boolean checkSecurity,
4009 boolean doRestrict,
4010 Lookup boundCaller) throws IllegalAccessException {
4011 checkMethod(refKind, refc, method);
4012 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4013 if (checkSecurity)
4014 checkSecurityManager(refc, method);
4015 assert(!method.isMethodHandleInvoke());
4016 if (refKind == REF_invokeSpecial &&
4017 refc != lookupClass() &&
4018 !refc.isInterface() &&
4019 refc != lookupClass().getSuperclass() &&
4020 refc.isAssignableFrom(lookupClass())) {
4021 assert(!method.getName().equals("<init>")); // not this code path
4022
4023 // Per JVMS 6.5, desc. of invokespecial instruction:
4024 // If the method is in a superclass of the LC,
4025 // and if our original search was above LC.super,
4026 // repeat the search (symbolic lookup) from LC.super
4027 // and continue with the direct superclass of that class,
4028 // and so forth, until a match is found or no further superclasses exist.
4029 // FIXME: MemberName.resolve should handle this instead.
4030 Class<?> refcAsSuper = lookupClass();
4031 MemberName m2;
4032 do {
4033 refcAsSuper = refcAsSuper.getSuperclass();
4034 m2 = new MemberName(refcAsSuper,
4035 method.getName(),
4036 method.getMethodType(),
4037 REF_invokeSpecial);
4038 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull(), allowedModes);
4039 } while (m2 == null && // no method is found yet
4040 refc != refcAsSuper); // search up to refc
4041 if (m2 == null) throw new InternalError(method.toString());
4042 method = m2;
4043 refc = refcAsSuper;
4044 // redo basic checks
4045 checkMethod(refKind, refc, method);
4046 }
4047 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
4048 MethodHandle mh = dmh;
4049 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
4050 if ((doRestrict && refKind == REF_invokeSpecial) ||
4051 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
4052 mh = restrictReceiver(method, dmh, lookupClass());
4053 }
4054 mh = maybeBindCaller(method, mh, boundCaller);
4055 mh = mh.setVarargs(method);
4056 return mh;
4057 }
4058 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller)
4059 throws IllegalAccessException {
4060 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
4061 return mh;
4062
4063 // boundCaller must have full privilege access.
4064 // It should have been checked by findBoundCallerLookup. Safe to check this again.
4065 if ((boundCaller.lookupModes() & ORIGINAL) == 0)
4066 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
4067
4068 assert boundCaller.hasFullPrivilegeAccess();
4069
4070 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass);
4071 // Note: caller will apply varargs after this step happens.
4072 return cbmh;
4073 }
4074
4075 /** Check access and get the requested field. */
4076 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4077 final boolean checkSecurity = true;
4078 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4079 }
4080 /** Check access and get the requested field, eliding security manager checks. */
4081 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4082 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4083 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4084 }
4085 /** Common code for all fields; do not call directly except from immediately above. */
4086 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
4087 boolean checkSecurity) throws IllegalAccessException {
4088 checkField(refKind, refc, field);
4089 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4090 if (checkSecurity)
4091 checkSecurityManager(refc, field);
4092 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
4093 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
4094 restrictProtectedReceiver(field));
4095 if (doRestrict)
4096 return restrictReceiver(field, dmh, lookupClass());
4097 return dmh;
4098 }
4099 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
4100 Class<?> refc, MemberName getField, MemberName putField)
4101 throws IllegalAccessException {
4102 final boolean checkSecurity = true;
4103 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4104 }
4105 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
4106 Class<?> refc, MemberName getField, MemberName putField)
4107 throws IllegalAccessException {
4108 final boolean checkSecurity = false;
4109 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4110 }
4111 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
4112 Class<?> refc, MemberName getField, MemberName putField,
4113 boolean checkSecurity) throws IllegalAccessException {
4114 assert getField.isStatic() == putField.isStatic();
4115 assert getField.isGetter() && putField.isSetter();
4116 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
4117 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
4118
4119 checkField(getRefKind, refc, getField);
4120 if (checkSecurity)
4121 checkSecurityManager(refc, getField);
4122
4123 if (!putField.isFinal()) {
4124 // A VarHandle does not support updates to final fields, any
4125 // such VarHandle to a final field will be read-only and
4126 // therefore the following write-based accessibility checks are
4127 // only required for non-final fields
4128 checkField(putRefKind, refc, putField);
4129 if (checkSecurity)
4130 checkSecurityManager(refc, putField);
4131 }
4132
4133 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
4134 restrictProtectedReceiver(getField));
4135 if (doRestrict) {
4136 assert !getField.isStatic();
4137 // receiver type of VarHandle is too wide; narrow to caller
4138 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
4139 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
4140 }
4141 refc = lookupClass();
4142 }
4143 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(),
4144 this.allowedModes == TRUSTED && !getField.isTrustedFinalField());
4145 }
4146 /** Check access and get the requested constructor. */
4147 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4148 final boolean checkSecurity = true;
4149 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4150 }
4151 /** Check access and get the requested constructor, eliding security manager checks. */
4152 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4153 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4154 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4155 }
4156 /** Common code for all constructors; do not call directly except from immediately above. */
4157 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
4158 boolean checkSecurity) throws IllegalAccessException {
4159 assert(ctor.isObjectConstructor());
4160 checkAccess(REF_newInvokeSpecial, refc, ctor);
4161 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4162 if (checkSecurity)
4163 checkSecurityManager(refc, ctor);
4164 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
4165 return DirectMethodHandle.make(ctor).setVarargs(ctor);
4166 }
4167
4168 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
4169 */
4170 /*non-public*/
4171 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
4172 throws ReflectiveOperationException {
4173 if (!(type instanceof Class || type instanceof MethodType))
4174 throw new InternalError("unresolved MemberName");
4175 MemberName member = new MemberName(refKind, defc, name, type);
4176 MethodHandle mh = LOOKASIDE_TABLE.get(member);
4177 if (mh != null) {
4178 checkSymbolicClass(defc);
4179 return mh;
4180 }
4181 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
4182 // Treat MethodHandle.invoke and invokeExact specially.
4183 mh = findVirtualForMH(member.getName(), member.getMethodType());
4184 if (mh != null) {
4185 return mh;
4186 }
4187 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
4188 // Treat signature-polymorphic methods on VarHandle specially.
4189 mh = findVirtualForVH(member.getName(), member.getMethodType());
4190 if (mh != null) {
4191 return mh;
4192 }
4193 }
4194 MemberName resolved = resolveOrFail(refKind, member);
4195 mh = getDirectMethodForConstant(refKind, defc, resolved);
4196 if (mh instanceof DirectMethodHandle
4197 && canBeCached(refKind, defc, resolved)) {
4198 MemberName key = mh.internalMemberName();
4199 if (key != null) {
4200 key = key.asNormalOriginal();
4201 }
4202 if (member.equals(key)) { // better safe than sorry
4203 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
4204 }
4205 }
4206 return mh;
4207 }
4208 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
4209 if (refKind == REF_invokeSpecial) {
4210 return false;
4211 }
4212 if (!Modifier.isPublic(defc.getModifiers()) ||
4213 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
4214 !member.isPublic() ||
4215 member.isCallerSensitive()) {
4216 return false;
4217 }
4218 ClassLoader loader = defc.getClassLoader();
4219 if (loader != null) {
4220 ClassLoader sysl = ClassLoader.getSystemClassLoader();
4221 boolean found = false;
4222 while (sysl != null) {
4223 if (loader == sysl) { found = true; break; }
4224 sysl = sysl.getParent();
4225 }
4226 if (!found) {
4227 return false;
4228 }
4229 }
4230 try {
4231 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
4232 new MemberName(refKind, defc, member.getName(), member.getType()));
4233 if (resolved2 == null) {
4234 return false;
4235 }
4236 checkSecurityManager(defc, resolved2);
4237 } catch (SecurityException ex) {
4238 return false;
4239 }
4240 return true;
4241 }
4242 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
4243 throws ReflectiveOperationException {
4244 if (MethodHandleNatives.refKindIsField(refKind)) {
4245 return getDirectFieldNoSecurityManager(refKind, defc, member);
4246 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
4247 return getDirectMethodNoSecurityManager(refKind, defc, member, findBoundCallerLookup(member));
4248 } else if (refKind == REF_newInvokeSpecial) {
4249 return getDirectConstructorNoSecurityManager(defc, member);
4250 }
4251 // oops
4252 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
4253 }
4254
4255 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
4256 }
4257
4258 /**
4259 * Produces a method handle constructing arrays of a desired type,
4260 * as if by the {@code anewarray} bytecode.
4261 * The return type of the method handle will be the array type.
4262 * The type of its sole argument will be {@code int}, which specifies the size of the array.
4263 *
4264 * <p> If the returned method handle is invoked with a negative
4265 * array size, a {@code NegativeArraySizeException} will be thrown.
4266 *
4267 * @param arrayClass an array type
4268 * @return a method handle which can create arrays of the given type
4269 * @throws NullPointerException if the argument is {@code null}
4270 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
4271 * @see java.lang.reflect.Array#newInstance(Class, int)
4272 * @jvms 6.5 {@code anewarray} Instruction
4273 * @since 9
4274 */
4275 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
4276 if (!arrayClass.isArray()) {
4277 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
4278 }
4279 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
4280 bindTo(arrayClass.getComponentType());
4281 return ani.asType(ani.type().changeReturnType(arrayClass));
4282 }
4283
4284 /**
4285 * Produces a method handle returning the length of an array,
4286 * as if by the {@code arraylength} bytecode.
4287 * The type of the method handle will have {@code int} as return type,
4288 * and its sole argument will be the array type.
4289 *
4290 * <p> If the returned method handle is invoked with a {@code null}
4291 * array reference, a {@code NullPointerException} will be thrown.
4292 *
4293 * @param arrayClass an array type
4294 * @return a method handle which can retrieve the length of an array of the given array type
4295 * @throws NullPointerException if the argument is {@code null}
4296 * @throws IllegalArgumentException if arrayClass is not an array type
4297 * @jvms 6.5 {@code arraylength} Instruction
4298 * @since 9
4299 */
4300 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
4301 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
4302 }
4303
4304 /**
4305 * Produces a method handle giving read access to elements of an array,
4306 * as if by the {@code aaload} bytecode.
4307 * The type of the method handle will have a return type of the array's
4308 * element type. Its first argument will be the array type,
4309 * and the second will be {@code int}.
4310 *
4311 * <p> When the returned method handle is invoked,
4312 * the array reference and array index are checked.
4313 * A {@code NullPointerException} will be thrown if the array reference
4314 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4315 * thrown if the index is negative or if it is greater than or equal to
4316 * the length of the array.
4317 *
4318 * @param arrayClass an array type
4319 * @return a method handle which can load values from the given array type
4320 * @throws NullPointerException if the argument is null
4321 * @throws IllegalArgumentException if arrayClass is not an array type
4322 * @jvms 6.5 {@code aaload} Instruction
4323 */
4324 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
4325 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
4326 }
4327
4328 /**
4329 * Produces a method handle giving write access to elements of an array,
4330 * as if by the {@code astore} bytecode.
4331 * The type of the method handle will have a void return type.
4332 * Its last argument will be the array's element type.
4333 * The first and second arguments will be the array type and int.
4334 *
4335 * <p> When the returned method handle is invoked,
4336 * the array reference and array index are checked.
4337 * A {@code NullPointerException} will be thrown if the array reference
4338 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4339 * thrown if the index is negative or if it is greater than or equal to
4340 * the length of the array.
4341 *
4342 * @param arrayClass the class of an array
4343 * @return a method handle which can store values into the array type
4344 * @throws NullPointerException if the argument is null
4345 * @throws IllegalArgumentException if arrayClass is not an array type
4346 * @jvms 6.5 {@code aastore} Instruction
4347 */
4348 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
4349 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
4350 }
4351
4352 /**
4353 * Produces a VarHandle giving access to elements of an array of type
4354 * {@code arrayClass}. The VarHandle's variable type is the component type
4355 * of {@code arrayClass} and the list of coordinate types is
4356 * {@code (arrayClass, int)}, where the {@code int} coordinate type
4357 * corresponds to an argument that is an index into an array.
4358 * <p>
4359 * Certain access modes of the returned VarHandle are unsupported under
4360 * the following conditions:
4361 * <ul>
4362 * <li>if the component type is anything other than {@code byte},
4363 * {@code short}, {@code char}, {@code int}, {@code long},
4364 * {@code float}, or {@code double} then numeric atomic update access
4365 * modes are unsupported.
4366 * <li>if the component type is anything other than {@code boolean},
4367 * {@code byte}, {@code short}, {@code char}, {@code int} or
4368 * {@code long} then bitwise atomic update access modes are
4369 * unsupported.
4370 * </ul>
4371 * <p>
4372 * If the component type is {@code float} or {@code double} then numeric
4373 * and atomic update access modes compare values using their bitwise
4374 * representation (see {@link Float#floatToRawIntBits} and
4375 * {@link Double#doubleToRawLongBits}, respectively).
4376 *
4377 * <p> When the returned {@code VarHandle} is invoked,
4378 * the array reference and array index are checked.
4379 * A {@code NullPointerException} will be thrown if the array reference
4380 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4381 * thrown if the index is negative or if it is greater than or equal to
4382 * the length of the array.
4383 *
4384 * @apiNote
4385 * Bitwise comparison of {@code float} values or {@code double} values,
4386 * as performed by the numeric and atomic update access modes, differ
4387 * from the primitive {@code ==} operator and the {@link Float#equals}
4388 * and {@link Double#equals} methods, specifically with respect to
4389 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
4390 * Care should be taken when performing a compare and set or a compare
4391 * and exchange operation with such values since the operation may
4392 * unexpectedly fail.
4393 * There are many possible NaN values that are considered to be
4394 * {@code NaN} in Java, although no IEEE 754 floating-point operation
4395 * provided by Java can distinguish between them. Operation failure can
4396 * occur if the expected or witness value is a NaN value and it is
4397 * transformed (perhaps in a platform specific manner) into another NaN
4398 * value, and thus has a different bitwise representation (see
4399 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
4400 * details).
4401 * The values {@code -0.0} and {@code +0.0} have different bitwise
4402 * representations but are considered equal when using the primitive
4403 * {@code ==} operator. Operation failure can occur if, for example, a
4404 * numeric algorithm computes an expected value to be say {@code -0.0}
4405 * and previously computed the witness value to be say {@code +0.0}.
4406 * @param arrayClass the class of an array, of type {@code T[]}
4407 * @return a VarHandle giving access to elements of an array
4408 * @throws NullPointerException if the arrayClass is null
4409 * @throws IllegalArgumentException if arrayClass is not an array type
4410 * @since 9
4411 */
4412 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
4413 return VarHandles.makeArrayElementHandle(arrayClass);
4414 }
4415
4416 /**
4417 * Produces a VarHandle giving access to elements of a {@code byte[]} array
4418 * viewed as if it were a different primitive array type, such as
4419 * {@code int[]} or {@code long[]}.
4420 * The VarHandle's variable type is the component type of
4421 * {@code viewArrayClass} and the list of coordinate types is
4422 * {@code (byte[], int)}, where the {@code int} coordinate type
4423 * corresponds to an argument that is an index into a {@code byte[]} array.
4424 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
4425 * array, composing bytes to or from a value of the component type of
4426 * {@code viewArrayClass} according to the given endianness.
4427 * <p>
4428 * The supported component types (variables types) are {@code short},
4429 * {@code char}, {@code int}, {@code long}, {@code float} and
4430 * {@code double}.
4431 * <p>
4432 * Access of bytes at a given index will result in an
4433 * {@code ArrayIndexOutOfBoundsException} if the index is less than {@code 0}
4434 * or greater than the {@code byte[]} array length minus the size (in bytes)
4435 * of {@code T}.
4436 * <p>
4437 * Access of bytes at an index may be aligned or misaligned for {@code T},
4438 * with respect to the underlying memory address, {@code A} say, associated
4439 * with the array and index.
4440 * If access is misaligned then access for anything other than the
4441 * {@code get} and {@code set} access modes will result in an
4442 * {@code IllegalStateException}. In such cases atomic access is only
4443 * guaranteed with respect to the largest power of two that divides the GCD
4444 * of {@code A} and the size (in bytes) of {@code T}.
4445 * If access is aligned then following access modes are supported and are
4446 * guaranteed to support atomic access:
4447 * <ul>
4448 * <li>read write access modes for all {@code T}, with the exception of
4449 * access modes {@code get} and {@code set} for {@code long} and
4450 * {@code double} on 32-bit platforms.
4451 * <li>atomic update access modes for {@code int}, {@code long},
4452 * {@code float} or {@code double}.
4453 * (Future major platform releases of the JDK may support additional
4454 * types for certain currently unsupported access modes.)
4455 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4456 * (Future major platform releases of the JDK may support additional
4457 * numeric types for certain currently unsupported access modes.)
4458 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4459 * (Future major platform releases of the JDK may support additional
4460 * numeric types for certain currently unsupported access modes.)
4461 * </ul>
4462 * <p>
4463 * Misaligned access, and therefore atomicity guarantees, may be determined
4464 * for {@code byte[]} arrays without operating on a specific array. Given
4465 * an {@code index}, {@code T} and its corresponding boxed type,
4466 * {@code T_BOX}, misalignment may be determined as follows:
4467 * <pre>{@code
4468 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4469 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
4470 * alignmentOffset(0, sizeOfT);
4471 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
4472 * boolean isMisaligned = misalignedAtIndex != 0;
4473 * }</pre>
4474 * <p>
4475 * If the variable type is {@code float} or {@code double} then atomic
4476 * update access modes compare values using their bitwise representation
4477 * (see {@link Float#floatToRawIntBits} and
4478 * {@link Double#doubleToRawLongBits}, respectively).
4479 * @param viewArrayClass the view array class, with a component type of
4480 * type {@code T}
4481 * @param byteOrder the endianness of the view array elements, as
4482 * stored in the underlying {@code byte} array
4483 * @return a VarHandle giving access to elements of a {@code byte[]} array
4484 * viewed as if elements corresponding to the components type of the view
4485 * array class
4486 * @throws NullPointerException if viewArrayClass or byteOrder is null
4487 * @throws IllegalArgumentException if viewArrayClass is not an array type
4488 * @throws UnsupportedOperationException if the component type of
4489 * viewArrayClass is not supported as a variable type
4490 * @since 9
4491 */
4492 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
4493 ByteOrder byteOrder) throws IllegalArgumentException {
4494 Objects.requireNonNull(byteOrder);
4495 return VarHandles.byteArrayViewHandle(viewArrayClass,
4496 byteOrder == ByteOrder.BIG_ENDIAN);
4497 }
4498
4499 /**
4500 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
4501 * viewed as if it were an array of elements of a different primitive
4502 * component type to that of {@code byte}, such as {@code int[]} or
4503 * {@code long[]}.
4504 * The VarHandle's variable type is the component type of
4505 * {@code viewArrayClass} and the list of coordinate types is
4506 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
4507 * corresponds to an argument that is an index into a {@code byte[]} array.
4508 * The returned VarHandle accesses bytes at an index in a
4509 * {@code ByteBuffer}, composing bytes to or from a value of the component
4510 * type of {@code viewArrayClass} according to the given endianness.
4511 * <p>
4512 * The supported component types (variables types) are {@code short},
4513 * {@code char}, {@code int}, {@code long}, {@code float} and
4514 * {@code double}.
4515 * <p>
4516 * Access will result in a {@code ReadOnlyBufferException} for anything
4517 * other than the read access modes if the {@code ByteBuffer} is read-only.
4518 * <p>
4519 * Access of bytes at a given index will result in an
4520 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
4521 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
4522 * {@code T}.
4523 * <p>
4524 * Access of bytes at an index may be aligned or misaligned for {@code T},
4525 * with respect to the underlying memory address, {@code A} say, associated
4526 * with the {@code ByteBuffer} and index.
4527 * If access is misaligned then access for anything other than the
4528 * {@code get} and {@code set} access modes will result in an
4529 * {@code IllegalStateException}. In such cases atomic access is only
4530 * guaranteed with respect to the largest power of two that divides the GCD
4531 * of {@code A} and the size (in bytes) of {@code T}.
4532 * If access is aligned then following access modes are supported and are
4533 * guaranteed to support atomic access:
4534 * <ul>
4535 * <li>read write access modes for all {@code T}, with the exception of
4536 * access modes {@code get} and {@code set} for {@code long} and
4537 * {@code double} on 32-bit platforms.
4538 * <li>atomic update access modes for {@code int}, {@code long},
4539 * {@code float} or {@code double}.
4540 * (Future major platform releases of the JDK may support additional
4541 * types for certain currently unsupported access modes.)
4542 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4543 * (Future major platform releases of the JDK may support additional
4544 * numeric types for certain currently unsupported access modes.)
4545 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4546 * (Future major platform releases of the JDK may support additional
4547 * numeric types for certain currently unsupported access modes.)
4548 * </ul>
4549 * <p>
4550 * Misaligned access, and therefore atomicity guarantees, may be determined
4551 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
4552 * {@code index}, {@code T} and its corresponding boxed type,
4553 * {@code T_BOX}, as follows:
4554 * <pre>{@code
4555 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4556 * ByteBuffer bb = ...
4557 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
4558 * boolean isMisaligned = misalignedAtIndex != 0;
4559 * }</pre>
4560 * <p>
4561 * If the variable type is {@code float} or {@code double} then atomic
4562 * update access modes compare values using their bitwise representation
4563 * (see {@link Float#floatToRawIntBits} and
4564 * {@link Double#doubleToRawLongBits}, respectively).
4565 * @param viewArrayClass the view array class, with a component type of
4566 * type {@code T}
4567 * @param byteOrder the endianness of the view array elements, as
4568 * stored in the underlying {@code ByteBuffer} (Note this overrides the
4569 * endianness of a {@code ByteBuffer})
4570 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
4571 * viewed as if elements corresponding to the components type of the view
4572 * array class
4573 * @throws NullPointerException if viewArrayClass or byteOrder is null
4574 * @throws IllegalArgumentException if viewArrayClass is not an array type
4575 * @throws UnsupportedOperationException if the component type of
4576 * viewArrayClass is not supported as a variable type
4577 * @since 9
4578 */
4579 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
4580 ByteOrder byteOrder) throws IllegalArgumentException {
4581 Objects.requireNonNull(byteOrder);
4582 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
4583 byteOrder == ByteOrder.BIG_ENDIAN);
4584 }
4585
4586
4587 /// method handle invocation (reflective style)
4588
4589 /**
4590 * Produces a method handle which will invoke any method handle of the
4591 * given {@code type}, with a given number of trailing arguments replaced by
4592 * a single trailing {@code Object[]} array.
4593 * The resulting invoker will be a method handle with the following
4594 * arguments:
4595 * <ul>
4596 * <li>a single {@code MethodHandle} target
4597 * <li>zero or more leading values (counted by {@code leadingArgCount})
4598 * <li>an {@code Object[]} array containing trailing arguments
4599 * </ul>
4600 * <p>
4601 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
4602 * the indicated {@code type}.
4603 * That is, if the target is exactly of the given {@code type}, it will behave
4604 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
4605 * is used to convert the target to the required {@code type}.
4606 * <p>
4607 * The type of the returned invoker will not be the given {@code type}, but rather
4608 * will have all parameters except the first {@code leadingArgCount}
4609 * replaced by a single array of type {@code Object[]}, which will be
4610 * the final parameter.
4611 * <p>
4612 * Before invoking its target, the invoker will spread the final array, apply
4613 * reference casts as necessary, and unbox and widen primitive arguments.
4614 * If, when the invoker is called, the supplied array argument does
4615 * not have the correct number of elements, the invoker will throw
4616 * an {@link IllegalArgumentException} instead of invoking the target.
4617 * <p>
4618 * This method is equivalent to the following code (though it may be more efficient):
4619 * {@snippet lang="java" :
4620 MethodHandle invoker = MethodHandles.invoker(type);
4621 int spreadArgCount = type.parameterCount() - leadingArgCount;
4622 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
4623 return invoker;
4624 * }
4625 * This method throws no reflective or security exceptions.
4626 * @param type the desired target type
4627 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
4628 * @return a method handle suitable for invoking any method handle of the given type
4629 * @throws NullPointerException if {@code type} is null
4630 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
4631 * the range from 0 to {@code type.parameterCount()} inclusive,
4632 * or if the resulting method handle's type would have
4633 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4634 */
4635 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
4636 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
4637 throw newIllegalArgumentException("bad argument count", leadingArgCount);
4638 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
4639 return type.invokers().spreadInvoker(leadingArgCount);
4640 }
4641
4642 /**
4643 * Produces a special <em>invoker method handle</em> which can be used to
4644 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
4645 * The resulting invoker will have a type which is
4646 * exactly equal to the desired type, except that it will accept
4647 * an additional leading argument of type {@code MethodHandle}.
4648 * <p>
4649 * This method is equivalent to the following code (though it may be more efficient):
4650 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
4651 *
4652 * <p style="font-size:smaller;">
4653 * <em>Discussion:</em>
4654 * Invoker method handles can be useful when working with variable method handles
4655 * of unknown types.
4656 * For example, to emulate an {@code invokeExact} call to a variable method
4657 * handle {@code M}, extract its type {@code T},
4658 * look up the invoker method {@code X} for {@code T},
4659 * and call the invoker method, as {@code X.invoke(T, A...)}.
4660 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
4661 * is unknown.)
4662 * If spreading, collecting, or other argument transformations are required,
4663 * they can be applied once to the invoker {@code X} and reused on many {@code M}
4664 * method handle values, as long as they are compatible with the type of {@code X}.
4665 * <p style="font-size:smaller;">
4666 * <em>(Note: The invoker method is not available via the Core Reflection API.
4667 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4668 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4669 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4670 * <p>
4671 * This method throws no reflective or security exceptions.
4672 * @param type the desired target type
4673 * @return a method handle suitable for invoking any method handle of the given type
4674 * @throws IllegalArgumentException if the resulting method handle's type would have
4675 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4676 */
4677 public static MethodHandle exactInvoker(MethodType type) {
4678 return type.invokers().exactInvoker();
4679 }
4680
4681 /**
4682 * Produces a special <em>invoker method handle</em> which can be used to
4683 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
4684 * The resulting invoker will have a type which is
4685 * exactly equal to the desired type, except that it will accept
4686 * an additional leading argument of type {@code MethodHandle}.
4687 * <p>
4688 * Before invoking its target, if the target differs from the expected type,
4689 * the invoker will apply reference casts as
4690 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
4691 * Similarly, the return value will be converted as necessary.
4692 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
4693 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
4694 * <p>
4695 * This method is equivalent to the following code (though it may be more efficient):
4696 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
4697 * <p style="font-size:smaller;">
4698 * <em>Discussion:</em>
4699 * A {@linkplain MethodType#genericMethodType general method type} is one which
4700 * mentions only {@code Object} arguments and return values.
4701 * An invoker for such a type is capable of calling any method handle
4702 * of the same arity as the general type.
4703 * <p style="font-size:smaller;">
4704 * <em>(Note: The invoker method is not available via the Core Reflection API.
4705 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4706 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4707 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4708 * <p>
4709 * This method throws no reflective or security exceptions.
4710 * @param type the desired target type
4711 * @return a method handle suitable for invoking any method handle convertible to the given type
4712 * @throws IllegalArgumentException if the resulting method handle's type would have
4713 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4714 */
4715 public static MethodHandle invoker(MethodType type) {
4716 return type.invokers().genericInvoker();
4717 }
4718
4719 /**
4720 * Produces a special <em>invoker method handle</em> which can be used to
4721 * invoke a signature-polymorphic access mode method on any VarHandle whose
4722 * associated access mode type is compatible with the given type.
4723 * The resulting invoker will have a type which is exactly equal to the
4724 * desired given type, except that it will accept an additional leading
4725 * argument of type {@code VarHandle}.
4726 *
4727 * @param accessMode the VarHandle access mode
4728 * @param type the desired target type
4729 * @return a method handle suitable for invoking an access mode method of
4730 * any VarHandle whose access mode type is of the given type.
4731 * @since 9
4732 */
4733 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4734 return type.invokers().varHandleMethodExactInvoker(accessMode);
4735 }
4736
4737 /**
4738 * Produces a special <em>invoker method handle</em> which can be used to
4739 * invoke a signature-polymorphic access mode method on any VarHandle whose
4740 * associated access mode type is compatible with the given type.
4741 * The resulting invoker will have a type which is exactly equal to the
4742 * desired given type, except that it will accept an additional leading
4743 * argument of type {@code VarHandle}.
4744 * <p>
4745 * Before invoking its target, if the access mode type differs from the
4746 * desired given type, the invoker will apply reference casts as necessary
4747 * and box, unbox, or widen primitive values, as if by
4748 * {@link MethodHandle#asType asType}. Similarly, the return value will be
4749 * converted as necessary.
4750 * <p>
4751 * This method is equivalent to the following code (though it may be more
4752 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
4753 *
4754 * @param accessMode the VarHandle access mode
4755 * @param type the desired target type
4756 * @return a method handle suitable for invoking an access mode method of
4757 * any VarHandle whose access mode type is convertible to the given
4758 * type.
4759 * @since 9
4760 */
4761 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4762 return type.invokers().varHandleMethodInvoker(accessMode);
4763 }
4764
4765 /*non-public*/
4766 static MethodHandle basicInvoker(MethodType type) {
4767 return type.invokers().basicInvoker();
4768 }
4769
4770 /// method handle modification (creation from other method handles)
4771
4772 /**
4773 * Produces a method handle which adapts the type of the
4774 * given method handle to a new type by pairwise argument and return type conversion.
4775 * The original type and new type must have the same number of arguments.
4776 * The resulting method handle is guaranteed to report a type
4777 * which is equal to the desired new type.
4778 * <p>
4779 * If the original type and new type are equal, returns target.
4780 * <p>
4781 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
4782 * and some additional conversions are also applied if those conversions fail.
4783 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
4784 * if possible, before or instead of any conversions done by {@code asType}:
4785 * <ul>
4786 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
4787 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
4788 * (This treatment of interfaces follows the usage of the bytecode verifier.)
4789 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
4790 * the boolean is converted to a byte value, 1 for true, 0 for false.
4791 * (This treatment follows the usage of the bytecode verifier.)
4792 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
4793 * <em>T0</em> is converted to byte via Java casting conversion (JLS {@jls 5.5}),
4794 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
4795 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
4796 * then a Java casting conversion (JLS {@jls 5.5}) is applied.
4797 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
4798 * widening and/or narrowing.)
4799 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
4800 * conversion will be applied at runtime, possibly followed
4801 * by a Java casting conversion (JLS {@jls 5.5}) on the primitive value,
4802 * possibly followed by a conversion from byte to boolean by testing
4803 * the low-order bit.
4804 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
4805 * and if the reference is null at runtime, a zero value is introduced.
4806 * </ul>
4807 * @param target the method handle to invoke after arguments are retyped
4808 * @param newType the expected type of the new method handle
4809 * @return a method handle which delegates to the target after performing
4810 * any necessary argument conversions, and arranges for any
4811 * necessary return value conversions
4812 * @throws NullPointerException if either argument is null
4813 * @throws WrongMethodTypeException if the conversion cannot be made
4814 * @see MethodHandle#asType
4815 */
4816 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
4817 explicitCastArgumentsChecks(target, newType);
4818 // use the asTypeCache when possible:
4819 MethodType oldType = target.type();
4820 if (oldType == newType) return target;
4821 if (oldType.explicitCastEquivalentToAsType(newType)) {
4822 return target.asFixedArity().asType(newType);
4823 }
4824 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
4825 }
4826
4827 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
4828 if (target.type().parameterCount() != newType.parameterCount()) {
4829 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
4830 }
4831 }
4832
4833 /**
4834 * Produces a method handle which adapts the calling sequence of the
4835 * given method handle to a new type, by reordering the arguments.
4836 * The resulting method handle is guaranteed to report a type
4837 * which is equal to the desired new type.
4838 * <p>
4839 * The given array controls the reordering.
4840 * Call {@code #I} the number of incoming parameters (the value
4841 * {@code newType.parameterCount()}, and call {@code #O} the number
4842 * of outgoing parameters (the value {@code target.type().parameterCount()}).
4843 * Then the length of the reordering array must be {@code #O},
4844 * and each element must be a non-negative number less than {@code #I}.
4845 * For every {@code N} less than {@code #O}, the {@code N}-th
4846 * outgoing argument will be taken from the {@code I}-th incoming
4847 * argument, where {@code I} is {@code reorder[N]}.
4848 * <p>
4849 * No argument or return value conversions are applied.
4850 * The type of each incoming argument, as determined by {@code newType},
4851 * must be identical to the type of the corresponding outgoing parameter
4852 * or parameters in the target method handle.
4853 * The return type of {@code newType} must be identical to the return
4854 * type of the original target.
4855 * <p>
4856 * The reordering array need not specify an actual permutation.
4857 * An incoming argument will be duplicated if its index appears
4858 * more than once in the array, and an incoming argument will be dropped
4859 * if its index does not appear in the array.
4860 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
4861 * incoming arguments which are not mentioned in the reordering array
4862 * may be of any type, as determined only by {@code newType}.
4863 * {@snippet lang="java" :
4864 import static java.lang.invoke.MethodHandles.*;
4865 import static java.lang.invoke.MethodType.*;
4866 ...
4867 MethodType intfn1 = methodType(int.class, int.class);
4868 MethodType intfn2 = methodType(int.class, int.class, int.class);
4869 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
4870 assert(sub.type().equals(intfn2));
4871 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
4872 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
4873 assert((int)rsub.invokeExact(1, 100) == 99);
4874 MethodHandle add = ... (int x, int y) -> (x+y) ...;
4875 assert(add.type().equals(intfn2));
4876 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
4877 assert(twice.type().equals(intfn1));
4878 assert((int)twice.invokeExact(21) == 42);
4879 * }
4880 * <p>
4881 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4882 * variable-arity method handle}, even if the original target method handle was.
4883 * @param target the method handle to invoke after arguments are reordered
4884 * @param newType the expected type of the new method handle
4885 * @param reorder an index array which controls the reordering
4886 * @return a method handle which delegates to the target after it
4887 * drops unused arguments and moves and/or duplicates the other arguments
4888 * @throws NullPointerException if any argument is null
4889 * @throws IllegalArgumentException if the index array length is not equal to
4890 * the arity of the target, or if any index array element
4891 * not a valid index for a parameter of {@code newType},
4892 * or if two corresponding parameter types in
4893 * {@code target.type()} and {@code newType} are not identical,
4894 */
4895 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
4896 reorder = reorder.clone(); // get a private copy
4897 MethodType oldType = target.type();
4898 permuteArgumentChecks(reorder, newType, oldType);
4899 // first detect dropped arguments and handle them separately
4900 int[] originalReorder = reorder;
4901 BoundMethodHandle result = target.rebind();
4902 LambdaForm form = result.form;
4903 int newArity = newType.parameterCount();
4904 // Normalize the reordering into a real permutation,
4905 // by removing duplicates and adding dropped elements.
4906 // This somewhat improves lambda form caching, as well
4907 // as simplifying the transform by breaking it up into steps.
4908 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
4909 if (ddIdx > 0) {
4910 // We found a duplicated entry at reorder[ddIdx].
4911 // Example: (x,y,z)->asList(x,y,z)
4912 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
4913 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
4914 // The starred element corresponds to the argument
4915 // deleted by the dupArgumentForm transform.
4916 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
4917 boolean killFirst = false;
4918 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
4919 // Set killFirst if the dup is larger than an intervening position.
4920 // This will remove at least one inversion from the permutation.
4921 if (dupVal > val) killFirst = true;
4922 }
4923 if (!killFirst) {
4924 srcPos = dstPos;
4925 dstPos = ddIdx;
4926 }
4927 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
4928 assert (reorder[srcPos] == reorder[dstPos]);
4929 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
4930 // contract the reordering by removing the element at dstPos
4931 int tailPos = dstPos + 1;
4932 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
4933 reorder = Arrays.copyOf(reorder, reorder.length - 1);
4934 } else {
4935 int dropVal = ~ddIdx, insPos = 0;
4936 while (insPos < reorder.length && reorder[insPos] < dropVal) {
4937 // Find first element of reorder larger than dropVal.
4938 // This is where we will insert the dropVal.
4939 insPos += 1;
4940 }
4941 Class<?> ptype = newType.parameterType(dropVal);
4942 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
4943 oldType = oldType.insertParameterTypes(insPos, ptype);
4944 // expand the reordering by inserting an element at insPos
4945 int tailPos = insPos + 1;
4946 reorder = Arrays.copyOf(reorder, reorder.length + 1);
4947 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
4948 reorder[insPos] = dropVal;
4949 }
4950 assert (permuteArgumentChecks(reorder, newType, oldType));
4951 }
4952 assert (reorder.length == newArity); // a perfect permutation
4953 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
4954 form = form.editor().permuteArgumentsForm(1, reorder);
4955 if (newType == result.type() && form == result.internalForm())
4956 return result;
4957 return result.copyWith(newType, form);
4958 }
4959
4960 /**
4961 * Return an indication of any duplicate or omission in reorder.
4962 * If the reorder contains a duplicate entry, return the index of the second occurrence.
4963 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
4964 * Otherwise, return zero.
4965 * If an element not in [0..newArity-1] is encountered, return reorder.length.
4966 */
4967 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
4968 final int BIT_LIMIT = 63; // max number of bits in bit mask
4969 if (newArity < BIT_LIMIT) {
4970 long mask = 0;
4971 for (int i = 0; i < reorder.length; i++) {
4972 int arg = reorder[i];
4973 if (arg >= newArity) {
4974 return reorder.length;
4975 }
4976 long bit = 1L << arg;
4977 if ((mask & bit) != 0) {
4978 return i; // >0 indicates a dup
4979 }
4980 mask |= bit;
4981 }
4982 if (mask == (1L << newArity) - 1) {
4983 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
4984 return 0;
4985 }
4986 // find first zero
4987 long zeroBit = Long.lowestOneBit(~mask);
4988 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
4989 assert(zeroPos <= newArity);
4990 if (zeroPos == newArity) {
4991 return 0;
4992 }
4993 return ~zeroPos;
4994 } else {
4995 // same algorithm, different bit set
4996 BitSet mask = new BitSet(newArity);
4997 for (int i = 0; i < reorder.length; i++) {
4998 int arg = reorder[i];
4999 if (arg >= newArity) {
5000 return reorder.length;
5001 }
5002 if (mask.get(arg)) {
5003 return i; // >0 indicates a dup
5004 }
5005 mask.set(arg);
5006 }
5007 int zeroPos = mask.nextClearBit(0);
5008 assert(zeroPos <= newArity);
5009 if (zeroPos == newArity) {
5010 return 0;
5011 }
5012 return ~zeroPos;
5013 }
5014 }
5015
5016 static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
5017 if (newType.returnType() != oldType.returnType())
5018 throw newIllegalArgumentException("return types do not match",
5019 oldType, newType);
5020 if (reorder.length != oldType.parameterCount())
5021 throw newIllegalArgumentException("old type parameter count and reorder array length do not match",
5022 oldType, Arrays.toString(reorder));
5023
5024 int limit = newType.parameterCount();
5025 for (int j = 0; j < reorder.length; j++) {
5026 int i = reorder[j];
5027 if (i < 0 || i >= limit) {
5028 throw newIllegalArgumentException("index is out of bounds for new type",
5029 i, newType);
5030 }
5031 Class<?> src = newType.parameterType(i);
5032 Class<?> dst = oldType.parameterType(j);
5033 if (src != dst)
5034 throw newIllegalArgumentException("parameter types do not match after reorder",
5035 oldType, newType);
5036 }
5037 return true;
5038 }
5039
5040 /**
5041 * Produces a method handle of the requested return type which returns the given
5042 * constant value every time it is invoked.
5043 * <p>
5044 * Before the method handle is returned, the passed-in value is converted to the requested type.
5045 * If the requested type is primitive, widening primitive conversions are attempted,
5046 * else reference conversions are attempted.
5047 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
5048 * @param type the return type of the desired method handle
5049 * @param value the value to return
5050 * @return a method handle of the given return type and no arguments, which always returns the given value
5051 * @throws NullPointerException if the {@code type} argument is null
5052 * @throws ClassCastException if the value cannot be converted to the required return type
5053 * @throws IllegalArgumentException if the given type is {@code void.class}
5054 */
5055 public static MethodHandle constant(Class<?> type, Object value) {
5056 if (type.isPrimitive()) {
5057 if (type == void.class)
5058 throw newIllegalArgumentException("void type");
5059 Wrapper w = Wrapper.forPrimitiveType(type);
5060 value = w.convert(value, type);
5061 if (w.zero().equals(value))
5062 return zero(w, type);
5063 return insertArguments(identity(type), 0, value);
5064 } else {
5065 if (!PrimitiveClass.isPrimitiveValueType(type) && value == null)
5066 return zero(Wrapper.OBJECT, type);
5067 return identity(type).bindTo(value);
5068 }
5069 }
5070
5071 /**
5072 * Produces a method handle which returns its sole argument when invoked.
5073 * @param type the type of the sole parameter and return value of the desired method handle
5074 * @return a unary method handle which accepts and returns the given type
5075 * @throws NullPointerException if the argument is null
5076 * @throws IllegalArgumentException if the given type is {@code void.class}
5077 */
5078 public static MethodHandle identity(Class<?> type) {
5079 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
5080 int pos = btw.ordinal();
5081 MethodHandle ident = IDENTITY_MHS[pos];
5082 if (ident == null) {
5083 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
5084 }
5085 if (ident.type().returnType() == type)
5086 return ident;
5087 // something like identity(Foo.class); do not bother to intern these
5088 assert (btw == Wrapper.OBJECT);
5089 return makeIdentity(type);
5090 }
5091
5092 /**
5093 * Produces a constant method handle of the requested return type which
5094 * returns the default value for that type every time it is invoked.
5095 * The resulting constant method handle will have no side effects.
5096 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
5097 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
5098 * since {@code explicitCastArguments} converts {@code null} to default values.
5099 * @param type the expected return type of the desired method handle
5100 * @return a constant method handle that takes no arguments
5101 * and returns the default value of the given type (or void, if the type is void)
5102 * @throws NullPointerException if the argument is null
5103 * @see MethodHandles#constant
5104 * @see MethodHandles#empty
5105 * @see MethodHandles#explicitCastArguments
5106 * @since 9
5107 */
5108 public static MethodHandle zero(Class<?> type) {
5109 Objects.requireNonNull(type);
5110 if (type.isPrimitive()) {
5111 return zero(Wrapper.forPrimitiveType(type), type);
5112 } else if (PrimitiveClass.isPrimitiveValueType(type)) {
5113 // singleton default value
5114 Object value = UNSAFE.uninitializedDefaultValue(type);
5115 return identity(type).bindTo(value);
5116 } else {
5117 return zero(Wrapper.OBJECT, type);
5118 }
5119 }
5120
5121 private static MethodHandle identityOrVoid(Class<?> type) {
5122 return type == void.class ? zero(type) : identity(type);
5123 }
5124
5125 /**
5126 * Produces a method handle of the requested type which ignores any arguments, does nothing,
5127 * and returns a suitable default depending on the return type.
5128 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
5129 * <p>The returned method handle is equivalent to
5130 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
5131 *
5132 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
5133 * {@code guardWithTest(pred, target, empty(target.type())}.
5134 * @param type the type of the desired method handle
5135 * @return a constant method handle of the given type, which returns a default value of the given return type
5136 * @throws NullPointerException if the argument is null
5137 * @see MethodHandles#zero
5138 * @see MethodHandles#constant
5139 * @since 9
5140 */
5141 public static MethodHandle empty(MethodType type) {
5142 Objects.requireNonNull(type);
5143 return dropArgumentsTrusted(zero(type.returnType()), 0, type.ptypes());
5144 }
5145
5146 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
5147 private static MethodHandle makeIdentity(Class<?> ptype) {
5148 MethodType mtype = MethodType.methodType(ptype, ptype);
5149 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
5150 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
5151 }
5152
5153 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
5154 int pos = btw.ordinal();
5155 MethodHandle zero = ZERO_MHS[pos];
5156 if (zero == null) {
5157 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
5158 }
5159 if (zero.type().returnType() == rtype)
5160 return zero;
5161 assert(btw == Wrapper.OBJECT);
5162 return makeZero(rtype);
5163 }
5164 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
5165 private static MethodHandle makeZero(Class<?> rtype) {
5166 MethodType mtype = methodType(rtype);
5167 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
5168 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
5169 }
5170
5171 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
5172 // Simulate a CAS, to avoid racy duplication of results.
5173 MethodHandle prev = cache[pos];
5174 if (prev != null) return prev;
5175 return cache[pos] = value;
5176 }
5177
5178 /**
5179 * Provides a target method handle with one or more <em>bound arguments</em>
5180 * in advance of the method handle's invocation.
5181 * The formal parameters to the target corresponding to the bound
5182 * arguments are called <em>bound parameters</em>.
5183 * Returns a new method handle which saves away the bound arguments.
5184 * When it is invoked, it receives arguments for any non-bound parameters,
5185 * binds the saved arguments to their corresponding parameters,
5186 * and calls the original target.
5187 * <p>
5188 * The type of the new method handle will drop the types for the bound
5189 * parameters from the original target type, since the new method handle
5190 * will no longer require those arguments to be supplied by its callers.
5191 * <p>
5192 * Each given argument object must match the corresponding bound parameter type.
5193 * If a bound parameter type is a primitive, the argument object
5194 * must be a wrapper, and will be unboxed to produce the primitive value.
5195 * <p>
5196 * The {@code pos} argument selects which parameters are to be bound.
5197 * It may range between zero and <i>N-L</i> (inclusively),
5198 * where <i>N</i> is the arity of the target method handle
5199 * and <i>L</i> is the length of the values array.
5200 * <p>
5201 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5202 * variable-arity method handle}, even if the original target method handle was.
5203 * @param target the method handle to invoke after the argument is inserted
5204 * @param pos where to insert the argument (zero for the first)
5205 * @param values the series of arguments to insert
5206 * @return a method handle which inserts an additional argument,
5207 * before calling the original method handle
5208 * @throws NullPointerException if the target or the {@code values} array is null
5209 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than
5210 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
5211 * is the length of the values array.
5212 * @throws ClassCastException if an argument does not match the corresponding bound parameter
5213 * type.
5214 * @see MethodHandle#bindTo
5215 */
5216 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
5217 int insCount = values.length;
5218 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
5219 if (insCount == 0) return target;
5220 BoundMethodHandle result = target.rebind();
5221 for (int i = 0; i < insCount; i++) {
5222 Object value = values[i];
5223 Class<?> ptype = ptypes[pos+i];
5224 if (ptype.isPrimitive()) {
5225 result = insertArgumentPrimitive(result, pos, ptype, value);
5226 } else {
5227 value = ptype.cast(value); // throw CCE if needed
5228 result = result.bindArgumentL(pos, value);
5229 }
5230 }
5231 return result;
5232 }
5233
5234 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
5235 Class<?> ptype, Object value) {
5236 Wrapper w = Wrapper.forPrimitiveType(ptype);
5237 // perform unboxing and/or primitive conversion
5238 value = w.convert(value, ptype);
5239 return switch (w) {
5240 case INT -> result.bindArgumentI(pos, (int) value);
5241 case LONG -> result.bindArgumentJ(pos, (long) value);
5242 case FLOAT -> result.bindArgumentF(pos, (float) value);
5243 case DOUBLE -> result.bindArgumentD(pos, (double) value);
5244 default -> result.bindArgumentI(pos, ValueConversions.widenSubword(value));
5245 };
5246 }
5247
5248 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
5249 MethodType oldType = target.type();
5250 int outargs = oldType.parameterCount();
5251 int inargs = outargs - insCount;
5252 if (inargs < 0)
5253 throw newIllegalArgumentException("too many values to insert");
5254 if (pos < 0 || pos > inargs)
5255 throw newIllegalArgumentException("no argument type to append");
5256 return oldType.ptypes();
5257 }
5258
5259 /**
5260 * Produces a method handle which will discard some dummy arguments
5261 * before calling some other specified <i>target</i> method handle.
5262 * The type of the new method handle will be the same as the target's type,
5263 * except it will also include the dummy argument types,
5264 * at some given position.
5265 * <p>
5266 * The {@code pos} argument may range between zero and <i>N</i>,
5267 * where <i>N</i> is the arity of the target.
5268 * If {@code pos} is zero, the dummy arguments will precede
5269 * the target's real arguments; if {@code pos} is <i>N</i>
5270 * they will come after.
5271 * <p>
5272 * <b>Example:</b>
5273 * {@snippet lang="java" :
5274 import static java.lang.invoke.MethodHandles.*;
5275 import static java.lang.invoke.MethodType.*;
5276 ...
5277 MethodHandle cat = lookup().findVirtual(String.class,
5278 "concat", methodType(String.class, String.class));
5279 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5280 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
5281 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
5282 assertEquals(bigType, d0.type());
5283 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
5284 * }
5285 * <p>
5286 * This method is also equivalent to the following code:
5287 * <blockquote><pre>
5288 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
5289 * </pre></blockquote>
5290 * @param target the method handle to invoke after the arguments are dropped
5291 * @param pos position of first argument to drop (zero for the leftmost)
5292 * @param valueTypes the type(s) of the argument(s) to drop
5293 * @return a method handle which drops arguments of the given types,
5294 * before calling the original method handle
5295 * @throws NullPointerException if the target is null,
5296 * or if the {@code valueTypes} list or any of its elements is null
5297 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5298 * or if {@code pos} is negative or greater than the arity of the target,
5299 * or if the new method handle's type would have too many parameters
5300 */
5301 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
5302 return dropArgumentsTrusted(target, pos, valueTypes.toArray(new Class<?>[0]).clone());
5303 }
5304
5305 static MethodHandle dropArgumentsTrusted(MethodHandle target, int pos, Class<?>[] valueTypes) {
5306 MethodType oldType = target.type(); // get NPE
5307 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
5308 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
5309 if (dropped == 0) return target;
5310 BoundMethodHandle result = target.rebind();
5311 LambdaForm lform = result.form;
5312 int insertFormArg = 1 + pos;
5313 for (Class<?> ptype : valueTypes) {
5314 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
5315 }
5316 result = result.copyWith(newType, lform);
5317 return result;
5318 }
5319
5320 private static int dropArgumentChecks(MethodType oldType, int pos, Class<?>[] valueTypes) {
5321 int dropped = valueTypes.length;
5322 MethodType.checkSlotCount(dropped);
5323 int outargs = oldType.parameterCount();
5324 int inargs = outargs + dropped;
5325 if (pos < 0 || pos > outargs)
5326 throw newIllegalArgumentException("no argument type to remove"
5327 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
5328 );
5329 return dropped;
5330 }
5331
5332 /**
5333 * Produces a method handle which will discard some dummy arguments
5334 * before calling some other specified <i>target</i> method handle.
5335 * The type of the new method handle will be the same as the target's type,
5336 * except it will also include the dummy argument types,
5337 * at some given position.
5338 * <p>
5339 * The {@code pos} argument may range between zero and <i>N</i>,
5340 * where <i>N</i> is the arity of the target.
5341 * If {@code pos} is zero, the dummy arguments will precede
5342 * the target's real arguments; if {@code pos} is <i>N</i>
5343 * they will come after.
5344 * @apiNote
5345 * {@snippet lang="java" :
5346 import static java.lang.invoke.MethodHandles.*;
5347 import static java.lang.invoke.MethodType.*;
5348 ...
5349 MethodHandle cat = lookup().findVirtual(String.class,
5350 "concat", methodType(String.class, String.class));
5351 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5352 MethodHandle d0 = dropArguments(cat, 0, String.class);
5353 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
5354 MethodHandle d1 = dropArguments(cat, 1, String.class);
5355 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
5356 MethodHandle d2 = dropArguments(cat, 2, String.class);
5357 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
5358 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
5359 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
5360 * }
5361 * <p>
5362 * This method is also equivalent to the following code:
5363 * <blockquote><pre>
5364 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
5365 * </pre></blockquote>
5366 * @param target the method handle to invoke after the arguments are dropped
5367 * @param pos position of first argument to drop (zero for the leftmost)
5368 * @param valueTypes the type(s) of the argument(s) to drop
5369 * @return a method handle which drops arguments of the given types,
5370 * before calling the original method handle
5371 * @throws NullPointerException if the target is null,
5372 * or if the {@code valueTypes} array or any of its elements is null
5373 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5374 * or if {@code pos} is negative or greater than the arity of the target,
5375 * or if the new method handle's type would have
5376 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5377 */
5378 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
5379 return dropArgumentsTrusted(target, pos, valueTypes.clone());
5380 }
5381
5382 /* Convenience overloads for trusting internal low-arity call-sites */
5383 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1) {
5384 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1 });
5385 }
5386 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1, Class<?> valueType2) {
5387 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1, valueType2 });
5388 }
5389
5390 // private version which allows caller some freedom with error handling
5391 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, Class<?>[] newTypes, int pos,
5392 boolean nullOnFailure) {
5393 Class<?>[] oldTypes = target.type().ptypes();
5394 int match = oldTypes.length;
5395 if (skip != 0) {
5396 if (skip < 0 || skip > match) {
5397 throw newIllegalArgumentException("illegal skip", skip, target);
5398 }
5399 oldTypes = Arrays.copyOfRange(oldTypes, skip, match);
5400 match -= skip;
5401 }
5402 Class<?>[] addTypes = newTypes;
5403 int add = addTypes.length;
5404 if (pos != 0) {
5405 if (pos < 0 || pos > add) {
5406 throw newIllegalArgumentException("illegal pos", pos, Arrays.toString(newTypes));
5407 }
5408 addTypes = Arrays.copyOfRange(addTypes, pos, add);
5409 add -= pos;
5410 assert(addTypes.length == add);
5411 }
5412 // Do not add types which already match the existing arguments.
5413 if (match > add || !Arrays.equals(oldTypes, 0, oldTypes.length, addTypes, 0, match)) {
5414 if (nullOnFailure) {
5415 return null;
5416 }
5417 throw newIllegalArgumentException("argument lists do not match",
5418 Arrays.toString(oldTypes), Arrays.toString(newTypes));
5419 }
5420 addTypes = Arrays.copyOfRange(addTypes, match, add);
5421 add -= match;
5422 assert(addTypes.length == add);
5423 // newTypes: ( P*[pos], M*[match], A*[add] )
5424 // target: ( S*[skip], M*[match] )
5425 MethodHandle adapter = target;
5426 if (add > 0) {
5427 adapter = dropArgumentsTrusted(adapter, skip+ match, addTypes);
5428 }
5429 // adapter: (S*[skip], M*[match], A*[add] )
5430 if (pos > 0) {
5431 adapter = dropArgumentsTrusted(adapter, skip, Arrays.copyOfRange(newTypes, 0, pos));
5432 }
5433 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
5434 return adapter;
5435 }
5436
5437 /**
5438 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
5439 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
5440 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
5441 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
5442 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
5443 * {@link #dropArguments(MethodHandle, int, Class[])}.
5444 * <p>
5445 * The resulting handle will have the same return type as the target handle.
5446 * <p>
5447 * In more formal terms, assume these two type lists:<ul>
5448 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
5449 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
5450 * {@code newTypes}.
5451 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
5452 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
5453 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
5454 * sub-list.
5455 * </ul>
5456 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
5457 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
5458 * {@link #dropArguments(MethodHandle, int, Class[])}.
5459 *
5460 * @apiNote
5461 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
5462 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
5463 * {@snippet lang="java" :
5464 import static java.lang.invoke.MethodHandles.*;
5465 import static java.lang.invoke.MethodType.*;
5466 ...
5467 ...
5468 MethodHandle h0 = constant(boolean.class, true);
5469 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
5470 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
5471 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
5472 if (h1.type().parameterCount() < h2.type().parameterCount())
5473 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
5474 else
5475 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
5476 MethodHandle h3 = guardWithTest(h0, h1, h2);
5477 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
5478 * }
5479 * @param target the method handle to adapt
5480 * @param skip number of targets parameters to disregard (they will be unchanged)
5481 * @param newTypes the list of types to match {@code target}'s parameter type list to
5482 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
5483 * @return a possibly adapted method handle
5484 * @throws NullPointerException if either argument is null
5485 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
5486 * or if {@code skip} is negative or greater than the arity of the target,
5487 * or if {@code pos} is negative or greater than the newTypes list size,
5488 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
5489 * {@code pos}.
5490 * @since 9
5491 */
5492 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
5493 Objects.requireNonNull(target);
5494 Objects.requireNonNull(newTypes);
5495 return dropArgumentsToMatch(target, skip, newTypes.toArray(new Class<?>[0]).clone(), pos, false);
5496 }
5497
5498 /**
5499 * Drop the return value of the target handle (if any).
5500 * The returned method handle will have a {@code void} return type.
5501 *
5502 * @param target the method handle to adapt
5503 * @return a possibly adapted method handle
5504 * @throws NullPointerException if {@code target} is null
5505 * @since 16
5506 */
5507 public static MethodHandle dropReturn(MethodHandle target) {
5508 Objects.requireNonNull(target);
5509 MethodType oldType = target.type();
5510 Class<?> oldReturnType = oldType.returnType();
5511 if (oldReturnType == void.class)
5512 return target;
5513 MethodType newType = oldType.changeReturnType(void.class);
5514 BoundMethodHandle result = target.rebind();
5515 LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true);
5516 result = result.copyWith(newType, lform);
5517 return result;
5518 }
5519
5520 /**
5521 * Adapts a target method handle by pre-processing
5522 * one or more of its arguments, each with its own unary filter function,
5523 * and then calling the target with each pre-processed argument
5524 * replaced by the result of its corresponding filter function.
5525 * <p>
5526 * The pre-processing is performed by one or more method handles,
5527 * specified in the elements of the {@code filters} array.
5528 * The first element of the filter array corresponds to the {@code pos}
5529 * argument of the target, and so on in sequence.
5530 * The filter functions are invoked in left to right order.
5531 * <p>
5532 * Null arguments in the array are treated as identity functions,
5533 * and the corresponding arguments left unchanged.
5534 * (If there are no non-null elements in the array, the original target is returned.)
5535 * Each filter is applied to the corresponding argument of the adapter.
5536 * <p>
5537 * If a filter {@code F} applies to the {@code N}th argument of
5538 * the target, then {@code F} must be a method handle which
5539 * takes exactly one argument. The type of {@code F}'s sole argument
5540 * replaces the corresponding argument type of the target
5541 * in the resulting adapted method handle.
5542 * The return type of {@code F} must be identical to the corresponding
5543 * parameter type of the target.
5544 * <p>
5545 * It is an error if there are elements of {@code filters}
5546 * (null or not)
5547 * which do not correspond to argument positions in the target.
5548 * <p><b>Example:</b>
5549 * {@snippet lang="java" :
5550 import static java.lang.invoke.MethodHandles.*;
5551 import static java.lang.invoke.MethodType.*;
5552 ...
5553 MethodHandle cat = lookup().findVirtual(String.class,
5554 "concat", methodType(String.class, String.class));
5555 MethodHandle upcase = lookup().findVirtual(String.class,
5556 "toUpperCase", methodType(String.class));
5557 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5558 MethodHandle f0 = filterArguments(cat, 0, upcase);
5559 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
5560 MethodHandle f1 = filterArguments(cat, 1, upcase);
5561 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
5562 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
5563 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
5564 * }
5565 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5566 * denotes the return type of both the {@code target} and resulting adapter.
5567 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
5568 * of the parameters and arguments that precede and follow the filter position
5569 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
5570 * values of the filtered parameters and arguments; they also represent the
5571 * return types of the {@code filter[i]} handles. The latter accept arguments
5572 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
5573 * the resulting adapter.
5574 * {@snippet lang="java" :
5575 * T target(P... p, A[i]... a[i], B... b);
5576 * A[i] filter[i](V[i]);
5577 * T adapter(P... p, V[i]... v[i], B... b) {
5578 * return target(p..., filter[i](v[i])..., b...);
5579 * }
5580 * }
5581 * <p>
5582 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5583 * variable-arity method handle}, even if the original target method handle was.
5584 *
5585 * @param target the method handle to invoke after arguments are filtered
5586 * @param pos the position of the first argument to filter
5587 * @param filters method handles to call initially on filtered arguments
5588 * @return method handle which incorporates the specified argument filtering logic
5589 * @throws NullPointerException if the target is null
5590 * or if the {@code filters} array is null
5591 * @throws IllegalArgumentException if a non-null element of {@code filters}
5592 * does not match a corresponding argument type of target as described above,
5593 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
5594 * or if the resulting method handle's type would have
5595 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5596 */
5597 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
5598 // In method types arguments start at index 0, while the LF
5599 // editor have the MH receiver at position 0 - adjust appropriately.
5600 final int MH_RECEIVER_OFFSET = 1;
5601 filterArgumentsCheckArity(target, pos, filters);
5602 MethodHandle adapter = target;
5603
5604 // keep track of currently matched filters, as to optimize repeated filters
5605 int index = 0;
5606 int[] positions = new int[filters.length];
5607 MethodHandle filter = null;
5608
5609 // process filters in reverse order so that the invocation of
5610 // the resulting adapter will invoke the filters in left-to-right order
5611 for (int i = filters.length - 1; i >= 0; --i) {
5612 MethodHandle newFilter = filters[i];
5613 if (newFilter == null) continue; // ignore null elements of filters
5614
5615 // flush changes on update
5616 if (filter != newFilter) {
5617 if (filter != null) {
5618 if (index > 1) {
5619 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5620 } else {
5621 adapter = filterArgument(adapter, positions[0] - 1, filter);
5622 }
5623 }
5624 filter = newFilter;
5625 index = 0;
5626 }
5627
5628 filterArgumentChecks(target, pos + i, newFilter);
5629 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
5630 }
5631 if (index > 1) {
5632 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5633 } else if (index == 1) {
5634 adapter = filterArgument(adapter, positions[0] - 1, filter);
5635 }
5636 return adapter;
5637 }
5638
5639 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
5640 MethodType targetType = adapter.type();
5641 MethodType filterType = filter.type();
5642 BoundMethodHandle result = adapter.rebind();
5643 Class<?> newParamType = filterType.parameterType(0);
5644
5645 Class<?>[] ptypes = targetType.ptypes().clone();
5646 for (int pos : positions) {
5647 ptypes[pos - 1] = newParamType;
5648 }
5649 MethodType newType = MethodType.methodType(targetType.rtype(), ptypes, true);
5650
5651 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
5652 return result.copyWithExtendL(newType, lform, filter);
5653 }
5654
5655 /*non-public*/
5656 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
5657 filterArgumentChecks(target, pos, filter);
5658 MethodType targetType = target.type();
5659 MethodType filterType = filter.type();
5660 BoundMethodHandle result = target.rebind();
5661 Class<?> newParamType = filterType.parameterType(0);
5662 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
5663 MethodType newType = targetType.changeParameterType(pos, newParamType);
5664 result = result.copyWithExtendL(newType, lform, filter);
5665 return result;
5666 }
5667
5668 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
5669 MethodType targetType = target.type();
5670 int maxPos = targetType.parameterCount();
5671 if (pos + filters.length > maxPos)
5672 throw newIllegalArgumentException("too many filters");
5673 }
5674
5675 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5676 MethodType targetType = target.type();
5677 MethodType filterType = filter.type();
5678 if (filterType.parameterCount() != 1
5679 || filterType.returnType() != targetType.parameterType(pos))
5680 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5681 }
5682
5683 /**
5684 * Adapts a target method handle by pre-processing
5685 * a sub-sequence of its arguments with a filter (another method handle).
5686 * The pre-processed arguments are replaced by the result (if any) of the
5687 * filter function.
5688 * The target is then called on the modified (usually shortened) argument list.
5689 * <p>
5690 * If the filter returns a value, the target must accept that value as
5691 * its argument in position {@code pos}, preceded and/or followed by
5692 * any arguments not passed to the filter.
5693 * If the filter returns void, the target must accept all arguments
5694 * not passed to the filter.
5695 * No arguments are reordered, and a result returned from the filter
5696 * replaces (in order) the whole subsequence of arguments originally
5697 * passed to the adapter.
5698 * <p>
5699 * The argument types (if any) of the filter
5700 * replace zero or one argument types of the target, at position {@code pos},
5701 * in the resulting adapted method handle.
5702 * The return type of the filter (if any) must be identical to the
5703 * argument type of the target at position {@code pos}, and that target argument
5704 * is supplied by the return value of the filter.
5705 * <p>
5706 * In all cases, {@code pos} must be greater than or equal to zero, and
5707 * {@code pos} must also be less than or equal to the target's arity.
5708 * <p><b>Example:</b>
5709 * {@snippet lang="java" :
5710 import static java.lang.invoke.MethodHandles.*;
5711 import static java.lang.invoke.MethodType.*;
5712 ...
5713 MethodHandle deepToString = publicLookup()
5714 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
5715
5716 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
5717 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
5718
5719 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
5720 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
5721
5722 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
5723 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
5724 assertEquals("[top, [up, down], strange]",
5725 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
5726
5727 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
5728 assertEquals("[top, [up, down], [strange]]",
5729 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
5730
5731 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
5732 assertEquals("[top, [[up, down, strange], charm], bottom]",
5733 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
5734 * }
5735 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5736 * represents the return type of the {@code target} and resulting adapter.
5737 * {@code V}/{@code v} stand for the return type and value of the
5738 * {@code filter}, which are also found in the signature and arguments of
5739 * the {@code target}, respectively, unless {@code V} is {@code void}.
5740 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
5741 * and values preceding and following the collection position, {@code pos},
5742 * in the {@code target}'s signature. They also turn up in the resulting
5743 * adapter's signature and arguments, where they surround
5744 * {@code B}/{@code b}, which represent the parameter types and arguments
5745 * to the {@code filter} (if any).
5746 * {@snippet lang="java" :
5747 * T target(A...,V,C...);
5748 * V filter(B...);
5749 * T adapter(A... a,B... b,C... c) {
5750 * V v = filter(b...);
5751 * return target(a...,v,c...);
5752 * }
5753 * // and if the filter has no arguments:
5754 * T target2(A...,V,C...);
5755 * V filter2();
5756 * T adapter2(A... a,C... c) {
5757 * V v = filter2();
5758 * return target2(a...,v,c...);
5759 * }
5760 * // and if the filter has a void return:
5761 * T target3(A...,C...);
5762 * void filter3(B...);
5763 * T adapter3(A... a,B... b,C... c) {
5764 * filter3(b...);
5765 * return target3(a...,c...);
5766 * }
5767 * }
5768 * <p>
5769 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
5770 * one which first "folds" the affected arguments, and then drops them, in separate
5771 * steps as follows:
5772 * {@snippet lang="java" :
5773 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
5774 * mh = MethodHandles.foldArguments(mh, coll); //step 1
5775 * }
5776 * If the target method handle consumes no arguments besides than the result
5777 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
5778 * is equivalent to {@code filterReturnValue(coll, mh)}.
5779 * If the filter method handle {@code coll} consumes one argument and produces
5780 * a non-void result, then {@code collectArguments(mh, N, coll)}
5781 * is equivalent to {@code filterArguments(mh, N, coll)}.
5782 * Other equivalences are possible but would require argument permutation.
5783 * <p>
5784 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5785 * variable-arity method handle}, even if the original target method handle was.
5786 *
5787 * @param target the method handle to invoke after filtering the subsequence of arguments
5788 * @param pos the position of the first adapter argument to pass to the filter,
5789 * and/or the target argument which receives the result of the filter
5790 * @param filter method handle to call on the subsequence of arguments
5791 * @return method handle which incorporates the specified argument subsequence filtering logic
5792 * @throws NullPointerException if either argument is null
5793 * @throws IllegalArgumentException if the return type of {@code filter}
5794 * is non-void and is not the same as the {@code pos} argument of the target,
5795 * or if {@code pos} is not between 0 and the target's arity, inclusive,
5796 * or if the resulting method handle's type would have
5797 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5798 * @see MethodHandles#foldArguments
5799 * @see MethodHandles#filterArguments
5800 * @see MethodHandles#filterReturnValue
5801 */
5802 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
5803 MethodType newType = collectArgumentsChecks(target, pos, filter);
5804 MethodType collectorType = filter.type();
5805 BoundMethodHandle result = target.rebind();
5806 LambdaForm lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
5807 return result.copyWithExtendL(newType, lform, filter);
5808 }
5809
5810 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5811 MethodType targetType = target.type();
5812 MethodType filterType = filter.type();
5813 Class<?> rtype = filterType.returnType();
5814 Class<?>[] filterArgs = filterType.ptypes();
5815 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) ||
5816 (rtype != void.class && pos >= targetType.parameterCount())) {
5817 throw newIllegalArgumentException("position is out of range for target", target, pos);
5818 }
5819 if (rtype == void.class) {
5820 return targetType.insertParameterTypes(pos, filterArgs);
5821 }
5822 if (rtype != targetType.parameterType(pos)) {
5823 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5824 }
5825 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs);
5826 }
5827
5828 /**
5829 * Adapts a target method handle by post-processing
5830 * its return value (if any) with a filter (another method handle).
5831 * The result of the filter is returned from the adapter.
5832 * <p>
5833 * If the target returns a value, the filter must accept that value as
5834 * its only argument.
5835 * If the target returns void, the filter must accept no arguments.
5836 * <p>
5837 * The return type of the filter
5838 * replaces the return type of the target
5839 * in the resulting adapted method handle.
5840 * The argument type of the filter (if any) must be identical to the
5841 * return type of the target.
5842 * <p><b>Example:</b>
5843 * {@snippet lang="java" :
5844 import static java.lang.invoke.MethodHandles.*;
5845 import static java.lang.invoke.MethodType.*;
5846 ...
5847 MethodHandle cat = lookup().findVirtual(String.class,
5848 "concat", methodType(String.class, String.class));
5849 MethodHandle length = lookup().findVirtual(String.class,
5850 "length", methodType(int.class));
5851 System.out.println((String) cat.invokeExact("x", "y")); // xy
5852 MethodHandle f0 = filterReturnValue(cat, length);
5853 System.out.println((int) f0.invokeExact("x", "y")); // 2
5854 * }
5855 * <p>Here is pseudocode for the resulting adapter. In the code,
5856 * {@code T}/{@code t} represent the result type and value of the
5857 * {@code target}; {@code V}, the result type of the {@code filter}; and
5858 * {@code A}/{@code a}, the types and values of the parameters and arguments
5859 * of the {@code target} as well as the resulting adapter.
5860 * {@snippet lang="java" :
5861 * T target(A...);
5862 * V filter(T);
5863 * V adapter(A... a) {
5864 * T t = target(a...);
5865 * return filter(t);
5866 * }
5867 * // and if the target has a void return:
5868 * void target2(A...);
5869 * V filter2();
5870 * V adapter2(A... a) {
5871 * target2(a...);
5872 * return filter2();
5873 * }
5874 * // and if the filter has a void return:
5875 * T target3(A...);
5876 * void filter3(V);
5877 * void adapter3(A... a) {
5878 * T t = target3(a...);
5879 * filter3(t);
5880 * }
5881 * }
5882 * <p>
5883 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5884 * variable-arity method handle}, even if the original target method handle was.
5885 * @param target the method handle to invoke before filtering the return value
5886 * @param filter method handle to call on the return value
5887 * @return method handle which incorporates the specified return value filtering logic
5888 * @throws NullPointerException if either argument is null
5889 * @throws IllegalArgumentException if the argument list of {@code filter}
5890 * does not match the return type of target as described above
5891 */
5892 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
5893 MethodType targetType = target.type();
5894 MethodType filterType = filter.type();
5895 filterReturnValueChecks(targetType, filterType);
5896 BoundMethodHandle result = target.rebind();
5897 BasicType rtype = BasicType.basicType(filterType.returnType());
5898 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
5899 MethodType newType = targetType.changeReturnType(filterType.returnType());
5900 result = result.copyWithExtendL(newType, lform, filter);
5901 return result;
5902 }
5903
5904 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
5905 Class<?> rtype = targetType.returnType();
5906 int filterValues = filterType.parameterCount();
5907 if (filterValues == 0
5908 ? (rtype != void.class)
5909 : (rtype != filterType.parameterType(0) || filterValues != 1))
5910 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5911 }
5912
5913 /**
5914 * Filter the return value of a target method handle with a filter function. The filter function is
5915 * applied to the return value of the original handle; if the filter specifies more than one parameters,
5916 * then any remaining parameter is appended to the adapter handle. In other words, the adaptation works
5917 * as follows:
5918 * {@snippet lang="java" :
5919 * T target(A...)
5920 * V filter(B... , T)
5921 * V adapter(A... a, B... b) {
5922 * T t = target(a...);
5923 * return filter(b..., t);
5924 * }
5925 * }
5926 * <p>
5927 * If the filter handle is a unary function, then this method behaves like {@link #filterReturnValue(MethodHandle, MethodHandle)}.
5928 *
5929 * @param target the target method handle
5930 * @param filter the filter method handle
5931 * @return the adapter method handle
5932 */
5933 /* package */ static MethodHandle collectReturnValue(MethodHandle target, MethodHandle filter) {
5934 MethodType targetType = target.type();
5935 MethodType filterType = filter.type();
5936 BoundMethodHandle result = target.rebind();
5937 LambdaForm lform = result.editor().collectReturnValueForm(filterType.basicType());
5938 MethodType newType = targetType.changeReturnType(filterType.returnType());
5939 if (filterType.parameterCount() > 1) {
5940 for (int i = 0 ; i < filterType.parameterCount() - 1 ; i++) {
5941 newType = newType.appendParameterTypes(filterType.parameterType(i));
5942 }
5943 }
5944 result = result.copyWithExtendL(newType, lform, filter);
5945 return result;
5946 }
5947
5948 /**
5949 * Adapts a target method handle by pre-processing
5950 * some of its arguments, and then calling the target with
5951 * the result of the pre-processing, inserted into the original
5952 * sequence of arguments.
5953 * <p>
5954 * The pre-processing is performed by {@code combiner}, a second method handle.
5955 * Of the arguments passed to the adapter, the first {@code N} arguments
5956 * are copied to the combiner, which is then called.
5957 * (Here, {@code N} is defined as the parameter count of the combiner.)
5958 * After this, control passes to the target, with any result
5959 * from the combiner inserted before the original {@code N} incoming
5960 * arguments.
5961 * <p>
5962 * If the combiner returns a value, the first parameter type of the target
5963 * must be identical with the return type of the combiner, and the next
5964 * {@code N} parameter types of the target must exactly match the parameters
5965 * of the combiner.
5966 * <p>
5967 * If the combiner has a void return, no result will be inserted,
5968 * and the first {@code N} parameter types of the target
5969 * must exactly match the parameters of the combiner.
5970 * <p>
5971 * The resulting adapter is the same type as the target, except that the
5972 * first parameter type is dropped,
5973 * if it corresponds to the result of the combiner.
5974 * <p>
5975 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
5976 * that either the combiner or the target does not wish to receive.
5977 * If some of the incoming arguments are destined only for the combiner,
5978 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
5979 * arguments will not need to be live on the stack on entry to the
5980 * target.)
5981 * <p><b>Example:</b>
5982 * {@snippet lang="java" :
5983 import static java.lang.invoke.MethodHandles.*;
5984 import static java.lang.invoke.MethodType.*;
5985 ...
5986 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5987 "println", methodType(void.class, String.class))
5988 .bindTo(System.out);
5989 MethodHandle cat = lookup().findVirtual(String.class,
5990 "concat", methodType(String.class, String.class));
5991 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5992 MethodHandle catTrace = foldArguments(cat, trace);
5993 // also prints "boo":
5994 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5995 * }
5996 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5997 * represents the result type of the {@code target} and resulting adapter.
5998 * {@code V}/{@code v} represent the type and value of the parameter and argument
5999 * of {@code target} that precedes the folding position; {@code V} also is
6000 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6001 * types and values of the {@code N} parameters and arguments at the folding
6002 * position. {@code B}/{@code b} represent the types and values of the
6003 * {@code target} parameters and arguments that follow the folded parameters
6004 * and arguments.
6005 * {@snippet lang="java" :
6006 * // there are N arguments in A...
6007 * T target(V, A[N]..., B...);
6008 * V combiner(A...);
6009 * T adapter(A... a, B... b) {
6010 * V v = combiner(a...);
6011 * return target(v, a..., b...);
6012 * }
6013 * // and if the combiner has a void return:
6014 * T target2(A[N]..., B...);
6015 * void combiner2(A...);
6016 * T adapter2(A... a, B... b) {
6017 * combiner2(a...);
6018 * return target2(a..., b...);
6019 * }
6020 * }
6021 * <p>
6022 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6023 * variable-arity method handle}, even if the original target method handle was.
6024 * @param target the method handle to invoke after arguments are combined
6025 * @param combiner method handle to call initially on the incoming arguments
6026 * @return method handle which incorporates the specified argument folding logic
6027 * @throws NullPointerException if either argument is null
6028 * @throws IllegalArgumentException if {@code combiner}'s return type
6029 * is non-void and not the same as the first argument type of
6030 * the target, or if the initial {@code N} argument types
6031 * of the target
6032 * (skipping one matching the {@code combiner}'s return type)
6033 * are not identical with the argument types of {@code combiner}
6034 */
6035 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
6036 return foldArguments(target, 0, combiner);
6037 }
6038
6039 /**
6040 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
6041 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
6042 * before the folded arguments.
6043 * <p>
6044 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
6045 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
6046 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
6047 * 0.
6048 *
6049 * @apiNote Example:
6050 * {@snippet lang="java" :
6051 import static java.lang.invoke.MethodHandles.*;
6052 import static java.lang.invoke.MethodType.*;
6053 ...
6054 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6055 "println", methodType(void.class, String.class))
6056 .bindTo(System.out);
6057 MethodHandle cat = lookup().findVirtual(String.class,
6058 "concat", methodType(String.class, String.class));
6059 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6060 MethodHandle catTrace = foldArguments(cat, 1, trace);
6061 // also prints "jum":
6062 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6063 * }
6064 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6065 * represents the result type of the {@code target} and resulting adapter.
6066 * {@code V}/{@code v} represent the type and value of the parameter and argument
6067 * of {@code target} that precedes the folding position; {@code V} also is
6068 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6069 * types and values of the {@code N} parameters and arguments at the folding
6070 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
6071 * and values of the {@code target} parameters and arguments that precede and
6072 * follow the folded parameters and arguments starting at {@code pos},
6073 * respectively.
6074 * {@snippet lang="java" :
6075 * // there are N arguments in A...
6076 * T target(Z..., V, A[N]..., B...);
6077 * V combiner(A...);
6078 * T adapter(Z... z, A... a, B... b) {
6079 * V v = combiner(a...);
6080 * return target(z..., v, a..., b...);
6081 * }
6082 * // and if the combiner has a void return:
6083 * T target2(Z..., A[N]..., B...);
6084 * void combiner2(A...);
6085 * T adapter2(Z... z, A... a, B... b) {
6086 * combiner2(a...);
6087 * return target2(z..., a..., b...);
6088 * }
6089 * }
6090 * <p>
6091 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6092 * variable-arity method handle}, even if the original target method handle was.
6093 *
6094 * @param target the method handle to invoke after arguments are combined
6095 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
6096 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6097 * @param combiner method handle to call initially on the incoming arguments
6098 * @return method handle which incorporates the specified argument folding logic
6099 * @throws NullPointerException if either argument is null
6100 * @throws IllegalArgumentException if either of the following two conditions holds:
6101 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6102 * {@code pos} of the target signature;
6103 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
6104 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
6105 *
6106 * @see #foldArguments(MethodHandle, MethodHandle)
6107 * @since 9
6108 */
6109 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
6110 MethodType targetType = target.type();
6111 MethodType combinerType = combiner.type();
6112 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
6113 BoundMethodHandle result = target.rebind();
6114 boolean dropResult = rtype == void.class;
6115 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
6116 MethodType newType = targetType;
6117 if (!dropResult) {
6118 newType = newType.dropParameterTypes(pos, pos + 1);
6119 }
6120 result = result.copyWithExtendL(newType, lform, combiner);
6121 return result;
6122 }
6123
6124 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
6125 int foldArgs = combinerType.parameterCount();
6126 Class<?> rtype = combinerType.returnType();
6127 int foldVals = rtype == void.class ? 0 : 1;
6128 int afterInsertPos = foldPos + foldVals;
6129 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
6130 if (ok) {
6131 for (int i = 0; i < foldArgs; i++) {
6132 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
6133 ok = false;
6134 break;
6135 }
6136 }
6137 }
6138 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
6139 ok = false;
6140 if (!ok)
6141 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6142 return rtype;
6143 }
6144
6145 /**
6146 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
6147 * of the pre-processing replacing the argument at the given position.
6148 *
6149 * @param target the method handle to invoke after arguments are combined
6150 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6151 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6152 * @param combiner method handle to call initially on the incoming arguments
6153 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6154 * @return method handle which incorporates the specified argument folding logic
6155 * @throws NullPointerException if either argument is null
6156 * @throws IllegalArgumentException if either of the following two conditions holds:
6157 * (1) {@code combiner}'s return type is not the same as the argument type at position
6158 * {@code pos} of the target signature;
6159 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
6160 * not identical with the argument types of {@code combiner}.
6161 */
6162 /*non-public*/
6163 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6164 return argumentsWithCombiner(true, target, position, combiner, argPositions);
6165 }
6166
6167 /**
6168 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
6169 * the pre-processing inserted into the original sequence of arguments at the given position.
6170 *
6171 * @param target the method handle to invoke after arguments are combined
6172 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6173 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6174 * @param combiner method handle to call initially on the incoming arguments
6175 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6176 * @return method handle which incorporates the specified argument folding logic
6177 * @throws NullPointerException if either argument is null
6178 * @throws IllegalArgumentException if either of the following two conditions holds:
6179 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6180 * {@code pos} of the target signature;
6181 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
6182 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
6183 * with the argument types of {@code combiner}.
6184 */
6185 /*non-public*/
6186 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6187 return argumentsWithCombiner(false, target, position, combiner, argPositions);
6188 }
6189
6190 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6191 MethodType targetType = target.type();
6192 MethodType combinerType = combiner.type();
6193 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
6194 BoundMethodHandle result = target.rebind();
6195
6196 MethodType newType = targetType;
6197 LambdaForm lform;
6198 if (filter) {
6199 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
6200 } else {
6201 boolean dropResult = rtype == void.class;
6202 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
6203 if (!dropResult) {
6204 newType = newType.dropParameterTypes(position, position + 1);
6205 }
6206 }
6207 result = result.copyWithExtendL(newType, lform, combiner);
6208 return result;
6209 }
6210
6211 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
6212 int combinerArgs = combinerType.parameterCount();
6213 if (argPos.length != combinerArgs) {
6214 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
6215 }
6216 Class<?> rtype = combinerType.returnType();
6217
6218 for (int i = 0; i < combinerArgs; i++) {
6219 int arg = argPos[i];
6220 if (arg < 0 || arg > targetType.parameterCount()) {
6221 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
6222 }
6223 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
6224 throw newIllegalArgumentException("target argument type at position " + arg
6225 + " must match combiner argument type at index " + i + ": " + targetType
6226 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
6227 }
6228 }
6229 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
6230 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6231 }
6232 return rtype;
6233 }
6234
6235 /**
6236 * Makes a method handle which adapts a target method handle,
6237 * by guarding it with a test, a boolean-valued method handle.
6238 * If the guard fails, a fallback handle is called instead.
6239 * All three method handles must have the same corresponding
6240 * argument and return types, except that the return type
6241 * of the test must be boolean, and the test is allowed
6242 * to have fewer arguments than the other two method handles.
6243 * <p>
6244 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6245 * represents the uniform result type of the three involved handles;
6246 * {@code A}/{@code a}, the types and values of the {@code target}
6247 * parameters and arguments that are consumed by the {@code test}; and
6248 * {@code B}/{@code b}, those types and values of the {@code target}
6249 * parameters and arguments that are not consumed by the {@code test}.
6250 * {@snippet lang="java" :
6251 * boolean test(A...);
6252 * T target(A...,B...);
6253 * T fallback(A...,B...);
6254 * T adapter(A... a,B... b) {
6255 * if (test(a...))
6256 * return target(a..., b...);
6257 * else
6258 * return fallback(a..., b...);
6259 * }
6260 * }
6261 * Note that the test arguments ({@code a...} in the pseudocode) cannot
6262 * be modified by execution of the test, and so are passed unchanged
6263 * from the caller to the target or fallback as appropriate.
6264 * @param test method handle used for test, must return boolean
6265 * @param target method handle to call if test passes
6266 * @param fallback method handle to call if test fails
6267 * @return method handle which incorporates the specified if/then/else logic
6268 * @throws NullPointerException if any argument is null
6269 * @throws IllegalArgumentException if {@code test} does not return boolean,
6270 * or if all three method types do not match (with the return
6271 * type of {@code test} changed to match that of the target).
6272 */
6273 public static MethodHandle guardWithTest(MethodHandle test,
6274 MethodHandle target,
6275 MethodHandle fallback) {
6276 MethodType gtype = test.type();
6277 MethodType ttype = target.type();
6278 MethodType ftype = fallback.type();
6279 if (!ttype.equals(ftype))
6280 throw misMatchedTypes("target and fallback types", ttype, ftype);
6281 if (gtype.returnType() != boolean.class)
6282 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
6283
6284 test = dropArgumentsToMatch(test, 0, ttype.ptypes(), 0, true);
6285 if (test == null) {
6286 throw misMatchedTypes("target and test types", ttype, gtype);
6287 }
6288 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
6289 }
6290
6291 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
6292 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
6293 }
6294
6295 /**
6296 * Makes a method handle which adapts a target method handle,
6297 * by running it inside an exception handler.
6298 * If the target returns normally, the adapter returns that value.
6299 * If an exception matching the specified type is thrown, the fallback
6300 * handle is called instead on the exception, plus the original arguments.
6301 * <p>
6302 * The target and handler must have the same corresponding
6303 * argument and return types, except that handler may omit trailing arguments
6304 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
6305 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
6306 * <p>
6307 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6308 * represents the return type of the {@code target} and {@code handler},
6309 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
6310 * the types and values of arguments to the resulting handle consumed by
6311 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
6312 * resulting handle discarded by {@code handler}.
6313 * {@snippet lang="java" :
6314 * T target(A..., B...);
6315 * T handler(ExType, A...);
6316 * T adapter(A... a, B... b) {
6317 * try {
6318 * return target(a..., b...);
6319 * } catch (ExType ex) {
6320 * return handler(ex, a...);
6321 * }
6322 * }
6323 * }
6324 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6325 * be modified by execution of the target, and so are passed unchanged
6326 * from the caller to the handler, if the handler is invoked.
6327 * <p>
6328 * The target and handler must return the same type, even if the handler
6329 * always throws. (This might happen, for instance, because the handler
6330 * is simulating a {@code finally} clause).
6331 * To create such a throwing handler, compose the handler creation logic
6332 * with {@link #throwException throwException},
6333 * in order to create a method handle of the correct return type.
6334 * @param target method handle to call
6335 * @param exType the type of exception which the handler will catch
6336 * @param handler method handle to call if a matching exception is thrown
6337 * @return method handle which incorporates the specified try/catch logic
6338 * @throws NullPointerException if any argument is null
6339 * @throws IllegalArgumentException if {@code handler} does not accept
6340 * the given exception type, or if the method handle types do
6341 * not match in their return types and their
6342 * corresponding parameters
6343 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
6344 */
6345 public static MethodHandle catchException(MethodHandle target,
6346 Class<? extends Throwable> exType,
6347 MethodHandle handler) {
6348 MethodType ttype = target.type();
6349 MethodType htype = handler.type();
6350 if (!Throwable.class.isAssignableFrom(exType))
6351 throw new ClassCastException(exType.getName());
6352 if (htype.parameterCount() < 1 ||
6353 !htype.parameterType(0).isAssignableFrom(exType))
6354 throw newIllegalArgumentException("handler does not accept exception type "+exType);
6355 if (htype.returnType() != ttype.returnType())
6356 throw misMatchedTypes("target and handler return types", ttype, htype);
6357 handler = dropArgumentsToMatch(handler, 1, ttype.ptypes(), 0, true);
6358 if (handler == null) {
6359 throw misMatchedTypes("target and handler types", ttype, htype);
6360 }
6361 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
6362 }
6363
6364 /**
6365 * Produces a method handle which will throw exceptions of the given {@code exType}.
6366 * The method handle will accept a single argument of {@code exType},
6367 * and immediately throw it as an exception.
6368 * The method type will nominally specify a return of {@code returnType}.
6369 * The return type may be anything convenient: It doesn't matter to the
6370 * method handle's behavior, since it will never return normally.
6371 * @param returnType the return type of the desired method handle
6372 * @param exType the parameter type of the desired method handle
6373 * @return method handle which can throw the given exceptions
6374 * @throws NullPointerException if either argument is null
6375 */
6376 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
6377 if (!Throwable.class.isAssignableFrom(exType))
6378 throw new ClassCastException(exType.getName());
6379 return MethodHandleImpl.throwException(methodType(returnType, exType));
6380 }
6381
6382 /**
6383 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
6384 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
6385 * delivers the loop's result, which is the return value of the resulting handle.
6386 * <p>
6387 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
6388 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
6389 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
6390 * terms of method handles, each clause will specify up to four independent actions:<ul>
6391 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
6392 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
6393 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
6394 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
6395 * </ul>
6396 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
6397 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
6398 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
6399 * <p>
6400 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
6401 * this case. See below for a detailed description.
6402 * <p>
6403 * <em>Parameters optional everywhere:</em>
6404 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
6405 * As an exception, the init functions cannot take any {@code v} parameters,
6406 * because those values are not yet computed when the init functions are executed.
6407 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
6408 * In fact, any clause function may take no arguments at all.
6409 * <p>
6410 * <em>Loop parameters:</em>
6411 * A clause function may take all the iteration variable values it is entitled to, in which case
6412 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
6413 * with their types and values notated as {@code (A...)} and {@code (a...)}.
6414 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
6415 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
6416 * init function is automatically a loop parameter {@code a}.)
6417 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
6418 * These loop parameters act as loop-invariant values visible across the whole loop.
6419 * <p>
6420 * <em>Parameters visible everywhere:</em>
6421 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
6422 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
6423 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
6424 * Most clause functions will not need all of this information, but they will be formally connected to it
6425 * as if by {@link #dropArguments}.
6426 * <a id="astar"></a>
6427 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
6428 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
6429 * In that notation, the general form of an init function parameter list
6430 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
6431 * <p>
6432 * <em>Checking clause structure:</em>
6433 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
6434 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
6435 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
6436 * met by the inputs to the loop combinator.
6437 * <p>
6438 * <em>Effectively identical sequences:</em>
6439 * <a id="effid"></a>
6440 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
6441 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
6442 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
6443 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
6444 * that longest list.
6445 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
6446 * and the same is true if more sequences of the form {@code (V... A*)} are added.
6447 * <p>
6448 * <em>Step 0: Determine clause structure.</em><ol type="a">
6449 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
6450 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
6451 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
6452 * four. Padding takes place by appending elements to the array.
6453 * <li>Clauses with all {@code null}s are disregarded.
6454 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
6455 * </ol>
6456 * <p>
6457 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
6458 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
6459 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
6460 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
6461 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
6462 * iteration variable type.
6463 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
6464 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
6465 * </ol>
6466 * <p>
6467 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
6468 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
6469 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
6470 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
6471 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
6472 * (These types will be checked in step 2, along with all the clause function types.)
6473 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
6474 * <li>All of the collected parameter lists must be effectively identical.
6475 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
6476 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
6477 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
6478 * the "internal parameter list".
6479 * </ul>
6480 * <p>
6481 * <em>Step 1C: Determine loop return type.</em><ol type="a">
6482 * <li>Examine fini function return types, disregarding omitted fini functions.
6483 * <li>If there are no fini functions, the loop return type is {@code void}.
6484 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
6485 * type.
6486 * </ol>
6487 * <p>
6488 * <em>Step 1D: Check other types.</em><ol type="a">
6489 * <li>There must be at least one non-omitted pred function.
6490 * <li>Every non-omitted pred function must have a {@code boolean} return type.
6491 * </ol>
6492 * <p>
6493 * <em>Step 2: Determine parameter lists.</em><ol type="a">
6494 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
6495 * <li>The parameter list for init functions will be adjusted to the external parameter list.
6496 * (Note that their parameter lists are already effectively identical to this list.)
6497 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
6498 * effectively identical to the internal parameter list {@code (V... A...)}.
6499 * </ol>
6500 * <p>
6501 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
6502 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
6503 * type.
6504 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
6505 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
6506 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
6507 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
6508 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
6509 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
6510 * loop return type.
6511 * </ol>
6512 * <p>
6513 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
6514 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
6515 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
6516 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
6517 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
6518 * pad out the end of the list.
6519 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
6520 * </ol>
6521 * <p>
6522 * <em>Final observations.</em><ol type="a">
6523 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
6524 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
6525 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
6526 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
6527 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
6528 * <li>Each pair of init and step functions agrees in their return type {@code V}.
6529 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
6530 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
6531 * </ol>
6532 * <p>
6533 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
6534 * <ul>
6535 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
6536 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
6537 * (Only one {@code Pn} has to be non-{@code null}.)
6538 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
6539 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
6540 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
6541 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
6542 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
6543 * the resulting loop handle's parameter types {@code (A...)}.
6544 * </ul>
6545 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
6546 * which is natural if most of the loop computation happens in the steps. For some loops,
6547 * the burden of computation might be heaviest in the pred functions, and so the pred functions
6548 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
6549 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
6550 * where the init functions will need the extra parameters. For such reasons, the rules for
6551 * determining these parameters are as symmetric as possible, across all clause parts.
6552 * In general, the loop parameters function as common invariant values across the whole
6553 * loop, while the iteration variables function as common variant values, or (if there is
6554 * no step function) as internal loop invariant temporaries.
6555 * <p>
6556 * <em>Loop execution.</em><ol type="a">
6557 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
6558 * every clause function. These locals are loop invariant.
6559 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
6560 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
6561 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
6562 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
6563 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
6564 * (in argument order).
6565 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
6566 * returns {@code false}.
6567 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
6568 * sequence {@code (v...)} of loop variables.
6569 * The updated value is immediately visible to all subsequent function calls.
6570 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
6571 * (of type {@code R}) is returned from the loop as a whole.
6572 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
6573 * except by throwing an exception.
6574 * </ol>
6575 * <p>
6576 * <em>Usage tips.</em>
6577 * <ul>
6578 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
6579 * sometimes a step function only needs to observe the current value of its own variable.
6580 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
6581 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
6582 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
6583 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
6584 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
6585 * <li>If some of the clause functions are virtual methods on an instance, the instance
6586 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
6587 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
6588 * will be the first iteration variable value, and it will be easy to use virtual
6589 * methods as clause parts, since all of them will take a leading instance reference matching that value.
6590 * </ul>
6591 * <p>
6592 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
6593 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
6594 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
6595 * {@snippet lang="java" :
6596 * V... init...(A...);
6597 * boolean pred...(V..., A...);
6598 * V... step...(V..., A...);
6599 * R fini...(V..., A...);
6600 * R loop(A... a) {
6601 * V... v... = init...(a...);
6602 * for (;;) {
6603 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
6604 * v = s(v..., a...);
6605 * if (!p(v..., a...)) {
6606 * return f(v..., a...);
6607 * }
6608 * }
6609 * }
6610 * }
6611 * }
6612 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
6613 * to their full length, even though individual clause functions may neglect to take them all.
6614 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
6615 *
6616 * @apiNote Example:
6617 * {@snippet lang="java" :
6618 * // iterative implementation of the factorial function as a loop handle
6619 * static int one(int k) { return 1; }
6620 * static int inc(int i, int acc, int k) { return i + 1; }
6621 * static int mult(int i, int acc, int k) { return i * acc; }
6622 * static boolean pred(int i, int acc, int k) { return i < k; }
6623 * static int fin(int i, int acc, int k) { return acc; }
6624 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6625 * // null initializer for counter, should initialize to 0
6626 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6627 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6628 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6629 * assertEquals(120, loop.invoke(5));
6630 * }
6631 * The same example, dropping arguments and using combinators:
6632 * {@snippet lang="java" :
6633 * // simplified implementation of the factorial function as a loop handle
6634 * static int inc(int i) { return i + 1; } // drop acc, k
6635 * static int mult(int i, int acc) { return i * acc; } //drop k
6636 * static boolean cmp(int i, int k) { return i < k; }
6637 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
6638 * // null initializer for counter, should initialize to 0
6639 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6640 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
6641 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
6642 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6643 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6644 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6645 * assertEquals(720, loop.invoke(6));
6646 * }
6647 * A similar example, using a helper object to hold a loop parameter:
6648 * {@snippet lang="java" :
6649 * // instance-based implementation of the factorial function as a loop handle
6650 * static class FacLoop {
6651 * final int k;
6652 * FacLoop(int k) { this.k = k; }
6653 * int inc(int i) { return i + 1; }
6654 * int mult(int i, int acc) { return i * acc; }
6655 * boolean pred(int i) { return i < k; }
6656 * int fin(int i, int acc) { return acc; }
6657 * }
6658 * // assume MH_FacLoop is a handle to the constructor
6659 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6660 * // null initializer for counter, should initialize to 0
6661 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6662 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
6663 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6664 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6665 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
6666 * assertEquals(5040, loop.invoke(7));
6667 * }
6668 *
6669 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
6670 *
6671 * @return a method handle embodying the looping behavior as defined by the arguments.
6672 *
6673 * @throws IllegalArgumentException in case any of the constraints described above is violated.
6674 *
6675 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
6676 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6677 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
6678 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
6679 * @since 9
6680 */
6681 public static MethodHandle loop(MethodHandle[]... clauses) {
6682 // Step 0: determine clause structure.
6683 loopChecks0(clauses);
6684
6685 List<MethodHandle> init = new ArrayList<>();
6686 List<MethodHandle> step = new ArrayList<>();
6687 List<MethodHandle> pred = new ArrayList<>();
6688 List<MethodHandle> fini = new ArrayList<>();
6689
6690 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
6691 init.add(clause[0]); // all clauses have at least length 1
6692 step.add(clause.length <= 1 ? null : clause[1]);
6693 pred.add(clause.length <= 2 ? null : clause[2]);
6694 fini.add(clause.length <= 3 ? null : clause[3]);
6695 });
6696
6697 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
6698 final int nclauses = init.size();
6699
6700 // Step 1A: determine iteration variables (V...).
6701 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
6702 for (int i = 0; i < nclauses; ++i) {
6703 MethodHandle in = init.get(i);
6704 MethodHandle st = step.get(i);
6705 if (in == null && st == null) {
6706 iterationVariableTypes.add(void.class);
6707 } else if (in != null && st != null) {
6708 loopChecks1a(i, in, st);
6709 iterationVariableTypes.add(in.type().returnType());
6710 } else {
6711 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
6712 }
6713 }
6714 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).toList();
6715
6716 // Step 1B: determine loop parameters (A...).
6717 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
6718 loopChecks1b(init, commonSuffix);
6719
6720 // Step 1C: determine loop return type.
6721 // Step 1D: check other types.
6722 // local variable required here; see JDK-8223553
6723 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
6724 .map(MethodType::returnType);
6725 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
6726 loopChecks1cd(pred, fini, loopReturnType);
6727
6728 // Step 2: determine parameter lists.
6729 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
6730 commonParameterSequence.addAll(commonSuffix);
6731 loopChecks2(step, pred, fini, commonParameterSequence);
6732 // Step 3: fill in omitted functions.
6733 for (int i = 0; i < nclauses; ++i) {
6734 Class<?> t = iterationVariableTypes.get(i);
6735 if (init.get(i) == null) {
6736 init.set(i, empty(methodType(t, commonSuffix)));
6737 }
6738 if (step.get(i) == null) {
6739 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
6740 }
6741 if (pred.get(i) == null) {
6742 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence));
6743 }
6744 if (fini.get(i) == null) {
6745 fini.set(i, empty(methodType(t, commonParameterSequence)));
6746 }
6747 }
6748
6749 // Step 4: fill in missing parameter types.
6750 // Also convert all handles to fixed-arity handles.
6751 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
6752 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
6753 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
6754 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
6755
6756 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
6757 allMatch(pl -> pl.equals(commonSuffix));
6758 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
6759 allMatch(pl -> pl.equals(commonParameterSequence));
6760
6761 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
6762 }
6763
6764 private static void loopChecks0(MethodHandle[][] clauses) {
6765 if (clauses == null || clauses.length == 0) {
6766 throw newIllegalArgumentException("null or no clauses passed");
6767 }
6768 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
6769 throw newIllegalArgumentException("null clauses are not allowed");
6770 }
6771 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
6772 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
6773 }
6774 }
6775
6776 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
6777 if (in.type().returnType() != st.type().returnType()) {
6778 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
6779 st.type().returnType());
6780 }
6781 }
6782
6783 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
6784 final List<Class<?>> empty = List.of();
6785 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
6786 // take only those that can contribute to a common suffix because they are longer than the prefix
6787 map(MethodHandle::type).
6788 filter(t -> t.parameterCount() > skipSize).
6789 map(MethodType::parameterList).
6790 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
6791 return longest.isEmpty() ? empty : longest.subList(skipSize, longest.size());
6792 }
6793
6794 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
6795 final List<Class<?>> empty = List.of();
6796 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
6797 }
6798
6799 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
6800 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
6801 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
6802 return longestParameterList(List.of(longest1, longest2));
6803 }
6804
6805 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
6806 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
6807 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
6808 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
6809 " (common suffix: " + commonSuffix + ")");
6810 }
6811 }
6812
6813 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
6814 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6815 anyMatch(t -> t != loopReturnType)) {
6816 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
6817 loopReturnType + ")");
6818 }
6819
6820 if (pred.stream().noneMatch(Objects::nonNull)) {
6821 throw newIllegalArgumentException("no predicate found", pred);
6822 }
6823 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6824 anyMatch(t -> t != boolean.class)) {
6825 throw newIllegalArgumentException("predicates must have boolean return type", pred);
6826 }
6827 }
6828
6829 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
6830 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
6831 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
6832 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
6833 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
6834 }
6835 }
6836
6837 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
6838 return hs.stream().map(h -> {
6839 int pc = h.type().parameterCount();
6840 int tpsize = targetParams.size();
6841 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h;
6842 }).toList();
6843 }
6844
6845 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
6846 return hs.stream().map(MethodHandle::asFixedArity).toList();
6847 }
6848
6849 /**
6850 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
6851 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6852 * <p>
6853 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6854 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
6855 * evaluates to {@code true}).
6856 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
6857 * <p>
6858 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6859 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6860 * and updated with the value returned from its invocation. The result of loop execution will be
6861 * the final value of the additional loop-local variable (if present).
6862 * <p>
6863 * The following rules hold for these argument handles:<ul>
6864 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6865 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6866 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6867 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6868 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6869 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6870 * It will constrain the parameter lists of the other loop parts.
6871 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6872 * list {@code (A...)} is called the <em>external parameter list</em>.
6873 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6874 * additional state variable of the loop.
6875 * The body must both accept and return a value of this type {@code V}.
6876 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6877 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6878 * <a href="MethodHandles.html#effid">effectively identical</a>
6879 * to the external parameter list {@code (A...)}.
6880 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6881 * {@linkplain #empty default value}.
6882 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6883 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6884 * effectively identical to the internal parameter list.
6885 * </ul>
6886 * <p>
6887 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6888 * <li>The loop handle's result type is the result type {@code V} of the body.
6889 * <li>The loop handle's parameter types are the types {@code (A...)},
6890 * from the external parameter list.
6891 * </ul>
6892 * <p>
6893 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6894 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6895 * passed to the loop.
6896 * {@snippet lang="java" :
6897 * V init(A...);
6898 * boolean pred(V, A...);
6899 * V body(V, A...);
6900 * V whileLoop(A... a...) {
6901 * V v = init(a...);
6902 * while (pred(v, a...)) {
6903 * v = body(v, a...);
6904 * }
6905 * return v;
6906 * }
6907 * }
6908 *
6909 * @apiNote Example:
6910 * {@snippet lang="java" :
6911 * // implement the zip function for lists as a loop handle
6912 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
6913 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
6914 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
6915 * zip.add(a.next());
6916 * zip.add(b.next());
6917 * return zip;
6918 * }
6919 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
6920 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
6921 * List<String> a = Arrays.asList("a", "b", "c", "d");
6922 * List<String> b = Arrays.asList("e", "f", "g", "h");
6923 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
6924 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
6925 * }
6926 *
6927 *
6928 * @apiNote The implementation of this method can be expressed as follows:
6929 * {@snippet lang="java" :
6930 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6931 * MethodHandle fini = (body.type().returnType() == void.class
6932 * ? null : identity(body.type().returnType()));
6933 * MethodHandle[]
6934 * checkExit = { null, null, pred, fini },
6935 * varBody = { init, body };
6936 * return loop(checkExit, varBody);
6937 * }
6938 * }
6939 *
6940 * @param init optional initializer, providing the initial value of the loop variable.
6941 * May be {@code null}, implying a default initial value. See above for other constraints.
6942 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6943 * above for other constraints.
6944 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6945 * See above for other constraints.
6946 *
6947 * @return a method handle implementing the {@code while} loop as described by the arguments.
6948 * @throws IllegalArgumentException if the rules for the arguments are violated.
6949 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6950 *
6951 * @see #loop(MethodHandle[][])
6952 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6953 * @since 9
6954 */
6955 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6956 whileLoopChecks(init, pred, body);
6957 MethodHandle fini = identityOrVoid(body.type().returnType());
6958 MethodHandle[] checkExit = { null, null, pred, fini };
6959 MethodHandle[] varBody = { init, body };
6960 return loop(checkExit, varBody);
6961 }
6962
6963 /**
6964 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
6965 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6966 * <p>
6967 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6968 * method will, in each iteration, first execute its body and then evaluate the predicate.
6969 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
6970 * <p>
6971 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6972 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6973 * and updated with the value returned from its invocation. The result of loop execution will be
6974 * the final value of the additional loop-local variable (if present).
6975 * <p>
6976 * The following rules hold for these argument handles:<ul>
6977 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6978 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6979 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6980 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6981 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6982 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6983 * It will constrain the parameter lists of the other loop parts.
6984 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6985 * list {@code (A...)} is called the <em>external parameter list</em>.
6986 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6987 * additional state variable of the loop.
6988 * The body must both accept and return a value of this type {@code V}.
6989 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6990 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6991 * <a href="MethodHandles.html#effid">effectively identical</a>
6992 * to the external parameter list {@code (A...)}.
6993 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6994 * {@linkplain #empty default value}.
6995 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6996 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6997 * effectively identical to the internal parameter list.
6998 * </ul>
6999 * <p>
7000 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7001 * <li>The loop handle's result type is the result type {@code V} of the body.
7002 * <li>The loop handle's parameter types are the types {@code (A...)},
7003 * from the external parameter list.
7004 * </ul>
7005 * <p>
7006 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7007 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
7008 * passed to the loop.
7009 * {@snippet lang="java" :
7010 * V init(A...);
7011 * boolean pred(V, A...);
7012 * V body(V, A...);
7013 * V doWhileLoop(A... a...) {
7014 * V v = init(a...);
7015 * do {
7016 * v = body(v, a...);
7017 * } while (pred(v, a...));
7018 * return v;
7019 * }
7020 * }
7021 *
7022 * @apiNote Example:
7023 * {@snippet lang="java" :
7024 * // int i = 0; while (i < limit) { ++i; } return i; => limit
7025 * static int zero(int limit) { return 0; }
7026 * static int step(int i, int limit) { return i + 1; }
7027 * static boolean pred(int i, int limit) { return i < limit; }
7028 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
7029 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
7030 * assertEquals(23, loop.invoke(23));
7031 * }
7032 *
7033 *
7034 * @apiNote The implementation of this method can be expressed as follows:
7035 * {@snippet lang="java" :
7036 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7037 * MethodHandle fini = (body.type().returnType() == void.class
7038 * ? null : identity(body.type().returnType()));
7039 * MethodHandle[] clause = { init, body, pred, fini };
7040 * return loop(clause);
7041 * }
7042 * }
7043 *
7044 * @param init optional initializer, providing the initial value of the loop variable.
7045 * May be {@code null}, implying a default initial value. See above for other constraints.
7046 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
7047 * See above for other constraints.
7048 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
7049 * above for other constraints.
7050 *
7051 * @return a method handle implementing the {@code while} loop as described by the arguments.
7052 * @throws IllegalArgumentException if the rules for the arguments are violated.
7053 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
7054 *
7055 * @see #loop(MethodHandle[][])
7056 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
7057 * @since 9
7058 */
7059 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7060 whileLoopChecks(init, pred, body);
7061 MethodHandle fini = identityOrVoid(body.type().returnType());
7062 MethodHandle[] clause = {init, body, pred, fini };
7063 return loop(clause);
7064 }
7065
7066 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
7067 Objects.requireNonNull(pred);
7068 Objects.requireNonNull(body);
7069 MethodType bodyType = body.type();
7070 Class<?> returnType = bodyType.returnType();
7071 List<Class<?>> innerList = bodyType.parameterList();
7072 List<Class<?>> outerList = innerList;
7073 if (returnType == void.class) {
7074 // OK
7075 } else if (innerList.isEmpty() || innerList.get(0) != returnType) {
7076 // leading V argument missing => error
7077 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7078 throw misMatchedTypes("body function", bodyType, expected);
7079 } else {
7080 outerList = innerList.subList(1, innerList.size());
7081 }
7082 MethodType predType = pred.type();
7083 if (predType.returnType() != boolean.class ||
7084 !predType.effectivelyIdenticalParameters(0, innerList)) {
7085 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
7086 }
7087 if (init != null) {
7088 MethodType initType = init.type();
7089 if (initType.returnType() != returnType ||
7090 !initType.effectivelyIdenticalParameters(0, outerList)) {
7091 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7092 }
7093 }
7094 }
7095
7096 /**
7097 * Constructs a loop that runs a given number of iterations.
7098 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7099 * <p>
7100 * The number of iterations is determined by the {@code iterations} handle evaluation result.
7101 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
7102 * It will be initialized to 0 and incremented by 1 in each iteration.
7103 * <p>
7104 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7105 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7106 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7107 * <p>
7108 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7109 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7110 * iteration variable.
7111 * The result of the loop handle execution will be the final {@code V} value of that variable
7112 * (or {@code void} if there is no {@code V} variable).
7113 * <p>
7114 * The following rules hold for the argument handles:<ul>
7115 * <li>The {@code iterations} handle must not be {@code null}, and must return
7116 * the type {@code int}, referred to here as {@code I} in parameter type lists.
7117 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7118 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7119 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7120 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7121 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7122 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7123 * of types called the <em>internal parameter list</em>.
7124 * It will constrain the parameter lists of the other loop parts.
7125 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7126 * with no additional {@code A} types, then the internal parameter list is extended by
7127 * the argument types {@code A...} of the {@code iterations} handle.
7128 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7129 * list {@code (A...)} is called the <em>external parameter list</em>.
7130 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7131 * additional state variable of the loop.
7132 * The body must both accept a leading parameter and return a value of this type {@code V}.
7133 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7134 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7135 * <a href="MethodHandles.html#effid">effectively identical</a>
7136 * to the external parameter list {@code (A...)}.
7137 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7138 * {@linkplain #empty default value}.
7139 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
7140 * effectively identical to the external parameter list {@code (A...)}.
7141 * </ul>
7142 * <p>
7143 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7144 * <li>The loop handle's result type is the result type {@code V} of the body.
7145 * <li>The loop handle's parameter types are the types {@code (A...)},
7146 * from the external parameter list.
7147 * </ul>
7148 * <p>
7149 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7150 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7151 * arguments passed to the loop.
7152 * {@snippet lang="java" :
7153 * int iterations(A...);
7154 * V init(A...);
7155 * V body(V, int, A...);
7156 * V countedLoop(A... a...) {
7157 * int end = iterations(a...);
7158 * V v = init(a...);
7159 * for (int i = 0; i < end; ++i) {
7160 * v = body(v, i, a...);
7161 * }
7162 * return v;
7163 * }
7164 * }
7165 *
7166 * @apiNote Example with a fully conformant body method:
7167 * {@snippet lang="java" :
7168 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7169 * // => a variation on a well known theme
7170 * static String step(String v, int counter, String init) { return "na " + v; }
7171 * // assume MH_step is a handle to the method above
7172 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
7173 * MethodHandle start = MethodHandles.identity(String.class);
7174 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
7175 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
7176 * }
7177 *
7178 * @apiNote Example with the simplest possible body method type,
7179 * and passing the number of iterations to the loop invocation:
7180 * {@snippet lang="java" :
7181 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7182 * // => a variation on a well known theme
7183 * static String step(String v, int counter ) { return "na " + v; }
7184 * // assume MH_step is a handle to the method above
7185 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
7186 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
7187 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
7188 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
7189 * }
7190 *
7191 * @apiNote Example that treats the number of iterations, string to append to, and string to append
7192 * as loop parameters:
7193 * {@snippet lang="java" :
7194 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7195 * // => a variation on a well known theme
7196 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
7197 * // assume MH_step is a handle to the method above
7198 * MethodHandle count = MethodHandles.identity(int.class);
7199 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
7200 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
7201 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
7202 * }
7203 *
7204 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
7205 * to enforce a loop type:
7206 * {@snippet lang="java" :
7207 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7208 * // => a variation on a well known theme
7209 * static String step(String v, int counter, String pre) { return pre + " " + v; }
7210 * // assume MH_step is a handle to the method above
7211 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
7212 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
7213 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
7214 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
7215 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
7216 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
7217 * }
7218 *
7219 * @apiNote The implementation of this method can be expressed as follows:
7220 * {@snippet lang="java" :
7221 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7222 * return countedLoop(empty(iterations.type()), iterations, init, body);
7223 * }
7224 * }
7225 *
7226 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
7227 * result type must be {@code int}. See above for other constraints.
7228 * @param init optional initializer, providing the initial value of the loop variable.
7229 * May be {@code null}, implying a default initial value. See above for other constraints.
7230 * @param body body of the loop, which may not be {@code null}.
7231 * It controls the loop parameters and result type in the standard case (see above for details).
7232 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7233 * and may accept any number of additional types.
7234 * See above for other constraints.
7235 *
7236 * @return a method handle representing the loop.
7237 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
7238 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7239 *
7240 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
7241 * @since 9
7242 */
7243 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7244 return countedLoop(empty(iterations.type()), iterations, init, body);
7245 }
7246
7247 /**
7248 * Constructs a loop that counts over a range of numbers.
7249 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7250 * <p>
7251 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
7252 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
7253 * values of the loop counter.
7254 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
7255 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
7256 * <p>
7257 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7258 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7259 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7260 * <p>
7261 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7262 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7263 * iteration variable.
7264 * The result of the loop handle execution will be the final {@code V} value of that variable
7265 * (or {@code void} if there is no {@code V} variable).
7266 * <p>
7267 * The following rules hold for the argument handles:<ul>
7268 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
7269 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
7270 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7271 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7272 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7273 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7274 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7275 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7276 * of types called the <em>internal parameter list</em>.
7277 * It will constrain the parameter lists of the other loop parts.
7278 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7279 * with no additional {@code A} types, then the internal parameter list is extended by
7280 * the argument types {@code A...} of the {@code end} handle.
7281 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7282 * list {@code (A...)} is called the <em>external parameter list</em>.
7283 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7284 * additional state variable of the loop.
7285 * The body must both accept a leading parameter and return a value of this type {@code V}.
7286 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7287 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7288 * <a href="MethodHandles.html#effid">effectively identical</a>
7289 * to the external parameter list {@code (A...)}.
7290 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7291 * {@linkplain #empty default value}.
7292 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
7293 * effectively identical to the external parameter list {@code (A...)}.
7294 * <li>Likewise, the parameter list of {@code end} must be effectively identical
7295 * to the external parameter list.
7296 * </ul>
7297 * <p>
7298 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7299 * <li>The loop handle's result type is the result type {@code V} of the body.
7300 * <li>The loop handle's parameter types are the types {@code (A...)},
7301 * from the external parameter list.
7302 * </ul>
7303 * <p>
7304 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7305 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7306 * arguments passed to the loop.
7307 * {@snippet lang="java" :
7308 * int start(A...);
7309 * int end(A...);
7310 * V init(A...);
7311 * V body(V, int, A...);
7312 * V countedLoop(A... a...) {
7313 * int e = end(a...);
7314 * int s = start(a...);
7315 * V v = init(a...);
7316 * for (int i = s; i < e; ++i) {
7317 * v = body(v, i, a...);
7318 * }
7319 * return v;
7320 * }
7321 * }
7322 *
7323 * @apiNote The implementation of this method can be expressed as follows:
7324 * {@snippet lang="java" :
7325 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7326 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
7327 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
7328 * // the following semantics:
7329 * // MH_increment: (int limit, int counter) -> counter + 1
7330 * // MH_predicate: (int limit, int counter) -> counter < limit
7331 * Class<?> counterType = start.type().returnType(); // int
7332 * Class<?> returnType = body.type().returnType();
7333 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
7334 * if (returnType != void.class) { // ignore the V variable
7335 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7336 * pred = dropArguments(pred, 1, returnType); // ditto
7337 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
7338 * }
7339 * body = dropArguments(body, 0, counterType); // ignore the limit variable
7340 * MethodHandle[]
7341 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7342 * bodyClause = { init, body }, // v = init(); v = body(v, i)
7343 * indexVar = { start, incr }; // i = start(); i = i + 1
7344 * return loop(loopLimit, bodyClause, indexVar);
7345 * }
7346 * }
7347 *
7348 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
7349 * See above for other constraints.
7350 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
7351 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
7352 * @param init optional initializer, providing the initial value of the loop variable.
7353 * May be {@code null}, implying a default initial value. See above for other constraints.
7354 * @param body body of the loop, which may not be {@code null}.
7355 * It controls the loop parameters and result type in the standard case (see above for details).
7356 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7357 * and may accept any number of additional types.
7358 * See above for other constraints.
7359 *
7360 * @return a method handle representing the loop.
7361 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
7362 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7363 *
7364 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
7365 * @since 9
7366 */
7367 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7368 countedLoopChecks(start, end, init, body);
7369 Class<?> counterType = start.type().returnType(); // int, but who's counting?
7370 Class<?> limitType = end.type().returnType(); // yes, int again
7371 Class<?> returnType = body.type().returnType();
7372 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
7373 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
7374 MethodHandle retv = null;
7375 if (returnType != void.class) {
7376 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7377 pred = dropArguments(pred, 1, returnType); // ditto
7378 retv = dropArguments(identity(returnType), 0, counterType);
7379 }
7380 body = dropArguments(body, 0, counterType); // ignore the limit variable
7381 MethodHandle[]
7382 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7383 bodyClause = { init, body }, // v = init(); v = body(v, i)
7384 indexVar = { start, incr }; // i = start(); i = i + 1
7385 return loop(loopLimit, bodyClause, indexVar);
7386 }
7387
7388 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7389 Objects.requireNonNull(start);
7390 Objects.requireNonNull(end);
7391 Objects.requireNonNull(body);
7392 Class<?> counterType = start.type().returnType();
7393 if (counterType != int.class) {
7394 MethodType expected = start.type().changeReturnType(int.class);
7395 throw misMatchedTypes("start function", start.type(), expected);
7396 } else if (end.type().returnType() != counterType) {
7397 MethodType expected = end.type().changeReturnType(counterType);
7398 throw misMatchedTypes("end function", end.type(), expected);
7399 }
7400 MethodType bodyType = body.type();
7401 Class<?> returnType = bodyType.returnType();
7402 List<Class<?>> innerList = bodyType.parameterList();
7403 // strip leading V value if present
7404 int vsize = (returnType == void.class ? 0 : 1);
7405 if (vsize != 0 && (innerList.isEmpty() || innerList.get(0) != returnType)) {
7406 // argument list has no "V" => error
7407 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7408 throw misMatchedTypes("body function", bodyType, expected);
7409 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
7410 // missing I type => error
7411 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
7412 throw misMatchedTypes("body function", bodyType, expected);
7413 }
7414 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
7415 if (outerList.isEmpty()) {
7416 // special case; take lists from end handle
7417 outerList = end.type().parameterList();
7418 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
7419 }
7420 MethodType expected = methodType(counterType, outerList);
7421 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
7422 throw misMatchedTypes("start parameter types", start.type(), expected);
7423 }
7424 if (end.type() != start.type() &&
7425 !end.type().effectivelyIdenticalParameters(0, outerList)) {
7426 throw misMatchedTypes("end parameter types", end.type(), expected);
7427 }
7428 if (init != null) {
7429 MethodType initType = init.type();
7430 if (initType.returnType() != returnType ||
7431 !initType.effectivelyIdenticalParameters(0, outerList)) {
7432 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7433 }
7434 }
7435 }
7436
7437 /**
7438 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
7439 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7440 * <p>
7441 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
7442 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
7443 * <p>
7444 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7445 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7446 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7447 * <p>
7448 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7449 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7450 * iteration variable.
7451 * The result of the loop handle execution will be the final {@code V} value of that variable
7452 * (or {@code void} if there is no {@code V} variable).
7453 * <p>
7454 * The following rules hold for the argument handles:<ul>
7455 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7456 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
7457 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7458 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
7459 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
7460 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
7461 * of types called the <em>internal parameter list</em>.
7462 * It will constrain the parameter lists of the other loop parts.
7463 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
7464 * with no additional {@code A} types, then the internal parameter list is extended by
7465 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
7466 * single type {@code Iterable} is added and constitutes the {@code A...} list.
7467 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
7468 * list {@code (A...)} is called the <em>external parameter list</em>.
7469 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7470 * additional state variable of the loop.
7471 * The body must both accept a leading parameter and return a value of this type {@code V}.
7472 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7473 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7474 * <a href="MethodHandles.html#effid">effectively identical</a>
7475 * to the external parameter list {@code (A...)}.
7476 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7477 * {@linkplain #empty default value}.
7478 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
7479 * type {@code java.util.Iterator} or a subtype thereof.
7480 * The iterator it produces when the loop is executed will be assumed
7481 * to yield values which can be converted to type {@code T}.
7482 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
7483 * effectively identical to the external parameter list {@code (A...)}.
7484 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
7485 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
7486 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
7487 * handle parameter is adjusted to accept the leading {@code A} type, as if by
7488 * the {@link MethodHandle#asType asType} conversion method.
7489 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
7490 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
7491 * </ul>
7492 * <p>
7493 * The type {@code T} may be either a primitive or reference.
7494 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
7495 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
7496 * as if by the {@link MethodHandle#asType asType} conversion method.
7497 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
7498 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
7499 * <p>
7500 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7501 * <li>The loop handle's result type is the result type {@code V} of the body.
7502 * <li>The loop handle's parameter types are the types {@code (A...)},
7503 * from the external parameter list.
7504 * </ul>
7505 * <p>
7506 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7507 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
7508 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
7509 * {@snippet lang="java" :
7510 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
7511 * V init(A...);
7512 * V body(V,T,A...);
7513 * V iteratedLoop(A... a...) {
7514 * Iterator<T> it = iterator(a...);
7515 * V v = init(a...);
7516 * while (it.hasNext()) {
7517 * T t = it.next();
7518 * v = body(v, t, a...);
7519 * }
7520 * return v;
7521 * }
7522 * }
7523 *
7524 * @apiNote Example:
7525 * {@snippet lang="java" :
7526 * // get an iterator from a list
7527 * static List<String> reverseStep(List<String> r, String e) {
7528 * r.add(0, e);
7529 * return r;
7530 * }
7531 * static List<String> newArrayList() { return new ArrayList<>(); }
7532 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
7533 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
7534 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
7535 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
7536 * assertEquals(reversedList, (List<String>) loop.invoke(list));
7537 * }
7538 *
7539 * @apiNote The implementation of this method can be expressed approximately as follows:
7540 * {@snippet lang="java" :
7541 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7542 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
7543 * Class<?> returnType = body.type().returnType();
7544 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7545 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
7546 * MethodHandle retv = null, step = body, startIter = iterator;
7547 * if (returnType != void.class) {
7548 * // the simple thing first: in (I V A...), drop the I to get V
7549 * retv = dropArguments(identity(returnType), 0, Iterator.class);
7550 * // body type signature (V T A...), internal loop types (I V A...)
7551 * step = swapArguments(body, 0, 1); // swap V <-> T
7552 * }
7553 * if (startIter == null) startIter = MH_getIter;
7554 * MethodHandle[]
7555 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
7556 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
7557 * return loop(iterVar, bodyClause);
7558 * }
7559 * }
7560 *
7561 * @param iterator an optional handle to return the iterator to start the loop.
7562 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
7563 * See above for other constraints.
7564 * @param init optional initializer, providing the initial value of the loop variable.
7565 * May be {@code null}, implying a default initial value. See above for other constraints.
7566 * @param body body of the loop, which may not be {@code null}.
7567 * It controls the loop parameters and result type in the standard case (see above for details).
7568 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
7569 * and may accept any number of additional types.
7570 * See above for other constraints.
7571 *
7572 * @return a method handle embodying the iteration loop functionality.
7573 * @throws NullPointerException if the {@code body} handle is {@code null}.
7574 * @throws IllegalArgumentException if any argument violates the above requirements.
7575 *
7576 * @since 9
7577 */
7578 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7579 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
7580 Class<?> returnType = body.type().returnType();
7581 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
7582 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
7583 MethodHandle startIter;
7584 MethodHandle nextVal;
7585 {
7586 MethodType iteratorType;
7587 if (iterator == null) {
7588 // derive argument type from body, if available, else use Iterable
7589 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
7590 iteratorType = startIter.type().changeParameterType(0, iterableType);
7591 } else {
7592 // force return type to the internal iterator class
7593 iteratorType = iterator.type().changeReturnType(Iterator.class);
7594 startIter = iterator;
7595 }
7596 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7597 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
7598
7599 // perform the asType transforms under an exception transformer, as per spec.:
7600 try {
7601 startIter = startIter.asType(iteratorType);
7602 nextVal = nextRaw.asType(nextValType);
7603 } catch (WrongMethodTypeException ex) {
7604 throw new IllegalArgumentException(ex);
7605 }
7606 }
7607
7608 MethodHandle retv = null, step = body;
7609 if (returnType != void.class) {
7610 // the simple thing first: in (I V A...), drop the I to get V
7611 retv = dropArguments(identity(returnType), 0, Iterator.class);
7612 // body type signature (V T A...), internal loop types (I V A...)
7613 step = swapArguments(body, 0, 1); // swap V <-> T
7614 }
7615
7616 MethodHandle[]
7617 iterVar = { startIter, null, hasNext, retv },
7618 bodyClause = { init, filterArgument(step, 0, nextVal) };
7619 return loop(iterVar, bodyClause);
7620 }
7621
7622 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7623 Objects.requireNonNull(body);
7624 MethodType bodyType = body.type();
7625 Class<?> returnType = bodyType.returnType();
7626 List<Class<?>> internalParamList = bodyType.parameterList();
7627 // strip leading V value if present
7628 int vsize = (returnType == void.class ? 0 : 1);
7629 if (vsize != 0 && (internalParamList.isEmpty() || internalParamList.get(0) != returnType)) {
7630 // argument list has no "V" => error
7631 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7632 throw misMatchedTypes("body function", bodyType, expected);
7633 } else if (internalParamList.size() <= vsize) {
7634 // missing T type => error
7635 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
7636 throw misMatchedTypes("body function", bodyType, expected);
7637 }
7638 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
7639 Class<?> iterableType = null;
7640 if (iterator != null) {
7641 // special case; if the body handle only declares V and T then
7642 // the external parameter list is obtained from iterator handle
7643 if (externalParamList.isEmpty()) {
7644 externalParamList = iterator.type().parameterList();
7645 }
7646 MethodType itype = iterator.type();
7647 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
7648 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
7649 }
7650 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
7651 MethodType expected = methodType(itype.returnType(), externalParamList);
7652 throw misMatchedTypes("iterator parameters", itype, expected);
7653 }
7654 } else {
7655 if (externalParamList.isEmpty()) {
7656 // special case; if the iterator handle is null and the body handle
7657 // only declares V and T then the external parameter list consists
7658 // of Iterable
7659 externalParamList = List.of(Iterable.class);
7660 iterableType = Iterable.class;
7661 } else {
7662 // special case; if the iterator handle is null and the external
7663 // parameter list is not empty then the first parameter must be
7664 // assignable to Iterable
7665 iterableType = externalParamList.get(0);
7666 if (!Iterable.class.isAssignableFrom(iterableType)) {
7667 throw newIllegalArgumentException(
7668 "inferred first loop argument must inherit from Iterable: " + iterableType);
7669 }
7670 }
7671 }
7672 if (init != null) {
7673 MethodType initType = init.type();
7674 if (initType.returnType() != returnType ||
7675 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
7676 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
7677 }
7678 }
7679 return iterableType; // help the caller a bit
7680 }
7681
7682 /*non-public*/
7683 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
7684 // there should be a better way to uncross my wires
7685 int arity = mh.type().parameterCount();
7686 int[] order = new int[arity];
7687 for (int k = 0; k < arity; k++) order[k] = k;
7688 order[i] = j; order[j] = i;
7689 Class<?>[] types = mh.type().parameterArray();
7690 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
7691 MethodType swapType = methodType(mh.type().returnType(), types);
7692 return permuteArguments(mh, swapType, order);
7693 }
7694
7695 /**
7696 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
7697 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
7698 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
7699 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
7700 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
7701 * {@code try-finally} handle.
7702 * <p>
7703 * The {@code cleanup} handle will be passed one or two additional leading arguments.
7704 * The first is the exception thrown during the
7705 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
7706 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
7707 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
7708 * The second argument is not present if the {@code target} handle has a {@code void} return type.
7709 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
7710 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
7711 * <p>
7712 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
7713 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
7714 * two extra leading parameters:<ul>
7715 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
7716 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
7717 * the result from the execution of the {@code target} handle.
7718 * This parameter is not present if the {@code target} returns {@code void}.
7719 * </ul>
7720 * <p>
7721 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
7722 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
7723 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
7724 * the cleanup.
7725 * {@snippet lang="java" :
7726 * V target(A..., B...);
7727 * V cleanup(Throwable, V, A...);
7728 * V adapter(A... a, B... b) {
7729 * V result = (zero value for V);
7730 * Throwable throwable = null;
7731 * try {
7732 * result = target(a..., b...);
7733 * } catch (Throwable t) {
7734 * throwable = t;
7735 * throw t;
7736 * } finally {
7737 * result = cleanup(throwable, result, a...);
7738 * }
7739 * return result;
7740 * }
7741 * }
7742 * <p>
7743 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
7744 * be modified by execution of the target, and so are passed unchanged
7745 * from the caller to the cleanup, if it is invoked.
7746 * <p>
7747 * The target and cleanup must return the same type, even if the cleanup
7748 * always throws.
7749 * To create such a throwing cleanup, compose the cleanup logic
7750 * with {@link #throwException throwException},
7751 * in order to create a method handle of the correct return type.
7752 * <p>
7753 * Note that {@code tryFinally} never converts exceptions into normal returns.
7754 * In rare cases where exceptions must be converted in that way, first wrap
7755 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
7756 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
7757 * <p>
7758 * It is recommended that the first parameter type of {@code cleanup} be
7759 * declared {@code Throwable} rather than a narrower subtype. This ensures
7760 * {@code cleanup} will always be invoked with whatever exception that
7761 * {@code target} throws. Declaring a narrower type may result in a
7762 * {@code ClassCastException} being thrown by the {@code try-finally}
7763 * handle if the type of the exception thrown by {@code target} is not
7764 * assignable to the first parameter type of {@code cleanup}. Note that
7765 * various exception types of {@code VirtualMachineError},
7766 * {@code LinkageError}, and {@code RuntimeException} can in principle be
7767 * thrown by almost any kind of Java code, and a finally clause that
7768 * catches (say) only {@code IOException} would mask any of the others
7769 * behind a {@code ClassCastException}.
7770 *
7771 * @param target the handle whose execution is to be wrapped in a {@code try} block.
7772 * @param cleanup the handle that is invoked in the finally block.
7773 *
7774 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
7775 * @throws NullPointerException if any argument is null
7776 * @throws IllegalArgumentException if {@code cleanup} does not accept
7777 * the required leading arguments, or if the method handle types do
7778 * not match in their return types and their
7779 * corresponding trailing parameters
7780 *
7781 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
7782 * @since 9
7783 */
7784 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
7785 Class<?>[] targetParamTypes = target.type().ptypes();
7786 Class<?> rtype = target.type().returnType();
7787
7788 tryFinallyChecks(target, cleanup);
7789
7790 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
7791 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7792 // target parameter list.
7793 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0, false);
7794
7795 // Ensure that the intrinsic type checks the instance thrown by the
7796 // target against the first parameter of cleanup
7797 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
7798
7799 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
7800 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
7801 }
7802
7803 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
7804 Class<?> rtype = target.type().returnType();
7805 if (rtype != cleanup.type().returnType()) {
7806 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
7807 }
7808 MethodType cleanupType = cleanup.type();
7809 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
7810 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
7811 }
7812 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
7813 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
7814 }
7815 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7816 // target parameter list.
7817 int cleanupArgIndex = rtype == void.class ? 1 : 2;
7818 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
7819 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
7820 cleanup.type(), target.type());
7821 }
7822 }
7823
7824 /**
7825 * Creates a table switch method handle, which can be used to switch over a set of target
7826 * method handles, based on a given target index, called selector.
7827 * <p>
7828 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)},
7829 * and where {@code N} is the number of target method handles, the table switch method
7830 * handle will invoke the n-th target method handle from the list of target method handles.
7831 * <p>
7832 * For a selector value that does not fall in the range {@code [0, N)}, the table switch
7833 * method handle will invoke the given fallback method handle.
7834 * <p>
7835 * All method handles passed to this method must have the same type, with the additional
7836 * requirement that the leading parameter be of type {@code int}. The leading parameter
7837 * represents the selector.
7838 * <p>
7839 * Any trailing parameters present in the type will appear on the returned table switch
7840 * method handle as well. Any arguments assigned to these parameters will be forwarded,
7841 * together with the selector value, to the selected method handle when invoking it.
7842 *
7843 * @apiNote Example:
7844 * The cases each drop the {@code selector} value they are given, and take an additional
7845 * {@code String} argument, which is concatenated (using {@link String#concat(String)})
7846 * to a specific constant label string for each case:
7847 * {@snippet lang="java" :
7848 * MethodHandles.Lookup lookup = MethodHandles.lookup();
7849 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat",
7850 * MethodType.methodType(String.class, String.class));
7851 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class);
7852 *
7853 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: ");
7854 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: ");
7855 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: ");
7856 *
7857 * MethodHandle mhSwitch = MethodHandles.tableSwitch(
7858 * caseDefault,
7859 * case0,
7860 * case1
7861 * );
7862 *
7863 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data"));
7864 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data"));
7865 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data"));
7866 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data"));
7867 * }
7868 *
7869 * @param fallback the fallback method handle that is called when the selector is not
7870 * within the range {@code [0, N)}.
7871 * @param targets array of target method handles.
7872 * @return the table switch method handle.
7873 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any
7874 * any of the elements of the {@code targets} array are
7875 * {@code null}.
7876 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading
7877 * parameter of the fallback handle or any of the target
7878 * handles is not {@code int}, or if the types of
7879 * the fallback handle and all of target handles are
7880 * not the same.
7881 */
7882 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) {
7883 Objects.requireNonNull(fallback);
7884 Objects.requireNonNull(targets);
7885 targets = targets.clone();
7886 MethodType type = tableSwitchChecks(fallback, targets);
7887 return MethodHandleImpl.makeTableSwitch(type, fallback, targets);
7888 }
7889
7890 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) {
7891 if (caseActions.length == 0)
7892 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions));
7893
7894 MethodType expectedType = defaultCase.type();
7895
7896 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class)
7897 throw new IllegalArgumentException(
7898 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions));
7899
7900 for (MethodHandle mh : caseActions) {
7901 Objects.requireNonNull(mh);
7902 if (mh.type() != expectedType)
7903 throw new IllegalArgumentException(
7904 "Case actions must have the same type: " + Arrays.toString(caseActions));
7905 }
7906
7907 return expectedType;
7908 }
7909
7910 /**
7911 * Creates a var handle object, which can be used to dereference a {@linkplain java.lang.foreign.MemorySegment memory segment}
7912 * by viewing its contents as a sequence of the provided value layout.
7913 *
7914 * <p>The provided layout specifies the {@linkplain ValueLayout#carrier() carrier type},
7915 * the {@linkplain ValueLayout#byteSize() byte size},
7916 * the {@linkplain ValueLayout#byteAlignment() byte alignment} and the {@linkplain ValueLayout#order() byte order}
7917 * associated with the returned var handle.
7918 *
7919 * <p>The returned var handle's type is {@code carrier} and the list of coordinate types is
7920 * {@code (MemorySegment, long)}, where the {@code long} coordinate type corresponds to byte offset into
7921 * a given memory segment. The returned var handle accesses bytes at an offset in a given
7922 * memory segment, composing bytes to or from a value of the type {@code carrier} according to the given endianness;
7923 * the alignment constraint (in bytes) for the resulting var handle is given by {@code alignmentBytes}.
7924 *
7925 * <p>As an example, consider the memory layout expressed by a {@link GroupLayout} instance constructed as follows:
7926 * {@snippet lang="java" :
7927 * GroupLayout seq = java.lang.foreign.MemoryLayout.structLayout(
7928 * MemoryLayout.paddingLayout(32),
7929 * ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN).withName("value")
7930 * );
7931 * }
7932 * To access the member layout named {@code value}, we can construct a memory segment view var handle as follows:
7933 * {@snippet lang="java" :
7934 * VarHandle handle = MethodHandles.memorySegmentViewVarHandle(ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN)); //(MemorySegment, long) -> int
7935 * handle = MethodHandles.insertCoordinates(handle, 1, 4); //(MemorySegment) -> int
7936 * }
7937 *
7938 * @apiNote The resulting var handle features certain <i>access mode restrictions</i>,
7939 * which are common to all memory segment view var handles. A memory segment view var handle is associated
7940 * with an access size {@code S} and an alignment constraint {@code B}
7941 * (both expressed in bytes). We say that a memory access operation is <em>fully aligned</em> if it occurs
7942 * at a memory address {@code A} which is compatible with both alignment constraints {@code S} and {@code B}.
7943 * If access is fully aligned then following access modes are supported and are
7944 * guaranteed to support atomic access:
7945 * <ul>
7946 * <li>read write access modes for all {@code T}, with the exception of
7947 * access modes {@code get} and {@code set} for {@code long} and
7948 * {@code double} on 32-bit platforms.
7949 * <li>atomic update access modes for {@code int}, {@code long},
7950 * {@code float}, {@code double} or {@link MemorySegment}.
7951 * (Future major platform releases of the JDK may support additional
7952 * types for certain currently unsupported access modes.)
7953 * <li>numeric atomic update access modes for {@code int}, {@code long} and {@link MemorySegment}.
7954 * (Future major platform releases of the JDK may support additional
7955 * numeric types for certain currently unsupported access modes.)
7956 * <li>bitwise atomic update access modes for {@code int}, {@code long} and {@link MemorySegment}.
7957 * (Future major platform releases of the JDK may support additional
7958 * numeric types for certain currently unsupported access modes.)
7959 * </ul>
7960 *
7961 * If {@code T} is {@code float}, {@code double} or {@link MemorySegment} then atomic
7962 * update access modes compare values using their bitwise representation
7963 * (see {@link Float#floatToRawIntBits},
7964 * {@link Double#doubleToRawLongBits} and {@link MemorySegment#address()}, respectively).
7965 * <p>
7966 * Alternatively, a memory access operation is <em>partially aligned</em> if it occurs at a memory address {@code A}
7967 * which is only compatible with the alignment constraint {@code B}; in such cases, access for anything other than the
7968 * {@code get} and {@code set} access modes will result in an {@code IllegalStateException}. If access is partially aligned,
7969 * atomic access is only guaranteed with respect to the largest power of two that divides the GCD of {@code A} and {@code S}.
7970 * <p>
7971 * In all other cases, we say that a memory access operation is <em>misaligned</em>; in such cases an
7972 * {@code IllegalStateException} is thrown, irrespective of the access mode being used.
7973 * <p>
7974 * Finally, if {@code T} is {@code MemorySegment} all write access modes throw {@link IllegalArgumentException}
7975 * unless the value to be written is a {@linkplain MemorySegment#isNative() native} memory segment.
7976 *
7977 * @param layout the value layout for which a memory access handle is to be obtained.
7978 * @return the new memory segment view var handle.
7979 * @throws IllegalArgumentException if an illegal carrier type is used, or if {@code alignmentBytes} is not a power of two.
7980 * @throws NullPointerException if {@code layout} is {@code null}.
7981 * @see MemoryLayout#varHandle(MemoryLayout.PathElement...)
7982 * @since 19
7983 */
7984 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
7985 public static VarHandle memorySegmentViewVarHandle(ValueLayout layout) {
7986 Objects.requireNonNull(layout);
7987 return Utils.makeSegmentViewVarHandle(layout);
7988 }
7989
7990 /**
7991 * Adapts a target var handle by pre-processing incoming and outgoing values using a pair of filter functions.
7992 * <p>
7993 * When calling e.g. {@link VarHandle#set(Object...)} on the resulting var handle, the incoming value (of type {@code T}, where
7994 * {@code T} is the <em>last</em> parameter type of the first filter function) is processed using the first filter and then passed
7995 * to the target var handle.
7996 * Conversely, when calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the return value obtained from
7997 * the target var handle (of type {@code T}, where {@code T} is the <em>last</em> parameter type of the second filter function)
7998 * is processed using the second filter and returned to the caller. More advanced access mode types, such as
7999 * {@link VarHandle.AccessMode#COMPARE_AND_EXCHANGE} might apply both filters at the same time.
8000 * <p>
8001 * For the boxing and unboxing filters to be well-formed, their types must be of the form {@code (A... , S) -> T} and
8002 * {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle. If this is the case,
8003 * the resulting var handle will have type {@code S} and will feature the additional coordinates {@code A...} (which
8004 * will be appended to the coordinates of the target var handle).
8005 * <p>
8006 * If the boxing and unboxing filters throw any checked exceptions when invoked, the resulting var handle will
8007 * throw an {@link IllegalStateException}.
8008 * <p>
8009 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8010 * atomic access guarantees as those featured by the target var handle.
8011 *
8012 * @param target the target var handle
8013 * @param filterToTarget a filter to convert some type {@code S} into the type of {@code target}
8014 * @param filterFromTarget a filter to convert the type of {@code target} to some type {@code S}
8015 * @return an adapter var handle which accepts a new type, performing the provided boxing/unboxing conversions.
8016 * @throws IllegalArgumentException if {@code filterFromTarget} and {@code filterToTarget} are not well-formed, that is, they have types
8017 * other than {@code (A... , S) -> T} and {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle,
8018 * or if it's determined that either {@code filterFromTarget} or {@code filterToTarget} throws any checked exceptions.
8019 * @throws NullPointerException if any of the arguments is {@code null}.
8020 * @since 19
8021 */
8022 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8023 public static VarHandle filterValue(VarHandle target, MethodHandle filterToTarget, MethodHandle filterFromTarget) {
8024 return VarHandles.filterValue(target, filterToTarget, filterFromTarget);
8025 }
8026
8027 /**
8028 * Adapts a target var handle by pre-processing incoming coordinate values using unary filter functions.
8029 * <p>
8030 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the incoming coordinate values
8031 * starting at position {@code pos} (of type {@code C1, C2 ... Cn}, where {@code C1, C2 ... Cn} are the return types
8032 * of the unary filter functions) are transformed into new values (of type {@code S1, S2 ... Sn}, where {@code S1, S2 ... Sn} are the
8033 * parameter types of the unary filter functions), and then passed (along with any coordinate that was left unaltered
8034 * by the adaptation) to the target var handle.
8035 * <p>
8036 * For the coordinate filters to be well-formed, their types must be of the form {@code S1 -> T1, S2 -> T1 ... Sn -> Tn},
8037 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
8038 * <p>
8039 * If any of the filters throws a checked exception when invoked, the resulting var handle will
8040 * throw an {@link IllegalStateException}.
8041 * <p>
8042 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8043 * atomic access guarantees as those featured by the target var handle.
8044 *
8045 * @param target the target var handle
8046 * @param pos the position of the first coordinate to be transformed
8047 * @param filters the unary functions which are used to transform coordinates starting at position {@code pos}
8048 * @return an adapter var handle which accepts new coordinate types, applying the provided transformation
8049 * to the new coordinate values.
8050 * @throws IllegalArgumentException if the handles in {@code filters} are not well-formed, that is, they have types
8051 * other than {@code S1 -> T1, S2 -> T2, ... Sn -> Tn} where {@code T1, T2 ... Tn} are the coordinate types starting
8052 * at position {@code pos} of the target var handle, if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8053 * or if more filters are provided than the actual number of coordinate types available starting at {@code pos},
8054 * or if it's determined that any of the filters throws any checked exceptions.
8055 * @throws NullPointerException if any of the arguments is {@code null} or {@code filters} contains {@code null}.
8056 * @since 19
8057 */
8058 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8059 public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) {
8060 return VarHandles.filterCoordinates(target, pos, filters);
8061 }
8062
8063 /**
8064 * Provides a target var handle with one or more <em>bound coordinates</em>
8065 * in advance of the var handle's invocation. As a consequence, the resulting var handle will feature less
8066 * coordinate types than the target var handle.
8067 * <p>
8068 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, incoming coordinate values
8069 * are joined with bound coordinate values, and then passed to the target var handle.
8070 * <p>
8071 * For the bound coordinates to be well-formed, their types must be {@code T1, T2 ... Tn },
8072 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
8073 * <p>
8074 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8075 * atomic access guarantees as those featured by the target var handle.
8076 *
8077 * @param target the var handle to invoke after the bound coordinates are inserted
8078 * @param pos the position of the first coordinate to be inserted
8079 * @param values the series of bound coordinates to insert
8080 * @return an adapter var handle which inserts additional coordinates,
8081 * before calling the target var handle
8082 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8083 * or if more values are provided than the actual number of coordinate types available starting at {@code pos}.
8084 * @throws ClassCastException if the bound coordinates in {@code values} are not well-formed, that is, they have types
8085 * other than {@code T1, T2 ... Tn }, where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos}
8086 * of the target var handle.
8087 * @throws NullPointerException if any of the arguments is {@code null} or {@code values} contains {@code null}.
8088 * @since 19
8089 */
8090 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8091 public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) {
8092 return VarHandles.insertCoordinates(target, pos, values);
8093 }
8094
8095 /**
8096 * Provides a var handle which adapts the coordinate values of the target var handle, by re-arranging them
8097 * so that the new coordinates match the provided ones.
8098 * <p>
8099 * The given array controls the reordering.
8100 * Call {@code #I} the number of incoming coordinates (the value
8101 * {@code newCoordinates.size()}), and call {@code #O} the number
8102 * of outgoing coordinates (the number of coordinates associated with the target var handle).
8103 * Then the length of the reordering array must be {@code #O},
8104 * and each element must be a non-negative number less than {@code #I}.
8105 * For every {@code N} less than {@code #O}, the {@code N}-th
8106 * outgoing coordinate will be taken from the {@code I}-th incoming
8107 * coordinate, where {@code I} is {@code reorder[N]}.
8108 * <p>
8109 * No coordinate value conversions are applied.
8110 * The type of each incoming coordinate, as determined by {@code newCoordinates},
8111 * must be identical to the type of the corresponding outgoing coordinate
8112 * in the target var handle.
8113 * <p>
8114 * The reordering array need not specify an actual permutation.
8115 * An incoming coordinate will be duplicated if its index appears
8116 * more than once in the array, and an incoming coordinate will be dropped
8117 * if its index does not appear in the array.
8118 * <p>
8119 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8120 * atomic access guarantees as those featured by the target var handle.
8121 * @param target the var handle to invoke after the coordinates have been reordered
8122 * @param newCoordinates the new coordinate types
8123 * @param reorder an index array which controls the reordering
8124 * @return an adapter var handle which re-arranges the incoming coordinate values,
8125 * before calling the target var handle
8126 * @throws IllegalArgumentException if the index array length is not equal to
8127 * the number of coordinates of the target var handle, or if any index array element is not a valid index for
8128 * a coordinate of {@code newCoordinates}, or if two corresponding coordinate types in
8129 * the target var handle and in {@code newCoordinates} are not identical.
8130 * @throws NullPointerException if any of the arguments is {@code null} or {@code newCoordinates} contains {@code null}.
8131 * @since 19
8132 */
8133 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8134 public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) {
8135 return VarHandles.permuteCoordinates(target, newCoordinates, reorder);
8136 }
8137
8138 /**
8139 * Adapts a target var handle by pre-processing
8140 * a sub-sequence of its coordinate values with a filter (a method handle).
8141 * The pre-processed coordinates are replaced by the result (if any) of the
8142 * filter function and the target var handle is then called on the modified (usually shortened)
8143 * coordinate list.
8144 * <p>
8145 * If {@code R} is the return type of the filter (which cannot be void), the target var handle must accept a value of
8146 * type {@code R} as its coordinate in position {@code pos}, preceded and/or followed by
8147 * any coordinate not passed to the filter.
8148 * No coordinates are reordered, and the result returned from the filter
8149 * replaces (in order) the whole subsequence of coordinates originally
8150 * passed to the adapter.
8151 * <p>
8152 * The argument types (if any) of the filter
8153 * replace zero or one coordinate types of the target var handle, at position {@code pos},
8154 * in the resulting adapted var handle.
8155 * The return type of the filter must be identical to the
8156 * coordinate type of the target var handle at position {@code pos}, and that target var handle
8157 * coordinate is supplied by the return value of the filter.
8158 * <p>
8159 * If any of the filters throws a checked exception when invoked, the resulting var handle will
8160 * throw an {@link IllegalStateException}.
8161 * <p>
8162 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8163 * atomic access guarantees as those featured by the target var handle.
8164 *
8165 * @param target the var handle to invoke after the coordinates have been filtered
8166 * @param pos the position of the coordinate to be filtered
8167 * @param filter the filter method handle
8168 * @return an adapter var handle which filters the incoming coordinate values,
8169 * before calling the target var handle
8170 * @throws IllegalArgumentException if the return type of {@code filter}
8171 * is void, or it is not the same as the {@code pos} coordinate of the target var handle,
8172 * if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8173 * if the resulting var handle's type would have <a href="MethodHandle.html#maxarity">too many coordinates</a>,
8174 * or if it's determined that {@code filter} throws any checked exceptions.
8175 * @throws NullPointerException if any of the arguments is {@code null}.
8176 * @since 19
8177 */
8178 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8179 public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle filter) {
8180 return VarHandles.collectCoordinates(target, pos, filter);
8181 }
8182
8183 /**
8184 * Returns a var handle which will discard some dummy coordinates before delegating to the
8185 * target var handle. As a consequence, the resulting var handle will feature more
8186 * coordinate types than the target var handle.
8187 * <p>
8188 * The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is the arity of the
8189 * target var handle's coordinate types. If {@code pos} is zero, the dummy coordinates will precede
8190 * the target's real arguments; if {@code pos} is <i>N</i> they will come after.
8191 * <p>
8192 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8193 * atomic access guarantees as those featured by the target var handle.
8194 *
8195 * @param target the var handle to invoke after the dummy coordinates are dropped
8196 * @param pos position of the first coordinate to drop (zero for the leftmost)
8197 * @param valueTypes the type(s) of the coordinate(s) to drop
8198 * @return an adapter var handle which drops some dummy coordinates,
8199 * before calling the target var handle
8200 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive.
8201 * @throws NullPointerException if any of the arguments is {@code null} or {@code valueTypes} contains {@code null}.
8202 * @since 19
8203 */
8204 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8205 public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) {
8206 return VarHandles.dropCoordinates(target, pos, valueTypes);
8207 }
8208 }