1 /*
2 * Copyright (c) 2008, 2024, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.access.SharedSecrets;
29 import jdk.internal.misc.Unsafe;
30 import jdk.internal.misc.VM;
31 import jdk.internal.reflect.CallerSensitive;
32 import jdk.internal.reflect.CallerSensitiveAdapter;
33 import jdk.internal.reflect.Reflection;
34 import jdk.internal.util.ClassFileDumper;
35 import jdk.internal.vm.annotation.ForceInline;
36 import sun.invoke.util.ValueConversions;
37 import sun.invoke.util.VerifyAccess;
38 import sun.invoke.util.Wrapper;
39 import sun.reflect.misc.ReflectUtil;
40 import sun.security.util.SecurityConstants;
41
42 import java.lang.classfile.ClassModel;
43 import java.lang.constant.ConstantDescs;
44 import java.lang.invoke.LambdaForm.BasicType;
45 import java.lang.invoke.MethodHandleImpl.Intrinsic;
46 import java.lang.reflect.Constructor;
47 import java.lang.reflect.Field;
48 import java.lang.reflect.Member;
49 import java.lang.reflect.Method;
50 import java.lang.reflect.Modifier;
51 import java.nio.ByteOrder;
52 import java.security.ProtectionDomain;
53 import java.util.ArrayList;
54 import java.util.Arrays;
55 import java.util.BitSet;
56 import java.util.Comparator;
57 import java.util.Iterator;
58 import java.util.List;
59 import java.util.Objects;
60 import java.util.Set;
61 import java.util.concurrent.ConcurrentHashMap;
62 import java.util.stream.Stream;
63
64 import static java.lang.classfile.ClassFile.*;
65 import static java.lang.invoke.LambdaForm.BasicType.V_TYPE;
66 import static java.lang.invoke.MethodHandleNatives.Constants.*;
67 import static java.lang.invoke.MethodHandleStatics.UNSAFE;
68 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
69 import static java.lang.invoke.MethodHandleStatics.newInternalError;
70 import static java.lang.invoke.MethodType.methodType;
71
72 /**
73 * This class consists exclusively of static methods that operate on or return
74 * method handles. They fall into several categories:
75 * <ul>
76 * <li>Lookup methods which help create method handles for methods and fields.
77 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
78 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
79 * </ul>
80 * A lookup, combinator, or factory method will fail and throw an
81 * {@code IllegalArgumentException} if the created method handle's type
82 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
83 *
84 * @author John Rose, JSR 292 EG
85 * @since 1.7
86 */
87 public class MethodHandles {
88
89 private MethodHandles() { } // do not instantiate
90
91 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
92
93 // See IMPL_LOOKUP below.
94
95 //--- Method handle creation from ordinary methods.
96
97 /**
98 * Returns a {@link Lookup lookup object} with
99 * full capabilities to emulate all supported bytecode behaviors of the caller.
100 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller.
101 * Factory methods on the lookup object can create
102 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
103 * for any member that the caller has access to via bytecodes,
104 * including protected and private fields and methods.
105 * This lookup object is created by the original lookup class
106 * and has the {@link Lookup#ORIGINAL ORIGINAL} bit set.
107 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
108 * Do not store it in place where untrusted code can access it.
109 * <p>
110 * This method is caller sensitive, which means that it may return different
111 * values to different callers.
112 * In cases where {@code MethodHandles.lookup} is called from a context where
113 * there is no caller frame on the stack (e.g. when called directly
114 * from a JNI attached thread), {@code IllegalCallerException} is thrown.
115 * To obtain a {@link Lookup lookup object} in such a context, use an auxiliary class that will
116 * implicitly be identified as the caller, or use {@link MethodHandles#publicLookup()}
117 * to obtain a low-privileged lookup instead.
118 * @return a lookup object for the caller of this method, with
119 * {@linkplain Lookup#ORIGINAL original} and
120 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}.
121 * @throws IllegalCallerException if there is no caller frame on the stack.
122 */
123 @CallerSensitive
124 @ForceInline // to ensure Reflection.getCallerClass optimization
125 public static Lookup lookup() {
126 final Class<?> c = Reflection.getCallerClass();
127 if (c == null) {
128 throw new IllegalCallerException("no caller frame");
129 }
130 return new Lookup(c);
131 }
132
133 /**
134 * This lookup method is the alternate implementation of
135 * the lookup method with a leading caller class argument which is
136 * non-caller-sensitive. This method is only invoked by reflection
137 * and method handle.
138 */
139 @CallerSensitiveAdapter
140 private static Lookup lookup(Class<?> caller) {
141 if (caller.getClassLoader() == null) {
142 throw newInternalError("calling lookup() reflectively is not supported: "+caller);
143 }
144 return new Lookup(caller);
145 }
146
147 /**
148 * Returns a {@link Lookup lookup object} which is trusted minimally.
149 * The lookup has the {@code UNCONDITIONAL} mode.
150 * It can only be used to create method handles to public members of
151 * public classes in packages that are exported unconditionally.
152 * <p>
153 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
154 * of this lookup object will be {@link java.lang.Object}.
155 *
156 * @apiNote The use of Object is conventional, and because the lookup modes are
157 * limited, there is no special access provided to the internals of Object, its package
158 * or its module. This public lookup object or other lookup object with
159 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
160 * is not used to determine the lookup context.
161 *
162 * <p style="font-size:smaller;">
163 * <em>Discussion:</em>
164 * The lookup class can be changed to any other class {@code C} using an expression of the form
165 * {@link Lookup#in publicLookup().in(C.class)}.
166 * A public lookup object is always subject to
167 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
168 * Also, it cannot access
169 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
170 * @return a lookup object which is trusted minimally
171 */
172 public static Lookup publicLookup() {
173 return Lookup.PUBLIC_LOOKUP;
174 }
175
176 /**
177 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
178 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>.
179 * The returned lookup object can provide access to classes in modules and packages,
180 * and members of those classes, outside the normal rules of Java access control,
181 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
182 * <p>
183 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
184 * allowed to do deep reflection on module {@code M2} and package of the target class
185 * if and only if all of the following conditions are {@code true}:
186 * <ul>
187 * <li>If there is a security manager, its {@code checkPermission} method is
188 * called to check {@code ReflectPermission("suppressAccessChecks")} and
189 * that must return normally.
190 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess()
191 * full privilege access}. Specifically:
192 * <ul>
193 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
194 * (This is because otherwise there would be no way to ensure the original lookup
195 * creator was a member of any particular module, and so any subsequent checks
196 * for readability and qualified exports would become ineffective.)
197 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
198 * (This is because an application intending to share intra-module access
199 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
200 * deep reflection to its own module.)
201 * </ul>
202 * <li>The target class must be a proper class, not a primitive or array class.
203 * (Thus, {@code M2} is well-defined.)
204 * <li>If the caller module {@code M1} differs from
205 * the target module {@code M2} then both of the following must be true:
206 * <ul>
207 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
208 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
209 * containing the target class to at least {@code M1}.</li>
210 * </ul>
211 * </ul>
212 * <p>
213 * If any of the above checks is violated, this method fails with an
214 * exception.
215 * <p>
216 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
217 * returns a {@code Lookup} on {@code targetClass} with
218 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}
219 * with {@code null} previous lookup class.
220 * <p>
221 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
222 * returns a {@code Lookup} on {@code targetClass} that records
223 * the lookup class of the caller as the new previous lookup class with
224 * {@code PRIVATE} access but no {@code MODULE} access.
225 * <p>
226 * The resulting {@code Lookup} object has no {@code ORIGINAL} access.
227 *
228 * @apiNote The {@code Lookup} object returned by this method is allowed to
229 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
230 * of {@code targetClass}. Extreme caution should be taken when opening a package
231 * to another module as such defined classes have the same full privilege
232 * access as other members in {@code targetClass}'s module.
233 *
234 * @param targetClass the target class
235 * @param caller the caller lookup object
236 * @return a lookup object for the target class, with private access
237 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class
238 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
239 * @throws SecurityException if denied by the security manager
240 * @throws IllegalAccessException if any of the other access checks specified above fails
241 * @since 9
242 * @see Lookup#dropLookupMode
243 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
244 */
245 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
246 if (caller.allowedModes == Lookup.TRUSTED) {
247 return new Lookup(targetClass);
248 }
249
250 @SuppressWarnings("removal")
251 SecurityManager sm = System.getSecurityManager();
252 if (sm != null) sm.checkPermission(SecurityConstants.ACCESS_PERMISSION);
253 if (targetClass.isPrimitive())
254 throw new IllegalArgumentException(targetClass + " is a primitive class");
255 if (targetClass.isArray())
256 throw new IllegalArgumentException(targetClass + " is an array class");
257 // Ensure that we can reason accurately about private and module access.
258 int requireAccess = Lookup.PRIVATE|Lookup.MODULE;
259 if ((caller.lookupModes() & requireAccess) != requireAccess)
260 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode");
261
262 // previous lookup class is never set if it has MODULE access
263 assert caller.previousLookupClass() == null;
264
265 Class<?> callerClass = caller.lookupClass();
266 Module callerModule = callerClass.getModule(); // M1
267 Module targetModule = targetClass.getModule(); // M2
268 Class<?> newPreviousClass = null;
269 int newModes = Lookup.FULL_POWER_MODES & ~Lookup.ORIGINAL;
270
271 if (targetModule != callerModule) {
272 if (!callerModule.canRead(targetModule))
273 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
274 if (targetModule.isNamed()) {
275 String pn = targetClass.getPackageName();
276 assert !pn.isEmpty() : "unnamed package cannot be in named module";
277 if (!targetModule.isOpen(pn, callerModule))
278 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
279 }
280
281 // M2 != M1, set previous lookup class to M1 and drop MODULE access
282 newPreviousClass = callerClass;
283 newModes &= ~Lookup.MODULE;
284 }
285 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
286 }
287
288 /**
289 * Returns the <em>class data</em> associated with the lookup class
290 * of the given {@code caller} lookup object, or {@code null}.
291 *
292 * <p> A hidden class with class data can be created by calling
293 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
294 * Lookup::defineHiddenClassWithClassData}.
295 * This method will cause the static class initializer of the lookup
296 * class of the given {@code caller} lookup object be executed if
297 * it has not been initialized.
298 *
299 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
300 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
301 * {@code null} is returned if this method is called on the lookup object
302 * on these classes.
303 *
304 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
305 * must have {@linkplain Lookup#ORIGINAL original access}
306 * in order to retrieve the class data.
307 *
308 * @apiNote
309 * This method can be called as a bootstrap method for a dynamically computed
310 * constant. A framework can create a hidden class with class data, for
311 * example that can be {@code Class} or {@code MethodHandle} object.
312 * The class data is accessible only to the lookup object
313 * created by the original caller but inaccessible to other members
314 * in the same nest. If a framework passes security sensitive objects
315 * to a hidden class via class data, it is recommended to load the value
316 * of class data as a dynamically computed constant instead of storing
317 * the class data in private static field(s) which are accessible to
318 * other nestmates.
319 *
320 * @param <T> the type to cast the class data object to
321 * @param caller the lookup context describing the class performing the
322 * operation (normally stacked by the JVM)
323 * @param name must be {@link ConstantDescs#DEFAULT_NAME}
324 * ({@code "_"})
325 * @param type the type of the class data
326 * @return the value of the class data if present in the lookup class;
327 * otherwise {@code null}
328 * @throws IllegalArgumentException if name is not {@code "_"}
329 * @throws IllegalAccessException if the lookup context does not have
330 * {@linkplain Lookup#ORIGINAL original} access
331 * @throws ClassCastException if the class data cannot be converted to
332 * the given {@code type}
333 * @throws NullPointerException if {@code caller} or {@code type} argument
334 * is {@code null}
335 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
336 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
337 * @since 16
338 * @jvms 5.5 Initialization
339 */
340 public static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException {
341 Objects.requireNonNull(caller);
342 Objects.requireNonNull(type);
343 if (!ConstantDescs.DEFAULT_NAME.equals(name)) {
344 throw new IllegalArgumentException("name must be \"_\": " + name);
345 }
346
347 if ((caller.lookupModes() & Lookup.ORIGINAL) != Lookup.ORIGINAL) {
348 throw new IllegalAccessException(caller + " does not have ORIGINAL access");
349 }
350
351 Object classdata = classData(caller.lookupClass());
352 if (classdata == null) return null;
353
354 try {
355 return BootstrapMethodInvoker.widenAndCast(classdata, type);
356 } catch (RuntimeException|Error e) {
357 throw e; // let CCE and other runtime exceptions through
358 } catch (Throwable e) {
359 throw new InternalError(e);
360 }
361 }
362
363 /*
364 * Returns the class data set by the VM in the Class::classData field.
365 *
366 * This is also invoked by LambdaForms as it cannot use condy via
367 * MethodHandles::classData due to bootstrapping issue.
368 */
369 static Object classData(Class<?> c) {
370 UNSAFE.ensureClassInitialized(c);
371 return SharedSecrets.getJavaLangAccess().classData(c);
372 }
373
374 /**
375 * Returns the element at the specified index in the
376 * {@linkplain #classData(Lookup, String, Class) class data},
377 * if the class data associated with the lookup class
378 * of the given {@code caller} lookup object is a {@code List}.
379 * If the class data is not present in this lookup class, this method
380 * returns {@code null}.
381 *
382 * <p> A hidden class with class data can be created by calling
383 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
384 * Lookup::defineHiddenClassWithClassData}.
385 * This method will cause the static class initializer of the lookup
386 * class of the given {@code caller} lookup object be executed if
387 * it has not been initialized.
388 *
389 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
390 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
391 * {@code null} is returned if this method is called on the lookup object
392 * on these classes.
393 *
394 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
395 * must have {@linkplain Lookup#ORIGINAL original access}
396 * in order to retrieve the class data.
397 *
398 * @apiNote
399 * This method can be called as a bootstrap method for a dynamically computed
400 * constant. A framework can create a hidden class with class data, for
401 * example that can be {@code List.of(o1, o2, o3....)} containing more than
402 * one object and use this method to load one element at a specific index.
403 * The class data is accessible only to the lookup object
404 * created by the original caller but inaccessible to other members
405 * in the same nest. If a framework passes security sensitive objects
406 * to a hidden class via class data, it is recommended to load the value
407 * of class data as a dynamically computed constant instead of storing
408 * the class data in private static field(s) which are accessible to other
409 * nestmates.
410 *
411 * @param <T> the type to cast the result object to
412 * @param caller the lookup context describing the class performing the
413 * operation (normally stacked by the JVM)
414 * @param name must be {@link java.lang.constant.ConstantDescs#DEFAULT_NAME}
415 * ({@code "_"})
416 * @param type the type of the element at the given index in the class data
417 * @param index index of the element in the class data
418 * @return the element at the given index in the class data
419 * if the class data is present; otherwise {@code null}
420 * @throws IllegalArgumentException if name is not {@code "_"}
421 * @throws IllegalAccessException if the lookup context does not have
422 * {@linkplain Lookup#ORIGINAL original} access
423 * @throws ClassCastException if the class data cannot be converted to {@code List}
424 * or the element at the specified index cannot be converted to the given type
425 * @throws IndexOutOfBoundsException if the index is out of range
426 * @throws NullPointerException if {@code caller} or {@code type} argument is
427 * {@code null}; or if unboxing operation fails because
428 * the element at the given index is {@code null}
429 *
430 * @since 16
431 * @see #classData(Lookup, String, Class)
432 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
433 */
434 public static <T> T classDataAt(Lookup caller, String name, Class<T> type, int index)
435 throws IllegalAccessException
436 {
437 @SuppressWarnings("unchecked")
438 List<Object> classdata = (List<Object>)classData(caller, name, List.class);
439 if (classdata == null) return null;
440
441 try {
442 Object element = classdata.get(index);
443 return BootstrapMethodInvoker.widenAndCast(element, type);
444 } catch (RuntimeException|Error e) {
445 throw e; // let specified exceptions and other runtime exceptions/errors through
446 } catch (Throwable e) {
447 throw new InternalError(e);
448 }
449 }
450
451 /**
452 * Performs an unchecked "crack" of a
453 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
454 * The result is as if the user had obtained a lookup object capable enough
455 * to crack the target method handle, called
456 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
457 * on the target to obtain its symbolic reference, and then called
458 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
459 * to resolve the symbolic reference to a member.
460 * <p>
461 * If there is a security manager, its {@code checkPermission} method
462 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
463 * @param <T> the desired type of the result, either {@link Member} or a subtype
464 * @param target a direct method handle to crack into symbolic reference components
465 * @param expected a class object representing the desired result type {@code T}
466 * @return a reference to the method, constructor, or field object
467 * @throws SecurityException if the caller is not privileged to call {@code setAccessible}
468 * @throws NullPointerException if either argument is {@code null}
469 * @throws IllegalArgumentException if the target is not a direct method handle
470 * @throws ClassCastException if the member is not of the expected type
471 * @since 1.8
472 */
473 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) {
474 @SuppressWarnings("removal")
475 SecurityManager smgr = System.getSecurityManager();
476 if (smgr != null) smgr.checkPermission(SecurityConstants.ACCESS_PERMISSION);
477 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
478 return lookup.revealDirect(target).reflectAs(expected, lookup);
479 }
480
481 /**
482 * A <em>lookup object</em> is a factory for creating method handles,
483 * when the creation requires access checking.
484 * Method handles do not perform
485 * access checks when they are called, but rather when they are created.
486 * Therefore, method handle access
487 * restrictions must be enforced when a method handle is created.
488 * The caller class against which those restrictions are enforced
489 * is known as the {@linkplain #lookupClass() lookup class}.
490 * <p>
491 * A lookup class which needs to create method handles will call
492 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
493 * When the {@code Lookup} factory object is created, the identity of the lookup class is
494 * determined, and securely stored in the {@code Lookup} object.
495 * The lookup class (or its delegates) may then use factory methods
496 * on the {@code Lookup} object to create method handles for access-checked members.
497 * This includes all methods, constructors, and fields which are allowed to the lookup class,
498 * even private ones.
499 *
500 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
501 * The factory methods on a {@code Lookup} object correspond to all major
502 * use cases for methods, constructors, and fields.
503 * Each method handle created by a factory method is the functional
504 * equivalent of a particular <em>bytecode behavior</em>.
505 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of
506 * the Java Virtual Machine Specification.)
507 * Here is a summary of the correspondence between these factory methods and
508 * the behavior of the resulting method handles:
509 * <table class="striped">
510 * <caption style="display:none">lookup method behaviors</caption>
511 * <thead>
512 * <tr>
513 * <th scope="col"><a id="equiv"></a>lookup expression</th>
514 * <th scope="col">member</th>
515 * <th scope="col">bytecode behavior</th>
516 * </tr>
517 * </thead>
518 * <tbody>
519 * <tr>
520 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
521 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
522 * </tr>
523 * <tr>
524 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
525 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
526 * </tr>
527 * <tr>
528 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
529 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
530 * </tr>
531 * <tr>
532 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
533 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
534 * </tr>
535 * <tr>
536 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
537 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
538 * </tr>
539 * <tr>
540 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
541 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
542 * </tr>
543 * <tr>
544 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
545 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
546 * </tr>
547 * <tr>
548 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
549 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
550 * </tr>
551 * <tr>
552 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
553 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
554 * </tr>
555 * <tr>
556 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
557 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
558 * </tr>
559 * <tr>
560 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
561 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
562 * </tr>
563 * <tr>
564 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
565 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
566 * </tr>
567 * <tr>
568 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th>
569 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
570 * </tr>
571 * <tr>
572 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
573 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
574 * </tr>
575 * </tbody>
576 * </table>
577 *
578 * Here, the type {@code C} is the class or interface being searched for a member,
579 * documented as a parameter named {@code refc} in the lookup methods.
580 * The method type {@code MT} is composed from the return type {@code T}
581 * and the sequence of argument types {@code A*}.
582 * The constructor also has a sequence of argument types {@code A*} and
583 * is deemed to return the newly-created object of type {@code C}.
584 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
585 * The formal parameter {@code this} stands for the self-reference of type {@code C};
586 * if it is present, it is always the leading argument to the method handle invocation.
587 * (In the case of some {@code protected} members, {@code this} may be
588 * restricted in type to the lookup class; see below.)
589 * The name {@code arg} stands for all the other method handle arguments.
590 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
591 * stands for a null reference if the accessed method or field is static,
592 * and {@code this} otherwise.
593 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
594 * for reflective objects corresponding to the given members declared in type {@code C}.
595 * <p>
596 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
597 * as if by {@code ldc CONSTANT_Class}.
598 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
599 * <p>
600 * In cases where the given member is of variable arity (i.e., a method or constructor)
601 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
602 * In all other cases, the returned method handle will be of fixed arity.
603 * <p style="font-size:smaller;">
604 * <em>Discussion:</em>
605 * The equivalence between looked-up method handles and underlying
606 * class members and bytecode behaviors
607 * can break down in a few ways:
608 * <ul style="font-size:smaller;">
609 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
610 * the lookup can still succeed, even when there is no equivalent
611 * Java expression or bytecoded constant.
612 * <li>Likewise, if {@code T} or {@code MT}
613 * is not symbolically accessible from the lookup class's loader,
614 * the lookup can still succeed.
615 * For example, lookups for {@code MethodHandle.invokeExact} and
616 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
617 * <li>If there is a security manager installed, it can forbid the lookup
618 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
619 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
620 * constant is not subject to security manager checks.
621 * <li>If the looked-up method has a
622 * <a href="MethodHandle.html#maxarity">very large arity</a>,
623 * the method handle creation may fail with an
624 * {@code IllegalArgumentException}, due to the method handle type having
625 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
626 * </ul>
627 *
628 * <h2><a id="access"></a>Access checking</h2>
629 * Access checks are applied in the factory methods of {@code Lookup},
630 * when a method handle is created.
631 * This is a key difference from the Core Reflection API, since
632 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
633 * performs access checking against every caller, on every call.
634 * <p>
635 * All access checks start from a {@code Lookup} object, which
636 * compares its recorded lookup class against all requests to
637 * create method handles.
638 * A single {@code Lookup} object can be used to create any number
639 * of access-checked method handles, all checked against a single
640 * lookup class.
641 * <p>
642 * A {@code Lookup} object can be shared with other trusted code,
643 * such as a metaobject protocol.
644 * A shared {@code Lookup} object delegates the capability
645 * to create method handles on private members of the lookup class.
646 * Even if privileged code uses the {@code Lookup} object,
647 * the access checking is confined to the privileges of the
648 * original lookup class.
649 * <p>
650 * A lookup can fail, because
651 * the containing class is not accessible to the lookup class, or
652 * because the desired class member is missing, or because the
653 * desired class member is not accessible to the lookup class, or
654 * because the lookup object is not trusted enough to access the member.
655 * In the case of a field setter function on a {@code final} field,
656 * finality enforcement is treated as a kind of access control,
657 * and the lookup will fail, except in special cases of
658 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
659 * In any of these cases, a {@code ReflectiveOperationException} will be
660 * thrown from the attempted lookup. The exact class will be one of
661 * the following:
662 * <ul>
663 * <li>NoSuchMethodException — if a method is requested but does not exist
664 * <li>NoSuchFieldException — if a field is requested but does not exist
665 * <li>IllegalAccessException — if the member exists but an access check fails
666 * </ul>
667 * <p>
668 * In general, the conditions under which a method handle may be
669 * looked up for a method {@code M} are no more restrictive than the conditions
670 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
671 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
672 * a method handle lookup will generally raise a corresponding
673 * checked exception, such as {@code NoSuchMethodException}.
674 * And the effect of invoking the method handle resulting from the lookup
675 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
676 * to executing the compiled, verified, and resolved call to {@code M}.
677 * The same point is true of fields and constructors.
678 * <p style="font-size:smaller;">
679 * <em>Discussion:</em>
680 * Access checks only apply to named and reflected methods,
681 * constructors, and fields.
682 * Other method handle creation methods, such as
683 * {@link MethodHandle#asType MethodHandle.asType},
684 * do not require any access checks, and are used
685 * independently of any {@code Lookup} object.
686 * <p>
687 * If the desired member is {@code protected}, the usual JVM rules apply,
688 * including the requirement that the lookup class must either be in the
689 * same package as the desired member, or must inherit that member.
690 * (See the Java Virtual Machine Specification, sections {@jvms
691 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.)
692 * In addition, if the desired member is a non-static field or method
693 * in a different package, the resulting method handle may only be applied
694 * to objects of the lookup class or one of its subclasses.
695 * This requirement is enforced by narrowing the type of the leading
696 * {@code this} parameter from {@code C}
697 * (which will necessarily be a superclass of the lookup class)
698 * to the lookup class itself.
699 * <p>
700 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
701 * that the receiver argument must match both the resolved method <em>and</em>
702 * the current class. Again, this requirement is enforced by narrowing the
703 * type of the leading parameter to the resulting method handle.
704 * (See the Java Virtual Machine Specification, section {@jvms 4.10.1.9}.)
705 * <p>
706 * The JVM represents constructors and static initializer blocks as internal methods
707 * with special names ({@value ConstantDescs#INIT_NAME} and {@value
708 * ConstantDescs#CLASS_INIT_NAME}).
709 * The internal syntax of invocation instructions allows them to refer to such internal
710 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
711 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
712 * <p>
713 * If the relationship between nested types is expressed directly through the
714 * {@code NestHost} and {@code NestMembers} attributes
715 * (see the Java Virtual Machine Specification, sections {@jvms
716 * 4.7.28} and {@jvms 4.7.29}),
717 * then the associated {@code Lookup} object provides direct access to
718 * the lookup class and all of its nestmates
719 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
720 * Otherwise, access between nested classes is obtained by the Java compiler creating
721 * a wrapper method to access a private method of another class in the same nest.
722 * For example, a nested class {@code C.D}
723 * can access private members within other related classes such as
724 * {@code C}, {@code C.D.E}, or {@code C.B},
725 * but the Java compiler may need to generate wrapper methods in
726 * those related classes. In such cases, a {@code Lookup} object on
727 * {@code C.E} would be unable to access those private members.
728 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
729 * which can transform a lookup on {@code C.E} into one on any of those other
730 * classes, without special elevation of privilege.
731 * <p>
732 * The accesses permitted to a given lookup object may be limited,
733 * according to its set of {@link #lookupModes lookupModes},
734 * to a subset of members normally accessible to the lookup class.
735 * For example, the {@link MethodHandles#publicLookup publicLookup}
736 * method produces a lookup object which is only allowed to access
737 * public members in public classes of exported packages.
738 * The caller sensitive method {@link MethodHandles#lookup lookup}
739 * produces a lookup object with full capabilities relative to
740 * its caller class, to emulate all supported bytecode behaviors.
741 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
742 * with fewer access modes than the original lookup object.
743 *
744 * <p style="font-size:smaller;">
745 * <a id="privacc"></a>
746 * <em>Discussion of private and module access:</em>
747 * We say that a lookup has <em>private access</em>
748 * if its {@linkplain #lookupModes lookup modes}
749 * include the possibility of accessing {@code private} members
750 * (which includes the private members of nestmates).
751 * As documented in the relevant methods elsewhere,
752 * only lookups with private access possess the following capabilities:
753 * <ul style="font-size:smaller;">
754 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
755 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
756 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
757 * for classes accessible to the lookup class
758 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
759 * within the same package member
760 * </ul>
761 * <p style="font-size:smaller;">
762 * Similarly, a lookup with module access ensures that the original lookup creator was
763 * a member in the same module as the lookup class.
764 * <p style="font-size:smaller;">
765 * Private and module access are independently determined modes; a lookup may have
766 * either or both or neither. A lookup which possesses both access modes is said to
767 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}.
768 * <p style="font-size:smaller;">
769 * A lookup with <em>original access</em> ensures that this lookup is created by
770 * the original lookup class and the bootstrap method invoked by the VM.
771 * Such a lookup with original access also has private and module access
772 * which has the following additional capability:
773 * <ul style="font-size:smaller;">
774 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
775 * such as {@code Class.forName}
776 * <li>obtain the {@linkplain MethodHandles#classData(Lookup, String, Class)
777 * class data} associated with the lookup class</li>
778 * </ul>
779 * <p style="font-size:smaller;">
780 * Each of these permissions is a consequence of the fact that a lookup object
781 * with private access can be securely traced back to an originating class,
782 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
783 * can be reliably determined and emulated by method handles.
784 *
785 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
786 * When a lookup class in one module {@code M1} accesses a class in another module
787 * {@code M2}, extra access checking is performed beyond the access mode bits.
788 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
789 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
790 * and when the type is in a package of {@code M2} that is exported to
791 * at least {@code M1}.
792 * <p>
793 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
794 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
795 * MethodHandles.privateLookupIn} methods.
796 * Teleporting across modules will always record the original lookup class as
797 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
798 * and drops {@link Lookup#MODULE MODULE} access.
799 * If the target class is in the same module as the lookup class {@code C},
800 * then the target class becomes the new lookup class
801 * and there is no change to the previous lookup class.
802 * If the target class is in a different module from {@code M1} ({@code C}'s module),
803 * {@code C} becomes the new previous lookup class
804 * and the target class becomes the new lookup class.
805 * In that case, if there was already a previous lookup class in {@code M0},
806 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
807 * drops all privileges.
808 * For example,
809 * {@snippet lang="java" :
810 * Lookup lookup = MethodHandles.lookup(); // in class C
811 * Lookup lookup2 = lookup.in(D.class);
812 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
813 * }
814 * <p>
815 * The {@link #lookup()} factory method produces a {@code Lookup} object
816 * with {@code null} previous lookup class.
817 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
818 * to class {@code D} without elevation of privileges.
819 * If {@code C} and {@code D} are in the same module,
820 * {@code lookup2} records {@code D} as the new lookup class and keeps the
821 * same previous lookup class as the original {@code lookup}, or
822 * {@code null} if not present.
823 * <p>
824 * When a {@code Lookup} teleports from a class
825 * in one nest to another nest, {@code PRIVATE} access is dropped.
826 * When a {@code Lookup} teleports from a class in one package to
827 * another package, {@code PACKAGE} access is dropped.
828 * When a {@code Lookup} teleports from a class in one module to another module,
829 * {@code MODULE} access is dropped.
830 * Teleporting across modules drops the ability to access non-exported classes
831 * in both the module of the new lookup class and the module of the old lookup class
832 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
833 * A {@code Lookup} can teleport back and forth to a class in the module of
834 * the lookup class and the module of the previous class lookup.
835 * Teleporting across modules can only decrease access but cannot increase it.
836 * Teleporting to some third module drops all accesses.
837 * <p>
838 * In the above example, if {@code C} and {@code D} are in different modules,
839 * {@code lookup2} records {@code D} as its lookup class and
840 * {@code C} as its previous lookup class and {@code lookup2} has only
841 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
842 * {@code C}'s module and {@code D}'s module.
843 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
844 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
845 * class {@code D} is recorded as its previous lookup class.
846 * <p>
847 * Teleporting across modules restricts access to the public types that
848 * both the lookup class and the previous lookup class can equally access
849 * (see below).
850 * <p>
851 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
852 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
853 * and produce a new {@code Lookup} with <a href="#privacc">private access</a>
854 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
855 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
856 * to call {@code privateLookupIn}.
857 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
858 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
859 * produces a new {@code Lookup} on {@code T} with full capabilities.
860 * A {@code lookup} on {@code C} is also allowed
861 * to do deep reflection on {@code T} in another module {@code M2} if
862 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
863 * the package containing {@code T} to at least {@code M1}.
864 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
865 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
866 * The resulting {@code Lookup} can be used to do member lookup or teleport
867 * to another lookup class by calling {@link #in Lookup::in}. But
868 * it cannot be used to obtain another private {@code Lookup} by calling
869 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
870 * because it has no {@code MODULE} access.
871 * <p>
872 * The {@code Lookup} object returned by {@code privateLookupIn} is allowed to
873 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
874 * of {@code T}. Extreme caution should be taken when opening a package
875 * to another module as such defined classes have the same full privilege
876 * access as other members in {@code M2}.
877 *
878 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
879 *
880 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
881 * allows cross-module access. The access checking is performed with respect
882 * to both the lookup class and the previous lookup class if present.
883 * <p>
884 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
885 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
886 * exported unconditionally}.
887 * <p>
888 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
889 * the lookup with {@link #PUBLIC} mode can access all public types in modules
890 * that are readable to {@code M1} and the type is in a package that is exported
891 * at least to {@code M1}.
892 * <p>
893 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
894 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
895 * the intersection of all public types that are accessible to {@code M1}
896 * with all public types that are accessible to {@code M0}. {@code M0}
897 * reads {@code M1} and hence the set of accessible types includes:
898 *
899 * <ul>
900 * <li>unconditional-exported packages from {@code M1}</li>
901 * <li>unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</li>
902 * <li>
903 * unconditional-exported packages from a third module {@code M2}if both {@code M0}
904 * and {@code M1} read {@code M2}
905 * </li>
906 * <li>qualified-exported packages from {@code M1} to {@code M0}</li>
907 * <li>qualified-exported packages from {@code M0} to {@code M1} if {@code M1} reads {@code M0}</li>
908 * <li>
909 * qualified-exported packages from a third module {@code M2} to both {@code M0} and
910 * {@code M1} if both {@code M0} and {@code M1} read {@code M2}
911 * </li>
912 * </ul>
913 *
914 * <h2><a id="access-modes"></a>Access modes</h2>
915 *
916 * The table below shows the access modes of a {@code Lookup} produced by
917 * any of the following factory or transformation methods:
918 * <ul>
919 * <li>{@link #lookup() MethodHandles::lookup}</li>
920 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li>
921 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li>
922 * <li>{@link Lookup#in Lookup::in}</li>
923 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li>
924 * </ul>
925 *
926 * <table class="striped">
927 * <caption style="display:none">
928 * Access mode summary
929 * </caption>
930 * <thead>
931 * <tr>
932 * <th scope="col">Lookup object</th>
933 * <th style="text-align:center">original</th>
934 * <th style="text-align:center">protected</th>
935 * <th style="text-align:center">private</th>
936 * <th style="text-align:center">package</th>
937 * <th style="text-align:center">module</th>
938 * <th style="text-align:center">public</th>
939 * </tr>
940 * </thead>
941 * <tbody>
942 * <tr>
943 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
944 * <td style="text-align:center">ORI</td>
945 * <td style="text-align:center">PRO</td>
946 * <td style="text-align:center">PRI</td>
947 * <td style="text-align:center">PAC</td>
948 * <td style="text-align:center">MOD</td>
949 * <td style="text-align:center">1R</td>
950 * </tr>
951 * <tr>
952 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
953 * <td></td>
954 * <td></td>
955 * <td></td>
956 * <td style="text-align:center">PAC</td>
957 * <td style="text-align:center">MOD</td>
958 * <td style="text-align:center">1R</td>
959 * </tr>
960 * <tr>
961 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
962 * <td></td>
963 * <td></td>
964 * <td></td>
965 * <td></td>
966 * <td style="text-align:center">MOD</td>
967 * <td style="text-align:center">1R</td>
968 * </tr>
969 * <tr>
970 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
971 * <td></td>
972 * <td></td>
973 * <td></td>
974 * <td></td>
975 * <td></td>
976 * <td style="text-align:center">2R</td>
977 * </tr>
978 * <tr>
979 * <th scope="row" style="text-align:left">{@code CL.in(D).in(C)} hop back to module</th>
980 * <td></td>
981 * <td></td>
982 * <td></td>
983 * <td></td>
984 * <td></td>
985 * <td style="text-align:center">2R</td>
986 * </tr>
987 * <tr>
988 * <th scope="row" style="text-align:left">{@code PRI1 = privateLookupIn(C1,CL)}</th>
989 * <td></td>
990 * <td style="text-align:center">PRO</td>
991 * <td style="text-align:center">PRI</td>
992 * <td style="text-align:center">PAC</td>
993 * <td style="text-align:center">MOD</td>
994 * <td style="text-align:center">1R</td>
995 * </tr>
996 * <tr>
997 * <th scope="row" style="text-align:left">{@code PRI1a = privateLookupIn(C,PRI1)}</th>
998 * <td></td>
999 * <td style="text-align:center">PRO</td>
1000 * <td style="text-align:center">PRI</td>
1001 * <td style="text-align:center">PAC</td>
1002 * <td style="text-align:center">MOD</td>
1003 * <td style="text-align:center">1R</td>
1004 * </tr>
1005 * <tr>
1006 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} same package</th>
1007 * <td></td>
1008 * <td></td>
1009 * <td></td>
1010 * <td style="text-align:center">PAC</td>
1011 * <td style="text-align:center">MOD</td>
1012 * <td style="text-align:center">1R</td>
1013 * </tr>
1014 * <tr>
1015 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} different package</th>
1016 * <td></td>
1017 * <td></td>
1018 * <td></td>
1019 * <td></td>
1020 * <td style="text-align:center">MOD</td>
1021 * <td style="text-align:center">1R</td>
1022 * </tr>
1023 * <tr>
1024 * <th scope="row" style="text-align:left">{@code PRI1.in(D)} different module</th>
1025 * <td></td>
1026 * <td></td>
1027 * <td></td>
1028 * <td></td>
1029 * <td></td>
1030 * <td style="text-align:center">2R</td>
1031 * </tr>
1032 * <tr>
1033 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PROTECTED)}</th>
1034 * <td></td>
1035 * <td></td>
1036 * <td style="text-align:center">PRI</td>
1037 * <td style="text-align:center">PAC</td>
1038 * <td style="text-align:center">MOD</td>
1039 * <td style="text-align:center">1R</td>
1040 * </tr>
1041 * <tr>
1042 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PRIVATE)}</th>
1043 * <td></td>
1044 * <td></td>
1045 * <td></td>
1046 * <td style="text-align:center">PAC</td>
1047 * <td style="text-align:center">MOD</td>
1048 * <td style="text-align:center">1R</td>
1049 * </tr>
1050 * <tr>
1051 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PACKAGE)}</th>
1052 * <td></td>
1053 * <td></td>
1054 * <td></td>
1055 * <td></td>
1056 * <td style="text-align:center">MOD</td>
1057 * <td style="text-align:center">1R</td>
1058 * </tr>
1059 * <tr>
1060 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(MODULE)}</th>
1061 * <td></td>
1062 * <td></td>
1063 * <td></td>
1064 * <td></td>
1065 * <td></td>
1066 * <td style="text-align:center">1R</td>
1067 * </tr>
1068 * <tr>
1069 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PUBLIC)}</th>
1070 * <td></td>
1071 * <td></td>
1072 * <td></td>
1073 * <td></td>
1074 * <td></td>
1075 * <td style="text-align:center">none</td>
1076 * <tr>
1077 * <th scope="row" style="text-align:left">{@code PRI2 = privateLookupIn(D,CL)}</th>
1078 * <td></td>
1079 * <td style="text-align:center">PRO</td>
1080 * <td style="text-align:center">PRI</td>
1081 * <td style="text-align:center">PAC</td>
1082 * <td></td>
1083 * <td style="text-align:center">2R</td>
1084 * </tr>
1085 * <tr>
1086 * <th scope="row" style="text-align:left">{@code privateLookupIn(D,PRI1)}</th>
1087 * <td></td>
1088 * <td style="text-align:center">PRO</td>
1089 * <td style="text-align:center">PRI</td>
1090 * <td style="text-align:center">PAC</td>
1091 * <td></td>
1092 * <td style="text-align:center">2R</td>
1093 * </tr>
1094 * <tr>
1095 * <th scope="row" style="text-align:left">{@code privateLookupIn(C,PRI2)} fails</th>
1096 * <td></td>
1097 * <td></td>
1098 * <td></td>
1099 * <td></td>
1100 * <td></td>
1101 * <td style="text-align:center">IAE</td>
1102 * </tr>
1103 * <tr>
1104 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} same package</th>
1105 * <td></td>
1106 * <td></td>
1107 * <td></td>
1108 * <td style="text-align:center">PAC</td>
1109 * <td></td>
1110 * <td style="text-align:center">2R</td>
1111 * </tr>
1112 * <tr>
1113 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} different package</th>
1114 * <td></td>
1115 * <td></td>
1116 * <td></td>
1117 * <td></td>
1118 * <td></td>
1119 * <td style="text-align:center">2R</td>
1120 * </tr>
1121 * <tr>
1122 * <th scope="row" style="text-align:left">{@code PRI2.in(C1)} hop back to module</th>
1123 * <td></td>
1124 * <td></td>
1125 * <td></td>
1126 * <td></td>
1127 * <td></td>
1128 * <td style="text-align:center">2R</td>
1129 * </tr>
1130 * <tr>
1131 * <th scope="row" style="text-align:left">{@code PRI2.in(E)} hop to third module</th>
1132 * <td></td>
1133 * <td></td>
1134 * <td></td>
1135 * <td></td>
1136 * <td></td>
1137 * <td style="text-align:center">none</td>
1138 * </tr>
1139 * <tr>
1140 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PROTECTED)}</th>
1141 * <td></td>
1142 * <td></td>
1143 * <td style="text-align:center">PRI</td>
1144 * <td style="text-align:center">PAC</td>
1145 * <td></td>
1146 * <td style="text-align:center">2R</td>
1147 * </tr>
1148 * <tr>
1149 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PRIVATE)}</th>
1150 * <td></td>
1151 * <td></td>
1152 * <td></td>
1153 * <td style="text-align:center">PAC</td>
1154 * <td></td>
1155 * <td style="text-align:center">2R</td>
1156 * </tr>
1157 * <tr>
1158 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PACKAGE)}</th>
1159 * <td></td>
1160 * <td></td>
1161 * <td></td>
1162 * <td></td>
1163 * <td></td>
1164 * <td style="text-align:center">2R</td>
1165 * </tr>
1166 * <tr>
1167 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(MODULE)}</th>
1168 * <td></td>
1169 * <td></td>
1170 * <td></td>
1171 * <td></td>
1172 * <td></td>
1173 * <td style="text-align:center">2R</td>
1174 * </tr>
1175 * <tr>
1176 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PUBLIC)}</th>
1177 * <td></td>
1178 * <td></td>
1179 * <td></td>
1180 * <td></td>
1181 * <td></td>
1182 * <td style="text-align:center">none</td>
1183 * </tr>
1184 * <tr>
1185 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PROTECTED)}</th>
1186 * <td></td>
1187 * <td></td>
1188 * <td style="text-align:center">PRI</td>
1189 * <td style="text-align:center">PAC</td>
1190 * <td style="text-align:center">MOD</td>
1191 * <td style="text-align:center">1R</td>
1192 * </tr>
1193 * <tr>
1194 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PRIVATE)}</th>
1195 * <td></td>
1196 * <td></td>
1197 * <td></td>
1198 * <td style="text-align:center">PAC</td>
1199 * <td style="text-align:center">MOD</td>
1200 * <td style="text-align:center">1R</td>
1201 * </tr>
1202 * <tr>
1203 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PACKAGE)}</th>
1204 * <td></td>
1205 * <td></td>
1206 * <td></td>
1207 * <td></td>
1208 * <td style="text-align:center">MOD</td>
1209 * <td style="text-align:center">1R</td>
1210 * </tr>
1211 * <tr>
1212 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(MODULE)}</th>
1213 * <td></td>
1214 * <td></td>
1215 * <td></td>
1216 * <td></td>
1217 * <td></td>
1218 * <td style="text-align:center">1R</td>
1219 * </tr>
1220 * <tr>
1221 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PUBLIC)}</th>
1222 * <td></td>
1223 * <td></td>
1224 * <td></td>
1225 * <td></td>
1226 * <td></td>
1227 * <td style="text-align:center">none</td>
1228 * </tr>
1229 * <tr>
1230 * <th scope="row" style="text-align:left">{@code PUB = publicLookup()}</th>
1231 * <td></td>
1232 * <td></td>
1233 * <td></td>
1234 * <td></td>
1235 * <td></td>
1236 * <td style="text-align:center">U</td>
1237 * </tr>
1238 * <tr>
1239 * <th scope="row" style="text-align:left">{@code PUB.in(D)} different module</th>
1240 * <td></td>
1241 * <td></td>
1242 * <td></td>
1243 * <td></td>
1244 * <td></td>
1245 * <td style="text-align:center">U</td>
1246 * </tr>
1247 * <tr>
1248 * <th scope="row" style="text-align:left">{@code PUB.in(D).in(E)} third module</th>
1249 * <td></td>
1250 * <td></td>
1251 * <td></td>
1252 * <td></td>
1253 * <td></td>
1254 * <td style="text-align:center">U</td>
1255 * </tr>
1256 * <tr>
1257 * <th scope="row" style="text-align:left">{@code PUB.dropLookupMode(UNCONDITIONAL)}</th>
1258 * <td></td>
1259 * <td></td>
1260 * <td></td>
1261 * <td></td>
1262 * <td></td>
1263 * <td style="text-align:center">none</td>
1264 * </tr>
1265 * <tr>
1266 * <th scope="row" style="text-align:left">{@code privateLookupIn(C1,PUB)} fails</th>
1267 * <td></td>
1268 * <td></td>
1269 * <td></td>
1270 * <td></td>
1271 * <td></td>
1272 * <td style="text-align:center">IAE</td>
1273 * </tr>
1274 * <tr>
1275 * <th scope="row" style="text-align:left">{@code ANY.in(X)}, for inaccessible {@code X}</th>
1276 * <td></td>
1277 * <td></td>
1278 * <td></td>
1279 * <td></td>
1280 * <td></td>
1281 * <td style="text-align:center">none</td>
1282 * </tr>
1283 * </tbody>
1284 * </table>
1285 *
1286 * <p>
1287 * Notes:
1288 * <ul>
1289 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1290 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1291 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1292 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1293 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set,
1294 * {@code PRO} indicates {@link #PROTECTED} bit set,
1295 * {@code PRI} indicates {@link #PRIVATE} bit set,
1296 * {@code PAC} indicates {@link #PACKAGE} bit set,
1297 * {@code MOD} indicates {@link #MODULE} bit set,
1298 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1299 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1300 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1301 * <li>Public access comes in three kinds:
1302 * <ul>
1303 * <li>unconditional ({@code U}): the lookup assumes readability.
1304 * The lookup has {@code null} previous lookup class.
1305 * <li>one-module-reads ({@code 1R}): the module access checking is
1306 * performed with respect to the lookup class. The lookup has {@code null}
1307 * previous lookup class.
1308 * <li>two-module-reads ({@code 2R}): the module access checking is
1309 * performed with respect to the lookup class and the previous lookup class.
1310 * The lookup has a non-null previous lookup class which is in a
1311 * different module from the current lookup class.
1312 * </ul>
1313 * <li>Any attempt to reach a third module loses all access.</li>
1314 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1315 * all access modes are dropped.</li>
1316 * </ul>
1317 *
1318 * <h2><a id="secmgr"></a>Security manager interactions</h2>
1319 * Although bytecode instructions can only refer to classes in
1320 * a related class loader, this API can search for methods in any
1321 * class, as long as a reference to its {@code Class} object is
1322 * available. Such cross-loader references are also possible with the
1323 * Core Reflection API, and are impossible to bytecode instructions
1324 * such as {@code invokestatic} or {@code getfield}.
1325 * There is a {@linkplain java.lang.SecurityManager security manager API}
1326 * to allow applications to check such cross-loader references.
1327 * These checks apply to both the {@code MethodHandles.Lookup} API
1328 * and the Core Reflection API
1329 * (as found on {@link java.lang.Class Class}).
1330 * <p>
1331 * If a security manager is present, member and class lookups are subject to
1332 * additional checks.
1333 * From one to three calls are made to the security manager.
1334 * Any of these calls can refuse access by throwing a
1335 * {@link java.lang.SecurityException SecurityException}.
1336 * Define {@code smgr} as the security manager,
1337 * {@code lookc} as the lookup class of the current lookup object,
1338 * {@code refc} as the containing class in which the member
1339 * is being sought, and {@code defc} as the class in which the
1340 * member is actually defined.
1341 * (If a class or other type is being accessed,
1342 * the {@code refc} and {@code defc} values are the class itself.)
1343 * The value {@code lookc} is defined as <em>not present</em>
1344 * if the current lookup object does not have
1345 * {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1346 * The calls are made according to the following rules:
1347 * <ul>
1348 * <li><b>Step 1:</b>
1349 * If {@code lookc} is not present, or if its class loader is not
1350 * the same as or an ancestor of the class loader of {@code refc},
1351 * then {@link SecurityManager#checkPackageAccess
1352 * smgr.checkPackageAccess(refcPkg)} is called,
1353 * where {@code refcPkg} is the package of {@code refc}.
1354 * <li><b>Step 2a:</b>
1355 * If the retrieved member is not public and
1356 * {@code lookc} is not present, then
1357 * {@link SecurityManager#checkPermission smgr.checkPermission}
1358 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
1359 * <li><b>Step 2b:</b>
1360 * If the retrieved class has a {@code null} class loader,
1361 * and {@code lookc} is not present, then
1362 * {@link SecurityManager#checkPermission smgr.checkPermission}
1363 * with {@code RuntimePermission("getClassLoader")} is called.
1364 * <li><b>Step 3:</b>
1365 * If the retrieved member is not public,
1366 * and if {@code lookc} is not present,
1367 * and if {@code defc} and {@code refc} are different,
1368 * then {@link SecurityManager#checkPackageAccess
1369 * smgr.checkPackageAccess(defcPkg)} is called,
1370 * where {@code defcPkg} is the package of {@code defc}.
1371 * </ul>
1372 * Security checks are performed after other access checks have passed.
1373 * Therefore, the above rules presuppose a member or class that is public,
1374 * or else that is being accessed from a lookup class that has
1375 * rights to access the member or class.
1376 * <p>
1377 * If a security manager is present and the current lookup object does not have
1378 * {@linkplain #hasFullPrivilegeAccess() full privilege access}, then
1379 * {@link #defineClass(byte[]) defineClass},
1380 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass},
1381 * {@link #defineHiddenClassWithClassData(byte[], Object, boolean, ClassOption...)
1382 * defineHiddenClassWithClassData}
1383 * calls {@link SecurityManager#checkPermission smgr.checkPermission}
1384 * with {@code RuntimePermission("defineClass")}.
1385 *
1386 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1387 * A small number of Java methods have a special property called caller sensitivity.
1388 * A <em>caller-sensitive</em> method can behave differently depending on the
1389 * identity of its immediate caller.
1390 * <p>
1391 * If a method handle for a caller-sensitive method is requested,
1392 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1393 * but they take account of the lookup class in a special way.
1394 * The resulting method handle behaves as if it were called
1395 * from an instruction contained in the lookup class,
1396 * so that the caller-sensitive method detects the lookup class.
1397 * (By contrast, the invoker of the method handle is disregarded.)
1398 * Thus, in the case of caller-sensitive methods,
1399 * different lookup classes may give rise to
1400 * differently behaving method handles.
1401 * <p>
1402 * In cases where the lookup object is
1403 * {@link MethodHandles#publicLookup() publicLookup()},
1404 * or some other lookup object without the
1405 * {@linkplain #ORIGINAL original access},
1406 * the lookup class is disregarded.
1407 * In such cases, no caller-sensitive method handle can be created,
1408 * access is forbidden, and the lookup fails with an
1409 * {@code IllegalAccessException}.
1410 * <p style="font-size:smaller;">
1411 * <em>Discussion:</em>
1412 * For example, the caller-sensitive method
1413 * {@link java.lang.Class#forName(String) Class.forName(x)}
1414 * can return varying classes or throw varying exceptions,
1415 * depending on the class loader of the class that calls it.
1416 * A public lookup of {@code Class.forName} will fail, because
1417 * there is no reasonable way to determine its bytecode behavior.
1418 * <p style="font-size:smaller;">
1419 * If an application caches method handles for broad sharing,
1420 * it should use {@code publicLookup()} to create them.
1421 * If there is a lookup of {@code Class.forName}, it will fail,
1422 * and the application must take appropriate action in that case.
1423 * It may be that a later lookup, perhaps during the invocation of a
1424 * bootstrap method, can incorporate the specific identity
1425 * of the caller, making the method accessible.
1426 * <p style="font-size:smaller;">
1427 * The function {@code MethodHandles.lookup} is caller sensitive
1428 * so that there can be a secure foundation for lookups.
1429 * Nearly all other methods in the JSR 292 API rely on lookup
1430 * objects to check access requests.
1431 */
1432 public static final
1433 class Lookup {
1434 /** The class on behalf of whom the lookup is being performed. */
1435 private final Class<?> lookupClass;
1436
1437 /** previous lookup class */
1438 private final Class<?> prevLookupClass;
1439
1440 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1441 private final int allowedModes;
1442
1443 static {
1444 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1445 }
1446
1447 /** A single-bit mask representing {@code public} access,
1448 * which may contribute to the result of {@link #lookupModes lookupModes}.
1449 * The value, {@code 0x01}, happens to be the same as the value of the
1450 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1451 * <p>
1452 * A {@code Lookup} with this lookup mode performs cross-module access check
1453 * with respect to the {@linkplain #lookupClass() lookup class} and
1454 * {@linkplain #previousLookupClass() previous lookup class} if present.
1455 */
1456 public static final int PUBLIC = Modifier.PUBLIC;
1457
1458 /** A single-bit mask representing {@code private} access,
1459 * which may contribute to the result of {@link #lookupModes lookupModes}.
1460 * The value, {@code 0x02}, happens to be the same as the value of the
1461 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1462 */
1463 public static final int PRIVATE = Modifier.PRIVATE;
1464
1465 /** A single-bit mask representing {@code protected} access,
1466 * which may contribute to the result of {@link #lookupModes lookupModes}.
1467 * The value, {@code 0x04}, happens to be the same as the value of the
1468 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1469 */
1470 public static final int PROTECTED = Modifier.PROTECTED;
1471
1472 /** A single-bit mask representing {@code package} access (default access),
1473 * which may contribute to the result of {@link #lookupModes lookupModes}.
1474 * The value is {@code 0x08}, which does not correspond meaningfully to
1475 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1476 */
1477 public static final int PACKAGE = Modifier.STATIC;
1478
1479 /** A single-bit mask representing {@code module} access,
1480 * which may contribute to the result of {@link #lookupModes lookupModes}.
1481 * The value is {@code 0x10}, which does not correspond meaningfully to
1482 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1483 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1484 * with this lookup mode can access all public types in the module of the
1485 * lookup class and public types in packages exported by other modules
1486 * to the module of the lookup class.
1487 * <p>
1488 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1489 * previous lookup class} is always {@code null}.
1490 *
1491 * @since 9
1492 */
1493 public static final int MODULE = PACKAGE << 1;
1494
1495 /** A single-bit mask representing {@code unconditional} access
1496 * which may contribute to the result of {@link #lookupModes lookupModes}.
1497 * The value is {@code 0x20}, which does not correspond meaningfully to
1498 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1499 * A {@code Lookup} with this lookup mode assumes {@linkplain
1500 * java.lang.Module#canRead(java.lang.Module) readability}.
1501 * This lookup mode can access all public members of public types
1502 * of all modules when the type is in a package that is {@link
1503 * java.lang.Module#isExported(String) exported unconditionally}.
1504 *
1505 * <p>
1506 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1507 * previous lookup class} is always {@code null}.
1508 *
1509 * @since 9
1510 * @see #publicLookup()
1511 */
1512 public static final int UNCONDITIONAL = PACKAGE << 2;
1513
1514 /** A single-bit mask representing {@code original} access
1515 * which may contribute to the result of {@link #lookupModes lookupModes}.
1516 * The value is {@code 0x40}, which does not correspond meaningfully to
1517 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1518 *
1519 * <p>
1520 * If this lookup mode is set, the {@code Lookup} object must be
1521 * created by the original lookup class by calling
1522 * {@link MethodHandles#lookup()} method or by a bootstrap method
1523 * invoked by the VM. The {@code Lookup} object with this lookup
1524 * mode has {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1525 *
1526 * @since 16
1527 */
1528 public static final int ORIGINAL = PACKAGE << 3;
1529
1530 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL);
1531 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); // with original access
1532 private static final int TRUSTED = -1;
1533
1534 /*
1535 * Adjust PUBLIC => PUBLIC|MODULE|ORIGINAL|UNCONDITIONAL
1536 * Adjust 0 => PACKAGE
1537 */
1538 private static int fixmods(int mods) {
1539 mods &= (ALL_MODES - PACKAGE - MODULE - ORIGINAL - UNCONDITIONAL);
1540 if (Modifier.isPublic(mods))
1541 mods |= UNCONDITIONAL;
1542 return (mods != 0) ? mods : PACKAGE;
1543 }
1544
1545 /** Tells which class is performing the lookup. It is this class against
1546 * which checks are performed for visibility and access permissions.
1547 * <p>
1548 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1549 * access checks are performed against both the lookup class and the previous lookup class.
1550 * <p>
1551 * The class implies a maximum level of access permission,
1552 * but the permissions may be additionally limited by the bitmask
1553 * {@link #lookupModes lookupModes}, which controls whether non-public members
1554 * can be accessed.
1555 * @return the lookup class, on behalf of which this lookup object finds members
1556 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1557 */
1558 public Class<?> lookupClass() {
1559 return lookupClass;
1560 }
1561
1562 /** Reports a lookup class in another module that this lookup object
1563 * was previously teleported from, or {@code null}.
1564 * <p>
1565 * A {@code Lookup} object produced by the factory methods, such as the
1566 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1567 * has {@code null} previous lookup class.
1568 * A {@code Lookup} object has a non-null previous lookup class
1569 * when this lookup was teleported from an old lookup class
1570 * in one module to a new lookup class in another module.
1571 *
1572 * @return the lookup class in another module that this lookup object was
1573 * previously teleported from, or {@code null}
1574 * @since 14
1575 * @see #in(Class)
1576 * @see MethodHandles#privateLookupIn(Class, Lookup)
1577 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1578 */
1579 public Class<?> previousLookupClass() {
1580 return prevLookupClass;
1581 }
1582
1583 // This is just for calling out to MethodHandleImpl.
1584 private Class<?> lookupClassOrNull() {
1585 return (allowedModes == TRUSTED) ? null : lookupClass;
1586 }
1587
1588 /** Tells which access-protection classes of members this lookup object can produce.
1589 * The result is a bit-mask of the bits
1590 * {@linkplain #PUBLIC PUBLIC (0x01)},
1591 * {@linkplain #PRIVATE PRIVATE (0x02)},
1592 * {@linkplain #PROTECTED PROTECTED (0x04)},
1593 * {@linkplain #PACKAGE PACKAGE (0x08)},
1594 * {@linkplain #MODULE MODULE (0x10)},
1595 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)},
1596 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}.
1597 * <p>
1598 * A freshly-created lookup object
1599 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1600 * all possible bits set, except {@code UNCONDITIONAL}.
1601 * A lookup object on a new lookup class
1602 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1603 * may have some mode bits set to zero.
1604 * Mode bits can also be
1605 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1606 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1607 * The purpose of this is to restrict access via the new lookup object,
1608 * so that it can access only names which can be reached by the original
1609 * lookup object, and also by the new lookup class.
1610 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1611 * @see #in
1612 * @see #dropLookupMode
1613 */
1614 public int lookupModes() {
1615 return allowedModes & ALL_MODES;
1616 }
1617
1618 /** Embody the current class (the lookupClass) as a lookup class
1619 * for method handle creation.
1620 * Must be called by from a method in this package,
1621 * which in turn is called by a method not in this package.
1622 */
1623 Lookup(Class<?> lookupClass) {
1624 this(lookupClass, null, FULL_POWER_MODES);
1625 }
1626
1627 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
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 * @see #accessClass(Class)
1694 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1695 */
1696 public Lookup in(Class<?> requestedLookupClass) {
1697 Objects.requireNonNull(requestedLookupClass);
1698 if (requestedLookupClass.isPrimitive())
1699 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1700 if (requestedLookupClass.isArray())
1701 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1702
1703 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1704 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1705 if (requestedLookupClass == this.lookupClass)
1706 return this; // keep same capabilities
1707 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL;
1708 Module fromModule = this.lookupClass.getModule();
1709 Module targetModule = requestedLookupClass.getModule();
1710 Class<?> plc = this.previousLookupClass();
1711 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1712 assert plc == null;
1713 newModes = UNCONDITIONAL;
1714 } else if (fromModule != targetModule) {
1715 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1716 // allow hopping back and forth between fromModule and plc's module
1717 // but not the third module
1718 newModes = 0;
1719 }
1720 // drop MODULE access
1721 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1722 // teleport from this lookup class
1723 plc = this.lookupClass;
1724 }
1725 if ((newModes & PACKAGE) != 0
1726 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1727 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1728 }
1729 // Allow nestmate lookups to be created without special privilege:
1730 if ((newModes & PRIVATE) != 0
1731 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1732 newModes &= ~(PRIVATE|PROTECTED);
1733 }
1734 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1735 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1736 // The requested class it not accessible from the lookup class.
1737 // No permissions.
1738 newModes = 0;
1739 }
1740 return newLookup(requestedLookupClass, plc, newModes);
1741 }
1742
1743 /**
1744 * Creates a lookup on the same lookup class which this lookup object
1745 * finds members, but with a lookup mode that has lost the given lookup mode.
1746 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1747 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED},
1748 * {@link #PRIVATE PRIVATE}, {@link #ORIGINAL ORIGINAL}, or
1749 * {@link #UNCONDITIONAL UNCONDITIONAL}.
1750 *
1751 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup},
1752 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set.
1753 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting
1754 * lookup has no access.
1755 *
1756 * <p> If this lookup is not a public lookup, then the following applies
1757 * regardless of its {@linkplain #lookupModes() lookup modes}.
1758 * {@link #PROTECTED PROTECTED} and {@link #ORIGINAL ORIGINAL} are always
1759 * dropped and so the resulting lookup mode will never have these access
1760 * capabilities. When dropping {@code PACKAGE}
1761 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE}
1762 * access. When dropping {@code MODULE} then the resulting lookup will not
1763 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access.
1764 * When dropping {@code PUBLIC} then the resulting lookup has no access.
1765 *
1766 * @apiNote
1767 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1768 * delegate non-public access within the package of the lookup class without
1769 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1770 * A lookup with {@code MODULE} but not
1771 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1772 * the module of the lookup class without conferring package access.
1773 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1774 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1775 * to public classes accessible to both the module of the lookup class
1776 * and the module of the previous lookup class.
1777 *
1778 * @param modeToDrop the lookup mode to drop
1779 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1780 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1781 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE}, {@code ORIGINAL}
1782 * or {@code UNCONDITIONAL}
1783 * @see MethodHandles#privateLookupIn
1784 * @since 9
1785 */
1786 public Lookup dropLookupMode(int modeToDrop) {
1787 int oldModes = lookupModes();
1788 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL);
1789 switch (modeToDrop) {
1790 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1791 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1792 case PACKAGE: newModes &= ~(PRIVATE); break;
1793 case PROTECTED:
1794 case PRIVATE:
1795 case ORIGINAL:
1796 case UNCONDITIONAL: break;
1797 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1798 }
1799 if (newModes == oldModes) return this; // return self if no change
1800 return newLookup(lookupClass(), previousLookupClass(), newModes);
1801 }
1802
1803 /**
1804 * Creates and links a class or interface from {@code bytes}
1805 * with the same class loader and in the same runtime package and
1806 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1807 * {@linkplain #lookupClass() lookup class} as if calling
1808 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1809 * ClassLoader::defineClass}.
1810 *
1811 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1812 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1813 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1814 * that the lookup object was created by a caller in the runtime package (or derived
1815 * from a lookup originally created by suitably privileged code to a target class in
1816 * the runtime package). </p>
1817 *
1818 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1819 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1820 * same package as the lookup class. </p>
1821 *
1822 * <p> This method does not run the class initializer. The class initializer may
1823 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1824 * Specification</em>. </p>
1825 *
1826 * <p> If there is a security manager and this lookup does not have {@linkplain
1827 * #hasFullPrivilegeAccess() full privilege access}, its {@code checkPermission} method
1828 * is first called to check {@code RuntimePermission("defineClass")}. </p>
1829 *
1830 * @param bytes the class bytes
1831 * @return the {@code Class} object for the class
1832 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1833 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1834 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
1835 * than the lookup class or {@code bytes} is not a class or interface
1836 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
1837 * @throws VerifyError if the newly created class cannot be verified
1838 * @throws LinkageError if the newly created class cannot be linked for any other reason
1839 * @throws SecurityException if a security manager is present and it
1840 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1841 * @throws NullPointerException if {@code bytes} is {@code null}
1842 * @since 9
1843 * @see MethodHandles#privateLookupIn
1844 * @see Lookup#dropLookupMode
1845 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1846 */
1847 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1848 ensureDefineClassPermission();
1849 if ((lookupModes() & PACKAGE) == 0)
1850 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1851 return makeClassDefiner(bytes.clone()).defineClass(false);
1852 }
1853
1854 private void ensureDefineClassPermission() {
1855 if (allowedModes == TRUSTED) return;
1856
1857 if (!hasFullPrivilegeAccess()) {
1858 @SuppressWarnings("removal")
1859 SecurityManager sm = System.getSecurityManager();
1860 if (sm != null)
1861 sm.checkPermission(new RuntimePermission("defineClass"));
1862 }
1863 }
1864
1865 /**
1866 * The set of class options that specify whether a hidden class created by
1867 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
1868 * Lookup::defineHiddenClass} method is dynamically added as a new member
1869 * to the nest of a lookup class and/or whether a hidden class has
1870 * a strong relationship with the class loader marked as its defining loader.
1871 *
1872 * @since 15
1873 */
1874 public enum ClassOption {
1875 /**
1876 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest}
1877 * of a lookup class as a nestmate.
1878 *
1879 * <p> A hidden nestmate class has access to the private members of all
1880 * classes and interfaces in the same nest.
1881 *
1882 * @see Class#getNestHost()
1883 */
1884 NESTMATE(NESTMATE_CLASS),
1885
1886 /**
1887 * Specifies that a hidden class has a <em>strong</em>
1888 * relationship with the class loader marked as its defining loader,
1889 * as a normal class or interface has with its own defining loader.
1890 * This means that the hidden class may be unloaded if and only if
1891 * its defining loader is not reachable and thus may be reclaimed
1892 * by a garbage collector (JLS {@jls 12.7}).
1893 *
1894 * <p> By default, a hidden class or interface may be unloaded
1895 * even if the class loader that is marked as its defining loader is
1896 * <a href="../ref/package-summary.html#reachability">reachable</a>.
1897
1898 *
1899 * @jls 12.7 Unloading of Classes and Interfaces
1900 */
1901 STRONG(STRONG_LOADER_LINK);
1902
1903 /* the flag value is used by VM at define class time */
1904 private final int flag;
1905 ClassOption(int flag) {
1906 this.flag = flag;
1907 }
1908
1909 static int optionsToFlag(Set<ClassOption> options) {
1910 int flags = 0;
1911 for (ClassOption cp : options) {
1912 flags |= cp.flag;
1913 }
1914 return flags;
1915 }
1916 }
1917
1918 /**
1919 * Creates a <em>hidden</em> class or interface from {@code bytes},
1920 * returning a {@code Lookup} on the newly created class or interface.
1921 *
1922 * <p> Ordinarily, a class or interface {@code C} is created by a class loader,
1923 * which either defines {@code C} directly or delegates to another class loader.
1924 * A class loader defines {@code C} directly by invoking
1925 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1926 * ClassLoader::defineClass}, which causes the Java Virtual Machine
1927 * to derive {@code C} from a purported representation in {@code class} file format.
1928 * In situations where use of a class loader is undesirable, a class or interface
1929 * {@code C} can be created by this method instead. This method is capable of
1930 * defining {@code C}, and thereby creating it, without invoking
1931 * {@code ClassLoader::defineClass}.
1932 * Instead, this method defines {@code C} as if by arranging for
1933 * the Java Virtual Machine to derive a nonarray class or interface {@code C}
1934 * from a purported representation in {@code class} file format
1935 * using the following rules:
1936 *
1937 * <ol>
1938 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup}
1939 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access.
1940 * This level of access is needed to create {@code C} in the module
1941 * of the lookup class of this {@code Lookup}.</li>
1942 *
1943 * <li> The purported representation in {@code bytes} must be a {@code ClassFile}
1944 * structure (JVMS {@jvms 4.1}) of a supported major and minor version.
1945 * The major and minor version may differ from the {@code class} file version
1946 * of the lookup class of this {@code Lookup}.</li>
1947 *
1948 * <li> The value of {@code this_class} must be a valid index in the
1949 * {@code constant_pool} table, and the entry at that index must be a valid
1950 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name
1951 * encoded in internal form that is specified by this structure. {@code N} must
1952 * denote a class or interface in the same package as the lookup class.</li>
1953 *
1954 * <li> Let {@code CN} be the string {@code N + "." + <suffix>},
1955 * where {@code <suffix>} is an unqualified name.
1956 *
1957 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by
1958 * {@code bytes} with an additional entry in the {@code constant_pool} table,
1959 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and
1960 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class}
1961 * refers to the new {@code CONSTANT_Utf8_info} structure.
1962 *
1963 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}.
1964 *
1965 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and
1966 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5},
1967 * with the following adjustments:
1968 * <ul>
1969 * <li> The constant indicated by {@code this_class} is permitted to specify a name
1970 * that includes a single {@code "."} character, even though this is not a valid
1971 * binary class or interface name in internal form.</li>
1972 *
1973 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C},
1974 * but no class loader is recorded as an initiating class loader of {@code C}.</li>
1975 *
1976 * <li> {@code C} is considered to have the same runtime
1977 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module}
1978 * and {@linkplain java.security.ProtectionDomain protection domain}
1979 * as the lookup class of this {@code Lookup}.
1980 * <li> Let {@code GN} be the binary name obtained by taking {@code N}
1981 * (a binary name encoded in internal form) and replacing ASCII forward slashes with
1982 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}:
1983 * <ul>
1984 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>},
1985 * even though this is not a valid binary class or interface name.</li>
1986 * <li> {@link Class#descriptorString()} returns the string
1987 * {@code "L" + N + "." + <suffix> + ";"},
1988 * even though this is not a valid type descriptor name.</li>
1989 * <li> {@link Class#describeConstable()} returns an empty optional as {@code C}
1990 * cannot be described in {@linkplain java.lang.constant.ClassDesc nominal form}.</li>
1991 * </ul>
1992 * </ul>
1993 * </li>
1994 * </ol>
1995 *
1996 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine.
1997 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments:
1998 * <ul>
1999 * <li> During verification, whenever it is necessary to load the class named
2000 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is
2001 * made of any class loader.</li>
2002 *
2003 * <li> On any attempt to resolve the entry in the run-time constant pool indicated
2004 * by {@code this_class}, the symbolic reference is considered to be resolved to
2005 * {@code C} and resolution always succeeds immediately.</li>
2006 * </ul>
2007 *
2008 * <p> If the {@code initialize} parameter is {@code true},
2009 * then {@code C} is initialized by the Java Virtual Machine.
2010 *
2011 * <p> The newly created class or interface {@code C} serves as the
2012 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object
2013 * returned by this method. {@code C} is <em>hidden</em> in the sense that
2014 * no other class or interface can refer to {@code C} via a constant pool entry.
2015 * That is, a hidden class or interface cannot be named as a supertype, a field type,
2016 * a method parameter type, or a method return type by any other class.
2017 * This is because a hidden class or interface does not have a binary name, so
2018 * there is no internal form available to record in any class's constant pool.
2019 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)},
2020 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and
2021 * is not {@linkplain java.instrument/java.lang.instrument.Instrumentation#isModifiableClass(Class)
2022 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html">
2023 * JVM Tool Interface</a>.
2024 *
2025 * <p> A class or interface created by
2026 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
2027 * a class loader} has a strong relationship with that class loader.
2028 * That is, every {@code Class} object contains a reference to the {@code ClassLoader}
2029 * that {@linkplain Class#getClassLoader() defined it}.
2030 * This means that a class created by a class loader may be unloaded if and
2031 * only if its defining loader is not reachable and thus may be reclaimed
2032 * by a garbage collector (JLS {@jls 12.7}).
2033 *
2034 * By default, however, a hidden class or interface may be unloaded even if
2035 * the class loader that is marked as its defining loader is
2036 * <a href="../ref/package-summary.html#reachability">reachable</a>.
2037 * This behavior is useful when a hidden class or interface serves multiple
2038 * classes defined by arbitrary class loaders. In other cases, a hidden
2039 * class or interface may be linked to a single class (or a small number of classes)
2040 * with the same defining loader as the hidden class or interface.
2041 * In such cases, where the hidden class or interface must be coterminous
2042 * with a normal class or interface, the {@link ClassOption#STRONG STRONG}
2043 * option may be passed in {@code options}.
2044 * This arranges for a hidden class to have the same strong relationship
2045 * with the class loader marked as its defining loader,
2046 * as a normal class or interface has with its own defining loader.
2047 *
2048 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass}
2049 * may still prevent a hidden class or interface from being
2050 * unloaded by ensuring that the {@code Class} object is reachable.
2051 *
2052 * <p> The unloading characteristics are set for each hidden class when it is
2053 * defined, and cannot be changed later. An advantage of allowing hidden classes
2054 * to be unloaded independently of the class loader marked as their defining loader
2055 * is that a very large number of hidden classes may be created by an application.
2056 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory,
2057 * just as if normal classes were created by class loaders.
2058 *
2059 * <p> Classes and interfaces in a nest are allowed to have mutual access to
2060 * their private members. The nest relationship is determined by
2061 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and
2062 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file.
2063 * By default, a hidden class belongs to a nest consisting only of itself
2064 * because a hidden class has no binary name.
2065 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options}
2066 * to create a hidden class or interface {@code C} as a member of a nest.
2067 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute
2068 * in the {@code ClassFile} structure from which {@code C} was derived.
2069 * Instead, the following rules determine the nest host of {@code C}:
2070 * <ul>
2071 * <li>If the nest host of the lookup class of this {@code Lookup} has previously
2072 * been determined, then let {@code H} be the nest host of the lookup class.
2073 * Otherwise, the nest host of the lookup class is determined using the
2074 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li>
2075 * <li>The nest host of {@code C} is determined to be {@code H},
2076 * the nest host of the lookup class.</li>
2077 * </ul>
2078 *
2079 * <p> A hidden class or interface may be serializable, but this requires a custom
2080 * serialization mechanism in order to ensure that instances are properly serialized
2081 * and deserialized. The default serialization mechanism supports only classes and
2082 * interfaces that are discoverable by their class name.
2083 *
2084 * @param bytes the bytes that make up the class data,
2085 * in the format of a valid {@code class} file as defined by
2086 * <cite>The Java Virtual Machine Specification</cite>.
2087 * @param initialize if {@code true} the class will be initialized.
2088 * @param options {@linkplain ClassOption class options}
2089 * @return the {@code Lookup} object on the hidden class,
2090 * with {@linkplain #ORIGINAL original} and
2091 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2092 *
2093 * @throws IllegalAccessException if this {@code Lookup} does not have
2094 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2095 * @throws SecurityException if a security manager is present and it
2096 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2097 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2098 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2099 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2100 * than the lookup class or {@code bytes} is not a class or interface
2101 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2102 * @throws IncompatibleClassChangeError if the class or interface named as
2103 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2104 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2105 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2106 * {@code C} is {@code C} itself
2107 * @throws VerifyError if the newly created class cannot be verified
2108 * @throws LinkageError if the newly created class cannot be linked for any other reason
2109 * @throws NullPointerException if any parameter is {@code null}
2110 *
2111 * @since 15
2112 * @see Class#isHidden()
2113 * @jvms 4.2.1 Binary Class and Interface Names
2114 * @jvms 4.2.2 Unqualified Names
2115 * @jvms 4.7.28 The {@code NestHost} Attribute
2116 * @jvms 4.7.29 The {@code NestMembers} Attribute
2117 * @jvms 5.4.3.1 Class and Interface Resolution
2118 * @jvms 5.4.4 Access Control
2119 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2120 * @jvms 5.4 Linking
2121 * @jvms 5.5 Initialization
2122 * @jls 12.7 Unloading of Classes and Interfaces
2123 */
2124 @SuppressWarnings("doclint:reference") // cross-module links
2125 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options)
2126 throws IllegalAccessException
2127 {
2128 Objects.requireNonNull(bytes);
2129 Objects.requireNonNull(options);
2130
2131 ensureDefineClassPermission();
2132 if (!hasFullPrivilegeAccess()) {
2133 throw new IllegalAccessException(this + " does not have full privilege access");
2134 }
2135
2136 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false).defineClassAsLookup(initialize);
2137 }
2138
2139 /**
2140 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated
2141 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data},
2142 * returning a {@code Lookup} on the newly created class or interface.
2143 *
2144 * <p> This method is equivalent to calling
2145 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)}
2146 * as if the hidden class is injected with a private static final <i>unnamed</i>
2147 * field which is initialized with the given {@code classData} at
2148 * the first instruction of the class initializer.
2149 * The newly created class is linked by the Java Virtual Machine.
2150 *
2151 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData}
2152 * and {@link MethodHandles#classDataAt(Lookup, String, Class, int) MethodHandles::classDataAt}
2153 * methods can be used to retrieve the {@code classData}.
2154 *
2155 * @apiNote
2156 * A framework can create a hidden class with class data with one or more
2157 * objects and load the class data as dynamically-computed constant(s)
2158 * via a bootstrap method. {@link MethodHandles#classData(Lookup, String, Class)
2159 * Class data} is accessible only to the lookup object created by the newly
2160 * defined hidden class but inaccessible to other members in the same nest
2161 * (unlike private static fields that are accessible to nestmates).
2162 * Care should be taken w.r.t. mutability for example when passing
2163 * an array or other mutable structure through the class data.
2164 * Changing any value stored in the class data at runtime may lead to
2165 * unpredictable behavior.
2166 * If the class data is a {@code List}, it is good practice to make it
2167 * unmodifiable for example via {@link List#of List::of}.
2168 *
2169 * @param bytes the class bytes
2170 * @param classData pre-initialized class data
2171 * @param initialize if {@code true} the class will be initialized.
2172 * @param options {@linkplain ClassOption class options}
2173 * @return the {@code Lookup} object on the hidden class,
2174 * with {@linkplain #ORIGINAL original} and
2175 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2176 *
2177 * @throws IllegalAccessException if this {@code Lookup} does not have
2178 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2179 * @throws SecurityException if a security manager is present and it
2180 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2181 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2182 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2183 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2184 * than the lookup class or {@code bytes} is not a class or interface
2185 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2186 * @throws IncompatibleClassChangeError if the class or interface named as
2187 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2188 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2189 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2190 * {@code C} is {@code C} itself
2191 * @throws VerifyError if the newly created class cannot be verified
2192 * @throws LinkageError if the newly created class cannot be linked for any other reason
2193 * @throws NullPointerException if any parameter is {@code null}
2194 *
2195 * @since 16
2196 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
2197 * @see Class#isHidden()
2198 * @see MethodHandles#classData(Lookup, String, Class)
2199 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
2200 * @jvms 4.2.1 Binary Class and Interface Names
2201 * @jvms 4.2.2 Unqualified Names
2202 * @jvms 4.7.28 The {@code NestHost} Attribute
2203 * @jvms 4.7.29 The {@code NestMembers} Attribute
2204 * @jvms 5.4.3.1 Class and Interface Resolution
2205 * @jvms 5.4.4 Access Control
2206 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2207 * @jvms 5.4 Linking
2208 * @jvms 5.5 Initialization
2209 * @jls 12.7 Unloading of Classes and Interface
2210 */
2211 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options)
2212 throws IllegalAccessException
2213 {
2214 Objects.requireNonNull(bytes);
2215 Objects.requireNonNull(classData);
2216 Objects.requireNonNull(options);
2217
2218 ensureDefineClassPermission();
2219 if (!hasFullPrivilegeAccess()) {
2220 throw new IllegalAccessException(this + " does not have full privilege access");
2221 }
2222
2223 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false)
2224 .defineClassAsLookup(initialize, classData);
2225 }
2226
2227 // A default dumper for writing class files passed to Lookup::defineClass
2228 // and Lookup::defineHiddenClass to disk for debugging purposes. To enable,
2229 // set -Djdk.invoke.MethodHandle.dumpHiddenClassFiles or
2230 // -Djdk.invoke.MethodHandle.dumpHiddenClassFiles=true
2231 //
2232 // This default dumper does not dump hidden classes defined by LambdaMetafactory
2233 // and LambdaForms and method handle internals. They are dumped via
2234 // different ClassFileDumpers.
2235 private static ClassFileDumper defaultDumper() {
2236 return DEFAULT_DUMPER;
2237 }
2238
2239 private static final ClassFileDumper DEFAULT_DUMPER = ClassFileDumper.getInstance(
2240 "jdk.invoke.MethodHandle.dumpClassFiles", "DUMP_CLASS_FILES");
2241
2242 static class ClassFile {
2243 final String name; // internal name
2244 final int accessFlags;
2245 final byte[] bytes;
2246 ClassFile(String name, int accessFlags, byte[] bytes) {
2247 this.name = name;
2248 this.accessFlags = accessFlags;
2249 this.bytes = bytes;
2250 }
2251
2252 static ClassFile newInstanceNoCheck(String name, byte[] bytes) {
2253 return new ClassFile(name, 0, bytes);
2254 }
2255
2256 /**
2257 * This method checks the class file version and the structure of `this_class`.
2258 * and checks if the bytes is a class or interface (ACC_MODULE flag not set)
2259 * that is in the named package.
2260 *
2261 * @throws IllegalArgumentException if ACC_MODULE flag is set in access flags
2262 * or the class is not in the given package name.
2263 */
2264 static ClassFile newInstance(byte[] bytes, String pkgName) {
2265 var cf = readClassFile(bytes);
2266
2267 // check if it's in the named package
2268 int index = cf.name.lastIndexOf('/');
2269 String pn = (index == -1) ? "" : cf.name.substring(0, index).replace('/', '.');
2270 if (!pn.equals(pkgName)) {
2271 throw newIllegalArgumentException(cf.name + " not in same package as lookup class");
2272 }
2273 return cf;
2274 }
2275
2276 private static ClassFile readClassFile(byte[] bytes) {
2277 int magic = readInt(bytes, 0);
2278 if (magic != 0xCAFEBABE) {
2279 throw new ClassFormatError("Incompatible magic value: " + magic);
2280 }
2281 int minor = readUnsignedShort(bytes, 4);
2282 int major = readUnsignedShort(bytes, 6);
2283 if (!VM.isSupportedClassFileVersion(major, minor)) {
2284 throw new UnsupportedClassVersionError("Unsupported class file version " + major + "." + minor);
2285 }
2286
2287 String name;
2288 int accessFlags;
2289 try {
2290 ClassModel cm = java.lang.classfile.ClassFile.of().parse(bytes);
2291 name = cm.thisClass().asInternalName();
2292 accessFlags = cm.flags().flagsMask();
2293 } catch (IllegalArgumentException e) {
2294 ClassFormatError cfe = new ClassFormatError();
2295 cfe.initCause(e);
2296 throw cfe;
2297 }
2298 // must be a class or interface
2299 if ((accessFlags & ACC_MODULE) != 0) {
2300 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set");
2301 }
2302 return new ClassFile(name, accessFlags, bytes);
2303 }
2304
2305 private static int readInt(byte[] bytes, int offset) {
2306 if ((offset+4) > bytes.length) {
2307 throw new ClassFormatError("Invalid ClassFile structure");
2308 }
2309 return ((bytes[offset] & 0xFF) << 24)
2310 | ((bytes[offset + 1] & 0xFF) << 16)
2311 | ((bytes[offset + 2] & 0xFF) << 8)
2312 | (bytes[offset + 3] & 0xFF);
2313 }
2314
2315 private static int readUnsignedShort(byte[] bytes, int offset) {
2316 if ((offset+2) > bytes.length) {
2317 throw new ClassFormatError("Invalid ClassFile structure");
2318 }
2319 return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF);
2320 }
2321 }
2322
2323 /*
2324 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2325 * from the given bytes.
2326 *
2327 * Caller should make a defensive copy of the arguments if needed
2328 * before calling this factory method.
2329 *
2330 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2331 * {@code bytes} denotes a class in a different package than the lookup class
2332 */
2333 private ClassDefiner makeClassDefiner(byte[] bytes) {
2334 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2335 return new ClassDefiner(this, cf, STRONG_LOADER_LINK, defaultDumper());
2336 }
2337
2338 /**
2339 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2340 * from the given bytes. No package name check on the given bytes.
2341 *
2342 * @param name internal name
2343 * @param bytes class bytes
2344 * @param dumper dumper to write the given bytes to the dumper's output directory
2345 * @return ClassDefiner that defines a normal class of the given bytes.
2346 */
2347 ClassDefiner makeClassDefiner(String name, byte[] bytes, ClassFileDumper dumper) {
2348 // skip package name validation
2349 ClassFile cf = ClassFile.newInstanceNoCheck(name, bytes);
2350 return new ClassDefiner(this, cf, STRONG_LOADER_LINK, dumper);
2351 }
2352
2353 /**
2354 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2355 * from the given bytes. The name must be in the same package as the lookup class.
2356 *
2357 * Caller should make a defensive copy of the arguments if needed
2358 * before calling this factory method.
2359 *
2360 * @param bytes class bytes
2361 * @param dumper dumper to write the given bytes to the dumper's output directory
2362 * @return ClassDefiner that defines a hidden class of the given bytes.
2363 *
2364 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2365 * {@code bytes} denotes a class in a different package than the lookup class
2366 */
2367 ClassDefiner makeHiddenClassDefiner(byte[] bytes, ClassFileDumper dumper) {
2368 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2369 return makeHiddenClassDefiner(cf, Set.of(), false, dumper);
2370 }
2371
2372 /**
2373 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2374 * from the given bytes and options.
2375 * The name must be in the same package as the lookup class.
2376 *
2377 * Caller should make a defensive copy of the arguments if needed
2378 * before calling this factory method.
2379 *
2380 * @param bytes class bytes
2381 * @param options class options
2382 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2383 * @return ClassDefiner that defines a hidden class of the given bytes and options
2384 *
2385 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2386 * {@code bytes} denotes a class in a different package than the lookup class
2387 */
2388 private ClassDefiner makeHiddenClassDefiner(byte[] bytes,
2389 Set<ClassOption> options,
2390 boolean accessVmAnnotations) {
2391 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2392 return makeHiddenClassDefiner(cf, options, accessVmAnnotations, defaultDumper());
2393 }
2394
2395 /**
2396 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2397 * from the given bytes and the given options. No package name check on the given bytes.
2398 *
2399 * @param name internal name that specifies the prefix of the hidden class
2400 * @param bytes class bytes
2401 * @param options class options
2402 * @param dumper dumper to write the given bytes to the dumper's output directory
2403 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2404 */
2405 ClassDefiner makeHiddenClassDefiner(String name, byte[] bytes, Set<ClassOption> options, ClassFileDumper dumper) {
2406 Objects.requireNonNull(dumper);
2407 // skip name and access flags validation
2408 return makeHiddenClassDefiner(ClassFile.newInstanceNoCheck(name, bytes), options, false, dumper);
2409 }
2410
2411 /**
2412 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2413 * from the given class file and options.
2414 *
2415 * @param cf ClassFile
2416 * @param options class options
2417 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2418 * @param dumper dumper to write the given bytes to the dumper's output directory
2419 */
2420 private ClassDefiner makeHiddenClassDefiner(ClassFile cf,
2421 Set<ClassOption> options,
2422 boolean accessVmAnnotations,
2423 ClassFileDumper dumper) {
2424 int flags = HIDDEN_CLASS | ClassOption.optionsToFlag(options);
2425 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) {
2426 // jdk.internal.vm.annotations are permitted for classes
2427 // defined to boot loader and platform loader
2428 flags |= ACCESS_VM_ANNOTATIONS;
2429 }
2430
2431 return new ClassDefiner(this, cf, flags, dumper);
2432 }
2433
2434 static class ClassDefiner {
2435 private final Lookup lookup;
2436 private final String name; // internal name
2437 private final byte[] bytes;
2438 private final int classFlags;
2439 private final ClassFileDumper dumper;
2440
2441 private ClassDefiner(Lookup lookup, ClassFile cf, int flags, ClassFileDumper dumper) {
2442 assert ((flags & HIDDEN_CLASS) != 0 || (flags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK);
2443 this.lookup = lookup;
2444 this.bytes = cf.bytes;
2445 this.name = cf.name;
2446 this.classFlags = flags;
2447 this.dumper = dumper;
2448 }
2449
2450 String internalName() {
2451 return name;
2452 }
2453
2454 Class<?> defineClass(boolean initialize) {
2455 return defineClass(initialize, null);
2456 }
2457
2458 Lookup defineClassAsLookup(boolean initialize) {
2459 Class<?> c = defineClass(initialize, null);
2460 return new Lookup(c, null, FULL_POWER_MODES);
2461 }
2462
2463 /**
2464 * Defines the class of the given bytes and the given classData.
2465 * If {@code initialize} parameter is true, then the class will be initialized.
2466 *
2467 * @param initialize true if the class to be initialized
2468 * @param classData classData or null
2469 * @return the class
2470 *
2471 * @throws LinkageError linkage error
2472 */
2473 Class<?> defineClass(boolean initialize, Object classData) {
2474 Class<?> lookupClass = lookup.lookupClass();
2475 ClassLoader loader = lookupClass.getClassLoader();
2476 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null;
2477 Class<?> c = null;
2478 try {
2479 c = SharedSecrets.getJavaLangAccess()
2480 .defineClass(loader, lookupClass, name, bytes, pd, initialize, classFlags, classData);
2481 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost();
2482 return c;
2483 } finally {
2484 // dump the classfile for debugging
2485 if (dumper.isEnabled()) {
2486 String name = internalName();
2487 if (c != null) {
2488 dumper.dumpClass(name, c, bytes);
2489 } else {
2490 dumper.dumpFailedClass(name, bytes);
2491 }
2492 }
2493 }
2494 }
2495
2496 /**
2497 * Defines the class of the given bytes and the given classData.
2498 * If {@code initialize} parameter is true, then the class will be initialized.
2499 *
2500 * @param initialize true if the class to be initialized
2501 * @param classData classData or null
2502 * @return a Lookup for the defined class
2503 *
2504 * @throws LinkageError linkage error
2505 */
2506 Lookup defineClassAsLookup(boolean initialize, Object classData) {
2507 Class<?> c = defineClass(initialize, classData);
2508 return new Lookup(c, null, FULL_POWER_MODES);
2509 }
2510
2511 private boolean isNestmate() {
2512 return (classFlags & NESTMATE_CLASS) != 0;
2513 }
2514 }
2515
2516 private ProtectionDomain lookupClassProtectionDomain() {
2517 ProtectionDomain pd = cachedProtectionDomain;
2518 if (pd == null) {
2519 cachedProtectionDomain = pd = SharedSecrets.getJavaLangAccess().protectionDomain(lookupClass);
2520 }
2521 return pd;
2522 }
2523
2524 // cached protection domain
2525 private volatile ProtectionDomain cachedProtectionDomain;
2526
2527 // Make sure outer class is initialized first.
2528 static { IMPL_NAMES.getClass(); }
2529
2530 /** Package-private version of lookup which is trusted. */
2531 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
2532
2533 /** Version of lookup which is trusted minimally.
2534 * It can only be used to create method handles to publicly accessible
2535 * members in packages that are exported unconditionally.
2536 */
2537 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
2538
2539 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
2540 String name = lookupClass.getName();
2541 if (name.startsWith("java.lang.invoke."))
2542 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
2543 }
2544
2545 /**
2546 * Displays the name of the class from which lookups are to be made,
2547 * followed by "/" and the name of the {@linkplain #previousLookupClass()
2548 * previous lookup class} if present.
2549 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
2550 * If there are restrictions on the access permitted to this lookup,
2551 * this is indicated by adding a suffix to the class name, consisting
2552 * of a slash and a keyword. The keyword represents the strongest
2553 * allowed access, and is chosen as follows:
2554 * <ul>
2555 * <li>If no access is allowed, the suffix is "/noaccess".
2556 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
2557 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
2558 * <li>If only public and module access are allowed, the suffix is "/module".
2559 * <li>If public and package access are allowed, the suffix is "/package".
2560 * <li>If public, package, and private access are allowed, the suffix is "/private".
2561 * </ul>
2562 * If none of the above cases apply, it is the case that
2563 * {@linkplain #hasFullPrivilegeAccess() full privilege access}
2564 * (public, module, package, private, and protected) is allowed.
2565 * In this case, no suffix is added.
2566 * This is true only of an object obtained originally from
2567 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
2568 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
2569 * always have restricted access, and will display a suffix.
2570 * <p>
2571 * (It may seem strange that protected access should be
2572 * stronger than private access. Viewed independently from
2573 * package access, protected access is the first to be lost,
2574 * because it requires a direct subclass relationship between
2575 * caller and callee.)
2576 * @see #in
2577 */
2578 @Override
2579 public String toString() {
2580 String cname = lookupClass.getName();
2581 if (prevLookupClass != null)
2582 cname += "/" + prevLookupClass.getName();
2583 switch (allowedModes) {
2584 case 0: // no privileges
2585 return cname + "/noaccess";
2586 case UNCONDITIONAL:
2587 return cname + "/publicLookup";
2588 case PUBLIC:
2589 return cname + "/public";
2590 case PUBLIC|MODULE:
2591 return cname + "/module";
2592 case PUBLIC|PACKAGE:
2593 case PUBLIC|MODULE|PACKAGE:
2594 return cname + "/package";
2595 case PUBLIC|PACKAGE|PRIVATE:
2596 case PUBLIC|MODULE|PACKAGE|PRIVATE:
2597 return cname + "/private";
2598 case PUBLIC|PACKAGE|PRIVATE|PROTECTED:
2599 case PUBLIC|MODULE|PACKAGE|PRIVATE|PROTECTED:
2600 case FULL_POWER_MODES:
2601 return cname;
2602 case TRUSTED:
2603 return "/trusted"; // internal only; not exported
2604 default: // Should not happen, but it's a bitfield...
2605 cname = cname + "/" + Integer.toHexString(allowedModes);
2606 assert(false) : cname;
2607 return cname;
2608 }
2609 }
2610
2611 /**
2612 * Produces a method handle for a static method.
2613 * The type of the method handle will be that of the method.
2614 * (Since static methods do not take receivers, there is no
2615 * additional receiver argument inserted into the method handle type,
2616 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
2617 * The method and all its argument types must be accessible to the lookup object.
2618 * <p>
2619 * The returned method handle will have
2620 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2621 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2622 * <p>
2623 * If the returned method handle is invoked, the method's class will
2624 * be initialized, if it has not already been initialized.
2625 * <p><b>Example:</b>
2626 * {@snippet lang="java" :
2627 import static java.lang.invoke.MethodHandles.*;
2628 import static java.lang.invoke.MethodType.*;
2629 ...
2630 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
2631 "asList", methodType(List.class, Object[].class));
2632 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
2633 * }
2634 * @param refc the class from which the method is accessed
2635 * @param name the name of the method
2636 * @param type the type of the method
2637 * @return the desired method handle
2638 * @throws NoSuchMethodException if the method does not exist
2639 * @throws IllegalAccessException if access checking fails,
2640 * or if the method is not {@code static},
2641 * or if the method's variable arity modifier bit
2642 * is set and {@code asVarargsCollector} fails
2643 * @throws SecurityException if a security manager is present and it
2644 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2645 * @throws NullPointerException if any argument is null
2646 */
2647 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2648 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
2649 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method));
2650 }
2651
2652 /**
2653 * Produces a method handle for a virtual method.
2654 * The type of the method handle will be that of the method,
2655 * with the receiver type (usually {@code refc}) prepended.
2656 * The method and all its argument types must be accessible to the lookup object.
2657 * <p>
2658 * When called, the handle will treat the first argument as a receiver
2659 * and, for non-private methods, dispatch on the receiver's type to determine which method
2660 * implementation to enter.
2661 * For private methods the named method in {@code refc} will be invoked on the receiver.
2662 * (The dispatching action is identical with that performed by an
2663 * {@code invokevirtual} or {@code invokeinterface} instruction.)
2664 * <p>
2665 * The first argument will be of type {@code refc} if the lookup
2666 * class has full privileges to access the member. Otherwise
2667 * the member must be {@code protected} and the first argument
2668 * will be restricted in type to the lookup class.
2669 * <p>
2670 * The returned method handle will have
2671 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2672 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2673 * <p>
2674 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
2675 * instructions and method handles produced by {@code findVirtual},
2676 * if the class is {@code MethodHandle} and the name string is
2677 * {@code invokeExact} or {@code invoke}, the resulting
2678 * method handle is equivalent to one produced by
2679 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
2680 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
2681 * with the same {@code type} argument.
2682 * <p>
2683 * If the class is {@code VarHandle} and the name string corresponds to
2684 * the name of a signature-polymorphic access mode method, the resulting
2685 * method handle is equivalent to one produced by
2686 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
2687 * the access mode corresponding to the name string and with the same
2688 * {@code type} arguments.
2689 * <p>
2690 * <b>Example:</b>
2691 * {@snippet lang="java" :
2692 import static java.lang.invoke.MethodHandles.*;
2693 import static java.lang.invoke.MethodType.*;
2694 ...
2695 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
2696 "concat", methodType(String.class, String.class));
2697 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
2698 "hashCode", methodType(int.class));
2699 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
2700 "hashCode", methodType(int.class));
2701 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
2702 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
2703 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
2704 // interface method:
2705 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
2706 "subSequence", methodType(CharSequence.class, int.class, int.class));
2707 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
2708 // constructor "internal method" must be accessed differently:
2709 MethodType MT_newString = methodType(void.class); //()V for new String()
2710 try { assertEquals("impossible", lookup()
2711 .findVirtual(String.class, "<init>", MT_newString));
2712 } catch (NoSuchMethodException ex) { } // OK
2713 MethodHandle MH_newString = publicLookup()
2714 .findConstructor(String.class, MT_newString);
2715 assertEquals("", (String) MH_newString.invokeExact());
2716 * }
2717 *
2718 * @param refc the class or interface from which the method is accessed
2719 * @param name the name of the method
2720 * @param type the type of the method, with the receiver argument omitted
2721 * @return the desired method handle
2722 * @throws NoSuchMethodException if the method does not exist
2723 * @throws IllegalAccessException if access checking fails,
2724 * or if the method is {@code static},
2725 * or if the method's variable arity modifier bit
2726 * is set and {@code asVarargsCollector} fails
2727 * @throws SecurityException if a security manager is present and it
2728 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2729 * @throws NullPointerException if any argument is null
2730 */
2731 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2732 if (refc == MethodHandle.class) {
2733 MethodHandle mh = findVirtualForMH(name, type);
2734 if (mh != null) return mh;
2735 } else if (refc == VarHandle.class) {
2736 MethodHandle mh = findVirtualForVH(name, type);
2737 if (mh != null) return mh;
2738 }
2739 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
2740 MemberName method = resolveOrFail(refKind, refc, name, type);
2741 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method));
2742 }
2743 private MethodHandle findVirtualForMH(String name, MethodType type) {
2744 // these names require special lookups because of the implicit MethodType argument
2745 if ("invoke".equals(name))
2746 return invoker(type);
2747 if ("invokeExact".equals(name))
2748 return exactInvoker(type);
2749 assert(!MemberName.isMethodHandleInvokeName(name));
2750 return null;
2751 }
2752 private MethodHandle findVirtualForVH(String name, MethodType type) {
2753 try {
2754 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
2755 } catch (IllegalArgumentException e) {
2756 return null;
2757 }
2758 }
2759
2760 /**
2761 * Produces a method handle which creates an object and initializes it, using
2762 * the constructor of the specified type.
2763 * The parameter types of the method handle will be those of the constructor,
2764 * while the return type will be a reference to the constructor's class.
2765 * The constructor and all its argument types must be accessible to the lookup object.
2766 * <p>
2767 * The requested type must have a return type of {@code void}.
2768 * (This is consistent with the JVM's treatment of constructor type descriptors.)
2769 * <p>
2770 * The returned method handle will have
2771 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2772 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2773 * <p>
2774 * If the returned method handle is invoked, the constructor's class will
2775 * be initialized, if it has not already been initialized.
2776 * <p><b>Example:</b>
2777 * {@snippet lang="java" :
2778 import static java.lang.invoke.MethodHandles.*;
2779 import static java.lang.invoke.MethodType.*;
2780 ...
2781 MethodHandle MH_newArrayList = publicLookup().findConstructor(
2782 ArrayList.class, methodType(void.class, Collection.class));
2783 Collection orig = Arrays.asList("x", "y");
2784 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
2785 assert(orig != copy);
2786 assertEquals(orig, copy);
2787 // a variable-arity constructor:
2788 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
2789 ProcessBuilder.class, methodType(void.class, String[].class));
2790 ProcessBuilder pb = (ProcessBuilder)
2791 MH_newProcessBuilder.invoke("x", "y", "z");
2792 assertEquals("[x, y, z]", pb.command().toString());
2793 * }
2794 * @param refc the class or interface from which the method is accessed
2795 * @param type the type of the method, with the receiver argument omitted, and a void return type
2796 * @return the desired method handle
2797 * @throws NoSuchMethodException if the constructor does not exist
2798 * @throws IllegalAccessException if access checking fails
2799 * or if the method's variable arity modifier bit
2800 * is set and {@code asVarargsCollector} fails
2801 * @throws SecurityException if a security manager is present and it
2802 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2803 * @throws NullPointerException if any argument is null
2804 */
2805 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2806 if (refc.isArray()) {
2807 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
2808 }
2809 String name = ConstantDescs.INIT_NAME;
2810 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
2811 return getDirectConstructor(refc, ctor);
2812 }
2813
2814 /**
2815 * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
2816 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
2817 * Such a resolution, as specified in JVMS {@jvms 5.4.3.1}, attempts to locate and load the class,
2818 * and then determines whether the class is accessible to this lookup object.
2819 * <p>
2820 * For a class or an interface, the name is the {@linkplain ClassLoader##binary-name binary name}.
2821 * For an array class of {@code n} dimensions, the name begins with {@code n} occurrences
2822 * of {@code '['} and followed by the element type as encoded in the
2823 * {@linkplain Class##nameFormat table} specified in {@link Class#getName}.
2824 * <p>
2825 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
2826 * its class loader, and the {@linkplain #lookupModes() lookup modes}.
2827 *
2828 * @param targetName the {@linkplain ClassLoader##binary-name binary name} of the class
2829 * or the string representing an array class
2830 * @return the requested class.
2831 * @throws SecurityException if a security manager is present and it
2832 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2833 * @throws LinkageError if the linkage fails
2834 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
2835 * @throws IllegalAccessException if the class is not accessible, using the allowed access
2836 * modes.
2837 * @throws NullPointerException if {@code targetName} is null
2838 * @since 9
2839 * @jvms 5.4.3.1 Class and Interface Resolution
2840 */
2841 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
2842 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
2843 return accessClass(targetClass);
2844 }
2845
2846 /**
2847 * Ensures that {@code targetClass} has been initialized. The class
2848 * to be initialized must be {@linkplain #accessClass accessible}
2849 * to this {@code Lookup} object. This method causes {@code targetClass}
2850 * to be initialized if it has not been already initialized,
2851 * as specified in JVMS {@jvms 5.5}.
2852 *
2853 * <p>
2854 * This method returns when {@code targetClass} is fully initialized, or
2855 * when {@code targetClass} is being initialized by the current thread.
2856 *
2857 * @param <T> the type of the class to be initialized
2858 * @param targetClass the class to be initialized
2859 * @return {@code targetClass} that has been initialized, or that is being
2860 * initialized by the current thread.
2861 *
2862 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or {@code void}
2863 * or array class
2864 * @throws IllegalAccessException if {@code targetClass} is not
2865 * {@linkplain #accessClass accessible} to this lookup
2866 * @throws ExceptionInInitializerError if the class initialization provoked
2867 * by this method fails
2868 * @throws SecurityException if a security manager is present and it
2869 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2870 * @since 15
2871 * @jvms 5.5 Initialization
2872 */
2873 public <T> Class<T> ensureInitialized(Class<T> targetClass) throws IllegalAccessException {
2874 if (targetClass.isPrimitive())
2875 throw new IllegalArgumentException(targetClass + " is a primitive class");
2876 if (targetClass.isArray())
2877 throw new IllegalArgumentException(targetClass + " is an array class");
2878
2879 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2880 throw makeAccessException(targetClass);
2881 }
2882 checkSecurityManager(targetClass);
2883
2884 // ensure class initialization
2885 Unsafe.getUnsafe().ensureClassInitialized(targetClass);
2886 return targetClass;
2887 }
2888
2889 /*
2890 * Returns IllegalAccessException due to access violation to the given targetClass.
2891 *
2892 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized}
2893 * which verifies access to a class rather a member.
2894 */
2895 private IllegalAccessException makeAccessException(Class<?> targetClass) {
2896 String message = "access violation: "+ targetClass;
2897 if (this == MethodHandles.publicLookup()) {
2898 message += ", from public Lookup";
2899 } else {
2900 Module m = lookupClass().getModule();
2901 message += ", from " + lookupClass() + " (" + m + ")";
2902 if (prevLookupClass != null) {
2903 message += ", previous lookup " +
2904 prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")";
2905 }
2906 }
2907 return new IllegalAccessException(message);
2908 }
2909
2910 /**
2911 * Determines if a class can be accessed from the lookup context defined by
2912 * this {@code Lookup} object. The static initializer of the class is not run.
2913 * If {@code targetClass} is an array class, {@code targetClass} is accessible
2914 * if the element type of the array class is accessible. Otherwise,
2915 * {@code targetClass} is determined as accessible as follows.
2916 *
2917 * <p>
2918 * If {@code targetClass} is in the same module as the lookup class,
2919 * the lookup class is {@code LC} in module {@code M1} and
2920 * the previous lookup class is in module {@code M0} or
2921 * {@code null} if not present,
2922 * {@code targetClass} is accessible if and only if one of the following is true:
2923 * <ul>
2924 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
2925 * {@code LC} or other class in the same nest of {@code LC}.</li>
2926 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
2927 * in the same runtime package of {@code LC}.</li>
2928 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
2929 * a public type in {@code M1}.</li>
2930 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
2931 * a public type in a package exported by {@code M1} to at least {@code M0}
2932 * if the previous lookup class is present; otherwise, {@code targetClass}
2933 * is a public type in a package exported by {@code M1} unconditionally.</li>
2934 * </ul>
2935 *
2936 * <p>
2937 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2938 * can access public types in all modules when the type is in a package
2939 * that is exported unconditionally.
2940 * <p>
2941 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass},
2942 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2943 * is inaccessible.
2944 * <p>
2945 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2946 * {@code M1} is the module containing {@code lookupClass} and
2947 * {@code M2} is the module containing {@code targetClass},
2948 * then {@code targetClass} is accessible if and only if
2949 * <ul>
2950 * <li>{@code M1} reads {@code M2}, and
2951 * <li>{@code targetClass} is public and in a package exported by
2952 * {@code M2} at least to {@code M1}.
2953 * </ul>
2954 * <p>
2955 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2956 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2957 * containing the previous lookup class, then {@code targetClass} is accessible
2958 * if and only if one of the following is true:
2959 * <ul>
2960 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2961 * {@linkplain Module#reads reads} {@code M0} and the type is
2962 * in a package that is exported to at least {@code M1}.
2963 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2964 * {@linkplain Module#reads reads} {@code M1} and the type is
2965 * in a package that is exported to at least {@code M0}.
2966 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2967 * and {@code M1} reads {@code M2} and the type is in a package
2968 * that is exported to at least both {@code M0} and {@code M2}.
2969 * </ul>
2970 * <p>
2971 * Otherwise, {@code targetClass} is not accessible.
2972 *
2973 * @param <T> the type of the class to be access-checked
2974 * @param targetClass the class to be access-checked
2975 * @return {@code targetClass} that has been access-checked
2976 * @throws IllegalAccessException if the class is not accessible from the lookup class
2977 * and previous lookup class, if present, using the allowed access modes.
2978 * @throws SecurityException if a security manager is present and it
2979 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2980 * @throws NullPointerException if {@code targetClass} is {@code null}
2981 * @since 9
2982 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
2983 */
2984 public <T> Class<T> accessClass(Class<T> targetClass) throws IllegalAccessException {
2985 if (!isClassAccessible(targetClass)) {
2986 throw makeAccessException(targetClass);
2987 }
2988 checkSecurityManager(targetClass);
2989 return targetClass;
2990 }
2991
2992 /**
2993 * Produces an early-bound method handle for a virtual method.
2994 * It will bypass checks for overriding methods on the receiver,
2995 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2996 * instruction from within the explicitly specified {@code specialCaller}.
2997 * The type of the method handle will be that of the method,
2998 * with a suitably restricted receiver type prepended.
2999 * (The receiver type will be {@code specialCaller} or a subtype.)
3000 * The method and all its argument types must be accessible
3001 * to the lookup object.
3002 * <p>
3003 * Before method resolution,
3004 * if the explicitly specified caller class is not identical with the
3005 * lookup class, or if this lookup object does not have
3006 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3007 * privileges, the access fails.
3008 * <p>
3009 * The returned method handle will have
3010 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3011 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3012 * <p style="font-size:smaller;">
3013 * <em>(Note: JVM internal methods named {@value ConstantDescs#INIT_NAME}
3014 * are not visible to this API,
3015 * even though the {@code invokespecial} instruction can refer to them
3016 * in special circumstances. Use {@link #findConstructor findConstructor}
3017 * to access instance initialization methods in a safe manner.)</em>
3018 * <p><b>Example:</b>
3019 * {@snippet lang="java" :
3020 import static java.lang.invoke.MethodHandles.*;
3021 import static java.lang.invoke.MethodType.*;
3022 ...
3023 static class Listie extends ArrayList {
3024 public String toString() { return "[wee Listie]"; }
3025 static Lookup lookup() { return MethodHandles.lookup(); }
3026 }
3027 ...
3028 // no access to constructor via invokeSpecial:
3029 MethodHandle MH_newListie = Listie.lookup()
3030 .findConstructor(Listie.class, methodType(void.class));
3031 Listie l = (Listie) MH_newListie.invokeExact();
3032 try { assertEquals("impossible", Listie.lookup().findSpecial(
3033 Listie.class, "<init>", methodType(void.class), Listie.class));
3034 } catch (NoSuchMethodException ex) { } // OK
3035 // access to super and self methods via invokeSpecial:
3036 MethodHandle MH_super = Listie.lookup().findSpecial(
3037 ArrayList.class, "toString" , methodType(String.class), Listie.class);
3038 MethodHandle MH_this = Listie.lookup().findSpecial(
3039 Listie.class, "toString" , methodType(String.class), Listie.class);
3040 MethodHandle MH_duper = Listie.lookup().findSpecial(
3041 Object.class, "toString" , methodType(String.class), Listie.class);
3042 assertEquals("[]", (String) MH_super.invokeExact(l));
3043 assertEquals(""+l, (String) MH_this.invokeExact(l));
3044 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
3045 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
3046 String.class, "toString", methodType(String.class), Listie.class));
3047 } catch (IllegalAccessException ex) { } // OK
3048 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
3049 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
3050 * }
3051 *
3052 * @param refc the class or interface from which the method is accessed
3053 * @param name the name of the method (which must not be "<init>")
3054 * @param type the type of the method, with the receiver argument omitted
3055 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
3056 * @return the desired method handle
3057 * @throws NoSuchMethodException if the method does not exist
3058 * @throws IllegalAccessException if access checking fails,
3059 * or if the method is {@code static},
3060 * or if the method's variable arity modifier bit
3061 * is set and {@code asVarargsCollector} fails
3062 * @throws SecurityException if a security manager is present and it
3063 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3064 * @throws NullPointerException if any argument is null
3065 */
3066 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
3067 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
3068 checkSpecialCaller(specialCaller, refc);
3069 Lookup specialLookup = this.in(specialCaller);
3070 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
3071 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method));
3072 }
3073
3074 /**
3075 * Produces a method handle giving read access to a non-static field.
3076 * The type of the method handle will have a return type of the field's
3077 * value type.
3078 * The method handle's single argument will be the instance containing
3079 * the field.
3080 * Access checking is performed immediately on behalf of the lookup class.
3081 * @param refc the class or interface from which the method is accessed
3082 * @param name the field's name
3083 * @param type the field's type
3084 * @return a method handle which can load values from the field
3085 * @throws NoSuchFieldException if the field does not exist
3086 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3087 * @throws SecurityException if a security manager is present and it
3088 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3089 * @throws NullPointerException if any argument is null
3090 * @see #findVarHandle(Class, String, Class)
3091 */
3092 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3093 MemberName field = resolveOrFail(REF_getField, refc, name, type);
3094 return getDirectField(REF_getField, refc, field);
3095 }
3096
3097 /**
3098 * Produces a method handle giving write access to a non-static field.
3099 * The type of the method handle will have a void return type.
3100 * The method handle will take two arguments, the instance containing
3101 * the field, and the value to be stored.
3102 * The second argument will be of the field's value type.
3103 * Access checking is performed immediately on behalf of the lookup class.
3104 * @param refc the class or interface from which the method is accessed
3105 * @param name the field's name
3106 * @param type the field's type
3107 * @return a method handle which can store values into the field
3108 * @throws NoSuchFieldException if the field does not exist
3109 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3110 * or {@code final}
3111 * @throws SecurityException if a security manager is present and it
3112 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3113 * @throws NullPointerException if any argument is null
3114 * @see #findVarHandle(Class, String, Class)
3115 */
3116 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3117 MemberName field = resolveOrFail(REF_putField, refc, name, type);
3118 return getDirectField(REF_putField, refc, field);
3119 }
3120
3121 /**
3122 * Produces a VarHandle giving access to a non-static field {@code name}
3123 * of type {@code type} declared in a class of type {@code recv}.
3124 * The VarHandle's variable type is {@code type} and it has one
3125 * coordinate type, {@code recv}.
3126 * <p>
3127 * Access checking is performed immediately on behalf of the lookup
3128 * class.
3129 * <p>
3130 * Certain access modes of the returned VarHandle are unsupported under
3131 * the following conditions:
3132 * <ul>
3133 * <li>if the field is declared {@code final}, then the write, atomic
3134 * update, numeric atomic update, and bitwise atomic update access
3135 * modes are unsupported.
3136 * <li>if the field type is anything other than {@code byte},
3137 * {@code short}, {@code char}, {@code int}, {@code long},
3138 * {@code float}, or {@code double} then numeric atomic update
3139 * access modes are unsupported.
3140 * <li>if the field type is anything other than {@code boolean},
3141 * {@code byte}, {@code short}, {@code char}, {@code int} or
3142 * {@code long} then bitwise atomic update access modes are
3143 * unsupported.
3144 * </ul>
3145 * <p>
3146 * If the field is declared {@code volatile} then the returned VarHandle
3147 * will override access to the field (effectively ignore the
3148 * {@code volatile} declaration) in accordance to its specified
3149 * access modes.
3150 * <p>
3151 * If the field type is {@code float} or {@code double} then numeric
3152 * and atomic update access modes compare values using their bitwise
3153 * representation (see {@link Float#floatToRawIntBits} and
3154 * {@link Double#doubleToRawLongBits}, respectively).
3155 * @apiNote
3156 * Bitwise comparison of {@code float} values or {@code double} values,
3157 * as performed by the numeric and atomic update access modes, differ
3158 * from the primitive {@code ==} operator and the {@link Float#equals}
3159 * and {@link Double#equals} methods, specifically with respect to
3160 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3161 * Care should be taken when performing a compare and set or a compare
3162 * and exchange operation with such values since the operation may
3163 * unexpectedly fail.
3164 * There are many possible NaN values that are considered to be
3165 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3166 * provided by Java can distinguish between them. Operation failure can
3167 * occur if the expected or witness value is a NaN value and it is
3168 * transformed (perhaps in a platform specific manner) into another NaN
3169 * value, and thus has a different bitwise representation (see
3170 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3171 * details).
3172 * The values {@code -0.0} and {@code +0.0} have different bitwise
3173 * representations but are considered equal when using the primitive
3174 * {@code ==} operator. Operation failure can occur if, for example, a
3175 * numeric algorithm computes an expected value to be say {@code -0.0}
3176 * and previously computed the witness value to be say {@code +0.0}.
3177 * @param recv the receiver class, of type {@code R}, that declares the
3178 * non-static field
3179 * @param name the field's name
3180 * @param type the field's type, of type {@code T}
3181 * @return a VarHandle giving access to non-static fields.
3182 * @throws NoSuchFieldException if the field does not exist
3183 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3184 * @throws SecurityException if a security manager is present and it
3185 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3186 * @throws NullPointerException if any argument is null
3187 * @since 9
3188 */
3189 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3190 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
3191 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
3192 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
3193 }
3194
3195 /**
3196 * Produces a method handle giving read access to a static field.
3197 * The type of the method handle will have a return type of the field's
3198 * value type.
3199 * The method handle will take no arguments.
3200 * Access checking is performed immediately on behalf of the lookup class.
3201 * <p>
3202 * If the returned method handle is invoked, the field's class will
3203 * be initialized, if it has not already been initialized.
3204 * @param refc the class or interface from which the method is accessed
3205 * @param name the field's name
3206 * @param type the field's type
3207 * @return a method handle which can load values from the field
3208 * @throws NoSuchFieldException if the field does not exist
3209 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3210 * @throws SecurityException if a security manager is present and it
3211 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3212 * @throws NullPointerException if any argument is null
3213 */
3214 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3215 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
3216 return getDirectField(REF_getStatic, refc, field);
3217 }
3218
3219 /**
3220 * Produces a method handle giving write access to a static field.
3221 * The type of the method handle will have a void return type.
3222 * The method handle will take a single
3223 * argument, of the field's value type, the value to be stored.
3224 * Access checking is performed immediately on behalf of the lookup class.
3225 * <p>
3226 * If the returned method handle is invoked, the field's class will
3227 * be initialized, if it has not already been initialized.
3228 * @param refc the class or interface from which the method is accessed
3229 * @param name the field's name
3230 * @param type the field's type
3231 * @return a method handle which can store values into the field
3232 * @throws NoSuchFieldException if the field does not exist
3233 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3234 * or is {@code final}
3235 * @throws SecurityException if a security manager is present and it
3236 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3237 * @throws NullPointerException if any argument is null
3238 */
3239 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3240 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
3241 return getDirectField(REF_putStatic, refc, field);
3242 }
3243
3244 /**
3245 * Produces a VarHandle giving access to a static field {@code name} of
3246 * type {@code type} declared in a class of type {@code decl}.
3247 * The VarHandle's variable type is {@code type} and it has no
3248 * coordinate types.
3249 * <p>
3250 * Access checking is performed immediately on behalf of the lookup
3251 * class.
3252 * <p>
3253 * If the returned VarHandle is operated on, the declaring class will be
3254 * initialized, if it has not already been initialized.
3255 * <p>
3256 * Certain access modes of the returned VarHandle are unsupported under
3257 * the following conditions:
3258 * <ul>
3259 * <li>if the field is declared {@code final}, then the write, atomic
3260 * update, numeric atomic update, and bitwise atomic update access
3261 * modes are unsupported.
3262 * <li>if the field type is anything other than {@code byte},
3263 * {@code short}, {@code char}, {@code int}, {@code long},
3264 * {@code float}, or {@code double}, then numeric atomic update
3265 * access modes are unsupported.
3266 * <li>if the field type is anything other than {@code boolean},
3267 * {@code byte}, {@code short}, {@code char}, {@code int} or
3268 * {@code long} then bitwise atomic update access modes are
3269 * unsupported.
3270 * </ul>
3271 * <p>
3272 * If the field is declared {@code volatile} then the returned VarHandle
3273 * will override access to the field (effectively ignore the
3274 * {@code volatile} declaration) in accordance to its specified
3275 * access modes.
3276 * <p>
3277 * If the field type is {@code float} or {@code double} then numeric
3278 * and atomic update access modes compare values using their bitwise
3279 * representation (see {@link Float#floatToRawIntBits} and
3280 * {@link Double#doubleToRawLongBits}, respectively).
3281 * @apiNote
3282 * Bitwise comparison of {@code float} values or {@code double} values,
3283 * as performed by the numeric and atomic update access modes, differ
3284 * from the primitive {@code ==} operator and the {@link Float#equals}
3285 * and {@link Double#equals} methods, specifically with respect to
3286 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3287 * Care should be taken when performing a compare and set or a compare
3288 * and exchange operation with such values since the operation may
3289 * unexpectedly fail.
3290 * There are many possible NaN values that are considered to be
3291 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3292 * provided by Java can distinguish between them. Operation failure can
3293 * occur if the expected or witness value is a NaN value and it is
3294 * transformed (perhaps in a platform specific manner) into another NaN
3295 * value, and thus has a different bitwise representation (see
3296 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3297 * details).
3298 * The values {@code -0.0} and {@code +0.0} have different bitwise
3299 * representations but are considered equal when using the primitive
3300 * {@code ==} operator. Operation failure can occur if, for example, a
3301 * numeric algorithm computes an expected value to be say {@code -0.0}
3302 * and previously computed the witness value to be say {@code +0.0}.
3303 * @param decl the class that declares the static field
3304 * @param name the field's name
3305 * @param type the field's type, of type {@code T}
3306 * @return a VarHandle giving access to a static field
3307 * @throws NoSuchFieldException if the field does not exist
3308 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3309 * @throws SecurityException if a security manager is present and it
3310 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3311 * @throws NullPointerException if any argument is null
3312 * @since 9
3313 */
3314 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3315 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
3316 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
3317 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
3318 }
3319
3320 /**
3321 * Produces an early-bound method handle for a non-static method.
3322 * The receiver must have a supertype {@code defc} in which a method
3323 * of the given name and type is accessible to the lookup class.
3324 * The method and all its argument types must be accessible to the lookup object.
3325 * The type of the method handle will be that of the method,
3326 * without any insertion of an additional receiver parameter.
3327 * The given receiver will be bound into the method handle,
3328 * so that every call to the method handle will invoke the
3329 * requested method on the given receiver.
3330 * <p>
3331 * The returned method handle will have
3332 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3333 * the method's variable arity modifier bit ({@code 0x0080}) is set
3334 * <em>and</em> the trailing array argument is not the only argument.
3335 * (If the trailing array argument is the only argument,
3336 * the given receiver value will be bound to it.)
3337 * <p>
3338 * This is almost equivalent to the following code, with some differences noted below:
3339 * {@snippet lang="java" :
3340 import static java.lang.invoke.MethodHandles.*;
3341 import static java.lang.invoke.MethodType.*;
3342 ...
3343 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
3344 MethodHandle mh1 = mh0.bindTo(receiver);
3345 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
3346 return mh1;
3347 * }
3348 * where {@code defc} is either {@code receiver.getClass()} or a super
3349 * type of that class, in which the requested method is accessible
3350 * to the lookup class.
3351 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
3352 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
3353 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
3354 * the receiver is restricted by {@code findVirtual} to the lookup class.)
3355 * @param receiver the object from which the method is accessed
3356 * @param name the name of the method
3357 * @param type the type of the method, with the receiver argument omitted
3358 * @return the desired method handle
3359 * @throws NoSuchMethodException if the method does not exist
3360 * @throws IllegalAccessException if access checking fails
3361 * or if the method's variable arity modifier bit
3362 * is set and {@code asVarargsCollector} fails
3363 * @throws SecurityException if a security manager is present and it
3364 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3365 * @throws NullPointerException if any argument is null
3366 * @see MethodHandle#bindTo
3367 * @see #findVirtual
3368 */
3369 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3370 Class<? extends Object> refc = receiver.getClass(); // may get NPE
3371 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
3372 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method));
3373 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
3374 throw new IllegalAccessException("The restricted defining class " +
3375 mh.type().leadingReferenceParameter().getName() +
3376 " is not assignable from receiver class " +
3377 receiver.getClass().getName());
3378 }
3379 return mh.bindArgumentL(0, receiver).setVarargs(method);
3380 }
3381
3382 /**
3383 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3384 * to <i>m</i>, if the lookup class has permission.
3385 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
3386 * If <i>m</i> is virtual, overriding is respected on every call.
3387 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
3388 * The type of the method handle will be that of the method,
3389 * with the receiver type prepended (but only if it is non-static).
3390 * If the method's {@code accessible} flag is not set,
3391 * access checking is performed immediately on behalf of the lookup class.
3392 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
3393 * <p>
3394 * The returned method handle will have
3395 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3396 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3397 * <p>
3398 * If <i>m</i> is static, and
3399 * if the returned method handle is invoked, the method's class will
3400 * be initialized, if it has not already been initialized.
3401 * @param m the reflected method
3402 * @return a method handle which can invoke the reflected method
3403 * @throws IllegalAccessException if access checking fails
3404 * or if the method's variable arity modifier bit
3405 * is set and {@code asVarargsCollector} fails
3406 * @throws NullPointerException if the argument is null
3407 */
3408 public MethodHandle unreflect(Method m) throws IllegalAccessException {
3409 if (m.getDeclaringClass() == MethodHandle.class) {
3410 MethodHandle mh = unreflectForMH(m);
3411 if (mh != null) return mh;
3412 }
3413 if (m.getDeclaringClass() == VarHandle.class) {
3414 MethodHandle mh = unreflectForVH(m);
3415 if (mh != null) return mh;
3416 }
3417 MemberName method = new MemberName(m);
3418 byte refKind = method.getReferenceKind();
3419 if (refKind == REF_invokeSpecial)
3420 refKind = REF_invokeVirtual;
3421 assert(method.isMethod());
3422 @SuppressWarnings("deprecation")
3423 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
3424 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3425 }
3426 private MethodHandle unreflectForMH(Method m) {
3427 // these names require special lookups because they throw UnsupportedOperationException
3428 if (MemberName.isMethodHandleInvokeName(m.getName()))
3429 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
3430 return null;
3431 }
3432 private MethodHandle unreflectForVH(Method m) {
3433 // these names require special lookups because they throw UnsupportedOperationException
3434 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
3435 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
3436 return null;
3437 }
3438
3439 /**
3440 * Produces a method handle for a reflected method.
3441 * It will bypass checks for overriding methods on the receiver,
3442 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3443 * instruction from within the explicitly specified {@code specialCaller}.
3444 * The type of the method handle will be that of the method,
3445 * with a suitably restricted receiver type prepended.
3446 * (The receiver type will be {@code specialCaller} or a subtype.)
3447 * If the method's {@code accessible} flag is not set,
3448 * access checking is performed immediately on behalf of the lookup class,
3449 * as if {@code invokespecial} instruction were being linked.
3450 * <p>
3451 * Before method resolution,
3452 * if the explicitly specified caller class is not identical with the
3453 * lookup class, or if this lookup object does not have
3454 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3455 * privileges, the access fails.
3456 * <p>
3457 * The returned method handle will have
3458 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3459 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3460 * @param m the reflected method
3461 * @param specialCaller the class nominally calling the method
3462 * @return a method handle which can invoke the reflected method
3463 * @throws IllegalAccessException if access checking fails,
3464 * or if the method is {@code static},
3465 * or if the method's variable arity modifier bit
3466 * is set and {@code asVarargsCollector} fails
3467 * @throws NullPointerException if any argument is null
3468 */
3469 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
3470 checkSpecialCaller(specialCaller, m.getDeclaringClass());
3471 Lookup specialLookup = this.in(specialCaller);
3472 MemberName method = new MemberName(m, true);
3473 assert(method.isMethod());
3474 // ignore m.isAccessible: this is a new kind of access
3475 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3476 }
3477
3478 /**
3479 * Produces a method handle for a reflected constructor.
3480 * The type of the method handle will be that of the constructor,
3481 * with the return type changed to the declaring class.
3482 * The method handle will perform a {@code newInstance} operation,
3483 * creating a new instance of the constructor's class on the
3484 * arguments passed to the method handle.
3485 * <p>
3486 * If the constructor's {@code accessible} flag is not set,
3487 * access checking is performed immediately on behalf of the lookup class.
3488 * <p>
3489 * The returned method handle will have
3490 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3491 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
3492 * <p>
3493 * If the returned method handle is invoked, the constructor's class will
3494 * be initialized, if it has not already been initialized.
3495 * @param c the reflected constructor
3496 * @return a method handle which can invoke the reflected constructor
3497 * @throws IllegalAccessException if access checking fails
3498 * or if the method's variable arity modifier bit
3499 * is set and {@code asVarargsCollector} fails
3500 * @throws NullPointerException if the argument is null
3501 */
3502 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
3503 MemberName ctor = new MemberName(c);
3504 assert(ctor.isConstructor());
3505 @SuppressWarnings("deprecation")
3506 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
3507 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
3508 }
3509
3510 /*
3511 * Produces a method handle that is capable of creating instances of the given class
3512 * and instantiated by the given constructor. No security manager check.
3513 *
3514 * This method should only be used by ReflectionFactory::newConstructorForSerialization.
3515 */
3516 /* package-private */ MethodHandle serializableConstructor(Class<?> decl, Constructor<?> c) throws IllegalAccessException {
3517 MemberName ctor = new MemberName(c);
3518 assert(ctor.isConstructor() && constructorInSuperclass(decl, c));
3519 checkAccess(REF_newInvokeSpecial, decl, ctor);
3520 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3521 return DirectMethodHandle.makeAllocator(decl, ctor).setVarargs(ctor);
3522 }
3523
3524 private static boolean constructorInSuperclass(Class<?> decl, Constructor<?> ctor) {
3525 if (decl == ctor.getDeclaringClass())
3526 return true;
3527
3528 Class<?> cl = decl;
3529 while ((cl = cl.getSuperclass()) != null) {
3530 if (cl == ctor.getDeclaringClass()) {
3531 return true;
3532 }
3533 }
3534 return false;
3535 }
3536
3537 /**
3538 * Produces a method handle giving read access to a reflected field.
3539 * The type of the method handle will have a return type of the field's
3540 * value type.
3541 * If the field is {@code static}, the method handle will take no arguments.
3542 * Otherwise, its single argument will be the instance containing
3543 * the field.
3544 * If the {@code Field} object's {@code accessible} flag is not set,
3545 * access checking is performed immediately on behalf of the lookup class.
3546 * <p>
3547 * If the field is static, and
3548 * if the returned method handle is invoked, the field's class will
3549 * be initialized, if it has not already been initialized.
3550 * @param f the reflected field
3551 * @return a method handle which can load values from the reflected field
3552 * @throws IllegalAccessException if access checking fails
3553 * @throws NullPointerException if the argument is null
3554 */
3555 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
3556 return unreflectField(f, false);
3557 }
3558
3559 /**
3560 * Produces a method handle giving write access to a reflected field.
3561 * The type of the method handle will have a void return type.
3562 * If the field is {@code static}, the method handle will take a single
3563 * argument, of the field's value type, the value to be stored.
3564 * Otherwise, the two arguments will be the instance containing
3565 * the field, and the value to be stored.
3566 * If the {@code Field} object's {@code accessible} flag is not set,
3567 * access checking is performed immediately on behalf of the lookup class.
3568 * <p>
3569 * If the field is {@code final}, write access will not be
3570 * allowed and access checking will fail, except under certain
3571 * narrow circumstances documented for {@link Field#set Field.set}.
3572 * A method handle is returned only if a corresponding call to
3573 * the {@code Field} object's {@code set} method could return
3574 * normally. In particular, fields which are both {@code static}
3575 * and {@code final} may never be set.
3576 * <p>
3577 * If the field is {@code static}, and
3578 * if the returned method handle is invoked, the field's class will
3579 * be initialized, if it has not already been initialized.
3580 * @param f the reflected field
3581 * @return a method handle which can store values into the reflected field
3582 * @throws IllegalAccessException if access checking fails,
3583 * or if the field is {@code final} and write access
3584 * is not enabled on the {@code Field} object
3585 * @throws NullPointerException if the argument is null
3586 */
3587 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
3588 return unreflectField(f, true);
3589 }
3590
3591 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
3592 MemberName field = new MemberName(f, isSetter);
3593 if (isSetter && field.isFinal()) {
3594 if (field.isTrustedFinalField()) {
3595 String msg = field.isStatic() ? "static final field has no write access"
3596 : "final field has no write access";
3597 throw field.makeAccessException(msg, this);
3598 }
3599 }
3600 assert(isSetter
3601 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
3602 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
3603 @SuppressWarnings("deprecation")
3604 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
3605 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
3606 }
3607
3608 /**
3609 * Produces a VarHandle giving access to a reflected field {@code f}
3610 * of type {@code T} declared in a class of type {@code R}.
3611 * The VarHandle's variable type is {@code T}.
3612 * If the field is non-static the VarHandle has one coordinate type,
3613 * {@code R}. Otherwise, the field is static, and the VarHandle has no
3614 * coordinate types.
3615 * <p>
3616 * Access checking is performed immediately on behalf of the lookup
3617 * class, regardless of the value of the field's {@code accessible}
3618 * flag.
3619 * <p>
3620 * If the field is static, and if the returned VarHandle is operated
3621 * on, the field's declaring class will be initialized, if it has not
3622 * already been initialized.
3623 * <p>
3624 * Certain access modes of the returned VarHandle are unsupported under
3625 * the following conditions:
3626 * <ul>
3627 * <li>if the field is declared {@code final}, then the write, atomic
3628 * update, numeric atomic update, and bitwise atomic update access
3629 * modes are unsupported.
3630 * <li>if the field type is anything other than {@code byte},
3631 * {@code short}, {@code char}, {@code int}, {@code long},
3632 * {@code float}, or {@code double} then numeric atomic update
3633 * access modes are unsupported.
3634 * <li>if the field type is anything other than {@code boolean},
3635 * {@code byte}, {@code short}, {@code char}, {@code int} or
3636 * {@code long} then bitwise atomic update access modes are
3637 * unsupported.
3638 * </ul>
3639 * <p>
3640 * If the field is declared {@code volatile} then the returned VarHandle
3641 * will override access to the field (effectively ignore the
3642 * {@code volatile} declaration) in accordance to its specified
3643 * access modes.
3644 * <p>
3645 * If the field type is {@code float} or {@code double} then numeric
3646 * and atomic update access modes compare values using their bitwise
3647 * representation (see {@link Float#floatToRawIntBits} and
3648 * {@link Double#doubleToRawLongBits}, respectively).
3649 * @apiNote
3650 * Bitwise comparison of {@code float} values or {@code double} values,
3651 * as performed by the numeric and atomic update access modes, differ
3652 * from the primitive {@code ==} operator and the {@link Float#equals}
3653 * and {@link Double#equals} methods, specifically with respect to
3654 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3655 * Care should be taken when performing a compare and set or a compare
3656 * and exchange operation with such values since the operation may
3657 * unexpectedly fail.
3658 * There are many possible NaN values that are considered to be
3659 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3660 * provided by Java can distinguish between them. Operation failure can
3661 * occur if the expected or witness value is a NaN value and it is
3662 * transformed (perhaps in a platform specific manner) into another NaN
3663 * value, and thus has a different bitwise representation (see
3664 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3665 * details).
3666 * The values {@code -0.0} and {@code +0.0} have different bitwise
3667 * representations but are considered equal when using the primitive
3668 * {@code ==} operator. Operation failure can occur if, for example, a
3669 * numeric algorithm computes an expected value to be say {@code -0.0}
3670 * and previously computed the witness value to be say {@code +0.0}.
3671 * @param f the reflected field, with a field of type {@code T}, and
3672 * a declaring class of type {@code R}
3673 * @return a VarHandle giving access to non-static fields or a static
3674 * field
3675 * @throws IllegalAccessException if access checking fails
3676 * @throws NullPointerException if the argument is null
3677 * @since 9
3678 */
3679 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
3680 MemberName getField = new MemberName(f, false);
3681 MemberName putField = new MemberName(f, true);
3682 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
3683 f.getDeclaringClass(), getField, putField);
3684 }
3685
3686 /**
3687 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3688 * created by this lookup object or a similar one.
3689 * Security and access checks are performed to ensure that this lookup object
3690 * is capable of reproducing the target method handle.
3691 * This means that the cracking may fail if target is a direct method handle
3692 * but was created by an unrelated lookup object.
3693 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
3694 * and was created by a lookup object for a different class.
3695 * @param target a direct method handle to crack into symbolic reference components
3696 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
3697 * @throws SecurityException if a security manager is present and it
3698 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3699 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
3700 * @throws NullPointerException if the target is {@code null}
3701 * @see MethodHandleInfo
3702 * @since 1.8
3703 */
3704 public MethodHandleInfo revealDirect(MethodHandle target) {
3705 if (!target.isCrackable()) {
3706 throw newIllegalArgumentException("not a direct method handle");
3707 }
3708 MemberName member = target.internalMemberName();
3709 Class<?> defc = member.getDeclaringClass();
3710 byte refKind = member.getReferenceKind();
3711 assert(MethodHandleNatives.refKindIsValid(refKind));
3712 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
3713 // Devirtualized method invocation is usually formally virtual.
3714 // To avoid creating extra MemberName objects for this common case,
3715 // we encode this extra degree of freedom using MH.isInvokeSpecial.
3716 refKind = REF_invokeVirtual;
3717 if (refKind == REF_invokeVirtual && defc.isInterface())
3718 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
3719 refKind = REF_invokeInterface;
3720 // Check SM permissions and member access before cracking.
3721 try {
3722 checkAccess(refKind, defc, member);
3723 checkSecurityManager(defc, member);
3724 } catch (IllegalAccessException ex) {
3725 throw new IllegalArgumentException(ex);
3726 }
3727 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
3728 Class<?> callerClass = target.internalCallerClass();
3729 if ((lookupModes() & ORIGINAL) == 0 || callerClass != lookupClass())
3730 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
3731 }
3732 // Produce the handle to the results.
3733 return new InfoFromMemberName(this, member, refKind);
3734 }
3735
3736 //--- Helper methods, all package-private.
3737
3738 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3739 checkSymbolicClass(refc); // do this before attempting to resolve
3740 Objects.requireNonNull(name);
3741 Objects.requireNonNull(type);
3742 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3743 NoSuchFieldException.class);
3744 }
3745
3746 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3747 checkSymbolicClass(refc); // do this before attempting to resolve
3748 Objects.requireNonNull(type);
3749 checkMethodName(refKind, name); // implicit null-check of name
3750 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3751 NoSuchMethodException.class);
3752 }
3753
3754 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
3755 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
3756 Objects.requireNonNull(member.getName());
3757 Objects.requireNonNull(member.getType());
3758 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), allowedModes,
3759 ReflectiveOperationException.class);
3760 }
3761
3762 MemberName resolveOrNull(byte refKind, MemberName member) {
3763 // do this before attempting to resolve
3764 if (!isClassAccessible(member.getDeclaringClass())) {
3765 return null;
3766 }
3767 Objects.requireNonNull(member.getName());
3768 Objects.requireNonNull(member.getType());
3769 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull(), allowedModes);
3770 }
3771
3772 MemberName resolveOrNull(byte refKind, Class<?> refc, String name, MethodType type) {
3773 // do this before attempting to resolve
3774 if (!isClassAccessible(refc)) {
3775 return null;
3776 }
3777 Objects.requireNonNull(type);
3778 // implicit null-check of name
3779 if (name.startsWith("<") && refKind != REF_newInvokeSpecial) {
3780 return null;
3781 }
3782 return IMPL_NAMES.resolveOrNull(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes);
3783 }
3784
3785 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
3786 if (!isClassAccessible(refc)) {
3787 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
3788 }
3789 }
3790
3791 boolean isClassAccessible(Class<?> refc) {
3792 Objects.requireNonNull(refc);
3793 Class<?> caller = lookupClassOrNull();
3794 Class<?> type = refc;
3795 while (type.isArray()) {
3796 type = type.getComponentType();
3797 }
3798 return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes);
3799 }
3800
3801 /** Check name for an illegal leading "<" character. */
3802 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
3803 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
3804 throw new NoSuchMethodException("illegal method name: "+name);
3805 }
3806
3807 /**
3808 * Find my trustable caller class if m is a caller sensitive method.
3809 * If this lookup object has original full privilege access, then the caller class is the lookupClass.
3810 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
3811 */
3812 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException {
3813 if (MethodHandleNatives.isCallerSensitive(m) && (lookupModes() & ORIGINAL) == 0) {
3814 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods
3815 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3816 }
3817 return this;
3818 }
3819
3820 /**
3821 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3822 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3823 *
3824 * @deprecated This method was originally designed to test {@code PRIVATE} access
3825 * that implies full privilege access but {@code MODULE} access has since become
3826 * independent of {@code PRIVATE} access. It is recommended to call
3827 * {@link #hasFullPrivilegeAccess()} instead.
3828 * @since 9
3829 */
3830 @Deprecated(since="14")
3831 public boolean hasPrivateAccess() {
3832 return hasFullPrivilegeAccess();
3833 }
3834
3835 /**
3836 * Returns {@code true} if this lookup has <em>full privilege access</em>,
3837 * i.e. {@code PRIVATE} and {@code MODULE} access.
3838 * A {@code Lookup} object must have full privilege access in order to
3839 * access all members that are allowed to the
3840 * {@linkplain #lookupClass() lookup class}.
3841 *
3842 * @return {@code true} if this lookup has full privilege access.
3843 * @since 14
3844 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a>
3845 */
3846 public boolean hasFullPrivilegeAccess() {
3847 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE);
3848 }
3849
3850 /**
3851 * Perform steps 1 and 2b <a href="MethodHandles.Lookup.html#secmgr">access checks</a>
3852 * for ensureInitialized, findClass or accessClass.
3853 */
3854 void checkSecurityManager(Class<?> refc) {
3855 if (allowedModes == TRUSTED) return;
3856
3857 @SuppressWarnings("removal")
3858 SecurityManager smgr = System.getSecurityManager();
3859 if (smgr == null) return;
3860
3861 // Step 1:
3862 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3863 if (!fullPrivilegeLookup ||
3864 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3865 ReflectUtil.checkPackageAccess(refc);
3866 }
3867
3868 // Step 2b:
3869 if (!fullPrivilegeLookup) {
3870 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
3871 }
3872 }
3873
3874 /**
3875 * Perform steps 1, 2a and 3 <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
3876 * Determines a trustable caller class to compare with refc, the symbolic reference class.
3877 * If this lookup object has full privilege access except original access,
3878 * then the caller class is the lookupClass.
3879 *
3880 * Lookup object created by {@link MethodHandles#privateLookupIn(Class, Lookup)}
3881 * from the same module skips the security permission check.
3882 */
3883 void checkSecurityManager(Class<?> refc, MemberName m) {
3884 Objects.requireNonNull(refc);
3885 Objects.requireNonNull(m);
3886
3887 if (allowedModes == TRUSTED) return;
3888
3889 @SuppressWarnings("removal")
3890 SecurityManager smgr = System.getSecurityManager();
3891 if (smgr == null) return;
3892
3893 // Step 1:
3894 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3895 if (!fullPrivilegeLookup ||
3896 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3897 ReflectUtil.checkPackageAccess(refc);
3898 }
3899
3900 // Step 2a:
3901 if (m.isPublic()) return;
3902 if (!fullPrivilegeLookup) {
3903 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
3904 }
3905
3906 // Step 3:
3907 Class<?> defc = m.getDeclaringClass();
3908 if (!fullPrivilegeLookup && defc != refc) {
3909 ReflectUtil.checkPackageAccess(defc);
3910 }
3911 }
3912
3913 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3914 boolean wantStatic = (refKind == REF_invokeStatic);
3915 String message;
3916 if (m.isConstructor())
3917 message = "expected a method, not a constructor";
3918 else if (!m.isMethod())
3919 message = "expected a method";
3920 else if (wantStatic != m.isStatic())
3921 message = wantStatic ? "expected a static method" : "expected a non-static method";
3922 else
3923 { checkAccess(refKind, refc, m); return; }
3924 throw m.makeAccessException(message, this);
3925 }
3926
3927 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3928 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
3929 String message;
3930 if (wantStatic != m.isStatic())
3931 message = wantStatic ? "expected a static field" : "expected a non-static field";
3932 else
3933 { checkAccess(refKind, refc, m); return; }
3934 throw m.makeAccessException(message, this);
3935 }
3936
3937 private boolean isArrayClone(byte refKind, Class<?> refc, MemberName m) {
3938 return Modifier.isProtected(m.getModifiers()) &&
3939 refKind == REF_invokeVirtual &&
3940 m.getDeclaringClass() == Object.class &&
3941 m.getName().equals("clone") &&
3942 refc.isArray();
3943 }
3944
3945 /** Check public/protected/private bits on the symbolic reference class and its member. */
3946 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3947 assert(m.referenceKindIsConsistentWith(refKind) &&
3948 MethodHandleNatives.refKindIsValid(refKind) &&
3949 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
3950 int allowedModes = this.allowedModes;
3951 if (allowedModes == TRUSTED) return;
3952 int mods = m.getModifiers();
3953 if (isArrayClone(refKind, refc, m)) {
3954 // The JVM does this hack also.
3955 // (See ClassVerifier::verify_invoke_instructions
3956 // and LinkResolver::check_method_accessability.)
3957 // Because the JVM does not allow separate methods on array types,
3958 // there is no separate method for int[].clone.
3959 // All arrays simply inherit Object.clone.
3960 // But for access checking logic, we make Object.clone
3961 // (normally protected) appear to be public.
3962 // Later on, when the DirectMethodHandle is created,
3963 // its leading argument will be restricted to the
3964 // requested array type.
3965 // N.B. The return type is not adjusted, because
3966 // that is *not* the bytecode behavior.
3967 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
3968 }
3969 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
3970 // cannot "new" a protected ctor in a different package
3971 mods ^= Modifier.PROTECTED;
3972 }
3973 if (Modifier.isFinal(mods) &&
3974 MethodHandleNatives.refKindIsSetter(refKind))
3975 throw m.makeAccessException("unexpected set of a final field", this);
3976 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
3977 if ((requestedModes & allowedModes) != 0) {
3978 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
3979 mods, lookupClass(), previousLookupClass(), allowedModes))
3980 return;
3981 } else {
3982 // Protected members can also be checked as if they were package-private.
3983 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
3984 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
3985 return;
3986 }
3987 throw m.makeAccessException(accessFailedMessage(refc, m), this);
3988 }
3989
3990 String accessFailedMessage(Class<?> refc, MemberName m) {
3991 Class<?> defc = m.getDeclaringClass();
3992 int mods = m.getModifiers();
3993 // check the class first:
3994 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
3995 (defc == refc ||
3996 Modifier.isPublic(refc.getModifiers())));
3997 if (!classOK && (allowedModes & PACKAGE) != 0) {
3998 // ignore previous lookup class to check if default package access
3999 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
4000 (defc == refc ||
4001 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
4002 }
4003 if (!classOK)
4004 return "class is not public";
4005 if (Modifier.isPublic(mods))
4006 return "access to public member failed"; // (how?, module not readable?)
4007 if (Modifier.isPrivate(mods))
4008 return "member is private";
4009 if (Modifier.isProtected(mods))
4010 return "member is protected";
4011 return "member is private to package";
4012 }
4013
4014 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
4015 int allowedModes = this.allowedModes;
4016 if (allowedModes == TRUSTED) return;
4017 if ((lookupModes() & PRIVATE) == 0
4018 || (specialCaller != lookupClass()
4019 // ensure non-abstract methods in superinterfaces can be special-invoked
4020 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
4021 throw new MemberName(specialCaller).
4022 makeAccessException("no private access for invokespecial", this);
4023 }
4024
4025 private boolean restrictProtectedReceiver(MemberName method) {
4026 // The accessing class only has the right to use a protected member
4027 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
4028 if (!method.isProtected() || method.isStatic()
4029 || allowedModes == TRUSTED
4030 || method.getDeclaringClass() == lookupClass()
4031 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
4032 return false;
4033 return true;
4034 }
4035 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
4036 assert(!method.isStatic());
4037 // receiver type of mh is too wide; narrow to caller
4038 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
4039 throw method.makeAccessException("caller class must be a subclass below the method", caller);
4040 }
4041 MethodType rawType = mh.type();
4042 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
4043 MethodType narrowType = rawType.changeParameterType(0, caller);
4044 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
4045 assert(mh.viewAsTypeChecks(narrowType, true));
4046 return mh.copyWith(narrowType, mh.form);
4047 }
4048
4049 /** Check access and get the requested method. */
4050 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4051 final boolean doRestrict = true;
4052 final boolean checkSecurity = true;
4053 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4054 }
4055 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
4056 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4057 final boolean doRestrict = false;
4058 final boolean checkSecurity = true;
4059 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerLookup);
4060 }
4061 /** Check access and get the requested method, eliding security manager checks. */
4062 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4063 final boolean doRestrict = true;
4064 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4065 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4066 }
4067 /** Common code for all methods; do not call directly except from immediately above. */
4068 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
4069 boolean checkSecurity,
4070 boolean doRestrict,
4071 Lookup boundCaller) throws IllegalAccessException {
4072 checkMethod(refKind, refc, method);
4073 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4074 if (checkSecurity)
4075 checkSecurityManager(refc, method);
4076 assert(!method.isMethodHandleInvoke());
4077
4078 if (refKind == REF_invokeSpecial &&
4079 refc != lookupClass() &&
4080 !refc.isInterface() && !lookupClass().isInterface() &&
4081 refc != lookupClass().getSuperclass() &&
4082 refc.isAssignableFrom(lookupClass())) {
4083 assert(!method.getName().equals(ConstantDescs.INIT_NAME)); // not this code path
4084
4085 // Per JVMS 6.5, desc. of invokespecial instruction:
4086 // If the method is in a superclass of the LC,
4087 // and if our original search was above LC.super,
4088 // repeat the search (symbolic lookup) from LC.super
4089 // and continue with the direct superclass of that class,
4090 // and so forth, until a match is found or no further superclasses exist.
4091 // FIXME: MemberName.resolve should handle this instead.
4092 Class<?> refcAsSuper = lookupClass();
4093 MemberName m2;
4094 do {
4095 refcAsSuper = refcAsSuper.getSuperclass();
4096 m2 = new MemberName(refcAsSuper,
4097 method.getName(),
4098 method.getMethodType(),
4099 REF_invokeSpecial);
4100 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull(), allowedModes);
4101 } while (m2 == null && // no method is found yet
4102 refc != refcAsSuper); // search up to refc
4103 if (m2 == null) throw new InternalError(method.toString());
4104 method = m2;
4105 refc = refcAsSuper;
4106 // redo basic checks
4107 checkMethod(refKind, refc, method);
4108 }
4109 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
4110 MethodHandle mh = dmh;
4111 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
4112 if ((doRestrict && refKind == REF_invokeSpecial) ||
4113 (MethodHandleNatives.refKindHasReceiver(refKind) &&
4114 restrictProtectedReceiver(method) &&
4115 // All arrays simply inherit the protected Object.clone method.
4116 // The leading argument is already restricted to the requested
4117 // array type (not the lookup class).
4118 !isArrayClone(refKind, refc, method))) {
4119 mh = restrictReceiver(method, dmh, lookupClass());
4120 }
4121 mh = maybeBindCaller(method, mh, boundCaller);
4122 mh = mh.setVarargs(method);
4123 return mh;
4124 }
4125 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller)
4126 throws IllegalAccessException {
4127 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
4128 return mh;
4129
4130 // boundCaller must have full privilege access.
4131 // It should have been checked by findBoundCallerLookup. Safe to check this again.
4132 if ((boundCaller.lookupModes() & ORIGINAL) == 0)
4133 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
4134
4135 assert boundCaller.hasFullPrivilegeAccess();
4136
4137 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass);
4138 // Note: caller will apply varargs after this step happens.
4139 return cbmh;
4140 }
4141
4142 /** Check access and get the requested field. */
4143 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4144 final boolean checkSecurity = true;
4145 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4146 }
4147 /** Check access and get the requested field, eliding security manager checks. */
4148 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4149 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4150 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4151 }
4152 /** Common code for all fields; do not call directly except from immediately above. */
4153 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
4154 boolean checkSecurity) throws IllegalAccessException {
4155 checkField(refKind, refc, field);
4156 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4157 if (checkSecurity)
4158 checkSecurityManager(refc, field);
4159 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
4160 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
4161 restrictProtectedReceiver(field));
4162 if (doRestrict)
4163 return restrictReceiver(field, dmh, lookupClass());
4164 return dmh;
4165 }
4166 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
4167 Class<?> refc, MemberName getField, MemberName putField)
4168 throws IllegalAccessException {
4169 final boolean checkSecurity = true;
4170 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4171 }
4172 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
4173 Class<?> refc, MemberName getField, MemberName putField)
4174 throws IllegalAccessException {
4175 final boolean checkSecurity = false;
4176 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4177 }
4178 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
4179 Class<?> refc, MemberName getField, MemberName putField,
4180 boolean checkSecurity) throws IllegalAccessException {
4181 assert getField.isStatic() == putField.isStatic();
4182 assert getField.isGetter() && putField.isSetter();
4183 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
4184 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
4185
4186 checkField(getRefKind, refc, getField);
4187 if (checkSecurity)
4188 checkSecurityManager(refc, getField);
4189
4190 if (!putField.isFinal()) {
4191 // A VarHandle does not support updates to final fields, any
4192 // such VarHandle to a final field will be read-only and
4193 // therefore the following write-based accessibility checks are
4194 // only required for non-final fields
4195 checkField(putRefKind, refc, putField);
4196 if (checkSecurity)
4197 checkSecurityManager(refc, putField);
4198 }
4199
4200 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
4201 restrictProtectedReceiver(getField));
4202 if (doRestrict) {
4203 assert !getField.isStatic();
4204 // receiver type of VarHandle is too wide; narrow to caller
4205 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
4206 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
4207 }
4208 refc = lookupClass();
4209 }
4210 return VarHandles.makeFieldHandle(getField, refc,
4211 this.allowedModes == TRUSTED && !getField.isTrustedFinalField());
4212 }
4213 /** Check access and get the requested constructor. */
4214 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4215 final boolean checkSecurity = true;
4216 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4217 }
4218 /** Check access and get the requested constructor, eliding security manager checks. */
4219 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4220 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4221 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4222 }
4223 /** Common code for all constructors; do not call directly except from immediately above. */
4224 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
4225 boolean checkSecurity) throws IllegalAccessException {
4226 assert(ctor.isConstructor());
4227 checkAccess(REF_newInvokeSpecial, refc, ctor);
4228 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4229 if (checkSecurity)
4230 checkSecurityManager(refc, ctor);
4231 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
4232 return DirectMethodHandle.make(ctor).setVarargs(ctor);
4233 }
4234
4235 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
4236 */
4237 /*non-public*/
4238 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
4239 throws ReflectiveOperationException {
4240 if (!(type instanceof Class || type instanceof MethodType))
4241 throw new InternalError("unresolved MemberName");
4242 MemberName member = new MemberName(refKind, defc, name, type);
4243 MethodHandle mh = LOOKASIDE_TABLE.get(member);
4244 if (mh != null) {
4245 checkSymbolicClass(defc);
4246 return mh;
4247 }
4248 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
4249 // Treat MethodHandle.invoke and invokeExact specially.
4250 mh = findVirtualForMH(member.getName(), member.getMethodType());
4251 if (mh != null) {
4252 return mh;
4253 }
4254 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
4255 // Treat signature-polymorphic methods on VarHandle specially.
4256 mh = findVirtualForVH(member.getName(), member.getMethodType());
4257 if (mh != null) {
4258 return mh;
4259 }
4260 }
4261 MemberName resolved = resolveOrFail(refKind, member);
4262 mh = getDirectMethodForConstant(refKind, defc, resolved);
4263 if (mh instanceof DirectMethodHandle dmh
4264 && canBeCached(refKind, defc, resolved)) {
4265 MemberName key = mh.internalMemberName();
4266 if (key != null) {
4267 key = key.asNormalOriginal();
4268 }
4269 if (member.equals(key)) { // better safe than sorry
4270 LOOKASIDE_TABLE.put(key, dmh);
4271 }
4272 }
4273 return mh;
4274 }
4275 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
4276 if (refKind == REF_invokeSpecial) {
4277 return false;
4278 }
4279 if (!Modifier.isPublic(defc.getModifiers()) ||
4280 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
4281 !member.isPublic() ||
4282 member.isCallerSensitive()) {
4283 return false;
4284 }
4285 ClassLoader loader = defc.getClassLoader();
4286 if (loader != null) {
4287 ClassLoader sysl = ClassLoader.getSystemClassLoader();
4288 boolean found = false;
4289 while (sysl != null) {
4290 if (loader == sysl) { found = true; break; }
4291 sysl = sysl.getParent();
4292 }
4293 if (!found) {
4294 return false;
4295 }
4296 }
4297 try {
4298 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
4299 new MemberName(refKind, defc, member.getName(), member.getType()));
4300 if (resolved2 == null) {
4301 return false;
4302 }
4303 checkSecurityManager(defc, resolved2);
4304 } catch (SecurityException ex) {
4305 return false;
4306 }
4307 return true;
4308 }
4309 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
4310 throws ReflectiveOperationException {
4311 if (MethodHandleNatives.refKindIsField(refKind)) {
4312 return getDirectFieldNoSecurityManager(refKind, defc, member);
4313 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
4314 return getDirectMethodNoSecurityManager(refKind, defc, member, findBoundCallerLookup(member));
4315 } else if (refKind == REF_newInvokeSpecial) {
4316 return getDirectConstructorNoSecurityManager(defc, member);
4317 }
4318 // oops
4319 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
4320 }
4321
4322 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
4323 }
4324
4325 /**
4326 * Produces a method handle constructing arrays of a desired type,
4327 * as if by the {@code anewarray} bytecode.
4328 * The return type of the method handle will be the array type.
4329 * The type of its sole argument will be {@code int}, which specifies the size of the array.
4330 *
4331 * <p> If the returned method handle is invoked with a negative
4332 * array size, a {@code NegativeArraySizeException} will be thrown.
4333 *
4334 * @param arrayClass an array type
4335 * @return a method handle which can create arrays of the given type
4336 * @throws NullPointerException if the argument is {@code null}
4337 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
4338 * @see java.lang.reflect.Array#newInstance(Class, int)
4339 * @jvms 6.5 {@code anewarray} Instruction
4340 * @since 9
4341 */
4342 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
4343 if (!arrayClass.isArray()) {
4344 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
4345 }
4346 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
4347 bindTo(arrayClass.getComponentType());
4348 return ani.asType(ani.type().changeReturnType(arrayClass));
4349 }
4350
4351 /**
4352 * Produces a method handle returning the length of an array,
4353 * as if by the {@code arraylength} bytecode.
4354 * The type of the method handle will have {@code int} as return type,
4355 * and its sole argument will be the array type.
4356 *
4357 * <p> If the returned method handle is invoked with a {@code null}
4358 * array reference, a {@code NullPointerException} will be thrown.
4359 *
4360 * @param arrayClass an array type
4361 * @return a method handle which can retrieve the length of an array of the given array type
4362 * @throws NullPointerException if the argument is {@code null}
4363 * @throws IllegalArgumentException if arrayClass is not an array type
4364 * @jvms 6.5 {@code arraylength} Instruction
4365 * @since 9
4366 */
4367 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
4368 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
4369 }
4370
4371 /**
4372 * Produces a method handle giving read access to elements of an array,
4373 * as if by the {@code aaload} bytecode.
4374 * The type of the method handle will have a return type of the array's
4375 * element type. Its first argument will be the array type,
4376 * and the second will be {@code int}.
4377 *
4378 * <p> When the returned method handle is invoked,
4379 * the array reference and array index are checked.
4380 * A {@code NullPointerException} will be thrown if the array reference
4381 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4382 * thrown if the index is negative or if it is greater than or equal to
4383 * the length of the array.
4384 *
4385 * @param arrayClass an array type
4386 * @return a method handle which can load values from the given array type
4387 * @throws NullPointerException if the argument is null
4388 * @throws IllegalArgumentException if arrayClass is not an array type
4389 * @jvms 6.5 {@code aaload} Instruction
4390 */
4391 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
4392 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
4393 }
4394
4395 /**
4396 * Produces a method handle giving write access to elements of an array,
4397 * as if by the {@code astore} bytecode.
4398 * The type of the method handle will have a void return type.
4399 * Its last argument will be the array's element type.
4400 * The first and second arguments will be the array type and int.
4401 *
4402 * <p> When the returned method handle is invoked,
4403 * the array reference and array index are checked.
4404 * A {@code NullPointerException} will be thrown if the array reference
4405 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4406 * thrown if the index is negative or if it is greater than or equal to
4407 * the length of the array.
4408 *
4409 * @param arrayClass the class of an array
4410 * @return a method handle which can store values into the array type
4411 * @throws NullPointerException if the argument is null
4412 * @throws IllegalArgumentException if arrayClass is not an array type
4413 * @jvms 6.5 {@code aastore} Instruction
4414 */
4415 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
4416 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
4417 }
4418
4419 /**
4420 * Produces a VarHandle giving access to elements of an array of type
4421 * {@code arrayClass}. The VarHandle's variable type is the component type
4422 * of {@code arrayClass} and the list of coordinate types is
4423 * {@code (arrayClass, int)}, where the {@code int} coordinate type
4424 * corresponds to an argument that is an index into an array.
4425 * <p>
4426 * Certain access modes of the returned VarHandle are unsupported under
4427 * the following conditions:
4428 * <ul>
4429 * <li>if the component type is anything other than {@code byte},
4430 * {@code short}, {@code char}, {@code int}, {@code long},
4431 * {@code float}, or {@code double} then numeric atomic update access
4432 * modes are unsupported.
4433 * <li>if the component type is anything other than {@code boolean},
4434 * {@code byte}, {@code short}, {@code char}, {@code int} or
4435 * {@code long} then bitwise atomic update access modes are
4436 * unsupported.
4437 * </ul>
4438 * <p>
4439 * If the component type is {@code float} or {@code double} then numeric
4440 * and atomic update access modes compare values using their bitwise
4441 * representation (see {@link Float#floatToRawIntBits} and
4442 * {@link Double#doubleToRawLongBits}, respectively).
4443 *
4444 * <p> When the returned {@code VarHandle} is invoked,
4445 * the array reference and array index are checked.
4446 * A {@code NullPointerException} will be thrown if the array reference
4447 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4448 * thrown if the index is negative or if it is greater than or equal to
4449 * the length of the array.
4450 *
4451 * @apiNote
4452 * Bitwise comparison of {@code float} values or {@code double} values,
4453 * as performed by the numeric and atomic update access modes, differ
4454 * from the primitive {@code ==} operator and the {@link Float#equals}
4455 * and {@link Double#equals} methods, specifically with respect to
4456 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
4457 * Care should be taken when performing a compare and set or a compare
4458 * and exchange operation with such values since the operation may
4459 * unexpectedly fail.
4460 * There are many possible NaN values that are considered to be
4461 * {@code NaN} in Java, although no IEEE 754 floating-point operation
4462 * provided by Java can distinguish between them. Operation failure can
4463 * occur if the expected or witness value is a NaN value and it is
4464 * transformed (perhaps in a platform specific manner) into another NaN
4465 * value, and thus has a different bitwise representation (see
4466 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
4467 * details).
4468 * The values {@code -0.0} and {@code +0.0} have different bitwise
4469 * representations but are considered equal when using the primitive
4470 * {@code ==} operator. Operation failure can occur if, for example, a
4471 * numeric algorithm computes an expected value to be say {@code -0.0}
4472 * and previously computed the witness value to be say {@code +0.0}.
4473 * @param arrayClass the class of an array, of type {@code T[]}
4474 * @return a VarHandle giving access to elements of an array
4475 * @throws NullPointerException if the arrayClass is null
4476 * @throws IllegalArgumentException if arrayClass is not an array type
4477 * @since 9
4478 */
4479 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
4480 return VarHandles.makeArrayElementHandle(arrayClass);
4481 }
4482
4483 /**
4484 * Produces a VarHandle giving access to elements of a {@code byte[]} array
4485 * viewed as if it were a different primitive array type, such as
4486 * {@code int[]} or {@code long[]}.
4487 * The VarHandle's variable type is the component type of
4488 * {@code viewArrayClass} and the list of coordinate types is
4489 * {@code (byte[], int)}, where the {@code int} coordinate type
4490 * corresponds to an argument that is an index into a {@code byte[]} array.
4491 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
4492 * array, composing bytes to or from a value of the component type of
4493 * {@code viewArrayClass} according to the given endianness.
4494 * <p>
4495 * The supported component types (variables types) are {@code short},
4496 * {@code char}, {@code int}, {@code long}, {@code float} and
4497 * {@code double}.
4498 * <p>
4499 * Access of bytes at a given index will result in an
4500 * {@code ArrayIndexOutOfBoundsException} if the index is less than {@code 0}
4501 * or greater than the {@code byte[]} array length minus the size (in bytes)
4502 * of {@code T}.
4503 * <p>
4504 * Only plain {@linkplain VarHandle.AccessMode#GET get} and {@linkplain VarHandle.AccessMode#SET set}
4505 * access modes are supported by the returned var handle. For all other access modes, an
4506 * {@link UnsupportedOperationException} will be thrown.
4507 *
4508 * @apiNote if access modes other than plain access are required, clients should
4509 * consider using off-heap memory through
4510 * {@linkplain java.nio.ByteBuffer#allocateDirect(int) direct byte buffers} or
4511 * off-heap {@linkplain java.lang.foreign.MemorySegment memory segments},
4512 * or memory segments backed by a
4513 * {@linkplain java.lang.foreign.MemorySegment#ofArray(long[]) {@code long[]}},
4514 * for which stronger alignment guarantees can be made.
4515 *
4516 * @param viewArrayClass the view array class, with a component type of
4517 * type {@code T}
4518 * @param byteOrder the endianness of the view array elements, as
4519 * stored in the underlying {@code byte} array
4520 * @return a VarHandle giving access to elements of a {@code byte[]} array
4521 * viewed as if elements corresponding to the components type of the view
4522 * array class
4523 * @throws NullPointerException if viewArrayClass or byteOrder is null
4524 * @throws IllegalArgumentException if viewArrayClass is not an array type
4525 * @throws UnsupportedOperationException if the component type of
4526 * viewArrayClass is not supported as a variable type
4527 * @since 9
4528 */
4529 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
4530 ByteOrder byteOrder) throws IllegalArgumentException {
4531 Objects.requireNonNull(byteOrder);
4532 return VarHandles.byteArrayViewHandle(viewArrayClass,
4533 byteOrder == ByteOrder.BIG_ENDIAN);
4534 }
4535
4536 /**
4537 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
4538 * viewed as if it were an array of elements of a different primitive
4539 * component type to that of {@code byte}, such as {@code int[]} or
4540 * {@code long[]}.
4541 * The VarHandle's variable type is the component type of
4542 * {@code viewArrayClass} and the list of coordinate types is
4543 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
4544 * corresponds to an argument that is an index into a {@code byte[]} array.
4545 * The returned VarHandle accesses bytes at an index in a
4546 * {@code ByteBuffer}, composing bytes to or from a value of the component
4547 * type of {@code viewArrayClass} according to the given endianness.
4548 * <p>
4549 * The supported component types (variables types) are {@code short},
4550 * {@code char}, {@code int}, {@code long}, {@code float} and
4551 * {@code double}.
4552 * <p>
4553 * Access will result in a {@code ReadOnlyBufferException} for anything
4554 * other than the read access modes if the {@code ByteBuffer} is read-only.
4555 * <p>
4556 * Access of bytes at a given index will result in an
4557 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
4558 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
4559 * {@code T}.
4560 * <p>
4561 * For heap byte buffers, access is always unaligned. As a result, only the plain
4562 * {@linkplain VarHandle.AccessMode#GET get}
4563 * and {@linkplain VarHandle.AccessMode#SET set} access modes are supported by the
4564 * returned var handle. For all other access modes, an {@link IllegalStateException}
4565 * will be thrown.
4566 * <p>
4567 * For direct buffers only, access of bytes at an index may be aligned or misaligned for {@code T},
4568 * with respect to the underlying memory address, {@code A} say, associated
4569 * with the {@code ByteBuffer} and index.
4570 * If access is misaligned then access for anything other than the
4571 * {@code get} and {@code set} access modes will result in an
4572 * {@code IllegalStateException}. In such cases atomic access is only
4573 * guaranteed with respect to the largest power of two that divides the GCD
4574 * of {@code A} and the size (in bytes) of {@code T}.
4575 * If access is aligned then following access modes are supported and are
4576 * guaranteed to support atomic access:
4577 * <ul>
4578 * <li>read write access modes for all {@code T}, with the exception of
4579 * access modes {@code get} and {@code set} for {@code long} and
4580 * {@code double} on 32-bit platforms.
4581 * <li>atomic update access modes for {@code int}, {@code long},
4582 * {@code float} or {@code double}.
4583 * (Future major platform releases of the JDK may support additional
4584 * types for certain currently unsupported access modes.)
4585 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4586 * (Future major platform releases of the JDK may support additional
4587 * numeric types for certain currently unsupported access modes.)
4588 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4589 * (Future major platform releases of the JDK may support additional
4590 * numeric types for certain currently unsupported access modes.)
4591 * </ul>
4592 * <p>
4593 * Misaligned access, and therefore atomicity guarantees, may be determined
4594 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
4595 * {@code index}, {@code T} and its corresponding boxed type,
4596 * {@code T_BOX}, as follows:
4597 * <pre>{@code
4598 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4599 * ByteBuffer bb = ...
4600 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
4601 * boolean isMisaligned = misalignedAtIndex != 0;
4602 * }</pre>
4603 * <p>
4604 * If the variable type is {@code float} or {@code double} then atomic
4605 * update access modes compare values using their bitwise representation
4606 * (see {@link Float#floatToRawIntBits} and
4607 * {@link Double#doubleToRawLongBits}, respectively).
4608 * @param viewArrayClass the view array class, with a component type of
4609 * type {@code T}
4610 * @param byteOrder the endianness of the view array elements, as
4611 * stored in the underlying {@code ByteBuffer} (Note this overrides the
4612 * endianness of a {@code ByteBuffer})
4613 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
4614 * viewed as if elements corresponding to the components type of the view
4615 * array class
4616 * @throws NullPointerException if viewArrayClass or byteOrder is null
4617 * @throws IllegalArgumentException if viewArrayClass is not an array type
4618 * @throws UnsupportedOperationException if the component type of
4619 * viewArrayClass is not supported as a variable type
4620 * @since 9
4621 */
4622 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
4623 ByteOrder byteOrder) throws IllegalArgumentException {
4624 Objects.requireNonNull(byteOrder);
4625 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
4626 byteOrder == ByteOrder.BIG_ENDIAN);
4627 }
4628
4629
4630 //--- method handle invocation (reflective style)
4631
4632 /**
4633 * Produces a method handle which will invoke any method handle of the
4634 * given {@code type}, with a given number of trailing arguments replaced by
4635 * a single trailing {@code Object[]} array.
4636 * The resulting invoker will be a method handle with the following
4637 * arguments:
4638 * <ul>
4639 * <li>a single {@code MethodHandle} target
4640 * <li>zero or more leading values (counted by {@code leadingArgCount})
4641 * <li>an {@code Object[]} array containing trailing arguments
4642 * </ul>
4643 * <p>
4644 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
4645 * the indicated {@code type}.
4646 * That is, if the target is exactly of the given {@code type}, it will behave
4647 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
4648 * is used to convert the target to the required {@code type}.
4649 * <p>
4650 * The type of the returned invoker will not be the given {@code type}, but rather
4651 * will have all parameters except the first {@code leadingArgCount}
4652 * replaced by a single array of type {@code Object[]}, which will be
4653 * the final parameter.
4654 * <p>
4655 * Before invoking its target, the invoker will spread the final array, apply
4656 * reference casts as necessary, and unbox and widen primitive arguments.
4657 * If, when the invoker is called, the supplied array argument does
4658 * not have the correct number of elements, the invoker will throw
4659 * an {@link IllegalArgumentException} instead of invoking the target.
4660 * <p>
4661 * This method is equivalent to the following code (though it may be more efficient):
4662 * {@snippet lang="java" :
4663 MethodHandle invoker = MethodHandles.invoker(type);
4664 int spreadArgCount = type.parameterCount() - leadingArgCount;
4665 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
4666 return invoker;
4667 * }
4668 * This method throws no reflective or security exceptions.
4669 * @param type the desired target type
4670 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
4671 * @return a method handle suitable for invoking any method handle of the given type
4672 * @throws NullPointerException if {@code type} is null
4673 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
4674 * the range from 0 to {@code type.parameterCount()} inclusive,
4675 * or if the resulting method handle's type would have
4676 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4677 */
4678 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
4679 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
4680 throw newIllegalArgumentException("bad argument count", leadingArgCount);
4681 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
4682 return type.invokers().spreadInvoker(leadingArgCount);
4683 }
4684
4685 /**
4686 * Produces a special <em>invoker method handle</em> which can be used to
4687 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
4688 * The resulting invoker will have a type which is
4689 * exactly equal to the desired type, except that it will accept
4690 * an additional leading argument of type {@code MethodHandle}.
4691 * <p>
4692 * This method is equivalent to the following code (though it may be more efficient):
4693 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
4694 *
4695 * <p style="font-size:smaller;">
4696 * <em>Discussion:</em>
4697 * Invoker method handles can be useful when working with variable method handles
4698 * of unknown types.
4699 * For example, to emulate an {@code invokeExact} call to a variable method
4700 * handle {@code M}, extract its type {@code T},
4701 * look up the invoker method {@code X} for {@code T},
4702 * and call the invoker method, as {@code X.invoke(T, A...)}.
4703 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
4704 * is unknown.)
4705 * If spreading, collecting, or other argument transformations are required,
4706 * they can be applied once to the invoker {@code X} and reused on many {@code M}
4707 * method handle values, as long as they are compatible with the type of {@code X}.
4708 * <p style="font-size:smaller;">
4709 * <em>(Note: The invoker method is not available via the Core Reflection API.
4710 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4711 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4712 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4713 * <p>
4714 * This method throws no reflective or security exceptions.
4715 * @param type the desired target type
4716 * @return a method handle suitable for invoking any method handle of the given type
4717 * @throws IllegalArgumentException if the resulting method handle's type would have
4718 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4719 */
4720 public static MethodHandle exactInvoker(MethodType type) {
4721 return type.invokers().exactInvoker();
4722 }
4723
4724 /**
4725 * Produces a special <em>invoker method handle</em> which can be used to
4726 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
4727 * The resulting invoker will have a type which is
4728 * exactly equal to the desired type, except that it will accept
4729 * an additional leading argument of type {@code MethodHandle}.
4730 * <p>
4731 * Before invoking its target, if the target differs from the expected type,
4732 * the invoker will apply reference casts as
4733 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
4734 * Similarly, the return value will be converted as necessary.
4735 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
4736 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
4737 * <p>
4738 * This method is equivalent to the following code (though it may be more efficient):
4739 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
4740 * <p style="font-size:smaller;">
4741 * <em>Discussion:</em>
4742 * A {@linkplain MethodType#genericMethodType general method type} is one which
4743 * mentions only {@code Object} arguments and return values.
4744 * An invoker for such a type is capable of calling any method handle
4745 * of the same arity as the general type.
4746 * <p style="font-size:smaller;">
4747 * <em>(Note: The invoker method is not available via the Core Reflection API.
4748 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4749 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4750 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4751 * <p>
4752 * This method throws no reflective or security exceptions.
4753 * @param type the desired target type
4754 * @return a method handle suitable for invoking any method handle convertible to the given type
4755 * @throws IllegalArgumentException if the resulting method handle's type would have
4756 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4757 */
4758 public static MethodHandle invoker(MethodType type) {
4759 return type.invokers().genericInvoker();
4760 }
4761
4762 /**
4763 * Produces a special <em>invoker method handle</em> which can be used to
4764 * invoke a signature-polymorphic access mode method on any VarHandle whose
4765 * associated access mode type is compatible with the given type.
4766 * The resulting invoker will have a type which is exactly equal to the
4767 * desired given type, except that it will accept an additional leading
4768 * argument of type {@code VarHandle}.
4769 *
4770 * @param accessMode the VarHandle access mode
4771 * @param type the desired target type
4772 * @return a method handle suitable for invoking an access mode method of
4773 * any VarHandle whose access mode type is of the given type.
4774 * @since 9
4775 */
4776 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4777 return type.invokers().varHandleMethodExactInvoker(accessMode);
4778 }
4779
4780 /**
4781 * Produces a special <em>invoker method handle</em> which can be used to
4782 * invoke a signature-polymorphic access mode method on any VarHandle whose
4783 * associated access mode type is compatible with the given type.
4784 * The resulting invoker will have a type which is exactly equal to the
4785 * desired given type, except that it will accept an additional leading
4786 * argument of type {@code VarHandle}.
4787 * <p>
4788 * Before invoking its target, if the access mode type differs from the
4789 * desired given type, the invoker will apply reference casts as necessary
4790 * and box, unbox, or widen primitive values, as if by
4791 * {@link MethodHandle#asType asType}. Similarly, the return value will be
4792 * converted as necessary.
4793 * <p>
4794 * This method is equivalent to the following code (though it may be more
4795 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
4796 *
4797 * @param accessMode the VarHandle access mode
4798 * @param type the desired target type
4799 * @return a method handle suitable for invoking an access mode method of
4800 * any VarHandle whose access mode type is convertible to the given
4801 * type.
4802 * @since 9
4803 */
4804 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4805 return type.invokers().varHandleMethodInvoker(accessMode);
4806 }
4807
4808 /*non-public*/
4809 static MethodHandle basicInvoker(MethodType type) {
4810 return type.invokers().basicInvoker();
4811 }
4812
4813 //--- method handle modification (creation from other method handles)
4814
4815 /**
4816 * Produces a method handle which adapts the type of the
4817 * given method handle to a new type by pairwise argument and return type conversion.
4818 * The original type and new type must have the same number of arguments.
4819 * The resulting method handle is guaranteed to report a type
4820 * which is equal to the desired new type.
4821 * <p>
4822 * If the original type and new type are equal, returns target.
4823 * <p>
4824 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
4825 * and some additional conversions are also applied if those conversions fail.
4826 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
4827 * if possible, before or instead of any conversions done by {@code asType}:
4828 * <ul>
4829 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
4830 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
4831 * (This treatment of interfaces follows the usage of the bytecode verifier.)
4832 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
4833 * the boolean is converted to a byte value, 1 for true, 0 for false.
4834 * (This treatment follows the usage of the bytecode verifier.)
4835 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
4836 * <em>T0</em> is converted to byte via Java casting conversion (JLS {@jls 5.5}),
4837 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
4838 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
4839 * then a Java casting conversion (JLS {@jls 5.5}) is applied.
4840 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
4841 * widening and/or narrowing.)
4842 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
4843 * conversion will be applied at runtime, possibly followed
4844 * by a Java casting conversion (JLS {@jls 5.5}) on the primitive value,
4845 * possibly followed by a conversion from byte to boolean by testing
4846 * the low-order bit.
4847 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
4848 * and if the reference is null at runtime, a zero value is introduced.
4849 * </ul>
4850 * @param target the method handle to invoke after arguments are retyped
4851 * @param newType the expected type of the new method handle
4852 * @return a method handle which delegates to the target after performing
4853 * any necessary argument conversions, and arranges for any
4854 * necessary return value conversions
4855 * @throws NullPointerException if either argument is null
4856 * @throws WrongMethodTypeException if the conversion cannot be made
4857 * @see MethodHandle#asType
4858 */
4859 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
4860 explicitCastArgumentsChecks(target, newType);
4861 // use the asTypeCache when possible:
4862 MethodType oldType = target.type();
4863 if (oldType == newType) return target;
4864 if (oldType.explicitCastEquivalentToAsType(newType)) {
4865 return target.asFixedArity().asType(newType);
4866 }
4867 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
4868 }
4869
4870 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
4871 if (target.type().parameterCount() != newType.parameterCount()) {
4872 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
4873 }
4874 }
4875
4876 /**
4877 * Produces a method handle which adapts the calling sequence of the
4878 * given method handle to a new type, by reordering the arguments.
4879 * The resulting method handle is guaranteed to report a type
4880 * which is equal to the desired new type.
4881 * <p>
4882 * The given array controls the reordering.
4883 * Call {@code #I} the number of incoming parameters (the value
4884 * {@code newType.parameterCount()}, and call {@code #O} the number
4885 * of outgoing parameters (the value {@code target.type().parameterCount()}).
4886 * Then the length of the reordering array must be {@code #O},
4887 * and each element must be a non-negative number less than {@code #I}.
4888 * For every {@code N} less than {@code #O}, the {@code N}-th
4889 * outgoing argument will be taken from the {@code I}-th incoming
4890 * argument, where {@code I} is {@code reorder[N]}.
4891 * <p>
4892 * No argument or return value conversions are applied.
4893 * The type of each incoming argument, as determined by {@code newType},
4894 * must be identical to the type of the corresponding outgoing parameter
4895 * or parameters in the target method handle.
4896 * The return type of {@code newType} must be identical to the return
4897 * type of the original target.
4898 * <p>
4899 * The reordering array need not specify an actual permutation.
4900 * An incoming argument will be duplicated if its index appears
4901 * more than once in the array, and an incoming argument will be dropped
4902 * if its index does not appear in the array.
4903 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
4904 * incoming arguments which are not mentioned in the reordering array
4905 * may be of any type, as determined only by {@code newType}.
4906 * {@snippet lang="java" :
4907 import static java.lang.invoke.MethodHandles.*;
4908 import static java.lang.invoke.MethodType.*;
4909 ...
4910 MethodType intfn1 = methodType(int.class, int.class);
4911 MethodType intfn2 = methodType(int.class, int.class, int.class);
4912 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
4913 assert(sub.type().equals(intfn2));
4914 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
4915 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
4916 assert((int)rsub.invokeExact(1, 100) == 99);
4917 MethodHandle add = ... (int x, int y) -> (x+y) ...;
4918 assert(add.type().equals(intfn2));
4919 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
4920 assert(twice.type().equals(intfn1));
4921 assert((int)twice.invokeExact(21) == 42);
4922 * }
4923 * <p>
4924 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4925 * variable-arity method handle}, even if the original target method handle was.
4926 * @param target the method handle to invoke after arguments are reordered
4927 * @param newType the expected type of the new method handle
4928 * @param reorder an index array which controls the reordering
4929 * @return a method handle which delegates to the target after it
4930 * drops unused arguments and moves and/or duplicates the other arguments
4931 * @throws NullPointerException if any argument is null
4932 * @throws IllegalArgumentException if the index array length is not equal to
4933 * the arity of the target, or if any index array element
4934 * not a valid index for a parameter of {@code newType},
4935 * or if two corresponding parameter types in
4936 * {@code target.type()} and {@code newType} are not identical,
4937 */
4938 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
4939 reorder = reorder.clone(); // get a private copy
4940 MethodType oldType = target.type();
4941 permuteArgumentChecks(reorder, newType, oldType);
4942 // first detect dropped arguments and handle them separately
4943 int[] originalReorder = reorder;
4944 BoundMethodHandle result = target.rebind();
4945 LambdaForm form = result.form;
4946 int newArity = newType.parameterCount();
4947 // Normalize the reordering into a real permutation,
4948 // by removing duplicates and adding dropped elements.
4949 // This somewhat improves lambda form caching, as well
4950 // as simplifying the transform by breaking it up into steps.
4951 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
4952 if (ddIdx > 0) {
4953 // We found a duplicated entry at reorder[ddIdx].
4954 // Example: (x,y,z)->asList(x,y,z)
4955 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
4956 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
4957 // The starred element corresponds to the argument
4958 // deleted by the dupArgumentForm transform.
4959 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
4960 boolean killFirst = false;
4961 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
4962 // Set killFirst if the dup is larger than an intervening position.
4963 // This will remove at least one inversion from the permutation.
4964 if (dupVal > val) killFirst = true;
4965 }
4966 if (!killFirst) {
4967 srcPos = dstPos;
4968 dstPos = ddIdx;
4969 }
4970 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
4971 assert (reorder[srcPos] == reorder[dstPos]);
4972 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
4973 // contract the reordering by removing the element at dstPos
4974 int tailPos = dstPos + 1;
4975 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
4976 reorder = Arrays.copyOf(reorder, reorder.length - 1);
4977 } else {
4978 int dropVal = ~ddIdx, insPos = 0;
4979 while (insPos < reorder.length && reorder[insPos] < dropVal) {
4980 // Find first element of reorder larger than dropVal.
4981 // This is where we will insert the dropVal.
4982 insPos += 1;
4983 }
4984 Class<?> ptype = newType.parameterType(dropVal);
4985 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
4986 oldType = oldType.insertParameterTypes(insPos, ptype);
4987 // expand the reordering by inserting an element at insPos
4988 int tailPos = insPos + 1;
4989 reorder = Arrays.copyOf(reorder, reorder.length + 1);
4990 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
4991 reorder[insPos] = dropVal;
4992 }
4993 assert (permuteArgumentChecks(reorder, newType, oldType));
4994 }
4995 assert (reorder.length == newArity); // a perfect permutation
4996 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
4997 form = form.editor().permuteArgumentsForm(1, reorder);
4998 if (newType == result.type() && form == result.internalForm())
4999 return result;
5000 return result.copyWith(newType, form);
5001 }
5002
5003 /**
5004 * Return an indication of any duplicate or omission in reorder.
5005 * If the reorder contains a duplicate entry, return the index of the second occurrence.
5006 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
5007 * Otherwise, return zero.
5008 * If an element not in [0..newArity-1] is encountered, return reorder.length.
5009 */
5010 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
5011 final int BIT_LIMIT = 63; // max number of bits in bit mask
5012 if (newArity < BIT_LIMIT) {
5013 long mask = 0;
5014 for (int i = 0; i < reorder.length; i++) {
5015 int arg = reorder[i];
5016 if (arg >= newArity) {
5017 return reorder.length;
5018 }
5019 long bit = 1L << arg;
5020 if ((mask & bit) != 0) {
5021 return i; // >0 indicates a dup
5022 }
5023 mask |= bit;
5024 }
5025 if (mask == (1L << newArity) - 1) {
5026 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
5027 return 0;
5028 }
5029 // find first zero
5030 long zeroBit = Long.lowestOneBit(~mask);
5031 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
5032 assert(zeroPos <= newArity);
5033 if (zeroPos == newArity) {
5034 return 0;
5035 }
5036 return ~zeroPos;
5037 } else {
5038 // same algorithm, different bit set
5039 BitSet mask = new BitSet(newArity);
5040 for (int i = 0; i < reorder.length; i++) {
5041 int arg = reorder[i];
5042 if (arg >= newArity) {
5043 return reorder.length;
5044 }
5045 if (mask.get(arg)) {
5046 return i; // >0 indicates a dup
5047 }
5048 mask.set(arg);
5049 }
5050 int zeroPos = mask.nextClearBit(0);
5051 assert(zeroPos <= newArity);
5052 if (zeroPos == newArity) {
5053 return 0;
5054 }
5055 return ~zeroPos;
5056 }
5057 }
5058
5059 static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
5060 if (newType.returnType() != oldType.returnType())
5061 throw newIllegalArgumentException("return types do not match",
5062 oldType, newType);
5063 if (reorder.length != oldType.parameterCount())
5064 throw newIllegalArgumentException("old type parameter count and reorder array length do not match",
5065 oldType, Arrays.toString(reorder));
5066
5067 int limit = newType.parameterCount();
5068 for (int j = 0; j < reorder.length; j++) {
5069 int i = reorder[j];
5070 if (i < 0 || i >= limit) {
5071 throw newIllegalArgumentException("index is out of bounds for new type",
5072 i, newType);
5073 }
5074 Class<?> src = newType.parameterType(i);
5075 Class<?> dst = oldType.parameterType(j);
5076 if (src != dst)
5077 throw newIllegalArgumentException("parameter types do not match after reorder",
5078 oldType, newType);
5079 }
5080 return true;
5081 }
5082
5083 /**
5084 * Produces a method handle of the requested return type which returns the given
5085 * constant value every time it is invoked.
5086 * <p>
5087 * Before the method handle is returned, the passed-in value is converted to the requested type.
5088 * If the requested type is primitive, widening primitive conversions are attempted,
5089 * else reference conversions are attempted.
5090 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
5091 * @param type the return type of the desired method handle
5092 * @param value the value to return
5093 * @return a method handle of the given return type and no arguments, which always returns the given value
5094 * @throws NullPointerException if the {@code type} argument is null
5095 * @throws ClassCastException if the value cannot be converted to the required return type
5096 * @throws IllegalArgumentException if the given type is {@code void.class}
5097 */
5098 public static MethodHandle constant(Class<?> type, Object value) {
5099 if (type.isPrimitive()) {
5100 if (type == void.class)
5101 throw newIllegalArgumentException("void type");
5102 Wrapper w = Wrapper.forPrimitiveType(type);
5103 value = w.convert(value, type);
5104 if (w.zero().equals(value))
5105 return zero(w, type);
5106 return insertArguments(identity(type), 0, value);
5107 } else {
5108 if (value == null)
5109 return zero(Wrapper.OBJECT, type);
5110 return identity(type).bindTo(value);
5111 }
5112 }
5113
5114 /**
5115 * Produces a method handle which returns its sole argument when invoked.
5116 * @param type the type of the sole parameter and return value of the desired method handle
5117 * @return a unary method handle which accepts and returns the given type
5118 * @throws NullPointerException if the argument is null
5119 * @throws IllegalArgumentException if the given type is {@code void.class}
5120 */
5121 public static MethodHandle identity(Class<?> type) {
5122 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
5123 int pos = btw.ordinal();
5124 MethodHandle ident = IDENTITY_MHS[pos];
5125 if (ident == null) {
5126 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
5127 }
5128 if (ident.type().returnType() == type)
5129 return ident;
5130 // something like identity(Foo.class); do not bother to intern these
5131 assert (btw == Wrapper.OBJECT);
5132 return makeIdentity(type);
5133 }
5134
5135 /**
5136 * Produces a constant method handle of the requested return type which
5137 * returns the default value for that type every time it is invoked.
5138 * The resulting constant method handle will have no side effects.
5139 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
5140 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
5141 * since {@code explicitCastArguments} converts {@code null} to default values.
5142 * @param type the expected return type of the desired method handle
5143 * @return a constant method handle that takes no arguments
5144 * and returns the default value of the given type (or void, if the type is void)
5145 * @throws NullPointerException if the argument is null
5146 * @see MethodHandles#constant
5147 * @see MethodHandles#empty
5148 * @see MethodHandles#explicitCastArguments
5149 * @since 9
5150 */
5151 public static MethodHandle zero(Class<?> type) {
5152 Objects.requireNonNull(type);
5153 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
5154 }
5155
5156 private static MethodHandle identityOrVoid(Class<?> type) {
5157 return type == void.class ? zero(type) : identity(type);
5158 }
5159
5160 /**
5161 * Produces a method handle of the requested type which ignores any arguments, does nothing,
5162 * and returns a suitable default depending on the return type.
5163 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
5164 * <p>The returned method handle is equivalent to
5165 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
5166 *
5167 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
5168 * {@code guardWithTest(pred, target, empty(target.type())}.
5169 * @param type the type of the desired method handle
5170 * @return a constant method handle of the given type, which returns a default value of the given return type
5171 * @throws NullPointerException if the argument is null
5172 * @see MethodHandles#zero
5173 * @see MethodHandles#constant
5174 * @since 9
5175 */
5176 public static MethodHandle empty(MethodType type) {
5177 Objects.requireNonNull(type);
5178 return dropArgumentsTrusted(zero(type.returnType()), 0, type.ptypes());
5179 }
5180
5181 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
5182 private static MethodHandle makeIdentity(Class<?> ptype) {
5183 MethodType mtype = methodType(ptype, ptype);
5184 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
5185 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
5186 }
5187
5188 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
5189 int pos = btw.ordinal();
5190 MethodHandle zero = ZERO_MHS[pos];
5191 if (zero == null) {
5192 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
5193 }
5194 if (zero.type().returnType() == rtype)
5195 return zero;
5196 assert(btw == Wrapper.OBJECT);
5197 return makeZero(rtype);
5198 }
5199 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
5200 private static MethodHandle makeZero(Class<?> rtype) {
5201 MethodType mtype = methodType(rtype);
5202 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
5203 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
5204 }
5205
5206 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
5207 // Simulate a CAS, to avoid racy duplication of results.
5208 MethodHandle prev = cache[pos];
5209 if (prev != null) return prev;
5210 return cache[pos] = value;
5211 }
5212
5213 /**
5214 * Provides a target method handle with one or more <em>bound arguments</em>
5215 * in advance of the method handle's invocation.
5216 * The formal parameters to the target corresponding to the bound
5217 * arguments are called <em>bound parameters</em>.
5218 * Returns a new method handle which saves away the bound arguments.
5219 * When it is invoked, it receives arguments for any non-bound parameters,
5220 * binds the saved arguments to their corresponding parameters,
5221 * and calls the original target.
5222 * <p>
5223 * The type of the new method handle will drop the types for the bound
5224 * parameters from the original target type, since the new method handle
5225 * will no longer require those arguments to be supplied by its callers.
5226 * <p>
5227 * Each given argument object must match the corresponding bound parameter type.
5228 * If a bound parameter type is a primitive, the argument object
5229 * must be a wrapper, and will be unboxed to produce the primitive value.
5230 * <p>
5231 * The {@code pos} argument selects which parameters are to be bound.
5232 * It may range between zero and <i>N-L</i> (inclusively),
5233 * where <i>N</i> is the arity of the target method handle
5234 * and <i>L</i> is the length of the values array.
5235 * <p>
5236 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5237 * variable-arity method handle}, even if the original target method handle was.
5238 * @param target the method handle to invoke after the argument is inserted
5239 * @param pos where to insert the argument (zero for the first)
5240 * @param values the series of arguments to insert
5241 * @return a method handle which inserts an additional argument,
5242 * before calling the original method handle
5243 * @throws NullPointerException if the target or the {@code values} array is null
5244 * @throws IllegalArgumentException if {@code pos} is less than {@code 0} or greater than
5245 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
5246 * is the length of the values array.
5247 * @throws ClassCastException if an argument does not match the corresponding bound parameter
5248 * type.
5249 * @see MethodHandle#bindTo
5250 */
5251 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
5252 int insCount = values.length;
5253 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
5254 if (insCount == 0) return target;
5255 BoundMethodHandle result = target.rebind();
5256 for (int i = 0; i < insCount; i++) {
5257 Object value = values[i];
5258 Class<?> ptype = ptypes[pos+i];
5259 if (ptype.isPrimitive()) {
5260 result = insertArgumentPrimitive(result, pos, ptype, value);
5261 } else {
5262 value = ptype.cast(value); // throw CCE if needed
5263 result = result.bindArgumentL(pos, value);
5264 }
5265 }
5266 return result;
5267 }
5268
5269 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
5270 Class<?> ptype, Object value) {
5271 Wrapper w = Wrapper.forPrimitiveType(ptype);
5272 // perform unboxing and/or primitive conversion
5273 value = w.convert(value, ptype);
5274 return switch (w) {
5275 case INT -> result.bindArgumentI(pos, (int) value);
5276 case LONG -> result.bindArgumentJ(pos, (long) value);
5277 case FLOAT -> result.bindArgumentF(pos, (float) value);
5278 case DOUBLE -> result.bindArgumentD(pos, (double) value);
5279 default -> result.bindArgumentI(pos, ValueConversions.widenSubword(value));
5280 };
5281 }
5282
5283 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
5284 MethodType oldType = target.type();
5285 int outargs = oldType.parameterCount();
5286 int inargs = outargs - insCount;
5287 if (inargs < 0)
5288 throw newIllegalArgumentException("too many values to insert");
5289 if (pos < 0 || pos > inargs)
5290 throw newIllegalArgumentException("no argument type to append");
5291 return oldType.ptypes();
5292 }
5293
5294 /**
5295 * Produces a method handle which will discard some dummy arguments
5296 * before calling some other specified <i>target</i> method handle.
5297 * The type of the new method handle will be the same as the target's type,
5298 * except it will also include the dummy argument types,
5299 * at some given position.
5300 * <p>
5301 * The {@code pos} argument may range between zero and <i>N</i>,
5302 * where <i>N</i> is the arity of the target.
5303 * If {@code pos} is zero, the dummy arguments will precede
5304 * the target's real arguments; if {@code pos} is <i>N</i>
5305 * they will come after.
5306 * <p>
5307 * <b>Example:</b>
5308 * {@snippet lang="java" :
5309 import static java.lang.invoke.MethodHandles.*;
5310 import static java.lang.invoke.MethodType.*;
5311 ...
5312 MethodHandle cat = lookup().findVirtual(String.class,
5313 "concat", methodType(String.class, String.class));
5314 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5315 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
5316 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
5317 assertEquals(bigType, d0.type());
5318 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
5319 * }
5320 * <p>
5321 * This method is also equivalent to the following code:
5322 * <blockquote><pre>
5323 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
5324 * </pre></blockquote>
5325 * @param target the method handle to invoke after the arguments are dropped
5326 * @param pos position of first argument to drop (zero for the leftmost)
5327 * @param valueTypes the type(s) of the argument(s) to drop
5328 * @return a method handle which drops arguments of the given types,
5329 * before calling the original method handle
5330 * @throws NullPointerException if the target is null,
5331 * or if the {@code valueTypes} list or any of its elements is null
5332 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5333 * or if {@code pos} is negative or greater than the arity of the target,
5334 * or if the new method handle's type would have too many parameters
5335 */
5336 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
5337 return dropArgumentsTrusted(target, pos, valueTypes.toArray(new Class<?>[0]).clone());
5338 }
5339
5340 static MethodHandle dropArgumentsTrusted(MethodHandle target, int pos, Class<?>[] valueTypes) {
5341 MethodType oldType = target.type(); // get NPE
5342 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
5343 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
5344 if (dropped == 0) return target;
5345 BoundMethodHandle result = target.rebind();
5346 LambdaForm lform = result.form;
5347 int insertFormArg = 1 + pos;
5348 for (Class<?> ptype : valueTypes) {
5349 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
5350 }
5351 result = result.copyWith(newType, lform);
5352 return result;
5353 }
5354
5355 private static int dropArgumentChecks(MethodType oldType, int pos, Class<?>[] valueTypes) {
5356 int dropped = valueTypes.length;
5357 MethodType.checkSlotCount(dropped);
5358 int outargs = oldType.parameterCount();
5359 int inargs = outargs + dropped;
5360 if (pos < 0 || pos > outargs)
5361 throw newIllegalArgumentException("no argument type to remove"
5362 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
5363 );
5364 return dropped;
5365 }
5366
5367 /**
5368 * Produces a method handle which will discard some dummy arguments
5369 * before calling some other specified <i>target</i> method handle.
5370 * The type of the new method handle will be the same as the target's type,
5371 * except it will also include the dummy argument types,
5372 * at some given position.
5373 * <p>
5374 * The {@code pos} argument may range between zero and <i>N</i>,
5375 * where <i>N</i> is the arity of the target.
5376 * If {@code pos} is zero, the dummy arguments will precede
5377 * the target's real arguments; if {@code pos} is <i>N</i>
5378 * they will come after.
5379 * @apiNote
5380 * {@snippet lang="java" :
5381 import static java.lang.invoke.MethodHandles.*;
5382 import static java.lang.invoke.MethodType.*;
5383 ...
5384 MethodHandle cat = lookup().findVirtual(String.class,
5385 "concat", methodType(String.class, String.class));
5386 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5387 MethodHandle d0 = dropArguments(cat, 0, String.class);
5388 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
5389 MethodHandle d1 = dropArguments(cat, 1, String.class);
5390 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
5391 MethodHandle d2 = dropArguments(cat, 2, String.class);
5392 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
5393 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
5394 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
5395 * }
5396 * <p>
5397 * This method is also equivalent to the following code:
5398 * <blockquote><pre>
5399 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
5400 * </pre></blockquote>
5401 * @param target the method handle to invoke after the arguments are dropped
5402 * @param pos position of first argument to drop (zero for the leftmost)
5403 * @param valueTypes the type(s) of the argument(s) to drop
5404 * @return a method handle which drops arguments of the given types,
5405 * before calling the original method handle
5406 * @throws NullPointerException if the target is null,
5407 * or if the {@code valueTypes} array or any of its elements is null
5408 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5409 * or if {@code pos} is negative or greater than the arity of the target,
5410 * or if the new method handle's type would have
5411 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5412 */
5413 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
5414 return dropArgumentsTrusted(target, pos, valueTypes.clone());
5415 }
5416
5417 /* Convenience overloads for trusting internal low-arity call-sites */
5418 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1) {
5419 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1 });
5420 }
5421 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1, Class<?> valueType2) {
5422 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1, valueType2 });
5423 }
5424
5425 // private version which allows caller some freedom with error handling
5426 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, Class<?>[] newTypes, int pos,
5427 boolean nullOnFailure) {
5428 Class<?>[] oldTypes = target.type().ptypes();
5429 int match = oldTypes.length;
5430 if (skip != 0) {
5431 if (skip < 0 || skip > match) {
5432 throw newIllegalArgumentException("illegal skip", skip, target);
5433 }
5434 oldTypes = Arrays.copyOfRange(oldTypes, skip, match);
5435 match -= skip;
5436 }
5437 Class<?>[] addTypes = newTypes;
5438 int add = addTypes.length;
5439 if (pos != 0) {
5440 if (pos < 0 || pos > add) {
5441 throw newIllegalArgumentException("illegal pos", pos, Arrays.toString(newTypes));
5442 }
5443 addTypes = Arrays.copyOfRange(addTypes, pos, add);
5444 add -= pos;
5445 assert(addTypes.length == add);
5446 }
5447 // Do not add types which already match the existing arguments.
5448 if (match > add || !Arrays.equals(oldTypes, 0, oldTypes.length, addTypes, 0, match)) {
5449 if (nullOnFailure) {
5450 return null;
5451 }
5452 throw newIllegalArgumentException("argument lists do not match",
5453 Arrays.toString(oldTypes), Arrays.toString(newTypes));
5454 }
5455 addTypes = Arrays.copyOfRange(addTypes, match, add);
5456 add -= match;
5457 assert(addTypes.length == add);
5458 // newTypes: ( P*[pos], M*[match], A*[add] )
5459 // target: ( S*[skip], M*[match] )
5460 MethodHandle adapter = target;
5461 if (add > 0) {
5462 adapter = dropArgumentsTrusted(adapter, skip+ match, addTypes);
5463 }
5464 // adapter: (S*[skip], M*[match], A*[add] )
5465 if (pos > 0) {
5466 adapter = dropArgumentsTrusted(adapter, skip, Arrays.copyOfRange(newTypes, 0, pos));
5467 }
5468 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
5469 return adapter;
5470 }
5471
5472 /**
5473 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
5474 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
5475 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
5476 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
5477 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
5478 * {@link #dropArguments(MethodHandle, int, Class[])}.
5479 * <p>
5480 * The resulting handle will have the same return type as the target handle.
5481 * <p>
5482 * In more formal terms, assume these two type lists:<ul>
5483 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
5484 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
5485 * {@code newTypes}.
5486 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
5487 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
5488 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
5489 * sub-list.
5490 * </ul>
5491 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
5492 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
5493 * {@link #dropArguments(MethodHandle, int, Class[])}.
5494 *
5495 * @apiNote
5496 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
5497 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
5498 * {@snippet lang="java" :
5499 import static java.lang.invoke.MethodHandles.*;
5500 import static java.lang.invoke.MethodType.*;
5501 ...
5502 ...
5503 MethodHandle h0 = constant(boolean.class, true);
5504 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
5505 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
5506 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
5507 if (h1.type().parameterCount() < h2.type().parameterCount())
5508 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
5509 else
5510 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
5511 MethodHandle h3 = guardWithTest(h0, h1, h2);
5512 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
5513 * }
5514 * @param target the method handle to adapt
5515 * @param skip number of targets parameters to disregard (they will be unchanged)
5516 * @param newTypes the list of types to match {@code target}'s parameter type list to
5517 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
5518 * @return a possibly adapted method handle
5519 * @throws NullPointerException if either argument is null
5520 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
5521 * or if {@code skip} is negative or greater than the arity of the target,
5522 * or if {@code pos} is negative or greater than the newTypes list size,
5523 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
5524 * {@code pos}.
5525 * @since 9
5526 */
5527 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
5528 Objects.requireNonNull(target);
5529 Objects.requireNonNull(newTypes);
5530 return dropArgumentsToMatch(target, skip, newTypes.toArray(new Class<?>[0]).clone(), pos, false);
5531 }
5532
5533 /**
5534 * Drop the return value of the target handle (if any).
5535 * The returned method handle will have a {@code void} return type.
5536 *
5537 * @param target the method handle to adapt
5538 * @return a possibly adapted method handle
5539 * @throws NullPointerException if {@code target} is null
5540 * @since 16
5541 */
5542 public static MethodHandle dropReturn(MethodHandle target) {
5543 Objects.requireNonNull(target);
5544 MethodType oldType = target.type();
5545 Class<?> oldReturnType = oldType.returnType();
5546 if (oldReturnType == void.class)
5547 return target;
5548 MethodType newType = oldType.changeReturnType(void.class);
5549 BoundMethodHandle result = target.rebind();
5550 LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true);
5551 result = result.copyWith(newType, lform);
5552 return result;
5553 }
5554
5555 /**
5556 * Adapts a target method handle by pre-processing
5557 * one or more of its arguments, each with its own unary filter function,
5558 * and then calling the target with each pre-processed argument
5559 * replaced by the result of its corresponding filter function.
5560 * <p>
5561 * The pre-processing is performed by one or more method handles,
5562 * specified in the elements of the {@code filters} array.
5563 * The first element of the filter array corresponds to the {@code pos}
5564 * argument of the target, and so on in sequence.
5565 * The filter functions are invoked in left to right order.
5566 * <p>
5567 * Null arguments in the array are treated as identity functions,
5568 * and the corresponding arguments left unchanged.
5569 * (If there are no non-null elements in the array, the original target is returned.)
5570 * Each filter is applied to the corresponding argument of the adapter.
5571 * <p>
5572 * If a filter {@code F} applies to the {@code N}th argument of
5573 * the target, then {@code F} must be a method handle which
5574 * takes exactly one argument. The type of {@code F}'s sole argument
5575 * replaces the corresponding argument type of the target
5576 * in the resulting adapted method handle.
5577 * The return type of {@code F} must be identical to the corresponding
5578 * parameter type of the target.
5579 * <p>
5580 * It is an error if there are elements of {@code filters}
5581 * (null or not)
5582 * which do not correspond to argument positions in the target.
5583 * <p><b>Example:</b>
5584 * {@snippet lang="java" :
5585 import static java.lang.invoke.MethodHandles.*;
5586 import static java.lang.invoke.MethodType.*;
5587 ...
5588 MethodHandle cat = lookup().findVirtual(String.class,
5589 "concat", methodType(String.class, String.class));
5590 MethodHandle upcase = lookup().findVirtual(String.class,
5591 "toUpperCase", methodType(String.class));
5592 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5593 MethodHandle f0 = filterArguments(cat, 0, upcase);
5594 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
5595 MethodHandle f1 = filterArguments(cat, 1, upcase);
5596 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
5597 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
5598 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
5599 * }
5600 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5601 * denotes the return type of both the {@code target} and resulting adapter.
5602 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
5603 * of the parameters and arguments that precede and follow the filter position
5604 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
5605 * values of the filtered parameters and arguments; they also represent the
5606 * return types of the {@code filter[i]} handles. The latter accept arguments
5607 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
5608 * the resulting adapter.
5609 * {@snippet lang="java" :
5610 * T target(P... p, A[i]... a[i], B... b);
5611 * A[i] filter[i](V[i]);
5612 * T adapter(P... p, V[i]... v[i], B... b) {
5613 * return target(p..., filter[i](v[i])..., b...);
5614 * }
5615 * }
5616 * <p>
5617 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5618 * variable-arity method handle}, even if the original target method handle was.
5619 *
5620 * @param target the method handle to invoke after arguments are filtered
5621 * @param pos the position of the first argument to filter
5622 * @param filters method handles to call initially on filtered arguments
5623 * @return method handle which incorporates the specified argument filtering logic
5624 * @throws NullPointerException if the target is null
5625 * or if the {@code filters} array is null
5626 * @throws IllegalArgumentException if a non-null element of {@code filters}
5627 * does not match a corresponding argument type of target as described above,
5628 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
5629 * or if the resulting method handle's type would have
5630 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5631 */
5632 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
5633 // In method types arguments start at index 0, while the LF
5634 // editor have the MH receiver at position 0 - adjust appropriately.
5635 final int MH_RECEIVER_OFFSET = 1;
5636 filterArgumentsCheckArity(target, pos, filters);
5637 MethodHandle adapter = target;
5638
5639 // keep track of currently matched filters, as to optimize repeated filters
5640 int index = 0;
5641 int[] positions = new int[filters.length];
5642 MethodHandle filter = null;
5643
5644 // process filters in reverse order so that the invocation of
5645 // the resulting adapter will invoke the filters in left-to-right order
5646 for (int i = filters.length - 1; i >= 0; --i) {
5647 MethodHandle newFilter = filters[i];
5648 if (newFilter == null) continue; // ignore null elements of filters
5649
5650 // flush changes on update
5651 if (filter != newFilter) {
5652 if (filter != null) {
5653 if (index > 1) {
5654 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5655 } else {
5656 adapter = filterArgument(adapter, positions[0] - 1, filter);
5657 }
5658 }
5659 filter = newFilter;
5660 index = 0;
5661 }
5662
5663 filterArgumentChecks(target, pos + i, newFilter);
5664 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
5665 }
5666 if (index > 1) {
5667 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5668 } else if (index == 1) {
5669 adapter = filterArgument(adapter, positions[0] - 1, filter);
5670 }
5671 return adapter;
5672 }
5673
5674 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
5675 MethodType targetType = adapter.type();
5676 MethodType filterType = filter.type();
5677 BoundMethodHandle result = adapter.rebind();
5678 Class<?> newParamType = filterType.parameterType(0);
5679
5680 Class<?>[] ptypes = targetType.ptypes().clone();
5681 for (int pos : positions) {
5682 ptypes[pos - 1] = newParamType;
5683 }
5684 MethodType newType = MethodType.methodType(targetType.rtype(), ptypes, true);
5685
5686 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
5687 return result.copyWithExtendL(newType, lform, filter);
5688 }
5689
5690 /*non-public*/
5691 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
5692 filterArgumentChecks(target, pos, filter);
5693 MethodType targetType = target.type();
5694 MethodType filterType = filter.type();
5695 BoundMethodHandle result = target.rebind();
5696 Class<?> newParamType = filterType.parameterType(0);
5697 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
5698 MethodType newType = targetType.changeParameterType(pos, newParamType);
5699 result = result.copyWithExtendL(newType, lform, filter);
5700 return result;
5701 }
5702
5703 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
5704 MethodType targetType = target.type();
5705 int maxPos = targetType.parameterCount();
5706 if (pos + filters.length > maxPos)
5707 throw newIllegalArgumentException("too many filters");
5708 }
5709
5710 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5711 MethodType targetType = target.type();
5712 MethodType filterType = filter.type();
5713 if (filterType.parameterCount() != 1
5714 || filterType.returnType() != targetType.parameterType(pos))
5715 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5716 }
5717
5718 /**
5719 * Adapts a target method handle by pre-processing
5720 * a sub-sequence of its arguments with a filter (another method handle).
5721 * The pre-processed arguments are replaced by the result (if any) of the
5722 * filter function.
5723 * The target is then called on the modified (usually shortened) argument list.
5724 * <p>
5725 * If the filter returns a value, the target must accept that value as
5726 * its argument in position {@code pos}, preceded and/or followed by
5727 * any arguments not passed to the filter.
5728 * If the filter returns void, the target must accept all arguments
5729 * not passed to the filter.
5730 * No arguments are reordered, and a result returned from the filter
5731 * replaces (in order) the whole subsequence of arguments originally
5732 * passed to the adapter.
5733 * <p>
5734 * The argument types (if any) of the filter
5735 * replace zero or one argument types of the target, at position {@code pos},
5736 * in the resulting adapted method handle.
5737 * The return type of the filter (if any) must be identical to the
5738 * argument type of the target at position {@code pos}, and that target argument
5739 * is supplied by the return value of the filter.
5740 * <p>
5741 * In all cases, {@code pos} must be greater than or equal to zero, and
5742 * {@code pos} must also be less than or equal to the target's arity.
5743 * <p><b>Example:</b>
5744 * {@snippet lang="java" :
5745 import static java.lang.invoke.MethodHandles.*;
5746 import static java.lang.invoke.MethodType.*;
5747 ...
5748 MethodHandle deepToString = publicLookup()
5749 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
5750
5751 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
5752 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
5753
5754 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
5755 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
5756
5757 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
5758 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
5759 assertEquals("[top, [up, down], strange]",
5760 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
5761
5762 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
5763 assertEquals("[top, [up, down], [strange]]",
5764 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
5765
5766 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
5767 assertEquals("[top, [[up, down, strange], charm], bottom]",
5768 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
5769 * }
5770 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5771 * represents the return type of the {@code target} and resulting adapter.
5772 * {@code V}/{@code v} stand for the return type and value of the
5773 * {@code filter}, which are also found in the signature and arguments of
5774 * the {@code target}, respectively, unless {@code V} is {@code void}.
5775 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
5776 * and values preceding and following the collection position, {@code pos},
5777 * in the {@code target}'s signature. They also turn up in the resulting
5778 * adapter's signature and arguments, where they surround
5779 * {@code B}/{@code b}, which represent the parameter types and arguments
5780 * to the {@code filter} (if any).
5781 * {@snippet lang="java" :
5782 * T target(A...,V,C...);
5783 * V filter(B...);
5784 * T adapter(A... a,B... b,C... c) {
5785 * V v = filter(b...);
5786 * return target(a...,v,c...);
5787 * }
5788 * // and if the filter has no arguments:
5789 * T target2(A...,V,C...);
5790 * V filter2();
5791 * T adapter2(A... a,C... c) {
5792 * V v = filter2();
5793 * return target2(a...,v,c...);
5794 * }
5795 * // and if the filter has a void return:
5796 * T target3(A...,C...);
5797 * void filter3(B...);
5798 * T adapter3(A... a,B... b,C... c) {
5799 * filter3(b...);
5800 * return target3(a...,c...);
5801 * }
5802 * }
5803 * <p>
5804 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
5805 * one which first "folds" the affected arguments, and then drops them, in separate
5806 * steps as follows:
5807 * {@snippet lang="java" :
5808 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
5809 * mh = MethodHandles.foldArguments(mh, coll); //step 1
5810 * }
5811 * If the target method handle consumes no arguments besides than the result
5812 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
5813 * is equivalent to {@code filterReturnValue(coll, mh)}.
5814 * If the filter method handle {@code coll} consumes one argument and produces
5815 * a non-void result, then {@code collectArguments(mh, N, coll)}
5816 * is equivalent to {@code filterArguments(mh, N, coll)}.
5817 * Other equivalences are possible but would require argument permutation.
5818 * <p>
5819 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5820 * variable-arity method handle}, even if the original target method handle was.
5821 *
5822 * @param target the method handle to invoke after filtering the subsequence of arguments
5823 * @param pos the position of the first adapter argument to pass to the filter,
5824 * and/or the target argument which receives the result of the filter
5825 * @param filter method handle to call on the subsequence of arguments
5826 * @return method handle which incorporates the specified argument subsequence filtering logic
5827 * @throws NullPointerException if either argument is null
5828 * @throws IllegalArgumentException if the return type of {@code filter}
5829 * is non-void and is not the same as the {@code pos} argument of the target,
5830 * or if {@code pos} is not between 0 and the target's arity, inclusive,
5831 * or if the resulting method handle's type would have
5832 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5833 * @see MethodHandles#foldArguments
5834 * @see MethodHandles#filterArguments
5835 * @see MethodHandles#filterReturnValue
5836 */
5837 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
5838 MethodType newType = collectArgumentsChecks(target, pos, filter);
5839 MethodType collectorType = filter.type();
5840 BoundMethodHandle result = target.rebind();
5841 LambdaForm lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
5842 return result.copyWithExtendL(newType, lform, filter);
5843 }
5844
5845 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5846 MethodType targetType = target.type();
5847 MethodType filterType = filter.type();
5848 Class<?> rtype = filterType.returnType();
5849 Class<?>[] filterArgs = filterType.ptypes();
5850 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) ||
5851 (rtype != void.class && pos >= targetType.parameterCount())) {
5852 throw newIllegalArgumentException("position is out of range for target", target, pos);
5853 }
5854 if (rtype == void.class) {
5855 return targetType.insertParameterTypes(pos, filterArgs);
5856 }
5857 if (rtype != targetType.parameterType(pos)) {
5858 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5859 }
5860 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs);
5861 }
5862
5863 /**
5864 * Adapts a target method handle by post-processing
5865 * its return value (if any) with a filter (another method handle).
5866 * The result of the filter is returned from the adapter.
5867 * <p>
5868 * If the target returns a value, the filter must accept that value as
5869 * its only argument.
5870 * If the target returns void, the filter must accept no arguments.
5871 * <p>
5872 * The return type of the filter
5873 * replaces the return type of the target
5874 * in the resulting adapted method handle.
5875 * The argument type of the filter (if any) must be identical to the
5876 * return type of the target.
5877 * <p><b>Example:</b>
5878 * {@snippet lang="java" :
5879 import static java.lang.invoke.MethodHandles.*;
5880 import static java.lang.invoke.MethodType.*;
5881 ...
5882 MethodHandle cat = lookup().findVirtual(String.class,
5883 "concat", methodType(String.class, String.class));
5884 MethodHandle length = lookup().findVirtual(String.class,
5885 "length", methodType(int.class));
5886 System.out.println((String) cat.invokeExact("x", "y")); // xy
5887 MethodHandle f0 = filterReturnValue(cat, length);
5888 System.out.println((int) f0.invokeExact("x", "y")); // 2
5889 * }
5890 * <p>Here is pseudocode for the resulting adapter. In the code,
5891 * {@code T}/{@code t} represent the result type and value of the
5892 * {@code target}; {@code V}, the result type of the {@code filter}; and
5893 * {@code A}/{@code a}, the types and values of the parameters and arguments
5894 * of the {@code target} as well as the resulting adapter.
5895 * {@snippet lang="java" :
5896 * T target(A...);
5897 * V filter(T);
5898 * V adapter(A... a) {
5899 * T t = target(a...);
5900 * return filter(t);
5901 * }
5902 * // and if the target has a void return:
5903 * void target2(A...);
5904 * V filter2();
5905 * V adapter2(A... a) {
5906 * target2(a...);
5907 * return filter2();
5908 * }
5909 * // and if the filter has a void return:
5910 * T target3(A...);
5911 * void filter3(V);
5912 * void adapter3(A... a) {
5913 * T t = target3(a...);
5914 * filter3(t);
5915 * }
5916 * }
5917 * <p>
5918 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5919 * variable-arity method handle}, even if the original target method handle was.
5920 * @param target the method handle to invoke before filtering the return value
5921 * @param filter method handle to call on the return value
5922 * @return method handle which incorporates the specified return value filtering logic
5923 * @throws NullPointerException if either argument is null
5924 * @throws IllegalArgumentException if the argument list of {@code filter}
5925 * does not match the return type of target as described above
5926 */
5927 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
5928 MethodType targetType = target.type();
5929 MethodType filterType = filter.type();
5930 filterReturnValueChecks(targetType, filterType);
5931 BoundMethodHandle result = target.rebind();
5932 BasicType rtype = BasicType.basicType(filterType.returnType());
5933 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
5934 MethodType newType = targetType.changeReturnType(filterType.returnType());
5935 result = result.copyWithExtendL(newType, lform, filter);
5936 return result;
5937 }
5938
5939 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
5940 Class<?> rtype = targetType.returnType();
5941 int filterValues = filterType.parameterCount();
5942 if (filterValues == 0
5943 ? (rtype != void.class)
5944 : (rtype != filterType.parameterType(0) || filterValues != 1))
5945 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5946 }
5947
5948 /**
5949 * Filter the return value of a target method handle with a filter function. The filter function is
5950 * applied to the return value of the original handle; if the filter specifies more than one parameters,
5951 * then any remaining parameter is appended to the adapter handle. In other words, the adaptation works
5952 * as follows:
5953 * {@snippet lang="java" :
5954 * T target(A...)
5955 * V filter(B... , T)
5956 * V adapter(A... a, B... b) {
5957 * T t = target(a...);
5958 * return filter(b..., t);
5959 * }
5960 * }
5961 * <p>
5962 * If the filter handle is a unary function, then this method behaves like {@link #filterReturnValue(MethodHandle, MethodHandle)}.
5963 *
5964 * @param target the target method handle
5965 * @param filter the filter method handle
5966 * @return the adapter method handle
5967 */
5968 /* package */ static MethodHandle collectReturnValue(MethodHandle target, MethodHandle filter) {
5969 MethodType targetType = target.type();
5970 MethodType filterType = filter.type();
5971 BoundMethodHandle result = target.rebind();
5972 LambdaForm lform = result.editor().collectReturnValueForm(filterType.basicType());
5973 MethodType newType = targetType.changeReturnType(filterType.returnType());
5974 if (filterType.parameterCount() > 1) {
5975 for (int i = 0 ; i < filterType.parameterCount() - 1 ; i++) {
5976 newType = newType.appendParameterTypes(filterType.parameterType(i));
5977 }
5978 }
5979 result = result.copyWithExtendL(newType, lform, filter);
5980 return result;
5981 }
5982
5983 /**
5984 * Adapts a target method handle by pre-processing
5985 * some of its arguments, and then calling the target with
5986 * the result of the pre-processing, inserted into the original
5987 * sequence of arguments.
5988 * <p>
5989 * The pre-processing is performed by {@code combiner}, a second method handle.
5990 * Of the arguments passed to the adapter, the first {@code N} arguments
5991 * are copied to the combiner, which is then called.
5992 * (Here, {@code N} is defined as the parameter count of the combiner.)
5993 * After this, control passes to the target, with any result
5994 * from the combiner inserted before the original {@code N} incoming
5995 * arguments.
5996 * <p>
5997 * If the combiner returns a value, the first parameter type of the target
5998 * must be identical with the return type of the combiner, and the next
5999 * {@code N} parameter types of the target must exactly match the parameters
6000 * of the combiner.
6001 * <p>
6002 * If the combiner has a void return, no result will be inserted,
6003 * and the first {@code N} parameter types of the target
6004 * must exactly match the parameters of the combiner.
6005 * <p>
6006 * The resulting adapter is the same type as the target, except that the
6007 * first parameter type is dropped,
6008 * if it corresponds to the result of the combiner.
6009 * <p>
6010 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
6011 * that either the combiner or the target does not wish to receive.
6012 * If some of the incoming arguments are destined only for the combiner,
6013 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
6014 * arguments will not need to be live on the stack on entry to the
6015 * target.)
6016 * <p><b>Example:</b>
6017 * {@snippet lang="java" :
6018 import static java.lang.invoke.MethodHandles.*;
6019 import static java.lang.invoke.MethodType.*;
6020 ...
6021 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6022 "println", methodType(void.class, String.class))
6023 .bindTo(System.out);
6024 MethodHandle cat = lookup().findVirtual(String.class,
6025 "concat", methodType(String.class, String.class));
6026 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6027 MethodHandle catTrace = foldArguments(cat, trace);
6028 // also prints "boo":
6029 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6030 * }
6031 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6032 * represents the result type of the {@code target} and resulting adapter.
6033 * {@code V}/{@code v} represent the type and value of the parameter and argument
6034 * of {@code target} that precedes the folding position; {@code V} also is
6035 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6036 * types and values of the {@code N} parameters and arguments at the folding
6037 * position. {@code B}/{@code b} represent the types and values of the
6038 * {@code target} parameters and arguments that follow the folded parameters
6039 * and arguments.
6040 * {@snippet lang="java" :
6041 * // there are N arguments in A...
6042 * T target(V, A[N]..., B...);
6043 * V combiner(A...);
6044 * T adapter(A... a, B... b) {
6045 * V v = combiner(a...);
6046 * return target(v, a..., b...);
6047 * }
6048 * // and if the combiner has a void return:
6049 * T target2(A[N]..., B...);
6050 * void combiner2(A...);
6051 * T adapter2(A... a, B... b) {
6052 * combiner2(a...);
6053 * return target2(a..., b...);
6054 * }
6055 * }
6056 * <p>
6057 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6058 * variable-arity method handle}, even if the original target method handle was.
6059 * @param target the method handle to invoke after arguments are combined
6060 * @param combiner method handle to call initially on the incoming arguments
6061 * @return method handle which incorporates the specified argument folding logic
6062 * @throws NullPointerException if either argument is null
6063 * @throws IllegalArgumentException if {@code combiner}'s return type
6064 * is non-void and not the same as the first argument type of
6065 * the target, or if the initial {@code N} argument types
6066 * of the target
6067 * (skipping one matching the {@code combiner}'s return type)
6068 * are not identical with the argument types of {@code combiner}
6069 */
6070 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
6071 return foldArguments(target, 0, combiner);
6072 }
6073
6074 /**
6075 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
6076 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
6077 * before the folded arguments.
6078 * <p>
6079 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
6080 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
6081 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
6082 * 0.
6083 *
6084 * @apiNote Example:
6085 * {@snippet lang="java" :
6086 import static java.lang.invoke.MethodHandles.*;
6087 import static java.lang.invoke.MethodType.*;
6088 ...
6089 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6090 "println", methodType(void.class, String.class))
6091 .bindTo(System.out);
6092 MethodHandle cat = lookup().findVirtual(String.class,
6093 "concat", methodType(String.class, String.class));
6094 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6095 MethodHandle catTrace = foldArguments(cat, 1, trace);
6096 // also prints "jum":
6097 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6098 * }
6099 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6100 * represents the result type of the {@code target} and resulting adapter.
6101 * {@code V}/{@code v} represent the type and value of the parameter and argument
6102 * of {@code target} that precedes the folding position; {@code V} also is
6103 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6104 * types and values of the {@code N} parameters and arguments at the folding
6105 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
6106 * and values of the {@code target} parameters and arguments that precede and
6107 * follow the folded parameters and arguments starting at {@code pos},
6108 * respectively.
6109 * {@snippet lang="java" :
6110 * // there are N arguments in A...
6111 * T target(Z..., V, A[N]..., B...);
6112 * V combiner(A...);
6113 * T adapter(Z... z, A... a, B... b) {
6114 * V v = combiner(a...);
6115 * return target(z..., v, a..., b...);
6116 * }
6117 * // and if the combiner has a void return:
6118 * T target2(Z..., A[N]..., B...);
6119 * void combiner2(A...);
6120 * T adapter2(Z... z, A... a, B... b) {
6121 * combiner2(a...);
6122 * return target2(z..., a..., b...);
6123 * }
6124 * }
6125 * <p>
6126 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6127 * variable-arity method handle}, even if the original target method handle was.
6128 *
6129 * @param target the method handle to invoke after arguments are combined
6130 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
6131 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6132 * @param combiner method handle to call initially on the incoming arguments
6133 * @return method handle which incorporates the specified argument folding logic
6134 * @throws NullPointerException if either argument is null
6135 * @throws IllegalArgumentException if either of the following two conditions holds:
6136 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6137 * {@code pos} of the target signature;
6138 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
6139 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
6140 *
6141 * @see #foldArguments(MethodHandle, MethodHandle)
6142 * @since 9
6143 */
6144 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
6145 MethodType targetType = target.type();
6146 MethodType combinerType = combiner.type();
6147 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
6148 BoundMethodHandle result = target.rebind();
6149 boolean dropResult = rtype == void.class;
6150 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
6151 MethodType newType = targetType;
6152 if (!dropResult) {
6153 newType = newType.dropParameterTypes(pos, pos + 1);
6154 }
6155 result = result.copyWithExtendL(newType, lform, combiner);
6156 return result;
6157 }
6158
6159 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
6160 int foldArgs = combinerType.parameterCount();
6161 Class<?> rtype = combinerType.returnType();
6162 int foldVals = rtype == void.class ? 0 : 1;
6163 int afterInsertPos = foldPos + foldVals;
6164 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
6165 if (ok) {
6166 for (int i = 0; i < foldArgs; i++) {
6167 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
6168 ok = false;
6169 break;
6170 }
6171 }
6172 }
6173 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
6174 ok = false;
6175 if (!ok)
6176 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6177 return rtype;
6178 }
6179
6180 /**
6181 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
6182 * of the pre-processing replacing the argument at the given position.
6183 *
6184 * @param target the method handle to invoke after arguments are combined
6185 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6186 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6187 * @param combiner method handle to call initially on the incoming arguments
6188 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6189 * @return method handle which incorporates the specified argument folding logic
6190 * @throws NullPointerException if either argument is null
6191 * @throws IllegalArgumentException if either of the following two conditions holds:
6192 * (1) {@code combiner}'s return type is not the same as the argument type at position
6193 * {@code pos} of the target signature;
6194 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
6195 * not identical with the argument types of {@code combiner}.
6196 */
6197 /*non-public*/
6198 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6199 return argumentsWithCombiner(true, target, position, combiner, argPositions);
6200 }
6201
6202 /**
6203 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
6204 * the pre-processing inserted into the original sequence of arguments at the given position.
6205 *
6206 * @param target the method handle to invoke after arguments are combined
6207 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6208 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6209 * @param combiner method handle to call initially on the incoming arguments
6210 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6211 * @return method handle which incorporates the specified argument folding logic
6212 * @throws NullPointerException if either argument is null
6213 * @throws IllegalArgumentException if either of the following two conditions holds:
6214 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6215 * {@code pos} of the target signature;
6216 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
6217 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
6218 * with the argument types of {@code combiner}.
6219 */
6220 /*non-public*/
6221 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6222 return argumentsWithCombiner(false, target, position, combiner, argPositions);
6223 }
6224
6225 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6226 MethodType targetType = target.type();
6227 MethodType combinerType = combiner.type();
6228 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
6229 BoundMethodHandle result = target.rebind();
6230
6231 MethodType newType = targetType;
6232 LambdaForm lform;
6233 if (filter) {
6234 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
6235 } else {
6236 boolean dropResult = rtype == void.class;
6237 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
6238 if (!dropResult) {
6239 newType = newType.dropParameterTypes(position, position + 1);
6240 }
6241 }
6242 result = result.copyWithExtendL(newType, lform, combiner);
6243 return result;
6244 }
6245
6246 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
6247 int combinerArgs = combinerType.parameterCount();
6248 if (argPos.length != combinerArgs) {
6249 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
6250 }
6251 Class<?> rtype = combinerType.returnType();
6252
6253 for (int i = 0; i < combinerArgs; i++) {
6254 int arg = argPos[i];
6255 if (arg < 0 || arg > targetType.parameterCount()) {
6256 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
6257 }
6258 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
6259 throw newIllegalArgumentException("target argument type at position " + arg
6260 + " must match combiner argument type at index " + i + ": " + targetType
6261 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
6262 }
6263 }
6264 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
6265 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6266 }
6267 return rtype;
6268 }
6269
6270 /**
6271 * Makes a method handle which adapts a target method handle,
6272 * by guarding it with a test, a boolean-valued method handle.
6273 * If the guard fails, a fallback handle is called instead.
6274 * All three method handles must have the same corresponding
6275 * argument and return types, except that the return type
6276 * of the test must be boolean, and the test is allowed
6277 * to have fewer arguments than the other two method handles.
6278 * <p>
6279 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6280 * represents the uniform result type of the three involved handles;
6281 * {@code A}/{@code a}, the types and values of the {@code target}
6282 * parameters and arguments that are consumed by the {@code test}; and
6283 * {@code B}/{@code b}, those types and values of the {@code target}
6284 * parameters and arguments that are not consumed by the {@code test}.
6285 * {@snippet lang="java" :
6286 * boolean test(A...);
6287 * T target(A...,B...);
6288 * T fallback(A...,B...);
6289 * T adapter(A... a,B... b) {
6290 * if (test(a...))
6291 * return target(a..., b...);
6292 * else
6293 * return fallback(a..., b...);
6294 * }
6295 * }
6296 * Note that the test arguments ({@code a...} in the pseudocode) cannot
6297 * be modified by execution of the test, and so are passed unchanged
6298 * from the caller to the target or fallback as appropriate.
6299 * @param test method handle used for test, must return boolean
6300 * @param target method handle to call if test passes
6301 * @param fallback method handle to call if test fails
6302 * @return method handle which incorporates the specified if/then/else logic
6303 * @throws NullPointerException if any argument is null
6304 * @throws IllegalArgumentException if {@code test} does not return boolean,
6305 * or if all three method types do not match (with the return
6306 * type of {@code test} changed to match that of the target).
6307 */
6308 public static MethodHandle guardWithTest(MethodHandle test,
6309 MethodHandle target,
6310 MethodHandle fallback) {
6311 MethodType gtype = test.type();
6312 MethodType ttype = target.type();
6313 MethodType ftype = fallback.type();
6314 if (!ttype.equals(ftype))
6315 throw misMatchedTypes("target and fallback types", ttype, ftype);
6316 if (gtype.returnType() != boolean.class)
6317 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
6318
6319 test = dropArgumentsToMatch(test, 0, ttype.ptypes(), 0, true);
6320 if (test == null) {
6321 throw misMatchedTypes("target and test types", ttype, gtype);
6322 }
6323 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
6324 }
6325
6326 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
6327 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
6328 }
6329
6330 /**
6331 * Makes a method handle which adapts a target method handle,
6332 * by running it inside an exception handler.
6333 * If the target returns normally, the adapter returns that value.
6334 * If an exception matching the specified type is thrown, the fallback
6335 * handle is called instead on the exception, plus the original arguments.
6336 * <p>
6337 * The target and handler must have the same corresponding
6338 * argument and return types, except that handler may omit trailing arguments
6339 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
6340 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
6341 * <p>
6342 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6343 * represents the return type of the {@code target} and {@code handler},
6344 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
6345 * the types and values of arguments to the resulting handle consumed by
6346 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
6347 * resulting handle discarded by {@code handler}.
6348 * {@snippet lang="java" :
6349 * T target(A..., B...);
6350 * T handler(ExType, A...);
6351 * T adapter(A... a, B... b) {
6352 * try {
6353 * return target(a..., b...);
6354 * } catch (ExType ex) {
6355 * return handler(ex, a...);
6356 * }
6357 * }
6358 * }
6359 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6360 * be modified by execution of the target, and so are passed unchanged
6361 * from the caller to the handler, if the handler is invoked.
6362 * <p>
6363 * The target and handler must return the same type, even if the handler
6364 * always throws. (This might happen, for instance, because the handler
6365 * is simulating a {@code finally} clause).
6366 * To create such a throwing handler, compose the handler creation logic
6367 * with {@link #throwException throwException},
6368 * in order to create a method handle of the correct return type.
6369 * @param target method handle to call
6370 * @param exType the type of exception which the handler will catch
6371 * @param handler method handle to call if a matching exception is thrown
6372 * @return method handle which incorporates the specified try/catch logic
6373 * @throws NullPointerException if any argument is null
6374 * @throws IllegalArgumentException if {@code handler} does not accept
6375 * the given exception type, or if the method handle types do
6376 * not match in their return types and their
6377 * corresponding parameters
6378 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
6379 */
6380 public static MethodHandle catchException(MethodHandle target,
6381 Class<? extends Throwable> exType,
6382 MethodHandle handler) {
6383 MethodType ttype = target.type();
6384 MethodType htype = handler.type();
6385 if (!Throwable.class.isAssignableFrom(exType))
6386 throw new ClassCastException(exType.getName());
6387 if (htype.parameterCount() < 1 ||
6388 !htype.parameterType(0).isAssignableFrom(exType))
6389 throw newIllegalArgumentException("handler does not accept exception type "+exType);
6390 if (htype.returnType() != ttype.returnType())
6391 throw misMatchedTypes("target and handler return types", ttype, htype);
6392 handler = dropArgumentsToMatch(handler, 1, ttype.ptypes(), 0, true);
6393 if (handler == null) {
6394 throw misMatchedTypes("target and handler types", ttype, htype);
6395 }
6396 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
6397 }
6398
6399 /**
6400 * Produces a method handle which will throw exceptions of the given {@code exType}.
6401 * The method handle will accept a single argument of {@code exType},
6402 * and immediately throw it as an exception.
6403 * The method type will nominally specify a return of {@code returnType}.
6404 * The return type may be anything convenient: It doesn't matter to the
6405 * method handle's behavior, since it will never return normally.
6406 * @param returnType the return type of the desired method handle
6407 * @param exType the parameter type of the desired method handle
6408 * @return method handle which can throw the given exceptions
6409 * @throws NullPointerException if either argument is null
6410 */
6411 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
6412 if (!Throwable.class.isAssignableFrom(exType))
6413 throw new ClassCastException(exType.getName());
6414 return MethodHandleImpl.throwException(methodType(returnType, exType));
6415 }
6416
6417 /**
6418 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
6419 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
6420 * delivers the loop's result, which is the return value of the resulting handle.
6421 * <p>
6422 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
6423 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
6424 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
6425 * terms of method handles, each clause will specify up to four independent actions:<ul>
6426 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
6427 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
6428 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
6429 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
6430 * </ul>
6431 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
6432 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
6433 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
6434 * <p>
6435 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
6436 * this case. See below for a detailed description.
6437 * <p>
6438 * <em>Parameters optional everywhere:</em>
6439 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
6440 * As an exception, the init functions cannot take any {@code v} parameters,
6441 * because those values are not yet computed when the init functions are executed.
6442 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
6443 * In fact, any clause function may take no arguments at all.
6444 * <p>
6445 * <em>Loop parameters:</em>
6446 * A clause function may take all the iteration variable values it is entitled to, in which case
6447 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
6448 * with their types and values notated as {@code (A...)} and {@code (a...)}.
6449 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
6450 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
6451 * init function is automatically a loop parameter {@code a}.)
6452 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
6453 * These loop parameters act as loop-invariant values visible across the whole loop.
6454 * <p>
6455 * <em>Parameters visible everywhere:</em>
6456 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
6457 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
6458 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
6459 * Most clause functions will not need all of this information, but they will be formally connected to it
6460 * as if by {@link #dropArguments}.
6461 * <a id="astar"></a>
6462 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
6463 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
6464 * In that notation, the general form of an init function parameter list
6465 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
6466 * <p>
6467 * <em>Checking clause structure:</em>
6468 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
6469 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
6470 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
6471 * met by the inputs to the loop combinator.
6472 * <p>
6473 * <em>Effectively identical sequences:</em>
6474 * <a id="effid"></a>
6475 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
6476 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
6477 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
6478 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
6479 * that longest list.
6480 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
6481 * and the same is true if more sequences of the form {@code (V... A*)} are added.
6482 * <p>
6483 * <em>Step 0: Determine clause structure.</em><ol type="a">
6484 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
6485 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
6486 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
6487 * four. Padding takes place by appending elements to the array.
6488 * <li>Clauses with all {@code null}s are disregarded.
6489 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
6490 * </ol>
6491 * <p>
6492 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
6493 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
6494 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
6495 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
6496 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
6497 * iteration variable type.
6498 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
6499 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
6500 * </ol>
6501 * <p>
6502 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
6503 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
6504 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
6505 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
6506 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
6507 * (These types will be checked in step 2, along with all the clause function types.)
6508 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
6509 * <li>All of the collected parameter lists must be effectively identical.
6510 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
6511 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
6512 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
6513 * the "internal parameter list".
6514 * </ul>
6515 * <p>
6516 * <em>Step 1C: Determine loop return type.</em><ol type="a">
6517 * <li>Examine fini function return types, disregarding omitted fini functions.
6518 * <li>If there are no fini functions, the loop return type is {@code void}.
6519 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
6520 * type.
6521 * </ol>
6522 * <p>
6523 * <em>Step 1D: Check other types.</em><ol type="a">
6524 * <li>There must be at least one non-omitted pred function.
6525 * <li>Every non-omitted pred function must have a {@code boolean} return type.
6526 * </ol>
6527 * <p>
6528 * <em>Step 2: Determine parameter lists.</em><ol type="a">
6529 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
6530 * <li>The parameter list for init functions will be adjusted to the external parameter list.
6531 * (Note that their parameter lists are already effectively identical to this list.)
6532 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
6533 * effectively identical to the internal parameter list {@code (V... A...)}.
6534 * </ol>
6535 * <p>
6536 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
6537 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
6538 * type.
6539 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
6540 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
6541 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
6542 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
6543 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
6544 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
6545 * loop return type.
6546 * </ol>
6547 * <p>
6548 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
6549 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
6550 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
6551 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
6552 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
6553 * pad out the end of the list.
6554 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
6555 * </ol>
6556 * <p>
6557 * <em>Final observations.</em><ol type="a">
6558 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
6559 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
6560 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
6561 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
6562 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
6563 * <li>Each pair of init and step functions agrees in their return type {@code V}.
6564 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
6565 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
6566 * </ol>
6567 * <p>
6568 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
6569 * <ul>
6570 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
6571 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
6572 * (Only one {@code Pn} has to be non-{@code null}.)
6573 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
6574 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
6575 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
6576 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
6577 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
6578 * the resulting loop handle's parameter types {@code (A...)}.
6579 * </ul>
6580 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
6581 * which is natural if most of the loop computation happens in the steps. For some loops,
6582 * the burden of computation might be heaviest in the pred functions, and so the pred functions
6583 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
6584 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
6585 * where the init functions will need the extra parameters. For such reasons, the rules for
6586 * determining these parameters are as symmetric as possible, across all clause parts.
6587 * In general, the loop parameters function as common invariant values across the whole
6588 * loop, while the iteration variables function as common variant values, or (if there is
6589 * no step function) as internal loop invariant temporaries.
6590 * <p>
6591 * <em>Loop execution.</em><ol type="a">
6592 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
6593 * every clause function. These locals are loop invariant.
6594 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
6595 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
6596 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
6597 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
6598 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
6599 * (in argument order).
6600 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
6601 * returns {@code false}.
6602 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
6603 * sequence {@code (v...)} of loop variables.
6604 * The updated value is immediately visible to all subsequent function calls.
6605 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
6606 * (of type {@code R}) is returned from the loop as a whole.
6607 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
6608 * except by throwing an exception.
6609 * </ol>
6610 * <p>
6611 * <em>Usage tips.</em>
6612 * <ul>
6613 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
6614 * sometimes a step function only needs to observe the current value of its own variable.
6615 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
6616 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
6617 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
6618 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
6619 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
6620 * <li>If some of the clause functions are virtual methods on an instance, the instance
6621 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
6622 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
6623 * will be the first iteration variable value, and it will be easy to use virtual
6624 * methods as clause parts, since all of them will take a leading instance reference matching that value.
6625 * </ul>
6626 * <p>
6627 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
6628 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
6629 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
6630 * {@snippet lang="java" :
6631 * V... init...(A...);
6632 * boolean pred...(V..., A...);
6633 * V... step...(V..., A...);
6634 * R fini...(V..., A...);
6635 * R loop(A... a) {
6636 * V... v... = init...(a...);
6637 * for (;;) {
6638 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
6639 * v = s(v..., a...);
6640 * if (!p(v..., a...)) {
6641 * return f(v..., a...);
6642 * }
6643 * }
6644 * }
6645 * }
6646 * }
6647 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
6648 * to their full length, even though individual clause functions may neglect to take them all.
6649 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
6650 *
6651 * @apiNote Example:
6652 * {@snippet lang="java" :
6653 * // iterative implementation of the factorial function as a loop handle
6654 * static int one(int k) { return 1; }
6655 * static int inc(int i, int acc, int k) { return i + 1; }
6656 * static int mult(int i, int acc, int k) { return i * acc; }
6657 * static boolean pred(int i, int acc, int k) { return i < k; }
6658 * static int fin(int i, int acc, int k) { return acc; }
6659 * // assume MH_one, 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[] counterClause = new MethodHandle[]{null, MH_inc};
6662 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6663 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6664 * assertEquals(120, loop.invoke(5));
6665 * }
6666 * The same example, dropping arguments and using combinators:
6667 * {@snippet lang="java" :
6668 * // simplified implementation of the factorial function as a loop handle
6669 * static int inc(int i) { return i + 1; } // drop acc, k
6670 * static int mult(int i, int acc) { return i * acc; } //drop k
6671 * static boolean cmp(int i, int k) { return i < k; }
6672 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
6673 * // null initializer for counter, should initialize to 0
6674 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6675 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
6676 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
6677 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6678 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6679 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6680 * assertEquals(720, loop.invoke(6));
6681 * }
6682 * A similar example, using a helper object to hold a loop parameter:
6683 * {@snippet lang="java" :
6684 * // instance-based implementation of the factorial function as a loop handle
6685 * static class FacLoop {
6686 * final int k;
6687 * FacLoop(int k) { this.k = k; }
6688 * int inc(int i) { return i + 1; }
6689 * int mult(int i, int acc) { return i * acc; }
6690 * boolean pred(int i) { return i < k; }
6691 * int fin(int i, int acc) { return acc; }
6692 * }
6693 * // assume MH_FacLoop is a handle to the constructor
6694 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6695 * // null initializer for counter, should initialize to 0
6696 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6697 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
6698 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6699 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6700 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
6701 * assertEquals(5040, loop.invoke(7));
6702 * }
6703 *
6704 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
6705 *
6706 * @return a method handle embodying the looping behavior as defined by the arguments.
6707 *
6708 * @throws IllegalArgumentException in case any of the constraints described above is violated.
6709 *
6710 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
6711 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6712 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
6713 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
6714 * @since 9
6715 */
6716 public static MethodHandle loop(MethodHandle[]... clauses) {
6717 // Step 0: determine clause structure.
6718 loopChecks0(clauses);
6719
6720 List<MethodHandle> init = new ArrayList<>();
6721 List<MethodHandle> step = new ArrayList<>();
6722 List<MethodHandle> pred = new ArrayList<>();
6723 List<MethodHandle> fini = new ArrayList<>();
6724
6725 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
6726 init.add(clause[0]); // all clauses have at least length 1
6727 step.add(clause.length <= 1 ? null : clause[1]);
6728 pred.add(clause.length <= 2 ? null : clause[2]);
6729 fini.add(clause.length <= 3 ? null : clause[3]);
6730 });
6731
6732 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
6733 final int nclauses = init.size();
6734
6735 // Step 1A: determine iteration variables (V...).
6736 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
6737 for (int i = 0; i < nclauses; ++i) {
6738 MethodHandle in = init.get(i);
6739 MethodHandle st = step.get(i);
6740 if (in == null && st == null) {
6741 iterationVariableTypes.add(void.class);
6742 } else if (in != null && st != null) {
6743 loopChecks1a(i, in, st);
6744 iterationVariableTypes.add(in.type().returnType());
6745 } else {
6746 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
6747 }
6748 }
6749 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).toList();
6750
6751 // Step 1B: determine loop parameters (A...).
6752 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
6753 loopChecks1b(init, commonSuffix);
6754
6755 // Step 1C: determine loop return type.
6756 // Step 1D: check other types.
6757 // local variable required here; see JDK-8223553
6758 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
6759 .map(MethodType::returnType);
6760 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
6761 loopChecks1cd(pred, fini, loopReturnType);
6762
6763 // Step 2: determine parameter lists.
6764 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
6765 commonParameterSequence.addAll(commonSuffix);
6766 loopChecks2(step, pred, fini, commonParameterSequence);
6767 // Step 3: fill in omitted functions.
6768 for (int i = 0; i < nclauses; ++i) {
6769 Class<?> t = iterationVariableTypes.get(i);
6770 if (init.get(i) == null) {
6771 init.set(i, empty(methodType(t, commonSuffix)));
6772 }
6773 if (step.get(i) == null) {
6774 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
6775 }
6776 if (pred.get(i) == null) {
6777 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence));
6778 }
6779 if (fini.get(i) == null) {
6780 fini.set(i, empty(methodType(t, commonParameterSequence)));
6781 }
6782 }
6783
6784 // Step 4: fill in missing parameter types.
6785 // Also convert all handles to fixed-arity handles.
6786 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
6787 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
6788 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
6789 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
6790
6791 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
6792 allMatch(pl -> pl.equals(commonSuffix));
6793 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
6794 allMatch(pl -> pl.equals(commonParameterSequence));
6795
6796 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
6797 }
6798
6799 private static void loopChecks0(MethodHandle[][] clauses) {
6800 if (clauses == null || clauses.length == 0) {
6801 throw newIllegalArgumentException("null or no clauses passed");
6802 }
6803 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
6804 throw newIllegalArgumentException("null clauses are not allowed");
6805 }
6806 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
6807 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
6808 }
6809 }
6810
6811 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
6812 if (in.type().returnType() != st.type().returnType()) {
6813 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
6814 st.type().returnType());
6815 }
6816 }
6817
6818 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
6819 return mhs.filter(Objects::nonNull)
6820 // take only those that can contribute to a common suffix because they are longer than the prefix
6821 .map(MethodHandle::type)
6822 .filter(t -> t.parameterCount() > skipSize)
6823 .max(Comparator.comparingInt(MethodType::parameterCount))
6824 .map(methodType -> List.of(Arrays.copyOfRange(methodType.ptypes(), skipSize, methodType.parameterCount())))
6825 .orElse(List.of());
6826 }
6827
6828 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
6829 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
6830 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
6831 return longest1.size() >= longest2.size() ? longest1 : longest2;
6832 }
6833
6834 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
6835 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
6836 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
6837 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
6838 " (common suffix: " + commonSuffix + ")");
6839 }
6840 }
6841
6842 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
6843 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6844 anyMatch(t -> t != loopReturnType)) {
6845 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
6846 loopReturnType + ")");
6847 }
6848
6849 if (pred.stream().noneMatch(Objects::nonNull)) {
6850 throw newIllegalArgumentException("no predicate found", pred);
6851 }
6852 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6853 anyMatch(t -> t != boolean.class)) {
6854 throw newIllegalArgumentException("predicates must have boolean return type", pred);
6855 }
6856 }
6857
6858 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
6859 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
6860 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
6861 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
6862 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
6863 }
6864 }
6865
6866 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
6867 return hs.stream().map(h -> {
6868 int pc = h.type().parameterCount();
6869 int tpsize = targetParams.size();
6870 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h;
6871 }).toList();
6872 }
6873
6874 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
6875 return hs.stream().map(MethodHandle::asFixedArity).toList();
6876 }
6877
6878 /**
6879 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
6880 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6881 * <p>
6882 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6883 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
6884 * evaluates to {@code true}).
6885 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
6886 * <p>
6887 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6888 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6889 * and updated with the value returned from its invocation. The result of loop execution will be
6890 * the final value of the additional loop-local variable (if present).
6891 * <p>
6892 * The following rules hold for these argument handles:<ul>
6893 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6894 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6895 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6896 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6897 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6898 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6899 * It will constrain the parameter lists of the other loop parts.
6900 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6901 * list {@code (A...)} is called the <em>external parameter list</em>.
6902 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6903 * additional state variable of the loop.
6904 * The body must both accept and return a value of this type {@code V}.
6905 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6906 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6907 * <a href="MethodHandles.html#effid">effectively identical</a>
6908 * to the external parameter list {@code (A...)}.
6909 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6910 * {@linkplain #empty default value}.
6911 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6912 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6913 * effectively identical to the internal parameter list.
6914 * </ul>
6915 * <p>
6916 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6917 * <li>The loop handle's result type is the result type {@code V} of the body.
6918 * <li>The loop handle's parameter types are the types {@code (A...)},
6919 * from the external parameter list.
6920 * </ul>
6921 * <p>
6922 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6923 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6924 * passed to the loop.
6925 * {@snippet lang="java" :
6926 * V init(A...);
6927 * boolean pred(V, A...);
6928 * V body(V, A...);
6929 * V whileLoop(A... a...) {
6930 * V v = init(a...);
6931 * while (pred(v, a...)) {
6932 * v = body(v, a...);
6933 * }
6934 * return v;
6935 * }
6936 * }
6937 *
6938 * @apiNote Example:
6939 * {@snippet lang="java" :
6940 * // implement the zip function for lists as a loop handle
6941 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
6942 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
6943 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
6944 * zip.add(a.next());
6945 * zip.add(b.next());
6946 * return zip;
6947 * }
6948 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
6949 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
6950 * List<String> a = Arrays.asList("a", "b", "c", "d");
6951 * List<String> b = Arrays.asList("e", "f", "g", "h");
6952 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
6953 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
6954 * }
6955 *
6956 *
6957 * @apiNote The implementation of this method can be expressed as follows:
6958 * {@snippet lang="java" :
6959 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6960 * MethodHandle fini = (body.type().returnType() == void.class
6961 * ? null : identity(body.type().returnType()));
6962 * MethodHandle[]
6963 * checkExit = { null, null, pred, fini },
6964 * varBody = { init, body };
6965 * return loop(checkExit, varBody);
6966 * }
6967 * }
6968 *
6969 * @param init optional initializer, providing the initial value of the loop variable.
6970 * May be {@code null}, implying a default initial value. See above for other constraints.
6971 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6972 * above for other constraints.
6973 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6974 * See above for other constraints.
6975 *
6976 * @return a method handle implementing the {@code while} loop as described by the arguments.
6977 * @throws IllegalArgumentException if the rules for the arguments are violated.
6978 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6979 *
6980 * @see #loop(MethodHandle[][])
6981 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6982 * @since 9
6983 */
6984 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6985 whileLoopChecks(init, pred, body);
6986 MethodHandle fini = identityOrVoid(body.type().returnType());
6987 MethodHandle[] checkExit = { null, null, pred, fini };
6988 MethodHandle[] varBody = { init, body };
6989 return loop(checkExit, varBody);
6990 }
6991
6992 /**
6993 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
6994 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6995 * <p>
6996 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6997 * method will, in each iteration, first execute its body and then evaluate the predicate.
6998 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
6999 * <p>
7000 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
7001 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
7002 * and updated with the value returned from its invocation. The result of loop execution will be
7003 * the final value of the additional loop-local variable (if present).
7004 * <p>
7005 * The following rules hold for these argument handles:<ul>
7006 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7007 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
7008 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7009 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
7010 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
7011 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
7012 * It will constrain the parameter lists of the other loop parts.
7013 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
7014 * list {@code (A...)} is called the <em>external parameter list</em>.
7015 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7016 * additional state variable of the loop.
7017 * The body must both accept and return a value of this type {@code V}.
7018 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7019 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7020 * <a href="MethodHandles.html#effid">effectively identical</a>
7021 * to the external parameter list {@code (A...)}.
7022 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7023 * {@linkplain #empty default value}.
7024 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
7025 * Its parameter list (either empty or of the form {@code (V A*)}) must be
7026 * effectively identical to the internal parameter list.
7027 * </ul>
7028 * <p>
7029 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7030 * <li>The loop handle's result type is the result type {@code V} of the body.
7031 * <li>The loop handle's parameter types are the types {@code (A...)},
7032 * from the external parameter list.
7033 * </ul>
7034 * <p>
7035 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7036 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
7037 * passed to the loop.
7038 * {@snippet lang="java" :
7039 * V init(A...);
7040 * boolean pred(V, A...);
7041 * V body(V, A...);
7042 * V doWhileLoop(A... a...) {
7043 * V v = init(a...);
7044 * do {
7045 * v = body(v, a...);
7046 * } while (pred(v, a...));
7047 * return v;
7048 * }
7049 * }
7050 *
7051 * @apiNote Example:
7052 * {@snippet lang="java" :
7053 * // int i = 0; while (i < limit) { ++i; } return i; => limit
7054 * static int zero(int limit) { return 0; }
7055 * static int step(int i, int limit) { return i + 1; }
7056 * static boolean pred(int i, int limit) { return i < limit; }
7057 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
7058 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
7059 * assertEquals(23, loop.invoke(23));
7060 * }
7061 *
7062 *
7063 * @apiNote The implementation of this method can be expressed as follows:
7064 * {@snippet lang="java" :
7065 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7066 * MethodHandle fini = (body.type().returnType() == void.class
7067 * ? null : identity(body.type().returnType()));
7068 * MethodHandle[] clause = { init, body, pred, fini };
7069 * return loop(clause);
7070 * }
7071 * }
7072 *
7073 * @param init optional initializer, providing the initial value of the loop variable.
7074 * May be {@code null}, implying a default initial value. See above for other constraints.
7075 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
7076 * See above for other constraints.
7077 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
7078 * above for other constraints.
7079 *
7080 * @return a method handle implementing the {@code while} loop as described by the arguments.
7081 * @throws IllegalArgumentException if the rules for the arguments are violated.
7082 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
7083 *
7084 * @see #loop(MethodHandle[][])
7085 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
7086 * @since 9
7087 */
7088 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7089 whileLoopChecks(init, pred, body);
7090 MethodHandle fini = identityOrVoid(body.type().returnType());
7091 MethodHandle[] clause = {init, body, pred, fini };
7092 return loop(clause);
7093 }
7094
7095 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
7096 Objects.requireNonNull(pred);
7097 Objects.requireNonNull(body);
7098 MethodType bodyType = body.type();
7099 Class<?> returnType = bodyType.returnType();
7100 List<Class<?>> innerList = bodyType.parameterList();
7101 List<Class<?>> outerList = innerList;
7102 if (returnType == void.class) {
7103 // OK
7104 } else if (innerList.isEmpty() || innerList.get(0) != returnType) {
7105 // leading V argument missing => error
7106 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7107 throw misMatchedTypes("body function", bodyType, expected);
7108 } else {
7109 outerList = innerList.subList(1, innerList.size());
7110 }
7111 MethodType predType = pred.type();
7112 if (predType.returnType() != boolean.class ||
7113 !predType.effectivelyIdenticalParameters(0, innerList)) {
7114 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
7115 }
7116 if (init != null) {
7117 MethodType initType = init.type();
7118 if (initType.returnType() != returnType ||
7119 !initType.effectivelyIdenticalParameters(0, outerList)) {
7120 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7121 }
7122 }
7123 }
7124
7125 /**
7126 * Constructs a loop that runs a given number of iterations.
7127 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7128 * <p>
7129 * The number of iterations is determined by the {@code iterations} handle evaluation result.
7130 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
7131 * It will be initialized to 0 and incremented by 1 in each iteration.
7132 * <p>
7133 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7134 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7135 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7136 * <p>
7137 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7138 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7139 * iteration variable.
7140 * The result of the loop handle execution will be the final {@code V} value of that variable
7141 * (or {@code void} if there is no {@code V} variable).
7142 * <p>
7143 * The following rules hold for the argument handles:<ul>
7144 * <li>The {@code iterations} handle must not be {@code null}, and must return
7145 * the type {@code int}, referred to here as {@code I} in parameter type lists.
7146 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7147 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7148 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7149 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7150 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7151 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7152 * of types called the <em>internal parameter list</em>.
7153 * It will constrain the parameter lists of the other loop parts.
7154 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7155 * with no additional {@code A} types, then the internal parameter list is extended by
7156 * the argument types {@code A...} of the {@code iterations} handle.
7157 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7158 * list {@code (A...)} is called the <em>external parameter list</em>.
7159 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7160 * additional state variable of the loop.
7161 * The body must both accept a leading parameter and return a value of this type {@code V}.
7162 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7163 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7164 * <a href="MethodHandles.html#effid">effectively identical</a>
7165 * to the external parameter list {@code (A...)}.
7166 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7167 * {@linkplain #empty default value}.
7168 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
7169 * effectively identical to the external parameter list {@code (A...)}.
7170 * </ul>
7171 * <p>
7172 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7173 * <li>The loop handle's result type is the result type {@code V} of the body.
7174 * <li>The loop handle's parameter types are the types {@code (A...)},
7175 * from the external parameter list.
7176 * </ul>
7177 * <p>
7178 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7179 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7180 * arguments passed to the loop.
7181 * {@snippet lang="java" :
7182 * int iterations(A...);
7183 * V init(A...);
7184 * V body(V, int, A...);
7185 * V countedLoop(A... a...) {
7186 * int end = iterations(a...);
7187 * V v = init(a...);
7188 * for (int i = 0; i < end; ++i) {
7189 * v = body(v, i, a...);
7190 * }
7191 * return v;
7192 * }
7193 * }
7194 *
7195 * @apiNote Example with a fully conformant body method:
7196 * {@snippet lang="java" :
7197 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7198 * // => a variation on a well known theme
7199 * static String step(String v, int counter, String init) { return "na " + v; }
7200 * // assume MH_step is a handle to the method above
7201 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
7202 * MethodHandle start = MethodHandles.identity(String.class);
7203 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
7204 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
7205 * }
7206 *
7207 * @apiNote Example with the simplest possible body method type,
7208 * and passing the number of iterations to the loop invocation:
7209 * {@snippet lang="java" :
7210 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7211 * // => a variation on a well known theme
7212 * static String step(String v, int counter ) { return "na " + v; }
7213 * // assume MH_step is a handle to the method above
7214 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
7215 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
7216 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
7217 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
7218 * }
7219 *
7220 * @apiNote Example that treats the number of iterations, string to append to, and string to append
7221 * as loop parameters:
7222 * {@snippet lang="java" :
7223 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7224 * // => a variation on a well known theme
7225 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
7226 * // assume MH_step is a handle to the method above
7227 * MethodHandle count = MethodHandles.identity(int.class);
7228 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
7229 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
7230 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
7231 * }
7232 *
7233 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
7234 * to enforce a loop type:
7235 * {@snippet lang="java" :
7236 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7237 * // => a variation on a well known theme
7238 * static String step(String v, int counter, String pre) { return pre + " " + v; }
7239 * // assume MH_step is a handle to the method above
7240 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
7241 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
7242 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
7243 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
7244 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
7245 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
7246 * }
7247 *
7248 * @apiNote The implementation of this method can be expressed as follows:
7249 * {@snippet lang="java" :
7250 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7251 * return countedLoop(empty(iterations.type()), iterations, init, body);
7252 * }
7253 * }
7254 *
7255 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
7256 * result type must be {@code int}. See above for other constraints.
7257 * @param init optional initializer, providing the initial value of the loop variable.
7258 * May be {@code null}, implying a default initial value. See above for other constraints.
7259 * @param body body of the loop, which may not be {@code null}.
7260 * It controls the loop parameters and result type in the standard case (see above for details).
7261 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7262 * and may accept any number of additional types.
7263 * See above for other constraints.
7264 *
7265 * @return a method handle representing the loop.
7266 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
7267 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7268 *
7269 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
7270 * @since 9
7271 */
7272 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7273 return countedLoop(empty(iterations.type()), iterations, init, body);
7274 }
7275
7276 /**
7277 * Constructs a loop that counts over a range of numbers.
7278 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7279 * <p>
7280 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
7281 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
7282 * values of the loop counter.
7283 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
7284 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
7285 * <p>
7286 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7287 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7288 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7289 * <p>
7290 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7291 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7292 * iteration variable.
7293 * The result of the loop handle execution will be the final {@code V} value of that variable
7294 * (or {@code void} if there is no {@code V} variable).
7295 * <p>
7296 * The following rules hold for the argument handles:<ul>
7297 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
7298 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
7299 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7300 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7301 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7302 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7303 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7304 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7305 * of types called the <em>internal parameter list</em>.
7306 * It will constrain the parameter lists of the other loop parts.
7307 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7308 * with no additional {@code A} types, then the internal parameter list is extended by
7309 * the argument types {@code A...} of the {@code end} handle.
7310 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7311 * list {@code (A...)} is called the <em>external parameter list</em>.
7312 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7313 * additional state variable of the loop.
7314 * The body must both accept a leading parameter and return a value of this type {@code V}.
7315 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7316 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7317 * <a href="MethodHandles.html#effid">effectively identical</a>
7318 * to the external parameter list {@code (A...)}.
7319 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7320 * {@linkplain #empty default value}.
7321 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
7322 * effectively identical to the external parameter list {@code (A...)}.
7323 * <li>Likewise, the parameter list of {@code end} must be effectively identical
7324 * to the external parameter list.
7325 * </ul>
7326 * <p>
7327 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7328 * <li>The loop handle's result type is the result type {@code V} of the body.
7329 * <li>The loop handle's parameter types are the types {@code (A...)},
7330 * from the external parameter list.
7331 * </ul>
7332 * <p>
7333 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7334 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7335 * arguments passed to the loop.
7336 * {@snippet lang="java" :
7337 * int start(A...);
7338 * int end(A...);
7339 * V init(A...);
7340 * V body(V, int, A...);
7341 * V countedLoop(A... a...) {
7342 * int e = end(a...);
7343 * int s = start(a...);
7344 * V v = init(a...);
7345 * for (int i = s; i < e; ++i) {
7346 * v = body(v, i, a...);
7347 * }
7348 * return v;
7349 * }
7350 * }
7351 *
7352 * @apiNote The implementation of this method can be expressed as follows:
7353 * {@snippet lang="java" :
7354 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7355 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
7356 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
7357 * // the following semantics:
7358 * // MH_increment: (int limit, int counter) -> counter + 1
7359 * // MH_predicate: (int limit, int counter) -> counter < limit
7360 * Class<?> counterType = start.type().returnType(); // int
7361 * Class<?> returnType = body.type().returnType();
7362 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
7363 * if (returnType != void.class) { // ignore the V variable
7364 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7365 * pred = dropArguments(pred, 1, returnType); // ditto
7366 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
7367 * }
7368 * body = dropArguments(body, 0, counterType); // ignore the limit variable
7369 * MethodHandle[]
7370 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7371 * bodyClause = { init, body }, // v = init(); v = body(v, i)
7372 * indexVar = { start, incr }; // i = start(); i = i + 1
7373 * return loop(loopLimit, bodyClause, indexVar);
7374 * }
7375 * }
7376 *
7377 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
7378 * See above for other constraints.
7379 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
7380 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
7381 * @param init optional initializer, providing the initial value of the loop variable.
7382 * May be {@code null}, implying a default initial value. See above for other constraints.
7383 * @param body body of the loop, which may not be {@code null}.
7384 * It controls the loop parameters and result type in the standard case (see above for details).
7385 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7386 * and may accept any number of additional types.
7387 * See above for other constraints.
7388 *
7389 * @return a method handle representing the loop.
7390 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
7391 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7392 *
7393 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
7394 * @since 9
7395 */
7396 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7397 countedLoopChecks(start, end, init, body);
7398 Class<?> counterType = start.type().returnType(); // int, but who's counting?
7399 Class<?> limitType = end.type().returnType(); // yes, int again
7400 Class<?> returnType = body.type().returnType();
7401 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
7402 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
7403 MethodHandle retv = null;
7404 if (returnType != void.class) {
7405 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7406 pred = dropArguments(pred, 1, returnType); // ditto
7407 retv = dropArguments(identity(returnType), 0, counterType);
7408 }
7409 body = dropArguments(body, 0, counterType); // ignore the limit variable
7410 MethodHandle[]
7411 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7412 bodyClause = { init, body }, // v = init(); v = body(v, i)
7413 indexVar = { start, incr }; // i = start(); i = i + 1
7414 return loop(loopLimit, bodyClause, indexVar);
7415 }
7416
7417 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7418 Objects.requireNonNull(start);
7419 Objects.requireNonNull(end);
7420 Objects.requireNonNull(body);
7421 Class<?> counterType = start.type().returnType();
7422 if (counterType != int.class) {
7423 MethodType expected = start.type().changeReturnType(int.class);
7424 throw misMatchedTypes("start function", start.type(), expected);
7425 } else if (end.type().returnType() != counterType) {
7426 MethodType expected = end.type().changeReturnType(counterType);
7427 throw misMatchedTypes("end function", end.type(), expected);
7428 }
7429 MethodType bodyType = body.type();
7430 Class<?> returnType = bodyType.returnType();
7431 List<Class<?>> innerList = bodyType.parameterList();
7432 // strip leading V value if present
7433 int vsize = (returnType == void.class ? 0 : 1);
7434 if (vsize != 0 && (innerList.isEmpty() || innerList.get(0) != returnType)) {
7435 // argument list has no "V" => error
7436 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7437 throw misMatchedTypes("body function", bodyType, expected);
7438 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
7439 // missing I type => error
7440 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
7441 throw misMatchedTypes("body function", bodyType, expected);
7442 }
7443 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
7444 if (outerList.isEmpty()) {
7445 // special case; take lists from end handle
7446 outerList = end.type().parameterList();
7447 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
7448 }
7449 MethodType expected = methodType(counterType, outerList);
7450 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
7451 throw misMatchedTypes("start parameter types", start.type(), expected);
7452 }
7453 if (end.type() != start.type() &&
7454 !end.type().effectivelyIdenticalParameters(0, outerList)) {
7455 throw misMatchedTypes("end parameter types", end.type(), expected);
7456 }
7457 if (init != null) {
7458 MethodType initType = init.type();
7459 if (initType.returnType() != returnType ||
7460 !initType.effectivelyIdenticalParameters(0, outerList)) {
7461 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7462 }
7463 }
7464 }
7465
7466 /**
7467 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
7468 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7469 * <p>
7470 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
7471 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
7472 * <p>
7473 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7474 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7475 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7476 * <p>
7477 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7478 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7479 * iteration variable.
7480 * The result of the loop handle execution will be the final {@code V} value of that variable
7481 * (or {@code void} if there is no {@code V} variable).
7482 * <p>
7483 * The following rules hold for the argument handles:<ul>
7484 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7485 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
7486 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7487 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
7488 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
7489 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
7490 * of types called the <em>internal parameter list</em>.
7491 * It will constrain the parameter lists of the other loop parts.
7492 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
7493 * with no additional {@code A} types, then the internal parameter list is extended by
7494 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
7495 * single type {@code Iterable} is added and constitutes the {@code A...} list.
7496 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
7497 * list {@code (A...)} is called the <em>external parameter list</em>.
7498 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7499 * additional state variable of the loop.
7500 * The body must both accept a leading parameter and return a value of this type {@code V}.
7501 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7502 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7503 * <a href="MethodHandles.html#effid">effectively identical</a>
7504 * to the external parameter list {@code (A...)}.
7505 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7506 * {@linkplain #empty default value}.
7507 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
7508 * type {@code java.util.Iterator} or a subtype thereof.
7509 * The iterator it produces when the loop is executed will be assumed
7510 * to yield values which can be converted to type {@code T}.
7511 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
7512 * effectively identical to the external parameter list {@code (A...)}.
7513 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
7514 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
7515 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
7516 * handle parameter is adjusted to accept the leading {@code A} type, as if by
7517 * the {@link MethodHandle#asType asType} conversion method.
7518 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
7519 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
7520 * </ul>
7521 * <p>
7522 * The type {@code T} may be either a primitive or reference.
7523 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
7524 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
7525 * as if by the {@link MethodHandle#asType asType} conversion method.
7526 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
7527 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
7528 * <p>
7529 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7530 * <li>The loop handle's result type is the result type {@code V} of the body.
7531 * <li>The loop handle's parameter types are the types {@code (A...)},
7532 * from the external parameter list.
7533 * </ul>
7534 * <p>
7535 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7536 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
7537 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
7538 * {@snippet lang="java" :
7539 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
7540 * V init(A...);
7541 * V body(V,T,A...);
7542 * V iteratedLoop(A... a...) {
7543 * Iterator<T> it = iterator(a...);
7544 * V v = init(a...);
7545 * while (it.hasNext()) {
7546 * T t = it.next();
7547 * v = body(v, t, a...);
7548 * }
7549 * return v;
7550 * }
7551 * }
7552 *
7553 * @apiNote Example:
7554 * {@snippet lang="java" :
7555 * // get an iterator from a list
7556 * static List<String> reverseStep(List<String> r, String e) {
7557 * r.add(0, e);
7558 * return r;
7559 * }
7560 * static List<String> newArrayList() { return new ArrayList<>(); }
7561 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
7562 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
7563 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
7564 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
7565 * assertEquals(reversedList, (List<String>) loop.invoke(list));
7566 * }
7567 *
7568 * @apiNote The implementation of this method can be expressed approximately as follows:
7569 * {@snippet lang="java" :
7570 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7571 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
7572 * Class<?> returnType = body.type().returnType();
7573 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7574 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
7575 * MethodHandle retv = null, step = body, startIter = iterator;
7576 * if (returnType != void.class) {
7577 * // the simple thing first: in (I V A...), drop the I to get V
7578 * retv = dropArguments(identity(returnType), 0, Iterator.class);
7579 * // body type signature (V T A...), internal loop types (I V A...)
7580 * step = swapArguments(body, 0, 1); // swap V <-> T
7581 * }
7582 * if (startIter == null) startIter = MH_getIter;
7583 * MethodHandle[]
7584 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
7585 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
7586 * return loop(iterVar, bodyClause);
7587 * }
7588 * }
7589 *
7590 * @param iterator an optional handle to return the iterator to start the loop.
7591 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
7592 * See above for other constraints.
7593 * @param init optional initializer, providing the initial value of the loop variable.
7594 * May be {@code null}, implying a default initial value. See above for other constraints.
7595 * @param body body of the loop, which may not be {@code null}.
7596 * It controls the loop parameters and result type in the standard case (see above for details).
7597 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
7598 * and may accept any number of additional types.
7599 * See above for other constraints.
7600 *
7601 * @return a method handle embodying the iteration loop functionality.
7602 * @throws NullPointerException if the {@code body} handle is {@code null}.
7603 * @throws IllegalArgumentException if any argument violates the above requirements.
7604 *
7605 * @since 9
7606 */
7607 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7608 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
7609 Class<?> returnType = body.type().returnType();
7610 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
7611 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
7612 MethodHandle startIter;
7613 MethodHandle nextVal;
7614 {
7615 MethodType iteratorType;
7616 if (iterator == null) {
7617 // derive argument type from body, if available, else use Iterable
7618 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
7619 iteratorType = startIter.type().changeParameterType(0, iterableType);
7620 } else {
7621 // force return type to the internal iterator class
7622 iteratorType = iterator.type().changeReturnType(Iterator.class);
7623 startIter = iterator;
7624 }
7625 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7626 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
7627
7628 // perform the asType transforms under an exception transformer, as per spec.:
7629 try {
7630 startIter = startIter.asType(iteratorType);
7631 nextVal = nextRaw.asType(nextValType);
7632 } catch (WrongMethodTypeException ex) {
7633 throw new IllegalArgumentException(ex);
7634 }
7635 }
7636
7637 MethodHandle retv = null, step = body;
7638 if (returnType != void.class) {
7639 // the simple thing first: in (I V A...), drop the I to get V
7640 retv = dropArguments(identity(returnType), 0, Iterator.class);
7641 // body type signature (V T A...), internal loop types (I V A...)
7642 step = swapArguments(body, 0, 1); // swap V <-> T
7643 }
7644
7645 MethodHandle[]
7646 iterVar = { startIter, null, hasNext, retv },
7647 bodyClause = { init, filterArgument(step, 0, nextVal) };
7648 return loop(iterVar, bodyClause);
7649 }
7650
7651 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7652 Objects.requireNonNull(body);
7653 MethodType bodyType = body.type();
7654 Class<?> returnType = bodyType.returnType();
7655 List<Class<?>> internalParamList = bodyType.parameterList();
7656 // strip leading V value if present
7657 int vsize = (returnType == void.class ? 0 : 1);
7658 if (vsize != 0 && (internalParamList.isEmpty() || internalParamList.get(0) != returnType)) {
7659 // argument list has no "V" => error
7660 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7661 throw misMatchedTypes("body function", bodyType, expected);
7662 } else if (internalParamList.size() <= vsize) {
7663 // missing T type => error
7664 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
7665 throw misMatchedTypes("body function", bodyType, expected);
7666 }
7667 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
7668 Class<?> iterableType = null;
7669 if (iterator != null) {
7670 // special case; if the body handle only declares V and T then
7671 // the external parameter list is obtained from iterator handle
7672 if (externalParamList.isEmpty()) {
7673 externalParamList = iterator.type().parameterList();
7674 }
7675 MethodType itype = iterator.type();
7676 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
7677 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
7678 }
7679 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
7680 MethodType expected = methodType(itype.returnType(), externalParamList);
7681 throw misMatchedTypes("iterator parameters", itype, expected);
7682 }
7683 } else {
7684 if (externalParamList.isEmpty()) {
7685 // special case; if the iterator handle is null and the body handle
7686 // only declares V and T then the external parameter list consists
7687 // of Iterable
7688 externalParamList = List.of(Iterable.class);
7689 iterableType = Iterable.class;
7690 } else {
7691 // special case; if the iterator handle is null and the external
7692 // parameter list is not empty then the first parameter must be
7693 // assignable to Iterable
7694 iterableType = externalParamList.get(0);
7695 if (!Iterable.class.isAssignableFrom(iterableType)) {
7696 throw newIllegalArgumentException(
7697 "inferred first loop argument must inherit from Iterable: " + iterableType);
7698 }
7699 }
7700 }
7701 if (init != null) {
7702 MethodType initType = init.type();
7703 if (initType.returnType() != returnType ||
7704 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
7705 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
7706 }
7707 }
7708 return iterableType; // help the caller a bit
7709 }
7710
7711 /*non-public*/
7712 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
7713 // there should be a better way to uncross my wires
7714 int arity = mh.type().parameterCount();
7715 int[] order = new int[arity];
7716 for (int k = 0; k < arity; k++) order[k] = k;
7717 order[i] = j; order[j] = i;
7718 Class<?>[] types = mh.type().parameterArray();
7719 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
7720 MethodType swapType = methodType(mh.type().returnType(), types);
7721 return permuteArguments(mh, swapType, order);
7722 }
7723
7724 /**
7725 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
7726 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
7727 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
7728 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
7729 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
7730 * {@code try-finally} handle.
7731 * <p>
7732 * The {@code cleanup} handle will be passed one or two additional leading arguments.
7733 * The first is the exception thrown during the
7734 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
7735 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
7736 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
7737 * The second argument is not present if the {@code target} handle has a {@code void} return type.
7738 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
7739 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
7740 * <p>
7741 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
7742 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
7743 * two extra leading parameters:<ul>
7744 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
7745 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
7746 * the result from the execution of the {@code target} handle.
7747 * This parameter is not present if the {@code target} returns {@code void}.
7748 * </ul>
7749 * <p>
7750 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
7751 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
7752 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
7753 * the cleanup.
7754 * {@snippet lang="java" :
7755 * V target(A..., B...);
7756 * V cleanup(Throwable, V, A...);
7757 * V adapter(A... a, B... b) {
7758 * V result = (zero value for V);
7759 * Throwable throwable = null;
7760 * try {
7761 * result = target(a..., b...);
7762 * } catch (Throwable t) {
7763 * throwable = t;
7764 * throw t;
7765 * } finally {
7766 * result = cleanup(throwable, result, a...);
7767 * }
7768 * return result;
7769 * }
7770 * }
7771 * <p>
7772 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
7773 * be modified by execution of the target, and so are passed unchanged
7774 * from the caller to the cleanup, if it is invoked.
7775 * <p>
7776 * The target and cleanup must return the same type, even if the cleanup
7777 * always throws.
7778 * To create such a throwing cleanup, compose the cleanup logic
7779 * with {@link #throwException throwException},
7780 * in order to create a method handle of the correct return type.
7781 * <p>
7782 * Note that {@code tryFinally} never converts exceptions into normal returns.
7783 * In rare cases where exceptions must be converted in that way, first wrap
7784 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
7785 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
7786 * <p>
7787 * It is recommended that the first parameter type of {@code cleanup} be
7788 * declared {@code Throwable} rather than a narrower subtype. This ensures
7789 * {@code cleanup} will always be invoked with whatever exception that
7790 * {@code target} throws. Declaring a narrower type may result in a
7791 * {@code ClassCastException} being thrown by the {@code try-finally}
7792 * handle if the type of the exception thrown by {@code target} is not
7793 * assignable to the first parameter type of {@code cleanup}. Note that
7794 * various exception types of {@code VirtualMachineError},
7795 * {@code LinkageError}, and {@code RuntimeException} can in principle be
7796 * thrown by almost any kind of Java code, and a finally clause that
7797 * catches (say) only {@code IOException} would mask any of the others
7798 * behind a {@code ClassCastException}.
7799 *
7800 * @param target the handle whose execution is to be wrapped in a {@code try} block.
7801 * @param cleanup the handle that is invoked in the finally block.
7802 *
7803 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
7804 * @throws NullPointerException if any argument is null
7805 * @throws IllegalArgumentException if {@code cleanup} does not accept
7806 * the required leading arguments, or if the method handle types do
7807 * not match in their return types and their
7808 * corresponding trailing parameters
7809 *
7810 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
7811 * @since 9
7812 */
7813 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
7814 Class<?>[] targetParamTypes = target.type().ptypes();
7815 Class<?> rtype = target.type().returnType();
7816
7817 tryFinallyChecks(target, cleanup);
7818
7819 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
7820 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7821 // target parameter list.
7822 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0, false);
7823
7824 // Ensure that the intrinsic type checks the instance thrown by the
7825 // target against the first parameter of cleanup
7826 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
7827
7828 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
7829 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
7830 }
7831
7832 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
7833 Class<?> rtype = target.type().returnType();
7834 if (rtype != cleanup.type().returnType()) {
7835 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
7836 }
7837 MethodType cleanupType = cleanup.type();
7838 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
7839 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
7840 }
7841 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
7842 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
7843 }
7844 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7845 // target parameter list.
7846 int cleanupArgIndex = rtype == void.class ? 1 : 2;
7847 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
7848 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
7849 cleanup.type(), target.type());
7850 }
7851 }
7852
7853 /**
7854 * Creates a table switch method handle, which can be used to switch over a set of target
7855 * method handles, based on a given target index, called selector.
7856 * <p>
7857 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)},
7858 * and where {@code N} is the number of target method handles, the table switch method
7859 * handle will invoke the n-th target method handle from the list of target method handles.
7860 * <p>
7861 * For a selector value that does not fall in the range {@code [0, N)}, the table switch
7862 * method handle will invoke the given fallback method handle.
7863 * <p>
7864 * All method handles passed to this method must have the same type, with the additional
7865 * requirement that the leading parameter be of type {@code int}. The leading parameter
7866 * represents the selector.
7867 * <p>
7868 * Any trailing parameters present in the type will appear on the returned table switch
7869 * method handle as well. Any arguments assigned to these parameters will be forwarded,
7870 * together with the selector value, to the selected method handle when invoking it.
7871 *
7872 * @apiNote Example:
7873 * The cases each drop the {@code selector} value they are given, and take an additional
7874 * {@code String} argument, which is concatenated (using {@link String#concat(String)})
7875 * to a specific constant label string for each case:
7876 * {@snippet lang="java" :
7877 * MethodHandles.Lookup lookup = MethodHandles.lookup();
7878 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat",
7879 * MethodType.methodType(String.class, String.class));
7880 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class);
7881 *
7882 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: ");
7883 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: ");
7884 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: ");
7885 *
7886 * MethodHandle mhSwitch = MethodHandles.tableSwitch(
7887 * caseDefault,
7888 * case0,
7889 * case1
7890 * );
7891 *
7892 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data"));
7893 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data"));
7894 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data"));
7895 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data"));
7896 * }
7897 *
7898 * @param fallback the fallback method handle that is called when the selector is not
7899 * within the range {@code [0, N)}.
7900 * @param targets array of target method handles.
7901 * @return the table switch method handle.
7902 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any
7903 * any of the elements of the {@code targets} array are
7904 * {@code null}.
7905 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading
7906 * parameter of the fallback handle or any of the target
7907 * handles is not {@code int}, or if the types of
7908 * the fallback handle and all of target handles are
7909 * not the same.
7910 *
7911 * @since 17
7912 */
7913 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) {
7914 Objects.requireNonNull(fallback);
7915 Objects.requireNonNull(targets);
7916 targets = targets.clone();
7917 MethodType type = tableSwitchChecks(fallback, targets);
7918 return MethodHandleImpl.makeTableSwitch(type, fallback, targets);
7919 }
7920
7921 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) {
7922 if (caseActions.length == 0)
7923 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions));
7924
7925 MethodType expectedType = defaultCase.type();
7926
7927 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class)
7928 throw new IllegalArgumentException(
7929 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions));
7930
7931 for (MethodHandle mh : caseActions) {
7932 Objects.requireNonNull(mh);
7933 if (mh.type() != expectedType)
7934 throw new IllegalArgumentException(
7935 "Case actions must have the same type: " + Arrays.toString(caseActions));
7936 }
7937
7938 return expectedType;
7939 }
7940
7941 /**
7942 * Adapts a target var handle by pre-processing incoming and outgoing values using a pair of filter functions.
7943 * <p>
7944 * When calling e.g. {@link VarHandle#set(Object...)} on the resulting var handle, the incoming value (of type {@code T}, where
7945 * {@code T} is the <em>last</em> parameter type of the first filter function) is processed using the first filter and then passed
7946 * to the target var handle.
7947 * Conversely, when calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the return value obtained from
7948 * the target var handle (of type {@code T}, where {@code T} is the <em>last</em> parameter type of the second filter function)
7949 * is processed using the second filter and returned to the caller. More advanced access mode types, such as
7950 * {@link VarHandle.AccessMode#COMPARE_AND_EXCHANGE} might apply both filters at the same time.
7951 * <p>
7952 * For the boxing and unboxing filters to be well-formed, their types must be of the form {@code (A... , S) -> T} and
7953 * {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle. If this is the case,
7954 * the resulting var handle will have type {@code S} and will feature the additional coordinates {@code A...} (which
7955 * will be appended to the coordinates of the target var handle).
7956 * <p>
7957 * If the boxing and unboxing filters throw any checked exceptions when invoked, the resulting var handle will
7958 * throw an {@link IllegalStateException}.
7959 * <p>
7960 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7961 * atomic access guarantees as those featured by the target var handle.
7962 *
7963 * @param target the target var handle
7964 * @param filterToTarget a filter to convert some type {@code S} into the type of {@code target}
7965 * @param filterFromTarget a filter to convert the type of {@code target} to some type {@code S}
7966 * @return an adapter var handle which accepts a new type, performing the provided boxing/unboxing conversions.
7967 * @throws IllegalArgumentException if {@code filterFromTarget} and {@code filterToTarget} are not well-formed, that is, they have types
7968 * other than {@code (A... , S) -> T} and {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle,
7969 * or if it's determined that either {@code filterFromTarget} or {@code filterToTarget} throws any checked exceptions.
7970 * @throws NullPointerException if any of the arguments is {@code null}.
7971 * @since 22
7972 */
7973 public static VarHandle filterValue(VarHandle target, MethodHandle filterToTarget, MethodHandle filterFromTarget) {
7974 return VarHandles.filterValue(target, filterToTarget, filterFromTarget);
7975 }
7976
7977 /**
7978 * Adapts a target var handle by pre-processing incoming coordinate values using unary filter functions.
7979 * <p>
7980 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the incoming coordinate values
7981 * starting at position {@code pos} (of type {@code C1, C2 ... Cn}, where {@code C1, C2 ... Cn} are the return types
7982 * of the unary filter functions) are transformed into new values (of type {@code S1, S2 ... Sn}, where {@code S1, S2 ... Sn} are the
7983 * parameter types of the unary filter functions), and then passed (along with any coordinate that was left unaltered
7984 * by the adaptation) to the target var handle.
7985 * <p>
7986 * For the coordinate filters to be well-formed, their types must be of the form {@code S1 -> T1, S2 -> T1 ... Sn -> Tn},
7987 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
7988 * <p>
7989 * If any of the filters throws a checked exception when invoked, the resulting var handle will
7990 * throw an {@link IllegalStateException}.
7991 * <p>
7992 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7993 * atomic access guarantees as those featured by the target var handle.
7994 *
7995 * @param target the target var handle
7996 * @param pos the position of the first coordinate to be transformed
7997 * @param filters the unary functions which are used to transform coordinates starting at position {@code pos}
7998 * @return an adapter var handle which accepts new coordinate types, applying the provided transformation
7999 * to the new coordinate values.
8000 * @throws IllegalArgumentException if the handles in {@code filters} are not well-formed, that is, they have types
8001 * other than {@code S1 -> T1, S2 -> T2, ... Sn -> Tn} where {@code T1, T2 ... Tn} are the coordinate types starting
8002 * at position {@code pos} of the target var handle, if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8003 * or if more filters are provided than the actual number of coordinate types available starting at {@code pos},
8004 * or if it's determined that any of the filters throws any checked exceptions.
8005 * @throws NullPointerException if any of the arguments is {@code null} or {@code filters} contains {@code null}.
8006 * @since 22
8007 */
8008 public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) {
8009 return VarHandles.filterCoordinates(target, pos, filters);
8010 }
8011
8012 /**
8013 * Provides a target var handle with one or more <em>bound coordinates</em>
8014 * in advance of the var handle's invocation. As a consequence, the resulting var handle will feature less
8015 * coordinate types than the target var handle.
8016 * <p>
8017 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, incoming coordinate values
8018 * are joined with bound coordinate values, and then passed to the target var handle.
8019 * <p>
8020 * For the bound coordinates to be well-formed, their types must be {@code T1, T2 ... Tn },
8021 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
8022 * <p>
8023 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8024 * atomic access guarantees as those featured by the target var handle.
8025 *
8026 * @param target the var handle to invoke after the bound coordinates are inserted
8027 * @param pos the position of the first coordinate to be inserted
8028 * @param values the series of bound coordinates to insert
8029 * @return an adapter var handle which inserts additional coordinates,
8030 * before calling the target var handle
8031 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8032 * or if more values are provided than the actual number of coordinate types available starting at {@code pos}.
8033 * @throws ClassCastException if the bound coordinates in {@code values} are not well-formed, that is, they have types
8034 * other than {@code T1, T2 ... Tn }, where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos}
8035 * of the target var handle.
8036 * @throws NullPointerException if any of the arguments is {@code null} or {@code values} contains {@code null}.
8037 * @since 22
8038 */
8039 public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) {
8040 return VarHandles.insertCoordinates(target, pos, values);
8041 }
8042
8043 /**
8044 * Provides a var handle which adapts the coordinate values of the target var handle, by re-arranging them
8045 * so that the new coordinates match the provided ones.
8046 * <p>
8047 * The given array controls the reordering.
8048 * Call {@code #I} the number of incoming coordinates (the value
8049 * {@code newCoordinates.size()}), and call {@code #O} the number
8050 * of outgoing coordinates (the number of coordinates associated with the target var handle).
8051 * Then the length of the reordering array must be {@code #O},
8052 * and each element must be a non-negative number less than {@code #I}.
8053 * For every {@code N} less than {@code #O}, the {@code N}-th
8054 * outgoing coordinate will be taken from the {@code I}-th incoming
8055 * coordinate, where {@code I} is {@code reorder[N]}.
8056 * <p>
8057 * No coordinate value conversions are applied.
8058 * The type of each incoming coordinate, as determined by {@code newCoordinates},
8059 * must be identical to the type of the corresponding outgoing coordinate
8060 * in the target var handle.
8061 * <p>
8062 * The reordering array need not specify an actual permutation.
8063 * An incoming coordinate will be duplicated if its index appears
8064 * more than once in the array, and an incoming coordinate will be dropped
8065 * if its index does not appear in the array.
8066 * <p>
8067 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8068 * atomic access guarantees as those featured by the target var handle.
8069 * @param target the var handle to invoke after the coordinates have been reordered
8070 * @param newCoordinates the new coordinate types
8071 * @param reorder an index array which controls the reordering
8072 * @return an adapter var handle which re-arranges the incoming coordinate values,
8073 * before calling the target var handle
8074 * @throws IllegalArgumentException if the index array length is not equal to
8075 * the number of coordinates of the target var handle, or if any index array element is not a valid index for
8076 * a coordinate of {@code newCoordinates}, or if two corresponding coordinate types in
8077 * the target var handle and in {@code newCoordinates} are not identical.
8078 * @throws NullPointerException if any of the arguments is {@code null} or {@code newCoordinates} contains {@code null}.
8079 * @since 22
8080 */
8081 public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) {
8082 return VarHandles.permuteCoordinates(target, newCoordinates, reorder);
8083 }
8084
8085 /**
8086 * Adapts a target var handle by pre-processing
8087 * a sub-sequence of its coordinate values with a filter (a method handle).
8088 * The pre-processed coordinates are replaced by the result (if any) of the
8089 * filter function and the target var handle is then called on the modified (usually shortened)
8090 * coordinate list.
8091 * <p>
8092 * If {@code R} is the return type of the filter, then:
8093 * <ul>
8094 * <li>if {@code R} <em>is not</em> {@code void}, the target var handle must have a coordinate of type {@code R} in
8095 * position {@code pos}. The parameter types of the filter will replace the coordinate type at position {@code pos}
8096 * of the target var handle. When the returned var handle is invoked, it will be as if the filter is invoked first,
8097 * and its result is passed in place of the coordinate at position {@code pos} in a downstream invocation of the
8098 * target var handle.</li>
8099 * <li> if {@code R} <em>is</em> {@code void}, the parameter types (if any) of the filter will be inserted in the
8100 * coordinate type list of the target var handle at position {@code pos}. In this case, when the returned var handle
8101 * is invoked, the filter essentially acts as a side effect, consuming some of the coordinate values, before a
8102 * downstream invocation of the target var handle.</li>
8103 * </ul>
8104 * <p>
8105 * If any of the filters throws a checked exception when invoked, the resulting var handle will
8106 * throw an {@link IllegalStateException}.
8107 * <p>
8108 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8109 * atomic access guarantees as those featured by the target var handle.
8110 *
8111 * @param target the var handle to invoke after the coordinates have been filtered
8112 * @param pos the position in the coordinate list of the target var handle where the filter is to be inserted
8113 * @param filter the filter method handle
8114 * @return an adapter var handle which filters the incoming coordinate values,
8115 * before calling the target var handle
8116 * @throws IllegalArgumentException if the return type of {@code filter}
8117 * is not void, and it is not the same as the {@code pos} coordinate of the target var handle,
8118 * if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8119 * if the resulting var handle's type would have <a href="MethodHandle.html#maxarity">too many coordinates</a>,
8120 * or if it's determined that {@code filter} throws any checked exceptions.
8121 * @throws NullPointerException if any of the arguments is {@code null}.
8122 * @since 22
8123 */
8124 public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle filter) {
8125 return VarHandles.collectCoordinates(target, pos, filter);
8126 }
8127
8128 /**
8129 * Returns a var handle which will discard some dummy coordinates before delegating to the
8130 * target var handle. As a consequence, the resulting var handle will feature more
8131 * coordinate types than the target var handle.
8132 * <p>
8133 * The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is the arity of the
8134 * target var handle's coordinate types. If {@code pos} is zero, the dummy coordinates will precede
8135 * the target's real arguments; if {@code pos} is <i>N</i> they will come after.
8136 * <p>
8137 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8138 * atomic access guarantees as those featured by the target var handle.
8139 *
8140 * @param target the var handle to invoke after the dummy coordinates are dropped
8141 * @param pos position of the first coordinate to drop (zero for the leftmost)
8142 * @param valueTypes the type(s) of the coordinate(s) to drop
8143 * @return an adapter var handle which drops some dummy coordinates,
8144 * before calling the target var handle
8145 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive.
8146 * @throws NullPointerException if any of the arguments is {@code null} or {@code valueTypes} contains {@code null}.
8147 * @since 22
8148 */
8149 public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) {
8150 return VarHandles.dropCoordinates(target, pos, valueTypes);
8151 }
8152 }