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.ClassFile;
43 import java.lang.classfile.ClassModel;
44 import java.lang.constant.ClassDesc;
45 import java.lang.constant.ConstantDescs;
46 import java.lang.invoke.LambdaForm.BasicType;
47 import java.lang.invoke.MethodHandleImpl.Intrinsic;
48 import java.lang.reflect.Constructor;
49 import java.lang.reflect.Field;
50 import java.lang.reflect.Member;
51 import java.lang.reflect.Method;
52 import java.lang.reflect.Modifier;
53 import java.nio.ByteOrder;
54 import java.security.ProtectionDomain;
55 import java.util.ArrayList;
56 import java.util.Arrays;
57 import java.util.BitSet;
58 import java.util.Comparator;
59 import java.util.Iterator;
60 import java.util.List;
61 import java.util.Objects;
62 import java.util.Set;
63 import java.util.concurrent.ConcurrentHashMap;
64 import java.util.stream.Stream;
65
66 import static java.lang.classfile.ClassFile.*;
67 import static java.lang.invoke.LambdaForm.BasicType.V_TYPE;
68 import static java.lang.invoke.MethodHandleNatives.Constants.*;
69 import static java.lang.invoke.MethodHandleStatics.UNSAFE;
70 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
71 import static java.lang.invoke.MethodHandleStatics.newInternalError;
72 import static java.lang.invoke.MethodType.methodType;
73
74 /**
75 * This class consists exclusively of static methods that operate on or return
76 * method handles. They fall into several categories:
77 * <ul>
78 * <li>Lookup methods which help create method handles for methods and fields.
79 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
80 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
81 * </ul>
82 * A lookup, combinator, or factory method will fail and throw an
83 * {@code IllegalArgumentException} if the created method handle's type
84 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
85 *
86 * @author John Rose, JSR 292 EG
87 * @since 1.7
88 */
89 public class MethodHandles {
90
91 private MethodHandles() { } // do not instantiate
92
93 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
94
95 // See IMPL_LOOKUP below.
96
97 //--- Method handle creation from ordinary methods.
98
99 /**
100 * Returns a {@link Lookup lookup object} with
101 * full capabilities to emulate all supported bytecode behaviors of the caller.
102 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller.
103 * Factory methods on the lookup object can create
104 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
105 * for any member that the caller has access to via bytecodes,
106 * including protected and private fields and methods.
107 * This lookup object is created by the original lookup class
108 * and has the {@link Lookup#ORIGINAL ORIGINAL} bit set.
109 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
110 * Do not store it in place where untrusted code can access it.
111 * <p>
112 * This method is caller sensitive, which means that it may return different
113 * values to different callers.
114 * In cases where {@code MethodHandles.lookup} is called from a context where
115 * there is no caller frame on the stack (e.g. when called directly
116 * from a JNI attached thread), {@code IllegalCallerException} is thrown.
117 * To obtain a {@link Lookup lookup object} in such a context, use an auxiliary class that will
118 * implicitly be identified as the caller, or use {@link MethodHandles#publicLookup()}
119 * to obtain a low-privileged lookup instead.
120 * @return a lookup object for the caller of this method, with
121 * {@linkplain Lookup#ORIGINAL original} and
122 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}.
123 * @throws IllegalCallerException if there is no caller frame on the stack.
124 */
125 @CallerSensitive
126 @ForceInline // to ensure Reflection.getCallerClass optimization
127 public static Lookup lookup() {
128 final Class<?> c = Reflection.getCallerClass();
129 if (c == null) {
130 throw new IllegalCallerException("no caller frame");
131 }
132 return new Lookup(c);
133 }
134
135 /**
136 * This lookup method is the alternate implementation of
137 * the lookup method with a leading caller class argument which is
138 * non-caller-sensitive. This method is only invoked by reflection
139 * and method handle.
140 */
141 @CallerSensitiveAdapter
142 private static Lookup lookup(Class<?> caller) {
143 if (caller.getClassLoader() == null) {
144 throw newInternalError("calling lookup() reflectively is not supported: "+caller);
145 }
146 return new Lookup(caller);
147 }
148
149 /**
150 * Returns a {@link Lookup lookup object} which is trusted minimally.
151 * The lookup has the {@code UNCONDITIONAL} mode.
152 * It can only be used to create method handles to public members of
153 * public classes in packages that are exported unconditionally.
154 * <p>
155 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
156 * of this lookup object will be {@link java.lang.Object}.
157 *
158 * @apiNote The use of Object is conventional, and because the lookup modes are
159 * limited, there is no special access provided to the internals of Object, its package
160 * or its module. This public lookup object or other lookup object with
161 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
162 * is not used to determine the lookup context.
163 *
164 * <p style="font-size:smaller;">
165 * <em>Discussion:</em>
166 * The lookup class can be changed to any other class {@code C} using an expression of the form
167 * {@link Lookup#in publicLookup().in(C.class)}.
168 * A public lookup object is always subject to
169 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
170 * Also, it cannot access
171 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
172 * @return a lookup object which is trusted minimally
173 */
174 public static Lookup publicLookup() {
175 return Lookup.PUBLIC_LOOKUP;
176 }
177
178 /**
179 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
180 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>.
181 * The returned lookup object can provide access to classes in modules and packages,
182 * and members of those classes, outside the normal rules of Java access control,
183 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
184 * <p>
185 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
186 * allowed to do deep reflection on module {@code M2} and package of the target class
187 * if and only if all of the following conditions are {@code true}:
188 * <ul>
189 * <li>If there is a security manager, its {@code checkPermission} method is
190 * called to check {@code ReflectPermission("suppressAccessChecks")} and
191 * that must return normally.
192 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess()
193 * full privilege access}. Specifically:
194 * <ul>
195 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
196 * (This is because otherwise there would be no way to ensure the original lookup
197 * creator was a member of any particular module, and so any subsequent checks
198 * for readability and qualified exports would become ineffective.)
199 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
200 * (This is because an application intending to share intra-module access
201 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
202 * deep reflection to its own module.)
203 * </ul>
204 * <li>The target class must be a proper class, not a primitive or array class.
205 * (Thus, {@code M2} is well-defined.)
206 * <li>If the caller module {@code M1} differs from
207 * the target module {@code M2} then both of the following must be true:
208 * <ul>
209 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
210 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
211 * containing the target class to at least {@code M1}.</li>
212 * </ul>
213 * </ul>
214 * <p>
215 * If any of the above checks is violated, this method fails with an
216 * exception.
217 * <p>
218 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
219 * returns a {@code Lookup} on {@code targetClass} with
220 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}
221 * with {@code null} previous lookup class.
222 * <p>
223 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
224 * returns a {@code Lookup} on {@code targetClass} that records
225 * the lookup class of the caller as the new previous lookup class with
226 * {@code PRIVATE} access but no {@code MODULE} access.
227 * <p>
228 * The resulting {@code Lookup} object has no {@code ORIGINAL} access.
229 *
230 * @apiNote The {@code Lookup} object returned by this method is allowed to
231 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
232 * of {@code targetClass}. Extreme caution should be taken when opening a package
233 * to another module as such defined classes have the same full privilege
234 * access as other members in {@code targetClass}'s module.
235 *
236 * @param targetClass the target class
237 * @param caller the caller lookup object
238 * @return a lookup object for the target class, with private access
239 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class
240 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
241 * @throws SecurityException if denied by the security manager
242 * @throws IllegalAccessException if any of the other access checks specified above fails
243 * @since 9
244 * @see Lookup#dropLookupMode
245 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
246 */
247 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
248 if (caller.allowedModes == Lookup.TRUSTED) {
249 return new Lookup(targetClass);
250 }
251
252 @SuppressWarnings("removal")
253 SecurityManager sm = System.getSecurityManager();
254 if (sm != null) sm.checkPermission(SecurityConstants.ACCESS_PERMISSION);
255 if (targetClass.isPrimitive())
256 throw new IllegalArgumentException(targetClass + " is a primitive class");
257 if (targetClass.isArray())
258 throw new IllegalArgumentException(targetClass + " is an array class");
259 // Ensure that we can reason accurately about private and module access.
260 int requireAccess = Lookup.PRIVATE|Lookup.MODULE;
261 if ((caller.lookupModes() & requireAccess) != requireAccess)
262 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode");
263
264 // previous lookup class is never set if it has MODULE access
265 assert caller.previousLookupClass() == null;
266
267 Class<?> callerClass = caller.lookupClass();
268 Module callerModule = callerClass.getModule(); // M1
269 Module targetModule = targetClass.getModule(); // M2
270 Class<?> newPreviousClass = null;
271 int newModes = Lookup.FULL_POWER_MODES & ~Lookup.ORIGINAL;
272
273 if (targetModule != callerModule) {
274 if (!callerModule.canRead(targetModule))
275 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
276 if (targetModule.isNamed()) {
277 String pn = targetClass.getPackageName();
278 assert !pn.isEmpty() : "unnamed package cannot be in named module";
279 if (!targetModule.isOpen(pn, callerModule))
280 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
281 }
282
283 // M2 != M1, set previous lookup class to M1 and drop MODULE access
284 newPreviousClass = callerClass;
285 newModes &= ~Lookup.MODULE;
286 }
287 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
288 }
289
290 /**
291 * Returns the <em>class data</em> associated with the lookup class
292 * of the given {@code caller} lookup object, or {@code null}.
293 *
294 * <p> A hidden class with class data can be created by calling
295 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
296 * Lookup::defineHiddenClassWithClassData}.
297 * This method will cause the static class initializer of the lookup
298 * class of the given {@code caller} lookup object be executed if
299 * it has not been initialized.
300 *
301 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
302 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
303 * {@code null} is returned if this method is called on the lookup object
304 * on these classes.
305 *
306 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
307 * must have {@linkplain Lookup#ORIGINAL original access}
308 * in order to retrieve the class data.
309 *
310 * @apiNote
311 * This method can be called as a bootstrap method for a dynamically computed
312 * constant. A framework can create a hidden class with class data, for
313 * example that can be {@code Class} or {@code MethodHandle} object.
314 * The class data is accessible only to the lookup object
315 * created by the original caller but inaccessible to other members
316 * in the same nest. If a framework passes security sensitive objects
317 * to a hidden class via class data, it is recommended to load the value
318 * of class data as a dynamically computed constant instead of storing
319 * the class data in private static field(s) which are accessible to
320 * other nestmates.
321 *
322 * @param <T> the type to cast the class data object to
323 * @param caller the lookup context describing the class performing the
324 * operation (normally stacked by the JVM)
325 * @param name must be {@link ConstantDescs#DEFAULT_NAME}
326 * ({@code "_"})
327 * @param type the type of the class data
328 * @return the value of the class data if present in the lookup class;
329 * otherwise {@code null}
330 * @throws IllegalArgumentException if name is not {@code "_"}
331 * @throws IllegalAccessException if the lookup context does not have
332 * {@linkplain Lookup#ORIGINAL original} access
333 * @throws ClassCastException if the class data cannot be converted to
334 * the given {@code type}
335 * @throws NullPointerException if {@code caller} or {@code type} argument
336 * is {@code null}
337 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
338 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
339 * @since 16
340 * @jvms 5.5 Initialization
341 */
342 public static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException {
343 Objects.requireNonNull(caller);
344 Objects.requireNonNull(type);
345 if (!ConstantDescs.DEFAULT_NAME.equals(name)) {
346 throw new IllegalArgumentException("name must be \"_\": " + name);
347 }
348
349 if ((caller.lookupModes() & Lookup.ORIGINAL) != Lookup.ORIGINAL) {
350 throw new IllegalAccessException(caller + " does not have ORIGINAL access");
351 }
352
353 Object classdata = classData(caller.lookupClass());
354 if (classdata == null) return null;
355
356 try {
357 return BootstrapMethodInvoker.widenAndCast(classdata, type);
358 } catch (RuntimeException|Error e) {
359 throw e; // let CCE and other runtime exceptions through
360 } catch (Throwable e) {
361 throw new InternalError(e);
362 }
363 }
364
365 /*
366 * Returns the class data set by the VM in the Class::classData field.
367 *
368 * This is also invoked by LambdaForms as it cannot use condy via
369 * MethodHandles::classData due to bootstrapping issue.
370 */
371 static Object classData(Class<?> c) {
372 UNSAFE.ensureClassInitialized(c);
373 return SharedSecrets.getJavaLangAccess().classData(c);
374 }
375
376 /**
377 * Returns the element at the specified index in the
378 * {@linkplain #classData(Lookup, String, Class) class data},
379 * if the class data associated with the lookup class
380 * of the given {@code caller} lookup object is a {@code List}.
381 * If the class data is not present in this lookup class, this method
382 * returns {@code null}.
383 *
384 * <p> A hidden class with class data can be created by calling
385 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
386 * Lookup::defineHiddenClassWithClassData}.
387 * This method will cause the static class initializer of the lookup
388 * class of the given {@code caller} lookup object be executed if
389 * it has not been initialized.
390 *
391 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
392 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
393 * {@code null} is returned if this method is called on the lookup object
394 * on these classes.
395 *
396 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
397 * must have {@linkplain Lookup#ORIGINAL original access}
398 * in order to retrieve the class data.
399 *
400 * @apiNote
401 * This method can be called as a bootstrap method for a dynamically computed
402 * constant. A framework can create a hidden class with class data, for
403 * example that can be {@code List.of(o1, o2, o3....)} containing more than
404 * one object and use this method to load one element at a specific index.
405 * The class data is accessible only to the lookup object
406 * created by the original caller but inaccessible to other members
407 * in the same nest. If a framework passes security sensitive objects
408 * to a hidden class via class data, it is recommended to load the value
409 * of class data as a dynamically computed constant instead of storing
410 * the class data in private static field(s) which are accessible to other
411 * nestmates.
412 *
413 * @param <T> the type to cast the result object to
414 * @param caller the lookup context describing the class performing the
415 * operation (normally stacked by the JVM)
416 * @param name must be {@link java.lang.constant.ConstantDescs#DEFAULT_NAME}
417 * ({@code "_"})
418 * @param type the type of the element at the given index in the class data
419 * @param index index of the element in the class data
420 * @return the element at the given index in the class data
421 * if the class data is present; otherwise {@code null}
422 * @throws IllegalArgumentException if name is not {@code "_"}
423 * @throws IllegalAccessException if the lookup context does not have
424 * {@linkplain Lookup#ORIGINAL original} access
425 * @throws ClassCastException if the class data cannot be converted to {@code List}
426 * or the element at the specified index cannot be converted to the given type
427 * @throws IndexOutOfBoundsException if the index is out of range
428 * @throws NullPointerException if {@code caller} or {@code type} argument is
429 * {@code null}; or if unboxing operation fails because
430 * the element at the given index is {@code null}
431 *
432 * @since 16
433 * @see #classData(Lookup, String, Class)
434 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
435 */
436 public static <T> T classDataAt(Lookup caller, String name, Class<T> type, int index)
437 throws IllegalAccessException
438 {
439 @SuppressWarnings("unchecked")
440 List<Object> classdata = (List<Object>)classData(caller, name, List.class);
441 if (classdata == null) return null;
442
443 try {
444 Object element = classdata.get(index);
445 return BootstrapMethodInvoker.widenAndCast(element, type);
446 } catch (RuntimeException|Error e) {
447 throw e; // let specified exceptions and other runtime exceptions/errors through
448 } catch (Throwable e) {
449 throw new InternalError(e);
450 }
451 }
452
453 /**
454 * Performs an unchecked "crack" of a
455 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
456 * The result is as if the user had obtained a lookup object capable enough
457 * to crack the target method handle, called
458 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
459 * on the target to obtain its symbolic reference, and then called
460 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
461 * to resolve the symbolic reference to a member.
462 * <p>
463 * If there is a security manager, its {@code checkPermission} method
464 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
465 * @param <T> the desired type of the result, either {@link Member} or a subtype
466 * @param expected a class object representing the desired result type {@code T}
467 * @param target a direct method handle to crack into symbolic reference components
468 * @return a reference to the method, constructor, or field object
469 * @throws SecurityException if the caller is not privileged to call {@code setAccessible}
470 * @throws NullPointerException if either argument is {@code null}
471 * @throws IllegalArgumentException if the target is not a direct method handle
472 * @throws ClassCastException if the member is not of the expected type
473 * @since 1.8
474 */
475 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) {
476 @SuppressWarnings("removal")
477 SecurityManager smgr = System.getSecurityManager();
478 if (smgr != null) smgr.checkPermission(SecurityConstants.ACCESS_PERMISSION);
479 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
480 return lookup.revealDirect(target).reflectAs(expected, lookup);
481 }
482
483 /**
484 * A <em>lookup object</em> is a factory for creating method handles,
485 * when the creation requires access checking.
486 * Method handles do not perform
487 * access checks when they are called, but rather when they are created.
488 * Therefore, method handle access
489 * restrictions must be enforced when a method handle is created.
490 * The caller class against which those restrictions are enforced
491 * is known as the {@linkplain #lookupClass() lookup class}.
492 * <p>
493 * A lookup class which needs to create method handles will call
494 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
495 * When the {@code Lookup} factory object is created, the identity of the lookup class is
496 * determined, and securely stored in the {@code Lookup} object.
497 * The lookup class (or its delegates) may then use factory methods
498 * on the {@code Lookup} object to create method handles for access-checked members.
499 * This includes all methods, constructors, and fields which are allowed to the lookup class,
500 * even private ones.
501 *
502 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
503 * The factory methods on a {@code Lookup} object correspond to all major
504 * use cases for methods, constructors, and fields.
505 * Each method handle created by a factory method is the functional
506 * equivalent of a particular <em>bytecode behavior</em>.
507 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of
508 * the Java Virtual Machine Specification.)
509 * Here is a summary of the correspondence between these factory methods and
510 * the behavior of the resulting method handles:
511 * <table class="striped">
512 * <caption style="display:none">lookup method behaviors</caption>
513 * <thead>
514 * <tr>
515 * <th scope="col"><a id="equiv"></a>lookup expression</th>
516 * <th scope="col">member</th>
517 * <th scope="col">bytecode behavior</th>
518 * </tr>
519 * </thead>
520 * <tbody>
521 * <tr>
522 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
523 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
524 * </tr>
525 * <tr>
526 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
527 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
528 * </tr>
529 * <tr>
530 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
531 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
532 * </tr>
533 * <tr>
534 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
535 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
536 * </tr>
537 * <tr>
538 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
539 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
540 * </tr>
541 * <tr>
542 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
543 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
544 * </tr>
545 * <tr>
546 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
547 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
548 * </tr>
549 * <tr>
550 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
551 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
552 * </tr>
553 * <tr>
554 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
555 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
556 * </tr>
557 * <tr>
558 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
559 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
560 * </tr>
561 * <tr>
562 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
563 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
564 * </tr>
565 * <tr>
566 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
567 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
568 * </tr>
569 * <tr>
570 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th>
571 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
572 * </tr>
573 * <tr>
574 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
575 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
576 * </tr>
577 * </tbody>
578 * </table>
579 *
580 * Here, the type {@code C} is the class or interface being searched for a member,
581 * documented as a parameter named {@code refc} in the lookup methods.
582 * The method type {@code MT} is composed from the return type {@code T}
583 * and the sequence of argument types {@code A*}.
584 * The constructor also has a sequence of argument types {@code A*} and
585 * is deemed to return the newly-created object of type {@code C}.
586 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
587 * The formal parameter {@code this} stands for the self-reference of type {@code C};
588 * if it is present, it is always the leading argument to the method handle invocation.
589 * (In the case of some {@code protected} members, {@code this} may be
590 * restricted in type to the lookup class; see below.)
591 * The name {@code arg} stands for all the other method handle arguments.
592 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
593 * stands for a null reference if the accessed method or field is static,
594 * and {@code this} otherwise.
595 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
596 * for reflective objects corresponding to the given members declared in type {@code C}.
597 * <p>
598 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
599 * as if by {@code ldc CONSTANT_Class}.
600 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
601 * <p>
602 * In cases where the given member is of variable arity (i.e., a method or constructor)
603 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
604 * In all other cases, the returned method handle will be of fixed arity.
605 * <p style="font-size:smaller;">
606 * <em>Discussion:</em>
607 * The equivalence between looked-up method handles and underlying
608 * class members and bytecode behaviors
609 * can break down in a few ways:
610 * <ul style="font-size:smaller;">
611 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
612 * the lookup can still succeed, even when there is no equivalent
613 * Java expression or bytecoded constant.
614 * <li>Likewise, if {@code T} or {@code MT}
615 * is not symbolically accessible from the lookup class's loader,
616 * the lookup can still succeed.
617 * For example, lookups for {@code MethodHandle.invokeExact} and
618 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
619 * <li>If there is a security manager installed, it can forbid the lookup
620 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
621 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
622 * constant is not subject to security manager checks.
623 * <li>If the looked-up method has a
624 * <a href="MethodHandle.html#maxarity">very large arity</a>,
625 * the method handle creation may fail with an
626 * {@code IllegalArgumentException}, due to the method handle type having
627 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
628 * </ul>
629 *
630 * <h2><a id="access"></a>Access checking</h2>
631 * Access checks are applied in the factory methods of {@code Lookup},
632 * when a method handle is created.
633 * This is a key difference from the Core Reflection API, since
634 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
635 * performs access checking against every caller, on every call.
636 * <p>
637 * All access checks start from a {@code Lookup} object, which
638 * compares its recorded lookup class against all requests to
639 * create method handles.
640 * A single {@code Lookup} object can be used to create any number
641 * of access-checked method handles, all checked against a single
642 * lookup class.
643 * <p>
644 * A {@code Lookup} object can be shared with other trusted code,
645 * such as a metaobject protocol.
646 * A shared {@code Lookup} object delegates the capability
647 * to create method handles on private members of the lookup class.
648 * Even if privileged code uses the {@code Lookup} object,
649 * the access checking is confined to the privileges of the
650 * original lookup class.
651 * <p>
652 * A lookup can fail, because
653 * the containing class is not accessible to the lookup class, or
654 * because the desired class member is missing, or because the
655 * desired class member is not accessible to the lookup class, or
656 * because the lookup object is not trusted enough to access the member.
657 * In the case of a field setter function on a {@code final} field,
658 * finality enforcement is treated as a kind of access control,
659 * and the lookup will fail, except in special cases of
660 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
661 * In any of these cases, a {@code ReflectiveOperationException} will be
662 * thrown from the attempted lookup. The exact class will be one of
663 * the following:
664 * <ul>
665 * <li>NoSuchMethodException — if a method is requested but does not exist
666 * <li>NoSuchFieldException — if a field is requested but does not exist
667 * <li>IllegalAccessException — if the member exists but an access check fails
668 * </ul>
669 * <p>
670 * In general, the conditions under which a method handle may be
671 * looked up for a method {@code M} are no more restrictive than the conditions
672 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
673 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
674 * a method handle lookup will generally raise a corresponding
675 * checked exception, such as {@code NoSuchMethodException}.
676 * And the effect of invoking the method handle resulting from the lookup
677 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
678 * to executing the compiled, verified, and resolved call to {@code M}.
679 * The same point is true of fields and constructors.
680 * <p style="font-size:smaller;">
681 * <em>Discussion:</em>
682 * Access checks only apply to named and reflected methods,
683 * constructors, and fields.
684 * Other method handle creation methods, such as
685 * {@link MethodHandle#asType MethodHandle.asType},
686 * do not require any access checks, and are used
687 * independently of any {@code Lookup} object.
688 * <p>
689 * If the desired member is {@code protected}, the usual JVM rules apply,
690 * including the requirement that the lookup class must either be in the
691 * same package as the desired member, or must inherit that member.
692 * (See the Java Virtual Machine Specification, sections {@jvms
693 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.)
694 * In addition, if the desired member is a non-static field or method
695 * in a different package, the resulting method handle may only be applied
696 * to objects of the lookup class or one of its subclasses.
697 * This requirement is enforced by narrowing the type of the leading
698 * {@code this} parameter from {@code C}
699 * (which will necessarily be a superclass of the lookup class)
700 * to the lookup class itself.
701 * <p>
702 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
703 * that the receiver argument must match both the resolved method <em>and</em>
704 * the current class. Again, this requirement is enforced by narrowing the
705 * type of the leading parameter to the resulting method handle.
706 * (See the Java Virtual Machine Specification, section {@jvms 4.10.1.9}.)
707 * <p>
708 * The JVM represents constructors and static initializer blocks as internal methods
709 * with special names ({@value ConstantDescs#INIT_NAME} and {@value
710 * ConstantDescs#CLASS_INIT_NAME}).
711 * The internal syntax of invocation instructions allows them to refer to such internal
712 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
713 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
714 * <p>
715 * If the relationship between nested types is expressed directly through the
716 * {@code NestHost} and {@code NestMembers} attributes
717 * (see the Java Virtual Machine Specification, sections {@jvms
718 * 4.7.28} and {@jvms 4.7.29}),
719 * then the associated {@code Lookup} object provides direct access to
720 * the lookup class and all of its nestmates
721 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
722 * Otherwise, access between nested classes is obtained by the Java compiler creating
723 * a wrapper method to access a private method of another class in the same nest.
724 * For example, a nested class {@code C.D}
725 * can access private members within other related classes such as
726 * {@code C}, {@code C.D.E}, or {@code C.B},
727 * but the Java compiler may need to generate wrapper methods in
728 * those related classes. In such cases, a {@code Lookup} object on
729 * {@code C.E} would be unable to access those private members.
730 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
731 * which can transform a lookup on {@code C.E} into one on any of those other
732 * classes, without special elevation of privilege.
733 * <p>
734 * The accesses permitted to a given lookup object may be limited,
735 * according to its set of {@link #lookupModes lookupModes},
736 * to a subset of members normally accessible to the lookup class.
737 * For example, the {@link MethodHandles#publicLookup publicLookup}
738 * method produces a lookup object which is only allowed to access
739 * public members in public classes of exported packages.
740 * The caller sensitive method {@link MethodHandles#lookup lookup}
741 * produces a lookup object with full capabilities relative to
742 * its caller class, to emulate all supported bytecode behaviors.
743 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
744 * with fewer access modes than the original lookup object.
745 *
746 * <p style="font-size:smaller;">
747 * <a id="privacc"></a>
748 * <em>Discussion of private and module access:</em>
749 * We say that a lookup has <em>private access</em>
750 * if its {@linkplain #lookupModes lookup modes}
751 * include the possibility of accessing {@code private} members
752 * (which includes the private members of nestmates).
753 * As documented in the relevant methods elsewhere,
754 * only lookups with private access possess the following capabilities:
755 * <ul style="font-size:smaller;">
756 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
757 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
758 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
759 * for classes accessible to the lookup class
760 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
761 * within the same package member
762 * </ul>
763 * <p style="font-size:smaller;">
764 * Similarly, a lookup with module access ensures that the original lookup creator was
765 * a member in the same module as the lookup class.
766 * <p style="font-size:smaller;">
767 * Private and module access are independently determined modes; a lookup may have
768 * either or both or neither. A lookup which possesses both access modes is said to
769 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}.
770 * <p style="font-size:smaller;">
771 * A lookup with <em>original access</em> ensures that this lookup is created by
772 * the original lookup class and the bootstrap method invoked by the VM.
773 * Such a lookup with original access also has private and module access
774 * which has the following additional capability:
775 * <ul style="font-size:smaller;">
776 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
777 * such as {@code Class.forName}
778 * <li>obtain the {@linkplain MethodHandles#classData(Lookup, String, Class)
779 * class data} associated with the lookup class</li>
780 * </ul>
781 * <p style="font-size:smaller;">
782 * Each of these permissions is a consequence of the fact that a lookup object
783 * with private access can be securely traced back to an originating class,
784 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
785 * can be reliably determined and emulated by method handles.
786 *
787 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
788 * When a lookup class in one module {@code M1} accesses a class in another module
789 * {@code M2}, extra access checking is performed beyond the access mode bits.
790 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
791 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
792 * and when the type is in a package of {@code M2} that is exported to
793 * at least {@code M1}.
794 * <p>
795 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
796 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
797 * MethodHandles.privateLookupIn} methods.
798 * Teleporting across modules will always record the original lookup class as
799 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
800 * and drops {@link Lookup#MODULE MODULE} access.
801 * If the target class is in the same module as the lookup class {@code C},
802 * then the target class becomes the new lookup class
803 * and there is no change to the previous lookup class.
804 * If the target class is in a different module from {@code M1} ({@code C}'s module),
805 * {@code C} becomes the new previous lookup class
806 * and the target class becomes the new lookup class.
807 * In that case, if there was already a previous lookup class in {@code M0},
808 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
809 * drops all privileges.
810 * For example,
811 * {@snippet lang="java" :
812 * Lookup lookup = MethodHandles.lookup(); // in class C
813 * Lookup lookup2 = lookup.in(D.class);
814 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
815 * }
816 * <p>
817 * The {@link #lookup()} factory method produces a {@code Lookup} object
818 * with {@code null} previous lookup class.
819 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
820 * to class {@code D} without elevation of privileges.
821 * If {@code C} and {@code D} are in the same module,
822 * {@code lookup2} records {@code D} as the new lookup class and keeps the
823 * same previous lookup class as the original {@code lookup}, or
824 * {@code null} if not present.
825 * <p>
826 * When a {@code Lookup} teleports from a class
827 * in one nest to another nest, {@code PRIVATE} access is dropped.
828 * When a {@code Lookup} teleports from a class in one package to
829 * another package, {@code PACKAGE} access is dropped.
830 * When a {@code Lookup} teleports from a class in one module to another module,
831 * {@code MODULE} access is dropped.
832 * Teleporting across modules drops the ability to access non-exported classes
833 * in both the module of the new lookup class and the module of the old lookup class
834 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
835 * A {@code Lookup} can teleport back and forth to a class in the module of
836 * the lookup class and the module of the previous class lookup.
837 * Teleporting across modules can only decrease access but cannot increase it.
838 * Teleporting to some third module drops all accesses.
839 * <p>
840 * In the above example, if {@code C} and {@code D} are in different modules,
841 * {@code lookup2} records {@code D} as its lookup class and
842 * {@code C} as its previous lookup class and {@code lookup2} has only
843 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
844 * {@code C}'s module and {@code D}'s module.
845 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
846 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
847 * class {@code D} is recorded as its previous lookup class.
848 * <p>
849 * Teleporting across modules restricts access to the public types that
850 * both the lookup class and the previous lookup class can equally access
851 * (see below).
852 * <p>
853 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
854 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
855 * and produce a new {@code Lookup} with <a href="#privacc">private access</a>
856 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
857 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
858 * to call {@code privateLookupIn}.
859 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
860 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
861 * produces a new {@code Lookup} on {@code T} with full capabilities.
862 * A {@code lookup} on {@code C} is also allowed
863 * to do deep reflection on {@code T} in another module {@code M2} if
864 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
865 * the package containing {@code T} to at least {@code M1}.
866 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
867 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
868 * The resulting {@code Lookup} can be used to do member lookup or teleport
869 * to another lookup class by calling {@link #in Lookup::in}. But
870 * it cannot be used to obtain another private {@code Lookup} by calling
871 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
872 * because it has no {@code MODULE} access.
873 * <p>
874 * The {@code Lookup} object returned by {@code privateLookupIn} is allowed to
875 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
876 * of {@code T}. Extreme caution should be taken when opening a package
877 * to another module as such defined classes have the same full privilege
878 * access as other members in {@code M2}.
879 *
880 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
881 *
882 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
883 * allows cross-module access. The access checking is performed with respect
884 * to both the lookup class and the previous lookup class if present.
885 * <p>
886 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
887 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
888 * exported unconditionally}.
889 * <p>
890 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
891 * the lookup with {@link #PUBLIC} mode can access all public types in modules
892 * that are readable to {@code M1} and the type is in a package that is exported
893 * at least to {@code M1}.
894 * <p>
895 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
896 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
897 * the intersection of all public types that are accessible to {@code M1}
898 * with all public types that are accessible to {@code M0}. {@code M0}
899 * reads {@code M1} and hence the set of accessible types includes:
900 *
901 * <ul>
902 * <li>unconditional-exported packages from {@code M1}</li>
903 * <li>unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</li>
904 * <li>
905 * unconditional-exported packages from a third module {@code M2}if both {@code M0}
906 * and {@code M1} read {@code M2}
907 * </li>
908 * <li>qualified-exported packages from {@code M1} to {@code M0}</li>
909 * <li>qualified-exported packages from {@code M0} to {@code M1} if {@code M1} reads {@code M0}</li>
910 * <li>
911 * qualified-exported packages from a third module {@code M2} to both {@code M0} and
912 * {@code M1} if both {@code M0} and {@code M1} read {@code M2}
913 * </li>
914 * </ul>
915 *
916 * <h2><a id="access-modes"></a>Access modes</h2>
917 *
918 * The table below shows the access modes of a {@code Lookup} produced by
919 * any of the following factory or transformation methods:
920 * <ul>
921 * <li>{@link #lookup() MethodHandles::lookup}</li>
922 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li>
923 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li>
924 * <li>{@link Lookup#in Lookup::in}</li>
925 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li>
926 * </ul>
927 *
928 * <table class="striped">
929 * <caption style="display:none">
930 * Access mode summary
931 * </caption>
932 * <thead>
933 * <tr>
934 * <th scope="col">Lookup object</th>
935 * <th style="text-align:center">original</th>
936 * <th style="text-align:center">protected</th>
937 * <th style="text-align:center">private</th>
938 * <th style="text-align:center">package</th>
939 * <th style="text-align:center">module</th>
940 * <th style="text-align:center">public</th>
941 * </tr>
942 * </thead>
943 * <tbody>
944 * <tr>
945 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
946 * <td style="text-align:center">ORI</td>
947 * <td style="text-align:center">PRO</td>
948 * <td style="text-align:center">PRI</td>
949 * <td style="text-align:center">PAC</td>
950 * <td style="text-align:center">MOD</td>
951 * <td style="text-align:center">1R</td>
952 * </tr>
953 * <tr>
954 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
955 * <td></td>
956 * <td></td>
957 * <td></td>
958 * <td style="text-align:center">PAC</td>
959 * <td style="text-align:center">MOD</td>
960 * <td style="text-align:center">1R</td>
961 * </tr>
962 * <tr>
963 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
964 * <td></td>
965 * <td></td>
966 * <td></td>
967 * <td></td>
968 * <td style="text-align:center">MOD</td>
969 * <td style="text-align:center">1R</td>
970 * </tr>
971 * <tr>
972 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
973 * <td></td>
974 * <td></td>
975 * <td></td>
976 * <td></td>
977 * <td></td>
978 * <td style="text-align:center">2R</td>
979 * </tr>
980 * <tr>
981 * <th scope="row" style="text-align:left">{@code CL.in(D).in(C)} hop back to module</th>
982 * <td></td>
983 * <td></td>
984 * <td></td>
985 * <td></td>
986 * <td></td>
987 * <td style="text-align:center">2R</td>
988 * </tr>
989 * <tr>
990 * <th scope="row" style="text-align:left">{@code PRI1 = privateLookupIn(C1,CL)}</th>
991 * <td></td>
992 * <td style="text-align:center">PRO</td>
993 * <td style="text-align:center">PRI</td>
994 * <td style="text-align:center">PAC</td>
995 * <td style="text-align:center">MOD</td>
996 * <td style="text-align:center">1R</td>
997 * </tr>
998 * <tr>
999 * <th scope="row" style="text-align:left">{@code PRI1a = privateLookupIn(C,PRI1)}</th>
1000 * <td></td>
1001 * <td style="text-align:center">PRO</td>
1002 * <td style="text-align:center">PRI</td>
1003 * <td style="text-align:center">PAC</td>
1004 * <td style="text-align:center">MOD</td>
1005 * <td style="text-align:center">1R</td>
1006 * </tr>
1007 * <tr>
1008 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} same package</th>
1009 * <td></td>
1010 * <td></td>
1011 * <td></td>
1012 * <td style="text-align:center">PAC</td>
1013 * <td style="text-align:center">MOD</td>
1014 * <td style="text-align:center">1R</td>
1015 * </tr>
1016 * <tr>
1017 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} different package</th>
1018 * <td></td>
1019 * <td></td>
1020 * <td></td>
1021 * <td></td>
1022 * <td style="text-align:center">MOD</td>
1023 * <td style="text-align:center">1R</td>
1024 * </tr>
1025 * <tr>
1026 * <th scope="row" style="text-align:left">{@code PRI1.in(D)} different module</th>
1027 * <td></td>
1028 * <td></td>
1029 * <td></td>
1030 * <td></td>
1031 * <td></td>
1032 * <td style="text-align:center">2R</td>
1033 * </tr>
1034 * <tr>
1035 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PROTECTED)}</th>
1036 * <td></td>
1037 * <td></td>
1038 * <td style="text-align:center">PRI</td>
1039 * <td style="text-align:center">PAC</td>
1040 * <td style="text-align:center">MOD</td>
1041 * <td style="text-align:center">1R</td>
1042 * </tr>
1043 * <tr>
1044 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PRIVATE)}</th>
1045 * <td></td>
1046 * <td></td>
1047 * <td></td>
1048 * <td style="text-align:center">PAC</td>
1049 * <td style="text-align:center">MOD</td>
1050 * <td style="text-align:center">1R</td>
1051 * </tr>
1052 * <tr>
1053 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PACKAGE)}</th>
1054 * <td></td>
1055 * <td></td>
1056 * <td></td>
1057 * <td></td>
1058 * <td style="text-align:center">MOD</td>
1059 * <td style="text-align:center">1R</td>
1060 * </tr>
1061 * <tr>
1062 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(MODULE)}</th>
1063 * <td></td>
1064 * <td></td>
1065 * <td></td>
1066 * <td></td>
1067 * <td></td>
1068 * <td style="text-align:center">1R</td>
1069 * </tr>
1070 * <tr>
1071 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PUBLIC)}</th>
1072 * <td></td>
1073 * <td></td>
1074 * <td></td>
1075 * <td></td>
1076 * <td></td>
1077 * <td style="text-align:center">none</td>
1078 * <tr>
1079 * <th scope="row" style="text-align:left">{@code PRI2 = privateLookupIn(D,CL)}</th>
1080 * <td></td>
1081 * <td style="text-align:center">PRO</td>
1082 * <td style="text-align:center">PRI</td>
1083 * <td style="text-align:center">PAC</td>
1084 * <td></td>
1085 * <td style="text-align:center">2R</td>
1086 * </tr>
1087 * <tr>
1088 * <th scope="row" style="text-align:left">{@code privateLookupIn(D,PRI1)}</th>
1089 * <td></td>
1090 * <td style="text-align:center">PRO</td>
1091 * <td style="text-align:center">PRI</td>
1092 * <td style="text-align:center">PAC</td>
1093 * <td></td>
1094 * <td style="text-align:center">2R</td>
1095 * </tr>
1096 * <tr>
1097 * <th scope="row" style="text-align:left">{@code privateLookupIn(C,PRI2)} fails</th>
1098 * <td></td>
1099 * <td></td>
1100 * <td></td>
1101 * <td></td>
1102 * <td></td>
1103 * <td style="text-align:center">IAE</td>
1104 * </tr>
1105 * <tr>
1106 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} same package</th>
1107 * <td></td>
1108 * <td></td>
1109 * <td></td>
1110 * <td style="text-align:center">PAC</td>
1111 * <td></td>
1112 * <td style="text-align:center">2R</td>
1113 * </tr>
1114 * <tr>
1115 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} different package</th>
1116 * <td></td>
1117 * <td></td>
1118 * <td></td>
1119 * <td></td>
1120 * <td></td>
1121 * <td style="text-align:center">2R</td>
1122 * </tr>
1123 * <tr>
1124 * <th scope="row" style="text-align:left">{@code PRI2.in(C1)} hop back to module</th>
1125 * <td></td>
1126 * <td></td>
1127 * <td></td>
1128 * <td></td>
1129 * <td></td>
1130 * <td style="text-align:center">2R</td>
1131 * </tr>
1132 * <tr>
1133 * <th scope="row" style="text-align:left">{@code PRI2.in(E)} hop to third module</th>
1134 * <td></td>
1135 * <td></td>
1136 * <td></td>
1137 * <td></td>
1138 * <td></td>
1139 * <td style="text-align:center">none</td>
1140 * </tr>
1141 * <tr>
1142 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PROTECTED)}</th>
1143 * <td></td>
1144 * <td></td>
1145 * <td style="text-align:center">PRI</td>
1146 * <td style="text-align:center">PAC</td>
1147 * <td></td>
1148 * <td style="text-align:center">2R</td>
1149 * </tr>
1150 * <tr>
1151 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PRIVATE)}</th>
1152 * <td></td>
1153 * <td></td>
1154 * <td></td>
1155 * <td style="text-align:center">PAC</td>
1156 * <td></td>
1157 * <td style="text-align:center">2R</td>
1158 * </tr>
1159 * <tr>
1160 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PACKAGE)}</th>
1161 * <td></td>
1162 * <td></td>
1163 * <td></td>
1164 * <td></td>
1165 * <td></td>
1166 * <td style="text-align:center">2R</td>
1167 * </tr>
1168 * <tr>
1169 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(MODULE)}</th>
1170 * <td></td>
1171 * <td></td>
1172 * <td></td>
1173 * <td></td>
1174 * <td></td>
1175 * <td style="text-align:center">2R</td>
1176 * </tr>
1177 * <tr>
1178 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PUBLIC)}</th>
1179 * <td></td>
1180 * <td></td>
1181 * <td></td>
1182 * <td></td>
1183 * <td></td>
1184 * <td style="text-align:center">none</td>
1185 * </tr>
1186 * <tr>
1187 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PROTECTED)}</th>
1188 * <td></td>
1189 * <td></td>
1190 * <td style="text-align:center">PRI</td>
1191 * <td style="text-align:center">PAC</td>
1192 * <td style="text-align:center">MOD</td>
1193 * <td style="text-align:center">1R</td>
1194 * </tr>
1195 * <tr>
1196 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PRIVATE)}</th>
1197 * <td></td>
1198 * <td></td>
1199 * <td></td>
1200 * <td style="text-align:center">PAC</td>
1201 * <td style="text-align:center">MOD</td>
1202 * <td style="text-align:center">1R</td>
1203 * </tr>
1204 * <tr>
1205 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PACKAGE)}</th>
1206 * <td></td>
1207 * <td></td>
1208 * <td></td>
1209 * <td></td>
1210 * <td style="text-align:center">MOD</td>
1211 * <td style="text-align:center">1R</td>
1212 * </tr>
1213 * <tr>
1214 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(MODULE)}</th>
1215 * <td></td>
1216 * <td></td>
1217 * <td></td>
1218 * <td></td>
1219 * <td></td>
1220 * <td style="text-align:center">1R</td>
1221 * </tr>
1222 * <tr>
1223 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PUBLIC)}</th>
1224 * <td></td>
1225 * <td></td>
1226 * <td></td>
1227 * <td></td>
1228 * <td></td>
1229 * <td style="text-align:center">none</td>
1230 * </tr>
1231 * <tr>
1232 * <th scope="row" style="text-align:left">{@code PUB = publicLookup()}</th>
1233 * <td></td>
1234 * <td></td>
1235 * <td></td>
1236 * <td></td>
1237 * <td></td>
1238 * <td style="text-align:center">U</td>
1239 * </tr>
1240 * <tr>
1241 * <th scope="row" style="text-align:left">{@code PUB.in(D)} different module</th>
1242 * <td></td>
1243 * <td></td>
1244 * <td></td>
1245 * <td></td>
1246 * <td></td>
1247 * <td style="text-align:center">U</td>
1248 * </tr>
1249 * <tr>
1250 * <th scope="row" style="text-align:left">{@code PUB.in(D).in(E)} third module</th>
1251 * <td></td>
1252 * <td></td>
1253 * <td></td>
1254 * <td></td>
1255 * <td></td>
1256 * <td style="text-align:center">U</td>
1257 * </tr>
1258 * <tr>
1259 * <th scope="row" style="text-align:left">{@code PUB.dropLookupMode(UNCONDITIONAL)}</th>
1260 * <td></td>
1261 * <td></td>
1262 * <td></td>
1263 * <td></td>
1264 * <td></td>
1265 * <td style="text-align:center">none</td>
1266 * </tr>
1267 * <tr>
1268 * <th scope="row" style="text-align:left">{@code privateLookupIn(C1,PUB)} fails</th>
1269 * <td></td>
1270 * <td></td>
1271 * <td></td>
1272 * <td></td>
1273 * <td></td>
1274 * <td style="text-align:center">IAE</td>
1275 * </tr>
1276 * <tr>
1277 * <th scope="row" style="text-align:left">{@code ANY.in(X)}, for inaccessible {@code X}</th>
1278 * <td></td>
1279 * <td></td>
1280 * <td></td>
1281 * <td></td>
1282 * <td></td>
1283 * <td style="text-align:center">none</td>
1284 * </tr>
1285 * </tbody>
1286 * </table>
1287 *
1288 * <p>
1289 * Notes:
1290 * <ul>
1291 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1292 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1293 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1294 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1295 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set,
1296 * {@code PRO} indicates {@link #PROTECTED} bit set,
1297 * {@code PRI} indicates {@link #PRIVATE} bit set,
1298 * {@code PAC} indicates {@link #PACKAGE} bit set,
1299 * {@code MOD} indicates {@link #MODULE} bit set,
1300 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1301 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1302 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1303 * <li>Public access comes in three kinds:
1304 * <ul>
1305 * <li>unconditional ({@code U}): the lookup assumes readability.
1306 * The lookup has {@code null} previous lookup class.
1307 * <li>one-module-reads ({@code 1R}): the module access checking is
1308 * performed with respect to the lookup class. The lookup has {@code null}
1309 * previous lookup class.
1310 * <li>two-module-reads ({@code 2R}): the module access checking is
1311 * performed with respect to the lookup class and the previous lookup class.
1312 * The lookup has a non-null previous lookup class which is in a
1313 * different module from the current lookup class.
1314 * </ul>
1315 * <li>Any attempt to reach a third module loses all access.</li>
1316 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1317 * all access modes are dropped.</li>
1318 * </ul>
1319 *
1320 * <h2><a id="secmgr"></a>Security manager interactions</h2>
1321 * Although bytecode instructions can only refer to classes in
1322 * a related class loader, this API can search for methods in any
1323 * class, as long as a reference to its {@code Class} object is
1324 * available. Such cross-loader references are also possible with the
1325 * Core Reflection API, and are impossible to bytecode instructions
1326 * such as {@code invokestatic} or {@code getfield}.
1327 * There is a {@linkplain java.lang.SecurityManager security manager API}
1328 * to allow applications to check such cross-loader references.
1329 * These checks apply to both the {@code MethodHandles.Lookup} API
1330 * and the Core Reflection API
1331 * (as found on {@link java.lang.Class Class}).
1332 * <p>
1333 * If a security manager is present, member and class lookups are subject to
1334 * additional checks.
1335 * From one to three calls are made to the security manager.
1336 * Any of these calls can refuse access by throwing a
1337 * {@link java.lang.SecurityException SecurityException}.
1338 * Define {@code smgr} as the security manager,
1339 * {@code lookc} as the lookup class of the current lookup object,
1340 * {@code refc} as the containing class in which the member
1341 * is being sought, and {@code defc} as the class in which the
1342 * member is actually defined.
1343 * (If a class or other type is being accessed,
1344 * the {@code refc} and {@code defc} values are the class itself.)
1345 * The value {@code lookc} is defined as <em>not present</em>
1346 * if the current lookup object does not have
1347 * {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1348 * The calls are made according to the following rules:
1349 * <ul>
1350 * <li><b>Step 1:</b>
1351 * If {@code lookc} is not present, or if its class loader is not
1352 * the same as or an ancestor of the class loader of {@code refc},
1353 * then {@link SecurityManager#checkPackageAccess
1354 * smgr.checkPackageAccess(refcPkg)} is called,
1355 * where {@code refcPkg} is the package of {@code refc}.
1356 * <li><b>Step 2a:</b>
1357 * If the retrieved member is not public and
1358 * {@code lookc} is not present, then
1359 * {@link SecurityManager#checkPermission smgr.checkPermission}
1360 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
1361 * <li><b>Step 2b:</b>
1362 * If the retrieved class has a {@code null} class loader,
1363 * and {@code lookc} is not present, then
1364 * {@link SecurityManager#checkPermission smgr.checkPermission}
1365 * with {@code RuntimePermission("getClassLoader")} is called.
1366 * <li><b>Step 3:</b>
1367 * If the retrieved member is not public,
1368 * and if {@code lookc} is not present,
1369 * and if {@code defc} and {@code refc} are different,
1370 * then {@link SecurityManager#checkPackageAccess
1371 * smgr.checkPackageAccess(defcPkg)} is called,
1372 * where {@code defcPkg} is the package of {@code defc}.
1373 * </ul>
1374 * Security checks are performed after other access checks have passed.
1375 * Therefore, the above rules presuppose a member or class that is public,
1376 * or else that is being accessed from a lookup class that has
1377 * rights to access the member or class.
1378 * <p>
1379 * If a security manager is present and the current lookup object does not have
1380 * {@linkplain #hasFullPrivilegeAccess() full privilege access}, then
1381 * {@link #defineClass(byte[]) defineClass},
1382 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass},
1383 * {@link #defineHiddenClassWithClassData(byte[], Object, boolean, ClassOption...)
1384 * defineHiddenClassWithClassData}
1385 * calls {@link SecurityManager#checkPermission smgr.checkPermission}
1386 * with {@code RuntimePermission("defineClass")}.
1387 *
1388 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1389 * A small number of Java methods have a special property called caller sensitivity.
1390 * A <em>caller-sensitive</em> method can behave differently depending on the
1391 * identity of its immediate caller.
1392 * <p>
1393 * If a method handle for a caller-sensitive method is requested,
1394 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1395 * but they take account of the lookup class in a special way.
1396 * The resulting method handle behaves as if it were called
1397 * from an instruction contained in the lookup class,
1398 * so that the caller-sensitive method detects the lookup class.
1399 * (By contrast, the invoker of the method handle is disregarded.)
1400 * Thus, in the case of caller-sensitive methods,
1401 * different lookup classes may give rise to
1402 * differently behaving method handles.
1403 * <p>
1404 * In cases where the lookup object is
1405 * {@link MethodHandles#publicLookup() publicLookup()},
1406 * or some other lookup object without the
1407 * {@linkplain #ORIGINAL original access},
1408 * the lookup class is disregarded.
1409 * In such cases, no caller-sensitive method handle can be created,
1410 * access is forbidden, and the lookup fails with an
1411 * {@code IllegalAccessException}.
1412 * <p style="font-size:smaller;">
1413 * <em>Discussion:</em>
1414 * For example, the caller-sensitive method
1415 * {@link java.lang.Class#forName(String) Class.forName(x)}
1416 * can return varying classes or throw varying exceptions,
1417 * depending on the class loader of the class that calls it.
1418 * A public lookup of {@code Class.forName} will fail, because
1419 * there is no reasonable way to determine its bytecode behavior.
1420 * <p style="font-size:smaller;">
1421 * If an application caches method handles for broad sharing,
1422 * it should use {@code publicLookup()} to create them.
1423 * If there is a lookup of {@code Class.forName}, it will fail,
1424 * and the application must take appropriate action in that case.
1425 * It may be that a later lookup, perhaps during the invocation of a
1426 * bootstrap method, can incorporate the specific identity
1427 * of the caller, making the method accessible.
1428 * <p style="font-size:smaller;">
1429 * The function {@code MethodHandles.lookup} is caller sensitive
1430 * so that there can be a secure foundation for lookups.
1431 * Nearly all other methods in the JSR 292 API rely on lookup
1432 * objects to check access requests.
1433 */
1434 public static final
1435 class Lookup {
1436 /** The class on behalf of whom the lookup is being performed. */
1437 private final Class<?> lookupClass;
1438
1439 /** previous lookup class */
1440 private final Class<?> prevLookupClass;
1441
1442 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1443 private final int allowedModes;
1444
1445 static {
1446 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1447 }
1448
1449 /** A single-bit mask representing {@code public} access,
1450 * which may contribute to the result of {@link #lookupModes lookupModes}.
1451 * The value, {@code 0x01}, happens to be the same as the value of the
1452 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1453 * <p>
1454 * A {@code Lookup} with this lookup mode performs cross-module access check
1455 * with respect to the {@linkplain #lookupClass() lookup class} and
1456 * {@linkplain #previousLookupClass() previous lookup class} if present.
1457 */
1458 public static final int PUBLIC = Modifier.PUBLIC;
1459
1460 /** A single-bit mask representing {@code private} access,
1461 * which may contribute to the result of {@link #lookupModes lookupModes}.
1462 * The value, {@code 0x02}, happens to be the same as the value of the
1463 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1464 */
1465 public static final int PRIVATE = Modifier.PRIVATE;
1466
1467 /** A single-bit mask representing {@code protected} access,
1468 * which may contribute to the result of {@link #lookupModes lookupModes}.
1469 * The value, {@code 0x04}, happens to be the same as the value of the
1470 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1471 */
1472 public static final int PROTECTED = Modifier.PROTECTED;
1473
1474 /** A single-bit mask representing {@code package} access (default access),
1475 * which may contribute to the result of {@link #lookupModes lookupModes}.
1476 * The value is {@code 0x08}, which does not correspond meaningfully to
1477 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1478 */
1479 public static final int PACKAGE = Modifier.STATIC;
1480
1481 /** A single-bit mask representing {@code module} access,
1482 * which may contribute to the result of {@link #lookupModes lookupModes}.
1483 * The value is {@code 0x10}, which does not correspond meaningfully to
1484 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1485 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1486 * with this lookup mode can access all public types in the module of the
1487 * lookup class and public types in packages exported by other modules
1488 * to the module of the lookup class.
1489 * <p>
1490 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1491 * previous lookup class} is always {@code null}.
1492 *
1493 * @since 9
1494 */
1495 public static final int MODULE = PACKAGE << 1;
1496
1497 /** A single-bit mask representing {@code unconditional} access
1498 * which may contribute to the result of {@link #lookupModes lookupModes}.
1499 * The value is {@code 0x20}, which does not correspond meaningfully to
1500 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1501 * A {@code Lookup} with this lookup mode assumes {@linkplain
1502 * java.lang.Module#canRead(java.lang.Module) readability}.
1503 * This lookup mode can access all public members of public types
1504 * of all modules when the type is in a package that is {@link
1505 * java.lang.Module#isExported(String) exported unconditionally}.
1506 *
1507 * <p>
1508 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1509 * previous lookup class} is always {@code null}.
1510 *
1511 * @since 9
1512 * @see #publicLookup()
1513 */
1514 public static final int UNCONDITIONAL = PACKAGE << 2;
1515
1516 /** A single-bit mask representing {@code original} access
1517 * which may contribute to the result of {@link #lookupModes lookupModes}.
1518 * The value is {@code 0x40}, which does not correspond meaningfully to
1519 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1520 *
1521 * <p>
1522 * If this lookup mode is set, the {@code Lookup} object must be
1523 * created by the original lookup class by calling
1524 * {@link MethodHandles#lookup()} method or by a bootstrap method
1525 * invoked by the VM. The {@code Lookup} object with this lookup
1526 * mode has {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1527 *
1528 * @since 16
1529 */
1530 public static final int ORIGINAL = PACKAGE << 3;
1531
1532 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL);
1533 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); // with original access
1534 private static final int TRUSTED = -1;
1535
1536 /*
1537 * Adjust PUBLIC => PUBLIC|MODULE|ORIGINAL|UNCONDITIONAL
1538 * Adjust 0 => PACKAGE
1539 */
1540 private static int fixmods(int mods) {
1541 mods &= (ALL_MODES - PACKAGE - MODULE - ORIGINAL - UNCONDITIONAL);
1542 if (Modifier.isPublic(mods))
1543 mods |= UNCONDITIONAL;
1544 return (mods != 0) ? mods : PACKAGE;
1545 }
1546
1547 /** Tells which class is performing the lookup. It is this class against
1548 * which checks are performed for visibility and access permissions.
1549 * <p>
1550 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1551 * access checks are performed against both the lookup class and the previous lookup class.
1552 * <p>
1553 * The class implies a maximum level of access permission,
1554 * but the permissions may be additionally limited by the bitmask
1555 * {@link #lookupModes lookupModes}, which controls whether non-public members
1556 * can be accessed.
1557 * @return the lookup class, on behalf of which this lookup object finds members
1558 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1559 */
1560 public Class<?> lookupClass() {
1561 return lookupClass;
1562 }
1563
1564 /** Reports a lookup class in another module that this lookup object
1565 * was previously teleported from, or {@code null}.
1566 * <p>
1567 * A {@code Lookup} object produced by the factory methods, such as the
1568 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1569 * has {@code null} previous lookup class.
1570 * A {@code Lookup} object has a non-null previous lookup class
1571 * when this lookup was teleported from an old lookup class
1572 * in one module to a new lookup class in another module.
1573 *
1574 * @return the lookup class in another module that this lookup object was
1575 * previously teleported from, or {@code null}
1576 * @since 14
1577 * @see #in(Class)
1578 * @see MethodHandles#privateLookupIn(Class, Lookup)
1579 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1580 */
1581 public Class<?> previousLookupClass() {
1582 return prevLookupClass;
1583 }
1584
1585 // This is just for calling out to MethodHandleImpl.
1586 private Class<?> lookupClassOrNull() {
1587 return (allowedModes == TRUSTED) ? null : lookupClass;
1588 }
1589
1590 /** Tells which access-protection classes of members this lookup object can produce.
1591 * The result is a bit-mask of the bits
1592 * {@linkplain #PUBLIC PUBLIC (0x01)},
1593 * {@linkplain #PRIVATE PRIVATE (0x02)},
1594 * {@linkplain #PROTECTED PROTECTED (0x04)},
1595 * {@linkplain #PACKAGE PACKAGE (0x08)},
1596 * {@linkplain #MODULE MODULE (0x10)},
1597 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)},
1598 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}.
1599 * <p>
1600 * A freshly-created lookup object
1601 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1602 * all possible bits set, except {@code UNCONDITIONAL}.
1603 * A lookup object on a new lookup class
1604 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1605 * may have some mode bits set to zero.
1606 * Mode bits can also be
1607 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1608 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1609 * The purpose of this is to restrict access via the new lookup object,
1610 * so that it can access only names which can be reached by the original
1611 * lookup object, and also by the new lookup class.
1612 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1613 * @see #in
1614 * @see #dropLookupMode
1615 */
1616 public int lookupModes() {
1617 return allowedModes & ALL_MODES;
1618 }
1619
1620 /** Embody the current class (the lookupClass) as a lookup class
1621 * for method handle creation.
1622 * Must be called by from a method in this package,
1623 * which in turn is called by a method not in this package.
1624 */
1625 Lookup(Class<?> lookupClass) {
1626 this(lookupClass, null, FULL_POWER_MODES);
1627 }
1628
1629 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1630 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1631 && prevLookupClass.getModule() != lookupClass.getModule());
1632 assert !lookupClass.isArray() && !lookupClass.isPrimitive();
1633 this.lookupClass = lookupClass;
1634 this.prevLookupClass = prevLookupClass;
1635 this.allowedModes = allowedModes;
1636 }
1637
1638 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1639 // make sure we haven't accidentally picked up a privileged class:
1640 checkUnprivilegedlookupClass(lookupClass);
1641 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1642 }
1643
1644 /**
1645 * Creates a lookup on the specified new lookup class.
1646 * The resulting object will report the specified
1647 * class as its own {@link #lookupClass() lookupClass}.
1648 *
1649 * <p>
1650 * However, the resulting {@code Lookup} object is guaranteed
1651 * to have no more access capabilities than the original.
1652 * In particular, access capabilities can be lost as follows:<ul>
1653 * <li>If the new lookup class is different from the old lookup class,
1654 * i.e. {@link #ORIGINAL ORIGINAL} access is lost.
1655 * <li>If the new lookup class is in a different module from the old one,
1656 * i.e. {@link #MODULE MODULE} access is lost.
1657 * <li>If the new lookup class is in a different package
1658 * than the old one, protected and default (package) members will not be accessible,
1659 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1660 * <li>If the new lookup class is not within the same package member
1661 * as the old one, private members will not be accessible, and protected members
1662 * will not be accessible by virtue of inheritance,
1663 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1664 * (Protected members may continue to be accessible because of package sharing.)
1665 * <li>If the new lookup class is not
1666 * {@linkplain #accessClass(Class) accessible} to this lookup,
1667 * then no members, not even public members, will be accessible
1668 * i.e. all access modes are lost.
1669 * <li>If the new lookup class, the old lookup class and the previous lookup class
1670 * are all in different modules i.e. teleporting to a third module,
1671 * all access modes are lost.
1672 * </ul>
1673 * <p>
1674 * The new previous lookup class is chosen as follows:
1675 * <ul>
1676 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1677 * the new previous lookup class is {@code null}.
1678 * <li>If the new lookup class is in the same module as the old lookup class,
1679 * the new previous lookup class is the old previous lookup class.
1680 * <li>If the new lookup class is in a different module from the old lookup class,
1681 * the new previous lookup class is the old lookup class.
1682 *</ul>
1683 * <p>
1684 * The resulting lookup's capabilities for loading classes
1685 * (used during {@link #findClass} invocations)
1686 * are determined by the lookup class' loader,
1687 * which may change due to this operation.
1688 *
1689 * @param requestedLookupClass the desired lookup class for the new lookup object
1690 * @return a lookup object which reports the desired lookup class, or the same object
1691 * if there is no change
1692 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class
1693 * @throws NullPointerException if the argument is null
1694 *
1695 * @see #accessClass(Class)
1696 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1697 */
1698 public Lookup in(Class<?> requestedLookupClass) {
1699 Objects.requireNonNull(requestedLookupClass);
1700 if (requestedLookupClass.isPrimitive())
1701 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1702 if (requestedLookupClass.isArray())
1703 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1704
1705 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1706 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1707 if (requestedLookupClass == this.lookupClass)
1708 return this; // keep same capabilities
1709 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL;
1710 Module fromModule = this.lookupClass.getModule();
1711 Module targetModule = requestedLookupClass.getModule();
1712 Class<?> plc = this.previousLookupClass();
1713 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1714 assert plc == null;
1715 newModes = UNCONDITIONAL;
1716 } else if (fromModule != targetModule) {
1717 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1718 // allow hopping back and forth between fromModule and plc's module
1719 // but not the third module
1720 newModes = 0;
1721 }
1722 // drop MODULE access
1723 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1724 // teleport from this lookup class
1725 plc = this.lookupClass;
1726 }
1727 if ((newModes & PACKAGE) != 0
1728 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1729 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1730 }
1731 // Allow nestmate lookups to be created without special privilege:
1732 if ((newModes & PRIVATE) != 0
1733 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1734 newModes &= ~(PRIVATE|PROTECTED);
1735 }
1736 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1737 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1738 // The requested class it not accessible from the lookup class.
1739 // No permissions.
1740 newModes = 0;
1741 }
1742 return newLookup(requestedLookupClass, plc, newModes);
1743 }
1744
1745 /**
1746 * Creates a lookup on the same lookup class which this lookup object
1747 * finds members, but with a lookup mode that has lost the given lookup mode.
1748 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1749 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED},
1750 * {@link #PRIVATE PRIVATE}, {@link #ORIGINAL ORIGINAL}, or
1751 * {@link #UNCONDITIONAL UNCONDITIONAL}.
1752 *
1753 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup},
1754 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set.
1755 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting
1756 * lookup has no access.
1757 *
1758 * <p> If this lookup is not a public lookup, then the following applies
1759 * regardless of its {@linkplain #lookupModes() lookup modes}.
1760 * {@link #PROTECTED PROTECTED} and {@link #ORIGINAL ORIGINAL} are always
1761 * dropped and so the resulting lookup mode will never have these access
1762 * capabilities. When dropping {@code PACKAGE}
1763 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE}
1764 * access. When dropping {@code MODULE} then the resulting lookup will not
1765 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access.
1766 * When dropping {@code PUBLIC} then the resulting lookup has no access.
1767 *
1768 * @apiNote
1769 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1770 * delegate non-public access within the package of the lookup class without
1771 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1772 * A lookup with {@code MODULE} but not
1773 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1774 * the module of the lookup class without conferring package access.
1775 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1776 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1777 * to public classes accessible to both the module of the lookup class
1778 * and the module of the previous lookup class.
1779 *
1780 * @param modeToDrop the lookup mode to drop
1781 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1782 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1783 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE}, {@code ORIGINAL}
1784 * or {@code UNCONDITIONAL}
1785 * @see MethodHandles#privateLookupIn
1786 * @since 9
1787 */
1788 public Lookup dropLookupMode(int modeToDrop) {
1789 int oldModes = lookupModes();
1790 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL);
1791 switch (modeToDrop) {
1792 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1793 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1794 case PACKAGE: newModes &= ~(PRIVATE); break;
1795 case PROTECTED:
1796 case PRIVATE:
1797 case ORIGINAL:
1798 case UNCONDITIONAL: break;
1799 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1800 }
1801 if (newModes == oldModes) return this; // return self if no change
1802 return newLookup(lookupClass(), previousLookupClass(), newModes);
1803 }
1804
1805 /**
1806 * Creates and links a class or interface from {@code bytes}
1807 * with the same class loader and in the same runtime package and
1808 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1809 * {@linkplain #lookupClass() lookup class} as if calling
1810 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1811 * ClassLoader::defineClass}.
1812 *
1813 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1814 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1815 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1816 * that the lookup object was created by a caller in the runtime package (or derived
1817 * from a lookup originally created by suitably privileged code to a target class in
1818 * the runtime package). </p>
1819 *
1820 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1821 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1822 * same package as the lookup class. </p>
1823 *
1824 * <p> This method does not run the class initializer. The class initializer may
1825 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1826 * Specification</em>. </p>
1827 *
1828 * <p> If there is a security manager and this lookup does not have {@linkplain
1829 * #hasFullPrivilegeAccess() full privilege access}, its {@code checkPermission} method
1830 * is first called to check {@code RuntimePermission("defineClass")}. </p>
1831 *
1832 * @param bytes the class bytes
1833 * @return the {@code Class} object for the class
1834 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1835 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1836 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
1837 * than the lookup class or {@code bytes} is not a class or interface
1838 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
1839 * @throws VerifyError if the newly created class cannot be verified
1840 * @throws LinkageError if the newly created class cannot be linked for any other reason
1841 * @throws SecurityException if a security manager is present and it
1842 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1843 * @throws NullPointerException if {@code bytes} is {@code null}
1844 * @since 9
1845 * @see MethodHandles#privateLookupIn
1846 * @see Lookup#dropLookupMode
1847 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1848 */
1849 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1850 ensureDefineClassPermission();
1851 if ((lookupModes() & PACKAGE) == 0)
1852 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1853 return makeClassDefiner(bytes.clone()).defineClass(false);
1854 }
1855
1856 private void ensureDefineClassPermission() {
1857 if (allowedModes == TRUSTED) return;
1858
1859 if (!hasFullPrivilegeAccess()) {
1860 @SuppressWarnings("removal")
1861 SecurityManager sm = System.getSecurityManager();
1862 if (sm != null)
1863 sm.checkPermission(new RuntimePermission("defineClass"));
1864 }
1865 }
1866
1867 /**
1868 * The set of class options that specify whether a hidden class created by
1869 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
1870 * Lookup::defineHiddenClass} method is dynamically added as a new member
1871 * to the nest of a lookup class and/or whether a hidden class has
1872 * a strong relationship with the class loader marked as its defining loader.
1873 *
1874 * @since 15
1875 */
1876 public enum ClassOption {
1877 /**
1878 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest}
1879 * of a lookup class as a nestmate.
1880 *
1881 * <p> A hidden nestmate class has access to the private members of all
1882 * classes and interfaces in the same nest.
1883 *
1884 * @see Class#getNestHost()
1885 */
1886 NESTMATE(NESTMATE_CLASS),
1887
1888 /**
1889 * Specifies that a hidden class has a <em>strong</em>
1890 * relationship with the class loader marked as its defining loader,
1891 * as a normal class or interface has with its own defining loader.
1892 * This means that the hidden class may be unloaded if and only if
1893 * its defining loader is not reachable and thus may be reclaimed
1894 * by a garbage collector (JLS {@jls 12.7}).
1895 *
1896 * <p> By default, a hidden class or interface may be unloaded
1897 * even if the class loader that is marked as its defining loader is
1898 * <a href="../ref/package-summary.html#reachability">reachable</a>.
1899
1900 *
1901 * @jls 12.7 Unloading of Classes and Interfaces
1902 */
1903 STRONG(STRONG_LOADER_LINK);
1904
1905 /* the flag value is used by VM at define class time */
1906 private final int flag;
1907 ClassOption(int flag) {
1908 this.flag = flag;
1909 }
1910
1911 static int optionsToFlag(ClassOption[] options) {
1912 int flags = 0;
1913 for (ClassOption cp : options) {
1914 if ((flags & cp.flag) != 0) {
1915 throw new IllegalArgumentException("Duplicate ClassOption " + cp);
1916 }
1917 flags |= cp.flag;
1918 }
1919 return flags;
1920 }
1921 }
1922
1923 /**
1924 * Creates a <em>hidden</em> class or interface from {@code bytes},
1925 * returning a {@code Lookup} on the newly created class or interface.
1926 *
1927 * <p> Ordinarily, a class or interface {@code C} is created by a class loader,
1928 * which either defines {@code C} directly or delegates to another class loader.
1929 * A class loader defines {@code C} directly by invoking
1930 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1931 * ClassLoader::defineClass}, which causes the Java Virtual Machine
1932 * to derive {@code C} from a purported representation in {@code class} file format.
1933 * In situations where use of a class loader is undesirable, a class or interface
1934 * {@code C} can be created by this method instead. This method is capable of
1935 * defining {@code C}, and thereby creating it, without invoking
1936 * {@code ClassLoader::defineClass}.
1937 * Instead, this method defines {@code C} as if by arranging for
1938 * the Java Virtual Machine to derive a nonarray class or interface {@code C}
1939 * from a purported representation in {@code class} file format
1940 * using the following rules:
1941 *
1942 * <ol>
1943 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup}
1944 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access.
1945 * This level of access is needed to create {@code C} in the module
1946 * of the lookup class of this {@code Lookup}.</li>
1947 *
1948 * <li> The purported representation in {@code bytes} must be a {@code ClassFile}
1949 * structure (JVMS {@jvms 4.1}) of a supported major and minor version.
1950 * The major and minor version may differ from the {@code class} file version
1951 * of the lookup class of this {@code Lookup}.</li>
1952 *
1953 * <li> The value of {@code this_class} must be a valid index in the
1954 * {@code constant_pool} table, and the entry at that index must be a valid
1955 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name
1956 * encoded in internal form that is specified by this structure. {@code N} must
1957 * denote a class or interface in the same package as the lookup class.</li>
1958 *
1959 * <li> Let {@code CN} be the string {@code N + "." + <suffix>},
1960 * where {@code <suffix>} is an unqualified name.
1961 *
1962 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by
1963 * {@code bytes} with an additional entry in the {@code constant_pool} table,
1964 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and
1965 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class}
1966 * refers to the new {@code CONSTANT_Utf8_info} structure.
1967 *
1968 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}.
1969 *
1970 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and
1971 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5},
1972 * with the following adjustments:
1973 * <ul>
1974 * <li> The constant indicated by {@code this_class} is permitted to specify a name
1975 * that includes a single {@code "."} character, even though this is not a valid
1976 * binary class or interface name in internal form.</li>
1977 *
1978 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C},
1979 * but no class loader is recorded as an initiating class loader of {@code C}.</li>
1980 *
1981 * <li> {@code C} is considered to have the same runtime
1982 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module}
1983 * and {@linkplain java.security.ProtectionDomain protection domain}
1984 * as the lookup class of this {@code Lookup}.
1985 * <li> Let {@code GN} be the binary name obtained by taking {@code N}
1986 * (a binary name encoded in internal form) and replacing ASCII forward slashes with
1987 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}:
1988 * <ul>
1989 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>},
1990 * even though this is not a valid binary class or interface name.</li>
1991 * <li> {@link Class#descriptorString()} returns the string
1992 * {@code "L" + N + "." + <suffix> + ";"},
1993 * even though this is not a valid type descriptor name.</li>
1994 * <li> {@link Class#describeConstable()} returns an empty optional as {@code C}
1995 * cannot be described in {@linkplain java.lang.constant.ClassDesc nominal form}.</li>
1996 * </ul>
1997 * </ul>
1998 * </li>
1999 * </ol>
2000 *
2001 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine.
2002 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments:
2003 * <ul>
2004 * <li> During verification, whenever it is necessary to load the class named
2005 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is
2006 * made of any class loader.</li>
2007 *
2008 * <li> On any attempt to resolve the entry in the run-time constant pool indicated
2009 * by {@code this_class}, the symbolic reference is considered to be resolved to
2010 * {@code C} and resolution always succeeds immediately.</li>
2011 * </ul>
2012 *
2013 * <p> If the {@code initialize} parameter is {@code true},
2014 * then {@code C} is initialized by the Java Virtual Machine.
2015 *
2016 * <p> The newly created class or interface {@code C} serves as the
2017 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object
2018 * returned by this method. {@code C} is <em>hidden</em> in the sense that
2019 * no other class or interface can refer to {@code C} via a constant pool entry.
2020 * That is, a hidden class or interface cannot be named as a supertype, a field type,
2021 * a method parameter type, or a method return type by any other class.
2022 * This is because a hidden class or interface does not have a binary name, so
2023 * there is no internal form available to record in any class's constant pool.
2024 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)},
2025 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and
2026 * is not {@linkplain java.instrument/java.lang.instrument.Instrumentation#isModifiableClass(Class)
2027 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html">
2028 * JVM Tool Interface</a>.
2029 *
2030 * <p> A class or interface created by
2031 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
2032 * a class loader} has a strong relationship with that class loader.
2033 * That is, every {@code Class} object contains a reference to the {@code ClassLoader}
2034 * that {@linkplain Class#getClassLoader() defined it}.
2035 * This means that a class created by a class loader may be unloaded if and
2036 * only if its defining loader is not reachable and thus may be reclaimed
2037 * by a garbage collector (JLS {@jls 12.7}).
2038 *
2039 * By default, however, a hidden class or interface may be unloaded even if
2040 * the class loader that is marked as its defining loader is
2041 * <a href="../ref/package-summary.html#reachability">reachable</a>.
2042 * This behavior is useful when a hidden class or interface serves multiple
2043 * classes defined by arbitrary class loaders. In other cases, a hidden
2044 * class or interface may be linked to a single class (or a small number of classes)
2045 * with the same defining loader as the hidden class or interface.
2046 * In such cases, where the hidden class or interface must be coterminous
2047 * with a normal class or interface, the {@link ClassOption#STRONG STRONG}
2048 * option may be passed in {@code options}.
2049 * This arranges for a hidden class to have the same strong relationship
2050 * with the class loader marked as its defining loader,
2051 * as a normal class or interface has with its own defining loader.
2052 *
2053 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass}
2054 * may still prevent a hidden class or interface from being
2055 * unloaded by ensuring that the {@code Class} object is reachable.
2056 *
2057 * <p> The unloading characteristics are set for each hidden class when it is
2058 * defined, and cannot be changed later. An advantage of allowing hidden classes
2059 * to be unloaded independently of the class loader marked as their defining loader
2060 * is that a very large number of hidden classes may be created by an application.
2061 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory,
2062 * just as if normal classes were created by class loaders.
2063 *
2064 * <p> Classes and interfaces in a nest are allowed to have mutual access to
2065 * their private members. The nest relationship is determined by
2066 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and
2067 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file.
2068 * By default, a hidden class belongs to a nest consisting only of itself
2069 * because a hidden class has no binary name.
2070 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options}
2071 * to create a hidden class or interface {@code C} as a member of a nest.
2072 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute
2073 * in the {@code ClassFile} structure from which {@code C} was derived.
2074 * Instead, the following rules determine the nest host of {@code C}:
2075 * <ul>
2076 * <li>If the nest host of the lookup class of this {@code Lookup} has previously
2077 * been determined, then let {@code H} be the nest host of the lookup class.
2078 * Otherwise, the nest host of the lookup class is determined using the
2079 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li>
2080 * <li>The nest host of {@code C} is determined to be {@code H},
2081 * the nest host of the lookup class.</li>
2082 * </ul>
2083 *
2084 * <p> A hidden class or interface may be serializable, but this requires a custom
2085 * serialization mechanism in order to ensure that instances are properly serialized
2086 * and deserialized. The default serialization mechanism supports only classes and
2087 * interfaces that are discoverable by their class name.
2088 *
2089 * @param bytes the bytes that make up the class data,
2090 * in the format of a valid {@code class} file as defined by
2091 * <cite>The Java Virtual Machine Specification</cite>.
2092 * @param initialize if {@code true} the class will be initialized.
2093 * @param options {@linkplain ClassOption class options}
2094 * @return the {@code Lookup} object on the hidden class,
2095 * with {@linkplain #ORIGINAL original} and
2096 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2097 *
2098 * @throws IllegalAccessException if this {@code Lookup} does not have
2099 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2100 * @throws SecurityException if a security manager is present and it
2101 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2102 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2103 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2104 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2105 * than the lookup class or {@code bytes} is not a class or interface
2106 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2107 * @throws IncompatibleClassChangeError if the class or interface named as
2108 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2109 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2110 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2111 * {@code C} is {@code C} itself
2112 * @throws VerifyError if the newly created class cannot be verified
2113 * @throws LinkageError if the newly created class cannot be linked for any other reason
2114 * @throws NullPointerException if any parameter is {@code null}
2115 *
2116 * @since 15
2117 * @see Class#isHidden()
2118 * @jvms 4.2.1 Binary Class and Interface Names
2119 * @jvms 4.2.2 Unqualified Names
2120 * @jvms 4.7.28 The {@code NestHost} Attribute
2121 * @jvms 4.7.29 The {@code NestMembers} Attribute
2122 * @jvms 5.4.3.1 Class and Interface Resolution
2123 * @jvms 5.4.4 Access Control
2124 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2125 * @jvms 5.4 Linking
2126 * @jvms 5.5 Initialization
2127 * @jls 12.7 Unloading of Classes and Interfaces
2128 */
2129 @SuppressWarnings("doclint:reference") // cross-module links
2130 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options)
2131 throws IllegalAccessException
2132 {
2133 Objects.requireNonNull(bytes);
2134 int flags = ClassOption.optionsToFlag(options);
2135 ensureDefineClassPermission();
2136 if (!hasFullPrivilegeAccess()) {
2137 throw new IllegalAccessException(this + " does not have full privilege access");
2138 }
2139
2140 return makeHiddenClassDefiner(bytes.clone(), false, flags).defineClassAsLookup(initialize);
2141 }
2142
2143 /**
2144 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated
2145 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data},
2146 * returning a {@code Lookup} on the newly created class or interface.
2147 *
2148 * <p> This method is equivalent to calling
2149 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)}
2150 * as if the hidden class is injected with a private static final <i>unnamed</i>
2151 * field which is initialized with the given {@code classData} at
2152 * the first instruction of the class initializer.
2153 * The newly created class is linked by the Java Virtual Machine.
2154 *
2155 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData}
2156 * and {@link MethodHandles#classDataAt(Lookup, String, Class, int) MethodHandles::classDataAt}
2157 * methods can be used to retrieve the {@code classData}.
2158 *
2159 * @apiNote
2160 * A framework can create a hidden class with class data with one or more
2161 * objects and load the class data as dynamically-computed constant(s)
2162 * via a bootstrap method. {@link MethodHandles#classData(Lookup, String, Class)
2163 * Class data} is accessible only to the lookup object created by the newly
2164 * defined hidden class but inaccessible to other members in the same nest
2165 * (unlike private static fields that are accessible to nestmates).
2166 * Care should be taken w.r.t. mutability for example when passing
2167 * an array or other mutable structure through the class data.
2168 * Changing any value stored in the class data at runtime may lead to
2169 * unpredictable behavior.
2170 * If the class data is a {@code List}, it is good practice to make it
2171 * unmodifiable for example via {@link List#of List::of}.
2172 *
2173 * @param bytes the class bytes
2174 * @param classData pre-initialized class data
2175 * @param initialize if {@code true} the class will be initialized.
2176 * @param options {@linkplain ClassOption class options}
2177 * @return the {@code Lookup} object on the hidden class,
2178 * with {@linkplain #ORIGINAL original} and
2179 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2180 *
2181 * @throws IllegalAccessException if this {@code Lookup} does not have
2182 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2183 * @throws SecurityException if a security manager is present and it
2184 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2185 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2186 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2187 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2188 * than the lookup class or {@code bytes} is not a class or interface
2189 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2190 * @throws IncompatibleClassChangeError if the class or interface named as
2191 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2192 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2193 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2194 * {@code C} is {@code C} itself
2195 * @throws VerifyError if the newly created class cannot be verified
2196 * @throws LinkageError if the newly created class cannot be linked for any other reason
2197 * @throws NullPointerException if any parameter is {@code null}
2198 *
2199 * @since 16
2200 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
2201 * @see Class#isHidden()
2202 * @see MethodHandles#classData(Lookup, String, Class)
2203 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
2204 * @jvms 4.2.1 Binary Class and Interface Names
2205 * @jvms 4.2.2 Unqualified Names
2206 * @jvms 4.7.28 The {@code NestHost} Attribute
2207 * @jvms 4.7.29 The {@code NestMembers} Attribute
2208 * @jvms 5.4.3.1 Class and Interface Resolution
2209 * @jvms 5.4.4 Access Control
2210 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2211 * @jvms 5.4 Linking
2212 * @jvms 5.5 Initialization
2213 * @jls 12.7 Unloading of Classes and Interfaces
2214 */
2215 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options)
2216 throws IllegalAccessException
2217 {
2218 Objects.requireNonNull(bytes);
2219 Objects.requireNonNull(classData);
2220
2221 int flags = ClassOption.optionsToFlag(options);
2222
2223 ensureDefineClassPermission();
2224 if (!hasFullPrivilegeAccess()) {
2225 throw new IllegalAccessException(this + " does not have full privilege access");
2226 }
2227
2228 return makeHiddenClassDefiner(bytes.clone(), false, flags)
2229 .defineClassAsLookup(initialize, classData);
2230 }
2231
2232 // A default dumper for writing class files passed to Lookup::defineClass
2233 // and Lookup::defineHiddenClass to disk for debugging purposes. To enable,
2234 // set -Djdk.invoke.MethodHandle.dumpHiddenClassFiles or
2235 // -Djdk.invoke.MethodHandle.dumpHiddenClassFiles=true
2236 //
2237 // This default dumper does not dump hidden classes defined by LambdaMetafactory
2238 // and LambdaForms and method handle internals. They are dumped via
2239 // different ClassFileDumpers.
2240 private static ClassFileDumper defaultDumper() {
2241 return DEFAULT_DUMPER;
2242 }
2243
2244 private static final ClassFileDumper DEFAULT_DUMPER = ClassFileDumper.getInstance(
2245 "jdk.invoke.MethodHandle.dumpClassFiles", "DUMP_CLASS_FILES");
2246
2247 /**
2248 * This method checks the class file version and the structure of `this_class`.
2249 * and checks if the bytes is a class or interface (ACC_MODULE flag not set)
2250 * that is in the named package.
2251 *
2252 * @throws IllegalArgumentException if ACC_MODULE flag is set in access flags
2253 * or the class is not in the given package name.
2254 */
2255 static String validateAndFindInternalName(byte[] bytes, String pkgName) {
2256 int magic = readInt(bytes, 0);
2257 if (magic != ClassFile.MAGIC_NUMBER) {
2258 throw new ClassFormatError("Incompatible magic value: " + magic);
2259 }
2260 // We have to read major and minor this way as ClassFile API throws IAE
2261 // yet we want distinct ClassFormatError and UnsupportedClassVersionError
2262 int minor = readUnsignedShort(bytes, 4);
2263 int major = readUnsignedShort(bytes, 6);
2264
2265 if (!VM.isSupportedClassFileVersion(major, minor)) {
2266 throw new UnsupportedClassVersionError("Unsupported class file version " + major + "." + minor);
2267 }
2268
2269 String name;
2270 ClassDesc sym;
2271 int accessFlags;
2272 try {
2273 ClassModel cm = ClassFile.of().parse(bytes);
2274 var thisClass = cm.thisClass();
2275 name = thisClass.asInternalName();
2276 sym = thisClass.asSymbol();
2277 accessFlags = cm.flags().flagsMask();
2278 } catch (IllegalArgumentException e) {
2279 ClassFormatError cfe = new ClassFormatError();
2280 cfe.initCause(e);
2281 throw cfe;
2282 }
2283 // must be a class or interface
2284 if ((accessFlags & ACC_MODULE) != 0) {
2285 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set");
2286 }
2287
2288 String pn = sym.packageName();
2289 if (!pn.equals(pkgName)) {
2290 throw newIllegalArgumentException(name + " not in same package as lookup class");
2291 }
2292
2293 return name;
2294 }
2295
2296 private static int readInt(byte[] bytes, int offset) {
2297 if ((offset + 4) > bytes.length) {
2298 throw new ClassFormatError("Invalid ClassFile structure");
2299 }
2300 return ((bytes[offset] & 0xFF) << 24)
2301 | ((bytes[offset + 1] & 0xFF) << 16)
2302 | ((bytes[offset + 2] & 0xFF) << 8)
2303 | (bytes[offset + 3] & 0xFF);
2304 }
2305
2306 private static int readUnsignedShort(byte[] bytes, int offset) {
2307 if ((offset+2) > bytes.length) {
2308 throw new ClassFormatError("Invalid ClassFile structure");
2309 }
2310 return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF);
2311 }
2312
2313 /*
2314 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2315 * from the given bytes.
2316 *
2317 * Caller should make a defensive copy of the arguments if needed
2318 * before calling this factory method.
2319 *
2320 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2321 * {@code bytes} denotes a class in a different package than the lookup class
2322 */
2323 private ClassDefiner makeClassDefiner(byte[] bytes) {
2324 var internalName = validateAndFindInternalName(bytes, lookupClass().getPackageName());
2325 return new ClassDefiner(this, internalName, bytes, STRONG_LOADER_LINK, defaultDumper());
2326 }
2327
2328 /**
2329 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2330 * from the given bytes. No package name check on the given bytes.
2331 *
2332 * @param internalName internal name
2333 * @param bytes class bytes
2334 * @param dumper dumper to write the given bytes to the dumper's output directory
2335 * @return ClassDefiner that defines a normal class of the given bytes.
2336 */
2337 ClassDefiner makeClassDefiner(String internalName, byte[] bytes, ClassFileDumper dumper) {
2338 // skip package name validation
2339 return new ClassDefiner(this, internalName, bytes, STRONG_LOADER_LINK, dumper);
2340 }
2341
2342 /**
2343 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2344 * from the given bytes. The name must be in the same package as the lookup class.
2345 *
2346 * Caller should make a defensive copy of the arguments if needed
2347 * before calling this factory method.
2348 *
2349 * @param bytes class bytes
2350 * @param dumper dumper to write the given bytes to the dumper's output directory
2351 * @return ClassDefiner that defines a hidden class of the given bytes.
2352 *
2353 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2354 * {@code bytes} denotes a class in a different package than the lookup class
2355 */
2356 ClassDefiner makeHiddenClassDefiner(byte[] bytes, ClassFileDumper dumper) {
2357 var internalName = validateAndFindInternalName(bytes, lookupClass().getPackageName());
2358 return makeHiddenClassDefiner(internalName, bytes, false, dumper, 0);
2359 }
2360
2361 /**
2362 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2363 * from the given bytes and options.
2364 * The name must be in the same package as the lookup class.
2365 *
2366 * Caller should make a defensive copy of the arguments if needed
2367 * before calling this factory method.
2368 *
2369 * @param bytes class bytes
2370 * @param flags class option flag mask
2371 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2372 * @return ClassDefiner that defines a hidden class of the given bytes and options
2373 *
2374 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2375 * {@code bytes} denotes a class in a different package than the lookup class
2376 */
2377 private ClassDefiner makeHiddenClassDefiner(byte[] bytes,
2378 boolean accessVmAnnotations,
2379 int flags) {
2380 var internalName = validateAndFindInternalName(bytes, lookupClass().getPackageName());
2381 return makeHiddenClassDefiner(internalName, bytes, accessVmAnnotations, defaultDumper(), flags);
2382 }
2383
2384 /**
2385 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2386 * from the given bytes and the given options. No package name check on the given bytes.
2387 *
2388 * @param internalName internal name that specifies the prefix of the hidden class
2389 * @param bytes class bytes
2390 * @param dumper dumper to write the given bytes to the dumper's output directory
2391 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2392 */
2393 ClassDefiner makeHiddenClassDefiner(String internalName, byte[] bytes, ClassFileDumper dumper) {
2394 Objects.requireNonNull(dumper);
2395 // skip name and access flags validation
2396 return makeHiddenClassDefiner(internalName, bytes, false, dumper, 0);
2397 }
2398
2399 /**
2400 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2401 * from the given bytes and the given options. No package name check on the given bytes.
2402 *
2403 * @param internalName internal name that specifies the prefix of the hidden class
2404 * @param bytes class bytes
2405 * @param flags class options flag mask
2406 * @param dumper dumper to write the given bytes to the dumper's output directory
2407 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2408 */
2409 ClassDefiner makeHiddenClassDefiner(String internalName, byte[] bytes, ClassFileDumper dumper, int flags) {
2410 Objects.requireNonNull(dumper);
2411 // skip name and access flags validation
2412 return makeHiddenClassDefiner(internalName, bytes, false, dumper, flags);
2413 }
2414
2415 /**
2416 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2417 * from the given class file and options.
2418 *
2419 * @param internalName internal name
2420 * @param bytes Class byte array
2421 * @param flags class option flag mask
2422 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2423 * @param dumper dumper to write the given bytes to the dumper's output directory
2424 */
2425 private ClassDefiner makeHiddenClassDefiner(String internalName,
2426 byte[] bytes,
2427 boolean accessVmAnnotations,
2428 ClassFileDumper dumper,
2429 int flags) {
2430 flags |= HIDDEN_CLASS;
2431 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) {
2432 // jdk.internal.vm.annotations are permitted for classes
2433 // defined to boot loader and platform loader
2434 flags |= ACCESS_VM_ANNOTATIONS;
2435 }
2436
2437 return new ClassDefiner(this, internalName, bytes, flags, dumper);
2438 }
2439
2440 record ClassDefiner(Lookup lookup, String internalName, byte[] bytes, int classFlags, ClassFileDumper dumper) {
2441 ClassDefiner {
2442 assert ((classFlags & HIDDEN_CLASS) != 0 || (classFlags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK);
2443 }
2444
2445 Class<?> defineClass(boolean initialize) {
2446 return defineClass(initialize, null);
2447 }
2448
2449 Lookup defineClassAsLookup(boolean initialize) {
2450 Class<?> c = defineClass(initialize, null);
2451 return new Lookup(c, null, FULL_POWER_MODES);
2452 }
2453
2454 /**
2455 * Defines the class of the given bytes and the given classData.
2456 * If {@code initialize} parameter is true, then the class will be initialized.
2457 *
2458 * @param initialize true if the class to be initialized
2459 * @param classData classData or null
2460 * @return the class
2461 *
2462 * @throws LinkageError linkage error
2463 */
2464 Class<?> defineClass(boolean initialize, Object classData) {
2465 Class<?> lookupClass = lookup.lookupClass();
2466 ClassLoader loader = lookupClass.getClassLoader();
2467 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null;
2468 Class<?> c = null;
2469 try {
2470 c = SharedSecrets.getJavaLangAccess()
2471 .defineClass(loader, lookupClass, internalName, bytes, pd, initialize, classFlags, classData);
2472 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost();
2473 return c;
2474 } finally {
2475 // dump the classfile for debugging
2476 if (dumper.isEnabled()) {
2477 String name = internalName();
2478 if (c != null) {
2479 dumper.dumpClass(name, c, bytes);
2480 } else {
2481 dumper.dumpFailedClass(name, bytes);
2482 }
2483 }
2484 }
2485 }
2486
2487 /**
2488 * Defines the class of the given bytes and the given classData.
2489 * If {@code initialize} parameter is true, then the class will be initialized.
2490 *
2491 * @param initialize true if the class to be initialized
2492 * @param classData classData or null
2493 * @return a Lookup for the defined class
2494 *
2495 * @throws LinkageError linkage error
2496 */
2497 Lookup defineClassAsLookup(boolean initialize, Object classData) {
2498 Class<?> c = defineClass(initialize, classData);
2499 return new Lookup(c, null, FULL_POWER_MODES);
2500 }
2501
2502 private boolean isNestmate() {
2503 return (classFlags & NESTMATE_CLASS) != 0;
2504 }
2505 }
2506
2507 private ProtectionDomain lookupClassProtectionDomain() {
2508 ProtectionDomain pd = cachedProtectionDomain;
2509 if (pd == null) {
2510 cachedProtectionDomain = pd = SharedSecrets.getJavaLangAccess().protectionDomain(lookupClass);
2511 }
2512 return pd;
2513 }
2514
2515 // cached protection domain
2516 private volatile ProtectionDomain cachedProtectionDomain;
2517
2518 // Make sure outer class is initialized first.
2519 static { IMPL_NAMES.getClass(); }
2520
2521 /** Package-private version of lookup which is trusted. */
2522 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
2523
2524 /** Version of lookup which is trusted minimally.
2525 * It can only be used to create method handles to publicly accessible
2526 * members in packages that are exported unconditionally.
2527 */
2528 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
2529
2530 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
2531 String name = lookupClass.getName();
2532 if (name.startsWith("java.lang.invoke."))
2533 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
2534 }
2535
2536 /**
2537 * Displays the name of the class from which lookups are to be made,
2538 * followed by "/" and the name of the {@linkplain #previousLookupClass()
2539 * previous lookup class} if present.
2540 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
2541 * If there are restrictions on the access permitted to this lookup,
2542 * this is indicated by adding a suffix to the class name, consisting
2543 * of a slash and a keyword. The keyword represents the strongest
2544 * allowed access, and is chosen as follows:
2545 * <ul>
2546 * <li>If no access is allowed, the suffix is "/noaccess".
2547 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
2548 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
2549 * <li>If only public and module access are allowed, the suffix is "/module".
2550 * <li>If public and package access are allowed, the suffix is "/package".
2551 * <li>If public, package, and private access are allowed, the suffix is "/private".
2552 * </ul>
2553 * If none of the above cases apply, it is the case that
2554 * {@linkplain #hasFullPrivilegeAccess() full privilege access}
2555 * (public, module, package, private, and protected) is allowed.
2556 * In this case, no suffix is added.
2557 * This is true only of an object obtained originally from
2558 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
2559 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
2560 * always have restricted access, and will display a suffix.
2561 * <p>
2562 * (It may seem strange that protected access should be
2563 * stronger than private access. Viewed independently from
2564 * package access, protected access is the first to be lost,
2565 * because it requires a direct subclass relationship between
2566 * caller and callee.)
2567 * @see #in
2568 */
2569 @Override
2570 public String toString() {
2571 String cname = lookupClass.getName();
2572 if (prevLookupClass != null)
2573 cname += "/" + prevLookupClass.getName();
2574 switch (allowedModes) {
2575 case 0: // no privileges
2576 return cname + "/noaccess";
2577 case UNCONDITIONAL:
2578 return cname + "/publicLookup";
2579 case PUBLIC:
2580 return cname + "/public";
2581 case PUBLIC|MODULE:
2582 return cname + "/module";
2583 case PUBLIC|PACKAGE:
2584 case PUBLIC|MODULE|PACKAGE:
2585 return cname + "/package";
2586 case PUBLIC|PACKAGE|PRIVATE:
2587 case PUBLIC|MODULE|PACKAGE|PRIVATE:
2588 return cname + "/private";
2589 case PUBLIC|PACKAGE|PRIVATE|PROTECTED:
2590 case PUBLIC|MODULE|PACKAGE|PRIVATE|PROTECTED:
2591 case FULL_POWER_MODES:
2592 return cname;
2593 case TRUSTED:
2594 return "/trusted"; // internal only; not exported
2595 default: // Should not happen, but it's a bitfield...
2596 cname = cname + "/" + Integer.toHexString(allowedModes);
2597 assert(false) : cname;
2598 return cname;
2599 }
2600 }
2601
2602 /**
2603 * Produces a method handle for a static method.
2604 * The type of the method handle will be that of the method.
2605 * (Since static methods do not take receivers, there is no
2606 * additional receiver argument inserted into the method handle type,
2607 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
2608 * The method and all its argument types must be accessible to the lookup object.
2609 * <p>
2610 * The returned method handle will have
2611 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2612 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2613 * <p>
2614 * If the returned method handle is invoked, the method's class will
2615 * be initialized, if it has not already been initialized.
2616 * <p><b>Example:</b>
2617 * {@snippet lang="java" :
2618 import static java.lang.invoke.MethodHandles.*;
2619 import static java.lang.invoke.MethodType.*;
2620 ...
2621 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
2622 "asList", methodType(List.class, Object[].class));
2623 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
2624 * }
2625 * @param refc the class from which the method is accessed
2626 * @param name the name of the method
2627 * @param type the type of the method
2628 * @return the desired method handle
2629 * @throws NoSuchMethodException if the method does not exist
2630 * @throws IllegalAccessException if access checking fails,
2631 * or if the method is not {@code static},
2632 * or if the method's variable arity modifier bit
2633 * is set and {@code asVarargsCollector} fails
2634 * @throws SecurityException if a security manager is present and it
2635 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2636 * @throws NullPointerException if any argument is null
2637 */
2638 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2639 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
2640 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method));
2641 }
2642
2643 /**
2644 * Produces a method handle for a virtual method.
2645 * The type of the method handle will be that of the method,
2646 * with the receiver type (usually {@code refc}) prepended.
2647 * The method and all its argument types must be accessible to the lookup object.
2648 * <p>
2649 * When called, the handle will treat the first argument as a receiver
2650 * and, for non-private methods, dispatch on the receiver's type to determine which method
2651 * implementation to enter.
2652 * For private methods the named method in {@code refc} will be invoked on the receiver.
2653 * (The dispatching action is identical with that performed by an
2654 * {@code invokevirtual} or {@code invokeinterface} instruction.)
2655 * <p>
2656 * The first argument will be of type {@code refc} if the lookup
2657 * class has full privileges to access the member. Otherwise
2658 * the member must be {@code protected} and the first argument
2659 * will be restricted in type to the lookup class.
2660 * <p>
2661 * The returned method handle will have
2662 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2663 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2664 * <p>
2665 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
2666 * instructions and method handles produced by {@code findVirtual},
2667 * if the class is {@code MethodHandle} and the name string is
2668 * {@code invokeExact} or {@code invoke}, the resulting
2669 * method handle is equivalent to one produced by
2670 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
2671 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
2672 * with the same {@code type} argument.
2673 * <p>
2674 * If the class is {@code VarHandle} and the name string corresponds to
2675 * the name of a signature-polymorphic access mode method, the resulting
2676 * method handle is equivalent to one produced by
2677 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
2678 * the access mode corresponding to the name string and with the same
2679 * {@code type} arguments.
2680 * <p>
2681 * <b>Example:</b>
2682 * {@snippet lang="java" :
2683 import static java.lang.invoke.MethodHandles.*;
2684 import static java.lang.invoke.MethodType.*;
2685 ...
2686 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
2687 "concat", methodType(String.class, String.class));
2688 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
2689 "hashCode", methodType(int.class));
2690 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
2691 "hashCode", methodType(int.class));
2692 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
2693 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
2694 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
2695 // interface method:
2696 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
2697 "subSequence", methodType(CharSequence.class, int.class, int.class));
2698 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
2699 // constructor "internal method" must be accessed differently:
2700 MethodType MT_newString = methodType(void.class); //()V for new String()
2701 try { assertEquals("impossible", lookup()
2702 .findVirtual(String.class, "<init>", MT_newString));
2703 } catch (NoSuchMethodException ex) { } // OK
2704 MethodHandle MH_newString = publicLookup()
2705 .findConstructor(String.class, MT_newString);
2706 assertEquals("", (String) MH_newString.invokeExact());
2707 * }
2708 *
2709 * @param refc the class or interface from which the method is accessed
2710 * @param name the name of the method
2711 * @param type the type of the method, with the receiver argument omitted
2712 * @return the desired method handle
2713 * @throws NoSuchMethodException if the method does not exist
2714 * @throws IllegalAccessException if access checking fails,
2715 * or if the method is {@code static},
2716 * or if the method's variable arity modifier bit
2717 * is set and {@code asVarargsCollector} fails
2718 * @throws SecurityException if a security manager is present and it
2719 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2720 * @throws NullPointerException if any argument is null
2721 */
2722 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2723 if (refc == MethodHandle.class) {
2724 MethodHandle mh = findVirtualForMH(name, type);
2725 if (mh != null) return mh;
2726 } else if (refc == VarHandle.class) {
2727 MethodHandle mh = findVirtualForVH(name, type);
2728 if (mh != null) return mh;
2729 }
2730 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
2731 MemberName method = resolveOrFail(refKind, refc, name, type);
2732 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method));
2733 }
2734 private MethodHandle findVirtualForMH(String name, MethodType type) {
2735 // these names require special lookups because of the implicit MethodType argument
2736 if ("invoke".equals(name))
2737 return invoker(type);
2738 if ("invokeExact".equals(name))
2739 return exactInvoker(type);
2740 assert(!MemberName.isMethodHandleInvokeName(name));
2741 return null;
2742 }
2743 private MethodHandle findVirtualForVH(String name, MethodType type) {
2744 try {
2745 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
2746 } catch (IllegalArgumentException e) {
2747 return null;
2748 }
2749 }
2750
2751 /**
2752 * Produces a method handle which creates an object and initializes it, using
2753 * the constructor of the specified type.
2754 * The parameter types of the method handle will be those of the constructor,
2755 * while the return type will be a reference to the constructor's class.
2756 * The constructor and all its argument types must be accessible to the lookup object.
2757 * <p>
2758 * The requested type must have a return type of {@code void}.
2759 * (This is consistent with the JVM's treatment of constructor type descriptors.)
2760 * <p>
2761 * The returned method handle will have
2762 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2763 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2764 * <p>
2765 * If the returned method handle is invoked, the constructor's class will
2766 * be initialized, if it has not already been initialized.
2767 * <p><b>Example:</b>
2768 * {@snippet lang="java" :
2769 import static java.lang.invoke.MethodHandles.*;
2770 import static java.lang.invoke.MethodType.*;
2771 ...
2772 MethodHandle MH_newArrayList = publicLookup().findConstructor(
2773 ArrayList.class, methodType(void.class, Collection.class));
2774 Collection orig = Arrays.asList("x", "y");
2775 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
2776 assert(orig != copy);
2777 assertEquals(orig, copy);
2778 // a variable-arity constructor:
2779 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
2780 ProcessBuilder.class, methodType(void.class, String[].class));
2781 ProcessBuilder pb = (ProcessBuilder)
2782 MH_newProcessBuilder.invoke("x", "y", "z");
2783 assertEquals("[x, y, z]", pb.command().toString());
2784 * }
2785 * @param refc the class or interface from which the method is accessed
2786 * @param type the type of the method, with the receiver argument omitted, and a void return type
2787 * @return the desired method handle
2788 * @throws NoSuchMethodException if the constructor does not exist
2789 * @throws IllegalAccessException if access checking fails
2790 * or if the method's variable arity modifier bit
2791 * is set and {@code asVarargsCollector} fails
2792 * @throws SecurityException if a security manager is present and it
2793 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2794 * @throws NullPointerException if any argument is null
2795 */
2796 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2797 if (refc.isArray()) {
2798 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
2799 }
2800 String name = ConstantDescs.INIT_NAME;
2801 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
2802 return getDirectConstructor(refc, ctor);
2803 }
2804
2805 /**
2806 * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
2807 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
2808 * Such a resolution, as specified in JVMS {@jvms 5.4.3.1}, attempts to locate and load the class,
2809 * and then determines whether the class is accessible to this lookup object.
2810 * <p>
2811 * For a class or an interface, the name is the {@linkplain ClassLoader##binary-name binary name}.
2812 * For an array class of {@code n} dimensions, the name begins with {@code n} occurrences
2813 * of {@code '['} and followed by the element type as encoded in the
2814 * {@linkplain Class##nameFormat table} specified in {@link Class#getName}.
2815 * <p>
2816 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
2817 * its class loader, and the {@linkplain #lookupModes() lookup modes}.
2818 *
2819 * @param targetName the {@linkplain ClassLoader##binary-name binary name} of the class
2820 * or the string representing an array class
2821 * @return the requested class.
2822 * @throws SecurityException if a security manager is present and it
2823 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2824 * @throws LinkageError if the linkage fails
2825 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
2826 * @throws IllegalAccessException if the class is not accessible, using the allowed access
2827 * modes.
2828 * @throws NullPointerException if {@code targetName} is null
2829 * @since 9
2830 * @jvms 5.4.3.1 Class and Interface Resolution
2831 */
2832 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
2833 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
2834 return accessClass(targetClass);
2835 }
2836
2837 /**
2838 * Ensures that {@code targetClass} has been initialized. The class
2839 * to be initialized must be {@linkplain #accessClass accessible}
2840 * to this {@code Lookup} object. This method causes {@code targetClass}
2841 * to be initialized if it has not been already initialized,
2842 * as specified in JVMS {@jvms 5.5}.
2843 *
2844 * <p>
2845 * This method returns when {@code targetClass} is fully initialized, or
2846 * when {@code targetClass} is being initialized by the current thread.
2847 *
2848 * @param <T> the type of the class to be initialized
2849 * @param targetClass the class to be initialized
2850 * @return {@code targetClass} that has been initialized, or that is being
2851 * initialized by the current thread.
2852 *
2853 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or {@code void}
2854 * or array class
2855 * @throws IllegalAccessException if {@code targetClass} is not
2856 * {@linkplain #accessClass accessible} to this lookup
2857 * @throws ExceptionInInitializerError if the class initialization provoked
2858 * by this method fails
2859 * @throws SecurityException if a security manager is present and it
2860 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2861 * @since 15
2862 * @jvms 5.5 Initialization
2863 */
2864 public <T> Class<T> ensureInitialized(Class<T> targetClass) throws IllegalAccessException {
2865 if (targetClass.isPrimitive())
2866 throw new IllegalArgumentException(targetClass + " is a primitive class");
2867 if (targetClass.isArray())
2868 throw new IllegalArgumentException(targetClass + " is an array class");
2869
2870 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2871 throw makeAccessException(targetClass);
2872 }
2873 checkSecurityManager(targetClass);
2874
2875 // ensure class initialization
2876 Unsafe.getUnsafe().ensureClassInitialized(targetClass);
2877 return targetClass;
2878 }
2879
2880 /*
2881 * Returns IllegalAccessException due to access violation to the given targetClass.
2882 *
2883 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized}
2884 * which verifies access to a class rather a member.
2885 */
2886 private IllegalAccessException makeAccessException(Class<?> targetClass) {
2887 String message = "access violation: "+ targetClass;
2888 if (this == MethodHandles.publicLookup()) {
2889 message += ", from public Lookup";
2890 } else {
2891 Module m = lookupClass().getModule();
2892 message += ", from " + lookupClass() + " (" + m + ")";
2893 if (prevLookupClass != null) {
2894 message += ", previous lookup " +
2895 prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")";
2896 }
2897 }
2898 return new IllegalAccessException(message);
2899 }
2900
2901 /**
2902 * Determines if a class can be accessed from the lookup context defined by
2903 * this {@code Lookup} object. The static initializer of the class is not run.
2904 * If {@code targetClass} is an array class, {@code targetClass} is accessible
2905 * if the element type of the array class is accessible. Otherwise,
2906 * {@code targetClass} is determined as accessible as follows.
2907 *
2908 * <p>
2909 * If {@code targetClass} is in the same module as the lookup class,
2910 * the lookup class is {@code LC} in module {@code M1} and
2911 * the previous lookup class is in module {@code M0} or
2912 * {@code null} if not present,
2913 * {@code targetClass} is accessible if and only if one of the following is true:
2914 * <ul>
2915 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
2916 * {@code LC} or other class in the same nest of {@code LC}.</li>
2917 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
2918 * in the same runtime package of {@code LC}.</li>
2919 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
2920 * a public type in {@code M1}.</li>
2921 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
2922 * a public type in a package exported by {@code M1} to at least {@code M0}
2923 * if the previous lookup class is present; otherwise, {@code targetClass}
2924 * is a public type in a package exported by {@code M1} unconditionally.</li>
2925 * </ul>
2926 *
2927 * <p>
2928 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2929 * can access public types in all modules when the type is in a package
2930 * that is exported unconditionally.
2931 * <p>
2932 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass},
2933 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2934 * is inaccessible.
2935 * <p>
2936 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2937 * {@code M1} is the module containing {@code lookupClass} and
2938 * {@code M2} is the module containing {@code targetClass},
2939 * then {@code targetClass} is accessible if and only if
2940 * <ul>
2941 * <li>{@code M1} reads {@code M2}, and
2942 * <li>{@code targetClass} is public and in a package exported by
2943 * {@code M2} at least to {@code M1}.
2944 * </ul>
2945 * <p>
2946 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2947 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2948 * containing the previous lookup class, then {@code targetClass} is accessible
2949 * if and only if one of the following is true:
2950 * <ul>
2951 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2952 * {@linkplain Module#reads reads} {@code M0} and the type is
2953 * in a package that is exported to at least {@code M1}.
2954 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2955 * {@linkplain Module#reads reads} {@code M1} and the type is
2956 * in a package that is exported to at least {@code M0}.
2957 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2958 * and {@code M1} reads {@code M2} and the type is in a package
2959 * that is exported to at least both {@code M0} and {@code M2}.
2960 * </ul>
2961 * <p>
2962 * Otherwise, {@code targetClass} is not accessible.
2963 *
2964 * @param <T> the type of the class to be access-checked
2965 * @param targetClass the class to be access-checked
2966 * @return {@code targetClass} that has been access-checked
2967 * @throws IllegalAccessException if the class is not accessible from the lookup class
2968 * and previous lookup class, if present, using the allowed access modes.
2969 * @throws SecurityException if a security manager is present and it
2970 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2971 * @throws NullPointerException if {@code targetClass} is {@code null}
2972 * @since 9
2973 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
2974 */
2975 public <T> Class<T> accessClass(Class<T> targetClass) throws IllegalAccessException {
2976 if (!isClassAccessible(targetClass)) {
2977 throw makeAccessException(targetClass);
2978 }
2979 checkSecurityManager(targetClass);
2980 return targetClass;
2981 }
2982
2983 /**
2984 * Produces an early-bound method handle for a virtual method.
2985 * It will bypass checks for overriding methods on the receiver,
2986 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2987 * instruction from within the explicitly specified {@code specialCaller}.
2988 * The type of the method handle will be that of the method,
2989 * with a suitably restricted receiver type prepended.
2990 * (The receiver type will be {@code specialCaller} or a subtype.)
2991 * The method and all its argument types must be accessible
2992 * to the lookup object.
2993 * <p>
2994 * Before method resolution,
2995 * if the explicitly specified caller class is not identical with the
2996 * lookup class, or if this lookup object does not have
2997 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2998 * privileges, the access fails.
2999 * <p>
3000 * The returned method handle will have
3001 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3002 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3003 * <p style="font-size:smaller;">
3004 * <em>(Note: JVM internal methods named {@value ConstantDescs#INIT_NAME}
3005 * are not visible to this API,
3006 * even though the {@code invokespecial} instruction can refer to them
3007 * in special circumstances. Use {@link #findConstructor findConstructor}
3008 * to access instance initialization methods in a safe manner.)</em>
3009 * <p><b>Example:</b>
3010 * {@snippet lang="java" :
3011 import static java.lang.invoke.MethodHandles.*;
3012 import static java.lang.invoke.MethodType.*;
3013 ...
3014 static class Listie extends ArrayList {
3015 public String toString() { return "[wee Listie]"; }
3016 static Lookup lookup() { return MethodHandles.lookup(); }
3017 }
3018 ...
3019 // no access to constructor via invokeSpecial:
3020 MethodHandle MH_newListie = Listie.lookup()
3021 .findConstructor(Listie.class, methodType(void.class));
3022 Listie l = (Listie) MH_newListie.invokeExact();
3023 try { assertEquals("impossible", Listie.lookup().findSpecial(
3024 Listie.class, "<init>", methodType(void.class), Listie.class));
3025 } catch (NoSuchMethodException ex) { } // OK
3026 // access to super and self methods via invokeSpecial:
3027 MethodHandle MH_super = Listie.lookup().findSpecial(
3028 ArrayList.class, "toString" , methodType(String.class), Listie.class);
3029 MethodHandle MH_this = Listie.lookup().findSpecial(
3030 Listie.class, "toString" , methodType(String.class), Listie.class);
3031 MethodHandle MH_duper = Listie.lookup().findSpecial(
3032 Object.class, "toString" , methodType(String.class), Listie.class);
3033 assertEquals("[]", (String) MH_super.invokeExact(l));
3034 assertEquals(""+l, (String) MH_this.invokeExact(l));
3035 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
3036 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
3037 String.class, "toString", methodType(String.class), Listie.class));
3038 } catch (IllegalAccessException ex) { } // OK
3039 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
3040 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
3041 * }
3042 *
3043 * @param refc the class or interface from which the method is accessed
3044 * @param name the name of the method (which must not be "<init>")
3045 * @param type the type of the method, with the receiver argument omitted
3046 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
3047 * @return the desired method handle
3048 * @throws NoSuchMethodException if the method does not exist
3049 * @throws IllegalAccessException if access checking fails,
3050 * or if the method is {@code static},
3051 * or if the method's variable arity modifier bit
3052 * is set and {@code asVarargsCollector} fails
3053 * @throws SecurityException if a security manager is present and it
3054 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3055 * @throws NullPointerException if any argument is null
3056 */
3057 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
3058 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
3059 checkSpecialCaller(specialCaller, refc);
3060 Lookup specialLookup = this.in(specialCaller);
3061 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
3062 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method));
3063 }
3064
3065 /**
3066 * Produces a method handle giving read access to a non-static field.
3067 * The type of the method handle will have a return type of the field's
3068 * value type.
3069 * The method handle's single argument will be the instance containing
3070 * the field.
3071 * Access checking is performed immediately on behalf of the lookup class.
3072 * @param refc the class or interface from which the method is accessed
3073 * @param name the field's name
3074 * @param type the field's type
3075 * @return a method handle which can load values from the field
3076 * @throws NoSuchFieldException if the field does not exist
3077 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3078 * @throws SecurityException if a security manager is present and it
3079 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3080 * @throws NullPointerException if any argument is null
3081 * @see #findVarHandle(Class, String, Class)
3082 */
3083 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3084 MemberName field = resolveOrFail(REF_getField, refc, name, type);
3085 return getDirectField(REF_getField, refc, field);
3086 }
3087
3088 /**
3089 * Produces a method handle giving write access to a non-static field.
3090 * The type of the method handle will have a void return type.
3091 * The method handle will take two arguments, the instance containing
3092 * the field, and the value to be stored.
3093 * The second argument will be of the field's value type.
3094 * Access checking is performed immediately on behalf of the lookup class.
3095 * @param refc the class or interface from which the method is accessed
3096 * @param name the field's name
3097 * @param type the field's type
3098 * @return a method handle which can store values into the field
3099 * @throws NoSuchFieldException if the field does not exist
3100 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3101 * or {@code final}
3102 * @throws SecurityException if a security manager is present and it
3103 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3104 * @throws NullPointerException if any argument is null
3105 * @see #findVarHandle(Class, String, Class)
3106 */
3107 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3108 MemberName field = resolveOrFail(REF_putField, refc, name, type);
3109 return getDirectField(REF_putField, refc, field);
3110 }
3111
3112 /**
3113 * Produces a VarHandle giving access to a non-static field {@code name}
3114 * of type {@code type} declared in a class of type {@code recv}.
3115 * The VarHandle's variable type is {@code type} and it has one
3116 * coordinate type, {@code recv}.
3117 * <p>
3118 * Access checking is performed immediately on behalf of the lookup
3119 * class.
3120 * <p>
3121 * Certain access modes of the returned VarHandle are unsupported under
3122 * the following conditions:
3123 * <ul>
3124 * <li>if the field is declared {@code final}, then the write, atomic
3125 * update, numeric atomic update, and bitwise atomic update access
3126 * modes are unsupported.
3127 * <li>if the field type is anything other than {@code byte},
3128 * {@code short}, {@code char}, {@code int}, {@code long},
3129 * {@code float}, or {@code double} then numeric atomic update
3130 * access modes are unsupported.
3131 * <li>if the field type is anything other than {@code boolean},
3132 * {@code byte}, {@code short}, {@code char}, {@code int} or
3133 * {@code long} then bitwise atomic update access modes are
3134 * unsupported.
3135 * </ul>
3136 * <p>
3137 * If the field is declared {@code volatile} then the returned VarHandle
3138 * will override access to the field (effectively ignore the
3139 * {@code volatile} declaration) in accordance to its specified
3140 * access modes.
3141 * <p>
3142 * If the field type is {@code float} or {@code double} then numeric
3143 * and atomic update access modes compare values using their bitwise
3144 * representation (see {@link Float#floatToRawIntBits} and
3145 * {@link Double#doubleToRawLongBits}, respectively).
3146 * @apiNote
3147 * Bitwise comparison of {@code float} values or {@code double} values,
3148 * as performed by the numeric and atomic update access modes, differ
3149 * from the primitive {@code ==} operator and the {@link Float#equals}
3150 * and {@link Double#equals} methods, specifically with respect to
3151 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3152 * Care should be taken when performing a compare and set or a compare
3153 * and exchange operation with such values since the operation may
3154 * unexpectedly fail.
3155 * There are many possible NaN values that are considered to be
3156 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3157 * provided by Java can distinguish between them. Operation failure can
3158 * occur if the expected or witness value is a NaN value and it is
3159 * transformed (perhaps in a platform specific manner) into another NaN
3160 * value, and thus has a different bitwise representation (see
3161 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3162 * details).
3163 * The values {@code -0.0} and {@code +0.0} have different bitwise
3164 * representations but are considered equal when using the primitive
3165 * {@code ==} operator. Operation failure can occur if, for example, a
3166 * numeric algorithm computes an expected value to be say {@code -0.0}
3167 * and previously computed the witness value to be say {@code +0.0}.
3168 * @param recv the receiver class, of type {@code R}, that declares the
3169 * non-static field
3170 * @param name the field's name
3171 * @param type the field's type, of type {@code T}
3172 * @return a VarHandle giving access to non-static fields.
3173 * @throws NoSuchFieldException if the field does not exist
3174 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3175 * @throws SecurityException if a security manager is present and it
3176 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3177 * @throws NullPointerException if any argument is null
3178 * @since 9
3179 */
3180 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3181 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
3182 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
3183 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
3184 }
3185
3186 /**
3187 * Produces a method handle giving read access to a static field.
3188 * The type of the method handle will have a return type of the field's
3189 * value type.
3190 * The method handle will take no arguments.
3191 * Access checking is performed immediately on behalf of the lookup class.
3192 * <p>
3193 * If the returned method handle is invoked, the field's class will
3194 * be initialized, if it has not already been initialized.
3195 * @param refc the class or interface from which the method is accessed
3196 * @param name the field's name
3197 * @param type the field's type
3198 * @return a method handle which can load values from the field
3199 * @throws NoSuchFieldException if the field does not exist
3200 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3201 * @throws SecurityException if a security manager is present and it
3202 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3203 * @throws NullPointerException if any argument is null
3204 */
3205 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3206 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
3207 return getDirectField(REF_getStatic, refc, field);
3208 }
3209
3210 /**
3211 * Produces a method handle giving write access to a static field.
3212 * The type of the method handle will have a void return type.
3213 * The method handle will take a single
3214 * argument, of the field's value type, the value to be stored.
3215 * Access checking is performed immediately on behalf of the lookup class.
3216 * <p>
3217 * If the returned method handle is invoked, the field's class will
3218 * be initialized, if it has not already been initialized.
3219 * @param refc the class or interface from which the method is accessed
3220 * @param name the field's name
3221 * @param type the field's type
3222 * @return a method handle which can store values into the field
3223 * @throws NoSuchFieldException if the field does not exist
3224 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3225 * or is {@code final}
3226 * @throws SecurityException if a security manager is present and it
3227 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3228 * @throws NullPointerException if any argument is null
3229 */
3230 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3231 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
3232 return getDirectField(REF_putStatic, refc, field);
3233 }
3234
3235 /**
3236 * Produces a VarHandle giving access to a static field {@code name} of
3237 * type {@code type} declared in a class of type {@code decl}.
3238 * The VarHandle's variable type is {@code type} and it has no
3239 * coordinate types.
3240 * <p>
3241 * Access checking is performed immediately on behalf of the lookup
3242 * class.
3243 * <p>
3244 * If the returned VarHandle is operated on, the declaring class will be
3245 * initialized, if it has not already been initialized.
3246 * <p>
3247 * Certain access modes of the returned VarHandle are unsupported under
3248 * the following conditions:
3249 * <ul>
3250 * <li>if the field is declared {@code final}, then the write, atomic
3251 * update, numeric atomic update, and bitwise atomic update access
3252 * modes are unsupported.
3253 * <li>if the field type is anything other than {@code byte},
3254 * {@code short}, {@code char}, {@code int}, {@code long},
3255 * {@code float}, or {@code double}, then numeric atomic update
3256 * access modes are unsupported.
3257 * <li>if the field type is anything other than {@code boolean},
3258 * {@code byte}, {@code short}, {@code char}, {@code int} or
3259 * {@code long} then bitwise atomic update access modes are
3260 * unsupported.
3261 * </ul>
3262 * <p>
3263 * If the field is declared {@code volatile} then the returned VarHandle
3264 * will override access to the field (effectively ignore the
3265 * {@code volatile} declaration) in accordance to its specified
3266 * access modes.
3267 * <p>
3268 * If the field type is {@code float} or {@code double} then numeric
3269 * and atomic update access modes compare values using their bitwise
3270 * representation (see {@link Float#floatToRawIntBits} and
3271 * {@link Double#doubleToRawLongBits}, respectively).
3272 * @apiNote
3273 * Bitwise comparison of {@code float} values or {@code double} values,
3274 * as performed by the numeric and atomic update access modes, differ
3275 * from the primitive {@code ==} operator and the {@link Float#equals}
3276 * and {@link Double#equals} methods, specifically with respect to
3277 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3278 * Care should be taken when performing a compare and set or a compare
3279 * and exchange operation with such values since the operation may
3280 * unexpectedly fail.
3281 * There are many possible NaN values that are considered to be
3282 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3283 * provided by Java can distinguish between them. Operation failure can
3284 * occur if the expected or witness value is a NaN value and it is
3285 * transformed (perhaps in a platform specific manner) into another NaN
3286 * value, and thus has a different bitwise representation (see
3287 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3288 * details).
3289 * The values {@code -0.0} and {@code +0.0} have different bitwise
3290 * representations but are considered equal when using the primitive
3291 * {@code ==} operator. Operation failure can occur if, for example, a
3292 * numeric algorithm computes an expected value to be say {@code -0.0}
3293 * and previously computed the witness value to be say {@code +0.0}.
3294 * @param decl the class that declares the static field
3295 * @param name the field's name
3296 * @param type the field's type, of type {@code T}
3297 * @return a VarHandle giving access to a static field
3298 * @throws NoSuchFieldException if the field does not exist
3299 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3300 * @throws SecurityException if a security manager is present and it
3301 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3302 * @throws NullPointerException if any argument is null
3303 * @since 9
3304 */
3305 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3306 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
3307 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
3308 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
3309 }
3310
3311 /**
3312 * Produces an early-bound method handle for a non-static method.
3313 * The receiver must have a supertype {@code defc} in which a method
3314 * of the given name and type is accessible to the lookup class.
3315 * The method and all its argument types must be accessible to the lookup object.
3316 * The type of the method handle will be that of the method,
3317 * without any insertion of an additional receiver parameter.
3318 * The given receiver will be bound into the method handle,
3319 * so that every call to the method handle will invoke the
3320 * requested method on the given receiver.
3321 * <p>
3322 * The returned method handle will have
3323 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3324 * the method's variable arity modifier bit ({@code 0x0080}) is set
3325 * <em>and</em> the trailing array argument is not the only argument.
3326 * (If the trailing array argument is the only argument,
3327 * the given receiver value will be bound to it.)
3328 * <p>
3329 * This is almost equivalent to the following code, with some differences noted below:
3330 * {@snippet lang="java" :
3331 import static java.lang.invoke.MethodHandles.*;
3332 import static java.lang.invoke.MethodType.*;
3333 ...
3334 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
3335 MethodHandle mh1 = mh0.bindTo(receiver);
3336 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
3337 return mh1;
3338 * }
3339 * where {@code defc} is either {@code receiver.getClass()} or a super
3340 * type of that class, in which the requested method is accessible
3341 * to the lookup class.
3342 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
3343 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
3344 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
3345 * the receiver is restricted by {@code findVirtual} to the lookup class.)
3346 * @param receiver the object from which the method is accessed
3347 * @param name the name of the method
3348 * @param type the type of the method, with the receiver argument omitted
3349 * @return the desired method handle
3350 * @throws NoSuchMethodException if the method does not exist
3351 * @throws IllegalAccessException if access checking fails
3352 * or if the method's variable arity modifier bit
3353 * is set and {@code asVarargsCollector} fails
3354 * @throws SecurityException if a security manager is present and it
3355 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3356 * @throws NullPointerException if any argument is null
3357 * @see MethodHandle#bindTo
3358 * @see #findVirtual
3359 */
3360 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3361 Class<? extends Object> refc = receiver.getClass(); // may get NPE
3362 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
3363 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method));
3364 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
3365 throw new IllegalAccessException("The restricted defining class " +
3366 mh.type().leadingReferenceParameter().getName() +
3367 " is not assignable from receiver class " +
3368 receiver.getClass().getName());
3369 }
3370 return mh.bindArgumentL(0, receiver).setVarargs(method);
3371 }
3372
3373 /**
3374 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3375 * to <i>m</i>, if the lookup class has permission.
3376 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
3377 * If <i>m</i> is virtual, overriding is respected on every call.
3378 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
3379 * The type of the method handle will be that of the method,
3380 * with the receiver type prepended (but only if it is non-static).
3381 * If the method's {@code accessible} flag is not set,
3382 * access checking is performed immediately on behalf of the lookup class.
3383 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
3384 * <p>
3385 * The returned method handle will have
3386 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3387 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3388 * <p>
3389 * If <i>m</i> is static, and
3390 * if the returned method handle is invoked, the method's class will
3391 * be initialized, if it has not already been initialized.
3392 * @param m the reflected method
3393 * @return a method handle which can invoke the reflected method
3394 * @throws IllegalAccessException if access checking fails
3395 * or if the method's variable arity modifier bit
3396 * is set and {@code asVarargsCollector} fails
3397 * @throws NullPointerException if the argument is null
3398 */
3399 public MethodHandle unreflect(Method m) throws IllegalAccessException {
3400 if (m.getDeclaringClass() == MethodHandle.class) {
3401 MethodHandle mh = unreflectForMH(m);
3402 if (mh != null) return mh;
3403 }
3404 if (m.getDeclaringClass() == VarHandle.class) {
3405 MethodHandle mh = unreflectForVH(m);
3406 if (mh != null) return mh;
3407 }
3408 MemberName method = new MemberName(m);
3409 byte refKind = method.getReferenceKind();
3410 if (refKind == REF_invokeSpecial)
3411 refKind = REF_invokeVirtual;
3412 assert(method.isMethod());
3413 @SuppressWarnings("deprecation")
3414 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
3415 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3416 }
3417 private MethodHandle unreflectForMH(Method m) {
3418 // these names require special lookups because they throw UnsupportedOperationException
3419 if (MemberName.isMethodHandleInvokeName(m.getName()))
3420 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
3421 return null;
3422 }
3423 private MethodHandle unreflectForVH(Method m) {
3424 // these names require special lookups because they throw UnsupportedOperationException
3425 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
3426 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
3427 return null;
3428 }
3429
3430 /**
3431 * Produces a method handle for a reflected method.
3432 * It will bypass checks for overriding methods on the receiver,
3433 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3434 * instruction from within the explicitly specified {@code specialCaller}.
3435 * The type of the method handle will be that of the method,
3436 * with a suitably restricted receiver type prepended.
3437 * (The receiver type will be {@code specialCaller} or a subtype.)
3438 * If the method's {@code accessible} flag is not set,
3439 * access checking is performed immediately on behalf of the lookup class,
3440 * as if {@code invokespecial} instruction were being linked.
3441 * <p>
3442 * Before method resolution,
3443 * if the explicitly specified caller class is not identical with the
3444 * lookup class, or if this lookup object does not have
3445 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3446 * privileges, the access fails.
3447 * <p>
3448 * The returned method handle will have
3449 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3450 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3451 * @param m the reflected method
3452 * @param specialCaller the class nominally calling the method
3453 * @return a method handle which can invoke the reflected method
3454 * @throws IllegalAccessException if access checking fails,
3455 * or if the method is {@code static},
3456 * or if the method's variable arity modifier bit
3457 * is set and {@code asVarargsCollector} fails
3458 * @throws NullPointerException if any argument is null
3459 */
3460 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
3461 checkSpecialCaller(specialCaller, m.getDeclaringClass());
3462 Lookup specialLookup = this.in(specialCaller);
3463 MemberName method = new MemberName(m, true);
3464 assert(method.isMethod());
3465 // ignore m.isAccessible: this is a new kind of access
3466 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3467 }
3468
3469 /**
3470 * Produces a method handle for a reflected constructor.
3471 * The type of the method handle will be that of the constructor,
3472 * with the return type changed to the declaring class.
3473 * The method handle will perform a {@code newInstance} operation,
3474 * creating a new instance of the constructor's class on the
3475 * arguments passed to the method handle.
3476 * <p>
3477 * If the constructor's {@code accessible} flag is not set,
3478 * access checking is performed immediately on behalf of the lookup class.
3479 * <p>
3480 * The returned method handle will have
3481 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3482 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
3483 * <p>
3484 * If the returned method handle is invoked, the constructor's class will
3485 * be initialized, if it has not already been initialized.
3486 * @param c the reflected constructor
3487 * @return a method handle which can invoke the reflected constructor
3488 * @throws IllegalAccessException if access checking fails
3489 * or if the method's variable arity modifier bit
3490 * is set and {@code asVarargsCollector} fails
3491 * @throws NullPointerException if the argument is null
3492 */
3493 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
3494 MemberName ctor = new MemberName(c);
3495 assert(ctor.isConstructor());
3496 @SuppressWarnings("deprecation")
3497 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
3498 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
3499 }
3500
3501 /*
3502 * Produces a method handle that is capable of creating instances of the given class
3503 * and instantiated by the given constructor. No security manager check.
3504 *
3505 * This method should only be used by ReflectionFactory::newConstructorForSerialization.
3506 */
3507 /* package-private */ MethodHandle serializableConstructor(Class<?> decl, Constructor<?> c) throws IllegalAccessException {
3508 MemberName ctor = new MemberName(c);
3509 assert(ctor.isConstructor() && constructorInSuperclass(decl, c));
3510 checkAccess(REF_newInvokeSpecial, decl, ctor);
3511 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3512 return DirectMethodHandle.makeAllocator(decl, ctor).setVarargs(ctor);
3513 }
3514
3515 private static boolean constructorInSuperclass(Class<?> decl, Constructor<?> ctor) {
3516 if (decl == ctor.getDeclaringClass())
3517 return true;
3518
3519 Class<?> cl = decl;
3520 while ((cl = cl.getSuperclass()) != null) {
3521 if (cl == ctor.getDeclaringClass()) {
3522 return true;
3523 }
3524 }
3525 return false;
3526 }
3527
3528 /**
3529 * Produces a method handle giving read access to a reflected field.
3530 * The type of the method handle will have a return type of the field's
3531 * value type.
3532 * If the field is {@code static}, the method handle will take no arguments.
3533 * Otherwise, its single argument will be the instance containing
3534 * the field.
3535 * If the {@code Field} object's {@code accessible} flag is not set,
3536 * access checking is performed immediately on behalf of the lookup class.
3537 * <p>
3538 * If the field is static, and
3539 * if the returned method handle is invoked, the field's class will
3540 * be initialized, if it has not already been initialized.
3541 * @param f the reflected field
3542 * @return a method handle which can load values from the reflected field
3543 * @throws IllegalAccessException if access checking fails
3544 * @throws NullPointerException if the argument is null
3545 */
3546 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
3547 return unreflectField(f, false);
3548 }
3549
3550 /**
3551 * Produces a method handle giving write access to a reflected field.
3552 * The type of the method handle will have a void return type.
3553 * If the field is {@code static}, the method handle will take a single
3554 * argument, of the field's value type, the value to be stored.
3555 * Otherwise, the two arguments will be the instance containing
3556 * the field, and the value to be stored.
3557 * If the {@code Field} object's {@code accessible} flag is not set,
3558 * access checking is performed immediately on behalf of the lookup class.
3559 * <p>
3560 * If the field is {@code final}, write access will not be
3561 * allowed and access checking will fail, except under certain
3562 * narrow circumstances documented for {@link Field#set Field.set}.
3563 * A method handle is returned only if a corresponding call to
3564 * the {@code Field} object's {@code set} method could return
3565 * normally. In particular, fields which are both {@code static}
3566 * and {@code final} may never be set.
3567 * <p>
3568 * If the field is {@code static}, and
3569 * if the returned method handle is invoked, the field's class will
3570 * be initialized, if it has not already been initialized.
3571 * @param f the reflected field
3572 * @return a method handle which can store values into the reflected field
3573 * @throws IllegalAccessException if access checking fails,
3574 * or if the field is {@code final} and write access
3575 * is not enabled on the {@code Field} object
3576 * @throws NullPointerException if the argument is null
3577 */
3578 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
3579 return unreflectField(f, true);
3580 }
3581
3582 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
3583 MemberName field = new MemberName(f, isSetter);
3584 if (isSetter && field.isFinal()) {
3585 if (field.isTrustedFinalField()) {
3586 String msg = field.isStatic() ? "static final field has no write access"
3587 : "final field has no write access";
3588 throw field.makeAccessException(msg, this);
3589 }
3590 }
3591 assert(isSetter
3592 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
3593 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
3594 @SuppressWarnings("deprecation")
3595 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
3596 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
3597 }
3598
3599 /**
3600 * Produces a VarHandle giving access to a reflected field {@code f}
3601 * of type {@code T} declared in a class of type {@code R}.
3602 * The VarHandle's variable type is {@code T}.
3603 * If the field is non-static the VarHandle has one coordinate type,
3604 * {@code R}. Otherwise, the field is static, and the VarHandle has no
3605 * coordinate types.
3606 * <p>
3607 * Access checking is performed immediately on behalf of the lookup
3608 * class, regardless of the value of the field's {@code accessible}
3609 * flag.
3610 * <p>
3611 * If the field is static, and if the returned VarHandle is operated
3612 * on, the field's declaring class will be initialized, if it has not
3613 * already been initialized.
3614 * <p>
3615 * Certain access modes of the returned VarHandle are unsupported under
3616 * the following conditions:
3617 * <ul>
3618 * <li>if the field is declared {@code final}, then the write, atomic
3619 * update, numeric atomic update, and bitwise atomic update access
3620 * modes are unsupported.
3621 * <li>if the field type is anything other than {@code byte},
3622 * {@code short}, {@code char}, {@code int}, {@code long},
3623 * {@code float}, or {@code double} then numeric atomic update
3624 * access modes are unsupported.
3625 * <li>if the field type is anything other than {@code boolean},
3626 * {@code byte}, {@code short}, {@code char}, {@code int} or
3627 * {@code long} then bitwise atomic update access modes are
3628 * unsupported.
3629 * </ul>
3630 * <p>
3631 * If the field is declared {@code volatile} then the returned VarHandle
3632 * will override access to the field (effectively ignore the
3633 * {@code volatile} declaration) in accordance to its specified
3634 * access modes.
3635 * <p>
3636 * If the field type is {@code float} or {@code double} then numeric
3637 * and atomic update access modes compare values using their bitwise
3638 * representation (see {@link Float#floatToRawIntBits} and
3639 * {@link Double#doubleToRawLongBits}, respectively).
3640 * @apiNote
3641 * Bitwise comparison of {@code float} values or {@code double} values,
3642 * as performed by the numeric and atomic update access modes, differ
3643 * from the primitive {@code ==} operator and the {@link Float#equals}
3644 * and {@link Double#equals} methods, specifically with respect to
3645 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3646 * Care should be taken when performing a compare and set or a compare
3647 * and exchange operation with such values since the operation may
3648 * unexpectedly fail.
3649 * There are many possible NaN values that are considered to be
3650 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3651 * provided by Java can distinguish between them. Operation failure can
3652 * occur if the expected or witness value is a NaN value and it is
3653 * transformed (perhaps in a platform specific manner) into another NaN
3654 * value, and thus has a different bitwise representation (see
3655 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3656 * details).
3657 * The values {@code -0.0} and {@code +0.0} have different bitwise
3658 * representations but are considered equal when using the primitive
3659 * {@code ==} operator. Operation failure can occur if, for example, a
3660 * numeric algorithm computes an expected value to be say {@code -0.0}
3661 * and previously computed the witness value to be say {@code +0.0}.
3662 * @param f the reflected field, with a field of type {@code T}, and
3663 * a declaring class of type {@code R}
3664 * @return a VarHandle giving access to non-static fields or a static
3665 * field
3666 * @throws IllegalAccessException if access checking fails
3667 * @throws NullPointerException if the argument is null
3668 * @since 9
3669 */
3670 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
3671 MemberName getField = new MemberName(f, false);
3672 MemberName putField = new MemberName(f, true);
3673 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
3674 f.getDeclaringClass(), getField, putField);
3675 }
3676
3677 /**
3678 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3679 * created by this lookup object or a similar one.
3680 * Security and access checks are performed to ensure that this lookup object
3681 * is capable of reproducing the target method handle.
3682 * This means that the cracking may fail if target is a direct method handle
3683 * but was created by an unrelated lookup object.
3684 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
3685 * and was created by a lookup object for a different class.
3686 * @param target a direct method handle to crack into symbolic reference components
3687 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
3688 * @throws SecurityException if a security manager is present and it
3689 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3690 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
3691 * @throws NullPointerException if the target is {@code null}
3692 * @see MethodHandleInfo
3693 * @since 1.8
3694 */
3695 public MethodHandleInfo revealDirect(MethodHandle target) {
3696 if (!target.isCrackable()) {
3697 throw newIllegalArgumentException("not a direct method handle");
3698 }
3699 MemberName member = target.internalMemberName();
3700 Class<?> defc = member.getDeclaringClass();
3701 byte refKind = member.getReferenceKind();
3702 assert(MethodHandleNatives.refKindIsValid(refKind));
3703 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
3704 // Devirtualized method invocation is usually formally virtual.
3705 // To avoid creating extra MemberName objects for this common case,
3706 // we encode this extra degree of freedom using MH.isInvokeSpecial.
3707 refKind = REF_invokeVirtual;
3708 if (refKind == REF_invokeVirtual && defc.isInterface())
3709 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
3710 refKind = REF_invokeInterface;
3711 // Check SM permissions and member access before cracking.
3712 try {
3713 checkAccess(refKind, defc, member);
3714 checkSecurityManager(defc, member);
3715 } catch (IllegalAccessException ex) {
3716 throw new IllegalArgumentException(ex);
3717 }
3718 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
3719 Class<?> callerClass = target.internalCallerClass();
3720 if ((lookupModes() & ORIGINAL) == 0 || callerClass != lookupClass())
3721 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
3722 }
3723 // Produce the handle to the results.
3724 return new InfoFromMemberName(this, member, refKind);
3725 }
3726
3727 //--- Helper methods, all package-private.
3728
3729 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3730 checkSymbolicClass(refc); // do this before attempting to resolve
3731 Objects.requireNonNull(name);
3732 Objects.requireNonNull(type);
3733 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3734 NoSuchFieldException.class);
3735 }
3736
3737 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3738 checkSymbolicClass(refc); // do this before attempting to resolve
3739 Objects.requireNonNull(type);
3740 checkMethodName(refKind, name); // implicit null-check of name
3741 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3742 NoSuchMethodException.class);
3743 }
3744
3745 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
3746 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
3747 Objects.requireNonNull(member.getName());
3748 Objects.requireNonNull(member.getType());
3749 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), allowedModes,
3750 ReflectiveOperationException.class);
3751 }
3752
3753 MemberName resolveOrNull(byte refKind, MemberName member) {
3754 // do this before attempting to resolve
3755 if (!isClassAccessible(member.getDeclaringClass())) {
3756 return null;
3757 }
3758 Objects.requireNonNull(member.getName());
3759 Objects.requireNonNull(member.getType());
3760 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull(), allowedModes);
3761 }
3762
3763 MemberName resolveOrNull(byte refKind, Class<?> refc, String name, MethodType type) {
3764 // do this before attempting to resolve
3765 if (!isClassAccessible(refc)) {
3766 return null;
3767 }
3768 Objects.requireNonNull(type);
3769 // implicit null-check of name
3770 if (name.startsWith("<") && refKind != REF_newInvokeSpecial) {
3771 return null;
3772 }
3773 return IMPL_NAMES.resolveOrNull(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes);
3774 }
3775
3776 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
3777 if (!isClassAccessible(refc)) {
3778 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
3779 }
3780 }
3781
3782 boolean isClassAccessible(Class<?> refc) {
3783 Objects.requireNonNull(refc);
3784 Class<?> caller = lookupClassOrNull();
3785 Class<?> type = refc;
3786 while (type.isArray()) {
3787 type = type.getComponentType();
3788 }
3789 return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes);
3790 }
3791
3792 /** Check name for an illegal leading "<" character. */
3793 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
3794 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
3795 throw new NoSuchMethodException("illegal method name: "+name);
3796 }
3797
3798 /**
3799 * Find my trustable caller class if m is a caller sensitive method.
3800 * If this lookup object has original full privilege access, then the caller class is the lookupClass.
3801 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
3802 */
3803 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException {
3804 if (MethodHandleNatives.isCallerSensitive(m) && (lookupModes() & ORIGINAL) == 0) {
3805 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods
3806 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3807 }
3808 return this;
3809 }
3810
3811 /**
3812 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3813 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3814 *
3815 * @deprecated This method was originally designed to test {@code PRIVATE} access
3816 * that implies full privilege access but {@code MODULE} access has since become
3817 * independent of {@code PRIVATE} access. It is recommended to call
3818 * {@link #hasFullPrivilegeAccess()} instead.
3819 * @since 9
3820 */
3821 @Deprecated(since="14")
3822 public boolean hasPrivateAccess() {
3823 return hasFullPrivilegeAccess();
3824 }
3825
3826 /**
3827 * Returns {@code true} if this lookup has <em>full privilege access</em>,
3828 * i.e. {@code PRIVATE} and {@code MODULE} access.
3829 * A {@code Lookup} object must have full privilege access in order to
3830 * access all members that are allowed to the
3831 * {@linkplain #lookupClass() lookup class}.
3832 *
3833 * @return {@code true} if this lookup has full privilege access.
3834 * @since 14
3835 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a>
3836 */
3837 public boolean hasFullPrivilegeAccess() {
3838 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE);
3839 }
3840
3841 /**
3842 * Perform steps 1 and 2b <a href="MethodHandles.Lookup.html#secmgr">access checks</a>
3843 * for ensureInitialized, findClass or accessClass.
3844 */
3845 void checkSecurityManager(Class<?> refc) {
3846 if (allowedModes == TRUSTED) return;
3847
3848 @SuppressWarnings("removal")
3849 SecurityManager smgr = System.getSecurityManager();
3850 if (smgr == null) return;
3851
3852 // Step 1:
3853 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3854 if (!fullPrivilegeLookup ||
3855 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3856 ReflectUtil.checkPackageAccess(refc);
3857 }
3858
3859 // Step 2b:
3860 if (!fullPrivilegeLookup) {
3861 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
3862 }
3863 }
3864
3865 /**
3866 * Perform steps 1, 2a and 3 <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
3867 * Determines a trustable caller class to compare with refc, the symbolic reference class.
3868 * If this lookup object has full privilege access except original access,
3869 * then the caller class is the lookupClass.
3870 *
3871 * Lookup object created by {@link MethodHandles#privateLookupIn(Class, Lookup)}
3872 * from the same module skips the security permission check.
3873 */
3874 void checkSecurityManager(Class<?> refc, MemberName m) {
3875 Objects.requireNonNull(refc);
3876 Objects.requireNonNull(m);
3877
3878 if (allowedModes == TRUSTED) return;
3879
3880 @SuppressWarnings("removal")
3881 SecurityManager smgr = System.getSecurityManager();
3882 if (smgr == null) return;
3883
3884 // Step 1:
3885 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3886 if (!fullPrivilegeLookup ||
3887 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3888 ReflectUtil.checkPackageAccess(refc);
3889 }
3890
3891 // Step 2a:
3892 if (m.isPublic()) return;
3893 if (!fullPrivilegeLookup) {
3894 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
3895 }
3896
3897 // Step 3:
3898 Class<?> defc = m.getDeclaringClass();
3899 if (!fullPrivilegeLookup && defc != refc) {
3900 ReflectUtil.checkPackageAccess(defc);
3901 }
3902 }
3903
3904 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3905 boolean wantStatic = (refKind == REF_invokeStatic);
3906 String message;
3907 if (m.isConstructor())
3908 message = "expected a method, not a constructor";
3909 else if (!m.isMethod())
3910 message = "expected a method";
3911 else if (wantStatic != m.isStatic())
3912 message = wantStatic ? "expected a static method" : "expected a non-static method";
3913 else
3914 { checkAccess(refKind, refc, m); return; }
3915 throw m.makeAccessException(message, this);
3916 }
3917
3918 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3919 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
3920 String message;
3921 if (wantStatic != m.isStatic())
3922 message = wantStatic ? "expected a static field" : "expected a non-static field";
3923 else
3924 { checkAccess(refKind, refc, m); return; }
3925 throw m.makeAccessException(message, this);
3926 }
3927
3928 private boolean isArrayClone(byte refKind, Class<?> refc, MemberName m) {
3929 return Modifier.isProtected(m.getModifiers()) &&
3930 refKind == REF_invokeVirtual &&
3931 m.getDeclaringClass() == Object.class &&
3932 m.getName().equals("clone") &&
3933 refc.isArray();
3934 }
3935
3936 /** Check public/protected/private bits on the symbolic reference class and its member. */
3937 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3938 assert(m.referenceKindIsConsistentWith(refKind) &&
3939 MethodHandleNatives.refKindIsValid(refKind) &&
3940 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
3941 int allowedModes = this.allowedModes;
3942 if (allowedModes == TRUSTED) return;
3943 int mods = m.getModifiers();
3944 if (isArrayClone(refKind, refc, m)) {
3945 // The JVM does this hack also.
3946 // (See ClassVerifier::verify_invoke_instructions
3947 // and LinkResolver::check_method_accessability.)
3948 // Because the JVM does not allow separate methods on array types,
3949 // there is no separate method for int[].clone.
3950 // All arrays simply inherit Object.clone.
3951 // But for access checking logic, we make Object.clone
3952 // (normally protected) appear to be public.
3953 // Later on, when the DirectMethodHandle is created,
3954 // its leading argument will be restricted to the
3955 // requested array type.
3956 // N.B. The return type is not adjusted, because
3957 // that is *not* the bytecode behavior.
3958 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
3959 }
3960 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
3961 // cannot "new" a protected ctor in a different package
3962 mods ^= Modifier.PROTECTED;
3963 }
3964 if (Modifier.isFinal(mods) &&
3965 MethodHandleNatives.refKindIsSetter(refKind))
3966 throw m.makeAccessException("unexpected set of a final field", this);
3967 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
3968 if ((requestedModes & allowedModes) != 0) {
3969 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
3970 mods, lookupClass(), previousLookupClass(), allowedModes))
3971 return;
3972 } else {
3973 // Protected members can also be checked as if they were package-private.
3974 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
3975 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
3976 return;
3977 }
3978 throw m.makeAccessException(accessFailedMessage(refc, m), this);
3979 }
3980
3981 String accessFailedMessage(Class<?> refc, MemberName m) {
3982 Class<?> defc = m.getDeclaringClass();
3983 int mods = m.getModifiers();
3984 // check the class first:
3985 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
3986 (defc == refc ||
3987 Modifier.isPublic(refc.getModifiers())));
3988 if (!classOK && (allowedModes & PACKAGE) != 0) {
3989 // ignore previous lookup class to check if default package access
3990 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
3991 (defc == refc ||
3992 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
3993 }
3994 if (!classOK)
3995 return "class is not public";
3996 if (Modifier.isPublic(mods))
3997 return "access to public member failed"; // (how?, module not readable?)
3998 if (Modifier.isPrivate(mods))
3999 return "member is private";
4000 if (Modifier.isProtected(mods))
4001 return "member is protected";
4002 return "member is private to package";
4003 }
4004
4005 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
4006 int allowedModes = this.allowedModes;
4007 if (allowedModes == TRUSTED) return;
4008 if ((lookupModes() & PRIVATE) == 0
4009 || (specialCaller != lookupClass()
4010 // ensure non-abstract methods in superinterfaces can be special-invoked
4011 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
4012 throw new MemberName(specialCaller).
4013 makeAccessException("no private access for invokespecial", this);
4014 }
4015
4016 private boolean restrictProtectedReceiver(MemberName method) {
4017 // The accessing class only has the right to use a protected member
4018 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
4019 if (!method.isProtected() || method.isStatic()
4020 || allowedModes == TRUSTED
4021 || method.getDeclaringClass() == lookupClass()
4022 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
4023 return false;
4024 return true;
4025 }
4026 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
4027 assert(!method.isStatic());
4028 // receiver type of mh is too wide; narrow to caller
4029 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
4030 throw method.makeAccessException("caller class must be a subclass below the method", caller);
4031 }
4032 MethodType rawType = mh.type();
4033 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
4034 MethodType narrowType = rawType.changeParameterType(0, caller);
4035 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
4036 assert(mh.viewAsTypeChecks(narrowType, true));
4037 return mh.copyWith(narrowType, mh.form);
4038 }
4039
4040 /** Check access and get the requested method. */
4041 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4042 final boolean doRestrict = true;
4043 final boolean checkSecurity = true;
4044 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4045 }
4046 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
4047 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4048 final boolean doRestrict = false;
4049 final boolean checkSecurity = true;
4050 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerLookup);
4051 }
4052 /** Check access and get the requested method, eliding security manager checks. */
4053 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4054 final boolean doRestrict = true;
4055 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4056 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4057 }
4058 /** Common code for all methods; do not call directly except from immediately above. */
4059 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
4060 boolean checkSecurity,
4061 boolean doRestrict,
4062 Lookup boundCaller) throws IllegalAccessException {
4063 checkMethod(refKind, refc, method);
4064 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4065 if (checkSecurity)
4066 checkSecurityManager(refc, method);
4067 assert(!method.isMethodHandleInvoke());
4068
4069 if (refKind == REF_invokeSpecial &&
4070 refc != lookupClass() &&
4071 !refc.isInterface() && !lookupClass().isInterface() &&
4072 refc != lookupClass().getSuperclass() &&
4073 refc.isAssignableFrom(lookupClass())) {
4074 assert(!method.getName().equals(ConstantDescs.INIT_NAME)); // not this code path
4075
4076 // Per JVMS 6.5, desc. of invokespecial instruction:
4077 // If the method is in a superclass of the LC,
4078 // and if our original search was above LC.super,
4079 // repeat the search (symbolic lookup) from LC.super
4080 // and continue with the direct superclass of that class,
4081 // and so forth, until a match is found or no further superclasses exist.
4082 // FIXME: MemberName.resolve should handle this instead.
4083 Class<?> refcAsSuper = lookupClass();
4084 MemberName m2;
4085 do {
4086 refcAsSuper = refcAsSuper.getSuperclass();
4087 m2 = new MemberName(refcAsSuper,
4088 method.getName(),
4089 method.getMethodType(),
4090 REF_invokeSpecial);
4091 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull(), allowedModes);
4092 } while (m2 == null && // no method is found yet
4093 refc != refcAsSuper); // search up to refc
4094 if (m2 == null) throw new InternalError(method.toString());
4095 method = m2;
4096 refc = refcAsSuper;
4097 // redo basic checks
4098 checkMethod(refKind, refc, method);
4099 }
4100 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
4101 MethodHandle mh = dmh;
4102 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
4103 if ((doRestrict && refKind == REF_invokeSpecial) ||
4104 (MethodHandleNatives.refKindHasReceiver(refKind) &&
4105 restrictProtectedReceiver(method) &&
4106 // All arrays simply inherit the protected Object.clone method.
4107 // The leading argument is already restricted to the requested
4108 // array type (not the lookup class).
4109 !isArrayClone(refKind, refc, method))) {
4110 mh = restrictReceiver(method, dmh, lookupClass());
4111 }
4112 mh = maybeBindCaller(method, mh, boundCaller);
4113 mh = mh.setVarargs(method);
4114 return mh;
4115 }
4116 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller)
4117 throws IllegalAccessException {
4118 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
4119 return mh;
4120
4121 // boundCaller must have full privilege access.
4122 // It should have been checked by findBoundCallerLookup. Safe to check this again.
4123 if ((boundCaller.lookupModes() & ORIGINAL) == 0)
4124 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
4125
4126 assert boundCaller.hasFullPrivilegeAccess();
4127
4128 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass);
4129 // Note: caller will apply varargs after this step happens.
4130 return cbmh;
4131 }
4132
4133 /** Check access and get the requested field. */
4134 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4135 final boolean checkSecurity = true;
4136 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4137 }
4138 /** Check access and get the requested field, eliding security manager checks. */
4139 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4140 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4141 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4142 }
4143 /** Common code for all fields; do not call directly except from immediately above. */
4144 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
4145 boolean checkSecurity) throws IllegalAccessException {
4146 checkField(refKind, refc, field);
4147 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4148 if (checkSecurity)
4149 checkSecurityManager(refc, field);
4150 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
4151 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
4152 restrictProtectedReceiver(field));
4153 if (doRestrict)
4154 return restrictReceiver(field, dmh, lookupClass());
4155 return dmh;
4156 }
4157 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
4158 Class<?> refc, MemberName getField, MemberName putField)
4159 throws IllegalAccessException {
4160 final boolean checkSecurity = true;
4161 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4162 }
4163 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
4164 Class<?> refc, MemberName getField, MemberName putField)
4165 throws IllegalAccessException {
4166 final boolean checkSecurity = false;
4167 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4168 }
4169 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
4170 Class<?> refc, MemberName getField, MemberName putField,
4171 boolean checkSecurity) throws IllegalAccessException {
4172 assert getField.isStatic() == putField.isStatic();
4173 assert getField.isGetter() && putField.isSetter();
4174 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
4175 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
4176
4177 checkField(getRefKind, refc, getField);
4178 if (checkSecurity)
4179 checkSecurityManager(refc, getField);
4180
4181 if (!putField.isFinal()) {
4182 // A VarHandle does not support updates to final fields, any
4183 // such VarHandle to a final field will be read-only and
4184 // therefore the following write-based accessibility checks are
4185 // only required for non-final fields
4186 checkField(putRefKind, refc, putField);
4187 if (checkSecurity)
4188 checkSecurityManager(refc, putField);
4189 }
4190
4191 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
4192 restrictProtectedReceiver(getField));
4193 if (doRestrict) {
4194 assert !getField.isStatic();
4195 // receiver type of VarHandle is too wide; narrow to caller
4196 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
4197 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
4198 }
4199 refc = lookupClass();
4200 }
4201 return VarHandles.makeFieldHandle(getField, refc,
4202 this.allowedModes == TRUSTED && !getField.isTrustedFinalField());
4203 }
4204 /** Check access and get the requested constructor. */
4205 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4206 final boolean checkSecurity = true;
4207 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4208 }
4209 /** Check access and get the requested constructor, eliding security manager checks. */
4210 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4211 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4212 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4213 }
4214 /** Common code for all constructors; do not call directly except from immediately above. */
4215 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
4216 boolean checkSecurity) throws IllegalAccessException {
4217 assert(ctor.isConstructor());
4218 checkAccess(REF_newInvokeSpecial, refc, ctor);
4219 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4220 if (checkSecurity)
4221 checkSecurityManager(refc, ctor);
4222 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
4223 return DirectMethodHandle.make(ctor).setVarargs(ctor);
4224 }
4225
4226 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
4227 */
4228 /*non-public*/
4229 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
4230 throws ReflectiveOperationException {
4231 if (!(type instanceof Class || type instanceof MethodType))
4232 throw new InternalError("unresolved MemberName");
4233 MemberName member = new MemberName(refKind, defc, name, type);
4234 MethodHandle mh = LOOKASIDE_TABLE.get(member);
4235 if (mh != null) {
4236 checkSymbolicClass(defc);
4237 return mh;
4238 }
4239 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
4240 // Treat MethodHandle.invoke and invokeExact specially.
4241 mh = findVirtualForMH(member.getName(), member.getMethodType());
4242 if (mh != null) {
4243 return mh;
4244 }
4245 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
4246 // Treat signature-polymorphic methods on VarHandle specially.
4247 mh = findVirtualForVH(member.getName(), member.getMethodType());
4248 if (mh != null) {
4249 return mh;
4250 }
4251 }
4252 MemberName resolved = resolveOrFail(refKind, member);
4253 mh = getDirectMethodForConstant(refKind, defc, resolved);
4254 if (mh instanceof DirectMethodHandle dmh
4255 && canBeCached(refKind, defc, resolved)) {
4256 MemberName key = mh.internalMemberName();
4257 if (key != null) {
4258 key = key.asNormalOriginal();
4259 }
4260 if (member.equals(key)) { // better safe than sorry
4261 LOOKASIDE_TABLE.put(key, dmh);
4262 }
4263 }
4264 return mh;
4265 }
4266 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
4267 if (refKind == REF_invokeSpecial) {
4268 return false;
4269 }
4270 if (!Modifier.isPublic(defc.getModifiers()) ||
4271 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
4272 !member.isPublic() ||
4273 member.isCallerSensitive()) {
4274 return false;
4275 }
4276 ClassLoader loader = defc.getClassLoader();
4277 if (loader != null) {
4278 ClassLoader sysl = ClassLoader.getSystemClassLoader();
4279 boolean found = false;
4280 while (sysl != null) {
4281 if (loader == sysl) { found = true; break; }
4282 sysl = sysl.getParent();
4283 }
4284 if (!found) {
4285 return false;
4286 }
4287 }
4288 try {
4289 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
4290 new MemberName(refKind, defc, member.getName(), member.getType()));
4291 if (resolved2 == null) {
4292 return false;
4293 }
4294 checkSecurityManager(defc, resolved2);
4295 } catch (SecurityException ex) {
4296 return false;
4297 }
4298 return true;
4299 }
4300 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
4301 throws ReflectiveOperationException {
4302 if (MethodHandleNatives.refKindIsField(refKind)) {
4303 return getDirectFieldNoSecurityManager(refKind, defc, member);
4304 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
4305 return getDirectMethodNoSecurityManager(refKind, defc, member, findBoundCallerLookup(member));
4306 } else if (refKind == REF_newInvokeSpecial) {
4307 return getDirectConstructorNoSecurityManager(defc, member);
4308 }
4309 // oops
4310 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
4311 }
4312
4313 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
4314 }
4315
4316 /**
4317 * Produces a method handle constructing arrays of a desired type,
4318 * as if by the {@code anewarray} bytecode.
4319 * The return type of the method handle will be the array type.
4320 * The type of its sole argument will be {@code int}, which specifies the size of the array.
4321 *
4322 * <p> If the returned method handle is invoked with a negative
4323 * array size, a {@code NegativeArraySizeException} will be thrown.
4324 *
4325 * @param arrayClass an array type
4326 * @return a method handle which can create arrays of the given type
4327 * @throws NullPointerException if the argument is {@code null}
4328 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
4329 * @see java.lang.reflect.Array#newInstance(Class, int)
4330 * @jvms 6.5 {@code anewarray} Instruction
4331 * @since 9
4332 */
4333 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
4334 if (!arrayClass.isArray()) {
4335 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
4336 }
4337 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
4338 bindTo(arrayClass.getComponentType());
4339 return ani.asType(ani.type().changeReturnType(arrayClass));
4340 }
4341
4342 /**
4343 * Produces a method handle returning the length of an array,
4344 * as if by the {@code arraylength} bytecode.
4345 * The type of the method handle will have {@code int} as return type,
4346 * and its sole argument will be the array type.
4347 *
4348 * <p> If the returned method handle is invoked with a {@code null}
4349 * array reference, a {@code NullPointerException} will be thrown.
4350 *
4351 * @param arrayClass an array type
4352 * @return a method handle which can retrieve the length of an array of the given array type
4353 * @throws NullPointerException if the argument is {@code null}
4354 * @throws IllegalArgumentException if arrayClass is not an array type
4355 * @jvms 6.5 {@code arraylength} Instruction
4356 * @since 9
4357 */
4358 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
4359 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
4360 }
4361
4362 /**
4363 * Produces a method handle giving read access to elements of an array,
4364 * as if by the {@code aaload} bytecode.
4365 * The type of the method handle will have a return type of the array's
4366 * element type. Its first argument will be the array type,
4367 * and the second will be {@code int}.
4368 *
4369 * <p> When the returned method handle is invoked,
4370 * the array reference and array index are checked.
4371 * A {@code NullPointerException} will be thrown if the array reference
4372 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4373 * thrown if the index is negative or if it is greater than or equal to
4374 * the length of the array.
4375 *
4376 * @param arrayClass an array type
4377 * @return a method handle which can load values from the given array type
4378 * @throws NullPointerException if the argument is null
4379 * @throws IllegalArgumentException if arrayClass is not an array type
4380 * @jvms 6.5 {@code aaload} Instruction
4381 */
4382 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
4383 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
4384 }
4385
4386 /**
4387 * Produces a method handle giving write access to elements of an array,
4388 * as if by the {@code astore} bytecode.
4389 * The type of the method handle will have a void return type.
4390 * Its last argument will be the array's element type.
4391 * The first and second arguments will be the array type and int.
4392 *
4393 * <p> When the returned method handle is invoked,
4394 * the array reference and array index are checked.
4395 * A {@code NullPointerException} will be thrown if the array reference
4396 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4397 * thrown if the index is negative or if it is greater than or equal to
4398 * the length of the array.
4399 *
4400 * @param arrayClass the class of an array
4401 * @return a method handle which can store values into the array type
4402 * @throws NullPointerException if the argument is null
4403 * @throws IllegalArgumentException if arrayClass is not an array type
4404 * @jvms 6.5 {@code aastore} Instruction
4405 */
4406 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
4407 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
4408 }
4409
4410 /**
4411 * Produces a VarHandle giving access to elements of an array of type
4412 * {@code arrayClass}. The VarHandle's variable type is the component type
4413 * of {@code arrayClass} and the list of coordinate types is
4414 * {@code (arrayClass, int)}, where the {@code int} coordinate type
4415 * corresponds to an argument that is an index into an array.
4416 * <p>
4417 * Certain access modes of the returned VarHandle are unsupported under
4418 * the following conditions:
4419 * <ul>
4420 * <li>if the component type is anything other than {@code byte},
4421 * {@code short}, {@code char}, {@code int}, {@code long},
4422 * {@code float}, or {@code double} then numeric atomic update access
4423 * modes are unsupported.
4424 * <li>if the component type is anything other than {@code boolean},
4425 * {@code byte}, {@code short}, {@code char}, {@code int} or
4426 * {@code long} then bitwise atomic update access modes are
4427 * unsupported.
4428 * </ul>
4429 * <p>
4430 * If the component type is {@code float} or {@code double} then numeric
4431 * and atomic update access modes compare values using their bitwise
4432 * representation (see {@link Float#floatToRawIntBits} and
4433 * {@link Double#doubleToRawLongBits}, respectively).
4434 *
4435 * <p> When the returned {@code VarHandle} is invoked,
4436 * the array reference and array index are checked.
4437 * A {@code NullPointerException} will be thrown if the array reference
4438 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4439 * thrown if the index is negative or if it is greater than or equal to
4440 * the length of the array.
4441 *
4442 * @apiNote
4443 * Bitwise comparison of {@code float} values or {@code double} values,
4444 * as performed by the numeric and atomic update access modes, differ
4445 * from the primitive {@code ==} operator and the {@link Float#equals}
4446 * and {@link Double#equals} methods, specifically with respect to
4447 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
4448 * Care should be taken when performing a compare and set or a compare
4449 * and exchange operation with such values since the operation may
4450 * unexpectedly fail.
4451 * There are many possible NaN values that are considered to be
4452 * {@code NaN} in Java, although no IEEE 754 floating-point operation
4453 * provided by Java can distinguish between them. Operation failure can
4454 * occur if the expected or witness value is a NaN value and it is
4455 * transformed (perhaps in a platform specific manner) into another NaN
4456 * value, and thus has a different bitwise representation (see
4457 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
4458 * details).
4459 * The values {@code -0.0} and {@code +0.0} have different bitwise
4460 * representations but are considered equal when using the primitive
4461 * {@code ==} operator. Operation failure can occur if, for example, a
4462 * numeric algorithm computes an expected value to be say {@code -0.0}
4463 * and previously computed the witness value to be say {@code +0.0}.
4464 * @param arrayClass the class of an array, of type {@code T[]}
4465 * @return a VarHandle giving access to elements of an array
4466 * @throws NullPointerException if the arrayClass is null
4467 * @throws IllegalArgumentException if arrayClass is not an array type
4468 * @since 9
4469 */
4470 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
4471 return VarHandles.makeArrayElementHandle(arrayClass);
4472 }
4473
4474 /**
4475 * Produces a VarHandle giving access to elements of a {@code byte[]} array
4476 * viewed as if it were a different primitive array type, such as
4477 * {@code int[]} or {@code long[]}.
4478 * The VarHandle's variable type is the component type of
4479 * {@code viewArrayClass} and the list of coordinate types is
4480 * {@code (byte[], int)}, where the {@code int} coordinate type
4481 * corresponds to an argument that is an index into a {@code byte[]} array.
4482 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
4483 * array, composing bytes to or from a value of the component type of
4484 * {@code viewArrayClass} according to the given endianness.
4485 * <p>
4486 * The supported component types (variables types) are {@code short},
4487 * {@code char}, {@code int}, {@code long}, {@code float} and
4488 * {@code double}.
4489 * <p>
4490 * Access of bytes at a given index will result in an
4491 * {@code ArrayIndexOutOfBoundsException} if the index is less than {@code 0}
4492 * or greater than the {@code byte[]} array length minus the size (in bytes)
4493 * of {@code T}.
4494 * <p>
4495 * Only plain {@linkplain VarHandle.AccessMode#GET get} and {@linkplain VarHandle.AccessMode#SET set}
4496 * access modes are supported by the returned var handle. For all other access modes, an
4497 * {@link UnsupportedOperationException} will be thrown.
4498 *
4499 * @apiNote if access modes other than plain access are required, clients should
4500 * consider using off-heap memory through
4501 * {@linkplain java.nio.ByteBuffer#allocateDirect(int) direct byte buffers} or
4502 * off-heap {@linkplain java.lang.foreign.MemorySegment memory segments},
4503 * or memory segments backed by a
4504 * {@linkplain java.lang.foreign.MemorySegment#ofArray(long[]) {@code long[]}},
4505 * for which stronger alignment guarantees can be made.
4506 *
4507 * @param viewArrayClass the view array class, with a component type of
4508 * type {@code T}
4509 * @param byteOrder the endianness of the view array elements, as
4510 * stored in the underlying {@code byte} array
4511 * @return a VarHandle giving access to elements of a {@code byte[]} array
4512 * viewed as if elements corresponding to the components type of the view
4513 * array class
4514 * @throws NullPointerException if viewArrayClass or byteOrder is null
4515 * @throws IllegalArgumentException if viewArrayClass is not an array type
4516 * @throws UnsupportedOperationException if the component type of
4517 * viewArrayClass is not supported as a variable type
4518 * @since 9
4519 */
4520 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
4521 ByteOrder byteOrder) throws IllegalArgumentException {
4522 Objects.requireNonNull(byteOrder);
4523 return VarHandles.byteArrayViewHandle(viewArrayClass,
4524 byteOrder == ByteOrder.BIG_ENDIAN);
4525 }
4526
4527 /**
4528 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
4529 * viewed as if it were an array of elements of a different primitive
4530 * component type to that of {@code byte}, such as {@code int[]} or
4531 * {@code long[]}.
4532 * The VarHandle's variable type is the component type of
4533 * {@code viewArrayClass} and the list of coordinate types is
4534 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
4535 * corresponds to an argument that is an index into a {@code byte[]} array.
4536 * The returned VarHandle accesses bytes at an index in a
4537 * {@code ByteBuffer}, composing bytes to or from a value of the component
4538 * type of {@code viewArrayClass} according to the given endianness.
4539 * <p>
4540 * The supported component types (variables types) are {@code short},
4541 * {@code char}, {@code int}, {@code long}, {@code float} and
4542 * {@code double}.
4543 * <p>
4544 * Access will result in a {@code ReadOnlyBufferException} for anything
4545 * other than the read access modes if the {@code ByteBuffer} is read-only.
4546 * <p>
4547 * Access of bytes at a given index will result in an
4548 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
4549 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
4550 * {@code T}.
4551 * <p>
4552 * For heap byte buffers, access is always unaligned. As a result, only the plain
4553 * {@linkplain VarHandle.AccessMode#GET get}
4554 * and {@linkplain VarHandle.AccessMode#SET set} access modes are supported by the
4555 * returned var handle. For all other access modes, an {@link IllegalStateException}
4556 * will be thrown.
4557 * <p>
4558 * For direct buffers only, access of bytes at an index may be aligned or misaligned for {@code T},
4559 * with respect to the underlying memory address, {@code A} say, associated
4560 * with the {@code ByteBuffer} and index.
4561 * If access is misaligned then access for anything other than the
4562 * {@code get} and {@code set} access modes will result in an
4563 * {@code IllegalStateException}. In such cases atomic access is only
4564 * guaranteed with respect to the largest power of two that divides the GCD
4565 * of {@code A} and the size (in bytes) of {@code T}.
4566 * If access is aligned then following access modes are supported and are
4567 * guaranteed to support atomic access:
4568 * <ul>
4569 * <li>read write access modes for all {@code T}, with the exception of
4570 * access modes {@code get} and {@code set} for {@code long} and
4571 * {@code double} on 32-bit platforms.
4572 * <li>atomic update access modes for {@code int}, {@code long},
4573 * {@code float} or {@code double}.
4574 * (Future major platform releases of the JDK may support additional
4575 * types for certain currently unsupported access modes.)
4576 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4577 * (Future major platform releases of the JDK may support additional
4578 * numeric types for certain currently unsupported access modes.)
4579 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4580 * (Future major platform releases of the JDK may support additional
4581 * numeric types for certain currently unsupported access modes.)
4582 * </ul>
4583 * <p>
4584 * Misaligned access, and therefore atomicity guarantees, may be determined
4585 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
4586 * {@code index}, {@code T} and its corresponding boxed type,
4587 * {@code T_BOX}, as follows:
4588 * <pre>{@code
4589 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4590 * ByteBuffer bb = ...
4591 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
4592 * boolean isMisaligned = misalignedAtIndex != 0;
4593 * }</pre>
4594 * <p>
4595 * If the variable type is {@code float} or {@code double} then atomic
4596 * update access modes compare values using their bitwise representation
4597 * (see {@link Float#floatToRawIntBits} and
4598 * {@link Double#doubleToRawLongBits}, respectively).
4599 * @param viewArrayClass the view array class, with a component type of
4600 * type {@code T}
4601 * @param byteOrder the endianness of the view array elements, as
4602 * stored in the underlying {@code ByteBuffer} (Note this overrides the
4603 * endianness of a {@code ByteBuffer})
4604 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
4605 * viewed as if elements corresponding to the components type of the view
4606 * array class
4607 * @throws NullPointerException if viewArrayClass or byteOrder is null
4608 * @throws IllegalArgumentException if viewArrayClass is not an array type
4609 * @throws UnsupportedOperationException if the component type of
4610 * viewArrayClass is not supported as a variable type
4611 * @since 9
4612 */
4613 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
4614 ByteOrder byteOrder) throws IllegalArgumentException {
4615 Objects.requireNonNull(byteOrder);
4616 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
4617 byteOrder == ByteOrder.BIG_ENDIAN);
4618 }
4619
4620
4621 //--- method handle invocation (reflective style)
4622
4623 /**
4624 * Produces a method handle which will invoke any method handle of the
4625 * given {@code type}, with a given number of trailing arguments replaced by
4626 * a single trailing {@code Object[]} array.
4627 * The resulting invoker will be a method handle with the following
4628 * arguments:
4629 * <ul>
4630 * <li>a single {@code MethodHandle} target
4631 * <li>zero or more leading values (counted by {@code leadingArgCount})
4632 * <li>an {@code Object[]} array containing trailing arguments
4633 * </ul>
4634 * <p>
4635 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
4636 * the indicated {@code type}.
4637 * That is, if the target is exactly of the given {@code type}, it will behave
4638 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
4639 * is used to convert the target to the required {@code type}.
4640 * <p>
4641 * The type of the returned invoker will not be the given {@code type}, but rather
4642 * will have all parameters except the first {@code leadingArgCount}
4643 * replaced by a single array of type {@code Object[]}, which will be
4644 * the final parameter.
4645 * <p>
4646 * Before invoking its target, the invoker will spread the final array, apply
4647 * reference casts as necessary, and unbox and widen primitive arguments.
4648 * If, when the invoker is called, the supplied array argument does
4649 * not have the correct number of elements, the invoker will throw
4650 * an {@link IllegalArgumentException} instead of invoking the target.
4651 * <p>
4652 * This method is equivalent to the following code (though it may be more efficient):
4653 * {@snippet lang="java" :
4654 MethodHandle invoker = MethodHandles.invoker(type);
4655 int spreadArgCount = type.parameterCount() - leadingArgCount;
4656 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
4657 return invoker;
4658 * }
4659 * This method throws no reflective or security exceptions.
4660 * @param type the desired target type
4661 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
4662 * @return a method handle suitable for invoking any method handle of the given type
4663 * @throws NullPointerException if {@code type} is null
4664 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
4665 * the range from 0 to {@code type.parameterCount()} inclusive,
4666 * or if the resulting method handle's type would have
4667 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4668 */
4669 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
4670 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
4671 throw newIllegalArgumentException("bad argument count", leadingArgCount);
4672 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
4673 return type.invokers().spreadInvoker(leadingArgCount);
4674 }
4675
4676 /**
4677 * Produces a special <em>invoker method handle</em> which can be used to
4678 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
4679 * The resulting invoker will have a type which is
4680 * exactly equal to the desired type, except that it will accept
4681 * an additional leading argument of type {@code MethodHandle}.
4682 * <p>
4683 * This method is equivalent to the following code (though it may be more efficient):
4684 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
4685 *
4686 * <p style="font-size:smaller;">
4687 * <em>Discussion:</em>
4688 * Invoker method handles can be useful when working with variable method handles
4689 * of unknown types.
4690 * For example, to emulate an {@code invokeExact} call to a variable method
4691 * handle {@code M}, extract its type {@code T},
4692 * look up the invoker method {@code X} for {@code T},
4693 * and call the invoker method, as {@code X.invoke(T, A...)}.
4694 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
4695 * is unknown.)
4696 * If spreading, collecting, or other argument transformations are required,
4697 * they can be applied once to the invoker {@code X} and reused on many {@code M}
4698 * method handle values, as long as they are compatible with the type of {@code X}.
4699 * <p style="font-size:smaller;">
4700 * <em>(Note: The invoker method is not available via the Core Reflection API.
4701 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4702 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4703 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4704 * <p>
4705 * This method throws no reflective or security exceptions.
4706 * @param type the desired target type
4707 * @return a method handle suitable for invoking any method handle of the given type
4708 * @throws IllegalArgumentException if the resulting method handle's type would have
4709 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4710 */
4711 public static MethodHandle exactInvoker(MethodType type) {
4712 return type.invokers().exactInvoker();
4713 }
4714
4715 /**
4716 * Produces a special <em>invoker method handle</em> which can be used to
4717 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
4718 * The resulting invoker will have a type which is
4719 * exactly equal to the desired type, except that it will accept
4720 * an additional leading argument of type {@code MethodHandle}.
4721 * <p>
4722 * Before invoking its target, if the target differs from the expected type,
4723 * the invoker will apply reference casts as
4724 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
4725 * Similarly, the return value will be converted as necessary.
4726 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
4727 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
4728 * <p>
4729 * This method is equivalent to the following code (though it may be more efficient):
4730 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
4731 * <p style="font-size:smaller;">
4732 * <em>Discussion:</em>
4733 * A {@linkplain MethodType#genericMethodType general method type} is one which
4734 * mentions only {@code Object} arguments and return values.
4735 * An invoker for such a type is capable of calling any method handle
4736 * of the same arity as the general type.
4737 * <p style="font-size:smaller;">
4738 * <em>(Note: The invoker method is not available via the Core Reflection API.
4739 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4740 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4741 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4742 * <p>
4743 * This method throws no reflective or security exceptions.
4744 * @param type the desired target type
4745 * @return a method handle suitable for invoking any method handle convertible to the given type
4746 * @throws IllegalArgumentException if the resulting method handle's type would have
4747 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4748 */
4749 public static MethodHandle invoker(MethodType type) {
4750 return type.invokers().genericInvoker();
4751 }
4752
4753 /**
4754 * Produces a special <em>invoker method handle</em> which can be used to
4755 * invoke a signature-polymorphic access mode method on any VarHandle whose
4756 * associated access mode type is compatible with the given type.
4757 * The resulting invoker will have a type which is exactly equal to the
4758 * desired given type, except that it will accept an additional leading
4759 * argument of type {@code VarHandle}.
4760 *
4761 * @param accessMode the VarHandle access mode
4762 * @param type the desired target type
4763 * @return a method handle suitable for invoking an access mode method of
4764 * any VarHandle whose access mode type is of the given type.
4765 * @since 9
4766 */
4767 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4768 return type.invokers().varHandleMethodExactInvoker(accessMode);
4769 }
4770
4771 /**
4772 * Produces a special <em>invoker method handle</em> which can be used to
4773 * invoke a signature-polymorphic access mode method on any VarHandle whose
4774 * associated access mode type is compatible with the given type.
4775 * The resulting invoker will have a type which is exactly equal to the
4776 * desired given type, except that it will accept an additional leading
4777 * argument of type {@code VarHandle}.
4778 * <p>
4779 * Before invoking its target, if the access mode type differs from the
4780 * desired given type, the invoker will apply reference casts as necessary
4781 * and box, unbox, or widen primitive values, as if by
4782 * {@link MethodHandle#asType asType}. Similarly, the return value will be
4783 * converted as necessary.
4784 * <p>
4785 * This method is equivalent to the following code (though it may be more
4786 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
4787 *
4788 * @param accessMode the VarHandle access mode
4789 * @param type the desired target type
4790 * @return a method handle suitable for invoking an access mode method of
4791 * any VarHandle whose access mode type is convertible to the given
4792 * type.
4793 * @since 9
4794 */
4795 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4796 return type.invokers().varHandleMethodInvoker(accessMode);
4797 }
4798
4799 /*non-public*/
4800 static MethodHandle basicInvoker(MethodType type) {
4801 return type.invokers().basicInvoker();
4802 }
4803
4804 //--- method handle modification (creation from other method handles)
4805
4806 /**
4807 * Produces a method handle which adapts the type of the
4808 * given method handle to a new type by pairwise argument and return type conversion.
4809 * The original type and new type must have the same number of arguments.
4810 * The resulting method handle is guaranteed to report a type
4811 * which is equal to the desired new type.
4812 * <p>
4813 * If the original type and new type are equal, returns target.
4814 * <p>
4815 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
4816 * and some additional conversions are also applied if those conversions fail.
4817 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
4818 * if possible, before or instead of any conversions done by {@code asType}:
4819 * <ul>
4820 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
4821 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
4822 * (This treatment of interfaces follows the usage of the bytecode verifier.)
4823 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
4824 * the boolean is converted to a byte value, 1 for true, 0 for false.
4825 * (This treatment follows the usage of the bytecode verifier.)
4826 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
4827 * <em>T0</em> is converted to byte via Java casting conversion (JLS {@jls 5.5}),
4828 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
4829 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
4830 * then a Java casting conversion (JLS {@jls 5.5}) is applied.
4831 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
4832 * widening and/or narrowing.)
4833 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
4834 * conversion will be applied at runtime, possibly followed
4835 * by a Java casting conversion (JLS {@jls 5.5}) on the primitive value,
4836 * possibly followed by a conversion from byte to boolean by testing
4837 * the low-order bit.
4838 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
4839 * and if the reference is null at runtime, a zero value is introduced.
4840 * </ul>
4841 * @param target the method handle to invoke after arguments are retyped
4842 * @param newType the expected type of the new method handle
4843 * @return a method handle which delegates to the target after performing
4844 * any necessary argument conversions, and arranges for any
4845 * necessary return value conversions
4846 * @throws NullPointerException if either argument is null
4847 * @throws WrongMethodTypeException if the conversion cannot be made
4848 * @see MethodHandle#asType
4849 */
4850 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
4851 explicitCastArgumentsChecks(target, newType);
4852 // use the asTypeCache when possible:
4853 MethodType oldType = target.type();
4854 if (oldType == newType) return target;
4855 if (oldType.explicitCastEquivalentToAsType(newType)) {
4856 return target.asFixedArity().asType(newType);
4857 }
4858 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
4859 }
4860
4861 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
4862 if (target.type().parameterCount() != newType.parameterCount()) {
4863 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
4864 }
4865 }
4866
4867 /**
4868 * Produces a method handle which adapts the calling sequence of the
4869 * given method handle to a new type, by reordering the arguments.
4870 * The resulting method handle is guaranteed to report a type
4871 * which is equal to the desired new type.
4872 * <p>
4873 * The given array controls the reordering.
4874 * Call {@code #I} the number of incoming parameters (the value
4875 * {@code newType.parameterCount()}, and call {@code #O} the number
4876 * of outgoing parameters (the value {@code target.type().parameterCount()}).
4877 * Then the length of the reordering array must be {@code #O},
4878 * and each element must be a non-negative number less than {@code #I}.
4879 * For every {@code N} less than {@code #O}, the {@code N}-th
4880 * outgoing argument will be taken from the {@code I}-th incoming
4881 * argument, where {@code I} is {@code reorder[N]}.
4882 * <p>
4883 * No argument or return value conversions are applied.
4884 * The type of each incoming argument, as determined by {@code newType},
4885 * must be identical to the type of the corresponding outgoing parameter
4886 * or parameters in the target method handle.
4887 * The return type of {@code newType} must be identical to the return
4888 * type of the original target.
4889 * <p>
4890 * The reordering array need not specify an actual permutation.
4891 * An incoming argument will be duplicated if its index appears
4892 * more than once in the array, and an incoming argument will be dropped
4893 * if its index does not appear in the array.
4894 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
4895 * incoming arguments which are not mentioned in the reordering array
4896 * may be of any type, as determined only by {@code newType}.
4897 * {@snippet lang="java" :
4898 import static java.lang.invoke.MethodHandles.*;
4899 import static java.lang.invoke.MethodType.*;
4900 ...
4901 MethodType intfn1 = methodType(int.class, int.class);
4902 MethodType intfn2 = methodType(int.class, int.class, int.class);
4903 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
4904 assert(sub.type().equals(intfn2));
4905 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
4906 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
4907 assert((int)rsub.invokeExact(1, 100) == 99);
4908 MethodHandle add = ... (int x, int y) -> (x+y) ...;
4909 assert(add.type().equals(intfn2));
4910 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
4911 assert(twice.type().equals(intfn1));
4912 assert((int)twice.invokeExact(21) == 42);
4913 * }
4914 * <p>
4915 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4916 * variable-arity method handle}, even if the original target method handle was.
4917 * @param target the method handle to invoke after arguments are reordered
4918 * @param newType the expected type of the new method handle
4919 * @param reorder an index array which controls the reordering
4920 * @return a method handle which delegates to the target after it
4921 * drops unused arguments and moves and/or duplicates the other arguments
4922 * @throws NullPointerException if any argument is null
4923 * @throws IllegalArgumentException if the index array length is not equal to
4924 * the arity of the target, or if any index array element
4925 * not a valid index for a parameter of {@code newType},
4926 * or if two corresponding parameter types in
4927 * {@code target.type()} and {@code newType} are not identical,
4928 */
4929 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
4930 reorder = reorder.clone(); // get a private copy
4931 MethodType oldType = target.type();
4932 permuteArgumentChecks(reorder, newType, oldType);
4933 // first detect dropped arguments and handle them separately
4934 int[] originalReorder = reorder;
4935 BoundMethodHandle result = target.rebind();
4936 LambdaForm form = result.form;
4937 int newArity = newType.parameterCount();
4938 // Normalize the reordering into a real permutation,
4939 // by removing duplicates and adding dropped elements.
4940 // This somewhat improves lambda form caching, as well
4941 // as simplifying the transform by breaking it up into steps.
4942 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
4943 if (ddIdx > 0) {
4944 // We found a duplicated entry at reorder[ddIdx].
4945 // Example: (x,y,z)->asList(x,y,z)
4946 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
4947 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
4948 // The starred element corresponds to the argument
4949 // deleted by the dupArgumentForm transform.
4950 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
4951 boolean killFirst = false;
4952 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
4953 // Set killFirst if the dup is larger than an intervening position.
4954 // This will remove at least one inversion from the permutation.
4955 if (dupVal > val) killFirst = true;
4956 }
4957 if (!killFirst) {
4958 srcPos = dstPos;
4959 dstPos = ddIdx;
4960 }
4961 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
4962 assert (reorder[srcPos] == reorder[dstPos]);
4963 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
4964 // contract the reordering by removing the element at dstPos
4965 int tailPos = dstPos + 1;
4966 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
4967 reorder = Arrays.copyOf(reorder, reorder.length - 1);
4968 } else {
4969 int dropVal = ~ddIdx, insPos = 0;
4970 while (insPos < reorder.length && reorder[insPos] < dropVal) {
4971 // Find first element of reorder larger than dropVal.
4972 // This is where we will insert the dropVal.
4973 insPos += 1;
4974 }
4975 Class<?> ptype = newType.parameterType(dropVal);
4976 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
4977 oldType = oldType.insertParameterTypes(insPos, ptype);
4978 // expand the reordering by inserting an element at insPos
4979 int tailPos = insPos + 1;
4980 reorder = Arrays.copyOf(reorder, reorder.length + 1);
4981 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
4982 reorder[insPos] = dropVal;
4983 }
4984 assert (permuteArgumentChecks(reorder, newType, oldType));
4985 }
4986 assert (reorder.length == newArity); // a perfect permutation
4987 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
4988 form = form.editor().permuteArgumentsForm(1, reorder);
4989 if (newType == result.type() && form == result.internalForm())
4990 return result;
4991 return result.copyWith(newType, form);
4992 }
4993
4994 /**
4995 * Return an indication of any duplicate or omission in reorder.
4996 * If the reorder contains a duplicate entry, return the index of the second occurrence.
4997 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
4998 * Otherwise, return zero.
4999 * If an element not in [0..newArity-1] is encountered, return reorder.length.
5000 */
5001 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
5002 final int BIT_LIMIT = 63; // max number of bits in bit mask
5003 if (newArity < BIT_LIMIT) {
5004 long mask = 0;
5005 for (int i = 0; i < reorder.length; i++) {
5006 int arg = reorder[i];
5007 if (arg >= newArity) {
5008 return reorder.length;
5009 }
5010 long bit = 1L << arg;
5011 if ((mask & bit) != 0) {
5012 return i; // >0 indicates a dup
5013 }
5014 mask |= bit;
5015 }
5016 if (mask == (1L << newArity) - 1) {
5017 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
5018 return 0;
5019 }
5020 // find first zero
5021 long zeroBit = Long.lowestOneBit(~mask);
5022 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
5023 assert(zeroPos <= newArity);
5024 if (zeroPos == newArity) {
5025 return 0;
5026 }
5027 return ~zeroPos;
5028 } else {
5029 // same algorithm, different bit set
5030 BitSet mask = new BitSet(newArity);
5031 for (int i = 0; i < reorder.length; i++) {
5032 int arg = reorder[i];
5033 if (arg >= newArity) {
5034 return reorder.length;
5035 }
5036 if (mask.get(arg)) {
5037 return i; // >0 indicates a dup
5038 }
5039 mask.set(arg);
5040 }
5041 int zeroPos = mask.nextClearBit(0);
5042 assert(zeroPos <= newArity);
5043 if (zeroPos == newArity) {
5044 return 0;
5045 }
5046 return ~zeroPos;
5047 }
5048 }
5049
5050 static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
5051 if (newType.returnType() != oldType.returnType())
5052 throw newIllegalArgumentException("return types do not match",
5053 oldType, newType);
5054 if (reorder.length != oldType.parameterCount())
5055 throw newIllegalArgumentException("old type parameter count and reorder array length do not match",
5056 oldType, Arrays.toString(reorder));
5057
5058 int limit = newType.parameterCount();
5059 for (int j = 0; j < reorder.length; j++) {
5060 int i = reorder[j];
5061 if (i < 0 || i >= limit) {
5062 throw newIllegalArgumentException("index is out of bounds for new type",
5063 i, newType);
5064 }
5065 Class<?> src = newType.parameterType(i);
5066 Class<?> dst = oldType.parameterType(j);
5067 if (src != dst)
5068 throw newIllegalArgumentException("parameter types do not match after reorder",
5069 oldType, newType);
5070 }
5071 return true;
5072 }
5073
5074 /**
5075 * Produces a method handle of the requested return type which returns the given
5076 * constant value every time it is invoked.
5077 * <p>
5078 * Before the method handle is returned, the passed-in value is converted to the requested type.
5079 * If the requested type is primitive, widening primitive conversions are attempted,
5080 * else reference conversions are attempted.
5081 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
5082 * @param type the return type of the desired method handle
5083 * @param value the value to return
5084 * @return a method handle of the given return type and no arguments, which always returns the given value
5085 * @throws NullPointerException if the {@code type} argument is null
5086 * @throws ClassCastException if the value cannot be converted to the required return type
5087 * @throws IllegalArgumentException if the given type is {@code void.class}
5088 */
5089 public static MethodHandle constant(Class<?> type, Object value) {
5090 if (type.isPrimitive()) {
5091 if (type == void.class)
5092 throw newIllegalArgumentException("void type");
5093 Wrapper w = Wrapper.forPrimitiveType(type);
5094 value = w.convert(value, type);
5095 if (w.zero().equals(value))
5096 return zero(w, type);
5097 return insertArguments(identity(type), 0, value);
5098 } else {
5099 if (value == null)
5100 return zero(Wrapper.OBJECT, type);
5101 return identity(type).bindTo(value);
5102 }
5103 }
5104
5105 /**
5106 * Produces a method handle which returns its sole argument when invoked.
5107 * @param type the type of the sole parameter and return value of the desired method handle
5108 * @return a unary method handle which accepts and returns the given type
5109 * @throws NullPointerException if the argument is null
5110 * @throws IllegalArgumentException if the given type is {@code void.class}
5111 */
5112 public static MethodHandle identity(Class<?> type) {
5113 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
5114 int pos = btw.ordinal();
5115 MethodHandle ident = IDENTITY_MHS[pos];
5116 if (ident == null) {
5117 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
5118 }
5119 if (ident.type().returnType() == type)
5120 return ident;
5121 // something like identity(Foo.class); do not bother to intern these
5122 assert (btw == Wrapper.OBJECT);
5123 return makeIdentity(type);
5124 }
5125
5126 /**
5127 * Produces a constant method handle of the requested return type which
5128 * returns the default value for that type every time it is invoked.
5129 * The resulting constant method handle will have no side effects.
5130 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
5131 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
5132 * since {@code explicitCastArguments} converts {@code null} to default values.
5133 * @param type the expected return type of the desired method handle
5134 * @return a constant method handle that takes no arguments
5135 * and returns the default value of the given type (or void, if the type is void)
5136 * @throws NullPointerException if the argument is null
5137 * @see MethodHandles#constant
5138 * @see MethodHandles#empty
5139 * @see MethodHandles#explicitCastArguments
5140 * @since 9
5141 */
5142 public static MethodHandle zero(Class<?> type) {
5143 Objects.requireNonNull(type);
5144 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
5145 }
5146
5147 private static MethodHandle identityOrVoid(Class<?> type) {
5148 return type == void.class ? zero(type) : identity(type);
5149 }
5150
5151 /**
5152 * Produces a method handle of the requested type which ignores any arguments, does nothing,
5153 * and returns a suitable default depending on the return type.
5154 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
5155 * <p>The returned method handle is equivalent to
5156 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
5157 *
5158 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
5159 * {@code guardWithTest(pred, target, empty(target.type())}.
5160 * @param type the type of the desired method handle
5161 * @return a constant method handle of the given type, which returns a default value of the given return type
5162 * @throws NullPointerException if the argument is null
5163 * @see MethodHandles#zero
5164 * @see MethodHandles#constant
5165 * @since 9
5166 */
5167 public static MethodHandle empty(MethodType type) {
5168 Objects.requireNonNull(type);
5169 return dropArgumentsTrusted(zero(type.returnType()), 0, type.ptypes());
5170 }
5171
5172 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
5173 private static MethodHandle makeIdentity(Class<?> ptype) {
5174 MethodType mtype = methodType(ptype, ptype);
5175 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
5176 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
5177 }
5178
5179 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
5180 int pos = btw.ordinal();
5181 MethodHandle zero = ZERO_MHS[pos];
5182 if (zero == null) {
5183 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
5184 }
5185 if (zero.type().returnType() == rtype)
5186 return zero;
5187 assert(btw == Wrapper.OBJECT);
5188 return makeZero(rtype);
5189 }
5190 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
5191 private static MethodHandle makeZero(Class<?> rtype) {
5192 MethodType mtype = methodType(rtype);
5193 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
5194 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
5195 }
5196
5197 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
5198 // Simulate a CAS, to avoid racy duplication of results.
5199 MethodHandle prev = cache[pos];
5200 if (prev != null) return prev;
5201 return cache[pos] = value;
5202 }
5203
5204 /**
5205 * Provides a target method handle with one or more <em>bound arguments</em>
5206 * in advance of the method handle's invocation.
5207 * The formal parameters to the target corresponding to the bound
5208 * arguments are called <em>bound parameters</em>.
5209 * Returns a new method handle which saves away the bound arguments.
5210 * When it is invoked, it receives arguments for any non-bound parameters,
5211 * binds the saved arguments to their corresponding parameters,
5212 * and calls the original target.
5213 * <p>
5214 * The type of the new method handle will drop the types for the bound
5215 * parameters from the original target type, since the new method handle
5216 * will no longer require those arguments to be supplied by its callers.
5217 * <p>
5218 * Each given argument object must match the corresponding bound parameter type.
5219 * If a bound parameter type is a primitive, the argument object
5220 * must be a wrapper, and will be unboxed to produce the primitive value.
5221 * <p>
5222 * The {@code pos} argument selects which parameters are to be bound.
5223 * It may range between zero and <i>N-L</i> (inclusively),
5224 * where <i>N</i> is the arity of the target method handle
5225 * and <i>L</i> is the length of the values array.
5226 * <p>
5227 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5228 * variable-arity method handle}, even if the original target method handle was.
5229 * @param target the method handle to invoke after the argument is inserted
5230 * @param pos where to insert the argument (zero for the first)
5231 * @param values the series of arguments to insert
5232 * @return a method handle which inserts an additional argument,
5233 * before calling the original method handle
5234 * @throws NullPointerException if the target or the {@code values} array is null
5235 * @throws IllegalArgumentException if {@code pos} is less than {@code 0} or greater than
5236 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
5237 * is the length of the values array.
5238 * @throws ClassCastException if an argument does not match the corresponding bound parameter
5239 * type.
5240 * @see MethodHandle#bindTo
5241 */
5242 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
5243 int insCount = values.length;
5244 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
5245 if (insCount == 0) return target;
5246 BoundMethodHandle result = target.rebind();
5247 for (int i = 0; i < insCount; i++) {
5248 Object value = values[i];
5249 Class<?> ptype = ptypes[pos+i];
5250 if (ptype.isPrimitive()) {
5251 result = insertArgumentPrimitive(result, pos, ptype, value);
5252 } else {
5253 value = ptype.cast(value); // throw CCE if needed
5254 result = result.bindArgumentL(pos, value);
5255 }
5256 }
5257 return result;
5258 }
5259
5260 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
5261 Class<?> ptype, Object value) {
5262 Wrapper w = Wrapper.forPrimitiveType(ptype);
5263 // perform unboxing and/or primitive conversion
5264 value = w.convert(value, ptype);
5265 return switch (w) {
5266 case INT -> result.bindArgumentI(pos, (int) value);
5267 case LONG -> result.bindArgumentJ(pos, (long) value);
5268 case FLOAT -> result.bindArgumentF(pos, (float) value);
5269 case DOUBLE -> result.bindArgumentD(pos, (double) value);
5270 default -> result.bindArgumentI(pos, ValueConversions.widenSubword(value));
5271 };
5272 }
5273
5274 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
5275 MethodType oldType = target.type();
5276 int outargs = oldType.parameterCount();
5277 int inargs = outargs - insCount;
5278 if (inargs < 0)
5279 throw newIllegalArgumentException("too many values to insert");
5280 if (pos < 0 || pos > inargs)
5281 throw newIllegalArgumentException("no argument type to append");
5282 return oldType.ptypes();
5283 }
5284
5285 /**
5286 * Produces a method handle which will discard some dummy arguments
5287 * before calling some other specified <i>target</i> method handle.
5288 * The type of the new method handle will be the same as the target's type,
5289 * except it will also include the dummy argument types,
5290 * at some given position.
5291 * <p>
5292 * The {@code pos} argument may range between zero and <i>N</i>,
5293 * where <i>N</i> is the arity of the target.
5294 * If {@code pos} is zero, the dummy arguments will precede
5295 * the target's real arguments; if {@code pos} is <i>N</i>
5296 * they will come after.
5297 * <p>
5298 * <b>Example:</b>
5299 * {@snippet lang="java" :
5300 import static java.lang.invoke.MethodHandles.*;
5301 import static java.lang.invoke.MethodType.*;
5302 ...
5303 MethodHandle cat = lookup().findVirtual(String.class,
5304 "concat", methodType(String.class, String.class));
5305 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5306 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
5307 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
5308 assertEquals(bigType, d0.type());
5309 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
5310 * }
5311 * <p>
5312 * This method is also equivalent to the following code:
5313 * <blockquote><pre>
5314 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
5315 * </pre></blockquote>
5316 * @param target the method handle to invoke after the arguments are dropped
5317 * @param pos position of first argument to drop (zero for the leftmost)
5318 * @param valueTypes the type(s) of the argument(s) to drop
5319 * @return a method handle which drops arguments of the given types,
5320 * before calling the original method handle
5321 * @throws NullPointerException if the target is null,
5322 * or if the {@code valueTypes} list or any of its elements is null
5323 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5324 * or if {@code pos} is negative or greater than the arity of the target,
5325 * or if the new method handle's type would have too many parameters
5326 */
5327 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
5328 return dropArgumentsTrusted(target, pos, valueTypes.toArray(new Class<?>[0]).clone());
5329 }
5330
5331 static MethodHandle dropArgumentsTrusted(MethodHandle target, int pos, Class<?>[] valueTypes) {
5332 MethodType oldType = target.type(); // get NPE
5333 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
5334 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
5335 if (dropped == 0) return target;
5336 BoundMethodHandle result = target.rebind();
5337 LambdaForm lform = result.form;
5338 int insertFormArg = 1 + pos;
5339 for (Class<?> ptype : valueTypes) {
5340 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
5341 }
5342 result = result.copyWith(newType, lform);
5343 return result;
5344 }
5345
5346 private static int dropArgumentChecks(MethodType oldType, int pos, Class<?>[] valueTypes) {
5347 int dropped = valueTypes.length;
5348 MethodType.checkSlotCount(dropped);
5349 int outargs = oldType.parameterCount();
5350 int inargs = outargs + dropped;
5351 if (pos < 0 || pos > outargs)
5352 throw newIllegalArgumentException("no argument type to remove"
5353 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
5354 );
5355 return dropped;
5356 }
5357
5358 /**
5359 * Produces a method handle which will discard some dummy arguments
5360 * before calling some other specified <i>target</i> method handle.
5361 * The type of the new method handle will be the same as the target's type,
5362 * except it will also include the dummy argument types,
5363 * at some given position.
5364 * <p>
5365 * The {@code pos} argument may range between zero and <i>N</i>,
5366 * where <i>N</i> is the arity of the target.
5367 * If {@code pos} is zero, the dummy arguments will precede
5368 * the target's real arguments; if {@code pos} is <i>N</i>
5369 * they will come after.
5370 * @apiNote
5371 * {@snippet lang="java" :
5372 import static java.lang.invoke.MethodHandles.*;
5373 import static java.lang.invoke.MethodType.*;
5374 ...
5375 MethodHandle cat = lookup().findVirtual(String.class,
5376 "concat", methodType(String.class, String.class));
5377 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5378 MethodHandle d0 = dropArguments(cat, 0, String.class);
5379 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
5380 MethodHandle d1 = dropArguments(cat, 1, String.class);
5381 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
5382 MethodHandle d2 = dropArguments(cat, 2, String.class);
5383 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
5384 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
5385 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
5386 * }
5387 * <p>
5388 * This method is also equivalent to the following code:
5389 * <blockquote><pre>
5390 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
5391 * </pre></blockquote>
5392 * @param target the method handle to invoke after the arguments are dropped
5393 * @param pos position of first argument to drop (zero for the leftmost)
5394 * @param valueTypes the type(s) of the argument(s) to drop
5395 * @return a method handle which drops arguments of the given types,
5396 * before calling the original method handle
5397 * @throws NullPointerException if the target is null,
5398 * or if the {@code valueTypes} array or any of its elements is null
5399 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5400 * or if {@code pos} is negative or greater than the arity of the target,
5401 * or if the new method handle's type would have
5402 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5403 */
5404 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
5405 return dropArgumentsTrusted(target, pos, valueTypes.clone());
5406 }
5407
5408 /* Convenience overloads for trusting internal low-arity call-sites */
5409 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1) {
5410 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1 });
5411 }
5412 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1, Class<?> valueType2) {
5413 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1, valueType2 });
5414 }
5415
5416 // private version which allows caller some freedom with error handling
5417 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, Class<?>[] newTypes, int pos,
5418 boolean nullOnFailure) {
5419 Class<?>[] oldTypes = target.type().ptypes();
5420 int match = oldTypes.length;
5421 if (skip != 0) {
5422 if (skip < 0 || skip > match) {
5423 throw newIllegalArgumentException("illegal skip", skip, target);
5424 }
5425 oldTypes = Arrays.copyOfRange(oldTypes, skip, match);
5426 match -= skip;
5427 }
5428 Class<?>[] addTypes = newTypes;
5429 int add = addTypes.length;
5430 if (pos != 0) {
5431 if (pos < 0 || pos > add) {
5432 throw newIllegalArgumentException("illegal pos", pos, Arrays.toString(newTypes));
5433 }
5434 addTypes = Arrays.copyOfRange(addTypes, pos, add);
5435 add -= pos;
5436 assert(addTypes.length == add);
5437 }
5438 // Do not add types which already match the existing arguments.
5439 if (match > add || !Arrays.equals(oldTypes, 0, oldTypes.length, addTypes, 0, match)) {
5440 if (nullOnFailure) {
5441 return null;
5442 }
5443 throw newIllegalArgumentException("argument lists do not match",
5444 Arrays.toString(oldTypes), Arrays.toString(newTypes));
5445 }
5446 addTypes = Arrays.copyOfRange(addTypes, match, add);
5447 add -= match;
5448 assert(addTypes.length == add);
5449 // newTypes: ( P*[pos], M*[match], A*[add] )
5450 // target: ( S*[skip], M*[match] )
5451 MethodHandle adapter = target;
5452 if (add > 0) {
5453 adapter = dropArgumentsTrusted(adapter, skip+ match, addTypes);
5454 }
5455 // adapter: (S*[skip], M*[match], A*[add] )
5456 if (pos > 0) {
5457 adapter = dropArgumentsTrusted(adapter, skip, Arrays.copyOfRange(newTypes, 0, pos));
5458 }
5459 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
5460 return adapter;
5461 }
5462
5463 /**
5464 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
5465 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
5466 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
5467 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
5468 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
5469 * {@link #dropArguments(MethodHandle, int, Class[])}.
5470 * <p>
5471 * The resulting handle will have the same return type as the target handle.
5472 * <p>
5473 * In more formal terms, assume these two type lists:<ul>
5474 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
5475 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
5476 * {@code newTypes}.
5477 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
5478 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
5479 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
5480 * sub-list.
5481 * </ul>
5482 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
5483 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
5484 * {@link #dropArguments(MethodHandle, int, Class[])}.
5485 *
5486 * @apiNote
5487 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
5488 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
5489 * {@snippet lang="java" :
5490 import static java.lang.invoke.MethodHandles.*;
5491 import static java.lang.invoke.MethodType.*;
5492 ...
5493 ...
5494 MethodHandle h0 = constant(boolean.class, true);
5495 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
5496 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
5497 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
5498 if (h1.type().parameterCount() < h2.type().parameterCount())
5499 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
5500 else
5501 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
5502 MethodHandle h3 = guardWithTest(h0, h1, h2);
5503 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
5504 * }
5505 * @param target the method handle to adapt
5506 * @param skip number of targets parameters to disregard (they will be unchanged)
5507 * @param newTypes the list of types to match {@code target}'s parameter type list to
5508 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
5509 * @return a possibly adapted method handle
5510 * @throws NullPointerException if either argument is null
5511 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
5512 * or if {@code skip} is negative or greater than the arity of the target,
5513 * or if {@code pos} is negative or greater than the newTypes list size,
5514 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
5515 * {@code pos}.
5516 * @since 9
5517 */
5518 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
5519 Objects.requireNonNull(target);
5520 Objects.requireNonNull(newTypes);
5521 return dropArgumentsToMatch(target, skip, newTypes.toArray(new Class<?>[0]).clone(), pos, false);
5522 }
5523
5524 /**
5525 * Drop the return value of the target handle (if any).
5526 * The returned method handle will have a {@code void} return type.
5527 *
5528 * @param target the method handle to adapt
5529 * @return a possibly adapted method handle
5530 * @throws NullPointerException if {@code target} is null
5531 * @since 16
5532 */
5533 public static MethodHandle dropReturn(MethodHandle target) {
5534 Objects.requireNonNull(target);
5535 MethodType oldType = target.type();
5536 Class<?> oldReturnType = oldType.returnType();
5537 if (oldReturnType == void.class)
5538 return target;
5539 MethodType newType = oldType.changeReturnType(void.class);
5540 BoundMethodHandle result = target.rebind();
5541 LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true);
5542 result = result.copyWith(newType, lform);
5543 return result;
5544 }
5545
5546 /**
5547 * Adapts a target method handle by pre-processing
5548 * one or more of its arguments, each with its own unary filter function,
5549 * and then calling the target with each pre-processed argument
5550 * replaced by the result of its corresponding filter function.
5551 * <p>
5552 * The pre-processing is performed by one or more method handles,
5553 * specified in the elements of the {@code filters} array.
5554 * The first element of the filter array corresponds to the {@code pos}
5555 * argument of the target, and so on in sequence.
5556 * The filter functions are invoked in left to right order.
5557 * <p>
5558 * Null arguments in the array are treated as identity functions,
5559 * and the corresponding arguments left unchanged.
5560 * (If there are no non-null elements in the array, the original target is returned.)
5561 * Each filter is applied to the corresponding argument of the adapter.
5562 * <p>
5563 * If a filter {@code F} applies to the {@code N}th argument of
5564 * the target, then {@code F} must be a method handle which
5565 * takes exactly one argument. The type of {@code F}'s sole argument
5566 * replaces the corresponding argument type of the target
5567 * in the resulting adapted method handle.
5568 * The return type of {@code F} must be identical to the corresponding
5569 * parameter type of the target.
5570 * <p>
5571 * It is an error if there are elements of {@code filters}
5572 * (null or not)
5573 * which do not correspond to argument positions in the target.
5574 * <p><b>Example:</b>
5575 * {@snippet lang="java" :
5576 import static java.lang.invoke.MethodHandles.*;
5577 import static java.lang.invoke.MethodType.*;
5578 ...
5579 MethodHandle cat = lookup().findVirtual(String.class,
5580 "concat", methodType(String.class, String.class));
5581 MethodHandle upcase = lookup().findVirtual(String.class,
5582 "toUpperCase", methodType(String.class));
5583 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5584 MethodHandle f0 = filterArguments(cat, 0, upcase);
5585 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
5586 MethodHandle f1 = filterArguments(cat, 1, upcase);
5587 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
5588 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
5589 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
5590 * }
5591 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5592 * denotes the return type of both the {@code target} and resulting adapter.
5593 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
5594 * of the parameters and arguments that precede and follow the filter position
5595 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
5596 * values of the filtered parameters and arguments; they also represent the
5597 * return types of the {@code filter[i]} handles. The latter accept arguments
5598 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
5599 * the resulting adapter.
5600 * {@snippet lang="java" :
5601 * T target(P... p, A[i]... a[i], B... b);
5602 * A[i] filter[i](V[i]);
5603 * T adapter(P... p, V[i]... v[i], B... b) {
5604 * return target(p..., filter[i](v[i])..., b...);
5605 * }
5606 * }
5607 * <p>
5608 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5609 * variable-arity method handle}, even if the original target method handle was.
5610 *
5611 * @param target the method handle to invoke after arguments are filtered
5612 * @param pos the position of the first argument to filter
5613 * @param filters method handles to call initially on filtered arguments
5614 * @return method handle which incorporates the specified argument filtering logic
5615 * @throws NullPointerException if the target is null
5616 * or if the {@code filters} array is null
5617 * @throws IllegalArgumentException if a non-null element of {@code filters}
5618 * does not match a corresponding argument type of target as described above,
5619 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
5620 * or if the resulting method handle's type would have
5621 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5622 */
5623 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
5624 // In method types arguments start at index 0, while the LF
5625 // editor have the MH receiver at position 0 - adjust appropriately.
5626 final int MH_RECEIVER_OFFSET = 1;
5627 filterArgumentsCheckArity(target, pos, filters);
5628 MethodHandle adapter = target;
5629
5630 // keep track of currently matched filters, as to optimize repeated filters
5631 int index = 0;
5632 int[] positions = new int[filters.length];
5633 MethodHandle filter = null;
5634
5635 // process filters in reverse order so that the invocation of
5636 // the resulting adapter will invoke the filters in left-to-right order
5637 for (int i = filters.length - 1; i >= 0; --i) {
5638 MethodHandle newFilter = filters[i];
5639 if (newFilter == null) continue; // ignore null elements of filters
5640
5641 // flush changes on update
5642 if (filter != newFilter) {
5643 if (filter != null) {
5644 if (index > 1) {
5645 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5646 } else {
5647 adapter = filterArgument(adapter, positions[0] - 1, filter);
5648 }
5649 }
5650 filter = newFilter;
5651 index = 0;
5652 }
5653
5654 filterArgumentChecks(target, pos + i, newFilter);
5655 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
5656 }
5657 if (index > 1) {
5658 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5659 } else if (index == 1) {
5660 adapter = filterArgument(adapter, positions[0] - 1, filter);
5661 }
5662 return adapter;
5663 }
5664
5665 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
5666 MethodType targetType = adapter.type();
5667 MethodType filterType = filter.type();
5668 BoundMethodHandle result = adapter.rebind();
5669 Class<?> newParamType = filterType.parameterType(0);
5670
5671 Class<?>[] ptypes = targetType.ptypes().clone();
5672 for (int pos : positions) {
5673 ptypes[pos - 1] = newParamType;
5674 }
5675 MethodType newType = MethodType.methodType(targetType.rtype(), ptypes, true);
5676
5677 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
5678 return result.copyWithExtendL(newType, lform, filter);
5679 }
5680
5681 /*non-public*/
5682 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
5683 filterArgumentChecks(target, pos, filter);
5684 MethodType targetType = target.type();
5685 MethodType filterType = filter.type();
5686 BoundMethodHandle result = target.rebind();
5687 Class<?> newParamType = filterType.parameterType(0);
5688 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
5689 MethodType newType = targetType.changeParameterType(pos, newParamType);
5690 result = result.copyWithExtendL(newType, lform, filter);
5691 return result;
5692 }
5693
5694 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
5695 MethodType targetType = target.type();
5696 int maxPos = targetType.parameterCount();
5697 if (pos + filters.length > maxPos)
5698 throw newIllegalArgumentException("too many filters");
5699 }
5700
5701 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5702 MethodType targetType = target.type();
5703 MethodType filterType = filter.type();
5704 if (filterType.parameterCount() != 1
5705 || filterType.returnType() != targetType.parameterType(pos))
5706 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5707 }
5708
5709 /**
5710 * Adapts a target method handle by pre-processing
5711 * a sub-sequence of its arguments with a filter (another method handle).
5712 * The pre-processed arguments are replaced by the result (if any) of the
5713 * filter function.
5714 * The target is then called on the modified (usually shortened) argument list.
5715 * <p>
5716 * If the filter returns a value, the target must accept that value as
5717 * its argument in position {@code pos}, preceded and/or followed by
5718 * any arguments not passed to the filter.
5719 * If the filter returns void, the target must accept all arguments
5720 * not passed to the filter.
5721 * No arguments are reordered, and a result returned from the filter
5722 * replaces (in order) the whole subsequence of arguments originally
5723 * passed to the adapter.
5724 * <p>
5725 * The argument types (if any) of the filter
5726 * replace zero or one argument types of the target, at position {@code pos},
5727 * in the resulting adapted method handle.
5728 * The return type of the filter (if any) must be identical to the
5729 * argument type of the target at position {@code pos}, and that target argument
5730 * is supplied by the return value of the filter.
5731 * <p>
5732 * In all cases, {@code pos} must be greater than or equal to zero, and
5733 * {@code pos} must also be less than or equal to the target's arity.
5734 * <p><b>Example:</b>
5735 * {@snippet lang="java" :
5736 import static java.lang.invoke.MethodHandles.*;
5737 import static java.lang.invoke.MethodType.*;
5738 ...
5739 MethodHandle deepToString = publicLookup()
5740 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
5741
5742 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
5743 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
5744
5745 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
5746 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
5747
5748 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
5749 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
5750 assertEquals("[top, [up, down], strange]",
5751 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
5752
5753 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
5754 assertEquals("[top, [up, down], [strange]]",
5755 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
5756
5757 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
5758 assertEquals("[top, [[up, down, strange], charm], bottom]",
5759 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
5760 * }
5761 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5762 * represents the return type of the {@code target} and resulting adapter.
5763 * {@code V}/{@code v} stand for the return type and value of the
5764 * {@code filter}, which are also found in the signature and arguments of
5765 * the {@code target}, respectively, unless {@code V} is {@code void}.
5766 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
5767 * and values preceding and following the collection position, {@code pos},
5768 * in the {@code target}'s signature. They also turn up in the resulting
5769 * adapter's signature and arguments, where they surround
5770 * {@code B}/{@code b}, which represent the parameter types and arguments
5771 * to the {@code filter} (if any).
5772 * {@snippet lang="java" :
5773 * T target(A...,V,C...);
5774 * V filter(B...);
5775 * T adapter(A... a,B... b,C... c) {
5776 * V v = filter(b...);
5777 * return target(a...,v,c...);
5778 * }
5779 * // and if the filter has no arguments:
5780 * T target2(A...,V,C...);
5781 * V filter2();
5782 * T adapter2(A... a,C... c) {
5783 * V v = filter2();
5784 * return target2(a...,v,c...);
5785 * }
5786 * // and if the filter has a void return:
5787 * T target3(A...,C...);
5788 * void filter3(B...);
5789 * T adapter3(A... a,B... b,C... c) {
5790 * filter3(b...);
5791 * return target3(a...,c...);
5792 * }
5793 * }
5794 * <p>
5795 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
5796 * one which first "folds" the affected arguments, and then drops them, in separate
5797 * steps as follows:
5798 * {@snippet lang="java" :
5799 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
5800 * mh = MethodHandles.foldArguments(mh, coll); //step 1
5801 * }
5802 * If the target method handle consumes no arguments besides than the result
5803 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
5804 * is equivalent to {@code filterReturnValue(coll, mh)}.
5805 * If the filter method handle {@code coll} consumes one argument and produces
5806 * a non-void result, then {@code collectArguments(mh, N, coll)}
5807 * is equivalent to {@code filterArguments(mh, N, coll)}.
5808 * Other equivalences are possible but would require argument permutation.
5809 * <p>
5810 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5811 * variable-arity method handle}, even if the original target method handle was.
5812 *
5813 * @param target the method handle to invoke after filtering the subsequence of arguments
5814 * @param pos the position of the first adapter argument to pass to the filter,
5815 * and/or the target argument which receives the result of the filter
5816 * @param filter method handle to call on the subsequence of arguments
5817 * @return method handle which incorporates the specified argument subsequence filtering logic
5818 * @throws NullPointerException if either argument is null
5819 * @throws IllegalArgumentException if the return type of {@code filter}
5820 * is non-void and is not the same as the {@code pos} argument of the target,
5821 * or if {@code pos} is not between 0 and the target's arity, inclusive,
5822 * or if the resulting method handle's type would have
5823 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5824 * @see MethodHandles#foldArguments
5825 * @see MethodHandles#filterArguments
5826 * @see MethodHandles#filterReturnValue
5827 */
5828 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
5829 MethodType newType = collectArgumentsChecks(target, pos, filter);
5830 MethodType collectorType = filter.type();
5831 BoundMethodHandle result = target.rebind();
5832 LambdaForm lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
5833 return result.copyWithExtendL(newType, lform, filter);
5834 }
5835
5836 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5837 MethodType targetType = target.type();
5838 MethodType filterType = filter.type();
5839 Class<?> rtype = filterType.returnType();
5840 Class<?>[] filterArgs = filterType.ptypes();
5841 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) ||
5842 (rtype != void.class && pos >= targetType.parameterCount())) {
5843 throw newIllegalArgumentException("position is out of range for target", target, pos);
5844 }
5845 if (rtype == void.class) {
5846 return targetType.insertParameterTypes(pos, filterArgs);
5847 }
5848 if (rtype != targetType.parameterType(pos)) {
5849 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5850 }
5851 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs);
5852 }
5853
5854 /**
5855 * Adapts a target method handle by post-processing
5856 * its return value (if any) with a filter (another method handle).
5857 * The result of the filter is returned from the adapter.
5858 * <p>
5859 * If the target returns a value, the filter must accept that value as
5860 * its only argument.
5861 * If the target returns void, the filter must accept no arguments.
5862 * <p>
5863 * The return type of the filter
5864 * replaces the return type of the target
5865 * in the resulting adapted method handle.
5866 * The argument type of the filter (if any) must be identical to the
5867 * return type of the target.
5868 * <p><b>Example:</b>
5869 * {@snippet lang="java" :
5870 import static java.lang.invoke.MethodHandles.*;
5871 import static java.lang.invoke.MethodType.*;
5872 ...
5873 MethodHandle cat = lookup().findVirtual(String.class,
5874 "concat", methodType(String.class, String.class));
5875 MethodHandle length = lookup().findVirtual(String.class,
5876 "length", methodType(int.class));
5877 System.out.println((String) cat.invokeExact("x", "y")); // xy
5878 MethodHandle f0 = filterReturnValue(cat, length);
5879 System.out.println((int) f0.invokeExact("x", "y")); // 2
5880 * }
5881 * <p>Here is pseudocode for the resulting adapter. In the code,
5882 * {@code T}/{@code t} represent the result type and value of the
5883 * {@code target}; {@code V}, the result type of the {@code filter}; and
5884 * {@code A}/{@code a}, the types and values of the parameters and arguments
5885 * of the {@code target} as well as the resulting adapter.
5886 * {@snippet lang="java" :
5887 * T target(A...);
5888 * V filter(T);
5889 * V adapter(A... a) {
5890 * T t = target(a...);
5891 * return filter(t);
5892 * }
5893 * // and if the target has a void return:
5894 * void target2(A...);
5895 * V filter2();
5896 * V adapter2(A... a) {
5897 * target2(a...);
5898 * return filter2();
5899 * }
5900 * // and if the filter has a void return:
5901 * T target3(A...);
5902 * void filter3(V);
5903 * void adapter3(A... a) {
5904 * T t = target3(a...);
5905 * filter3(t);
5906 * }
5907 * }
5908 * <p>
5909 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5910 * variable-arity method handle}, even if the original target method handle was.
5911 * @param target the method handle to invoke before filtering the return value
5912 * @param filter method handle to call on the return value
5913 * @return method handle which incorporates the specified return value filtering logic
5914 * @throws NullPointerException if either argument is null
5915 * @throws IllegalArgumentException if the argument list of {@code filter}
5916 * does not match the return type of target as described above
5917 */
5918 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
5919 MethodType targetType = target.type();
5920 MethodType filterType = filter.type();
5921 filterReturnValueChecks(targetType, filterType);
5922 BoundMethodHandle result = target.rebind();
5923 BasicType rtype = BasicType.basicType(filterType.returnType());
5924 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
5925 MethodType newType = targetType.changeReturnType(filterType.returnType());
5926 result = result.copyWithExtendL(newType, lform, filter);
5927 return result;
5928 }
5929
5930 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
5931 Class<?> rtype = targetType.returnType();
5932 int filterValues = filterType.parameterCount();
5933 if (filterValues == 0
5934 ? (rtype != void.class)
5935 : (rtype != filterType.parameterType(0) || filterValues != 1))
5936 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5937 }
5938
5939 /**
5940 * Filter the return value of a target method handle with a filter function. The filter function is
5941 * applied to the return value of the original handle; if the filter specifies more than one parameters,
5942 * then any remaining parameter is appended to the adapter handle. In other words, the adaptation works
5943 * as follows:
5944 * {@snippet lang="java" :
5945 * T target(A...)
5946 * V filter(B... , T)
5947 * V adapter(A... a, B... b) {
5948 * T t = target(a...);
5949 * return filter(b..., t);
5950 * }
5951 * }
5952 * <p>
5953 * If the filter handle is a unary function, then this method behaves like {@link #filterReturnValue(MethodHandle, MethodHandle)}.
5954 *
5955 * @param target the target method handle
5956 * @param filter the filter method handle
5957 * @return the adapter method handle
5958 */
5959 /* package */ static MethodHandle collectReturnValue(MethodHandle target, MethodHandle filter) {
5960 MethodType targetType = target.type();
5961 MethodType filterType = filter.type();
5962 BoundMethodHandle result = target.rebind();
5963 LambdaForm lform = result.editor().collectReturnValueForm(filterType.basicType());
5964 MethodType newType = targetType.changeReturnType(filterType.returnType());
5965 if (filterType.parameterCount() > 1) {
5966 for (int i = 0 ; i < filterType.parameterCount() - 1 ; i++) {
5967 newType = newType.appendParameterTypes(filterType.parameterType(i));
5968 }
5969 }
5970 result = result.copyWithExtendL(newType, lform, filter);
5971 return result;
5972 }
5973
5974 /**
5975 * Adapts a target method handle by pre-processing
5976 * some of its arguments, and then calling the target with
5977 * the result of the pre-processing, inserted into the original
5978 * sequence of arguments.
5979 * <p>
5980 * The pre-processing is performed by {@code combiner}, a second method handle.
5981 * Of the arguments passed to the adapter, the first {@code N} arguments
5982 * are copied to the combiner, which is then called.
5983 * (Here, {@code N} is defined as the parameter count of the combiner.)
5984 * After this, control passes to the target, with any result
5985 * from the combiner inserted before the original {@code N} incoming
5986 * arguments.
5987 * <p>
5988 * If the combiner returns a value, the first parameter type of the target
5989 * must be identical with the return type of the combiner, and the next
5990 * {@code N} parameter types of the target must exactly match the parameters
5991 * of the combiner.
5992 * <p>
5993 * If the combiner has a void return, no result will be inserted,
5994 * and the first {@code N} parameter types of the target
5995 * must exactly match the parameters of the combiner.
5996 * <p>
5997 * The resulting adapter is the same type as the target, except that the
5998 * first parameter type is dropped,
5999 * if it corresponds to the result of the combiner.
6000 * <p>
6001 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
6002 * that either the combiner or the target does not wish to receive.
6003 * If some of the incoming arguments are destined only for the combiner,
6004 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
6005 * arguments will not need to be live on the stack on entry to the
6006 * target.)
6007 * <p><b>Example:</b>
6008 * {@snippet lang="java" :
6009 import static java.lang.invoke.MethodHandles.*;
6010 import static java.lang.invoke.MethodType.*;
6011 ...
6012 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6013 "println", methodType(void.class, String.class))
6014 .bindTo(System.out);
6015 MethodHandle cat = lookup().findVirtual(String.class,
6016 "concat", methodType(String.class, String.class));
6017 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6018 MethodHandle catTrace = foldArguments(cat, trace);
6019 // also prints "boo":
6020 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6021 * }
6022 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6023 * represents the result type of the {@code target} and resulting adapter.
6024 * {@code V}/{@code v} represent the type and value of the parameter and argument
6025 * of {@code target} that precedes the folding position; {@code V} also is
6026 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6027 * types and values of the {@code N} parameters and arguments at the folding
6028 * position. {@code B}/{@code b} represent the types and values of the
6029 * {@code target} parameters and arguments that follow the folded parameters
6030 * and arguments.
6031 * {@snippet lang="java" :
6032 * // there are N arguments in A...
6033 * T target(V, A[N]..., B...);
6034 * V combiner(A...);
6035 * T adapter(A... a, B... b) {
6036 * V v = combiner(a...);
6037 * return target(v, a..., b...);
6038 * }
6039 * // and if the combiner has a void return:
6040 * T target2(A[N]..., B...);
6041 * void combiner2(A...);
6042 * T adapter2(A... a, B... b) {
6043 * combiner2(a...);
6044 * return target2(a..., b...);
6045 * }
6046 * }
6047 * <p>
6048 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6049 * variable-arity method handle}, even if the original target method handle was.
6050 * @param target the method handle to invoke after arguments are combined
6051 * @param combiner method handle to call initially on the incoming arguments
6052 * @return method handle which incorporates the specified argument folding logic
6053 * @throws NullPointerException if either argument is null
6054 * @throws IllegalArgumentException if {@code combiner}'s return type
6055 * is non-void and not the same as the first argument type of
6056 * the target, or if the initial {@code N} argument types
6057 * of the target
6058 * (skipping one matching the {@code combiner}'s return type)
6059 * are not identical with the argument types of {@code combiner}
6060 */
6061 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
6062 return foldArguments(target, 0, combiner);
6063 }
6064
6065 /**
6066 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
6067 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
6068 * before the folded arguments.
6069 * <p>
6070 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
6071 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
6072 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
6073 * 0.
6074 *
6075 * @apiNote Example:
6076 * {@snippet lang="java" :
6077 import static java.lang.invoke.MethodHandles.*;
6078 import static java.lang.invoke.MethodType.*;
6079 ...
6080 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6081 "println", methodType(void.class, String.class))
6082 .bindTo(System.out);
6083 MethodHandle cat = lookup().findVirtual(String.class,
6084 "concat", methodType(String.class, String.class));
6085 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6086 MethodHandle catTrace = foldArguments(cat, 1, trace);
6087 // also prints "jum":
6088 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6089 * }
6090 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6091 * represents the result type of the {@code target} and resulting adapter.
6092 * {@code V}/{@code v} represent the type and value of the parameter and argument
6093 * of {@code target} that precedes the folding position; {@code V} also is
6094 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6095 * types and values of the {@code N} parameters and arguments at the folding
6096 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
6097 * and values of the {@code target} parameters and arguments that precede and
6098 * follow the folded parameters and arguments starting at {@code pos},
6099 * respectively.
6100 * {@snippet lang="java" :
6101 * // there are N arguments in A...
6102 * T target(Z..., V, A[N]..., B...);
6103 * V combiner(A...);
6104 * T adapter(Z... z, A... a, B... b) {
6105 * V v = combiner(a...);
6106 * return target(z..., v, a..., b...);
6107 * }
6108 * // and if the combiner has a void return:
6109 * T target2(Z..., A[N]..., B...);
6110 * void combiner2(A...);
6111 * T adapter2(Z... z, A... a, B... b) {
6112 * combiner2(a...);
6113 * return target2(z..., a..., b...);
6114 * }
6115 * }
6116 * <p>
6117 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6118 * variable-arity method handle}, even if the original target method handle was.
6119 *
6120 * @param target the method handle to invoke after arguments are combined
6121 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
6122 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6123 * @param combiner method handle to call initially on the incoming arguments
6124 * @return method handle which incorporates the specified argument folding logic
6125 * @throws NullPointerException if either argument is null
6126 * @throws IllegalArgumentException if either of the following two conditions holds:
6127 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6128 * {@code pos} of the target signature;
6129 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
6130 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
6131 *
6132 * @see #foldArguments(MethodHandle, MethodHandle)
6133 * @since 9
6134 */
6135 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
6136 MethodType targetType = target.type();
6137 MethodType combinerType = combiner.type();
6138 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
6139 BoundMethodHandle result = target.rebind();
6140 boolean dropResult = rtype == void.class;
6141 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
6142 MethodType newType = targetType;
6143 if (!dropResult) {
6144 newType = newType.dropParameterTypes(pos, pos + 1);
6145 }
6146 result = result.copyWithExtendL(newType, lform, combiner);
6147 return result;
6148 }
6149
6150 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
6151 int foldArgs = combinerType.parameterCount();
6152 Class<?> rtype = combinerType.returnType();
6153 int foldVals = rtype == void.class ? 0 : 1;
6154 int afterInsertPos = foldPos + foldVals;
6155 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
6156 if (ok) {
6157 for (int i = 0; i < foldArgs; i++) {
6158 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
6159 ok = false;
6160 break;
6161 }
6162 }
6163 }
6164 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
6165 ok = false;
6166 if (!ok)
6167 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6168 return rtype;
6169 }
6170
6171 /**
6172 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
6173 * of the pre-processing replacing the argument at the given position.
6174 *
6175 * @param target the method handle to invoke after arguments are combined
6176 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6177 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6178 * @param combiner method handle to call initially on the incoming arguments
6179 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6180 * @return method handle which incorporates the specified argument folding logic
6181 * @throws NullPointerException if either argument is null
6182 * @throws IllegalArgumentException if either of the following two conditions holds:
6183 * (1) {@code combiner}'s return type is not the same as the argument type at position
6184 * {@code pos} of the target signature;
6185 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
6186 * not identical with the argument types of {@code combiner}.
6187 */
6188 /*non-public*/
6189 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6190 return argumentsWithCombiner(true, target, position, combiner, argPositions);
6191 }
6192
6193 /**
6194 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
6195 * the pre-processing inserted into the original sequence of arguments at the given position.
6196 *
6197 * @param target the method handle to invoke after arguments are combined
6198 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6199 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6200 * @param combiner method handle to call initially on the incoming arguments
6201 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6202 * @return method handle which incorporates the specified argument folding logic
6203 * @throws NullPointerException if either argument is null
6204 * @throws IllegalArgumentException if either of the following two conditions holds:
6205 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6206 * {@code pos} of the target signature;
6207 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
6208 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
6209 * with the argument types of {@code combiner}.
6210 */
6211 /*non-public*/
6212 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6213 return argumentsWithCombiner(false, target, position, combiner, argPositions);
6214 }
6215
6216 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6217 MethodType targetType = target.type();
6218 MethodType combinerType = combiner.type();
6219 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
6220 BoundMethodHandle result = target.rebind();
6221
6222 MethodType newType = targetType;
6223 LambdaForm lform;
6224 if (filter) {
6225 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
6226 } else {
6227 boolean dropResult = rtype == void.class;
6228 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
6229 if (!dropResult) {
6230 newType = newType.dropParameterTypes(position, position + 1);
6231 }
6232 }
6233 result = result.copyWithExtendL(newType, lform, combiner);
6234 return result;
6235 }
6236
6237 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
6238 int combinerArgs = combinerType.parameterCount();
6239 if (argPos.length != combinerArgs) {
6240 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
6241 }
6242 Class<?> rtype = combinerType.returnType();
6243
6244 for (int i = 0; i < combinerArgs; i++) {
6245 int arg = argPos[i];
6246 if (arg < 0 || arg > targetType.parameterCount()) {
6247 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
6248 }
6249 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
6250 throw newIllegalArgumentException("target argument type at position " + arg
6251 + " must match combiner argument type at index " + i + ": " + targetType
6252 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
6253 }
6254 }
6255 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
6256 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6257 }
6258 return rtype;
6259 }
6260
6261 /**
6262 * Makes a method handle which adapts a target method handle,
6263 * by guarding it with a test, a boolean-valued method handle.
6264 * If the guard fails, a fallback handle is called instead.
6265 * All three method handles must have the same corresponding
6266 * argument and return types, except that the return type
6267 * of the test must be boolean, and the test is allowed
6268 * to have fewer arguments than the other two method handles.
6269 * <p>
6270 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6271 * represents the uniform result type of the three involved handles;
6272 * {@code A}/{@code a}, the types and values of the {@code target}
6273 * parameters and arguments that are consumed by the {@code test}; and
6274 * {@code B}/{@code b}, those types and values of the {@code target}
6275 * parameters and arguments that are not consumed by the {@code test}.
6276 * {@snippet lang="java" :
6277 * boolean test(A...);
6278 * T target(A...,B...);
6279 * T fallback(A...,B...);
6280 * T adapter(A... a,B... b) {
6281 * if (test(a...))
6282 * return target(a..., b...);
6283 * else
6284 * return fallback(a..., b...);
6285 * }
6286 * }
6287 * Note that the test arguments ({@code a...} in the pseudocode) cannot
6288 * be modified by execution of the test, and so are passed unchanged
6289 * from the caller to the target or fallback as appropriate.
6290 * @param test method handle used for test, must return boolean
6291 * @param target method handle to call if test passes
6292 * @param fallback method handle to call if test fails
6293 * @return method handle which incorporates the specified if/then/else logic
6294 * @throws NullPointerException if any argument is null
6295 * @throws IllegalArgumentException if {@code test} does not return boolean,
6296 * or if all three method types do not match (with the return
6297 * type of {@code test} changed to match that of the target).
6298 */
6299 public static MethodHandle guardWithTest(MethodHandle test,
6300 MethodHandle target,
6301 MethodHandle fallback) {
6302 MethodType gtype = test.type();
6303 MethodType ttype = target.type();
6304 MethodType ftype = fallback.type();
6305 if (!ttype.equals(ftype))
6306 throw misMatchedTypes("target and fallback types", ttype, ftype);
6307 if (gtype.returnType() != boolean.class)
6308 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
6309
6310 test = dropArgumentsToMatch(test, 0, ttype.ptypes(), 0, true);
6311 if (test == null) {
6312 throw misMatchedTypes("target and test types", ttype, gtype);
6313 }
6314 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
6315 }
6316
6317 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
6318 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
6319 }
6320
6321 /**
6322 * Makes a method handle which adapts a target method handle,
6323 * by running it inside an exception handler.
6324 * If the target returns normally, the adapter returns that value.
6325 * If an exception matching the specified type is thrown, the fallback
6326 * handle is called instead on the exception, plus the original arguments.
6327 * <p>
6328 * The target and handler must have the same corresponding
6329 * argument and return types, except that handler may omit trailing arguments
6330 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
6331 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
6332 * <p>
6333 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6334 * represents the return type of the {@code target} and {@code handler},
6335 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
6336 * the types and values of arguments to the resulting handle consumed by
6337 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
6338 * resulting handle discarded by {@code handler}.
6339 * {@snippet lang="java" :
6340 * T target(A..., B...);
6341 * T handler(ExType, A...);
6342 * T adapter(A... a, B... b) {
6343 * try {
6344 * return target(a..., b...);
6345 * } catch (ExType ex) {
6346 * return handler(ex, a...);
6347 * }
6348 * }
6349 * }
6350 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6351 * be modified by execution of the target, and so are passed unchanged
6352 * from the caller to the handler, if the handler is invoked.
6353 * <p>
6354 * The target and handler must return the same type, even if the handler
6355 * always throws. (This might happen, for instance, because the handler
6356 * is simulating a {@code finally} clause).
6357 * To create such a throwing handler, compose the handler creation logic
6358 * with {@link #throwException throwException},
6359 * in order to create a method handle of the correct return type.
6360 * @param target method handle to call
6361 * @param exType the type of exception which the handler will catch
6362 * @param handler method handle to call if a matching exception is thrown
6363 * @return method handle which incorporates the specified try/catch logic
6364 * @throws NullPointerException if any argument is null
6365 * @throws IllegalArgumentException if {@code handler} does not accept
6366 * the given exception type, or if the method handle types do
6367 * not match in their return types and their
6368 * corresponding parameters
6369 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
6370 */
6371 public static MethodHandle catchException(MethodHandle target,
6372 Class<? extends Throwable> exType,
6373 MethodHandle handler) {
6374 MethodType ttype = target.type();
6375 MethodType htype = handler.type();
6376 if (!Throwable.class.isAssignableFrom(exType))
6377 throw new ClassCastException(exType.getName());
6378 if (htype.parameterCount() < 1 ||
6379 !htype.parameterType(0).isAssignableFrom(exType))
6380 throw newIllegalArgumentException("handler does not accept exception type "+exType);
6381 if (htype.returnType() != ttype.returnType())
6382 throw misMatchedTypes("target and handler return types", ttype, htype);
6383 handler = dropArgumentsToMatch(handler, 1, ttype.ptypes(), 0, true);
6384 if (handler == null) {
6385 throw misMatchedTypes("target and handler types", ttype, htype);
6386 }
6387 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
6388 }
6389
6390 /**
6391 * Produces a method handle which will throw exceptions of the given {@code exType}.
6392 * The method handle will accept a single argument of {@code exType},
6393 * and immediately throw it as an exception.
6394 * The method type will nominally specify a return of {@code returnType}.
6395 * The return type may be anything convenient: It doesn't matter to the
6396 * method handle's behavior, since it will never return normally.
6397 * @param returnType the return type of the desired method handle
6398 * @param exType the parameter type of the desired method handle
6399 * @return method handle which can throw the given exceptions
6400 * @throws NullPointerException if either argument is null
6401 */
6402 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
6403 if (!Throwable.class.isAssignableFrom(exType))
6404 throw new ClassCastException(exType.getName());
6405 return MethodHandleImpl.throwException(methodType(returnType, exType));
6406 }
6407
6408 /**
6409 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
6410 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
6411 * delivers the loop's result, which is the return value of the resulting handle.
6412 * <p>
6413 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
6414 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
6415 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
6416 * terms of method handles, each clause will specify up to four independent actions:<ul>
6417 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
6418 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
6419 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
6420 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
6421 * </ul>
6422 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
6423 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
6424 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
6425 * <p>
6426 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
6427 * this case. See below for a detailed description.
6428 * <p>
6429 * <em>Parameters optional everywhere:</em>
6430 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
6431 * As an exception, the init functions cannot take any {@code v} parameters,
6432 * because those values are not yet computed when the init functions are executed.
6433 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
6434 * In fact, any clause function may take no arguments at all.
6435 * <p>
6436 * <em>Loop parameters:</em>
6437 * A clause function may take all the iteration variable values it is entitled to, in which case
6438 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
6439 * with their types and values notated as {@code (A...)} and {@code (a...)}.
6440 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
6441 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
6442 * init function is automatically a loop parameter {@code a}.)
6443 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
6444 * These loop parameters act as loop-invariant values visible across the whole loop.
6445 * <p>
6446 * <em>Parameters visible everywhere:</em>
6447 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
6448 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
6449 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
6450 * Most clause functions will not need all of this information, but they will be formally connected to it
6451 * as if by {@link #dropArguments}.
6452 * <a id="astar"></a>
6453 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
6454 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
6455 * In that notation, the general form of an init function parameter list
6456 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
6457 * <p>
6458 * <em>Checking clause structure:</em>
6459 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
6460 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
6461 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
6462 * met by the inputs to the loop combinator.
6463 * <p>
6464 * <em>Effectively identical sequences:</em>
6465 * <a id="effid"></a>
6466 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
6467 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
6468 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
6469 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
6470 * that longest list.
6471 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
6472 * and the same is true if more sequences of the form {@code (V... A*)} are added.
6473 * <p>
6474 * <em>Step 0: Determine clause structure.</em><ol type="a">
6475 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
6476 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
6477 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
6478 * four. Padding takes place by appending elements to the array.
6479 * <li>Clauses with all {@code null}s are disregarded.
6480 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
6481 * </ol>
6482 * <p>
6483 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
6484 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
6485 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
6486 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
6487 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
6488 * iteration variable type.
6489 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
6490 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
6491 * </ol>
6492 * <p>
6493 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
6494 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
6495 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
6496 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
6497 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
6498 * (These types will be checked in step 2, along with all the clause function types.)
6499 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
6500 * <li>All of the collected parameter lists must be effectively identical.
6501 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
6502 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
6503 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
6504 * the "internal parameter list".
6505 * </ul>
6506 * <p>
6507 * <em>Step 1C: Determine loop return type.</em><ol type="a">
6508 * <li>Examine fini function return types, disregarding omitted fini functions.
6509 * <li>If there are no fini functions, the loop return type is {@code void}.
6510 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
6511 * type.
6512 * </ol>
6513 * <p>
6514 * <em>Step 1D: Check other types.</em><ol type="a">
6515 * <li>There must be at least one non-omitted pred function.
6516 * <li>Every non-omitted pred function must have a {@code boolean} return type.
6517 * </ol>
6518 * <p>
6519 * <em>Step 2: Determine parameter lists.</em><ol type="a">
6520 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
6521 * <li>The parameter list for init functions will be adjusted to the external parameter list.
6522 * (Note that their parameter lists are already effectively identical to this list.)
6523 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
6524 * effectively identical to the internal parameter list {@code (V... A...)}.
6525 * </ol>
6526 * <p>
6527 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
6528 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
6529 * type.
6530 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
6531 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
6532 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
6533 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
6534 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
6535 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
6536 * loop return type.
6537 * </ol>
6538 * <p>
6539 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
6540 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
6541 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
6542 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
6543 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
6544 * pad out the end of the list.
6545 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
6546 * </ol>
6547 * <p>
6548 * <em>Final observations.</em><ol type="a">
6549 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
6550 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
6551 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
6552 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
6553 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
6554 * <li>Each pair of init and step functions agrees in their return type {@code V}.
6555 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
6556 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
6557 * </ol>
6558 * <p>
6559 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
6560 * <ul>
6561 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
6562 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
6563 * (Only one {@code Pn} has to be non-{@code null}.)
6564 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
6565 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
6566 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
6567 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
6568 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
6569 * the resulting loop handle's parameter types {@code (A...)}.
6570 * </ul>
6571 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
6572 * which is natural if most of the loop computation happens in the steps. For some loops,
6573 * the burden of computation might be heaviest in the pred functions, and so the pred functions
6574 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
6575 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
6576 * where the init functions will need the extra parameters. For such reasons, the rules for
6577 * determining these parameters are as symmetric as possible, across all clause parts.
6578 * In general, the loop parameters function as common invariant values across the whole
6579 * loop, while the iteration variables function as common variant values, or (if there is
6580 * no step function) as internal loop invariant temporaries.
6581 * <p>
6582 * <em>Loop execution.</em><ol type="a">
6583 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
6584 * every clause function. These locals are loop invariant.
6585 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
6586 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
6587 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
6588 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
6589 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
6590 * (in argument order).
6591 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
6592 * returns {@code false}.
6593 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
6594 * sequence {@code (v...)} of loop variables.
6595 * The updated value is immediately visible to all subsequent function calls.
6596 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
6597 * (of type {@code R}) is returned from the loop as a whole.
6598 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
6599 * except by throwing an exception.
6600 * </ol>
6601 * <p>
6602 * <em>Usage tips.</em>
6603 * <ul>
6604 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
6605 * sometimes a step function only needs to observe the current value of its own variable.
6606 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
6607 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
6608 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
6609 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
6610 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
6611 * <li>If some of the clause functions are virtual methods on an instance, the instance
6612 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
6613 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
6614 * will be the first iteration variable value, and it will be easy to use virtual
6615 * methods as clause parts, since all of them will take a leading instance reference matching that value.
6616 * </ul>
6617 * <p>
6618 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
6619 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
6620 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
6621 * {@snippet lang="java" :
6622 * V... init...(A...);
6623 * boolean pred...(V..., A...);
6624 * V... step...(V..., A...);
6625 * R fini...(V..., A...);
6626 * R loop(A... a) {
6627 * V... v... = init...(a...);
6628 * for (;;) {
6629 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
6630 * v = s(v..., a...);
6631 * if (!p(v..., a...)) {
6632 * return f(v..., a...);
6633 * }
6634 * }
6635 * }
6636 * }
6637 * }
6638 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
6639 * to their full length, even though individual clause functions may neglect to take them all.
6640 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
6641 *
6642 * @apiNote Example:
6643 * {@snippet lang="java" :
6644 * // iterative implementation of the factorial function as a loop handle
6645 * static int one(int k) { return 1; }
6646 * static int inc(int i, int acc, int k) { return i + 1; }
6647 * static int mult(int i, int acc, int k) { return i * acc; }
6648 * static boolean pred(int i, int acc, int k) { return i < k; }
6649 * static int fin(int i, int acc, int k) { return acc; }
6650 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6651 * // null initializer for counter, should initialize to 0
6652 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6653 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6654 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6655 * assertEquals(120, loop.invoke(5));
6656 * }
6657 * The same example, dropping arguments and using combinators:
6658 * {@snippet lang="java" :
6659 * // simplified implementation of the factorial function as a loop handle
6660 * static int inc(int i) { return i + 1; } // drop acc, k
6661 * static int mult(int i, int acc) { return i * acc; } //drop k
6662 * static boolean cmp(int i, int k) { return i < k; }
6663 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
6664 * // null initializer for counter, should initialize to 0
6665 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6666 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
6667 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
6668 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6669 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6670 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6671 * assertEquals(720, loop.invoke(6));
6672 * }
6673 * A similar example, using a helper object to hold a loop parameter:
6674 * {@snippet lang="java" :
6675 * // instance-based implementation of the factorial function as a loop handle
6676 * static class FacLoop {
6677 * final int k;
6678 * FacLoop(int k) { this.k = k; }
6679 * int inc(int i) { return i + 1; }
6680 * int mult(int i, int acc) { return i * acc; }
6681 * boolean pred(int i) { return i < k; }
6682 * int fin(int i, int acc) { return acc; }
6683 * }
6684 * // assume MH_FacLoop is a handle to the constructor
6685 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6686 * // null initializer for counter, should initialize to 0
6687 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6688 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
6689 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6690 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6691 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
6692 * assertEquals(5040, loop.invoke(7));
6693 * }
6694 *
6695 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
6696 *
6697 * @return a method handle embodying the looping behavior as defined by the arguments.
6698 *
6699 * @throws IllegalArgumentException in case any of the constraints described above is violated.
6700 *
6701 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
6702 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6703 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
6704 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
6705 * @since 9
6706 */
6707 public static MethodHandle loop(MethodHandle[]... clauses) {
6708 // Step 0: determine clause structure.
6709 loopChecks0(clauses);
6710
6711 List<MethodHandle> init = new ArrayList<>();
6712 List<MethodHandle> step = new ArrayList<>();
6713 List<MethodHandle> pred = new ArrayList<>();
6714 List<MethodHandle> fini = new ArrayList<>();
6715
6716 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
6717 init.add(clause[0]); // all clauses have at least length 1
6718 step.add(clause.length <= 1 ? null : clause[1]);
6719 pred.add(clause.length <= 2 ? null : clause[2]);
6720 fini.add(clause.length <= 3 ? null : clause[3]);
6721 });
6722
6723 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
6724 final int nclauses = init.size();
6725
6726 // Step 1A: determine iteration variables (V...).
6727 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
6728 for (int i = 0; i < nclauses; ++i) {
6729 MethodHandle in = init.get(i);
6730 MethodHandle st = step.get(i);
6731 if (in == null && st == null) {
6732 iterationVariableTypes.add(void.class);
6733 } else if (in != null && st != null) {
6734 loopChecks1a(i, in, st);
6735 iterationVariableTypes.add(in.type().returnType());
6736 } else {
6737 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
6738 }
6739 }
6740 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).toList();
6741
6742 // Step 1B: determine loop parameters (A...).
6743 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
6744 loopChecks1b(init, commonSuffix);
6745
6746 // Step 1C: determine loop return type.
6747 // Step 1D: check other types.
6748 // local variable required here; see JDK-8223553
6749 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
6750 .map(MethodType::returnType);
6751 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
6752 loopChecks1cd(pred, fini, loopReturnType);
6753
6754 // Step 2: determine parameter lists.
6755 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
6756 commonParameterSequence.addAll(commonSuffix);
6757 loopChecks2(step, pred, fini, commonParameterSequence);
6758 // Step 3: fill in omitted functions.
6759 for (int i = 0; i < nclauses; ++i) {
6760 Class<?> t = iterationVariableTypes.get(i);
6761 if (init.get(i) == null) {
6762 init.set(i, empty(methodType(t, commonSuffix)));
6763 }
6764 if (step.get(i) == null) {
6765 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
6766 }
6767 if (pred.get(i) == null) {
6768 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence));
6769 }
6770 if (fini.get(i) == null) {
6771 fini.set(i, empty(methodType(t, commonParameterSequence)));
6772 }
6773 }
6774
6775 // Step 4: fill in missing parameter types.
6776 // Also convert all handles to fixed-arity handles.
6777 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
6778 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
6779 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
6780 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
6781
6782 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
6783 allMatch(pl -> pl.equals(commonSuffix));
6784 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
6785 allMatch(pl -> pl.equals(commonParameterSequence));
6786
6787 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
6788 }
6789
6790 private static void loopChecks0(MethodHandle[][] clauses) {
6791 if (clauses == null || clauses.length == 0) {
6792 throw newIllegalArgumentException("null or no clauses passed");
6793 }
6794 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
6795 throw newIllegalArgumentException("null clauses are not allowed");
6796 }
6797 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
6798 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
6799 }
6800 }
6801
6802 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
6803 if (in.type().returnType() != st.type().returnType()) {
6804 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
6805 st.type().returnType());
6806 }
6807 }
6808
6809 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
6810 return mhs.filter(Objects::nonNull)
6811 // take only those that can contribute to a common suffix because they are longer than the prefix
6812 .map(MethodHandle::type)
6813 .filter(t -> t.parameterCount() > skipSize)
6814 .max(Comparator.comparingInt(MethodType::parameterCount))
6815 .map(methodType -> List.of(Arrays.copyOfRange(methodType.ptypes(), skipSize, methodType.parameterCount())))
6816 .orElse(List.of());
6817 }
6818
6819 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
6820 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
6821 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
6822 return longest1.size() >= longest2.size() ? longest1 : longest2;
6823 }
6824
6825 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
6826 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
6827 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
6828 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
6829 " (common suffix: " + commonSuffix + ")");
6830 }
6831 }
6832
6833 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
6834 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6835 anyMatch(t -> t != loopReturnType)) {
6836 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
6837 loopReturnType + ")");
6838 }
6839
6840 if (pred.stream().noneMatch(Objects::nonNull)) {
6841 throw newIllegalArgumentException("no predicate found", pred);
6842 }
6843 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6844 anyMatch(t -> t != boolean.class)) {
6845 throw newIllegalArgumentException("predicates must have boolean return type", pred);
6846 }
6847 }
6848
6849 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
6850 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
6851 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
6852 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
6853 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
6854 }
6855 }
6856
6857 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
6858 return hs.stream().map(h -> {
6859 int pc = h.type().parameterCount();
6860 int tpsize = targetParams.size();
6861 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h;
6862 }).toList();
6863 }
6864
6865 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
6866 return hs.stream().map(MethodHandle::asFixedArity).toList();
6867 }
6868
6869 /**
6870 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
6871 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6872 * <p>
6873 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6874 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
6875 * evaluates to {@code true}).
6876 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
6877 * <p>
6878 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6879 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6880 * and updated with the value returned from its invocation. The result of loop execution will be
6881 * the final value of the additional loop-local variable (if present).
6882 * <p>
6883 * The following rules hold for these argument handles:<ul>
6884 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6885 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6886 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6887 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6888 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6889 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6890 * It will constrain the parameter lists of the other loop parts.
6891 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6892 * list {@code (A...)} is called the <em>external parameter list</em>.
6893 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6894 * additional state variable of the loop.
6895 * The body must both accept and return a value of this type {@code V}.
6896 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6897 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6898 * <a href="MethodHandles.html#effid">effectively identical</a>
6899 * to the external parameter list {@code (A...)}.
6900 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6901 * {@linkplain #empty default value}.
6902 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6903 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6904 * effectively identical to the internal parameter list.
6905 * </ul>
6906 * <p>
6907 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6908 * <li>The loop handle's result type is the result type {@code V} of the body.
6909 * <li>The loop handle's parameter types are the types {@code (A...)},
6910 * from the external parameter list.
6911 * </ul>
6912 * <p>
6913 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6914 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6915 * passed to the loop.
6916 * {@snippet lang="java" :
6917 * V init(A...);
6918 * boolean pred(V, A...);
6919 * V body(V, A...);
6920 * V whileLoop(A... a...) {
6921 * V v = init(a...);
6922 * while (pred(v, a...)) {
6923 * v = body(v, a...);
6924 * }
6925 * return v;
6926 * }
6927 * }
6928 *
6929 * @apiNote Example:
6930 * {@snippet lang="java" :
6931 * // implement the zip function for lists as a loop handle
6932 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
6933 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
6934 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
6935 * zip.add(a.next());
6936 * zip.add(b.next());
6937 * return zip;
6938 * }
6939 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
6940 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
6941 * List<String> a = Arrays.asList("a", "b", "c", "d");
6942 * List<String> b = Arrays.asList("e", "f", "g", "h");
6943 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
6944 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
6945 * }
6946 *
6947 *
6948 * @apiNote The implementation of this method can be expressed as follows:
6949 * {@snippet lang="java" :
6950 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6951 * MethodHandle fini = (body.type().returnType() == void.class
6952 * ? null : identity(body.type().returnType()));
6953 * MethodHandle[]
6954 * checkExit = { null, null, pred, fini },
6955 * varBody = { init, body };
6956 * return loop(checkExit, varBody);
6957 * }
6958 * }
6959 *
6960 * @param init optional initializer, providing the initial value of the loop variable.
6961 * May be {@code null}, implying a default initial value. See above for other constraints.
6962 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6963 * above for other constraints.
6964 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6965 * See above for other constraints.
6966 *
6967 * @return a method handle implementing the {@code while} loop as described by the arguments.
6968 * @throws IllegalArgumentException if the rules for the arguments are violated.
6969 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6970 *
6971 * @see #loop(MethodHandle[][])
6972 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6973 * @since 9
6974 */
6975 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6976 whileLoopChecks(init, pred, body);
6977 MethodHandle fini = identityOrVoid(body.type().returnType());
6978 MethodHandle[] checkExit = { null, null, pred, fini };
6979 MethodHandle[] varBody = { init, body };
6980 return loop(checkExit, varBody);
6981 }
6982
6983 /**
6984 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
6985 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6986 * <p>
6987 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6988 * method will, in each iteration, first execute its body and then evaluate the predicate.
6989 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
6990 * <p>
6991 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6992 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6993 * and updated with the value returned from its invocation. The result of loop execution will be
6994 * the final value of the additional loop-local variable (if present).
6995 * <p>
6996 * The following rules hold for these argument handles:<ul>
6997 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6998 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6999 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7000 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
7001 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
7002 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
7003 * It will constrain the parameter lists of the other loop parts.
7004 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
7005 * list {@code (A...)} is called the <em>external parameter list</em>.
7006 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7007 * additional state variable of the loop.
7008 * The body must both accept and return a value of this type {@code V}.
7009 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7010 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7011 * <a href="MethodHandles.html#effid">effectively identical</a>
7012 * to the external parameter list {@code (A...)}.
7013 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7014 * {@linkplain #empty default value}.
7015 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
7016 * Its parameter list (either empty or of the form {@code (V A*)}) must be
7017 * effectively identical to the internal parameter list.
7018 * </ul>
7019 * <p>
7020 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7021 * <li>The loop handle's result type is the result type {@code V} of the body.
7022 * <li>The loop handle's parameter types are the types {@code (A...)},
7023 * from the external parameter list.
7024 * </ul>
7025 * <p>
7026 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7027 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
7028 * passed to the loop.
7029 * {@snippet lang="java" :
7030 * V init(A...);
7031 * boolean pred(V, A...);
7032 * V body(V, A...);
7033 * V doWhileLoop(A... a...) {
7034 * V v = init(a...);
7035 * do {
7036 * v = body(v, a...);
7037 * } while (pred(v, a...));
7038 * return v;
7039 * }
7040 * }
7041 *
7042 * @apiNote Example:
7043 * {@snippet lang="java" :
7044 * // int i = 0; while (i < limit) { ++i; } return i; => limit
7045 * static int zero(int limit) { return 0; }
7046 * static int step(int i, int limit) { return i + 1; }
7047 * static boolean pred(int i, int limit) { return i < limit; }
7048 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
7049 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
7050 * assertEquals(23, loop.invoke(23));
7051 * }
7052 *
7053 *
7054 * @apiNote The implementation of this method can be expressed as follows:
7055 * {@snippet lang="java" :
7056 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7057 * MethodHandle fini = (body.type().returnType() == void.class
7058 * ? null : identity(body.type().returnType()));
7059 * MethodHandle[] clause = { init, body, pred, fini };
7060 * return loop(clause);
7061 * }
7062 * }
7063 *
7064 * @param init optional initializer, providing the initial value of the loop variable.
7065 * May be {@code null}, implying a default initial value. See above for other constraints.
7066 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
7067 * See above for other constraints.
7068 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
7069 * above for other constraints.
7070 *
7071 * @return a method handle implementing the {@code while} loop as described by the arguments.
7072 * @throws IllegalArgumentException if the rules for the arguments are violated.
7073 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
7074 *
7075 * @see #loop(MethodHandle[][])
7076 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
7077 * @since 9
7078 */
7079 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7080 whileLoopChecks(init, pred, body);
7081 MethodHandle fini = identityOrVoid(body.type().returnType());
7082 MethodHandle[] clause = {init, body, pred, fini };
7083 return loop(clause);
7084 }
7085
7086 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
7087 Objects.requireNonNull(pred);
7088 Objects.requireNonNull(body);
7089 MethodType bodyType = body.type();
7090 Class<?> returnType = bodyType.returnType();
7091 List<Class<?>> innerList = bodyType.parameterList();
7092 List<Class<?>> outerList = innerList;
7093 if (returnType == void.class) {
7094 // OK
7095 } else if (innerList.isEmpty() || innerList.get(0) != returnType) {
7096 // leading V argument missing => error
7097 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7098 throw misMatchedTypes("body function", bodyType, expected);
7099 } else {
7100 outerList = innerList.subList(1, innerList.size());
7101 }
7102 MethodType predType = pred.type();
7103 if (predType.returnType() != boolean.class ||
7104 !predType.effectivelyIdenticalParameters(0, innerList)) {
7105 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
7106 }
7107 if (init != null) {
7108 MethodType initType = init.type();
7109 if (initType.returnType() != returnType ||
7110 !initType.effectivelyIdenticalParameters(0, outerList)) {
7111 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7112 }
7113 }
7114 }
7115
7116 /**
7117 * Constructs a loop that runs a given number of iterations.
7118 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7119 * <p>
7120 * The number of iterations is determined by the {@code iterations} handle evaluation result.
7121 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
7122 * It will be initialized to 0 and incremented by 1 in each iteration.
7123 * <p>
7124 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7125 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7126 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7127 * <p>
7128 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7129 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7130 * iteration variable.
7131 * The result of the loop handle execution will be the final {@code V} value of that variable
7132 * (or {@code void} if there is no {@code V} variable).
7133 * <p>
7134 * The following rules hold for the argument handles:<ul>
7135 * <li>The {@code iterations} handle must not be {@code null}, and must return
7136 * the type {@code int}, referred to here as {@code I} in parameter type lists.
7137 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7138 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7139 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7140 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7141 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7142 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7143 * of types called the <em>internal parameter list</em>.
7144 * It will constrain the parameter lists of the other loop parts.
7145 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7146 * with no additional {@code A} types, then the internal parameter list is extended by
7147 * the argument types {@code A...} of the {@code iterations} handle.
7148 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7149 * list {@code (A...)} is called the <em>external parameter list</em>.
7150 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7151 * additional state variable of the loop.
7152 * The body must both accept a leading parameter and return a value of this type {@code V}.
7153 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7154 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7155 * <a href="MethodHandles.html#effid">effectively identical</a>
7156 * to the external parameter list {@code (A...)}.
7157 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7158 * {@linkplain #empty default value}.
7159 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
7160 * effectively identical to the external parameter list {@code (A...)}.
7161 * </ul>
7162 * <p>
7163 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7164 * <li>The loop handle's result type is the result type {@code V} of the body.
7165 * <li>The loop handle's parameter types are the types {@code (A...)},
7166 * from the external parameter list.
7167 * </ul>
7168 * <p>
7169 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7170 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7171 * arguments passed to the loop.
7172 * {@snippet lang="java" :
7173 * int iterations(A...);
7174 * V init(A...);
7175 * V body(V, int, A...);
7176 * V countedLoop(A... a...) {
7177 * int end = iterations(a...);
7178 * V v = init(a...);
7179 * for (int i = 0; i < end; ++i) {
7180 * v = body(v, i, a...);
7181 * }
7182 * return v;
7183 * }
7184 * }
7185 *
7186 * @apiNote Example with a fully conformant body method:
7187 * {@snippet lang="java" :
7188 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7189 * // => a variation on a well known theme
7190 * static String step(String v, int counter, String init) { return "na " + v; }
7191 * // assume MH_step is a handle to the method above
7192 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
7193 * MethodHandle start = MethodHandles.identity(String.class);
7194 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
7195 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
7196 * }
7197 *
7198 * @apiNote Example with the simplest possible body method type,
7199 * and passing the number of iterations to the loop invocation:
7200 * {@snippet lang="java" :
7201 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7202 * // => a variation on a well known theme
7203 * static String step(String v, int counter ) { return "na " + v; }
7204 * // assume MH_step is a handle to the method above
7205 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
7206 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
7207 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
7208 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
7209 * }
7210 *
7211 * @apiNote Example that treats the number of iterations, string to append to, and string to append
7212 * as loop parameters:
7213 * {@snippet lang="java" :
7214 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7215 * // => a variation on a well known theme
7216 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
7217 * // assume MH_step is a handle to the method above
7218 * MethodHandle count = MethodHandles.identity(int.class);
7219 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
7220 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
7221 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
7222 * }
7223 *
7224 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
7225 * to enforce a loop type:
7226 * {@snippet lang="java" :
7227 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7228 * // => a variation on a well known theme
7229 * static String step(String v, int counter, String pre) { return pre + " " + v; }
7230 * // assume MH_step is a handle to the method above
7231 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
7232 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
7233 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
7234 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
7235 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
7236 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
7237 * }
7238 *
7239 * @apiNote The implementation of this method can be expressed as follows:
7240 * {@snippet lang="java" :
7241 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7242 * return countedLoop(empty(iterations.type()), iterations, init, body);
7243 * }
7244 * }
7245 *
7246 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
7247 * result type must be {@code int}. See above for other constraints.
7248 * @param init optional initializer, providing the initial value of the loop variable.
7249 * May be {@code null}, implying a default initial value. See above for other constraints.
7250 * @param body body of the loop, which may not be {@code null}.
7251 * It controls the loop parameters and result type in the standard case (see above for details).
7252 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7253 * and may accept any number of additional types.
7254 * See above for other constraints.
7255 *
7256 * @return a method handle representing the loop.
7257 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
7258 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7259 *
7260 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
7261 * @since 9
7262 */
7263 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7264 return countedLoop(empty(iterations.type()), iterations, init, body);
7265 }
7266
7267 /**
7268 * Constructs a loop that counts over a range of numbers.
7269 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7270 * <p>
7271 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
7272 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
7273 * values of the loop counter.
7274 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
7275 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
7276 * <p>
7277 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7278 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7279 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7280 * <p>
7281 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7282 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7283 * iteration variable.
7284 * The result of the loop handle execution will be the final {@code V} value of that variable
7285 * (or {@code void} if there is no {@code V} variable).
7286 * <p>
7287 * The following rules hold for the argument handles:<ul>
7288 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
7289 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
7290 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7291 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7292 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7293 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7294 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7295 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7296 * of types called the <em>internal parameter list</em>.
7297 * It will constrain the parameter lists of the other loop parts.
7298 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7299 * with no additional {@code A} types, then the internal parameter list is extended by
7300 * the argument types {@code A...} of the {@code end} handle.
7301 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7302 * list {@code (A...)} is called the <em>external parameter list</em>.
7303 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7304 * additional state variable of the loop.
7305 * The body must both accept a leading parameter and return a value of this type {@code V}.
7306 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7307 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7308 * <a href="MethodHandles.html#effid">effectively identical</a>
7309 * to the external parameter list {@code (A...)}.
7310 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7311 * {@linkplain #empty default value}.
7312 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
7313 * effectively identical to the external parameter list {@code (A...)}.
7314 * <li>Likewise, the parameter list of {@code end} must be effectively identical
7315 * to the external parameter list.
7316 * </ul>
7317 * <p>
7318 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7319 * <li>The loop handle's result type is the result type {@code V} of the body.
7320 * <li>The loop handle's parameter types are the types {@code (A...)},
7321 * from the external parameter list.
7322 * </ul>
7323 * <p>
7324 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7325 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7326 * arguments passed to the loop.
7327 * {@snippet lang="java" :
7328 * int start(A...);
7329 * int end(A...);
7330 * V init(A...);
7331 * V body(V, int, A...);
7332 * V countedLoop(A... a...) {
7333 * int e = end(a...);
7334 * int s = start(a...);
7335 * V v = init(a...);
7336 * for (int i = s; i < e; ++i) {
7337 * v = body(v, i, a...);
7338 * }
7339 * return v;
7340 * }
7341 * }
7342 *
7343 * @apiNote The implementation of this method can be expressed as follows:
7344 * {@snippet lang="java" :
7345 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7346 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
7347 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
7348 * // the following semantics:
7349 * // MH_increment: (int limit, int counter) -> counter + 1
7350 * // MH_predicate: (int limit, int counter) -> counter < limit
7351 * Class<?> counterType = start.type().returnType(); // int
7352 * Class<?> returnType = body.type().returnType();
7353 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
7354 * if (returnType != void.class) { // ignore the V variable
7355 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7356 * pred = dropArguments(pred, 1, returnType); // ditto
7357 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
7358 * }
7359 * body = dropArguments(body, 0, counterType); // ignore the limit variable
7360 * MethodHandle[]
7361 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7362 * bodyClause = { init, body }, // v = init(); v = body(v, i)
7363 * indexVar = { start, incr }; // i = start(); i = i + 1
7364 * return loop(loopLimit, bodyClause, indexVar);
7365 * }
7366 * }
7367 *
7368 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
7369 * See above for other constraints.
7370 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
7371 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
7372 * @param init optional initializer, providing the initial value of the loop variable.
7373 * May be {@code null}, implying a default initial value. See above for other constraints.
7374 * @param body body of the loop, which may not be {@code null}.
7375 * It controls the loop parameters and result type in the standard case (see above for details).
7376 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7377 * and may accept any number of additional types.
7378 * See above for other constraints.
7379 *
7380 * @return a method handle representing the loop.
7381 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
7382 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7383 *
7384 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
7385 * @since 9
7386 */
7387 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7388 countedLoopChecks(start, end, init, body);
7389 Class<?> counterType = start.type().returnType(); // int, but who's counting?
7390 Class<?> limitType = end.type().returnType(); // yes, int again
7391 Class<?> returnType = body.type().returnType();
7392 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
7393 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
7394 MethodHandle retv = null;
7395 if (returnType != void.class) {
7396 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7397 pred = dropArguments(pred, 1, returnType); // ditto
7398 retv = dropArguments(identity(returnType), 0, counterType);
7399 }
7400 body = dropArguments(body, 0, counterType); // ignore the limit variable
7401 MethodHandle[]
7402 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7403 bodyClause = { init, body }, // v = init(); v = body(v, i)
7404 indexVar = { start, incr }; // i = start(); i = i + 1
7405 return loop(loopLimit, bodyClause, indexVar);
7406 }
7407
7408 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7409 Objects.requireNonNull(start);
7410 Objects.requireNonNull(end);
7411 Objects.requireNonNull(body);
7412 Class<?> counterType = start.type().returnType();
7413 if (counterType != int.class) {
7414 MethodType expected = start.type().changeReturnType(int.class);
7415 throw misMatchedTypes("start function", start.type(), expected);
7416 } else if (end.type().returnType() != counterType) {
7417 MethodType expected = end.type().changeReturnType(counterType);
7418 throw misMatchedTypes("end function", end.type(), expected);
7419 }
7420 MethodType bodyType = body.type();
7421 Class<?> returnType = bodyType.returnType();
7422 List<Class<?>> innerList = bodyType.parameterList();
7423 // strip leading V value if present
7424 int vsize = (returnType == void.class ? 0 : 1);
7425 if (vsize != 0 && (innerList.isEmpty() || innerList.get(0) != returnType)) {
7426 // argument list has no "V" => error
7427 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7428 throw misMatchedTypes("body function", bodyType, expected);
7429 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
7430 // missing I type => error
7431 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
7432 throw misMatchedTypes("body function", bodyType, expected);
7433 }
7434 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
7435 if (outerList.isEmpty()) {
7436 // special case; take lists from end handle
7437 outerList = end.type().parameterList();
7438 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
7439 }
7440 MethodType expected = methodType(counterType, outerList);
7441 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
7442 throw misMatchedTypes("start parameter types", start.type(), expected);
7443 }
7444 if (end.type() != start.type() &&
7445 !end.type().effectivelyIdenticalParameters(0, outerList)) {
7446 throw misMatchedTypes("end parameter types", end.type(), expected);
7447 }
7448 if (init != null) {
7449 MethodType initType = init.type();
7450 if (initType.returnType() != returnType ||
7451 !initType.effectivelyIdenticalParameters(0, outerList)) {
7452 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7453 }
7454 }
7455 }
7456
7457 /**
7458 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
7459 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7460 * <p>
7461 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
7462 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
7463 * <p>
7464 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7465 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7466 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7467 * <p>
7468 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7469 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7470 * iteration variable.
7471 * The result of the loop handle execution will be the final {@code V} value of that variable
7472 * (or {@code void} if there is no {@code V} variable).
7473 * <p>
7474 * The following rules hold for the argument handles:<ul>
7475 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7476 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
7477 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7478 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
7479 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
7480 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
7481 * of types called the <em>internal parameter list</em>.
7482 * It will constrain the parameter lists of the other loop parts.
7483 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
7484 * with no additional {@code A} types, then the internal parameter list is extended by
7485 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
7486 * single type {@code Iterable} is added and constitutes the {@code A...} list.
7487 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
7488 * list {@code (A...)} is called the <em>external parameter list</em>.
7489 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7490 * additional state variable of the loop.
7491 * The body must both accept a leading parameter and return a value of this type {@code V}.
7492 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7493 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7494 * <a href="MethodHandles.html#effid">effectively identical</a>
7495 * to the external parameter list {@code (A...)}.
7496 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7497 * {@linkplain #empty default value}.
7498 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
7499 * type {@code java.util.Iterator} or a subtype thereof.
7500 * The iterator it produces when the loop is executed will be assumed
7501 * to yield values which can be converted to type {@code T}.
7502 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
7503 * effectively identical to the external parameter list {@code (A...)}.
7504 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
7505 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
7506 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
7507 * handle parameter is adjusted to accept the leading {@code A} type, as if by
7508 * the {@link MethodHandle#asType asType} conversion method.
7509 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
7510 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
7511 * </ul>
7512 * <p>
7513 * The type {@code T} may be either a primitive or reference.
7514 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
7515 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
7516 * as if by the {@link MethodHandle#asType asType} conversion method.
7517 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
7518 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
7519 * <p>
7520 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7521 * <li>The loop handle's result type is the result type {@code V} of the body.
7522 * <li>The loop handle's parameter types are the types {@code (A...)},
7523 * from the external parameter list.
7524 * </ul>
7525 * <p>
7526 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7527 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
7528 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
7529 * {@snippet lang="java" :
7530 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
7531 * V init(A...);
7532 * V body(V,T,A...);
7533 * V iteratedLoop(A... a...) {
7534 * Iterator<T> it = iterator(a...);
7535 * V v = init(a...);
7536 * while (it.hasNext()) {
7537 * T t = it.next();
7538 * v = body(v, t, a...);
7539 * }
7540 * return v;
7541 * }
7542 * }
7543 *
7544 * @apiNote Example:
7545 * {@snippet lang="java" :
7546 * // get an iterator from a list
7547 * static List<String> reverseStep(List<String> r, String e) {
7548 * r.add(0, e);
7549 * return r;
7550 * }
7551 * static List<String> newArrayList() { return new ArrayList<>(); }
7552 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
7553 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
7554 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
7555 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
7556 * assertEquals(reversedList, (List<String>) loop.invoke(list));
7557 * }
7558 *
7559 * @apiNote The implementation of this method can be expressed approximately as follows:
7560 * {@snippet lang="java" :
7561 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7562 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
7563 * Class<?> returnType = body.type().returnType();
7564 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7565 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
7566 * MethodHandle retv = null, step = body, startIter = iterator;
7567 * if (returnType != void.class) {
7568 * // the simple thing first: in (I V A...), drop the I to get V
7569 * retv = dropArguments(identity(returnType), 0, Iterator.class);
7570 * // body type signature (V T A...), internal loop types (I V A...)
7571 * step = swapArguments(body, 0, 1); // swap V <-> T
7572 * }
7573 * if (startIter == null) startIter = MH_getIter;
7574 * MethodHandle[]
7575 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
7576 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
7577 * return loop(iterVar, bodyClause);
7578 * }
7579 * }
7580 *
7581 * @param iterator an optional handle to return the iterator to start the loop.
7582 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
7583 * See above for other constraints.
7584 * @param init optional initializer, providing the initial value of the loop variable.
7585 * May be {@code null}, implying a default initial value. See above for other constraints.
7586 * @param body body of the loop, which may not be {@code null}.
7587 * It controls the loop parameters and result type in the standard case (see above for details).
7588 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
7589 * and may accept any number of additional types.
7590 * See above for other constraints.
7591 *
7592 * @return a method handle embodying the iteration loop functionality.
7593 * @throws NullPointerException if the {@code body} handle is {@code null}.
7594 * @throws IllegalArgumentException if any argument violates the above requirements.
7595 *
7596 * @since 9
7597 */
7598 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7599 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
7600 Class<?> returnType = body.type().returnType();
7601 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
7602 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
7603 MethodHandle startIter;
7604 MethodHandle nextVal;
7605 {
7606 MethodType iteratorType;
7607 if (iterator == null) {
7608 // derive argument type from body, if available, else use Iterable
7609 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
7610 iteratorType = startIter.type().changeParameterType(0, iterableType);
7611 } else {
7612 // force return type to the internal iterator class
7613 iteratorType = iterator.type().changeReturnType(Iterator.class);
7614 startIter = iterator;
7615 }
7616 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7617 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
7618
7619 // perform the asType transforms under an exception transformer, as per spec.:
7620 try {
7621 startIter = startIter.asType(iteratorType);
7622 nextVal = nextRaw.asType(nextValType);
7623 } catch (WrongMethodTypeException ex) {
7624 throw new IllegalArgumentException(ex);
7625 }
7626 }
7627
7628 MethodHandle retv = null, step = body;
7629 if (returnType != void.class) {
7630 // the simple thing first: in (I V A...), drop the I to get V
7631 retv = dropArguments(identity(returnType), 0, Iterator.class);
7632 // body type signature (V T A...), internal loop types (I V A...)
7633 step = swapArguments(body, 0, 1); // swap V <-> T
7634 }
7635
7636 MethodHandle[]
7637 iterVar = { startIter, null, hasNext, retv },
7638 bodyClause = { init, filterArgument(step, 0, nextVal) };
7639 return loop(iterVar, bodyClause);
7640 }
7641
7642 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7643 Objects.requireNonNull(body);
7644 MethodType bodyType = body.type();
7645 Class<?> returnType = bodyType.returnType();
7646 List<Class<?>> internalParamList = bodyType.parameterList();
7647 // strip leading V value if present
7648 int vsize = (returnType == void.class ? 0 : 1);
7649 if (vsize != 0 && (internalParamList.isEmpty() || internalParamList.get(0) != returnType)) {
7650 // argument list has no "V" => error
7651 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7652 throw misMatchedTypes("body function", bodyType, expected);
7653 } else if (internalParamList.size() <= vsize) {
7654 // missing T type => error
7655 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
7656 throw misMatchedTypes("body function", bodyType, expected);
7657 }
7658 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
7659 Class<?> iterableType = null;
7660 if (iterator != null) {
7661 // special case; if the body handle only declares V and T then
7662 // the external parameter list is obtained from iterator handle
7663 if (externalParamList.isEmpty()) {
7664 externalParamList = iterator.type().parameterList();
7665 }
7666 MethodType itype = iterator.type();
7667 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
7668 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
7669 }
7670 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
7671 MethodType expected = methodType(itype.returnType(), externalParamList);
7672 throw misMatchedTypes("iterator parameters", itype, expected);
7673 }
7674 } else {
7675 if (externalParamList.isEmpty()) {
7676 // special case; if the iterator handle is null and the body handle
7677 // only declares V and T then the external parameter list consists
7678 // of Iterable
7679 externalParamList = List.of(Iterable.class);
7680 iterableType = Iterable.class;
7681 } else {
7682 // special case; if the iterator handle is null and the external
7683 // parameter list is not empty then the first parameter must be
7684 // assignable to Iterable
7685 iterableType = externalParamList.get(0);
7686 if (!Iterable.class.isAssignableFrom(iterableType)) {
7687 throw newIllegalArgumentException(
7688 "inferred first loop argument must inherit from Iterable: " + iterableType);
7689 }
7690 }
7691 }
7692 if (init != null) {
7693 MethodType initType = init.type();
7694 if (initType.returnType() != returnType ||
7695 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
7696 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
7697 }
7698 }
7699 return iterableType; // help the caller a bit
7700 }
7701
7702 /*non-public*/
7703 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
7704 // there should be a better way to uncross my wires
7705 int arity = mh.type().parameterCount();
7706 int[] order = new int[arity];
7707 for (int k = 0; k < arity; k++) order[k] = k;
7708 order[i] = j; order[j] = i;
7709 Class<?>[] types = mh.type().parameterArray();
7710 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
7711 MethodType swapType = methodType(mh.type().returnType(), types);
7712 return permuteArguments(mh, swapType, order);
7713 }
7714
7715 /**
7716 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
7717 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
7718 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
7719 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
7720 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
7721 * {@code try-finally} handle.
7722 * <p>
7723 * The {@code cleanup} handle will be passed one or two additional leading arguments.
7724 * The first is the exception thrown during the
7725 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
7726 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
7727 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
7728 * The second argument is not present if the {@code target} handle has a {@code void} return type.
7729 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
7730 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
7731 * <p>
7732 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
7733 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
7734 * two extra leading parameters:<ul>
7735 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
7736 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
7737 * the result from the execution of the {@code target} handle.
7738 * This parameter is not present if the {@code target} returns {@code void}.
7739 * </ul>
7740 * <p>
7741 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
7742 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
7743 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
7744 * the cleanup.
7745 * {@snippet lang="java" :
7746 * V target(A..., B...);
7747 * V cleanup(Throwable, V, A...);
7748 * V adapter(A... a, B... b) {
7749 * V result = (zero value for V);
7750 * Throwable throwable = null;
7751 * try {
7752 * result = target(a..., b...);
7753 * } catch (Throwable t) {
7754 * throwable = t;
7755 * throw t;
7756 * } finally {
7757 * result = cleanup(throwable, result, a...);
7758 * }
7759 * return result;
7760 * }
7761 * }
7762 * <p>
7763 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
7764 * be modified by execution of the target, and so are passed unchanged
7765 * from the caller to the cleanup, if it is invoked.
7766 * <p>
7767 * The target and cleanup must return the same type, even if the cleanup
7768 * always throws.
7769 * To create such a throwing cleanup, compose the cleanup logic
7770 * with {@link #throwException throwException},
7771 * in order to create a method handle of the correct return type.
7772 * <p>
7773 * Note that {@code tryFinally} never converts exceptions into normal returns.
7774 * In rare cases where exceptions must be converted in that way, first wrap
7775 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
7776 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
7777 * <p>
7778 * It is recommended that the first parameter type of {@code cleanup} be
7779 * declared {@code Throwable} rather than a narrower subtype. This ensures
7780 * {@code cleanup} will always be invoked with whatever exception that
7781 * {@code target} throws. Declaring a narrower type may result in a
7782 * {@code ClassCastException} being thrown by the {@code try-finally}
7783 * handle if the type of the exception thrown by {@code target} is not
7784 * assignable to the first parameter type of {@code cleanup}. Note that
7785 * various exception types of {@code VirtualMachineError},
7786 * {@code LinkageError}, and {@code RuntimeException} can in principle be
7787 * thrown by almost any kind of Java code, and a finally clause that
7788 * catches (say) only {@code IOException} would mask any of the others
7789 * behind a {@code ClassCastException}.
7790 *
7791 * @param target the handle whose execution is to be wrapped in a {@code try} block.
7792 * @param cleanup the handle that is invoked in the finally block.
7793 *
7794 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
7795 * @throws NullPointerException if any argument is null
7796 * @throws IllegalArgumentException if {@code cleanup} does not accept
7797 * the required leading arguments, or if the method handle types do
7798 * not match in their return types and their
7799 * corresponding trailing parameters
7800 *
7801 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
7802 * @since 9
7803 */
7804 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
7805 Class<?>[] targetParamTypes = target.type().ptypes();
7806 Class<?> rtype = target.type().returnType();
7807
7808 tryFinallyChecks(target, cleanup);
7809
7810 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
7811 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7812 // target parameter list.
7813 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0, false);
7814
7815 // Ensure that the intrinsic type checks the instance thrown by the
7816 // target against the first parameter of cleanup
7817 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
7818
7819 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
7820 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
7821 }
7822
7823 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
7824 Class<?> rtype = target.type().returnType();
7825 if (rtype != cleanup.type().returnType()) {
7826 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
7827 }
7828 MethodType cleanupType = cleanup.type();
7829 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
7830 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
7831 }
7832 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
7833 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
7834 }
7835 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7836 // target parameter list.
7837 int cleanupArgIndex = rtype == void.class ? 1 : 2;
7838 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
7839 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
7840 cleanup.type(), target.type());
7841 }
7842 }
7843
7844 /**
7845 * Creates a table switch method handle, which can be used to switch over a set of target
7846 * method handles, based on a given target index, called selector.
7847 * <p>
7848 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)},
7849 * and where {@code N} is the number of target method handles, the table switch method
7850 * handle will invoke the n-th target method handle from the list of target method handles.
7851 * <p>
7852 * For a selector value that does not fall in the range {@code [0, N)}, the table switch
7853 * method handle will invoke the given fallback method handle.
7854 * <p>
7855 * All method handles passed to this method must have the same type, with the additional
7856 * requirement that the leading parameter be of type {@code int}. The leading parameter
7857 * represents the selector.
7858 * <p>
7859 * Any trailing parameters present in the type will appear on the returned table switch
7860 * method handle as well. Any arguments assigned to these parameters will be forwarded,
7861 * together with the selector value, to the selected method handle when invoking it.
7862 *
7863 * @apiNote Example:
7864 * The cases each drop the {@code selector} value they are given, and take an additional
7865 * {@code String} argument, which is concatenated (using {@link String#concat(String)})
7866 * to a specific constant label string for each case:
7867 * {@snippet lang="java" :
7868 * MethodHandles.Lookup lookup = MethodHandles.lookup();
7869 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat",
7870 * MethodType.methodType(String.class, String.class));
7871 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class);
7872 *
7873 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: ");
7874 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: ");
7875 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: ");
7876 *
7877 * MethodHandle mhSwitch = MethodHandles.tableSwitch(
7878 * caseDefault,
7879 * case0,
7880 * case1
7881 * );
7882 *
7883 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data"));
7884 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data"));
7885 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data"));
7886 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data"));
7887 * }
7888 *
7889 * @param fallback the fallback method handle that is called when the selector is not
7890 * within the range {@code [0, N)}.
7891 * @param targets array of target method handles.
7892 * @return the table switch method handle.
7893 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any
7894 * any of the elements of the {@code targets} array are
7895 * {@code null}.
7896 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading
7897 * parameter of the fallback handle or any of the target
7898 * handles is not {@code int}, or if the types of
7899 * the fallback handle and all of target handles are
7900 * not the same.
7901 *
7902 * @since 17
7903 */
7904 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) {
7905 Objects.requireNonNull(fallback);
7906 Objects.requireNonNull(targets);
7907 targets = targets.clone();
7908 MethodType type = tableSwitchChecks(fallback, targets);
7909 return MethodHandleImpl.makeTableSwitch(type, fallback, targets);
7910 }
7911
7912 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) {
7913 if (caseActions.length == 0)
7914 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions));
7915
7916 MethodType expectedType = defaultCase.type();
7917
7918 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class)
7919 throw new IllegalArgumentException(
7920 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions));
7921
7922 for (MethodHandle mh : caseActions) {
7923 Objects.requireNonNull(mh);
7924 if (mh.type() != expectedType)
7925 throw new IllegalArgumentException(
7926 "Case actions must have the same type: " + Arrays.toString(caseActions));
7927 }
7928
7929 return expectedType;
7930 }
7931
7932 /**
7933 * Adapts a target var handle by pre-processing incoming and outgoing values using a pair of filter functions.
7934 * <p>
7935 * When calling e.g. {@link VarHandle#set(Object...)} on the resulting var handle, the incoming value (of type {@code T}, where
7936 * {@code T} is the <em>last</em> parameter type of the first filter function) is processed using the first filter and then passed
7937 * to the target var handle.
7938 * Conversely, when calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the return value obtained from
7939 * the target var handle (of type {@code T}, where {@code T} is the <em>last</em> parameter type of the second filter function)
7940 * is processed using the second filter and returned to the caller. More advanced access mode types, such as
7941 * {@link VarHandle.AccessMode#COMPARE_AND_EXCHANGE} might apply both filters at the same time.
7942 * <p>
7943 * For the boxing and unboxing filters to be well-formed, their types must be of the form {@code (A... , S) -> T} and
7944 * {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle. If this is the case,
7945 * the resulting var handle will have type {@code S} and will feature the additional coordinates {@code A...} (which
7946 * will be appended to the coordinates of the target var handle).
7947 * <p>
7948 * If the boxing and unboxing filters throw any checked exceptions when invoked, the resulting var handle will
7949 * throw an {@link IllegalStateException}.
7950 * <p>
7951 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7952 * atomic access guarantees as those featured by the target var handle.
7953 *
7954 * @param target the target var handle
7955 * @param filterToTarget a filter to convert some type {@code S} into the type of {@code target}
7956 * @param filterFromTarget a filter to convert the type of {@code target} to some type {@code S}
7957 * @return an adapter var handle which accepts a new type, performing the provided boxing/unboxing conversions.
7958 * @throws IllegalArgumentException if {@code filterFromTarget} and {@code filterToTarget} are not well-formed, that is, they have types
7959 * other than {@code (A... , S) -> T} and {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle,
7960 * or if it's determined that either {@code filterFromTarget} or {@code filterToTarget} throws any checked exceptions.
7961 * @throws NullPointerException if any of the arguments is {@code null}.
7962 * @since 22
7963 */
7964 public static VarHandle filterValue(VarHandle target, MethodHandle filterToTarget, MethodHandle filterFromTarget) {
7965 return VarHandles.filterValue(target, filterToTarget, filterFromTarget);
7966 }
7967
7968 /**
7969 * Adapts a target var handle by pre-processing incoming coordinate values using unary filter functions.
7970 * <p>
7971 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the incoming coordinate values
7972 * starting at position {@code pos} (of type {@code C1, C2 ... Cn}, where {@code C1, C2 ... Cn} are the return types
7973 * of the unary filter functions) are transformed into new values (of type {@code S1, S2 ... Sn}, where {@code S1, S2 ... Sn} are the
7974 * parameter types of the unary filter functions), and then passed (along with any coordinate that was left unaltered
7975 * by the adaptation) to the target var handle.
7976 * <p>
7977 * For the coordinate filters to be well-formed, their types must be of the form {@code S1 -> T1, S2 -> T1 ... Sn -> Tn},
7978 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
7979 * <p>
7980 * If any of the filters throws a checked exception when invoked, the resulting var handle will
7981 * throw an {@link IllegalStateException}.
7982 * <p>
7983 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7984 * atomic access guarantees as those featured by the target var handle.
7985 *
7986 * @param target the target var handle
7987 * @param pos the position of the first coordinate to be transformed
7988 * @param filters the unary functions which are used to transform coordinates starting at position {@code pos}
7989 * @return an adapter var handle which accepts new coordinate types, applying the provided transformation
7990 * to the new coordinate values.
7991 * @throws IllegalArgumentException if the handles in {@code filters} are not well-formed, that is, they have types
7992 * other than {@code S1 -> T1, S2 -> T2, ... Sn -> Tn} where {@code T1, T2 ... Tn} are the coordinate types starting
7993 * at position {@code pos} of the target var handle, if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
7994 * or if more filters are provided than the actual number of coordinate types available starting at {@code pos},
7995 * or if it's determined that any of the filters throws any checked exceptions.
7996 * @throws NullPointerException if any of the arguments is {@code null} or {@code filters} contains {@code null}.
7997 * @since 22
7998 */
7999 public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) {
8000 return VarHandles.filterCoordinates(target, pos, filters);
8001 }
8002
8003 /**
8004 * Provides a target var handle with one or more <em>bound coordinates</em>
8005 * in advance of the var handle's invocation. As a consequence, the resulting var handle will feature less
8006 * coordinate types than the target var handle.
8007 * <p>
8008 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, incoming coordinate values
8009 * are joined with bound coordinate values, and then passed to the target var handle.
8010 * <p>
8011 * For the bound coordinates to be well-formed, their types must be {@code T1, T2 ... Tn },
8012 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
8013 * <p>
8014 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8015 * atomic access guarantees as those featured by the target var handle.
8016 *
8017 * @param target the var handle to invoke after the bound coordinates are inserted
8018 * @param pos the position of the first coordinate to be inserted
8019 * @param values the series of bound coordinates to insert
8020 * @return an adapter var handle which inserts additional coordinates,
8021 * before calling the target var handle
8022 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8023 * or if more values are provided than the actual number of coordinate types available starting at {@code pos}.
8024 * @throws ClassCastException if the bound coordinates in {@code values} are not well-formed, that is, they have types
8025 * other than {@code T1, T2 ... Tn }, where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos}
8026 * of the target var handle.
8027 * @throws NullPointerException if any of the arguments is {@code null} or {@code values} contains {@code null}.
8028 * @since 22
8029 */
8030 public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) {
8031 return VarHandles.insertCoordinates(target, pos, values);
8032 }
8033
8034 /**
8035 * Provides a var handle which adapts the coordinate values of the target var handle, by re-arranging them
8036 * so that the new coordinates match the provided ones.
8037 * <p>
8038 * The given array controls the reordering.
8039 * Call {@code #I} the number of incoming coordinates (the value
8040 * {@code newCoordinates.size()}), and call {@code #O} the number
8041 * of outgoing coordinates (the number of coordinates associated with the target var handle).
8042 * Then the length of the reordering array must be {@code #O},
8043 * and each element must be a non-negative number less than {@code #I}.
8044 * For every {@code N} less than {@code #O}, the {@code N}-th
8045 * outgoing coordinate will be taken from the {@code I}-th incoming
8046 * coordinate, where {@code I} is {@code reorder[N]}.
8047 * <p>
8048 * No coordinate value conversions are applied.
8049 * The type of each incoming coordinate, as determined by {@code newCoordinates},
8050 * must be identical to the type of the corresponding outgoing coordinate
8051 * in the target var handle.
8052 * <p>
8053 * The reordering array need not specify an actual permutation.
8054 * An incoming coordinate will be duplicated if its index appears
8055 * more than once in the array, and an incoming coordinate will be dropped
8056 * if its index does not appear in the array.
8057 * <p>
8058 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8059 * atomic access guarantees as those featured by the target var handle.
8060 * @param target the var handle to invoke after the coordinates have been reordered
8061 * @param newCoordinates the new coordinate types
8062 * @param reorder an index array which controls the reordering
8063 * @return an adapter var handle which re-arranges the incoming coordinate values,
8064 * before calling the target var handle
8065 * @throws IllegalArgumentException if the index array length is not equal to
8066 * the number of coordinates of the target var handle, or if any index array element is not a valid index for
8067 * a coordinate of {@code newCoordinates}, or if two corresponding coordinate types in
8068 * the target var handle and in {@code newCoordinates} are not identical.
8069 * @throws NullPointerException if any of the arguments is {@code null} or {@code newCoordinates} contains {@code null}.
8070 * @since 22
8071 */
8072 public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) {
8073 return VarHandles.permuteCoordinates(target, newCoordinates, reorder);
8074 }
8075
8076 /**
8077 * Adapts a target var handle by pre-processing
8078 * a sub-sequence of its coordinate values with a filter (a method handle).
8079 * The pre-processed coordinates are replaced by the result (if any) of the
8080 * filter function and the target var handle is then called on the modified (usually shortened)
8081 * coordinate list.
8082 * <p>
8083 * If {@code R} is the return type of the filter, then:
8084 * <ul>
8085 * <li>if {@code R} <em>is not</em> {@code void}, the target var handle must have a coordinate of type {@code R} in
8086 * position {@code pos}. The parameter types of the filter will replace the coordinate type at position {@code pos}
8087 * of the target var handle. When the returned var handle is invoked, it will be as if the filter is invoked first,
8088 * and its result is passed in place of the coordinate at position {@code pos} in a downstream invocation of the
8089 * target var handle.</li>
8090 * <li> if {@code R} <em>is</em> {@code void}, the parameter types (if any) of the filter will be inserted in the
8091 * coordinate type list of the target var handle at position {@code pos}. In this case, when the returned var handle
8092 * is invoked, the filter essentially acts as a side effect, consuming some of the coordinate values, before a
8093 * downstream invocation of the target var handle.</li>
8094 * </ul>
8095 * <p>
8096 * If any of the filters throws a checked exception when invoked, the resulting var handle will
8097 * throw an {@link IllegalStateException}.
8098 * <p>
8099 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8100 * atomic access guarantees as those featured by the target var handle.
8101 *
8102 * @param target the var handle to invoke after the coordinates have been filtered
8103 * @param pos the position in the coordinate list of the target var handle where the filter is to be inserted
8104 * @param filter the filter method handle
8105 * @return an adapter var handle which filters the incoming coordinate values,
8106 * before calling the target var handle
8107 * @throws IllegalArgumentException if the return type of {@code filter}
8108 * is not void, and it is not the same as the {@code pos} coordinate of the target var handle,
8109 * if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8110 * if the resulting var handle's type would have <a href="MethodHandle.html#maxarity">too many coordinates</a>,
8111 * or if it's determined that {@code filter} throws any checked exceptions.
8112 * @throws NullPointerException if any of the arguments is {@code null}.
8113 * @since 22
8114 */
8115 public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle filter) {
8116 return VarHandles.collectCoordinates(target, pos, filter);
8117 }
8118
8119 /**
8120 * Returns a var handle which will discard some dummy coordinates before delegating to the
8121 * target var handle. As a consequence, the resulting var handle will feature more
8122 * coordinate types than the target var handle.
8123 * <p>
8124 * The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is the arity of the
8125 * target var handle's coordinate types. If {@code pos} is zero, the dummy coordinates will precede
8126 * the target's real arguments; if {@code pos} is <i>N</i> they will come after.
8127 * <p>
8128 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8129 * atomic access guarantees as those featured by the target var handle.
8130 *
8131 * @param target the var handle to invoke after the dummy coordinates are dropped
8132 * @param pos position of the first coordinate to drop (zero for the leftmost)
8133 * @param valueTypes the type(s) of the coordinate(s) to drop
8134 * @return an adapter var handle which drops some dummy coordinates,
8135 * before calling the target var handle
8136 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive.
8137 * @throws NullPointerException if any of the arguments is {@code null} or {@code valueTypes} contains {@code null}.
8138 * @since 22
8139 */
8140 public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) {
8141 return VarHandles.dropCoordinates(target, pos, valueTypes);
8142 }
8143 }