1 /*
2 * Copyright (c) 2008, 2017, 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.misc.SharedSecrets;
29 import jdk.internal.module.IllegalAccessLogger;
30 import jdk.internal.org.objectweb.asm.ClassReader;
31 import jdk.internal.reflect.CallerSensitive;
32 import jdk.internal.reflect.Reflection;
33 import jdk.internal.vm.annotation.ForceInline;
34 import sun.invoke.util.ValueConversions;
35 import sun.invoke.util.VerifyAccess;
36 import sun.invoke.util.Wrapper;
37 import sun.reflect.misc.ReflectUtil;
38 import sun.security.util.SecurityConstants;
39
40 import java.lang.invoke.LambdaForm.BasicType;
41 import java.lang.reflect.Constructor;
42 import java.lang.reflect.Field;
43 import java.lang.reflect.Member;
44 import java.lang.reflect.Method;
45 import java.lang.reflect.Modifier;
46 import java.lang.reflect.ReflectPermission;
47 import java.nio.ByteOrder;
48 import java.security.AccessController;
49 import java.security.PrivilegedAction;
50 import java.security.ProtectionDomain;
51 import java.util.ArrayList;
52 import java.util.Arrays;
53 import java.util.BitSet;
54 import java.util.Iterator;
55 import java.util.List;
56 import java.util.Objects;
57 import java.util.concurrent.ConcurrentHashMap;
58 import java.util.stream.Collectors;
59 import java.util.stream.Stream;
60
61 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
62 import static java.lang.invoke.MethodHandleNatives.Constants.*;
63 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
64 import static java.lang.invoke.MethodType.methodType;
65
66 /**
67 * This class consists exclusively of static methods that operate on or return
68 * method handles. They fall into several categories:
69 * <ul>
70 * <li>Lookup methods which help create method handles for methods and fields.
71 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
72 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
73 * </ul>
74 *
75 * @author John Rose, JSR 292 EG
76 * @since 1.7
77 */
78 public class MethodHandles {
79
80 private MethodHandles() { } // do not instantiate
81
82 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
83
84 // See IMPL_LOOKUP below.
85
86 //// Method handle creation from ordinary methods.
87
88 /**
89 * Returns a {@link Lookup lookup object} with
90 * full capabilities to emulate all supported bytecode behaviors of the caller.
91 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
92 * Factory methods on the lookup object can create
93 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
94 * for any member that the caller has access to via bytecodes,
95 * including protected and private fields and methods.
96 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
97 * Do not store it in place where untrusted code can access it.
98 * <p>
99 * This method is caller sensitive, which means that it may return different
100 * values to different callers.
101 * <p>
102 * For any given caller class {@code C}, the lookup object returned by this call
103 * has equivalent capabilities to any lookup object
104 * supplied by the JVM to the bootstrap method of an
105 * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>
106 * executing in the same caller class {@code C}.
107 * @return a lookup object for the caller of this method, with private access
108 */
109 @CallerSensitive
110 @ForceInline // to ensure Reflection.getCallerClass optimization
111 public static Lookup lookup() {
112 return new Lookup(Reflection.getCallerClass());
113 }
114
115 /**
116 * This reflected$lookup method is the alternate implementation of
117 * the lookup method when being invoked by reflection.
118 */
119 @CallerSensitive
120 private static Lookup reflected$lookup() {
121 Class<?> caller = Reflection.getCallerClass();
122 if (caller.getClassLoader() == null) {
123 throw newIllegalArgumentException("illegal lookupClass: "+caller);
124 }
125 return new Lookup(caller);
126 }
127
128 /**
129 * Returns a {@link Lookup lookup object} which is trusted minimally.
130 * The lookup has the {@code PUBLIC} and {@code UNCONDITIONAL} modes.
131 * It can only be used to create method handles to public members of
132 * public classes in packages that are exported unconditionally.
133 * <p>
134 * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
135 * of this lookup object will be {@link java.lang.Object}.
136 *
137 * @apiNote The use of Object is conventional, and because the lookup modes are
138 * limited, there is no special access provided to the internals of Object, its package
139 * or its module. Consequently, the lookup context of this lookup object will be the
140 * bootstrap class loader, which means it cannot find user classes.
141 *
142 * <p style="font-size:smaller;">
143 * <em>Discussion:</em>
144 * The lookup class can be changed to any other class {@code C} using an expression of the form
145 * {@link Lookup#in publicLookup().in(C.class)}.
146 * but may change the lookup context by virtue of changing the class loader.
147 * A public lookup object is always subject to
148 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
149 * Also, it cannot access
150 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
151 * @return a lookup object which is trusted minimally
152 *
153 * @revised 9
154 * @spec JPMS
155 */
156 public static Lookup publicLookup() {
157 return Lookup.PUBLIC_LOOKUP;
158 }
159
160 /**
161 * Returns a {@link Lookup lookup object} with full capabilities to emulate all
162 * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">
163 * private access</a>, on a target class.
164 * This method checks that a caller, specified as a {@code Lookup} object, is allowed to
165 * do <em>deep reflection</em> on the target class. If {@code m1} is the module containing
166 * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing
167 * the target class, then this check ensures that
168 * <ul>
169 * <li>{@code m1} {@link Module#canRead reads} {@code m2}.</li>
170 * <li>{@code m2} {@link Module#isOpen(String,Module) opens} the package containing
171 * the target class to at least {@code m1}.</li>
172 * <li>The lookup has the {@link Lookup#MODULE MODULE} lookup mode.</li>
173 * </ul>
174 * <p>
175 * If there is a security manager, its {@code checkPermission} method is called to
176 * check {@code ReflectPermission("suppressAccessChecks")}.
177 * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object
178 * was created by code in the caller module (or derived from a lookup object originally
179 * created by the caller). A lookup object with the {@code MODULE} lookup mode can be
180 * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE}
181 * access to the caller.
182 * @param targetClass the target class
183 * @param lookup the caller lookup object
184 * @return a lookup object for the target class, with private access
185 * @throws IllegalArgumentException if {@code targetClass} is a primitve type or array class
186 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
187 * @throws IllegalAccessException if the access check specified above fails
188 * @throws SecurityException if denied by the security manager
189 * @since 9
190 * @spec JPMS
191 * @see Lookup#dropLookupMode
192 */
193 public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException {
194 SecurityManager sm = System.getSecurityManager();
195 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
196 if (targetClass.isPrimitive())
197 throw new IllegalArgumentException(targetClass + " is a primitive class");
198 if (targetClass.isArray())
199 throw new IllegalArgumentException(targetClass + " is an array class");
200 Module targetModule = targetClass.getModule();
201 Module callerModule = lookup.lookupClass().getModule();
202 if (!callerModule.canRead(targetModule))
203 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
204 if (targetModule.isNamed()) {
205 String pn = targetClass.getPackageName();
206 assert pn.length() > 0 : "unnamed package cannot be in named module";
207 if (!targetModule.isOpen(pn, callerModule))
208 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
209 }
210 if ((lookup.lookupModes() & Lookup.MODULE) == 0)
211 throw new IllegalAccessException("lookup does not have MODULE lookup mode");
212 if (!callerModule.isNamed() && targetModule.isNamed()) {
213 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
214 if (logger != null) {
215 logger.logIfOpenedForIllegalAccess(lookup, targetClass);
216 }
217 }
218 return new Lookup(targetClass);
219 }
220
221 /**
222 * Performs an unchecked "crack" of a
223 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
224 * The result is as if the user had obtained a lookup object capable enough
225 * to crack the target method handle, called
226 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
227 * on the target to obtain its symbolic reference, and then called
228 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
229 * to resolve the symbolic reference to a member.
230 * <p>
231 * If there is a security manager, its {@code checkPermission} method
232 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
233 * @param <T> the desired type of the result, either {@link Member} or a subtype
234 * @param target a direct method handle to crack into symbolic reference components
235 * @param expected a class object representing the desired result type {@code T}
236 * @return a reference to the method, constructor, or field object
237 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
238 * @exception NullPointerException if either argument is {@code null}
239 * @exception IllegalArgumentException if the target is not a direct method handle
240 * @exception ClassCastException if the member is not of the expected type
241 * @since 1.8
242 */
243 public static <T extends Member> T
244 reflectAs(Class<T> expected, MethodHandle target) {
245 SecurityManager smgr = System.getSecurityManager();
246 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
247 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
248 return lookup.revealDirect(target).reflectAs(expected, lookup);
249 }
250 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
251 private static final java.security.Permission ACCESS_PERMISSION =
252 new ReflectPermission("suppressAccessChecks");
253
254 /**
255 * A <em>lookup object</em> is a factory for creating method handles,
256 * when the creation requires access checking.
257 * Method handles do not perform
258 * access checks when they are called, but rather when they are created.
259 * Therefore, method handle access
260 * restrictions must be enforced when a method handle is created.
261 * The caller class against which those restrictions are enforced
262 * is known as the {@linkplain #lookupClass lookup class}.
263 * <p>
264 * A lookup class which needs to create method handles will call
265 * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
266 * When the {@code Lookup} factory object is created, the identity of the lookup class is
267 * determined, and securely stored in the {@code Lookup} object.
268 * The lookup class (or its delegates) may then use factory methods
269 * on the {@code Lookup} object to create method handles for access-checked members.
270 * This includes all methods, constructors, and fields which are allowed to the lookup class,
271 * even private ones.
272 *
273 * <h1><a id="lookups"></a>Lookup Factory Methods</h1>
274 * The factory methods on a {@code Lookup} object correspond to all major
275 * use cases for methods, constructors, and fields.
276 * Each method handle created by a factory method is the functional
277 * equivalent of a particular <em>bytecode behavior</em>.
278 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
279 * Here is a summary of the correspondence between these factory methods and
280 * the behavior of the resulting method handles:
281 * <table class="striped">
282 * <caption style="display:none">lookup method behaviors</caption>
283 * <thead>
284 * <tr>
285 * <th scope="col"><a id="equiv"></a>lookup expression</th>
286 * <th scope="col">member</th>
287 * <th scope="col">bytecode behavior</th>
288 * </tr>
289 * </thead>
290 * <tbody>
291 * <tr>
292 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
293 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
294 * </tr>
295 * <tr>
296 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
297 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
298 * </tr>
299 * <tr>
300 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
301 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
302 * </tr>
303 * <tr>
304 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
305 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
306 * </tr>
307 * <tr>
308 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
309 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
310 * </tr>
311 * <tr>
312 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
313 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
314 * </tr>
315 * <tr>
316 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
317 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
318 * </tr>
319 * <tr>
320 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
321 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
322 * </tr>
323 * <tr>
324 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
325 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
326 * </tr>
327 * <tr>
328 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
329 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
330 * </tr>
331 * <tr>
332 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
333 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
334 * </tr>
335 * <tr>
336 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
337 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
338 * </tr>
339 * <tr>
340 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
341 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
342 * </tr>
343 * <tr>
344 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
345 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
346 * </tr>
347 * </tbody>
348 * </table>
349 *
350 * Here, the type {@code C} is the class or interface being searched for a member,
351 * documented as a parameter named {@code refc} in the lookup methods.
352 * The method type {@code MT} is composed from the return type {@code T}
353 * and the sequence of argument types {@code A*}.
354 * The constructor also has a sequence of argument types {@code A*} and
355 * is deemed to return the newly-created object of type {@code C}.
356 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
357 * The formal parameter {@code this} stands for the self-reference of type {@code C};
358 * if it is present, it is always the leading argument to the method handle invocation.
359 * (In the case of some {@code protected} members, {@code this} may be
360 * restricted in type to the lookup class; see below.)
361 * The name {@code arg} stands for all the other method handle arguments.
362 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
363 * stands for a null reference if the accessed method or field is static,
364 * and {@code this} otherwise.
365 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
366 * for reflective objects corresponding to the given members.
367 * <p>
368 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
369 * as if by {@code ldc CONSTANT_Class}.
370 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
371 * <p>
372 * In cases where the given member is of variable arity (i.e., a method or constructor)
373 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
374 * In all other cases, the returned method handle will be of fixed arity.
375 * <p style="font-size:smaller;">
376 * <em>Discussion:</em>
377 * The equivalence between looked-up method handles and underlying
378 * class members and bytecode behaviors
379 * can break down in a few ways:
380 * <ul style="font-size:smaller;">
381 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
382 * the lookup can still succeed, even when there is no equivalent
383 * Java expression or bytecoded constant.
384 * <li>Likewise, if {@code T} or {@code MT}
385 * is not symbolically accessible from the lookup class's loader,
386 * the lookup can still succeed.
387 * For example, lookups for {@code MethodHandle.invokeExact} and
388 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
389 * <li>If there is a security manager installed, it can forbid the lookup
390 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
391 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
392 * constant is not subject to security manager checks.
393 * <li>If the looked-up method has a
394 * <a href="MethodHandle.html#maxarity">very large arity</a>,
395 * the method handle creation may fail, due to the method handle
396 * type having too many parameters.
397 * </ul>
398 *
399 * <h1><a id="access"></a>Access checking</h1>
400 * Access checks are applied in the factory methods of {@code Lookup},
401 * when a method handle is created.
402 * This is a key difference from the Core Reflection API, since
403 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
404 * performs access checking against every caller, on every call.
405 * <p>
406 * All access checks start from a {@code Lookup} object, which
407 * compares its recorded lookup class against all requests to
408 * create method handles.
409 * A single {@code Lookup} object can be used to create any number
410 * of access-checked method handles, all checked against a single
411 * lookup class.
412 * <p>
413 * A {@code Lookup} object can be shared with other trusted code,
414 * such as a metaobject protocol.
415 * A shared {@code Lookup} object delegates the capability
416 * to create method handles on private members of the lookup class.
417 * Even if privileged code uses the {@code Lookup} object,
418 * the access checking is confined to the privileges of the
419 * original lookup class.
420 * <p>
421 * A lookup can fail, because
422 * the containing class is not accessible to the lookup class, or
423 * because the desired class member is missing, or because the
424 * desired class member is not accessible to the lookup class, or
425 * because the lookup object is not trusted enough to access the member.
426 * In any of these cases, a {@code ReflectiveOperationException} will be
427 * thrown from the attempted lookup. The exact class will be one of
428 * the following:
429 * <ul>
430 * <li>NoSuchMethodException — if a method is requested but does not exist
431 * <li>NoSuchFieldException — if a field is requested but does not exist
432 * <li>IllegalAccessException — if the member exists but an access check fails
433 * </ul>
434 * <p>
435 * In general, the conditions under which a method handle may be
436 * looked up for a method {@code M} are no more restrictive than the conditions
437 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
438 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
439 * a method handle lookup will generally raise a corresponding
440 * checked exception, such as {@code NoSuchMethodException}.
441 * And the effect of invoking the method handle resulting from the lookup
442 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
443 * to executing the compiled, verified, and resolved call to {@code M}.
444 * The same point is true of fields and constructors.
445 * <p style="font-size:smaller;">
446 * <em>Discussion:</em>
447 * Access checks only apply to named and reflected methods,
448 * constructors, and fields.
449 * Other method handle creation methods, such as
450 * {@link MethodHandle#asType MethodHandle.asType},
451 * do not require any access checks, and are used
452 * independently of any {@code Lookup} object.
453 * <p>
454 * If the desired member is {@code protected}, the usual JVM rules apply,
455 * including the requirement that the lookup class must be either be in the
456 * same package as the desired member, or must inherit that member.
457 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
458 * In addition, if the desired member is a non-static field or method
459 * in a different package, the resulting method handle may only be applied
460 * to objects of the lookup class or one of its subclasses.
461 * This requirement is enforced by narrowing the type of the leading
462 * {@code this} parameter from {@code C}
463 * (which will necessarily be a superclass of the lookup class)
464 * to the lookup class itself.
465 * <p>
466 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
467 * that the receiver argument must match both the resolved method <em>and</em>
468 * the current class. Again, this requirement is enforced by narrowing the
469 * type of the leading parameter to the resulting method handle.
470 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
471 * <p>
472 * The JVM represents constructors and static initializer blocks as internal methods
473 * with special names ({@code "<init>"} and {@code "<clinit>"}).
474 * The internal syntax of invocation instructions allows them to refer to such internal
475 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
476 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
477 * <p>
478 * In some cases, access between nested classes is obtained by the Java compiler by creating
479 * an wrapper method to access a private method of another class
480 * in the same top-level declaration.
481 * For example, a nested class {@code C.D}
482 * can access private members within other related classes such as
483 * {@code C}, {@code C.D.E}, or {@code C.B},
484 * but the Java compiler may need to generate wrapper methods in
485 * those related classes. In such cases, a {@code Lookup} object on
486 * {@code C.E} would be unable to those private members.
487 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
488 * which can transform a lookup on {@code C.E} into one on any of those other
489 * classes, without special elevation of privilege.
490 * <p>
491 * The accesses permitted to a given lookup object may be limited,
492 * according to its set of {@link #lookupModes lookupModes},
493 * to a subset of members normally accessible to the lookup class.
494 * For example, the {@link MethodHandles#publicLookup publicLookup}
495 * method produces a lookup object which is only allowed to access
496 * public members in public classes of exported packages.
497 * The caller sensitive method {@link MethodHandles#lookup lookup}
498 * produces a lookup object with full capabilities relative to
499 * its caller class, to emulate all supported bytecode behaviors.
500 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
501 * with fewer access modes than the original lookup object.
502 *
503 * <p style="font-size:smaller;">
504 * <a id="privacc"></a>
505 * <em>Discussion of private access:</em>
506 * We say that a lookup has <em>private access</em>
507 * if its {@linkplain #lookupModes lookup modes}
508 * include the possibility of accessing {@code private} members.
509 * As documented in the relevant methods elsewhere,
510 * only lookups with private access possess the following capabilities:
511 * <ul style="font-size:smaller;">
512 * <li>access private fields, methods, and constructors of the lookup class
513 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
514 * such as {@code Class.forName}
515 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
516 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
517 * for classes accessible to the lookup class
518 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
519 * within the same package member
520 * </ul>
521 * <p style="font-size:smaller;">
522 * Each of these permissions is a consequence of the fact that a lookup object
523 * with private access can be securely traced back to an originating class,
524 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
525 * can be reliably determined and emulated by method handles.
526 *
527 * <h1><a id="secmgr"></a>Security manager interactions</h1>
528 * Although bytecode instructions can only refer to classes in
529 * a related class loader, this API can search for methods in any
530 * class, as long as a reference to its {@code Class} object is
531 * available. Such cross-loader references are also possible with the
532 * Core Reflection API, and are impossible to bytecode instructions
533 * such as {@code invokestatic} or {@code getfield}.
534 * There is a {@linkplain java.lang.SecurityManager security manager API}
535 * to allow applications to check such cross-loader references.
536 * These checks apply to both the {@code MethodHandles.Lookup} API
537 * and the Core Reflection API
538 * (as found on {@link java.lang.Class Class}).
539 * <p>
540 * If a security manager is present, member and class lookups are subject to
541 * additional checks.
542 * From one to three calls are made to the security manager.
543 * Any of these calls can refuse access by throwing a
544 * {@link java.lang.SecurityException SecurityException}.
545 * Define {@code smgr} as the security manager,
546 * {@code lookc} as the lookup class of the current lookup object,
547 * {@code refc} as the containing class in which the member
548 * is being sought, and {@code defc} as the class in which the
549 * member is actually defined.
550 * (If a class or other type is being accessed,
551 * the {@code refc} and {@code defc} values are the class itself.)
552 * The value {@code lookc} is defined as <em>not present</em>
553 * if the current lookup object does not have
554 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
555 * The calls are made according to the following rules:
556 * <ul>
557 * <li><b>Step 1:</b>
558 * If {@code lookc} is not present, or if its class loader is not
559 * the same as or an ancestor of the class loader of {@code refc},
560 * then {@link SecurityManager#checkPackageAccess
561 * smgr.checkPackageAccess(refcPkg)} is called,
562 * where {@code refcPkg} is the package of {@code refc}.
563 * <li><b>Step 2a:</b>
564 * If the retrieved member is not public and
565 * {@code lookc} is not present, then
566 * {@link SecurityManager#checkPermission smgr.checkPermission}
567 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
568 * <li><b>Step 2b:</b>
569 * If the retrieved class has a {@code null} class loader,
570 * and {@code lookc} is not present, then
571 * {@link SecurityManager#checkPermission smgr.checkPermission}
572 * with {@code RuntimePermission("getClassLoader")} is called.
573 * <li><b>Step 3:</b>
574 * If the retrieved member is not public,
575 * and if {@code lookc} is not present,
576 * and if {@code defc} and {@code refc} are different,
577 * then {@link SecurityManager#checkPackageAccess
578 * smgr.checkPackageAccess(defcPkg)} is called,
579 * where {@code defcPkg} is the package of {@code defc}.
580 * </ul>
581 * Security checks are performed after other access checks have passed.
582 * Therefore, the above rules presuppose a member or class that is public,
583 * or else that is being accessed from a lookup class that has
584 * rights to access the member or class.
585 *
586 * <h1><a id="callsens"></a>Caller sensitive methods</h1>
587 * A small number of Java methods have a special property called caller sensitivity.
588 * A <em>caller-sensitive</em> method can behave differently depending on the
589 * identity of its immediate caller.
590 * <p>
591 * If a method handle for a caller-sensitive method is requested,
592 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
593 * but they take account of the lookup class in a special way.
594 * The resulting method handle behaves as if it were called
595 * from an instruction contained in the lookup class,
596 * so that the caller-sensitive method detects the lookup class.
597 * (By contrast, the invoker of the method handle is disregarded.)
598 * Thus, in the case of caller-sensitive methods,
599 * different lookup classes may give rise to
600 * differently behaving method handles.
601 * <p>
602 * In cases where the lookup object is
603 * {@link MethodHandles#publicLookup() publicLookup()},
604 * or some other lookup object without
605 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
606 * the lookup class is disregarded.
607 * In such cases, no caller-sensitive method handle can be created,
608 * access is forbidden, and the lookup fails with an
609 * {@code IllegalAccessException}.
610 * <p style="font-size:smaller;">
611 * <em>Discussion:</em>
612 * For example, the caller-sensitive method
613 * {@link java.lang.Class#forName(String) Class.forName(x)}
614 * can return varying classes or throw varying exceptions,
615 * depending on the class loader of the class that calls it.
616 * A public lookup of {@code Class.forName} will fail, because
617 * there is no reasonable way to determine its bytecode behavior.
618 * <p style="font-size:smaller;">
619 * If an application caches method handles for broad sharing,
620 * it should use {@code publicLookup()} to create them.
621 * If there is a lookup of {@code Class.forName}, it will fail,
622 * and the application must take appropriate action in that case.
623 * It may be that a later lookup, perhaps during the invocation of a
624 * bootstrap method, can incorporate the specific identity
625 * of the caller, making the method accessible.
626 * <p style="font-size:smaller;">
627 * The function {@code MethodHandles.lookup} is caller sensitive
628 * so that there can be a secure foundation for lookups.
629 * Nearly all other methods in the JSR 292 API rely on lookup
630 * objects to check access requests.
631 *
632 * @revised 9
633 */
634 public static final
635 class Lookup {
636 /** The class on behalf of whom the lookup is being performed. */
637 private final Class<?> lookupClass;
638
639 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
640 private final int allowedModes;
641
642 /** A single-bit mask representing {@code public} access,
643 * which may contribute to the result of {@link #lookupModes lookupModes}.
644 * The value, {@code 0x01}, happens to be the same as the value of the
645 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
646 */
647 public static final int PUBLIC = Modifier.PUBLIC;
648
649 /** A single-bit mask representing {@code private} access,
650 * which may contribute to the result of {@link #lookupModes lookupModes}.
651 * The value, {@code 0x02}, happens to be the same as the value of the
652 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
653 */
654 public static final int PRIVATE = Modifier.PRIVATE;
655
656 /** A single-bit mask representing {@code protected} access,
657 * which may contribute to the result of {@link #lookupModes lookupModes}.
658 * The value, {@code 0x04}, happens to be the same as the value of the
659 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
660 */
661 public static final int PROTECTED = Modifier.PROTECTED;
662
663 /** A single-bit mask representing {@code package} access (default access),
664 * which may contribute to the result of {@link #lookupModes lookupModes}.
665 * The value is {@code 0x08}, which does not correspond meaningfully to
666 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
667 */
668 public static final int PACKAGE = Modifier.STATIC;
669
670 /** A single-bit mask representing {@code module} access (default access),
671 * which may contribute to the result of {@link #lookupModes lookupModes}.
672 * The value is {@code 0x10}, which does not correspond meaningfully to
673 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
674 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
675 * with this lookup mode can access all public types in the module of the
676 * lookup class and public types in packages exported by other modules
677 * to the module of the lookup class.
678 * @since 9
679 * @spec JPMS
680 */
681 public static final int MODULE = PACKAGE << 1;
682
683 /** A single-bit mask representing {@code unconditional} access
684 * which may contribute to the result of {@link #lookupModes lookupModes}.
685 * The value is {@code 0x20}, which does not correspond meaningfully to
686 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
687 * A {@code Lookup} with this lookup mode assumes {@linkplain
688 * java.lang.Module#canRead(java.lang.Module) readability}.
689 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
690 * with this lookup mode can access all public members of public types
691 * of all modules where the type is in a package that is {@link
692 * java.lang.Module#isExported(String) exported unconditionally}.
693 * @since 9
694 * @spec JPMS
695 * @see #publicLookup()
696 */
697 public static final int UNCONDITIONAL = PACKAGE << 2;
698
699 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
700 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
701 private static final int TRUSTED = -1;
702
703 private static int fixmods(int mods) {
704 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
705 return (mods != 0) ? mods : (PACKAGE | MODULE | UNCONDITIONAL);
706 }
707
708 /** Tells which class is performing the lookup. It is this class against
709 * which checks are performed for visibility and access permissions.
710 * <p>
711 * The class implies a maximum level of access permission,
712 * but the permissions may be additionally limited by the bitmask
713 * {@link #lookupModes lookupModes}, which controls whether non-public members
714 * can be accessed.
715 * @return the lookup class, on behalf of which this lookup object finds members
716 */
717 public Class<?> lookupClass() {
718 return lookupClass;
719 }
720
721 // This is just for calling out to MethodHandleImpl.
722 private Class<?> lookupClassOrNull() {
723 return (allowedModes == TRUSTED) ? null : lookupClass;
724 }
725
726 /** Tells which access-protection classes of members this lookup object can produce.
727 * The result is a bit-mask of the bits
728 * {@linkplain #PUBLIC PUBLIC (0x01)},
729 * {@linkplain #PRIVATE PRIVATE (0x02)},
730 * {@linkplain #PROTECTED PROTECTED (0x04)},
731 * {@linkplain #PACKAGE PACKAGE (0x08)},
732 * {@linkplain #MODULE MODULE (0x10)},
733 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
734 * <p>
735 * A freshly-created lookup object
736 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
737 * all possible bits set, except {@code UNCONDITIONAL}. The lookup can be used to
738 * access all members of the caller's class, all public types in the caller's module,
739 * and all public types in packages exported by other modules to the caller's module.
740 * A lookup object on a new lookup class
741 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
742 * may have some mode bits set to zero.
743 * Mode bits can also be
744 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
745 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
746 * The purpose of this is to restrict access via the new lookup object,
747 * so that it can access only names which can be reached by the original
748 * lookup object, and also by the new lookup class.
749 * @return the lookup modes, which limit the kinds of access performed by this lookup object
750 * @see #in
751 * @see #dropLookupMode
752 *
753 * @revised 9
754 * @spec JPMS
755 */
756 public int lookupModes() {
757 return allowedModes & ALL_MODES;
758 }
759
760 /** Embody the current class (the lookupClass) as a lookup class
761 * for method handle creation.
762 * Must be called by from a method in this package,
763 * which in turn is called by a method not in this package.
764 */
765 Lookup(Class<?> lookupClass) {
766 this(lookupClass, FULL_POWER_MODES);
767 // make sure we haven't accidentally picked up a privileged class:
768 checkUnprivilegedlookupClass(lookupClass);
769 }
770
771 private Lookup(Class<?> lookupClass, int allowedModes) {
772 this.lookupClass = lookupClass;
773 this.allowedModes = allowedModes;
774 }
775
776 /**
777 * Creates a lookup on the specified new lookup class.
778 * The resulting object will report the specified
779 * class as its own {@link #lookupClass lookupClass}.
780 * <p>
781 * However, the resulting {@code Lookup} object is guaranteed
782 * to have no more access capabilities than the original.
783 * In particular, access capabilities can be lost as follows:<ul>
784 * <li>If the old lookup class is in a {@link Module#isNamed() named} module, and
785 * the new lookup class is in a different module {@code M}, then no members, not
786 * even public members in {@code M}'s exported packages, will be accessible.
787 * The exception to this is when this lookup is {@link #publicLookup()
788 * publicLookup}, in which case {@code PUBLIC} access is not lost.
789 * <li>If the old lookup class is in an unnamed module, and the new lookup class
790 * is a different module then {@link #MODULE MODULE} access is lost.
791 * <li>If the new lookup class differs from the old one then {@code UNCONDITIONAL} is lost.
792 * <li>If the new lookup class is in a different package
793 * than the old one, protected and default (package) members will not be accessible.
794 * <li>If the new lookup class is not within the same package member
795 * as the old one, private members will not be accessible, and protected members
796 * will not be accessible by virtue of inheritance.
797 * (Protected members may continue to be accessible because of package sharing.)
798 * <li>If the new lookup class is not accessible to the old lookup class,
799 * then no members, not even public members, will be accessible.
800 * (In all other cases, public members will continue to be accessible.)
801 * </ul>
802 * <p>
803 * The resulting lookup's capabilities for loading classes
804 * (used during {@link #findClass} invocations)
805 * are determined by the lookup class' loader,
806 * which may change due to this operation.
807 *
808 * @param requestedLookupClass the desired lookup class for the new lookup object
809 * @return a lookup object which reports the desired lookup class, or the same object
810 * if there is no change
811 * @throws NullPointerException if the argument is null
812 *
813 * @revised 9
814 * @spec JPMS
815 */
816 public Lookup in(Class<?> requestedLookupClass) {
817 Objects.requireNonNull(requestedLookupClass);
818 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
819 return new Lookup(requestedLookupClass, FULL_POWER_MODES);
820 if (requestedLookupClass == this.lookupClass)
821 return this; // keep same capabilities
822 int newModes = (allowedModes & FULL_POWER_MODES);
823 if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
824 // Need to drop all access when teleporting from a named module to another
825 // module. The exception is publicLookup where PUBLIC is not lost.
826 if (this.lookupClass.getModule().isNamed()
827 && (this.allowedModes & UNCONDITIONAL) == 0)
828 newModes = 0;
829 else
830 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
831 }
832 if ((newModes & PACKAGE) != 0
833 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
834 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
835 }
836 // Allow nestmate lookups to be created without special privilege:
837 if ((newModes & PRIVATE) != 0
838 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
839 newModes &= ~(PRIVATE|PROTECTED);
840 }
841 if ((newModes & PUBLIC) != 0
842 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
843 // The requested class it not accessible from the lookup class.
844 // No permissions.
845 newModes = 0;
846 }
847
848 checkUnprivilegedlookupClass(requestedLookupClass);
849 return new Lookup(requestedLookupClass, newModes);
850 }
851
852
853 /**
854 * Creates a lookup on the same lookup class which this lookup object
855 * finds members, but with a lookup mode that has lost the given lookup mode.
856 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
857 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
858 * {@link #PROTECTED PROTECTED} and {@link #UNCONDITIONAL UNCONDITIONAL} are always
859 * dropped and so the resulting lookup mode will never have these access capabilities.
860 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
861 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
862 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
863 * is dropped then the resulting lookup has no access.
864 * @param modeToDrop the lookup mode to drop
865 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
866 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
867 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
868 * @see MethodHandles#privateLookupIn
869 * @since 9
870 */
871 public Lookup dropLookupMode(int modeToDrop) {
872 int oldModes = lookupModes();
873 int newModes = oldModes & ~(modeToDrop | PROTECTED | UNCONDITIONAL);
874 switch (modeToDrop) {
875 case PUBLIC: newModes &= ~(ALL_MODES); break;
876 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
877 case PACKAGE: newModes &= ~(PRIVATE); break;
878 case PROTECTED:
879 case PRIVATE:
880 case UNCONDITIONAL: break;
881 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
882 }
883 if (newModes == oldModes) return this; // return self if no change
884 return new Lookup(lookupClass(), newModes);
885 }
886
887 /**
888 * Defines a class to the same class loader and in the same runtime package and
889 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
890 * {@linkplain #lookupClass() lookup class}.
891 *
892 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
893 * {@link #PACKAGE PACKAGE} access as default (package) members will be
894 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
895 * that the lookup object was created by a caller in the runtime package (or derived
896 * from a lookup originally created by suitably privileged code to a target class in
897 * the runtime package). </p>
898 *
899 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
900 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
901 * same package as the lookup class. </p>
902 *
903 * <p> This method does not run the class initializer. The class initializer may
904 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
905 * Specification</em>. </p>
906 *
907 * <p> If there is a security manager, its {@code checkPermission} method is first called
908 * to check {@code RuntimePermission("defineClass")}. </p>
909 *
910 * @param bytes the class bytes
911 * @return the {@code Class} object for the class
912 * @throws IllegalArgumentException the bytes are for a class in a different package
913 * to the lookup class
914 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
915 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
916 * verified ({@code VerifyError}), is already defined, or another linkage error occurs
917 * @throws SecurityException if denied by the security manager
918 * @throws NullPointerException if {@code bytes} is {@code null}
919 * @since 9
920 * @spec JPMS
921 * @see Lookup#privateLookupIn
922 * @see Lookup#dropLookupMode
923 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
924 */
925 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
926 SecurityManager sm = System.getSecurityManager();
927 if (sm != null)
928 sm.checkPermission(new RuntimePermission("defineClass"));
929 if ((lookupModes() & PACKAGE) == 0)
930 throw new IllegalAccessException("Lookup does not have PACKAGE access");
931 assert (lookupModes() & (MODULE|PUBLIC)) != 0;
932
933 // parse class bytes to get class name (in internal form)
934 bytes = bytes.clone();
935 String name;
936 try {
937 ClassReader reader = new ClassReader(bytes);
938 name = reader.getClassName();
939 } catch (RuntimeException e) {
940 // ASM exceptions are poorly specified
941 ClassFormatError cfe = new ClassFormatError();
942 cfe.initCause(e);
943 throw cfe;
944 }
945
946 // get package and class name in binary form
947 String cn, pn;
948 int index = name.lastIndexOf('/');
949 if (index == -1) {
950 cn = name;
951 pn = "";
952 } else {
953 cn = name.replace('/', '.');
954 pn = cn.substring(0, index);
955 }
956 if (!pn.equals(lookupClass.getPackageName())) {
957 throw new IllegalArgumentException("Class not in same package as lookup class");
958 }
959
960 // invoke the class loader's defineClass method
961 ClassLoader loader = lookupClass.getClassLoader();
962 ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null;
963 String source = "__Lookup_defineClass__";
964 Class<?> clazz = SharedSecrets.getJavaLangAccess().defineClass(loader, cn, bytes, pd, source);
965 assert clazz.getClassLoader() == lookupClass.getClassLoader()
966 && clazz.getPackageName().equals(lookupClass.getPackageName())
967 && protectionDomain(clazz) == lookupClassProtectionDomain();
968 return clazz;
969 }
970
971 private ProtectionDomain lookupClassProtectionDomain() {
972 ProtectionDomain pd = cachedProtectionDomain;
973 if (pd == null) {
974 cachedProtectionDomain = pd = protectionDomain(lookupClass);
975 }
976 return pd;
977 }
978
979 private ProtectionDomain protectionDomain(Class<?> clazz) {
980 PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain;
981 return AccessController.doPrivileged(pa);
982 }
983
984 // cached protection domain
985 private volatile ProtectionDomain cachedProtectionDomain;
986
987
988 // Make sure outer class is initialized first.
989 static { IMPL_NAMES.getClass(); }
990
991 /** Package-private version of lookup which is trusted. */
992 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
993
994 /** Version of lookup which is trusted minimally.
995 * It can only be used to create method handles to publicly accessible
996 * members in packages that are exported unconditionally.
997 */
998 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, (PUBLIC|UNCONDITIONAL));
999
1000 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
1001 String name = lookupClass.getName();
1002 if (name.startsWith("java.lang.invoke."))
1003 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
1004 }
1005
1006 /**
1007 * Displays the name of the class from which lookups are to be made.
1008 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
1009 * If there are restrictions on the access permitted to this lookup,
1010 * this is indicated by adding a suffix to the class name, consisting
1011 * of a slash and a keyword. The keyword represents the strongest
1012 * allowed access, and is chosen as follows:
1013 * <ul>
1014 * <li>If no access is allowed, the suffix is "/noaccess".
1015 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
1016 * <li>If only public access and unconditional access are allowed, the suffix is "/publicLookup".
1017 * <li>If only public and module access are allowed, the suffix is "/module".
1018 * <li>If only public, module and package access are allowed, the suffix is "/package".
1019 * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
1020 * </ul>
1021 * If none of the above cases apply, it is the case that full
1022 * access (public, module, package, private, and protected) is allowed.
1023 * In this case, no suffix is added.
1024 * This is true only of an object obtained originally from
1025 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
1026 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
1027 * always have restricted access, and will display a suffix.
1028 * <p>
1029 * (It may seem strange that protected access should be
1030 * stronger than private access. Viewed independently from
1031 * package access, protected access is the first to be lost,
1032 * because it requires a direct subclass relationship between
1033 * caller and callee.)
1034 * @see #in
1035 *
1036 * @revised 9
1037 * @spec JPMS
1038 */
1039 @Override
1040 public String toString() {
1041 String cname = lookupClass.getName();
1042 switch (allowedModes) {
1043 case 0: // no privileges
1044 return cname + "/noaccess";
1045 case PUBLIC:
1046 return cname + "/public";
1047 case PUBLIC|UNCONDITIONAL:
1048 return cname + "/publicLookup";
1049 case PUBLIC|MODULE:
1050 return cname + "/module";
1051 case PUBLIC|MODULE|PACKAGE:
1052 return cname + "/package";
1053 case FULL_POWER_MODES & ~PROTECTED:
1054 return cname + "/private";
1055 case FULL_POWER_MODES:
1056 return cname;
1057 case TRUSTED:
1058 return "/trusted"; // internal only; not exported
1059 default: // Should not happen, but it's a bitfield...
1060 cname = cname + "/" + Integer.toHexString(allowedModes);
1061 assert(false) : cname;
1062 return cname;
1063 }
1064 }
1065
1066 /**
1067 * Produces a method handle for a static method.
1068 * The type of the method handle will be that of the method.
1069 * (Since static methods do not take receivers, there is no
1070 * additional receiver argument inserted into the method handle type,
1071 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
1072 * The method and all its argument types must be accessible to the lookup object.
1073 * <p>
1074 * The returned method handle will have
1075 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1076 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1077 * <p>
1078 * If the returned method handle is invoked, the method's class will
1079 * be initialized, if it has not already been initialized.
1080 * <p><b>Example:</b>
1081 * <blockquote><pre>{@code
1082 import static java.lang.invoke.MethodHandles.*;
1083 import static java.lang.invoke.MethodType.*;
1084 ...
1085 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
1086 "asList", methodType(List.class, Object[].class));
1087 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
1088 * }</pre></blockquote>
1089 * @param refc the class from which the method is accessed
1090 * @param name the name of the method
1091 * @param type the type of the method
1092 * @return the desired method handle
1093 * @throws NoSuchMethodException if the method does not exist
1094 * @throws IllegalAccessException if access checking fails,
1095 * or if the method is not {@code static},
1096 * or if the method's variable arity modifier bit
1097 * is set and {@code asVarargsCollector} fails
1098 * @exception SecurityException if a security manager is present and it
1099 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1100 * @throws NullPointerException if any argument is null
1101 */
1102 public
1103 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1104 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
1105 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
1106 }
1107
1108 /**
1109 * Produces a method handle for a virtual method.
1110 * The type of the method handle will be that of the method,
1111 * with the receiver type (usually {@code refc}) prepended.
1112 * The method and all its argument types must be accessible to the lookup object.
1113 * <p>
1114 * When called, the handle will treat the first argument as a receiver
1115 * and dispatch on the receiver's type to determine which method
1116 * implementation to enter.
1117 * (The dispatching action is identical with that performed by an
1118 * {@code invokevirtual} or {@code invokeinterface} instruction.)
1119 * <p>
1120 * The first argument will be of type {@code refc} if the lookup
1121 * class has full privileges to access the member. Otherwise
1122 * the member must be {@code protected} and the first argument
1123 * will be restricted in type to the lookup class.
1124 * <p>
1125 * The returned method handle will have
1126 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1127 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1128 * <p>
1129 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
1130 * instructions and method handles produced by {@code findVirtual},
1131 * if the class is {@code MethodHandle} and the name string is
1132 * {@code invokeExact} or {@code invoke}, the resulting
1133 * method handle is equivalent to one produced by
1134 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
1135 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
1136 * with the same {@code type} argument.
1137 * <p>
1138 * If the class is {@code VarHandle} and the name string corresponds to
1139 * the name of a signature-polymorphic access mode method, the resulting
1140 * method handle is equivalent to one produced by
1141 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
1142 * the access mode corresponding to the name string and with the same
1143 * {@code type} arguments.
1144 * <p>
1145 * <b>Example:</b>
1146 * <blockquote><pre>{@code
1147 import static java.lang.invoke.MethodHandles.*;
1148 import static java.lang.invoke.MethodType.*;
1149 ...
1150 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
1151 "concat", methodType(String.class, String.class));
1152 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1153 "hashCode", methodType(int.class));
1154 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1155 "hashCode", methodType(int.class));
1156 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1157 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1158 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1159 // interface method:
1160 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1161 "subSequence", methodType(CharSequence.class, int.class, int.class));
1162 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1163 // constructor "internal method" must be accessed differently:
1164 MethodType MT_newString = methodType(void.class); //()V for new String()
1165 try { assertEquals("impossible", lookup()
1166 .findVirtual(String.class, "<init>", MT_newString));
1167 } catch (NoSuchMethodException ex) { } // OK
1168 MethodHandle MH_newString = publicLookup()
1169 .findConstructor(String.class, MT_newString);
1170 assertEquals("", (String) MH_newString.invokeExact());
1171 * }</pre></blockquote>
1172 *
1173 * @param refc the class or interface from which the method is accessed
1174 * @param name the name of the method
1175 * @param type the type of the method, with the receiver argument omitted
1176 * @return the desired method handle
1177 * @throws NoSuchMethodException if the method does not exist
1178 * @throws IllegalAccessException if access checking fails,
1179 * or if the method is {@code static},
1180 * or if the method is {@code private} method of interface,
1181 * or if the method's variable arity modifier bit
1182 * is set and {@code asVarargsCollector} fails
1183 * @exception SecurityException if a security manager is present and it
1184 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1185 * @throws NullPointerException if any argument is null
1186 */
1187 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1188 if (refc == MethodHandle.class) {
1189 MethodHandle mh = findVirtualForMH(name, type);
1190 if (mh != null) return mh;
1191 } else if (refc == VarHandle.class) {
1192 MethodHandle mh = findVirtualForVH(name, type);
1193 if (mh != null) return mh;
1194 }
1195 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1196 MemberName method = resolveOrFail(refKind, refc, name, type);
1197 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
1198 }
1199 private MethodHandle findVirtualForMH(String name, MethodType type) {
1200 // these names require special lookups because of the implicit MethodType argument
1201 if ("invoke".equals(name))
1202 return invoker(type);
1203 if ("invokeExact".equals(name))
1204 return exactInvoker(type);
1205 assert(!MemberName.isMethodHandleInvokeName(name));
1206 return null;
1207 }
1208 private MethodHandle findVirtualForVH(String name, MethodType type) {
1209 try {
1210 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1211 } catch (IllegalArgumentException e) {
1212 return null;
1213 }
1214 }
1215
1216 /**
1217 * Produces a method handle which creates an object and initializes it, using
1218 * the constructor of the specified type.
1219 * The parameter types of the method handle will be those of the constructor,
1220 * while the return type will be a reference to the constructor's class.
1221 * The constructor and all its argument types must be accessible to the lookup object.
1222 * <p>
1223 * The requested type must have a return type of {@code void}.
1224 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1225 * <p>
1226 * The returned method handle will have
1227 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1228 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1229 * <p>
1230 * If the returned method handle is invoked, the constructor's class will
1231 * be initialized, if it has not already been initialized.
1232 * <p><b>Example:</b>
1233 * <blockquote><pre>{@code
1234 import static java.lang.invoke.MethodHandles.*;
1235 import static java.lang.invoke.MethodType.*;
1236 ...
1237 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1238 ArrayList.class, methodType(void.class, Collection.class));
1239 Collection orig = Arrays.asList("x", "y");
1240 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1241 assert(orig != copy);
1242 assertEquals(orig, copy);
1243 // a variable-arity constructor:
1244 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1245 ProcessBuilder.class, methodType(void.class, String[].class));
1246 ProcessBuilder pb = (ProcessBuilder)
1247 MH_newProcessBuilder.invoke("x", "y", "z");
1248 assertEquals("[x, y, z]", pb.command().toString());
1249 * }</pre></blockquote>
1250 * @param refc the class or interface from which the method is accessed
1251 * @param type the type of the method, with the receiver argument omitted, and a void return type
1252 * @return the desired method handle
1253 * @throws NoSuchMethodException if the constructor does not exist
1254 * @throws IllegalAccessException if access checking fails
1255 * or if the method's variable arity modifier bit
1256 * is set and {@code asVarargsCollector} fails
1257 * @exception SecurityException if a security manager is present and it
1258 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1259 * @throws NullPointerException if any argument is null
1260 */
1261 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1262 if (refc.isArray()) {
1263 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1264 }
1265 String name = "<init>";
1266 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1267 return getDirectConstructor(refc, ctor);
1268 }
1269
1270 /**
1271 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1272 * initializer of the class is not run.
1273 * <p>
1274 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1275 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1276 * load the requested class, and then determines whether the class is accessible to this lookup object.
1277 *
1278 * @param targetName the fully qualified name of the class to be looked up.
1279 * @return the requested class.
1280 * @exception SecurityException if a security manager is present and it
1281 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1282 * @throws LinkageError if the linkage fails
1283 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1284 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1285 * modes.
1286 * @exception SecurityException if a security manager is present and it
1287 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1288 * @since 9
1289 */
1290 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1291 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1292 return accessClass(targetClass);
1293 }
1294
1295 /**
1296 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1297 * static initializer of the class is not run.
1298 * <p>
1299 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1300 * {@linkplain #lookupModes() lookup modes}.
1301 *
1302 * @param targetClass the class to be access-checked
1303 *
1304 * @return the class that has been access-checked
1305 *
1306 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1307 * modes.
1308 * @exception SecurityException if a security manager is present and it
1309 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1310 * @since 9
1311 */
1312 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1313 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1314 throw new MemberName(targetClass).makeAccessException("access violation", this);
1315 }
1316 checkSecurityManager(targetClass, null);
1317 return targetClass;
1318 }
1319
1320 /**
1321 * Produces an early-bound method handle for a virtual method.
1322 * It will bypass checks for overriding methods on the receiver,
1323 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1324 * instruction from within the explicitly specified {@code specialCaller}.
1325 * The type of the method handle will be that of the method,
1326 * with a suitably restricted receiver type prepended.
1327 * (The receiver type will be {@code specialCaller} or a subtype.)
1328 * The method and all its argument types must be accessible
1329 * to the lookup object.
1330 * <p>
1331 * Before method resolution,
1332 * if the explicitly specified caller class is not identical with the
1333 * lookup class, or if this lookup object does not have
1334 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1335 * privileges, the access fails.
1336 * <p>
1337 * The returned method handle will have
1338 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1339 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1340 * <p style="font-size:smaller;">
1341 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1342 * even though the {@code invokespecial} instruction can refer to them
1343 * in special circumstances. Use {@link #findConstructor findConstructor}
1344 * to access instance initialization methods in a safe manner.)</em>
1345 * <p><b>Example:</b>
1346 * <blockquote><pre>{@code
1347 import static java.lang.invoke.MethodHandles.*;
1348 import static java.lang.invoke.MethodType.*;
1349 ...
1350 static class Listie extends ArrayList {
1351 public String toString() { return "[wee Listie]"; }
1352 static Lookup lookup() { return MethodHandles.lookup(); }
1353 }
1354 ...
1355 // no access to constructor via invokeSpecial:
1356 MethodHandle MH_newListie = Listie.lookup()
1357 .findConstructor(Listie.class, methodType(void.class));
1358 Listie l = (Listie) MH_newListie.invokeExact();
1359 try { assertEquals("impossible", Listie.lookup().findSpecial(
1360 Listie.class, "<init>", methodType(void.class), Listie.class));
1361 } catch (NoSuchMethodException ex) { } // OK
1362 // access to super and self methods via invokeSpecial:
1363 MethodHandle MH_super = Listie.lookup().findSpecial(
1364 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1365 MethodHandle MH_this = Listie.lookup().findSpecial(
1366 Listie.class, "toString" , methodType(String.class), Listie.class);
1367 MethodHandle MH_duper = Listie.lookup().findSpecial(
1368 Object.class, "toString" , methodType(String.class), Listie.class);
1369 assertEquals("[]", (String) MH_super.invokeExact(l));
1370 assertEquals(""+l, (String) MH_this.invokeExact(l));
1371 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1372 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1373 String.class, "toString", methodType(String.class), Listie.class));
1374 } catch (IllegalAccessException ex) { } // OK
1375 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1376 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1377 * }</pre></blockquote>
1378 *
1379 * @param refc the class or interface from which the method is accessed
1380 * @param name the name of the method (which must not be "<init>")
1381 * @param type the type of the method, with the receiver argument omitted
1382 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1383 * @return the desired method handle
1384 * @throws NoSuchMethodException if the method does not exist
1385 * @throws IllegalAccessException if access checking fails,
1386 * or if the method is {@code static},
1387 * or if the method's variable arity modifier bit
1388 * is set and {@code asVarargsCollector} fails
1389 * @exception SecurityException if a security manager is present and it
1390 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1391 * @throws NullPointerException if any argument is null
1392 */
1393 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1394 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1395 checkSpecialCaller(specialCaller, refc);
1396 Lookup specialLookup = this.in(specialCaller);
1397 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1398 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1399 }
1400
1401 /**
1402 * Produces a method handle giving read access to a non-static field.
1403 * The type of the method handle will have a return type of the field's
1404 * value type.
1405 * The method handle's single argument will be the instance containing
1406 * the field.
1407 * Access checking is performed immediately on behalf of the lookup class.
1408 * @param refc the class or interface from which the method is accessed
1409 * @param name the field's name
1410 * @param type the field's type
1411 * @return a method handle which can load values from the field
1412 * @throws NoSuchFieldException if the field does not exist
1413 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1414 * @exception SecurityException if a security manager is present and it
1415 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1416 * @throws NullPointerException if any argument is null
1417 * @see #findVarHandle(Class, String, Class)
1418 */
1419 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1420 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1421 return getDirectField(REF_getField, refc, field);
1422 }
1423
1424 /**
1425 * Produces a method handle giving write access to a non-static field.
1426 * The type of the method handle will have a void return type.
1427 * The method handle will take two arguments, the instance containing
1428 * the field, and the value to be stored.
1429 * The second argument will be of the field's value type.
1430 * Access checking is performed immediately on behalf of the lookup class.
1431 * @param refc the class or interface from which the method is accessed
1432 * @param name the field's name
1433 * @param type the field's type
1434 * @return a method handle which can store values into the field
1435 * @throws NoSuchFieldException if the field does not exist
1436 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1437 * @exception SecurityException if a security manager is present and it
1438 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1439 * @throws NullPointerException if any argument is null
1440 * @see #findVarHandle(Class, String, Class)
1441 */
1442 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1443 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1444 return getDirectField(REF_putField, refc, field);
1445 }
1446
1447 /**
1448 * Produces a VarHandle giving access to a non-static field {@code name}
1449 * of type {@code type} declared in a class of type {@code recv}.
1450 * The VarHandle's variable type is {@code type} and it has one
1451 * coordinate type, {@code recv}.
1452 * <p>
1453 * Access checking is performed immediately on behalf of the lookup
1454 * class.
1455 * <p>
1456 * Certain access modes of the returned VarHandle are unsupported under
1457 * the following conditions:
1458 * <ul>
1459 * <li>if the field is declared {@code final}, then the write, atomic
1460 * update, numeric atomic update, and bitwise atomic update access
1461 * modes are unsupported.
1462 * <li>if the field type is anything other than {@code byte},
1463 * {@code short}, {@code char}, {@code int}, {@code long},
1464 * {@code float}, or {@code double} then numeric atomic update
1465 * access modes are unsupported.
1466 * <li>if the field type is anything other than {@code boolean},
1467 * {@code byte}, {@code short}, {@code char}, {@code int} or
1468 * {@code long} then bitwise atomic update access modes are
1469 * unsupported.
1470 * </ul>
1471 * <p>
1472 * If the field is declared {@code volatile} then the returned VarHandle
1473 * will override access to the field (effectively ignore the
1474 * {@code volatile} declaration) in accordance to its specified
1475 * access modes.
1476 * <p>
1477 * If the field type is {@code float} or {@code double} then numeric
1478 * and atomic update access modes compare values using their bitwise
1479 * representation (see {@link Float#floatToRawIntBits} and
1480 * {@link Double#doubleToRawLongBits}, respectively).
1481 * @apiNote
1482 * Bitwise comparison of {@code float} values or {@code double} values,
1483 * as performed by the numeric and atomic update access modes, differ
1484 * from the primitive {@code ==} operator and the {@link Float#equals}
1485 * and {@link Double#equals} methods, specifically with respect to
1486 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1487 * Care should be taken when performing a compare and set or a compare
1488 * and exchange operation with such values since the operation may
1489 * unexpectedly fail.
1490 * There are many possible NaN values that are considered to be
1491 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1492 * provided by Java can distinguish between them. Operation failure can
1493 * occur if the expected or witness value is a NaN value and it is
1494 * transformed (perhaps in a platform specific manner) into another NaN
1495 * value, and thus has a different bitwise representation (see
1496 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1497 * details).
1498 * The values {@code -0.0} and {@code +0.0} have different bitwise
1499 * representations but are considered equal when using the primitive
1500 * {@code ==} operator. Operation failure can occur if, for example, a
1501 * numeric algorithm computes an expected value to be say {@code -0.0}
1502 * and previously computed the witness value to be say {@code +0.0}.
1503 * @param recv the receiver class, of type {@code R}, that declares the
1504 * non-static field
1505 * @param name the field's name
1506 * @param type the field's type, of type {@code T}
1507 * @return a VarHandle giving access to non-static fields.
1508 * @throws NoSuchFieldException if the field does not exist
1509 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1510 * @exception SecurityException if a security manager is present and it
1511 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1512 * @throws NullPointerException if any argument is null
1513 * @since 9
1514 */
1515 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1516 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1517 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1518 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1519 }
1520
1521 /**
1522 * Produces a method handle giving read access to a static field.
1523 * The type of the method handle will have a return type of the field's
1524 * value type.
1525 * The method handle will take no arguments.
1526 * Access checking is performed immediately on behalf of the lookup class.
1527 * <p>
1528 * If the returned method handle is invoked, the field's class will
1529 * be initialized, if it has not already been initialized.
1530 * @param refc the class or interface from which the method is accessed
1531 * @param name the field's name
1532 * @param type the field's type
1533 * @return a method handle which can load values from the field
1534 * @throws NoSuchFieldException if the field does not exist
1535 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1536 * @exception SecurityException if a security manager is present and it
1537 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1538 * @throws NullPointerException if any argument is null
1539 */
1540 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1541 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1542 return getDirectField(REF_getStatic, refc, field);
1543 }
1544
1545 /**
1546 * Produces a method handle giving write access to a static field.
1547 * The type of the method handle will have a void return type.
1548 * The method handle will take a single
1549 * argument, of the field's value type, the value to be stored.
1550 * Access checking is performed immediately on behalf of the lookup class.
1551 * <p>
1552 * If the returned method handle is invoked, the field's class will
1553 * be initialized, if it has not already been initialized.
1554 * @param refc the class or interface from which the method is accessed
1555 * @param name the field's name
1556 * @param type the field's type
1557 * @return a method handle which can store values into the field
1558 * @throws NoSuchFieldException if the field does not exist
1559 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1560 * @exception SecurityException if a security manager is present and it
1561 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1562 * @throws NullPointerException if any argument is null
1563 */
1564 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1565 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1566 return getDirectField(REF_putStatic, refc, field);
1567 }
1568
1569 /**
1570 * Produces a VarHandle giving access to a static field {@code name} of
1571 * type {@code type} declared in a class of type {@code decl}.
1572 * The VarHandle's variable type is {@code type} and it has no
1573 * coordinate types.
1574 * <p>
1575 * Access checking is performed immediately on behalf of the lookup
1576 * class.
1577 * <p>
1578 * If the returned VarHandle is operated on, the declaring class will be
1579 * initialized, if it has not already been initialized.
1580 * <p>
1581 * Certain access modes of the returned VarHandle are unsupported under
1582 * the following conditions:
1583 * <ul>
1584 * <li>if the field is declared {@code final}, then the write, atomic
1585 * update, numeric atomic update, and bitwise atomic update access
1586 * modes are unsupported.
1587 * <li>if the field type is anything other than {@code byte},
1588 * {@code short}, {@code char}, {@code int}, {@code long},
1589 * {@code float}, or {@code double}, then numeric atomic update
1590 * access modes are unsupported.
1591 * <li>if the field type is anything other than {@code boolean},
1592 * {@code byte}, {@code short}, {@code char}, {@code int} or
1593 * {@code long} then bitwise atomic update access modes are
1594 * unsupported.
1595 * </ul>
1596 * <p>
1597 * If the field is declared {@code volatile} then the returned VarHandle
1598 * will override access to the field (effectively ignore the
1599 * {@code volatile} declaration) in accordance to its specified
1600 * access modes.
1601 * <p>
1602 * If the field type is {@code float} or {@code double} then numeric
1603 * and atomic update access modes compare values using their bitwise
1604 * representation (see {@link Float#floatToRawIntBits} and
1605 * {@link Double#doubleToRawLongBits}, respectively).
1606 * @apiNote
1607 * Bitwise comparison of {@code float} values or {@code double} values,
1608 * as performed by the numeric and atomic update access modes, differ
1609 * from the primitive {@code ==} operator and the {@link Float#equals}
1610 * and {@link Double#equals} methods, specifically with respect to
1611 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1612 * Care should be taken when performing a compare and set or a compare
1613 * and exchange operation with such values since the operation may
1614 * unexpectedly fail.
1615 * There are many possible NaN values that are considered to be
1616 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1617 * provided by Java can distinguish between them. Operation failure can
1618 * occur if the expected or witness value is a NaN value and it is
1619 * transformed (perhaps in a platform specific manner) into another NaN
1620 * value, and thus has a different bitwise representation (see
1621 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1622 * details).
1623 * The values {@code -0.0} and {@code +0.0} have different bitwise
1624 * representations but are considered equal when using the primitive
1625 * {@code ==} operator. Operation failure can occur if, for example, a
1626 * numeric algorithm computes an expected value to be say {@code -0.0}
1627 * and previously computed the witness value to be say {@code +0.0}.
1628 * @param decl the class that declares the static field
1629 * @param name the field's name
1630 * @param type the field's type, of type {@code T}
1631 * @return a VarHandle giving access to a static field
1632 * @throws NoSuchFieldException if the field does not exist
1633 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1634 * @exception SecurityException if a security manager is present and it
1635 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1636 * @throws NullPointerException if any argument is null
1637 * @since 9
1638 */
1639 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1640 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1641 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1642 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1643 }
1644
1645 /**
1646 * Produces an early-bound method handle for a non-static method.
1647 * The receiver must have a supertype {@code defc} in which a method
1648 * of the given name and type is accessible to the lookup class.
1649 * The method and all its argument types must be accessible to the lookup object.
1650 * The type of the method handle will be that of the method,
1651 * without any insertion of an additional receiver parameter.
1652 * The given receiver will be bound into the method handle,
1653 * so that every call to the method handle will invoke the
1654 * requested method on the given receiver.
1655 * <p>
1656 * The returned method handle will have
1657 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1658 * the method's variable arity modifier bit ({@code 0x0080}) is set
1659 * <em>and</em> the trailing array argument is not the only argument.
1660 * (If the trailing array argument is the only argument,
1661 * the given receiver value will be bound to it.)
1662 * <p>
1663 * This is almost equivalent to the following code, with some differences noted below:
1664 * <blockquote><pre>{@code
1665 import static java.lang.invoke.MethodHandles.*;
1666 import static java.lang.invoke.MethodType.*;
1667 ...
1668 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1669 MethodHandle mh1 = mh0.bindTo(receiver);
1670 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1671 return mh1;
1672 * }</pre></blockquote>
1673 * where {@code defc} is either {@code receiver.getClass()} or a super
1674 * type of that class, in which the requested method is accessible
1675 * to the lookup class.
1676 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
1677 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
1678 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
1679 * the receiver is restricted by {@code findVirtual} to the lookup class.)
1680 * @param receiver the object from which the method is accessed
1681 * @param name the name of the method
1682 * @param type the type of the method, with the receiver argument omitted
1683 * @return the desired method handle
1684 * @throws NoSuchMethodException if the method does not exist
1685 * @throws IllegalAccessException if access checking fails
1686 * or if the method's variable arity modifier bit
1687 * is set and {@code asVarargsCollector} fails
1688 * @exception SecurityException if a security manager is present and it
1689 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1690 * @throws NullPointerException if any argument is null
1691 * @see MethodHandle#bindTo
1692 * @see #findVirtual
1693 */
1694 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1695 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1696 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1697 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
1698 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
1699 throw new IllegalAccessException("The restricted defining class " +
1700 mh.type().leadingReferenceParameter().getName() +
1701 " is not assignable from receiver class " +
1702 receiver.getClass().getName());
1703 }
1704 return mh.bindArgumentL(0, receiver).setVarargs(method);
1705 }
1706
1707 /**
1708 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1709 * to <i>m</i>, if the lookup class has permission.
1710 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1711 * If <i>m</i> is virtual, overriding is respected on every call.
1712 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1713 * The type of the method handle will be that of the method,
1714 * with the receiver type prepended (but only if it is non-static).
1715 * If the method's {@code accessible} flag is not set,
1716 * access checking is performed immediately on behalf of the lookup class.
1717 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1718 * <p>
1719 * The returned method handle will have
1720 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1721 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1722 * <p>
1723 * If <i>m</i> is static, and
1724 * if the returned method handle is invoked, the method's class will
1725 * be initialized, if it has not already been initialized.
1726 * @param m the reflected method
1727 * @return a method handle which can invoke the reflected method
1728 * @throws IllegalAccessException if access checking fails
1729 * or if the method's variable arity modifier bit
1730 * is set and {@code asVarargsCollector} fails
1731 * @throws NullPointerException if the argument is null
1732 */
1733 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1734 if (m.getDeclaringClass() == MethodHandle.class) {
1735 MethodHandle mh = unreflectForMH(m);
1736 if (mh != null) return mh;
1737 }
1738 if (m.getDeclaringClass() == VarHandle.class) {
1739 MethodHandle mh = unreflectForVH(m);
1740 if (mh != null) return mh;
1741 }
1742 MemberName method = new MemberName(m);
1743 byte refKind = method.getReferenceKind();
1744 if (refKind == REF_invokeSpecial)
1745 refKind = REF_invokeVirtual;
1746 assert(method.isMethod());
1747 @SuppressWarnings("deprecation")
1748 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1749 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1750 }
1751 private MethodHandle unreflectForMH(Method m) {
1752 // these names require special lookups because they throw UnsupportedOperationException
1753 if (MemberName.isMethodHandleInvokeName(m.getName()))
1754 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1755 return null;
1756 }
1757 private MethodHandle unreflectForVH(Method m) {
1758 // these names require special lookups because they throw UnsupportedOperationException
1759 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
1760 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
1761 return null;
1762 }
1763
1764 /**
1765 * Produces a method handle for a reflected method.
1766 * It will bypass checks for overriding methods on the receiver,
1767 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1768 * instruction from within the explicitly specified {@code specialCaller}.
1769 * The type of the method handle will be that of the method,
1770 * with a suitably restricted receiver type prepended.
1771 * (The receiver type will be {@code specialCaller} or a subtype.)
1772 * If the method's {@code accessible} flag is not set,
1773 * access checking is performed immediately on behalf of the lookup class,
1774 * as if {@code invokespecial} instruction were being linked.
1775 * <p>
1776 * Before method resolution,
1777 * if the explicitly specified caller class is not identical with the
1778 * lookup class, or if this lookup object does not have
1779 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1780 * privileges, the access fails.
1781 * <p>
1782 * The returned method handle will have
1783 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1784 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1785 * @param m the reflected method
1786 * @param specialCaller the class nominally calling the method
1787 * @return a method handle which can invoke the reflected method
1788 * @throws IllegalAccessException if access checking fails,
1789 * or if the method is {@code static},
1790 * or if the method's variable arity modifier bit
1791 * is set and {@code asVarargsCollector} fails
1792 * @throws NullPointerException if any argument is null
1793 */
1794 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1795 checkSpecialCaller(specialCaller, null);
1796 Lookup specialLookup = this.in(specialCaller);
1797 MemberName method = new MemberName(m, true);
1798 assert(method.isMethod());
1799 // ignore m.isAccessible: this is a new kind of access
1800 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1801 }
1802
1803 /**
1804 * Produces a method handle for a reflected constructor.
1805 * The type of the method handle will be that of the constructor,
1806 * with the return type changed to the declaring class.
1807 * The method handle will perform a {@code newInstance} operation,
1808 * creating a new instance of the constructor's class on the
1809 * arguments passed to the method handle.
1810 * <p>
1811 * If the constructor's {@code accessible} flag is not set,
1812 * access checking is performed immediately on behalf of the lookup class.
1813 * <p>
1814 * The returned method handle will have
1815 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1816 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1817 * <p>
1818 * If the returned method handle is invoked, the constructor's class will
1819 * be initialized, if it has not already been initialized.
1820 * @param c the reflected constructor
1821 * @return a method handle which can invoke the reflected constructor
1822 * @throws IllegalAccessException if access checking fails
1823 * or if the method's variable arity modifier bit
1824 * is set and {@code asVarargsCollector} fails
1825 * @throws NullPointerException if the argument is null
1826 */
1827 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1828 MemberName ctor = new MemberName(c);
1829 assert(ctor.isConstructor());
1830 @SuppressWarnings("deprecation")
1831 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1832 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1833 }
1834
1835 /**
1836 * Produces a method handle giving read access to a reflected field.
1837 * The type of the method handle will have a return type of the field's
1838 * value type.
1839 * If the field is static, the method handle will take no arguments.
1840 * Otherwise, its single argument will be the instance containing
1841 * the field.
1842 * If the field's {@code accessible} flag is not set,
1843 * access checking is performed immediately on behalf of the lookup class.
1844 * <p>
1845 * If the field is static, and
1846 * if the returned method handle is invoked, the field's class will
1847 * be initialized, if it has not already been initialized.
1848 * @param f the reflected field
1849 * @return a method handle which can load values from the reflected field
1850 * @throws IllegalAccessException if access checking fails
1851 * @throws NullPointerException if the argument is null
1852 */
1853 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1854 return unreflectField(f, false);
1855 }
1856 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1857 MemberName field = new MemberName(f, isSetter);
1858 assert(isSetter
1859 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1860 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1861 @SuppressWarnings("deprecation")
1862 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1863 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1864 }
1865
1866 /**
1867 * Produces a method handle giving write access to a reflected field.
1868 * The type of the method handle will have a void return type.
1869 * If the field is static, the method handle will take a single
1870 * argument, of the field's value type, the value to be stored.
1871 * Otherwise, the two arguments will be the instance containing
1872 * the field, and the value to be stored.
1873 * If the field's {@code accessible} flag is not set,
1874 * access checking is performed immediately on behalf of the lookup class.
1875 * <p>
1876 * If the field is static, and
1877 * if the returned method handle is invoked, the field's class will
1878 * be initialized, if it has not already been initialized.
1879 * @param f the reflected field
1880 * @return a method handle which can store values into the reflected field
1881 * @throws IllegalAccessException if access checking fails
1882 * @throws NullPointerException if the argument is null
1883 */
1884 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1885 return unreflectField(f, true);
1886 }
1887
1888 /**
1889 * Produces a VarHandle giving access to a reflected field {@code f}
1890 * of type {@code T} declared in a class of type {@code R}.
1891 * The VarHandle's variable type is {@code T}.
1892 * If the field is non-static the VarHandle has one coordinate type,
1893 * {@code R}. Otherwise, the field is static, and the VarHandle has no
1894 * coordinate types.
1895 * <p>
1896 * Access checking is performed immediately on behalf of the lookup
1897 * class, regardless of the value of the field's {@code accessible}
1898 * flag.
1899 * <p>
1900 * If the field is static, and if the returned VarHandle is operated
1901 * on, the field's declaring class will be initialized, if it has not
1902 * already been initialized.
1903 * <p>
1904 * Certain access modes of the returned VarHandle are unsupported under
1905 * the following conditions:
1906 * <ul>
1907 * <li>if the field is declared {@code final}, then the write, atomic
1908 * update, numeric atomic update, and bitwise atomic update access
1909 * modes are unsupported.
1910 * <li>if the field type is anything other than {@code byte},
1911 * {@code short}, {@code char}, {@code int}, {@code long},
1912 * {@code float}, or {@code double} then numeric atomic update
1913 * access modes are unsupported.
1914 * <li>if the field type is anything other than {@code boolean},
1915 * {@code byte}, {@code short}, {@code char}, {@code int} or
1916 * {@code long} then bitwise atomic update access modes are
1917 * unsupported.
1918 * </ul>
1919 * <p>
1920 * If the field is declared {@code volatile} then the returned VarHandle
1921 * will override access to the field (effectively ignore the
1922 * {@code volatile} declaration) in accordance to its specified
1923 * access modes.
1924 * <p>
1925 * If the field type is {@code float} or {@code double} then numeric
1926 * and atomic update access modes compare values using their bitwise
1927 * representation (see {@link Float#floatToRawIntBits} and
1928 * {@link Double#doubleToRawLongBits}, respectively).
1929 * @apiNote
1930 * Bitwise comparison of {@code float} values or {@code double} values,
1931 * as performed by the numeric and atomic update access modes, differ
1932 * from the primitive {@code ==} operator and the {@link Float#equals}
1933 * and {@link Double#equals} methods, specifically with respect to
1934 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1935 * Care should be taken when performing a compare and set or a compare
1936 * and exchange operation with such values since the operation may
1937 * unexpectedly fail.
1938 * There are many possible NaN values that are considered to be
1939 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1940 * provided by Java can distinguish between them. Operation failure can
1941 * occur if the expected or witness value is a NaN value and it is
1942 * transformed (perhaps in a platform specific manner) into another NaN
1943 * value, and thus has a different bitwise representation (see
1944 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1945 * details).
1946 * The values {@code -0.0} and {@code +0.0} have different bitwise
1947 * representations but are considered equal when using the primitive
1948 * {@code ==} operator. Operation failure can occur if, for example, a
1949 * numeric algorithm computes an expected value to be say {@code -0.0}
1950 * and previously computed the witness value to be say {@code +0.0}.
1951 * @param f the reflected field, with a field of type {@code T}, and
1952 * a declaring class of type {@code R}
1953 * @return a VarHandle giving access to non-static fields or a static
1954 * field
1955 * @throws IllegalAccessException if access checking fails
1956 * @throws NullPointerException if the argument is null
1957 * @since 9
1958 */
1959 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
1960 MemberName getField = new MemberName(f, false);
1961 MemberName putField = new MemberName(f, true);
1962 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
1963 f.getDeclaringClass(), getField, putField);
1964 }
1965
1966 /**
1967 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1968 * created by this lookup object or a similar one.
1969 * Security and access checks are performed to ensure that this lookup object
1970 * is capable of reproducing the target method handle.
1971 * This means that the cracking may fail if target is a direct method handle
1972 * but was created by an unrelated lookup object.
1973 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1974 * and was created by a lookup object for a different class.
1975 * @param target a direct method handle to crack into symbolic reference components
1976 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1977 * @exception SecurityException if a security manager is present and it
1978 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1979 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1980 * @exception NullPointerException if the target is {@code null}
1981 * @see MethodHandleInfo
1982 * @since 1.8
1983 */
1984 public MethodHandleInfo revealDirect(MethodHandle target) {
1985 MemberName member = target.internalMemberName();
1986 if (member == null || (!member.isResolved() &&
1987 !member.isMethodHandleInvoke() &&
1988 !member.isVarHandleMethodInvoke()))
1989 throw newIllegalArgumentException("not a direct method handle");
1990 Class<?> defc = member.getDeclaringClass();
1991 byte refKind = member.getReferenceKind();
1992 assert(MethodHandleNatives.refKindIsValid(refKind));
1993 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1994 // Devirtualized method invocation is usually formally virtual.
1995 // To avoid creating extra MemberName objects for this common case,
1996 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1997 refKind = REF_invokeVirtual;
1998 if (refKind == REF_invokeVirtual && defc.isInterface())
1999 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
2000 refKind = REF_invokeInterface;
2001 // Check SM permissions and member access before cracking.
2002 try {
2003 checkAccess(refKind, defc, member);
2004 checkSecurityManager(defc, member);
2005 } catch (IllegalAccessException ex) {
2006 throw new IllegalArgumentException(ex);
2007 }
2008 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2009 Class<?> callerClass = target.internalCallerClass();
2010 if (!hasPrivateAccess() || callerClass != lookupClass())
2011 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2012 }
2013 // Produce the handle to the results.
2014 return new InfoFromMemberName(this, member, refKind);
2015 }
2016
2017 /// Helper methods, all package-private.
2018
2019 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2020 checkSymbolicClass(refc); // do this before attempting to resolve
2021 Objects.requireNonNull(name);
2022 Objects.requireNonNull(type);
2023 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2024 NoSuchFieldException.class);
2025 }
2026
2027 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2028 checkSymbolicClass(refc); // do this before attempting to resolve
2029 Objects.requireNonNull(name);
2030 Objects.requireNonNull(type);
2031 checkMethodName(refKind, name); // NPE check on name
2032 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2033 NoSuchMethodException.class);
2034 }
2035
2036 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2037 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2038 Objects.requireNonNull(member.getName());
2039 Objects.requireNonNull(member.getType());
2040 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2041 ReflectiveOperationException.class);
2042 }
2043
2044 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
2045 Objects.requireNonNull(refc);
2046 Class<?> caller = lookupClassOrNull();
2047 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
2048 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
2049 }
2050
2051 /** Check name for an illegal leading "<" character. */
2052 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
2053 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
2054 throw new NoSuchMethodException("illegal method name: "+name);
2055 }
2056
2057
2058 /**
2059 * Find my trustable caller class if m is a caller sensitive method.
2060 * If this lookup object has private access, then the caller class is the lookupClass.
2061 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
2062 */
2063 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
2064 Class<?> callerClass = null;
2065 if (MethodHandleNatives.isCallerSensitive(m)) {
2066 // Only lookups with private access are allowed to resolve caller-sensitive methods
2067 if (hasPrivateAccess()) {
2068 callerClass = lookupClass;
2069 } else {
2070 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
2071 }
2072 }
2073 return callerClass;
2074 }
2075
2076 /**
2077 * Returns {@code true} if this lookup has {@code PRIVATE} access.
2078 * @return {@code true} if this lookup has {@code PRIVATE} access.
2079 * @since 9
2080 */
2081 public boolean hasPrivateAccess() {
2082 return (allowedModes & PRIVATE) != 0;
2083 }
2084
2085 /**
2086 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
2087 * Determines a trustable caller class to compare with refc, the symbolic reference class.
2088 * If this lookup object has private access, then the caller class is the lookupClass.
2089 */
2090 void checkSecurityManager(Class<?> refc, MemberName m) {
2091 SecurityManager smgr = System.getSecurityManager();
2092 if (smgr == null) return;
2093 if (allowedModes == TRUSTED) return;
2094
2095 // Step 1:
2096 boolean fullPowerLookup = hasPrivateAccess();
2097 if (!fullPowerLookup ||
2098 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
2099 ReflectUtil.checkPackageAccess(refc);
2100 }
2101
2102 if (m == null) { // findClass or accessClass
2103 // Step 2b:
2104 if (!fullPowerLookup) {
2105 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2106 }
2107 return;
2108 }
2109
2110 // Step 2a:
2111 if (m.isPublic()) return;
2112 if (!fullPowerLookup) {
2113 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
2114 }
2115
2116 // Step 3:
2117 Class<?> defc = m.getDeclaringClass();
2118 if (!fullPowerLookup && defc != refc) {
2119 ReflectUtil.checkPackageAccess(defc);
2120 }
2121 }
2122
2123 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2124 boolean wantStatic = (refKind == REF_invokeStatic);
2125 String message;
2126 if (m.isConstructor())
2127 message = "expected a method, not a constructor";
2128 else if (!m.isMethod())
2129 message = "expected a method";
2130 else if (wantStatic != m.isStatic())
2131 message = wantStatic ? "expected a static method" : "expected a non-static method";
2132 else
2133 { checkAccess(refKind, refc, m); return; }
2134 throw m.makeAccessException(message, this);
2135 }
2136
2137 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2138 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2139 String message;
2140 if (wantStatic != m.isStatic())
2141 message = wantStatic ? "expected a static field" : "expected a non-static field";
2142 else
2143 { checkAccess(refKind, refc, m); return; }
2144 throw m.makeAccessException(message, this);
2145 }
2146
2147 /** Check public/protected/private bits on the symbolic reference class and its member. */
2148 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2149 assert(m.referenceKindIsConsistentWith(refKind) &&
2150 MethodHandleNatives.refKindIsValid(refKind) &&
2151 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2152 int allowedModes = this.allowedModes;
2153 if (allowedModes == TRUSTED) return;
2154 int mods = m.getModifiers();
2155 if (Modifier.isProtected(mods) &&
2156 refKind == REF_invokeVirtual &&
2157 m.getDeclaringClass() == Object.class &&
2158 m.getName().equals("clone") &&
2159 refc.isArray()) {
2160 // The JVM does this hack also.
2161 // (See ClassVerifier::verify_invoke_instructions
2162 // and LinkResolver::check_method_accessability.)
2163 // Because the JVM does not allow separate methods on array types,
2164 // there is no separate method for int[].clone.
2165 // All arrays simply inherit Object.clone.
2166 // But for access checking logic, we make Object.clone
2167 // (normally protected) appear to be public.
2168 // Later on, when the DirectMethodHandle is created,
2169 // its leading argument will be restricted to the
2170 // requested array type.
2171 // N.B. The return type is not adjusted, because
2172 // that is *not* the bytecode behavior.
2173 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2174 }
2175 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2176 // cannot "new" a protected ctor in a different package
2177 mods ^= Modifier.PROTECTED;
2178 }
2179 if (Modifier.isFinal(mods) &&
2180 MethodHandleNatives.refKindIsSetter(refKind))
2181 throw m.makeAccessException("unexpected set of a final field", this);
2182 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2183 if ((requestedModes & allowedModes) != 0) {
2184 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2185 mods, lookupClass(), allowedModes))
2186 return;
2187 } else {
2188 // Protected members can also be checked as if they were package-private.
2189 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2190 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2191 return;
2192 }
2193 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2194 }
2195
2196 String accessFailedMessage(Class<?> refc, MemberName m) {
2197 Class<?> defc = m.getDeclaringClass();
2198 int mods = m.getModifiers();
2199 // check the class first:
2200 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2201 (defc == refc ||
2202 Modifier.isPublic(refc.getModifiers())));
2203 if (!classOK && (allowedModes & PACKAGE) != 0) {
2204 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), FULL_POWER_MODES) &&
2205 (defc == refc ||
2206 VerifyAccess.isClassAccessible(refc, lookupClass(), FULL_POWER_MODES)));
2207 }
2208 if (!classOK)
2209 return "class is not public";
2210 if (Modifier.isPublic(mods))
2211 return "access to public member failed"; // (how?, module not readable?)
2212 if (Modifier.isPrivate(mods))
2213 return "member is private";
2214 if (Modifier.isProtected(mods))
2215 return "member is protected";
2216 return "member is private to package";
2217 }
2218
2219 private static final boolean ALLOW_NESTMATE_ACCESS = false;
2220
2221 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2222 int allowedModes = this.allowedModes;
2223 if (allowedModes == TRUSTED) return;
2224 if (!hasPrivateAccess()
2225 || (specialCaller != lookupClass()
2226 // ensure non-abstract methods in superinterfaces can be special-invoked
2227 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))
2228 && !(ALLOW_NESTMATE_ACCESS &&
2229 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
2230 throw new MemberName(specialCaller).
2231 makeAccessException("no private access for invokespecial", this);
2232 }
2233
2234 private boolean restrictProtectedReceiver(MemberName method) {
2235 // The accessing class only has the right to use a protected member
2236 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2237 if (!method.isProtected() || method.isStatic()
2238 || allowedModes == TRUSTED
2239 || method.getDeclaringClass() == lookupClass()
2240 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
2241 || (ALLOW_NESTMATE_ACCESS &&
2242 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
2243 return false;
2244 return true;
2245 }
2246 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2247 assert(!method.isStatic());
2248 // receiver type of mh is too wide; narrow to caller
2249 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2250 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2251 }
2252 MethodType rawType = mh.type();
2253 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
2254 MethodType narrowType = rawType.changeParameterType(0, caller);
2255 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2256 assert(mh.viewAsTypeChecks(narrowType, true));
2257 return mh.copyWith(narrowType, mh.form);
2258 }
2259
2260 /** Check access and get the requested method. */
2261 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2262 final boolean doRestrict = true;
2263 final boolean checkSecurity = true;
2264 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2265 }
2266 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
2267 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2268 final boolean doRestrict = false;
2269 final boolean checkSecurity = true;
2270 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerClass);
2271 }
2272 /** Check access and get the requested method, eliding security manager checks. */
2273 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2274 final boolean doRestrict = true;
2275 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2276 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2277 }
2278 /** Common code for all methods; do not call directly except from immediately above. */
2279 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
2280 boolean checkSecurity,
2281 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
2282 checkMethod(refKind, refc, method);
2283 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2284 if (checkSecurity)
2285 checkSecurityManager(refc, method);
2286 assert(!method.isMethodHandleInvoke());
2287
2288 if (refKind == REF_invokeSpecial &&
2289 refc != lookupClass() &&
2290 !refc.isInterface() &&
2291 refc != lookupClass().getSuperclass() &&
2292 refc.isAssignableFrom(lookupClass())) {
2293 assert(!method.getName().equals("<init>")); // not this code path
2294 // Per JVMS 6.5, desc. of invokespecial instruction:
2295 // If the method is in a superclass of the LC,
2296 // and if our original search was above LC.super,
2297 // repeat the search (symbolic lookup) from LC.super
2298 // and continue with the direct superclass of that class,
2299 // and so forth, until a match is found or no further superclasses exist.
2300 // FIXME: MemberName.resolve should handle this instead.
2301 Class<?> refcAsSuper = lookupClass();
2302 MemberName m2;
2303 do {
2304 refcAsSuper = refcAsSuper.getSuperclass();
2305 m2 = new MemberName(refcAsSuper,
2306 method.getName(),
2307 method.getMethodType(),
2308 REF_invokeSpecial);
2309 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2310 } while (m2 == null && // no method is found yet
2311 refc != refcAsSuper); // search up to refc
2312 if (m2 == null) throw new InternalError(method.toString());
2313 method = m2;
2314 refc = refcAsSuper;
2315 // redo basic checks
2316 checkMethod(refKind, refc, method);
2317 }
2318
2319 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method);
2320 MethodHandle mh = dmh;
2321 // Optionally narrow the receiver argument to refc using restrictReceiver.
2322 if ((doRestrict && refKind == REF_invokeSpecial) ||
2323 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
2324 mh = restrictReceiver(method, dmh, lookupClass());
2325 }
2326 mh = maybeBindCaller(method, mh, callerClass);
2327 mh = mh.setVarargs(method);
2328 return mh;
2329 }
2330 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2331 Class<?> callerClass)
2332 throws IllegalAccessException {
2333 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2334 return mh;
2335 Class<?> hostClass = lookupClass;
2336 if (!hasPrivateAccess()) // caller must have private access
2337 hostClass = callerClass; // callerClass came from a security manager style stack walk
2338 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2339 // Note: caller will apply varargs after this step happens.
2340 return cbmh;
2341 }
2342 /** Check access and get the requested field. */
2343 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2344 final boolean checkSecurity = true;
2345 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2346 }
2347 /** Check access and get the requested field, eliding security manager checks. */
2348 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2349 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2350 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2351 }
2352 /** Common code for all fields; do not call directly except from immediately above. */
2353 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2354 boolean checkSecurity) throws IllegalAccessException {
2355 checkField(refKind, refc, field);
2356 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2357 if (checkSecurity)
2358 checkSecurityManager(refc, field);
2359 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2360 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2361 restrictProtectedReceiver(field));
2362 if (doRestrict)
2363 return restrictReceiver(field, dmh, lookupClass());
2364 return dmh;
2365 }
2366 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2367 Class<?> refc, MemberName getField, MemberName putField)
2368 throws IllegalAccessException {
2369 final boolean checkSecurity = true;
2370 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2371 }
2372 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2373 Class<?> refc, MemberName getField, MemberName putField)
2374 throws IllegalAccessException {
2375 final boolean checkSecurity = false;
2376 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2377 }
2378 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2379 Class<?> refc, MemberName getField, MemberName putField,
2380 boolean checkSecurity) throws IllegalAccessException {
2381 assert getField.isStatic() == putField.isStatic();
2382 assert getField.isGetter() && putField.isSetter();
2383 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2384 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2385
2386 checkField(getRefKind, refc, getField);
2387 if (checkSecurity)
2388 checkSecurityManager(refc, getField);
2389
2390 if (!putField.isFinal()) {
2391 // A VarHandle does not support updates to final fields, any
2392 // such VarHandle to a final field will be read-only and
2393 // therefore the following write-based accessibility checks are
2394 // only required for non-final fields
2395 checkField(putRefKind, refc, putField);
2396 if (checkSecurity)
2397 checkSecurityManager(refc, putField);
2398 }
2399
2400 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2401 restrictProtectedReceiver(getField));
2402 if (doRestrict) {
2403 assert !getField.isStatic();
2404 // receiver type of VarHandle is too wide; narrow to caller
2405 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2406 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2407 }
2408 refc = lookupClass();
2409 }
2410 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2411 }
2412 /** Check access and get the requested constructor. */
2413 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2414 final boolean checkSecurity = true;
2415 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2416 }
2417 /** Check access and get the requested constructor, eliding security manager checks. */
2418 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2419 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2420 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2421 }
2422 /** Common code for all constructors; do not call directly except from immediately above. */
2423 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2424 boolean checkSecurity) throws IllegalAccessException {
2425 assert(ctor.isConstructor());
2426 checkAccess(REF_newInvokeSpecial, refc, ctor);
2427 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2428 if (checkSecurity)
2429 checkSecurityManager(refc, ctor);
2430 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2431 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2432 }
2433
2434 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2435 */
2436 /*non-public*/
2437 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2438 if (!(type instanceof Class || type instanceof MethodType))
2439 throw new InternalError("unresolved MemberName");
2440 MemberName member = new MemberName(refKind, defc, name, type);
2441 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2442 if (mh != null) {
2443 checkSymbolicClass(defc);
2444 return mh;
2445 }
2446 // Treat MethodHandle.invoke and invokeExact specially.
2447 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2448 mh = findVirtualForMH(member.getName(), member.getMethodType());
2449 if (mh != null) {
2450 return mh;
2451 }
2452 }
2453 MemberName resolved = resolveOrFail(refKind, member);
2454 mh = getDirectMethodForConstant(refKind, defc, resolved);
2455 if (mh instanceof DirectMethodHandle
2456 && canBeCached(refKind, defc, resolved)) {
2457 MemberName key = mh.internalMemberName();
2458 if (key != null) {
2459 key = key.asNormalOriginal();
2460 }
2461 if (member.equals(key)) { // better safe than sorry
2462 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2463 }
2464 }
2465 return mh;
2466 }
2467 private
2468 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2469 if (refKind == REF_invokeSpecial) {
2470 return false;
2471 }
2472 if (!Modifier.isPublic(defc.getModifiers()) ||
2473 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2474 !member.isPublic() ||
2475 member.isCallerSensitive()) {
2476 return false;
2477 }
2478 ClassLoader loader = defc.getClassLoader();
2479 if (loader != null) {
2480 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2481 boolean found = false;
2482 while (sysl != null) {
2483 if (loader == sysl) { found = true; break; }
2484 sysl = sysl.getParent();
2485 }
2486 if (!found) {
2487 return false;
2488 }
2489 }
2490 try {
2491 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
2492 new MemberName(refKind, defc, member.getName(), member.getType()));
2493 checkSecurityManager(defc, resolved2);
2494 } catch (ReflectiveOperationException | SecurityException ex) {
2495 return false;
2496 }
2497 return true;
2498 }
2499 private
2500 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2501 throws ReflectiveOperationException {
2502 if (MethodHandleNatives.refKindIsField(refKind)) {
2503 return getDirectFieldNoSecurityManager(refKind, defc, member);
2504 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2505 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2506 } else if (refKind == REF_newInvokeSpecial) {
2507 return getDirectConstructorNoSecurityManager(defc, member);
2508 }
2509 // oops
2510 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2511 }
2512
2513 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2514 }
2515
2516 /**
2517 * Produces a method handle constructing arrays of a desired type.
2518 * The return type of the method handle will be the array type.
2519 * The type of its sole argument will be {@code int}, which specifies the size of the array.
2520 * @param arrayClass an array type
2521 * @return a method handle which can create arrays of the given type
2522 * @throws NullPointerException if the argument is {@code null}
2523 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2524 * @see java.lang.reflect.Array#newInstance(Class, int)
2525 * @since 9
2526 */
2527 public static
2528 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2529 if (!arrayClass.isArray()) {
2530 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2531 }
2532 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2533 bindTo(arrayClass.getComponentType());
2534 return ani.asType(ani.type().changeReturnType(arrayClass));
2535 }
2536
2537 /**
2538 * Produces a method handle returning the length of an array.
2539 * The type of the method handle will have {@code int} as return type,
2540 * and its sole argument will be the array type.
2541 * @param arrayClass an array type
2542 * @return a method handle which can retrieve the length of an array of the given array type
2543 * @throws NullPointerException if the argument is {@code null}
2544 * @throws IllegalArgumentException if arrayClass is not an array type
2545 * @since 9
2546 */
2547 public static
2548 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2549 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2550 }
2551
2552 /**
2553 * Produces a method handle giving read access to elements of an array.
2554 * The type of the method handle will have a return type of the array's
2555 * element type. Its first argument will be the array type,
2556 * and the second will be {@code int}.
2557 * @param arrayClass an array type
2558 * @return a method handle which can load values from the given array type
2559 * @throws NullPointerException if the argument is null
2560 * @throws IllegalArgumentException if arrayClass is not an array type
2561 */
2562 public static
2563 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2564 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2565 }
2566
2567 /**
2568 * Produces a method handle giving write access to elements of an array.
2569 * The type of the method handle will have a void return type.
2570 * Its last argument will be the array's element type.
2571 * The first and second arguments will be the array type and int.
2572 * @param arrayClass the class of an array
2573 * @return a method handle which can store values into the array type
2574 * @throws NullPointerException if the argument is null
2575 * @throws IllegalArgumentException if arrayClass is not an array type
2576 */
2577 public static
2578 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2579 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2580 }
2581
2582 /**
2583 * Produces a VarHandle giving access to elements of an array of type
2584 * {@code arrayClass}. The VarHandle's variable type is the component type
2585 * of {@code arrayClass} and the list of coordinate types is
2586 * {@code (arrayClass, int)}, where the {@code int} coordinate type
2587 * corresponds to an argument that is an index into an array.
2588 * <p>
2589 * Certain access modes of the returned VarHandle are unsupported under
2590 * the following conditions:
2591 * <ul>
2592 * <li>if the component type is anything other than {@code byte},
2593 * {@code short}, {@code char}, {@code int}, {@code long},
2594 * {@code float}, or {@code double} then numeric atomic update access
2595 * modes are unsupported.
2596 * <li>if the field type is anything other than {@code boolean},
2597 * {@code byte}, {@code short}, {@code char}, {@code int} or
2598 * {@code long} then bitwise atomic update access modes are
2599 * unsupported.
2600 * </ul>
2601 * <p>
2602 * If the component type is {@code float} or {@code double} then numeric
2603 * and atomic update access modes compare values using their bitwise
2604 * representation (see {@link Float#floatToRawIntBits} and
2605 * {@link Double#doubleToRawLongBits}, respectively).
2606 * @apiNote
2607 * Bitwise comparison of {@code float} values or {@code double} values,
2608 * as performed by the numeric and atomic update access modes, differ
2609 * from the primitive {@code ==} operator and the {@link Float#equals}
2610 * and {@link Double#equals} methods, specifically with respect to
2611 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2612 * Care should be taken when performing a compare and set or a compare
2613 * and exchange operation with such values since the operation may
2614 * unexpectedly fail.
2615 * There are many possible NaN values that are considered to be
2616 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2617 * provided by Java can distinguish between them. Operation failure can
2618 * occur if the expected or witness value is a NaN value and it is
2619 * transformed (perhaps in a platform specific manner) into another NaN
2620 * value, and thus has a different bitwise representation (see
2621 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2622 * details).
2623 * The values {@code -0.0} and {@code +0.0} have different bitwise
2624 * representations but are considered equal when using the primitive
2625 * {@code ==} operator. Operation failure can occur if, for example, a
2626 * numeric algorithm computes an expected value to be say {@code -0.0}
2627 * and previously computed the witness value to be say {@code +0.0}.
2628 * @param arrayClass the class of an array, of type {@code T[]}
2629 * @return a VarHandle giving access to elements of an array
2630 * @throws NullPointerException if the arrayClass is null
2631 * @throws IllegalArgumentException if arrayClass is not an array type
2632 * @since 9
2633 */
2634 public static
2635 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
2636 return VarHandles.makeArrayElementHandle(arrayClass);
2637 }
2638
2639 /**
2640 * Produces a VarHandle giving access to elements of a {@code byte[]} array
2641 * viewed as if it were a different primitive array type, such as
2642 * {@code int[]} or {@code long[]}.
2643 * The VarHandle's variable type is the component type of
2644 * {@code viewArrayClass} and the list of coordinate types is
2645 * {@code (byte[], int)}, where the {@code int} coordinate type
2646 * corresponds to an argument that is an index into a {@code byte[]} array.
2647 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
2648 * array, composing bytes to or from a value of the component type of
2649 * {@code viewArrayClass} according to the given endianness.
2650 * <p>
2651 * The supported component types (variables types) are {@code short},
2652 * {@code char}, {@code int}, {@code long}, {@code float} and
2653 * {@code double}.
2654 * <p>
2655 * Access of bytes at a given index will result in an
2656 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2657 * or greater than the {@code byte[]} array length minus the size (in bytes)
2658 * of {@code T}.
2659 * <p>
2660 * Access of bytes at an index may be aligned or misaligned for {@code T},
2661 * with respect to the underlying memory address, {@code A} say, associated
2662 * with the array and index.
2663 * If access is misaligned then access for anything other than the
2664 * {@code get} and {@code set} access modes will result in an
2665 * {@code IllegalStateException}. In such cases atomic access is only
2666 * guaranteed with respect to the largest power of two that divides the GCD
2667 * of {@code A} and the size (in bytes) of {@code T}.
2668 * If access is aligned then following access modes are supported and are
2669 * guaranteed to support atomic access:
2670 * <ul>
2671 * <li>read write access modes for all {@code T}, with the exception of
2672 * access modes {@code get} and {@code set} for {@code long} and
2673 * {@code double} on 32-bit platforms.
2674 * <li>atomic update access modes for {@code int}, {@code long},
2675 * {@code float} or {@code double}.
2676 * (Future major platform releases of the JDK may support additional
2677 * types for certain currently unsupported access modes.)
2678 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2679 * (Future major platform releases of the JDK may support additional
2680 * numeric types for certain currently unsupported access modes.)
2681 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2682 * (Future major platform releases of the JDK may support additional
2683 * numeric types for certain currently unsupported access modes.)
2684 * </ul>
2685 * <p>
2686 * Misaligned access, and therefore atomicity guarantees, may be determined
2687 * for {@code byte[]} arrays without operating on a specific array. Given
2688 * an {@code index}, {@code T} and it's corresponding boxed type,
2689 * {@code T_BOX}, misalignment may be determined as follows:
2690 * <pre>{@code
2691 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2692 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
2693 * alignmentOffset(0, sizeOfT);
2694 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
2695 * boolean isMisaligned = misalignedAtIndex != 0;
2696 * }</pre>
2697 * <p>
2698 * If the variable type is {@code float} or {@code double} then atomic
2699 * update access modes compare values using their bitwise representation
2700 * (see {@link Float#floatToRawIntBits} and
2701 * {@link Double#doubleToRawLongBits}, respectively).
2702 * @param viewArrayClass the view array class, with a component type of
2703 * type {@code T}
2704 * @param byteOrder the endianness of the view array elements, as
2705 * stored in the underlying {@code byte} array
2706 * @return a VarHandle giving access to elements of a {@code byte[]} array
2707 * viewed as if elements corresponding to the components type of the view
2708 * array class
2709 * @throws NullPointerException if viewArrayClass or byteOrder is null
2710 * @throws IllegalArgumentException if viewArrayClass is not an array type
2711 * @throws UnsupportedOperationException if the component type of
2712 * viewArrayClass is not supported as a variable type
2713 * @since 9
2714 */
2715 public static
2716 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
2717 ByteOrder byteOrder) throws IllegalArgumentException {
2718 Objects.requireNonNull(byteOrder);
2719 return VarHandles.byteArrayViewHandle(viewArrayClass,
2720 byteOrder == ByteOrder.BIG_ENDIAN);
2721 }
2722
2723 /**
2724 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
2725 * viewed as if it were an array of elements of a different primitive
2726 * component type to that of {@code byte}, such as {@code int[]} or
2727 * {@code long[]}.
2728 * The VarHandle's variable type is the component type of
2729 * {@code viewArrayClass} and the list of coordinate types is
2730 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
2731 * corresponds to an argument that is an index into a {@code byte[]} array.
2732 * The returned VarHandle accesses bytes at an index in a
2733 * {@code ByteBuffer}, composing bytes to or from a value of the component
2734 * type of {@code viewArrayClass} according to the given endianness.
2735 * <p>
2736 * The supported component types (variables types) are {@code short},
2737 * {@code char}, {@code int}, {@code long}, {@code float} and
2738 * {@code double}.
2739 * <p>
2740 * Access will result in a {@code ReadOnlyBufferException} for anything
2741 * other than the read access modes if the {@code ByteBuffer} is read-only.
2742 * <p>
2743 * Access of bytes at a given index will result in an
2744 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2745 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
2746 * {@code T}.
2747 * <p>
2748 * Access of bytes at an index may be aligned or misaligned for {@code T},
2749 * with respect to the underlying memory address, {@code A} say, associated
2750 * with the {@code ByteBuffer} and index.
2751 * If access is misaligned then access for anything other than the
2752 * {@code get} and {@code set} access modes will result in an
2753 * {@code IllegalStateException}. In such cases atomic access is only
2754 * guaranteed with respect to the largest power of two that divides the GCD
2755 * of {@code A} and the size (in bytes) of {@code T}.
2756 * If access is aligned then following access modes are supported and are
2757 * guaranteed to support atomic access:
2758 * <ul>
2759 * <li>read write access modes for all {@code T}, with the exception of
2760 * access modes {@code get} and {@code set} for {@code long} and
2761 * {@code double} on 32-bit platforms.
2762 * <li>atomic update access modes for {@code int}, {@code long},
2763 * {@code float} or {@code double}.
2764 * (Future major platform releases of the JDK may support additional
2765 * types for certain currently unsupported access modes.)
2766 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2767 * (Future major platform releases of the JDK may support additional
2768 * numeric types for certain currently unsupported access modes.)
2769 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2770 * (Future major platform releases of the JDK may support additional
2771 * numeric types for certain currently unsupported access modes.)
2772 * </ul>
2773 * <p>
2774 * Misaligned access, and therefore atomicity guarantees, may be determined
2775 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
2776 * {@code index}, {@code T} and it's corresponding boxed type,
2777 * {@code T_BOX}, as follows:
2778 * <pre>{@code
2779 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2780 * ByteBuffer bb = ...
2781 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
2782 * boolean isMisaligned = misalignedAtIndex != 0;
2783 * }</pre>
2784 * <p>
2785 * If the variable type is {@code float} or {@code double} then atomic
2786 * update access modes compare values using their bitwise representation
2787 * (see {@link Float#floatToRawIntBits} and
2788 * {@link Double#doubleToRawLongBits}, respectively).
2789 * @param viewArrayClass the view array class, with a component type of
2790 * type {@code T}
2791 * @param byteOrder the endianness of the view array elements, as
2792 * stored in the underlying {@code ByteBuffer} (Note this overrides the
2793 * endianness of a {@code ByteBuffer})
2794 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
2795 * viewed as if elements corresponding to the components type of the view
2796 * array class
2797 * @throws NullPointerException if viewArrayClass or byteOrder is null
2798 * @throws IllegalArgumentException if viewArrayClass is not an array type
2799 * @throws UnsupportedOperationException if the component type of
2800 * viewArrayClass is not supported as a variable type
2801 * @since 9
2802 */
2803 public static
2804 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
2805 ByteOrder byteOrder) throws IllegalArgumentException {
2806 Objects.requireNonNull(byteOrder);
2807 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
2808 byteOrder == ByteOrder.BIG_ENDIAN);
2809 }
2810
2811
2812 /// method handle invocation (reflective style)
2813
2814 /**
2815 * Produces a method handle which will invoke any method handle of the
2816 * given {@code type}, with a given number of trailing arguments replaced by
2817 * a single trailing {@code Object[]} array.
2818 * The resulting invoker will be a method handle with the following
2819 * arguments:
2820 * <ul>
2821 * <li>a single {@code MethodHandle} target
2822 * <li>zero or more leading values (counted by {@code leadingArgCount})
2823 * <li>an {@code Object[]} array containing trailing arguments
2824 * </ul>
2825 * <p>
2826 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
2827 * the indicated {@code type}.
2828 * That is, if the target is exactly of the given {@code type}, it will behave
2829 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
2830 * is used to convert the target to the required {@code type}.
2831 * <p>
2832 * The type of the returned invoker will not be the given {@code type}, but rather
2833 * will have all parameters except the first {@code leadingArgCount}
2834 * replaced by a single array of type {@code Object[]}, which will be
2835 * the final parameter.
2836 * <p>
2837 * Before invoking its target, the invoker will spread the final array, apply
2838 * reference casts as necessary, and unbox and widen primitive arguments.
2839 * If, when the invoker is called, the supplied array argument does
2840 * not have the correct number of elements, the invoker will throw
2841 * an {@link IllegalArgumentException} instead of invoking the target.
2842 * <p>
2843 * This method is equivalent to the following code (though it may be more efficient):
2844 * <blockquote><pre>{@code
2845 MethodHandle invoker = MethodHandles.invoker(type);
2846 int spreadArgCount = type.parameterCount() - leadingArgCount;
2847 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
2848 return invoker;
2849 * }</pre></blockquote>
2850 * This method throws no reflective or security exceptions.
2851 * @param type the desired target type
2852 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
2853 * @return a method handle suitable for invoking any method handle of the given type
2854 * @throws NullPointerException if {@code type} is null
2855 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
2856 * the range from 0 to {@code type.parameterCount()} inclusive,
2857 * or if the resulting method handle's type would have
2858 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2859 */
2860 public static
2861 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
2862 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
2863 throw newIllegalArgumentException("bad argument count", leadingArgCount);
2864 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
2865 return type.invokers().spreadInvoker(leadingArgCount);
2866 }
2867
2868 /**
2869 * Produces a special <em>invoker method handle</em> which can be used to
2870 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
2871 * The resulting invoker will have a type which is
2872 * exactly equal to the desired type, except that it will accept
2873 * an additional leading argument of type {@code MethodHandle}.
2874 * <p>
2875 * This method is equivalent to the following code (though it may be more efficient):
2876 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
2877 *
2878 * <p style="font-size:smaller;">
2879 * <em>Discussion:</em>
2880 * Invoker method handles can be useful when working with variable method handles
2881 * of unknown types.
2882 * For example, to emulate an {@code invokeExact} call to a variable method
2883 * handle {@code M}, extract its type {@code T},
2884 * look up the invoker method {@code X} for {@code T},
2885 * and call the invoker method, as {@code X.invoke(T, A...)}.
2886 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
2887 * is unknown.)
2888 * If spreading, collecting, or other argument transformations are required,
2889 * they can be applied once to the invoker {@code X} and reused on many {@code M}
2890 * method handle values, as long as they are compatible with the type of {@code X}.
2891 * <p style="font-size:smaller;">
2892 * <em>(Note: The invoker method is not available via the Core Reflection API.
2893 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2894 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2895 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2896 * <p>
2897 * This method throws no reflective or security exceptions.
2898 * @param type the desired target type
2899 * @return a method handle suitable for invoking any method handle of the given type
2900 * @throws IllegalArgumentException if the resulting method handle's type would have
2901 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2902 */
2903 public static
2904 MethodHandle exactInvoker(MethodType type) {
2905 return type.invokers().exactInvoker();
2906 }
2907
2908 /**
2909 * Produces a special <em>invoker method handle</em> which can be used to
2910 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2911 * The resulting invoker will have a type which is
2912 * exactly equal to the desired type, except that it will accept
2913 * an additional leading argument of type {@code MethodHandle}.
2914 * <p>
2915 * Before invoking its target, if the target differs from the expected type,
2916 * the invoker will apply reference casts as
2917 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
2918 * Similarly, the return value will be converted as necessary.
2919 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
2920 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
2921 * <p>
2922 * This method is equivalent to the following code (though it may be more efficient):
2923 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
2924 * <p style="font-size:smaller;">
2925 * <em>Discussion:</em>
2926 * A {@linkplain MethodType#genericMethodType general method type} is one which
2927 * mentions only {@code Object} arguments and return values.
2928 * An invoker for such a type is capable of calling any method handle
2929 * of the same arity as the general type.
2930 * <p style="font-size:smaller;">
2931 * <em>(Note: The invoker method is not available via the Core Reflection API.
2932 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2933 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2934 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2935 * <p>
2936 * This method throws no reflective or security exceptions.
2937 * @param type the desired target type
2938 * @return a method handle suitable for invoking any method handle convertible to the given type
2939 * @throws IllegalArgumentException if the resulting method handle's type would have
2940 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2941 */
2942 public static
2943 MethodHandle invoker(MethodType type) {
2944 return type.invokers().genericInvoker();
2945 }
2946
2947 /**
2948 * Produces a special <em>invoker method handle</em> which can be used to
2949 * invoke a signature-polymorphic access mode method on any VarHandle whose
2950 * associated access mode type is compatible with the given type.
2951 * The resulting invoker will have a type which is exactly equal to the
2952 * desired given type, except that it will accept an additional leading
2953 * argument of type {@code VarHandle}.
2954 *
2955 * @param accessMode the VarHandle access mode
2956 * @param type the desired target type
2957 * @return a method handle suitable for invoking an access mode method of
2958 * any VarHandle whose access mode type is of the given type.
2959 * @since 9
2960 */
2961 static public
2962 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
2963 return type.invokers().varHandleMethodExactInvoker(accessMode);
2964 }
2965
2966 /**
2967 * Produces a special <em>invoker method handle</em> which can be used to
2968 * invoke a signature-polymorphic access mode method on any VarHandle whose
2969 * associated access mode type is compatible with the given type.
2970 * The resulting invoker will have a type which is exactly equal to the
2971 * desired given type, except that it will accept an additional leading
2972 * argument of type {@code VarHandle}.
2973 * <p>
2974 * Before invoking its target, if the access mode type differs from the
2975 * desired given type, the invoker will apply reference casts as necessary
2976 * and box, unbox, or widen primitive values, as if by
2977 * {@link MethodHandle#asType asType}. Similarly, the return value will be
2978 * converted as necessary.
2979 * <p>
2980 * This method is equivalent to the following code (though it may be more
2981 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
2982 *
2983 * @param accessMode the VarHandle access mode
2984 * @param type the desired target type
2985 * @return a method handle suitable for invoking an access mode method of
2986 * any VarHandle whose access mode type is convertible to the given
2987 * type.
2988 * @since 9
2989 */
2990 static public
2991 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
2992 return type.invokers().varHandleMethodInvoker(accessMode);
2993 }
2994
2995 static /*non-public*/
2996 MethodHandle basicInvoker(MethodType type) {
2997 return type.invokers().basicInvoker();
2998 }
2999
3000 /// method handle modification (creation from other method handles)
3001
3002 /**
3003 * Produces a method handle which adapts the type of the
3004 * given method handle to a new type by pairwise argument and return type conversion.
3005 * The original type and new type must have the same number of arguments.
3006 * The resulting method handle is guaranteed to report a type
3007 * which is equal to the desired new type.
3008 * <p>
3009 * If the original type and new type are equal, returns target.
3010 * <p>
3011 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
3012 * and some additional conversions are also applied if those conversions fail.
3013 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
3014 * if possible, before or instead of any conversions done by {@code asType}:
3015 * <ul>
3016 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
3017 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
3018 * (This treatment of interfaces follows the usage of the bytecode verifier.)
3019 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
3020 * the boolean is converted to a byte value, 1 for true, 0 for false.
3021 * (This treatment follows the usage of the bytecode verifier.)
3022 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
3023 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
3024 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
3025 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
3026 * then a Java casting conversion (JLS 5.5) is applied.
3027 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
3028 * widening and/or narrowing.)
3029 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
3030 * conversion will be applied at runtime, possibly followed
3031 * by a Java casting conversion (JLS 5.5) on the primitive value,
3032 * possibly followed by a conversion from byte to boolean by testing
3033 * the low-order bit.
3034 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
3035 * and if the reference is null at runtime, a zero value is introduced.
3036 * </ul>
3037 * @param target the method handle to invoke after arguments are retyped
3038 * @param newType the expected type of the new method handle
3039 * @return a method handle which delegates to the target after performing
3040 * any necessary argument conversions, and arranges for any
3041 * necessary return value conversions
3042 * @throws NullPointerException if either argument is null
3043 * @throws WrongMethodTypeException if the conversion cannot be made
3044 * @see MethodHandle#asType
3045 */
3046 public static
3047 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
3048 explicitCastArgumentsChecks(target, newType);
3049 // use the asTypeCache when possible:
3050 MethodType oldType = target.type();
3051 if (oldType == newType) return target;
3052 if (oldType.explicitCastEquivalentToAsType(newType)) {
3053 return target.asFixedArity().asType(newType);
3054 }
3055 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
3056 }
3057
3058 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
3059 if (target.type().parameterCount() != newType.parameterCount()) {
3060 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
3061 }
3062 }
3063
3064 /**
3065 * Produces a method handle which adapts the calling sequence of the
3066 * given method handle to a new type, by reordering the arguments.
3067 * The resulting method handle is guaranteed to report a type
3068 * which is equal to the desired new type.
3069 * <p>
3070 * The given array controls the reordering.
3071 * Call {@code #I} the number of incoming parameters (the value
3072 * {@code newType.parameterCount()}, and call {@code #O} the number
3073 * of outgoing parameters (the value {@code target.type().parameterCount()}).
3074 * Then the length of the reordering array must be {@code #O},
3075 * and each element must be a non-negative number less than {@code #I}.
3076 * For every {@code N} less than {@code #O}, the {@code N}-th
3077 * outgoing argument will be taken from the {@code I}-th incoming
3078 * argument, where {@code I} is {@code reorder[N]}.
3079 * <p>
3080 * No argument or return value conversions are applied.
3081 * The type of each incoming argument, as determined by {@code newType},
3082 * must be identical to the type of the corresponding outgoing parameter
3083 * or parameters in the target method handle.
3084 * The return type of {@code newType} must be identical to the return
3085 * type of the original target.
3086 * <p>
3087 * The reordering array need not specify an actual permutation.
3088 * An incoming argument will be duplicated if its index appears
3089 * more than once in the array, and an incoming argument will be dropped
3090 * if its index does not appear in the array.
3091 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
3092 * incoming arguments which are not mentioned in the reordering array
3093 * may be of any type, as determined only by {@code newType}.
3094 * <blockquote><pre>{@code
3095 import static java.lang.invoke.MethodHandles.*;
3096 import static java.lang.invoke.MethodType.*;
3097 ...
3098 MethodType intfn1 = methodType(int.class, int.class);
3099 MethodType intfn2 = methodType(int.class, int.class, int.class);
3100 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
3101 assert(sub.type().equals(intfn2));
3102 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
3103 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
3104 assert((int)rsub.invokeExact(1, 100) == 99);
3105 MethodHandle add = ... (int x, int y) -> (x+y) ...;
3106 assert(add.type().equals(intfn2));
3107 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
3108 assert(twice.type().equals(intfn1));
3109 assert((int)twice.invokeExact(21) == 42);
3110 * }</pre></blockquote>
3111 * <p>
3112 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3113 * variable-arity method handle}, even if the original target method handle was.
3114 * @param target the method handle to invoke after arguments are reordered
3115 * @param newType the expected type of the new method handle
3116 * @param reorder an index array which controls the reordering
3117 * @return a method handle which delegates to the target after it
3118 * drops unused arguments and moves and/or duplicates the other arguments
3119 * @throws NullPointerException if any argument is null
3120 * @throws IllegalArgumentException if the index array length is not equal to
3121 * the arity of the target, or if any index array element
3122 * not a valid index for a parameter of {@code newType},
3123 * or if two corresponding parameter types in
3124 * {@code target.type()} and {@code newType} are not identical,
3125 */
3126 public static
3127 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3128 reorder = reorder.clone(); // get a private copy
3129 MethodType oldType = target.type();
3130 permuteArgumentChecks(reorder, newType, oldType);
3131 // first detect dropped arguments and handle them separately
3132 int[] originalReorder = reorder;
3133 BoundMethodHandle result = target.rebind();
3134 LambdaForm form = result.form;
3135 int newArity = newType.parameterCount();
3136 // Normalize the reordering into a real permutation,
3137 // by removing duplicates and adding dropped elements.
3138 // This somewhat improves lambda form caching, as well
3139 // as simplifying the transform by breaking it up into steps.
3140 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3141 if (ddIdx > 0) {
3142 // We found a duplicated entry at reorder[ddIdx].
3143 // Example: (x,y,z)->asList(x,y,z)
3144 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3145 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3146 // The starred element corresponds to the argument
3147 // deleted by the dupArgumentForm transform.
3148 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3149 boolean killFirst = false;
3150 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3151 // Set killFirst if the dup is larger than an intervening position.
3152 // This will remove at least one inversion from the permutation.
3153 if (dupVal > val) killFirst = true;
3154 }
3155 if (!killFirst) {
3156 srcPos = dstPos;
3157 dstPos = ddIdx;
3158 }
3159 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3160 assert (reorder[srcPos] == reorder[dstPos]);
3161 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3162 // contract the reordering by removing the element at dstPos
3163 int tailPos = dstPos + 1;
3164 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3165 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3166 } else {
3167 int dropVal = ~ddIdx, insPos = 0;
3168 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3169 // Find first element of reorder larger than dropVal.
3170 // This is where we will insert the dropVal.
3171 insPos += 1;
3172 }
3173 Class<?> ptype = newType.parameterType(dropVal);
3174 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3175 oldType = oldType.insertParameterTypes(insPos, ptype);
3176 // expand the reordering by inserting an element at insPos
3177 int tailPos = insPos + 1;
3178 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3179 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3180 reorder[insPos] = dropVal;
3181 }
3182 assert (permuteArgumentChecks(reorder, newType, oldType));
3183 }
3184 assert (reorder.length == newArity); // a perfect permutation
3185 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3186 form = form.editor().permuteArgumentsForm(1, reorder);
3187 if (newType == result.type() && form == result.internalForm())
3188 return result;
3189 return result.copyWith(newType, form);
3190 }
3191
3192 /**
3193 * Return an indication of any duplicate or omission in reorder.
3194 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3195 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3196 * Otherwise, return zero.
3197 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3198 */
3199 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3200 final int BIT_LIMIT = 63; // max number of bits in bit mask
3201 if (newArity < BIT_LIMIT) {
3202 long mask = 0;
3203 for (int i = 0; i < reorder.length; i++) {
3204 int arg = reorder[i];
3205 if (arg >= newArity) {
3206 return reorder.length;
3207 }
3208 long bit = 1L << arg;
3209 if ((mask & bit) != 0) {
3210 return i; // >0 indicates a dup
3211 }
3212 mask |= bit;
3213 }
3214 if (mask == (1L << newArity) - 1) {
3215 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
3216 return 0;
3217 }
3218 // find first zero
3219 long zeroBit = Long.lowestOneBit(~mask);
3220 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
3221 assert(zeroPos <= newArity);
3222 if (zeroPos == newArity) {
3223 return 0;
3224 }
3225 return ~zeroPos;
3226 } else {
3227 // same algorithm, different bit set
3228 BitSet mask = new BitSet(newArity);
3229 for (int i = 0; i < reorder.length; i++) {
3230 int arg = reorder[i];
3231 if (arg >= newArity) {
3232 return reorder.length;
3233 }
3234 if (mask.get(arg)) {
3235 return i; // >0 indicates a dup
3236 }
3237 mask.set(arg);
3238 }
3239 int zeroPos = mask.nextClearBit(0);
3240 assert(zeroPos <= newArity);
3241 if (zeroPos == newArity) {
3242 return 0;
3243 }
3244 return ~zeroPos;
3245 }
3246 }
3247
3248 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
3249 if (newType.returnType() != oldType.returnType())
3250 throw newIllegalArgumentException("return types do not match",
3251 oldType, newType);
3252 if (reorder.length == oldType.parameterCount()) {
3253 int limit = newType.parameterCount();
3254 boolean bad = false;
3255 for (int j = 0; j < reorder.length; j++) {
3256 int i = reorder[j];
3257 if (i < 0 || i >= limit) {
3258 bad = true; break;
3259 }
3260 Class<?> src = newType.parameterType(i);
3261 Class<?> dst = oldType.parameterType(j);
3262 if (src != dst)
3263 throw newIllegalArgumentException("parameter types do not match after reorder",
3264 oldType, newType);
3265 }
3266 if (!bad) return true;
3267 }
3268 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3269 }
3270
3271 /**
3272 * Produces a method handle of the requested return type which returns the given
3273 * constant value every time it is invoked.
3274 * <p>
3275 * Before the method handle is returned, the passed-in value is converted to the requested type.
3276 * If the requested type is primitive, widening primitive conversions are attempted,
3277 * else reference conversions are attempted.
3278 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3279 * @param type the return type of the desired method handle
3280 * @param value the value to return
3281 * @return a method handle of the given return type and no arguments, which always returns the given value
3282 * @throws NullPointerException if the {@code type} argument is null
3283 * @throws ClassCastException if the value cannot be converted to the required return type
3284 * @throws IllegalArgumentException if the given type is {@code void.class}
3285 */
3286 public static
3287 MethodHandle constant(Class<?> type, Object value) {
3288 if (type.isPrimitive()) {
3289 if (type == void.class)
3290 throw newIllegalArgumentException("void type");
3291 Wrapper w = Wrapper.forPrimitiveType(type);
3292 value = w.convert(value, type);
3293 if (w.zero().equals(value))
3294 return zero(w, type);
3295 return insertArguments(identity(type), 0, value);
3296 } else {
3297 if (value == null)
3298 return zero(Wrapper.OBJECT, type);
3299 return identity(type).bindTo(value);
3300 }
3301 }
3302
3303 /**
3304 * Produces a method handle which returns its sole argument when invoked.
3305 * @param type the type of the sole parameter and return value of the desired method handle
3306 * @return a unary method handle which accepts and returns the given type
3307 * @throws NullPointerException if the argument is null
3308 * @throws IllegalArgumentException if the given type is {@code void.class}
3309 */
3310 public static
3311 MethodHandle identity(Class<?> type) {
3312 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3313 int pos = btw.ordinal();
3314 MethodHandle ident = IDENTITY_MHS[pos];
3315 if (ident == null) {
3316 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3317 }
3318 if (ident.type().returnType() == type)
3319 return ident;
3320 // something like identity(Foo.class); do not bother to intern these
3321 assert (btw == Wrapper.OBJECT);
3322 return makeIdentity(type);
3323 }
3324
3325 /**
3326 * Produces a constant method handle of the requested return type which
3327 * returns the default value for that type every time it is invoked.
3328 * The resulting constant method handle will have no side effects.
3329 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3330 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3331 * since {@code explicitCastArguments} converts {@code null} to default values.
3332 * @param type the expected return type of the desired method handle
3333 * @return a constant method handle that takes no arguments
3334 * and returns the default value of the given type (or void, if the type is void)
3335 * @throws NullPointerException if the argument is null
3336 * @see MethodHandles#constant
3337 * @see MethodHandles#empty
3338 * @see MethodHandles#explicitCastArguments
3339 * @since 9
3340 */
3341 public static MethodHandle zero(Class<?> type) {
3342 Objects.requireNonNull(type);
3343 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
3344 }
3345
3346 private static MethodHandle identityOrVoid(Class<?> type) {
3347 return type == void.class ? zero(type) : identity(type);
3348 }
3349
3350 /**
3351 * Produces a method handle of the requested type which ignores any arguments, does nothing,
3352 * and returns a suitable default depending on the return type.
3353 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3354 * <p>The returned method handle is equivalent to
3355 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3356 *
3357 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3358 * {@code guardWithTest(pred, target, empty(target.type())}.
3359 * @param type the type of the desired method handle
3360 * @return a constant method handle of the given type, which returns a default value of the given return type
3361 * @throws NullPointerException if the argument is null
3362 * @see MethodHandles#zero
3363 * @see MethodHandles#constant
3364 * @since 9
3365 */
3366 public static MethodHandle empty(MethodType type) {
3367 Objects.requireNonNull(type);
3368 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3369 }
3370
3371 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
3372 private static MethodHandle makeIdentity(Class<?> ptype) {
3373 MethodType mtype = methodType(ptype, ptype);
3374 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3375 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3376 }
3377
3378 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3379 int pos = btw.ordinal();
3380 MethodHandle zero = ZERO_MHS[pos];
3381 if (zero == null) {
3382 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3383 }
3384 if (zero.type().returnType() == rtype)
3385 return zero;
3386 assert(btw == Wrapper.OBJECT);
3387 return makeZero(rtype);
3388 }
3389 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
3390 private static MethodHandle makeZero(Class<?> rtype) {
3391 MethodType mtype = methodType(rtype);
3392 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3393 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3394 }
3395
3396 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3397 // Simulate a CAS, to avoid racy duplication of results.
3398 MethodHandle prev = cache[pos];
3399 if (prev != null) return prev;
3400 return cache[pos] = value;
3401 }
3402
3403 /**
3404 * Provides a target method handle with one or more <em>bound arguments</em>
3405 * in advance of the method handle's invocation.
3406 * The formal parameters to the target corresponding to the bound
3407 * arguments are called <em>bound parameters</em>.
3408 * Returns a new method handle which saves away the bound arguments.
3409 * When it is invoked, it receives arguments for any non-bound parameters,
3410 * binds the saved arguments to their corresponding parameters,
3411 * and calls the original target.
3412 * <p>
3413 * The type of the new method handle will drop the types for the bound
3414 * parameters from the original target type, since the new method handle
3415 * will no longer require those arguments to be supplied by its callers.
3416 * <p>
3417 * Each given argument object must match the corresponding bound parameter type.
3418 * If a bound parameter type is a primitive, the argument object
3419 * must be a wrapper, and will be unboxed to produce the primitive value.
3420 * <p>
3421 * The {@code pos} argument selects which parameters are to be bound.
3422 * It may range between zero and <i>N-L</i> (inclusively),
3423 * where <i>N</i> is the arity of the target method handle
3424 * and <i>L</i> is the length of the values array.
3425 * <p>
3426 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3427 * variable-arity method handle}, even if the original target method handle was.
3428 * @param target the method handle to invoke after the argument is inserted
3429 * @param pos where to insert the argument (zero for the first)
3430 * @param values the series of arguments to insert
3431 * @return a method handle which inserts an additional argument,
3432 * before calling the original method handle
3433 * @throws NullPointerException if the target or the {@code values} array is null
3434 * @see MethodHandle#bindTo
3435 */
3436 public static
3437 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3438 int insCount = values.length;
3439 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3440 if (insCount == 0) return target;
3441 BoundMethodHandle result = target.rebind();
3442 for (int i = 0; i < insCount; i++) {
3443 Object value = values[i];
3444 Class<?> ptype = ptypes[pos+i];
3445 if (ptype.isPrimitive()) {
3446 result = insertArgumentPrimitive(result, pos, ptype, value);
3447 } else {
3448 value = ptype.cast(value); // throw CCE if needed
3449 result = result.bindArgumentL(pos, value);
3450 }
3451 }
3452 return result;
3453 }
3454
3455 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3456 Class<?> ptype, Object value) {
3457 Wrapper w = Wrapper.forPrimitiveType(ptype);
3458 // perform unboxing and/or primitive conversion
3459 value = w.convert(value, ptype);
3460 switch (w) {
3461 case INT: return result.bindArgumentI(pos, (int)value);
3462 case LONG: return result.bindArgumentJ(pos, (long)value);
3463 case FLOAT: return result.bindArgumentF(pos, (float)value);
3464 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3465 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3466 }
3467 }
3468
3469 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3470 MethodType oldType = target.type();
3471 int outargs = oldType.parameterCount();
3472 int inargs = outargs - insCount;
3473 if (inargs < 0)
3474 throw newIllegalArgumentException("too many values to insert");
3475 if (pos < 0 || pos > inargs)
3476 throw newIllegalArgumentException("no argument type to append");
3477 return oldType.ptypes();
3478 }
3479
3480 /**
3481 * Produces a method handle which will discard some dummy arguments
3482 * before calling some other specified <i>target</i> method handle.
3483 * The type of the new method handle will be the same as the target's type,
3484 * except it will also include the dummy argument types,
3485 * at some given position.
3486 * <p>
3487 * The {@code pos} argument may range between zero and <i>N</i>,
3488 * where <i>N</i> is the arity of the target.
3489 * If {@code pos} is zero, the dummy arguments will precede
3490 * the target's real arguments; if {@code pos} is <i>N</i>
3491 * they will come after.
3492 * <p>
3493 * <b>Example:</b>
3494 * <blockquote><pre>{@code
3495 import static java.lang.invoke.MethodHandles.*;
3496 import static java.lang.invoke.MethodType.*;
3497 ...
3498 MethodHandle cat = lookup().findVirtual(String.class,
3499 "concat", methodType(String.class, String.class));
3500 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3501 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3502 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3503 assertEquals(bigType, d0.type());
3504 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3505 * }</pre></blockquote>
3506 * <p>
3507 * This method is also equivalent to the following code:
3508 * <blockquote><pre>
3509 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3510 * </pre></blockquote>
3511 * @param target the method handle to invoke after the arguments are dropped
3512 * @param valueTypes the type(s) of the argument(s) to drop
3513 * @param pos position of first argument to drop (zero for the leftmost)
3514 * @return a method handle which drops arguments of the given types,
3515 * before calling the original method handle
3516 * @throws NullPointerException if the target is null,
3517 * or if the {@code valueTypes} list or any of its elements is null
3518 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3519 * or if {@code pos} is negative or greater than the arity of the target,
3520 * or if the new method handle's type would have too many parameters
3521 */
3522 public static
3523 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3524 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
3525 }
3526
3527 private static List<Class<?>> copyTypes(Object[] array) {
3528 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
3529 }
3530
3531 private static
3532 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3533 MethodType oldType = target.type(); // get NPE
3534 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3535 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3536 if (dropped == 0) return target;
3537 BoundMethodHandle result = target.rebind();
3538 LambdaForm lform = result.form;
3539 int insertFormArg = 1 + pos;
3540 for (Class<?> ptype : valueTypes) {
3541 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3542 }
3543 result = result.copyWith(newType, lform);
3544 return result;
3545 }
3546
3547 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3548 int dropped = valueTypes.size();
3549 MethodType.checkSlotCount(dropped);
3550 int outargs = oldType.parameterCount();
3551 int inargs = outargs + dropped;
3552 if (pos < 0 || pos > outargs)
3553 throw newIllegalArgumentException("no argument type to remove"
3554 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3555 );
3556 return dropped;
3557 }
3558
3559 /**
3560 * Produces a method handle which will discard some dummy arguments
3561 * before calling some other specified <i>target</i> method handle.
3562 * The type of the new method handle will be the same as the target's type,
3563 * except it will also include the dummy argument types,
3564 * at some given position.
3565 * <p>
3566 * The {@code pos} argument may range between zero and <i>N</i>,
3567 * where <i>N</i> is the arity of the target.
3568 * If {@code pos} is zero, the dummy arguments will precede
3569 * the target's real arguments; if {@code pos} is <i>N</i>
3570 * they will come after.
3571 * @apiNote
3572 * <blockquote><pre>{@code
3573 import static java.lang.invoke.MethodHandles.*;
3574 import static java.lang.invoke.MethodType.*;
3575 ...
3576 MethodHandle cat = lookup().findVirtual(String.class,
3577 "concat", methodType(String.class, String.class));
3578 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3579 MethodHandle d0 = dropArguments(cat, 0, String.class);
3580 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3581 MethodHandle d1 = dropArguments(cat, 1, String.class);
3582 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
3583 MethodHandle d2 = dropArguments(cat, 2, String.class);
3584 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
3585 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
3586 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
3587 * }</pre></blockquote>
3588 * <p>
3589 * This method is also equivalent to the following code:
3590 * <blockquote><pre>
3591 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
3592 * </pre></blockquote>
3593 * @param target the method handle to invoke after the arguments are dropped
3594 * @param valueTypes the type(s) of the argument(s) to drop
3595 * @param pos position of first argument to drop (zero for the leftmost)
3596 * @return a method handle which drops arguments of the given types,
3597 * before calling the original method handle
3598 * @throws NullPointerException if the target is null,
3599 * or if the {@code valueTypes} array or any of its elements is null
3600 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3601 * or if {@code pos} is negative or greater than the arity of the target,
3602 * or if the new method handle's type would have
3603 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3604 */
3605 public static
3606 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
3607 return dropArguments0(target, pos, copyTypes(valueTypes));
3608 }
3609
3610 // private version which allows caller some freedom with error handling
3611 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
3612 boolean nullOnFailure) {
3613 newTypes = copyTypes(newTypes.toArray());
3614 List<Class<?>> oldTypes = target.type().parameterList();
3615 int match = oldTypes.size();
3616 if (skip != 0) {
3617 if (skip < 0 || skip > match) {
3618 throw newIllegalArgumentException("illegal skip", skip, target);
3619 }
3620 oldTypes = oldTypes.subList(skip, match);
3621 match -= skip;
3622 }
3623 List<Class<?>> addTypes = newTypes;
3624 int add = addTypes.size();
3625 if (pos != 0) {
3626 if (pos < 0 || pos > add) {
3627 throw newIllegalArgumentException("illegal pos", pos, newTypes);
3628 }
3629 addTypes = addTypes.subList(pos, add);
3630 add -= pos;
3631 assert(addTypes.size() == add);
3632 }
3633 // Do not add types which already match the existing arguments.
3634 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
3635 if (nullOnFailure) {
3636 return null;
3637 }
3638 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
3639 }
3640 addTypes = addTypes.subList(match, add);
3641 add -= match;
3642 assert(addTypes.size() == add);
3643 // newTypes: ( P*[pos], M*[match], A*[add] )
3644 // target: ( S*[skip], M*[match] )
3645 MethodHandle adapter = target;
3646 if (add > 0) {
3647 adapter = dropArguments0(adapter, skip+ match, addTypes);
3648 }
3649 // adapter: (S*[skip], M*[match], A*[add] )
3650 if (pos > 0) {
3651 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
3652 }
3653 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
3654 return adapter;
3655 }
3656
3657 /**
3658 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
3659 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
3660 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
3661 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
3662 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
3663 * {@link #dropArguments(MethodHandle, int, Class[])}.
3664 * <p>
3665 * The resulting handle will have the same return type as the target handle.
3666 * <p>
3667 * In more formal terms, assume these two type lists:<ul>
3668 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
3669 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
3670 * {@code newTypes}.
3671 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
3672 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
3673 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
3674 * sub-list.
3675 * </ul>
3676 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
3677 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
3678 * {@link #dropArguments(MethodHandle, int, Class[])}.
3679 *
3680 * @apiNote
3681 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
3682 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
3683 * <blockquote><pre>{@code
3684 import static java.lang.invoke.MethodHandles.*;
3685 import static java.lang.invoke.MethodType.*;
3686 ...
3687 ...
3688 MethodHandle h0 = constant(boolean.class, true);
3689 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
3690 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
3691 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
3692 if (h1.type().parameterCount() < h2.type().parameterCount())
3693 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
3694 else
3695 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
3696 MethodHandle h3 = guardWithTest(h0, h1, h2);
3697 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
3698 * }</pre></blockquote>
3699 * @param target the method handle to adapt
3700 * @param skip number of targets parameters to disregard (they will be unchanged)
3701 * @param newTypes the list of types to match {@code target}'s parameter type list to
3702 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
3703 * @return a possibly adapted method handle
3704 * @throws NullPointerException if either argument is null
3705 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
3706 * or if {@code skip} is negative or greater than the arity of the target,
3707 * or if {@code pos} is negative or greater than the newTypes list size,
3708 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
3709 * {@code pos}.
3710 * @since 9
3711 */
3712 public static
3713 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
3714 Objects.requireNonNull(target);
3715 Objects.requireNonNull(newTypes);
3716 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
3717 }
3718
3719 /**
3720 * Adapts a target method handle by pre-processing
3721 * one or more of its arguments, each with its own unary filter function,
3722 * and then calling the target with each pre-processed argument
3723 * replaced by the result of its corresponding filter function.
3724 * <p>
3725 * The pre-processing is performed by one or more method handles,
3726 * specified in the elements of the {@code filters} array.
3727 * The first element of the filter array corresponds to the {@code pos}
3728 * argument of the target, and so on in sequence.
3729 * <p>
3730 * Null arguments in the array are treated as identity functions,
3731 * and the corresponding arguments left unchanged.
3732 * (If there are no non-null elements in the array, the original target is returned.)
3733 * Each filter is applied to the corresponding argument of the adapter.
3734 * <p>
3735 * If a filter {@code F} applies to the {@code N}th argument of
3736 * the target, then {@code F} must be a method handle which
3737 * takes exactly one argument. The type of {@code F}'s sole argument
3738 * replaces the corresponding argument type of the target
3739 * in the resulting adapted method handle.
3740 * The return type of {@code F} must be identical to the corresponding
3741 * parameter type of the target.
3742 * <p>
3743 * It is an error if there are elements of {@code filters}
3744 * (null or not)
3745 * which do not correspond to argument positions in the target.
3746 * <p><b>Example:</b>
3747 * <blockquote><pre>{@code
3748 import static java.lang.invoke.MethodHandles.*;
3749 import static java.lang.invoke.MethodType.*;
3750 ...
3751 MethodHandle cat = lookup().findVirtual(String.class,
3752 "concat", methodType(String.class, String.class));
3753 MethodHandle upcase = lookup().findVirtual(String.class,
3754 "toUpperCase", methodType(String.class));
3755 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3756 MethodHandle f0 = filterArguments(cat, 0, upcase);
3757 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
3758 MethodHandle f1 = filterArguments(cat, 1, upcase);
3759 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
3760 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
3761 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
3762 * }</pre></blockquote>
3763 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3764 * denotes the return type of both the {@code target} and resulting adapter.
3765 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
3766 * of the parameters and arguments that precede and follow the filter position
3767 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
3768 * values of the filtered parameters and arguments; they also represent the
3769 * return types of the {@code filter[i]} handles. The latter accept arguments
3770 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
3771 * the resulting adapter.
3772 * <blockquote><pre>{@code
3773 * T target(P... p, A[i]... a[i], B... b);
3774 * A[i] filter[i](V[i]);
3775 * T adapter(P... p, V[i]... v[i], B... b) {
3776 * return target(p..., filter[i](v[i])..., b...);
3777 * }
3778 * }</pre></blockquote>
3779 * <p>
3780 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3781 * variable-arity method handle}, even if the original target method handle was.
3782 *
3783 * @param target the method handle to invoke after arguments are filtered
3784 * @param pos the position of the first argument to filter
3785 * @param filters method handles to call initially on filtered arguments
3786 * @return method handle which incorporates the specified argument filtering logic
3787 * @throws NullPointerException if the target is null
3788 * or if the {@code filters} array is null
3789 * @throws IllegalArgumentException if a non-null element of {@code filters}
3790 * does not match a corresponding argument type of target as described above,
3791 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
3792 * or if the resulting method handle's type would have
3793 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3794 */
3795 public static
3796 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
3797 filterArgumentsCheckArity(target, pos, filters);
3798 MethodHandle adapter = target;
3799 int curPos = pos-1; // pre-incremented
3800 for (MethodHandle filter : filters) {
3801 curPos += 1;
3802 if (filter == null) continue; // ignore null elements of filters
3803 adapter = filterArgument(adapter, curPos, filter);
3804 }
3805 return adapter;
3806 }
3807
3808 /*non-public*/ static
3809 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
3810 filterArgumentChecks(target, pos, filter);
3811 MethodType targetType = target.type();
3812 MethodType filterType = filter.type();
3813 BoundMethodHandle result = target.rebind();
3814 Class<?> newParamType = filterType.parameterType(0);
3815 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
3816 MethodType newType = targetType.changeParameterType(pos, newParamType);
3817 result = result.copyWithExtendL(newType, lform, filter);
3818 return result;
3819 }
3820
3821 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
3822 MethodType targetType = target.type();
3823 int maxPos = targetType.parameterCount();
3824 if (pos + filters.length > maxPos)
3825 throw newIllegalArgumentException("too many filters");
3826 }
3827
3828 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3829 MethodType targetType = target.type();
3830 MethodType filterType = filter.type();
3831 if (filterType.parameterCount() != 1
3832 || filterType.returnType() != targetType.parameterType(pos))
3833 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3834 }
3835
3836 /**
3837 * Adapts a target method handle by pre-processing
3838 * a sub-sequence of its arguments with a filter (another method handle).
3839 * The pre-processed arguments are replaced by the result (if any) of the
3840 * filter function.
3841 * The target is then called on the modified (usually shortened) argument list.
3842 * <p>
3843 * If the filter returns a value, the target must accept that value as
3844 * its argument in position {@code pos}, preceded and/or followed by
3845 * any arguments not passed to the filter.
3846 * If the filter returns void, the target must accept all arguments
3847 * not passed to the filter.
3848 * No arguments are reordered, and a result returned from the filter
3849 * replaces (in order) the whole subsequence of arguments originally
3850 * passed to the adapter.
3851 * <p>
3852 * The argument types (if any) of the filter
3853 * replace zero or one argument types of the target, at position {@code pos},
3854 * in the resulting adapted method handle.
3855 * The return type of the filter (if any) must be identical to the
3856 * argument type of the target at position {@code pos}, and that target argument
3857 * is supplied by the return value of the filter.
3858 * <p>
3859 * In all cases, {@code pos} must be greater than or equal to zero, and
3860 * {@code pos} must also be less than or equal to the target's arity.
3861 * <p><b>Example:</b>
3862 * <blockquote><pre>{@code
3863 import static java.lang.invoke.MethodHandles.*;
3864 import static java.lang.invoke.MethodType.*;
3865 ...
3866 MethodHandle deepToString = publicLookup()
3867 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
3868
3869 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
3870 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
3871
3872 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
3873 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
3874
3875 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
3876 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
3877 assertEquals("[top, [up, down], strange]",
3878 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
3879
3880 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
3881 assertEquals("[top, [up, down], [strange]]",
3882 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
3883
3884 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
3885 assertEquals("[top, [[up, down, strange], charm], bottom]",
3886 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
3887 * }</pre></blockquote>
3888 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3889 * represents the return type of the {@code target} and resulting adapter.
3890 * {@code V}/{@code v} stand for the return type and value of the
3891 * {@code filter}, which are also found in the signature and arguments of
3892 * the {@code target}, respectively, unless {@code V} is {@code void}.
3893 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
3894 * and values preceding and following the collection position, {@code pos},
3895 * in the {@code target}'s signature. They also turn up in the resulting
3896 * adapter's signature and arguments, where they surround
3897 * {@code B}/{@code b}, which represent the parameter types and arguments
3898 * to the {@code filter} (if any).
3899 * <blockquote><pre>{@code
3900 * T target(A...,V,C...);
3901 * V filter(B...);
3902 * T adapter(A... a,B... b,C... c) {
3903 * V v = filter(b...);
3904 * return target(a...,v,c...);
3905 * }
3906 * // and if the filter has no arguments:
3907 * T target2(A...,V,C...);
3908 * V filter2();
3909 * T adapter2(A... a,C... c) {
3910 * V v = filter2();
3911 * return target2(a...,v,c...);
3912 * }
3913 * // and if the filter has a void return:
3914 * T target3(A...,C...);
3915 * void filter3(B...);
3916 * T adapter3(A... a,B... b,C... c) {
3917 * filter3(b...);
3918 * return target3(a...,c...);
3919 * }
3920 * }</pre></blockquote>
3921 * <p>
3922 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
3923 * one which first "folds" the affected arguments, and then drops them, in separate
3924 * steps as follows:
3925 * <blockquote><pre>{@code
3926 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
3927 * mh = MethodHandles.foldArguments(mh, coll); //step 1
3928 * }</pre></blockquote>
3929 * If the target method handle consumes no arguments besides than the result
3930 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
3931 * is equivalent to {@code filterReturnValue(coll, mh)}.
3932 * If the filter method handle {@code coll} consumes one argument and produces
3933 * a non-void result, then {@code collectArguments(mh, N, coll)}
3934 * is equivalent to {@code filterArguments(mh, N, coll)}.
3935 * Other equivalences are possible but would require argument permutation.
3936 * <p>
3937 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3938 * variable-arity method handle}, even if the original target method handle was.
3939 *
3940 * @param target the method handle to invoke after filtering the subsequence of arguments
3941 * @param pos the position of the first adapter argument to pass to the filter,
3942 * and/or the target argument which receives the result of the filter
3943 * @param filter method handle to call on the subsequence of arguments
3944 * @return method handle which incorporates the specified argument subsequence filtering logic
3945 * @throws NullPointerException if either argument is null
3946 * @throws IllegalArgumentException if the return type of {@code filter}
3947 * is non-void and is not the same as the {@code pos} argument of the target,
3948 * or if {@code pos} is not between 0 and the target's arity, inclusive,
3949 * or if the resulting method handle's type would have
3950 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3951 * @see MethodHandles#foldArguments
3952 * @see MethodHandles#filterArguments
3953 * @see MethodHandles#filterReturnValue
3954 */
3955 public static
3956 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
3957 MethodType newType = collectArgumentsChecks(target, pos, filter);
3958 MethodType collectorType = filter.type();
3959 BoundMethodHandle result = target.rebind();
3960 LambdaForm lform;
3961 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
3962 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
3963 if (lform != null) {
3964 return result.copyWith(newType, lform);
3965 }
3966 }
3967 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
3968 return result.copyWithExtendL(newType, lform, filter);
3969 }
3970
3971 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3972 MethodType targetType = target.type();
3973 MethodType filterType = filter.type();
3974 Class<?> rtype = filterType.returnType();
3975 List<Class<?>> filterArgs = filterType.parameterList();
3976 if (rtype == void.class) {
3977 return targetType.insertParameterTypes(pos, filterArgs);
3978 }
3979 if (rtype != targetType.parameterType(pos)) {
3980 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3981 }
3982 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
3983 }
3984
3985 /**
3986 * Adapts a target method handle by post-processing
3987 * its return value (if any) with a filter (another method handle).
3988 * The result of the filter is returned from the adapter.
3989 * <p>
3990 * If the target returns a value, the filter must accept that value as
3991 * its only argument.
3992 * If the target returns void, the filter must accept no arguments.
3993 * <p>
3994 * The return type of the filter
3995 * replaces the return type of the target
3996 * in the resulting adapted method handle.
3997 * The argument type of the filter (if any) must be identical to the
3998 * return type of the target.
3999 * <p><b>Example:</b>
4000 * <blockquote><pre>{@code
4001 import static java.lang.invoke.MethodHandles.*;
4002 import static java.lang.invoke.MethodType.*;
4003 ...
4004 MethodHandle cat = lookup().findVirtual(String.class,
4005 "concat", methodType(String.class, String.class));
4006 MethodHandle length = lookup().findVirtual(String.class,
4007 "length", methodType(int.class));
4008 System.out.println((String) cat.invokeExact("x", "y")); // xy
4009 MethodHandle f0 = filterReturnValue(cat, length);
4010 System.out.println((int) f0.invokeExact("x", "y")); // 2
4011 * }</pre></blockquote>
4012 * <p>Here is pseudocode for the resulting adapter. In the code,
4013 * {@code T}/{@code t} represent the result type and value of the
4014 * {@code target}; {@code V}, the result type of the {@code filter}; and
4015 * {@code A}/{@code a}, the types and values of the parameters and arguments
4016 * of the {@code target} as well as the resulting adapter.
4017 * <blockquote><pre>{@code
4018 * T target(A...);
4019 * V filter(T);
4020 * V adapter(A... a) {
4021 * T t = target(a...);
4022 * return filter(t);
4023 * }
4024 * // and if the target has a void return:
4025 * void target2(A...);
4026 * V filter2();
4027 * V adapter2(A... a) {
4028 * target2(a...);
4029 * return filter2();
4030 * }
4031 * // and if the filter has a void return:
4032 * T target3(A...);
4033 * void filter3(V);
4034 * void adapter3(A... a) {
4035 * T t = target3(a...);
4036 * filter3(t);
4037 * }
4038 * }</pre></blockquote>
4039 * <p>
4040 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4041 * variable-arity method handle}, even if the original target method handle was.
4042 * @param target the method handle to invoke before filtering the return value
4043 * @param filter method handle to call on the return value
4044 * @return method handle which incorporates the specified return value filtering logic
4045 * @throws NullPointerException if either argument is null
4046 * @throws IllegalArgumentException if the argument list of {@code filter}
4047 * does not match the return type of target as described above
4048 */
4049 public static
4050 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
4051 MethodType targetType = target.type();
4052 MethodType filterType = filter.type();
4053 filterReturnValueChecks(targetType, filterType);
4054 BoundMethodHandle result = target.rebind();
4055 BasicType rtype = BasicType.basicType(filterType.returnType());
4056 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
4057 MethodType newType = targetType.changeReturnType(filterType.returnType());
4058 result = result.copyWithExtendL(newType, lform, filter);
4059 return result;
4060 }
4061
4062 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
4063 Class<?> rtype = targetType.returnType();
4064 int filterValues = filterType.parameterCount();
4065 if (filterValues == 0
4066 ? (rtype != void.class)
4067 : (rtype != filterType.parameterType(0) || filterValues != 1))
4068 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4069 }
4070
4071 /**
4072 * Adapts a target method handle by pre-processing
4073 * some of its arguments, and then calling the target with
4074 * the result of the pre-processing, inserted into the original
4075 * sequence of arguments.
4076 * <p>
4077 * The pre-processing is performed by {@code combiner}, a second method handle.
4078 * Of the arguments passed to the adapter, the first {@code N} arguments
4079 * are copied to the combiner, which is then called.
4080 * (Here, {@code N} is defined as the parameter count of the combiner.)
4081 * After this, control passes to the target, with any result
4082 * from the combiner inserted before the original {@code N} incoming
4083 * arguments.
4084 * <p>
4085 * If the combiner returns a value, the first parameter type of the target
4086 * must be identical with the return type of the combiner, and the next
4087 * {@code N} parameter types of the target must exactly match the parameters
4088 * of the combiner.
4089 * <p>
4090 * If the combiner has a void return, no result will be inserted,
4091 * and the first {@code N} parameter types of the target
4092 * must exactly match the parameters of the combiner.
4093 * <p>
4094 * The resulting adapter is the same type as the target, except that the
4095 * first parameter type is dropped,
4096 * if it corresponds to the result of the combiner.
4097 * <p>
4098 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
4099 * that either the combiner or the target does not wish to receive.
4100 * If some of the incoming arguments are destined only for the combiner,
4101 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
4102 * arguments will not need to be live on the stack on entry to the
4103 * target.)
4104 * <p><b>Example:</b>
4105 * <blockquote><pre>{@code
4106 import static java.lang.invoke.MethodHandles.*;
4107 import static java.lang.invoke.MethodType.*;
4108 ...
4109 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4110 "println", methodType(void.class, String.class))
4111 .bindTo(System.out);
4112 MethodHandle cat = lookup().findVirtual(String.class,
4113 "concat", methodType(String.class, String.class));
4114 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4115 MethodHandle catTrace = foldArguments(cat, trace);
4116 // also prints "boo":
4117 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4118 * }</pre></blockquote>
4119 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4120 * represents the result type of the {@code target} and resulting adapter.
4121 * {@code V}/{@code v} represent the type and value of the parameter and argument
4122 * of {@code target} that precedes the folding position; {@code V} also is
4123 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4124 * types and values of the {@code N} parameters and arguments at the folding
4125 * position. {@code B}/{@code b} represent the types and values of the
4126 * {@code target} parameters and arguments that follow the folded parameters
4127 * and arguments.
4128 * <blockquote><pre>{@code
4129 * // there are N arguments in A...
4130 * T target(V, A[N]..., B...);
4131 * V combiner(A...);
4132 * T adapter(A... a, B... b) {
4133 * V v = combiner(a...);
4134 * return target(v, a..., b...);
4135 * }
4136 * // and if the combiner has a void return:
4137 * T target2(A[N]..., B...);
4138 * void combiner2(A...);
4139 * T adapter2(A... a, B... b) {
4140 * combiner2(a...);
4141 * return target2(a..., b...);
4142 * }
4143 * }</pre></blockquote>
4144 * <p>
4145 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4146 * variable-arity method handle}, even if the original target method handle was.
4147 * @param target the method handle to invoke after arguments are combined
4148 * @param combiner method handle to call initially on the incoming arguments
4149 * @return method handle which incorporates the specified argument folding logic
4150 * @throws NullPointerException if either argument is null
4151 * @throws IllegalArgumentException if {@code combiner}'s return type
4152 * is non-void and not the same as the first argument type of
4153 * the target, or if the initial {@code N} argument types
4154 * of the target
4155 * (skipping one matching the {@code combiner}'s return type)
4156 * are not identical with the argument types of {@code combiner}
4157 */
4158 public static
4159 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
4160 return foldArguments(target, 0, combiner);
4161 }
4162
4163 /**
4164 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4165 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4166 * before the folded arguments.
4167 * <p>
4168 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4169 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4170 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4171 * 0.
4172 *
4173 * @apiNote Example:
4174 * <blockquote><pre>{@code
4175 import static java.lang.invoke.MethodHandles.*;
4176 import static java.lang.invoke.MethodType.*;
4177 ...
4178 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4179 "println", methodType(void.class, String.class))
4180 .bindTo(System.out);
4181 MethodHandle cat = lookup().findVirtual(String.class,
4182 "concat", methodType(String.class, String.class));
4183 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4184 MethodHandle catTrace = foldArguments(cat, 1, trace);
4185 // also prints "jum":
4186 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4187 * }</pre></blockquote>
4188 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4189 * represents the result type of the {@code target} and resulting adapter.
4190 * {@code V}/{@code v} represent the type and value of the parameter and argument
4191 * of {@code target} that precedes the folding position; {@code V} also is
4192 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4193 * types and values of the {@code N} parameters and arguments at the folding
4194 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4195 * and values of the {@code target} parameters and arguments that precede and
4196 * follow the folded parameters and arguments starting at {@code pos},
4197 * respectively.
4198 * <blockquote><pre>{@code
4199 * // there are N arguments in A...
4200 * T target(Z..., V, A[N]..., B...);
4201 * V combiner(A...);
4202 * T adapter(Z... z, A... a, B... b) {
4203 * V v = combiner(a...);
4204 * return target(z..., v, a..., b...);
4205 * }
4206 * // and if the combiner has a void return:
4207 * T target2(Z..., A[N]..., B...);
4208 * void combiner2(A...);
4209 * T adapter2(Z... z, A... a, B... b) {
4210 * combiner2(a...);
4211 * return target2(z..., a..., b...);
4212 * }
4213 * }</pre></blockquote>
4214 * <p>
4215 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4216 * variable-arity method handle}, even if the original target method handle was.
4217 *
4218 * @param target the method handle to invoke after arguments are combined
4219 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4220 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4221 * @param combiner method handle to call initially on the incoming arguments
4222 * @return method handle which incorporates the specified argument folding logic
4223 * @throws NullPointerException if either argument is null
4224 * @throws IllegalArgumentException if either of the following two conditions holds:
4225 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4226 * {@code pos} of the target signature;
4227 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
4228 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
4229 *
4230 * @see #foldArguments(MethodHandle, MethodHandle)
4231 * @since 9
4232 */
4233 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4234 MethodType targetType = target.type();
4235 MethodType combinerType = combiner.type();
4236 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4237 BoundMethodHandle result = target.rebind();
4238 boolean dropResult = rtype == void.class;
4239 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4240 MethodType newType = targetType;
4241 if (!dropResult) {
4242 newType = newType.dropParameterTypes(pos, pos + 1);
4243 }
4244 result = result.copyWithExtendL(newType, lform, combiner);
4245 return result;
4246 }
4247
4248 /**
4249 * As {@see foldArguments(MethodHandle, int, MethodHandle)}, but with the
4250 * added capability of selecting the arguments from the targets parameters
4251 * to call the combiner with. This allows us to avoid some simple cases of
4252 * permutations and padding the combiner with dropArguments to select the
4253 * right argument, which may ultimately produce fewer intermediaries.
4254 */
4255 static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner, int ... argPositions) {
4256 MethodType targetType = target.type();
4257 MethodType combinerType = combiner.type();
4258 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType, argPositions);
4259 BoundMethodHandle result = target.rebind();
4260 boolean dropResult = rtype == void.class;
4261 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType(), argPositions);
4262 MethodType newType = targetType;
4263 if (!dropResult) {
4264 newType = newType.dropParameterTypes(pos, pos + 1);
4265 }
4266 result = result.copyWithExtendL(newType, lform, combiner);
4267 return result;
4268 }
4269
4270 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
4271 int foldArgs = combinerType.parameterCount();
4272 Class<?> rtype = combinerType.returnType();
4273 int foldVals = rtype == void.class ? 0 : 1;
4274 int afterInsertPos = foldPos + foldVals;
4275 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
4276 if (ok) {
4277 for (int i = 0; i < foldArgs; i++) {
4278 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
4279 ok = false;
4280 break;
4281 }
4282 }
4283 }
4284 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
4285 ok = false;
4286 if (!ok)
4287 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4288 return rtype;
4289 }
4290
4291 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType, int ... argPos) {
4292 int foldArgs = combinerType.parameterCount();
4293 if (argPos.length != foldArgs) {
4294 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
4295 }
4296 Class<?> rtype = combinerType.returnType();
4297 int foldVals = rtype == void.class ? 0 : 1;
4298 boolean ok = true;
4299 for (int i = 0; i < foldArgs; i++) {
4300 int arg = argPos[i];
4301 if (arg < 0 || arg > targetType.parameterCount()) {
4302 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
4303 }
4304 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
4305 throw newIllegalArgumentException("target argument type at position " + arg
4306 + " must match combiner argument type at index " + i + ": " + targetType
4307 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
4308 }
4309 }
4310 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) {
4311 ok = false;
4312 }
4313 if (!ok)
4314 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4315 return rtype;
4316 }
4317
4318 /**
4319 * Makes a method handle which adapts a target method handle,
4320 * by guarding it with a test, a boolean-valued method handle.
4321 * If the guard fails, a fallback handle is called instead.
4322 * All three method handles must have the same corresponding
4323 * argument and return types, except that the return type
4324 * of the test must be boolean, and the test is allowed
4325 * to have fewer arguments than the other two method handles.
4326 * <p>
4327 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4328 * represents the uniform result type of the three involved handles;
4329 * {@code A}/{@code a}, the types and values of the {@code target}
4330 * parameters and arguments that are consumed by the {@code test}; and
4331 * {@code B}/{@code b}, those types and values of the {@code target}
4332 * parameters and arguments that are not consumed by the {@code test}.
4333 * <blockquote><pre>{@code
4334 * boolean test(A...);
4335 * T target(A...,B...);
4336 * T fallback(A...,B...);
4337 * T adapter(A... a,B... b) {
4338 * if (test(a...))
4339 * return target(a..., b...);
4340 * else
4341 * return fallback(a..., b...);
4342 * }
4343 * }</pre></blockquote>
4344 * Note that the test arguments ({@code a...} in the pseudocode) cannot
4345 * be modified by execution of the test, and so are passed unchanged
4346 * from the caller to the target or fallback as appropriate.
4347 * @param test method handle used for test, must return boolean
4348 * @param target method handle to call if test passes
4349 * @param fallback method handle to call if test fails
4350 * @return method handle which incorporates the specified if/then/else logic
4351 * @throws NullPointerException if any argument is null
4352 * @throws IllegalArgumentException if {@code test} does not return boolean,
4353 * or if all three method types do not match (with the return
4354 * type of {@code test} changed to match that of the target).
4355 */
4356 public static
4357 MethodHandle guardWithTest(MethodHandle test,
4358 MethodHandle target,
4359 MethodHandle fallback) {
4360 MethodType gtype = test.type();
4361 MethodType ttype = target.type();
4362 MethodType ftype = fallback.type();
4363 if (!ttype.equals(ftype))
4364 throw misMatchedTypes("target and fallback types", ttype, ftype);
4365 if (gtype.returnType() != boolean.class)
4366 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
4367 List<Class<?>> targs = ttype.parameterList();
4368 test = dropArgumentsToMatch(test, 0, targs, 0, true);
4369 if (test == null) {
4370 throw misMatchedTypes("target and test types", ttype, gtype);
4371 }
4372 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
4373 }
4374
4375 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
4376 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
4377 }
4378
4379 /**
4380 * Makes a method handle which adapts a target method handle,
4381 * by running it inside an exception handler.
4382 * If the target returns normally, the adapter returns that value.
4383 * If an exception matching the specified type is thrown, the fallback
4384 * handle is called instead on the exception, plus the original arguments.
4385 * <p>
4386 * The target and handler must have the same corresponding
4387 * argument and return types, except that handler may omit trailing arguments
4388 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
4389 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
4390 * <p>
4391 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4392 * represents the return type of the {@code target} and {@code handler},
4393 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
4394 * the types and values of arguments to the resulting handle consumed by
4395 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
4396 * resulting handle discarded by {@code handler}.
4397 * <blockquote><pre>{@code
4398 * T target(A..., B...);
4399 * T handler(ExType, A...);
4400 * T adapter(A... a, B... b) {
4401 * try {
4402 * return target(a..., b...);
4403 * } catch (ExType ex) {
4404 * return handler(ex, a...);
4405 * }
4406 * }
4407 * }</pre></blockquote>
4408 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4409 * be modified by execution of the target, and so are passed unchanged
4410 * from the caller to the handler, if the handler is invoked.
4411 * <p>
4412 * The target and handler must return the same type, even if the handler
4413 * always throws. (This might happen, for instance, because the handler
4414 * is simulating a {@code finally} clause).
4415 * To create such a throwing handler, compose the handler creation logic
4416 * with {@link #throwException throwException},
4417 * in order to create a method handle of the correct return type.
4418 * @param target method handle to call
4419 * @param exType the type of exception which the handler will catch
4420 * @param handler method handle to call if a matching exception is thrown
4421 * @return method handle which incorporates the specified try/catch logic
4422 * @throws NullPointerException if any argument is null
4423 * @throws IllegalArgumentException if {@code handler} does not accept
4424 * the given exception type, or if the method handle types do
4425 * not match in their return types and their
4426 * corresponding parameters
4427 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4428 */
4429 public static
4430 MethodHandle catchException(MethodHandle target,
4431 Class<? extends Throwable> exType,
4432 MethodHandle handler) {
4433 MethodType ttype = target.type();
4434 MethodType htype = handler.type();
4435 if (!Throwable.class.isAssignableFrom(exType))
4436 throw new ClassCastException(exType.getName());
4437 if (htype.parameterCount() < 1 ||
4438 !htype.parameterType(0).isAssignableFrom(exType))
4439 throw newIllegalArgumentException("handler does not accept exception type "+exType);
4440 if (htype.returnType() != ttype.returnType())
4441 throw misMatchedTypes("target and handler return types", ttype, htype);
4442 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4443 if (handler == null) {
4444 throw misMatchedTypes("target and handler types", ttype, htype);
4445 }
4446 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4447 }
4448
4449 /**
4450 * Produces a method handle which will throw exceptions of the given {@code exType}.
4451 * The method handle will accept a single argument of {@code exType},
4452 * and immediately throw it as an exception.
4453 * The method type will nominally specify a return of {@code returnType}.
4454 * The return type may be anything convenient: It doesn't matter to the
4455 * method handle's behavior, since it will never return normally.
4456 * @param returnType the return type of the desired method handle
4457 * @param exType the parameter type of the desired method handle
4458 * @return method handle which can throw the given exceptions
4459 * @throws NullPointerException if either argument is null
4460 */
4461 public static
4462 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4463 if (!Throwable.class.isAssignableFrom(exType))
4464 throw new ClassCastException(exType.getName());
4465 return MethodHandleImpl.throwException(methodType(returnType, exType));
4466 }
4467
4468 /**
4469 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4470 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4471 * delivers the loop's result, which is the return value of the resulting handle.
4472 * <p>
4473 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
4474 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4475 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4476 * terms of method handles, each clause will specify up to four independent actions:<ul>
4477 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
4478 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
4479 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
4480 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4481 * </ul>
4482 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
4483 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
4484 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
4485 * <p>
4486 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4487 * this case. See below for a detailed description.
4488 * <p>
4489 * <em>Parameters optional everywhere:</em>
4490 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
4491 * As an exception, the init functions cannot take any {@code v} parameters,
4492 * because those values are not yet computed when the init functions are executed.
4493 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
4494 * In fact, any clause function may take no arguments at all.
4495 * <p>
4496 * <em>Loop parameters:</em>
4497 * A clause function may take all the iteration variable values it is entitled to, in which case
4498 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
4499 * with their types and values notated as {@code (A...)} and {@code (a...)}.
4500 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
4501 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
4502 * init function is automatically a loop parameter {@code a}.)
4503 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
4504 * These loop parameters act as loop-invariant values visible across the whole loop.
4505 * <p>
4506 * <em>Parameters visible everywhere:</em>
4507 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
4508 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
4509 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
4510 * Most clause functions will not need all of this information, but they will be formally connected to it
4511 * as if by {@link #dropArguments}.
4512 * <a id="astar"></a>
4513 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
4514 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
4515 * In that notation, the general form of an init function parameter list
4516 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
4517 * <p>
4518 * <em>Checking clause structure:</em>
4519 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4520 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4521 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
4522 * met by the inputs to the loop combinator.
4523 * <p>
4524 * <em>Effectively identical sequences:</em>
4525 * <a id="effid"></a>
4526 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
4527 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
4528 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
4529 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
4530 * that longest list.
4531 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
4532 * and the same is true if more sequences of the form {@code (V... A*)} are added.
4533 * <p>
4534 * <em>Step 0: Determine clause structure.</em><ol type="a">
4535 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
4536 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4537 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4538 * four. Padding takes place by appending elements to the array.
4539 * <li>Clauses with all {@code null}s are disregarded.
4540 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4541 * </ol>
4542 * <p>
4543 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
4544 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
4545 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
4546 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
4547 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
4548 * iteration variable type.
4549 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
4550 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
4551 * </ol>
4552 * <p>
4553 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
4554 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
4555 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
4556 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
4557 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
4558 * (These types will checked in step 2, along with all the clause function types.)
4559 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
4560 * <li>All of the collected parameter lists must be effectively identical.
4561 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
4562 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
4563 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
4564 * the "internal parameter list".
4565 * </ul>
4566 * <p>
4567 * <em>Step 1C: Determine loop return type.</em><ol type="a">
4568 * <li>Examine fini function return types, disregarding omitted fini functions.
4569 * <li>If there are no fini functions, the loop return type is {@code void}.
4570 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
4571 * type.
4572 * </ol>
4573 * <p>
4574 * <em>Step 1D: Check other types.</em><ol type="a">
4575 * <li>There must be at least one non-omitted pred function.
4576 * <li>Every non-omitted pred function must have a {@code boolean} return type.
4577 * </ol>
4578 * <p>
4579 * <em>Step 2: Determine parameter lists.</em><ol type="a">
4580 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
4581 * <li>The parameter list for init functions will be adjusted to the external parameter list.
4582 * (Note that their parameter lists are already effectively identical to this list.)
4583 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
4584 * effectively identical to the internal parameter list {@code (V... A...)}.
4585 * </ol>
4586 * <p>
4587 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
4588 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
4589 * type.
4590 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
4591 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
4592 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
4593 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
4594 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
4595 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
4596 * loop return type.
4597 * </ol>
4598 * <p>
4599 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
4600 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
4601 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
4602 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
4603 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
4604 * pad out the end of the list.
4605 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch dropping unused trailing arguments}.
4606 * </ol>
4607 * <p>
4608 * <em>Final observations.</em><ol type="a">
4609 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
4610 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
4611 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
4612 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
4613 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
4614 * <li>Each pair of init and step functions agrees in their return type {@code V}.
4615 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
4616 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
4617 * </ol>
4618 * <p>
4619 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
4620 * <ul>
4621 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
4622 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
4623 * (Only one {@code Pn} has to be non-{@code null}.)
4624 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
4625 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
4626 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
4627 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
4628 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
4629 * the resulting loop handle's parameter types {@code (A...)}.
4630 * </ul>
4631 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
4632 * which is natural if most of the loop computation happens in the steps. For some loops,
4633 * the burden of computation might be heaviest in the pred functions, and so the pred functions
4634 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
4635 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
4636 * where the init functions will need the extra parameters. For such reasons, the rules for
4637 * determining these parameters are as symmetric as possible, across all clause parts.
4638 * In general, the loop parameters function as common invariant values across the whole
4639 * loop, while the iteration variables function as common variant values, or (if there is
4640 * no step function) as internal loop invariant temporaries.
4641 * <p>
4642 * <em>Loop execution.</em><ol type="a">
4643 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
4644 * every clause function. These locals are loop invariant.
4645 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
4646 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
4647 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
4648 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
4649 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
4650 * (in argument order).
4651 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
4652 * returns {@code false}.
4653 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
4654 * sequence {@code (v...)} of loop variables.
4655 * The updated value is immediately visible to all subsequent function calls.
4656 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
4657 * (of type {@code R}) is returned from the loop as a whole.
4658 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
4659 * except by throwing an exception.
4660 * </ol>
4661 * <p>
4662 * <em>Usage tips.</em>
4663 * <ul>
4664 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
4665 * sometimes a step function only needs to observe the current value of its own variable.
4666 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
4667 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
4668 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
4669 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
4670 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
4671 * <li>If some of the clause functions are virtual methods on an instance, the instance
4672 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
4673 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
4674 * will be the first iteration variable value, and it will be easy to use virtual
4675 * methods as clause parts, since all of them will take a leading instance reference matching that value.
4676 * </ul>
4677 * <p>
4678 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
4679 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
4680 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
4681 * <blockquote><pre>{@code
4682 * V... init...(A...);
4683 * boolean pred...(V..., A...);
4684 * V... step...(V..., A...);
4685 * R fini...(V..., A...);
4686 * R loop(A... a) {
4687 * V... v... = init...(a...);
4688 * for (;;) {
4689 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
4690 * v = s(v..., a...);
4691 * if (!p(v..., a...)) {
4692 * return f(v..., a...);
4693 * }
4694 * }
4695 * }
4696 * }
4697 * }</pre></blockquote>
4698 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
4699 * to their full length, even though individual clause functions may neglect to take them all.
4700 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch}.
4701 *
4702 * @apiNote Example:
4703 * <blockquote><pre>{@code
4704 * // iterative implementation of the factorial function as a loop handle
4705 * static int one(int k) { return 1; }
4706 * static int inc(int i, int acc, int k) { return i + 1; }
4707 * static int mult(int i, int acc, int k) { return i * acc; }
4708 * static boolean pred(int i, int acc, int k) { return i < k; }
4709 * static int fin(int i, int acc, int k) { return acc; }
4710 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4711 * // null initializer for counter, should initialize to 0
4712 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4713 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4714 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4715 * assertEquals(120, loop.invoke(5));
4716 * }</pre></blockquote>
4717 * The same example, dropping arguments and using combinators:
4718 * <blockquote><pre>{@code
4719 * // simplified implementation of the factorial function as a loop handle
4720 * static int inc(int i) { return i + 1; } // drop acc, k
4721 * static int mult(int i, int acc) { return i * acc; } //drop k
4722 * static boolean cmp(int i, int k) { return i < k; }
4723 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
4724 * // null initializer for counter, should initialize to 0
4725 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4726 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
4727 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
4728 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4729 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4730 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4731 * assertEquals(720, loop.invoke(6));
4732 * }</pre></blockquote>
4733 * A similar example, using a helper object to hold a loop parameter:
4734 * <blockquote><pre>{@code
4735 * // instance-based implementation of the factorial function as a loop handle
4736 * static class FacLoop {
4737 * final int k;
4738 * FacLoop(int k) { this.k = k; }
4739 * int inc(int i) { return i + 1; }
4740 * int mult(int i, int acc) { return i * acc; }
4741 * boolean pred(int i) { return i < k; }
4742 * int fin(int i, int acc) { return acc; }
4743 * }
4744 * // assume MH_FacLoop is a handle to the constructor
4745 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4746 * // null initializer for counter, should initialize to 0
4747 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4748 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
4749 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4750 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4751 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
4752 * assertEquals(5040, loop.invoke(7));
4753 * }</pre></blockquote>
4754 *
4755 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
4756 *
4757 * @return a method handle embodying the looping behavior as defined by the arguments.
4758 *
4759 * @throws IllegalArgumentException in case any of the constraints described above is violated.
4760 *
4761 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
4762 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4763 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
4764 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
4765 * @since 9
4766 */
4767 public static MethodHandle loop(MethodHandle[]... clauses) {
4768 // Step 0: determine clause structure.
4769 loopChecks0(clauses);
4770
4771 List<MethodHandle> init = new ArrayList<>();
4772 List<MethodHandle> step = new ArrayList<>();
4773 List<MethodHandle> pred = new ArrayList<>();
4774 List<MethodHandle> fini = new ArrayList<>();
4775
4776 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
4777 init.add(clause[0]); // all clauses have at least length 1
4778 step.add(clause.length <= 1 ? null : clause[1]);
4779 pred.add(clause.length <= 2 ? null : clause[2]);
4780 fini.add(clause.length <= 3 ? null : clause[3]);
4781 });
4782
4783 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
4784 final int nclauses = init.size();
4785
4786 // Step 1A: determine iteration variables (V...).
4787 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
4788 for (int i = 0; i < nclauses; ++i) {
4789 MethodHandle in = init.get(i);
4790 MethodHandle st = step.get(i);
4791 if (in == null && st == null) {
4792 iterationVariableTypes.add(void.class);
4793 } else if (in != null && st != null) {
4794 loopChecks1a(i, in, st);
4795 iterationVariableTypes.add(in.type().returnType());
4796 } else {
4797 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
4798 }
4799 }
4800 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
4801 collect(Collectors.toList());
4802
4803 // Step 1B: determine loop parameters (A...).
4804 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
4805 loopChecks1b(init, commonSuffix);
4806
4807 // Step 1C: determine loop return type.
4808 // Step 1D: check other types.
4809 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
4810 map(MethodType::returnType).findFirst().orElse(void.class);
4811 loopChecks1cd(pred, fini, loopReturnType);
4812
4813 // Step 2: determine parameter lists.
4814 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
4815 commonParameterSequence.addAll(commonSuffix);
4816 loopChecks2(step, pred, fini, commonParameterSequence);
4817
4818 // Step 3: fill in omitted functions.
4819 for (int i = 0; i < nclauses; ++i) {
4820 Class<?> t = iterationVariableTypes.get(i);
4821 if (init.get(i) == null) {
4822 init.set(i, empty(methodType(t, commonSuffix)));
4823 }
4824 if (step.get(i) == null) {
4825 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
4826 }
4827 if (pred.get(i) == null) {
4828 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
4829 }
4830 if (fini.get(i) == null) {
4831 fini.set(i, empty(methodType(t, commonParameterSequence)));
4832 }
4833 }
4834
4835 // Step 4: fill in missing parameter types.
4836 // Also convert all handles to fixed-arity handles.
4837 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
4838 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
4839 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
4840 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
4841
4842 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
4843 allMatch(pl -> pl.equals(commonSuffix));
4844 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
4845 allMatch(pl -> pl.equals(commonParameterSequence));
4846
4847 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
4848 }
4849
4850 private static void loopChecks0(MethodHandle[][] clauses) {
4851 if (clauses == null || clauses.length == 0) {
4852 throw newIllegalArgumentException("null or no clauses passed");
4853 }
4854 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
4855 throw newIllegalArgumentException("null clauses are not allowed");
4856 }
4857 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
4858 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
4859 }
4860 }
4861
4862 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
4863 if (in.type().returnType() != st.type().returnType()) {
4864 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
4865 st.type().returnType());
4866 }
4867 }
4868
4869 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
4870 final List<Class<?>> empty = List.of();
4871 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
4872 // take only those that can contribute to a common suffix because they are longer than the prefix
4873 map(MethodHandle::type).
4874 filter(t -> t.parameterCount() > skipSize).
4875 map(MethodType::parameterList).
4876 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4877 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
4878 }
4879
4880 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
4881 final List<Class<?>> empty = List.of();
4882 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4883 }
4884
4885 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
4886 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
4887 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
4888 return longestParameterList(Arrays.asList(longest1, longest2));
4889 }
4890
4891 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
4892 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
4893 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
4894 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
4895 " (common suffix: " + commonSuffix + ")");
4896 }
4897 }
4898
4899 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
4900 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4901 anyMatch(t -> t != loopReturnType)) {
4902 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
4903 loopReturnType + ")");
4904 }
4905
4906 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
4907 throw newIllegalArgumentException("no predicate found", pred);
4908 }
4909 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4910 anyMatch(t -> t != boolean.class)) {
4911 throw newIllegalArgumentException("predicates must have boolean return type", pred);
4912 }
4913 }
4914
4915 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
4916 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
4917 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
4918 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
4919 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
4920 }
4921 }
4922
4923 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
4924 return hs.stream().map(h -> {
4925 int pc = h.type().parameterCount();
4926 int tpsize = targetParams.size();
4927 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
4928 }).collect(Collectors.toList());
4929 }
4930
4931 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
4932 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
4933 }
4934
4935 /**
4936 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
4937 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
4938 * <p>
4939 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
4940 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
4941 * evaluates to {@code true}).
4942 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
4943 * <p>
4944 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
4945 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
4946 * and updated with the value returned from its invocation. The result of loop execution will be
4947 * the final value of the additional loop-local variable (if present).
4948 * <p>
4949 * The following rules hold for these argument handles:<ul>
4950 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
4951 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
4952 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
4953 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
4954 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
4955 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
4956 * It will constrain the parameter lists of the other loop parts.
4957 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
4958 * list {@code (A...)} is called the <em>external parameter list</em>.
4959 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
4960 * additional state variable of the loop.
4961 * The body must both accept and return a value of this type {@code V}.
4962 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
4963 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
4964 * <a href="MethodHandles.html#effid">effectively identical</a>
4965 * to the external parameter list {@code (A...)}.
4966 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
4967 * {@linkplain #empty default value}.
4968 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
4969 * Its parameter list (either empty or of the form {@code (V A*)}) must be
4970 * effectively identical to the internal parameter list.
4971 * </ul>
4972 * <p>
4973 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
4974 * <li>The loop handle's result type is the result type {@code V} of the body.
4975 * <li>The loop handle's parameter types are the types {@code (A...)},
4976 * from the external parameter list.
4977 * </ul>
4978 * <p>
4979 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4980 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4981 * passed to the loop.
4982 * <blockquote><pre>{@code
4983 * V init(A...);
4984 * boolean pred(V, A...);
4985 * V body(V, A...);
4986 * V whileLoop(A... a...) {
4987 * V v = init(a...);
4988 * while (pred(v, a...)) {
4989 * v = body(v, a...);
4990 * }
4991 * return v;
4992 * }
4993 * }</pre></blockquote>
4994 *
4995 * @apiNote Example:
4996 * <blockquote><pre>{@code
4997 * // implement the zip function for lists as a loop handle
4998 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
4999 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
5000 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
5001 * zip.add(a.next());
5002 * zip.add(b.next());
5003 * return zip;
5004 * }
5005 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
5006 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
5007 * List<String> a = Arrays.asList("a", "b", "c", "d");
5008 * List<String> b = Arrays.asList("e", "f", "g", "h");
5009 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
5010 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
5011 * }</pre></blockquote>
5012 *
5013 *
5014 * @apiNote The implementation of this method can be expressed as follows:
5015 * <blockquote><pre>{@code
5016 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5017 * MethodHandle fini = (body.type().returnType() == void.class
5018 * ? null : identity(body.type().returnType()));
5019 * MethodHandle[]
5020 * checkExit = { null, null, pred, fini },
5021 * varBody = { init, body };
5022 * return loop(checkExit, varBody);
5023 * }
5024 * }</pre></blockquote>
5025 *
5026 * @param init optional initializer, providing the initial value of the loop variable.
5027 * May be {@code null}, implying a default initial value. See above for other constraints.
5028 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5029 * above for other constraints.
5030 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5031 * See above for other constraints.
5032 *
5033 * @return a method handle implementing the {@code while} loop as described by the arguments.
5034 * @throws IllegalArgumentException if the rules for the arguments are violated.
5035 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5036 *
5037 * @see #loop(MethodHandle[][])
5038 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5039 * @since 9
5040 */
5041 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5042 whileLoopChecks(init, pred, body);
5043 MethodHandle fini = identityOrVoid(body.type().returnType());
5044 MethodHandle[] checkExit = { null, null, pred, fini };
5045 MethodHandle[] varBody = { init, body };
5046 return loop(checkExit, varBody);
5047 }
5048
5049 /**
5050 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
5051 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5052 * <p>
5053 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5054 * method will, in each iteration, first execute its body and then evaluate the predicate.
5055 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
5056 * <p>
5057 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5058 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5059 * and updated with the value returned from its invocation. The result of loop execution will be
5060 * the final value of the additional loop-local variable (if present).
5061 * <p>
5062 * The following rules hold for these argument handles:<ul>
5063 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5064 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5065 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5066 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5067 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5068 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5069 * It will constrain the parameter lists of the other loop parts.
5070 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5071 * list {@code (A...)} is called the <em>external parameter list</em>.
5072 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5073 * additional state variable of the loop.
5074 * The body must both accept and return a value of this type {@code V}.
5075 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5076 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5077 * <a href="MethodHandles.html#effid">effectively identical</a>
5078 * to the external parameter list {@code (A...)}.
5079 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5080 * {@linkplain #empty default value}.
5081 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5082 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5083 * effectively identical to the internal parameter list.
5084 * </ul>
5085 * <p>
5086 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5087 * <li>The loop handle's result type is the result type {@code V} of the body.
5088 * <li>The loop handle's parameter types are the types {@code (A...)},
5089 * from the external parameter list.
5090 * </ul>
5091 * <p>
5092 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5093 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5094 * passed to the loop.
5095 * <blockquote><pre>{@code
5096 * V init(A...);
5097 * boolean pred(V, A...);
5098 * V body(V, A...);
5099 * V doWhileLoop(A... a...) {
5100 * V v = init(a...);
5101 * do {
5102 * v = body(v, a...);
5103 * } while (pred(v, a...));
5104 * return v;
5105 * }
5106 * }</pre></blockquote>
5107 *
5108 * @apiNote Example:
5109 * <blockquote><pre>{@code
5110 * // int i = 0; while (i < limit) { ++i; } return i; => limit
5111 * static int zero(int limit) { return 0; }
5112 * static int step(int i, int limit) { return i + 1; }
5113 * static boolean pred(int i, int limit) { return i < limit; }
5114 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
5115 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
5116 * assertEquals(23, loop.invoke(23));
5117 * }</pre></blockquote>
5118 *
5119 *
5120 * @apiNote The implementation of this method can be expressed as follows:
5121 * <blockquote><pre>{@code
5122 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5123 * MethodHandle fini = (body.type().returnType() == void.class
5124 * ? null : identity(body.type().returnType()));
5125 * MethodHandle[] clause = { init, body, pred, fini };
5126 * return loop(clause);
5127 * }
5128 * }</pre></blockquote>
5129 *
5130 * @param init optional initializer, providing the initial value of the loop variable.
5131 * May be {@code null}, implying a default initial value. See above for other constraints.
5132 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5133 * See above for other constraints.
5134 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5135 * above for other constraints.
5136 *
5137 * @return a method handle implementing the {@code while} loop as described by the arguments.
5138 * @throws IllegalArgumentException if the rules for the arguments are violated.
5139 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5140 *
5141 * @see #loop(MethodHandle[][])
5142 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
5143 * @since 9
5144 */
5145 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5146 whileLoopChecks(init, pred, body);
5147 MethodHandle fini = identityOrVoid(body.type().returnType());
5148 MethodHandle[] clause = {init, body, pred, fini };
5149 return loop(clause);
5150 }
5151
5152 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
5153 Objects.requireNonNull(pred);
5154 Objects.requireNonNull(body);
5155 MethodType bodyType = body.type();
5156 Class<?> returnType = bodyType.returnType();
5157 List<Class<?>> innerList = bodyType.parameterList();
5158 List<Class<?>> outerList = innerList;
5159 if (returnType == void.class) {
5160 // OK
5161 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
5162 // leading V argument missing => error
5163 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5164 throw misMatchedTypes("body function", bodyType, expected);
5165 } else {
5166 outerList = innerList.subList(1, innerList.size());
5167 }
5168 MethodType predType = pred.type();
5169 if (predType.returnType() != boolean.class ||
5170 !predType.effectivelyIdenticalParameters(0, innerList)) {
5171 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
5172 }
5173 if (init != null) {
5174 MethodType initType = init.type();
5175 if (initType.returnType() != returnType ||
5176 !initType.effectivelyIdenticalParameters(0, outerList)) {
5177 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5178 }
5179 }
5180 }
5181
5182 /**
5183 * Constructs a loop that runs a given number of iterations.
5184 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5185 * <p>
5186 * The number of iterations is determined by the {@code iterations} handle evaluation result.
5187 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
5188 * It will be initialized to 0 and incremented by 1 in each iteration.
5189 * <p>
5190 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5191 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5192 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5193 * <p>
5194 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5195 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5196 * iteration variable.
5197 * The result of the loop handle execution will be the final {@code V} value of that variable
5198 * (or {@code void} if there is no {@code V} variable).
5199 * <p>
5200 * The following rules hold for the argument handles:<ul>
5201 * <li>The {@code iterations} handle must not be {@code null}, and must return
5202 * the type {@code int}, referred to here as {@code I} in parameter type lists.
5203 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5204 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5205 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5206 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5207 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5208 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5209 * of types called the <em>internal parameter list</em>.
5210 * It will constrain the parameter lists of the other loop parts.
5211 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5212 * with no additional {@code A} types, then the internal parameter list is extended by
5213 * the argument types {@code A...} of the {@code iterations} handle.
5214 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5215 * list {@code (A...)} is called the <em>external parameter list</em>.
5216 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5217 * additional state variable of the loop.
5218 * The body must both accept a leading parameter and return a value of this type {@code V}.
5219 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5220 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5221 * <a href="MethodHandles.html#effid">effectively identical</a>
5222 * to the external parameter list {@code (A...)}.
5223 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5224 * {@linkplain #empty default value}.
5225 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
5226 * effectively identical to the external parameter list {@code (A...)}.
5227 * </ul>
5228 * <p>
5229 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5230 * <li>The loop handle's result type is the result type {@code V} of the body.
5231 * <li>The loop handle's parameter types are the types {@code (A...)},
5232 * from the external parameter list.
5233 * </ul>
5234 * <p>
5235 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5236 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5237 * arguments passed to the loop.
5238 * <blockquote><pre>{@code
5239 * int iterations(A...);
5240 * V init(A...);
5241 * V body(V, int, A...);
5242 * V countedLoop(A... a...) {
5243 * int end = iterations(a...);
5244 * V v = init(a...);
5245 * for (int i = 0; i < end; ++i) {
5246 * v = body(v, i, a...);
5247 * }
5248 * return v;
5249 * }
5250 * }</pre></blockquote>
5251 *
5252 * @apiNote Example with a fully conformant body method:
5253 * <blockquote><pre>{@code
5254 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5255 * // => a variation on a well known theme
5256 * static String step(String v, int counter, String init) { return "na " + v; }
5257 * // assume MH_step is a handle to the method above
5258 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
5259 * MethodHandle start = MethodHandles.identity(String.class);
5260 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
5261 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
5262 * }</pre></blockquote>
5263 *
5264 * @apiNote Example with the simplest possible body method type,
5265 * and passing the number of iterations to the loop invocation:
5266 * <blockquote><pre>{@code
5267 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5268 * // => a variation on a well known theme
5269 * static String step(String v, int counter ) { return "na " + v; }
5270 * // assume MH_step is a handle to the method above
5271 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
5272 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
5273 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
5274 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
5275 * }</pre></blockquote>
5276 *
5277 * @apiNote Example that treats the number of iterations, string to append to, and string to append
5278 * as loop parameters:
5279 * <blockquote><pre>{@code
5280 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5281 * // => a variation on a well known theme
5282 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
5283 * // assume MH_step is a handle to the method above
5284 * MethodHandle count = MethodHandles.identity(int.class);
5285 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
5286 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
5287 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
5288 * }</pre></blockquote>
5289 *
5290 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
5291 * to enforce a loop type:
5292 * <blockquote><pre>{@code
5293 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5294 * // => a variation on a well known theme
5295 * static String step(String v, int counter, String pre) { return pre + " " + v; }
5296 * // assume MH_step is a handle to the method above
5297 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
5298 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
5299 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
5300 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
5301 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
5302 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
5303 * }</pre></blockquote>
5304 *
5305 * @apiNote The implementation of this method can be expressed as follows:
5306 * <blockquote><pre>{@code
5307 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5308 * return countedLoop(empty(iterations.type()), iterations, init, body);
5309 * }
5310 * }</pre></blockquote>
5311 *
5312 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
5313 * result type must be {@code int}. See above for other constraints.
5314 * @param init optional initializer, providing the initial value of the loop variable.
5315 * May be {@code null}, implying a default initial value. See above for other constraints.
5316 * @param body body of the loop, which may not be {@code null}.
5317 * It controls the loop parameters and result type in the standard case (see above for details).
5318 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5319 * and may accept any number of additional types.
5320 * See above for other constraints.
5321 *
5322 * @return a method handle representing the loop.
5323 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
5324 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5325 *
5326 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
5327 * @since 9
5328 */
5329 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5330 return countedLoop(empty(iterations.type()), iterations, init, body);
5331 }
5332
5333 /**
5334 * Constructs a loop that counts over a range of numbers.
5335 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5336 * <p>
5337 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
5338 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
5339 * values of the loop counter.
5340 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
5341 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
5342 * <p>
5343 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5344 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5345 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5346 * <p>
5347 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5348 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5349 * iteration variable.
5350 * The result of the loop handle execution will be the final {@code V} value of that variable
5351 * (or {@code void} if there is no {@code V} variable).
5352 * <p>
5353 * The following rules hold for the argument handles:<ul>
5354 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
5355 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
5356 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5357 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5358 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5359 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5360 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5361 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5362 * of types called the <em>internal parameter list</em>.
5363 * It will constrain the parameter lists of the other loop parts.
5364 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5365 * with no additional {@code A} types, then the internal parameter list is extended by
5366 * the argument types {@code A...} of the {@code end} handle.
5367 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5368 * list {@code (A...)} is called the <em>external parameter list</em>.
5369 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5370 * additional state variable of the loop.
5371 * The body must both accept a leading parameter and return a value of this type {@code V}.
5372 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5373 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5374 * <a href="MethodHandles.html#effid">effectively identical</a>
5375 * to the external parameter list {@code (A...)}.
5376 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5377 * {@linkplain #empty default value}.
5378 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
5379 * effectively identical to the external parameter list {@code (A...)}.
5380 * <li>Likewise, the parameter list of {@code end} must be effectively identical
5381 * to the external parameter list.
5382 * </ul>
5383 * <p>
5384 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5385 * <li>The loop handle's result type is the result type {@code V} of the body.
5386 * <li>The loop handle's parameter types are the types {@code (A...)},
5387 * from the external parameter list.
5388 * </ul>
5389 * <p>
5390 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5391 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5392 * arguments passed to the loop.
5393 * <blockquote><pre>{@code
5394 * int start(A...);
5395 * int end(A...);
5396 * V init(A...);
5397 * V body(V, int, A...);
5398 * V countedLoop(A... a...) {
5399 * int e = end(a...);
5400 * int s = start(a...);
5401 * V v = init(a...);
5402 * for (int i = s; i < e; ++i) {
5403 * v = body(v, i, a...);
5404 * }
5405 * return v;
5406 * }
5407 * }</pre></blockquote>
5408 *
5409 * @apiNote The implementation of this method can be expressed as follows:
5410 * <blockquote><pre>{@code
5411 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5412 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
5413 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
5414 * // the following semantics:
5415 * // MH_increment: (int limit, int counter) -> counter + 1
5416 * // MH_predicate: (int limit, int counter) -> counter < limit
5417 * Class<?> counterType = start.type().returnType(); // int
5418 * Class<?> returnType = body.type().returnType();
5419 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
5420 * if (returnType != void.class) { // ignore the V variable
5421 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5422 * pred = dropArguments(pred, 1, returnType); // ditto
5423 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
5424 * }
5425 * body = dropArguments(body, 0, counterType); // ignore the limit variable
5426 * MethodHandle[]
5427 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5428 * bodyClause = { init, body }, // v = init(); v = body(v, i)
5429 * indexVar = { start, incr }; // i = start(); i = i + 1
5430 * return loop(loopLimit, bodyClause, indexVar);
5431 * }
5432 * }</pre></blockquote>
5433 *
5434 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
5435 * See above for other constraints.
5436 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
5437 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
5438 * @param init optional initializer, providing the initial value of the loop variable.
5439 * May be {@code null}, implying a default initial value. See above for other constraints.
5440 * @param body body of the loop, which may not be {@code null}.
5441 * It controls the loop parameters and result type in the standard case (see above for details).
5442 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5443 * and may accept any number of additional types.
5444 * See above for other constraints.
5445 *
5446 * @return a method handle representing the loop.
5447 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
5448 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5449 *
5450 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
5451 * @since 9
5452 */
5453 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5454 countedLoopChecks(start, end, init, body);
5455 Class<?> counterType = start.type().returnType(); // int, but who's counting?
5456 Class<?> limitType = end.type().returnType(); // yes, int again
5457 Class<?> returnType = body.type().returnType();
5458 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
5459 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
5460 MethodHandle retv = null;
5461 if (returnType != void.class) {
5462 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5463 pred = dropArguments(pred, 1, returnType); // ditto
5464 retv = dropArguments(identity(returnType), 0, counterType);
5465 }
5466 body = dropArguments(body, 0, counterType); // ignore the limit variable
5467 MethodHandle[]
5468 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5469 bodyClause = { init, body }, // v = init(); v = body(v, i)
5470 indexVar = { start, incr }; // i = start(); i = i + 1
5471 return loop(loopLimit, bodyClause, indexVar);
5472 }
5473
5474 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5475 Objects.requireNonNull(start);
5476 Objects.requireNonNull(end);
5477 Objects.requireNonNull(body);
5478 Class<?> counterType = start.type().returnType();
5479 if (counterType != int.class) {
5480 MethodType expected = start.type().changeReturnType(int.class);
5481 throw misMatchedTypes("start function", start.type(), expected);
5482 } else if (end.type().returnType() != counterType) {
5483 MethodType expected = end.type().changeReturnType(counterType);
5484 throw misMatchedTypes("end function", end.type(), expected);
5485 }
5486 MethodType bodyType = body.type();
5487 Class<?> returnType = bodyType.returnType();
5488 List<Class<?>> innerList = bodyType.parameterList();
5489 // strip leading V value if present
5490 int vsize = (returnType == void.class ? 0 : 1);
5491 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
5492 // argument list has no "V" => error
5493 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5494 throw misMatchedTypes("body function", bodyType, expected);
5495 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
5496 // missing I type => error
5497 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
5498 throw misMatchedTypes("body function", bodyType, expected);
5499 }
5500 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
5501 if (outerList.isEmpty()) {
5502 // special case; take lists from end handle
5503 outerList = end.type().parameterList();
5504 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
5505 }
5506 MethodType expected = methodType(counterType, outerList);
5507 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
5508 throw misMatchedTypes("start parameter types", start.type(), expected);
5509 }
5510 if (end.type() != start.type() &&
5511 !end.type().effectivelyIdenticalParameters(0, outerList)) {
5512 throw misMatchedTypes("end parameter types", end.type(), expected);
5513 }
5514 if (init != null) {
5515 MethodType initType = init.type();
5516 if (initType.returnType() != returnType ||
5517 !initType.effectivelyIdenticalParameters(0, outerList)) {
5518 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5519 }
5520 }
5521 }
5522
5523 /**
5524 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
5525 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5526 * <p>
5527 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
5528 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
5529 * <p>
5530 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5531 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5532 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5533 * <p>
5534 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5535 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5536 * iteration variable.
5537 * The result of the loop handle execution will be the final {@code V} value of that variable
5538 * (or {@code void} if there is no {@code V} variable).
5539 * <p>
5540 * The following rules hold for the argument handles:<ul>
5541 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5542 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
5543 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5544 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
5545 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
5546 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
5547 * of types called the <em>internal parameter list</em>.
5548 * It will constrain the parameter lists of the other loop parts.
5549 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
5550 * with no additional {@code A} types, then the internal parameter list is extended by
5551 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
5552 * single type {@code Iterable} is added and constitutes the {@code A...} list.
5553 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
5554 * list {@code (A...)} is called the <em>external parameter list</em>.
5555 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5556 * additional state variable of the loop.
5557 * The body must both accept a leading parameter and return a value of this type {@code V}.
5558 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5559 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5560 * <a href="MethodHandles.html#effid">effectively identical</a>
5561 * to the external parameter list {@code (A...)}.
5562 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5563 * {@linkplain #empty default value}.
5564 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
5565 * type {@code java.util.Iterator} or a subtype thereof.
5566 * The iterator it produces when the loop is executed will be assumed
5567 * to yield values which can be converted to type {@code T}.
5568 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
5569 * effectively identical to the external parameter list {@code (A...)}.
5570 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
5571 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
5572 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
5573 * handle parameter is adjusted to accept the leading {@code A} type, as if by
5574 * the {@link MethodHandle#asType asType} conversion method.
5575 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
5576 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
5577 * </ul>
5578 * <p>
5579 * The type {@code T} may be either a primitive or reference.
5580 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
5581 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
5582 * as if by the {@link MethodHandle#asType asType} conversion method.
5583 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
5584 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
5585 * <p>
5586 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5587 * <li>The loop handle's result type is the result type {@code V} of the body.
5588 * <li>The loop handle's parameter types are the types {@code (A...)},
5589 * from the external parameter list.
5590 * </ul>
5591 * <p>
5592 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5593 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
5594 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
5595 * <blockquote><pre>{@code
5596 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
5597 * V init(A...);
5598 * V body(V,T,A...);
5599 * V iteratedLoop(A... a...) {
5600 * Iterator<T> it = iterator(a...);
5601 * V v = init(a...);
5602 * while (it.hasNext()) {
5603 * T t = it.next();
5604 * v = body(v, t, a...);
5605 * }
5606 * return v;
5607 * }
5608 * }</pre></blockquote>
5609 *
5610 * @apiNote Example:
5611 * <blockquote><pre>{@code
5612 * // get an iterator from a list
5613 * static List<String> reverseStep(List<String> r, String e) {
5614 * r.add(0, e);
5615 * return r;
5616 * }
5617 * static List<String> newArrayList() { return new ArrayList<>(); }
5618 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
5619 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
5620 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
5621 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
5622 * assertEquals(reversedList, (List<String>) loop.invoke(list));
5623 * }</pre></blockquote>
5624 *
5625 * @apiNote The implementation of this method can be expressed approximately as follows:
5626 * <blockquote><pre>{@code
5627 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5628 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
5629 * Class<?> returnType = body.type().returnType();
5630 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5631 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
5632 * MethodHandle retv = null, step = body, startIter = iterator;
5633 * if (returnType != void.class) {
5634 * // the simple thing first: in (I V A...), drop the I to get V
5635 * retv = dropArguments(identity(returnType), 0, Iterator.class);
5636 * // body type signature (V T A...), internal loop types (I V A...)
5637 * step = swapArguments(body, 0, 1); // swap V <-> T
5638 * }
5639 * if (startIter == null) startIter = MH_getIter;
5640 * MethodHandle[]
5641 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
5642 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
5643 * return loop(iterVar, bodyClause);
5644 * }
5645 * }</pre></blockquote>
5646 *
5647 * @param iterator an optional handle to return the iterator to start the loop.
5648 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
5649 * See above for other constraints.
5650 * @param init optional initializer, providing the initial value of the loop variable.
5651 * May be {@code null}, implying a default initial value. See above for other constraints.
5652 * @param body body of the loop, which may not be {@code null}.
5653 * It controls the loop parameters and result type in the standard case (see above for details).
5654 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
5655 * and may accept any number of additional types.
5656 * See above for other constraints.
5657 *
5658 * @return a method handle embodying the iteration loop functionality.
5659 * @throws NullPointerException if the {@code body} handle is {@code null}.
5660 * @throws IllegalArgumentException if any argument violates the above requirements.
5661 *
5662 * @since 9
5663 */
5664 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5665 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
5666 Class<?> returnType = body.type().returnType();
5667 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
5668 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
5669 MethodHandle startIter;
5670 MethodHandle nextVal;
5671 {
5672 MethodType iteratorType;
5673 if (iterator == null) {
5674 // derive argument type from body, if available, else use Iterable
5675 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
5676 iteratorType = startIter.type().changeParameterType(0, iterableType);
5677 } else {
5678 // force return type to the internal iterator class
5679 iteratorType = iterator.type().changeReturnType(Iterator.class);
5680 startIter = iterator;
5681 }
5682 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5683 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
5684
5685 // perform the asType transforms under an exception transformer, as per spec.:
5686 try {
5687 startIter = startIter.asType(iteratorType);
5688 nextVal = nextRaw.asType(nextValType);
5689 } catch (WrongMethodTypeException ex) {
5690 throw new IllegalArgumentException(ex);
5691 }
5692 }
5693
5694 MethodHandle retv = null, step = body;
5695 if (returnType != void.class) {
5696 // the simple thing first: in (I V A...), drop the I to get V
5697 retv = dropArguments(identity(returnType), 0, Iterator.class);
5698 // body type signature (V T A...), internal loop types (I V A...)
5699 step = swapArguments(body, 0, 1); // swap V <-> T
5700 }
5701
5702 MethodHandle[]
5703 iterVar = { startIter, null, hasNext, retv },
5704 bodyClause = { init, filterArgument(step, 0, nextVal) };
5705 return loop(iterVar, bodyClause);
5706 }
5707
5708 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5709 Objects.requireNonNull(body);
5710 MethodType bodyType = body.type();
5711 Class<?> returnType = bodyType.returnType();
5712 List<Class<?>> internalParamList = bodyType.parameterList();
5713 // strip leading V value if present
5714 int vsize = (returnType == void.class ? 0 : 1);
5715 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
5716 // argument list has no "V" => error
5717 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5718 throw misMatchedTypes("body function", bodyType, expected);
5719 } else if (internalParamList.size() <= vsize) {
5720 // missing T type => error
5721 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
5722 throw misMatchedTypes("body function", bodyType, expected);
5723 }
5724 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
5725 Class<?> iterableType = null;
5726 if (iterator != null) {
5727 // special case; if the body handle only declares V and T then
5728 // the external parameter list is obtained from iterator handle
5729 if (externalParamList.isEmpty()) {
5730 externalParamList = iterator.type().parameterList();
5731 }
5732 MethodType itype = iterator.type();
5733 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
5734 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
5735 }
5736 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
5737 MethodType expected = methodType(itype.returnType(), externalParamList);
5738 throw misMatchedTypes("iterator parameters", itype, expected);
5739 }
5740 } else {
5741 if (externalParamList.isEmpty()) {
5742 // special case; if the iterator handle is null and the body handle
5743 // only declares V and T then the external parameter list consists
5744 // of Iterable
5745 externalParamList = Arrays.asList(Iterable.class);
5746 iterableType = Iterable.class;
5747 } else {
5748 // special case; if the iterator handle is null and the external
5749 // parameter list is not empty then the first parameter must be
5750 // assignable to Iterable
5751 iterableType = externalParamList.get(0);
5752 if (!Iterable.class.isAssignableFrom(iterableType)) {
5753 throw newIllegalArgumentException(
5754 "inferred first loop argument must inherit from Iterable: " + iterableType);
5755 }
5756 }
5757 }
5758 if (init != null) {
5759 MethodType initType = init.type();
5760 if (initType.returnType() != returnType ||
5761 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
5762 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
5763 }
5764 }
5765 return iterableType; // help the caller a bit
5766 }
5767
5768 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
5769 // there should be a better way to uncross my wires
5770 int arity = mh.type().parameterCount();
5771 int[] order = new int[arity];
5772 for (int k = 0; k < arity; k++) order[k] = k;
5773 order[i] = j; order[j] = i;
5774 Class<?>[] types = mh.type().parameterArray();
5775 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
5776 MethodType swapType = methodType(mh.type().returnType(), types);
5777 return permuteArguments(mh, swapType, order);
5778 }
5779
5780 /**
5781 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
5782 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
5783 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
5784 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
5785 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
5786 * {@code try-finally} handle.
5787 * <p>
5788 * The {@code cleanup} handle will be passed one or two additional leading arguments.
5789 * The first is the exception thrown during the
5790 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
5791 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
5792 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
5793 * The second argument is not present if the {@code target} handle has a {@code void} return type.
5794 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
5795 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
5796 * <p>
5797 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
5798 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
5799 * two extra leading parameters:<ul>
5800 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
5801 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
5802 * the result from the execution of the {@code target} handle.
5803 * This parameter is not present if the {@code target} returns {@code void}.
5804 * </ul>
5805 * <p>
5806 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
5807 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
5808 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
5809 * the cleanup.
5810 * <blockquote><pre>{@code
5811 * V target(A..., B...);
5812 * V cleanup(Throwable, V, A...);
5813 * V adapter(A... a, B... b) {
5814 * V result = (zero value for V);
5815 * Throwable throwable = null;
5816 * try {
5817 * result = target(a..., b...);
5818 * } catch (Throwable t) {
5819 * throwable = t;
5820 * throw t;
5821 * } finally {
5822 * result = cleanup(throwable, result, a...);
5823 * }
5824 * return result;
5825 * }
5826 * }</pre></blockquote>
5827 * <p>
5828 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5829 * be modified by execution of the target, and so are passed unchanged
5830 * from the caller to the cleanup, if it is invoked.
5831 * <p>
5832 * The target and cleanup must return the same type, even if the cleanup
5833 * always throws.
5834 * To create such a throwing cleanup, compose the cleanup logic
5835 * with {@link #throwException throwException},
5836 * in order to create a method handle of the correct return type.
5837 * <p>
5838 * Note that {@code tryFinally} never converts exceptions into normal returns.
5839 * In rare cases where exceptions must be converted in that way, first wrap
5840 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
5841 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
5842 *
5843 * @param target the handle whose execution is to be wrapped in a {@code try} block.
5844 * @param cleanup the handle that is invoked in the finally block.
5845 *
5846 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
5847 * @throws NullPointerException if any argument is null
5848 * @throws IllegalArgumentException if {@code cleanup} does not accept
5849 * the required leading arguments, or if the method handle types do
5850 * not match in their return types and their
5851 * corresponding trailing parameters
5852 *
5853 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
5854 * @since 9
5855 */
5856 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
5857 List<Class<?>> targetParamTypes = target.type().parameterList();
5858 List<Class<?>> cleanupParamTypes = cleanup.type().parameterList();
5859 Class<?> rtype = target.type().returnType();
5860
5861 tryFinallyChecks(target, cleanup);
5862
5863 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
5864 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5865 // target parameter list.
5866 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
5867
5868 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
5869 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
5870 }
5871
5872 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
5873 Class<?> rtype = target.type().returnType();
5874 if (rtype != cleanup.type().returnType()) {
5875 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
5876 }
5877 MethodType cleanupType = cleanup.type();
5878 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
5879 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
5880 }
5881 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
5882 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
5883 }
5884 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5885 // target parameter list.
5886 int cleanupArgIndex = rtype == void.class ? 1 : 2;
5887 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
5888 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
5889 cleanup.type(), target.type());
5890 }
5891 }
5892
5893 }