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 Class<?> callerCls = findBoundCallerClass(method);
1399 boolean restrict = !(method.isPrivate() && Reflection.areNestMates(specialCaller, refc));
1400
1401 if (restrict)
1402 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, callerCls);
1403 else
1404 return specialLookup.getDirectMethodNoRestrictInvokeSpecial(refc, method, callerCls);
1405 }
1406
1407 /**
1408 * Produces a method handle giving read access to a non-static field.
1409 * The type of the method handle will have a return type of the field's
1410 * value type.
1411 * The method handle's single argument will be the instance containing
1412 * the field.
1413 * Access checking is performed immediately on behalf of the lookup class.
1414 * @param refc the class or interface from which the method is accessed
1415 * @param name the field's name
1416 * @param type the field's type
1417 * @return a method handle which can load values from the field
1418 * @throws NoSuchFieldException if the field does not exist
1419 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1420 * @exception SecurityException if a security manager is present and it
1421 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1422 * @throws NullPointerException if any argument is null
1423 * @see #findVarHandle(Class, String, Class)
1424 */
1425 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1426 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1427 return getDirectField(REF_getField, refc, field);
1428 }
1429
1430 /**
1431 * Produces a method handle giving write access to a non-static field.
1432 * The type of the method handle will have a void return type.
1433 * The method handle will take two arguments, the instance containing
1434 * the field, and the value to be stored.
1435 * The second argument will be of the field's value type.
1436 * Access checking is performed immediately on behalf of the lookup class.
1437 * @param refc the class or interface from which the method is accessed
1438 * @param name the field's name
1439 * @param type the field's type
1440 * @return a method handle which can store values into the field
1441 * @throws NoSuchFieldException if the field does not exist
1442 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1443 * @exception SecurityException if a security manager is present and it
1444 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1445 * @throws NullPointerException if any argument is null
1446 * @see #findVarHandle(Class, String, Class)
1447 */
1448 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1449 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1450 return getDirectField(REF_putField, refc, field);
1451 }
1452
1453 /**
1454 * Produces a VarHandle giving access to a non-static field {@code name}
1455 * of type {@code type} declared in a class of type {@code recv}.
1456 * The VarHandle's variable type is {@code type} and it has one
1457 * coordinate type, {@code recv}.
1458 * <p>
1459 * Access checking is performed immediately on behalf of the lookup
1460 * class.
1461 * <p>
1462 * Certain access modes of the returned VarHandle are unsupported under
1463 * the following conditions:
1464 * <ul>
1465 * <li>if the field is declared {@code final}, then the write, atomic
1466 * update, numeric atomic update, and bitwise atomic update access
1467 * modes are unsupported.
1468 * <li>if the field type is anything other than {@code byte},
1469 * {@code short}, {@code char}, {@code int}, {@code long},
1470 * {@code float}, or {@code double} then numeric atomic update
1471 * access modes are unsupported.
1472 * <li>if the field type is anything other than {@code boolean},
1473 * {@code byte}, {@code short}, {@code char}, {@code int} or
1474 * {@code long} then bitwise atomic update access modes are
1475 * unsupported.
1476 * </ul>
1477 * <p>
1478 * If the field is declared {@code volatile} then the returned VarHandle
1479 * will override access to the field (effectively ignore the
1480 * {@code volatile} declaration) in accordance to its specified
1481 * access modes.
1482 * <p>
1483 * If the field type is {@code float} or {@code double} then numeric
1484 * and atomic update access modes compare values using their bitwise
1485 * representation (see {@link Float#floatToRawIntBits} and
1486 * {@link Double#doubleToRawLongBits}, respectively).
1487 * @apiNote
1488 * Bitwise comparison of {@code float} values or {@code double} values,
1489 * as performed by the numeric and atomic update access modes, differ
1490 * from the primitive {@code ==} operator and the {@link Float#equals}
1491 * and {@link Double#equals} methods, specifically with respect to
1492 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1493 * Care should be taken when performing a compare and set or a compare
1494 * and exchange operation with such values since the operation may
1495 * unexpectedly fail.
1496 * There are many possible NaN values that are considered to be
1497 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1498 * provided by Java can distinguish between them. Operation failure can
1499 * occur if the expected or witness value is a NaN value and it is
1500 * transformed (perhaps in a platform specific manner) into another NaN
1501 * value, and thus has a different bitwise representation (see
1502 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1503 * details).
1504 * The values {@code -0.0} and {@code +0.0} have different bitwise
1505 * representations but are considered equal when using the primitive
1506 * {@code ==} operator. Operation failure can occur if, for example, a
1507 * numeric algorithm computes an expected value to be say {@code -0.0}
1508 * and previously computed the witness value to be say {@code +0.0}.
1509 * @param recv the receiver class, of type {@code R}, that declares the
1510 * non-static field
1511 * @param name the field's name
1512 * @param type the field's type, of type {@code T}
1513 * @return a VarHandle giving access to non-static fields.
1514 * @throws NoSuchFieldException if the field does not exist
1515 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1516 * @exception SecurityException if a security manager is present and it
1517 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1518 * @throws NullPointerException if any argument is null
1519 * @since 9
1520 */
1521 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1522 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1523 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1524 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1525 }
1526
1527 /**
1528 * Produces a method handle giving read access to a static field.
1529 * The type of the method handle will have a return type of the field's
1530 * value type.
1531 * The method handle will take no arguments.
1532 * Access checking is performed immediately on behalf of the lookup class.
1533 * <p>
1534 * If the returned method handle is invoked, the field's class will
1535 * be initialized, if it has not already been initialized.
1536 * @param refc the class or interface from which the method is accessed
1537 * @param name the field's name
1538 * @param type the field's type
1539 * @return a method handle which can load values from the field
1540 * @throws NoSuchFieldException if the field does not exist
1541 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1542 * @exception SecurityException if a security manager is present and it
1543 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1544 * @throws NullPointerException if any argument is null
1545 */
1546 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1547 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1548 return getDirectField(REF_getStatic, refc, field);
1549 }
1550
1551 /**
1552 * Produces a method handle giving write access to a static field.
1553 * The type of the method handle will have a void return type.
1554 * The method handle will take a single
1555 * argument, of the field's value type, the value to be stored.
1556 * Access checking is performed immediately on behalf of the lookup class.
1557 * <p>
1558 * If the returned method handle is invoked, the field's class will
1559 * be initialized, if it has not already been initialized.
1560 * @param refc the class or interface from which the method is accessed
1561 * @param name the field's name
1562 * @param type the field's type
1563 * @return a method handle which can store values into the field
1564 * @throws NoSuchFieldException if the field does not exist
1565 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1566 * @exception SecurityException if a security manager is present and it
1567 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1568 * @throws NullPointerException if any argument is null
1569 */
1570 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1571 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1572 return getDirectField(REF_putStatic, refc, field);
1573 }
1574
1575 /**
1576 * Produces a VarHandle giving access to a static field {@code name} of
1577 * type {@code type} declared in a class of type {@code decl}.
1578 * The VarHandle's variable type is {@code type} and it has no
1579 * coordinate types.
1580 * <p>
1581 * Access checking is performed immediately on behalf of the lookup
1582 * class.
1583 * <p>
1584 * If the returned VarHandle is operated on, the declaring class will be
1585 * initialized, if it has not already been initialized.
1586 * <p>
1587 * Certain access modes of the returned VarHandle are unsupported under
1588 * the following conditions:
1589 * <ul>
1590 * <li>if the field is declared {@code final}, then the write, atomic
1591 * update, numeric atomic update, and bitwise atomic update access
1592 * modes are unsupported.
1593 * <li>if the field type is anything other than {@code byte},
1594 * {@code short}, {@code char}, {@code int}, {@code long},
1595 * {@code float}, or {@code double}, then numeric atomic update
1596 * access modes are unsupported.
1597 * <li>if the field type is anything other than {@code boolean},
1598 * {@code byte}, {@code short}, {@code char}, {@code int} or
1599 * {@code long} then bitwise atomic update access modes are
1600 * unsupported.
1601 * </ul>
1602 * <p>
1603 * If the field is declared {@code volatile} then the returned VarHandle
1604 * will override access to the field (effectively ignore the
1605 * {@code volatile} declaration) in accordance to its specified
1606 * access modes.
1607 * <p>
1608 * If the field type is {@code float} or {@code double} then numeric
1609 * and atomic update access modes compare values using their bitwise
1610 * representation (see {@link Float#floatToRawIntBits} and
1611 * {@link Double#doubleToRawLongBits}, respectively).
1612 * @apiNote
1613 * Bitwise comparison of {@code float} values or {@code double} values,
1614 * as performed by the numeric and atomic update access modes, differ
1615 * from the primitive {@code ==} operator and the {@link Float#equals}
1616 * and {@link Double#equals} methods, specifically with respect to
1617 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1618 * Care should be taken when performing a compare and set or a compare
1619 * and exchange operation with such values since the operation may
1620 * unexpectedly fail.
1621 * There are many possible NaN values that are considered to be
1622 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1623 * provided by Java can distinguish between them. Operation failure can
1624 * occur if the expected or witness value is a NaN value and it is
1625 * transformed (perhaps in a platform specific manner) into another NaN
1626 * value, and thus has a different bitwise representation (see
1627 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1628 * details).
1629 * The values {@code -0.0} and {@code +0.0} have different bitwise
1630 * representations but are considered equal when using the primitive
1631 * {@code ==} operator. Operation failure can occur if, for example, a
1632 * numeric algorithm computes an expected value to be say {@code -0.0}
1633 * and previously computed the witness value to be say {@code +0.0}.
1634 * @param decl the class that declares the static field
1635 * @param name the field's name
1636 * @param type the field's type, of type {@code T}
1637 * @return a VarHandle giving access to a static field
1638 * @throws NoSuchFieldException if the field does not exist
1639 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1640 * @exception SecurityException if a security manager is present and it
1641 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1642 * @throws NullPointerException if any argument is null
1643 * @since 9
1644 */
1645 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1646 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1647 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1648 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1649 }
1650
1651 /**
1652 * Produces an early-bound method handle for a non-static method.
1653 * The receiver must have a supertype {@code defc} in which a method
1654 * of the given name and type is accessible to the lookup class.
1655 * The method and all its argument types must be accessible to the lookup object.
1656 * The type of the method handle will be that of the method,
1657 * without any insertion of an additional receiver parameter.
1658 * The given receiver will be bound into the method handle,
1659 * so that every call to the method handle will invoke the
1660 * requested method on the given receiver.
1661 * <p>
1662 * The returned method handle will have
1663 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1664 * the method's variable arity modifier bit ({@code 0x0080}) is set
1665 * <em>and</em> the trailing array argument is not the only argument.
1666 * (If the trailing array argument is the only argument,
1667 * the given receiver value will be bound to it.)
1668 * <p>
1669 * This is almost equivalent to the following code, with some differences noted below:
1670 * <blockquote><pre>{@code
1671 import static java.lang.invoke.MethodHandles.*;
1672 import static java.lang.invoke.MethodType.*;
1673 ...
1674 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1675 MethodHandle mh1 = mh0.bindTo(receiver);
1676 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1677 return mh1;
1678 * }</pre></blockquote>
1679 * where {@code defc} is either {@code receiver.getClass()} or a super
1680 * type of that class, in which the requested method is accessible
1681 * to the lookup class.
1682 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
1683 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
1684 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
1685 * the receiver is restricted by {@code findVirtual} to the lookup class.)
1686 * @param receiver the object from which the method is accessed
1687 * @param name the name of the method
1688 * @param type the type of the method, with the receiver argument omitted
1689 * @return the desired method handle
1690 * @throws NoSuchMethodException if the method does not exist
1691 * @throws IllegalAccessException if access checking fails
1692 * or if the method's variable arity modifier bit
1693 * is set and {@code asVarargsCollector} fails
1694 * @exception SecurityException if a security manager is present and it
1695 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1696 * @throws NullPointerException if any argument is null
1697 * @see MethodHandle#bindTo
1698 * @see #findVirtual
1699 */
1700 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1701 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1702 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1703 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
1704 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
1705 throw new IllegalAccessException("The restricted defining class " +
1706 mh.type().leadingReferenceParameter().getName() +
1707 " is not assignable from receiver class " +
1708 receiver.getClass().getName());
1709 }
1710 return mh.bindArgumentL(0, receiver).setVarargs(method);
1711 }
1712
1713 /**
1714 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1715 * to <i>m</i>, if the lookup class has permission.
1716 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1717 * If <i>m</i> is virtual, overriding is respected on every call.
1718 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1719 * The type of the method handle will be that of the method,
1720 * with the receiver type prepended (but only if it is non-static).
1721 * If the method's {@code accessible} flag is not set,
1722 * access checking is performed immediately on behalf of the lookup class.
1723 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1724 * <p>
1725 * The returned method handle will have
1726 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1727 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1728 * <p>
1729 * If <i>m</i> is static, and
1730 * if the returned method handle is invoked, the method's class will
1731 * be initialized, if it has not already been initialized.
1732 * @param m the reflected method
1733 * @return a method handle which can invoke the reflected method
1734 * @throws IllegalAccessException if access checking fails
1735 * or if the method's variable arity modifier bit
1736 * is set and {@code asVarargsCollector} fails
1737 * @throws NullPointerException if the argument is null
1738 */
1739 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1740 if (m.getDeclaringClass() == MethodHandle.class) {
1741 MethodHandle mh = unreflectForMH(m);
1742 if (mh != null) return mh;
1743 }
1744 if (m.getDeclaringClass() == VarHandle.class) {
1745 MethodHandle mh = unreflectForVH(m);
1746 if (mh != null) return mh;
1747 }
1748 MemberName method = new MemberName(m);
1749 byte refKind = method.getReferenceKind();
1750 if (refKind == REF_invokeSpecial)
1751 refKind = REF_invokeVirtual;
1752 assert(method.isMethod());
1753 @SuppressWarnings("deprecation")
1754 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1755 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1756 }
1757 private MethodHandle unreflectForMH(Method m) {
1758 // these names require special lookups because they throw UnsupportedOperationException
1759 if (MemberName.isMethodHandleInvokeName(m.getName()))
1760 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1761 return null;
1762 }
1763 private MethodHandle unreflectForVH(Method m) {
1764 // these names require special lookups because they throw UnsupportedOperationException
1765 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
1766 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
1767 return null;
1768 }
1769
1770 /**
1771 * Produces a method handle for a reflected method.
1772 * It will bypass checks for overriding methods on the receiver,
1773 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1774 * instruction from within the explicitly specified {@code specialCaller}.
1775 * The type of the method handle will be that of the method,
1776 * with a suitably restricted receiver type prepended.
1777 * (The receiver type will be {@code specialCaller} or a subtype.)
1778 * If the method's {@code accessible} flag is not set,
1779 * access checking is performed immediately on behalf of the lookup class,
1780 * as if {@code invokespecial} instruction were being linked.
1781 * <p>
1782 * Before method resolution,
1783 * if the explicitly specified caller class is not identical with the
1784 * lookup class, or if this lookup object does not have
1785 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1786 * privileges, the access fails.
1787 * <p>
1788 * The returned method handle will have
1789 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1790 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1791 * @param m the reflected method
1792 * @param specialCaller the class nominally calling the method
1793 * @return a method handle which can invoke the reflected method
1794 * @throws IllegalAccessException if access checking fails,
1795 * or if the method is {@code static},
1796 * or if the method's variable arity modifier bit
1797 * is set and {@code asVarargsCollector} fails
1798 * @throws NullPointerException if any argument is null
1799 */
1800 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1801 checkSpecialCaller(specialCaller, null);
1802 Lookup specialLookup = this.in(specialCaller);
1803 MemberName method = new MemberName(m, true);
1804 assert(method.isMethod());
1805 // ignore m.isAccessible: this is a new kind of access
1806 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1807 }
1808
1809 /**
1810 * Produces a method handle for a reflected constructor.
1811 * The type of the method handle will be that of the constructor,
1812 * with the return type changed to the declaring class.
1813 * The method handle will perform a {@code newInstance} operation,
1814 * creating a new instance of the constructor's class on the
1815 * arguments passed to the method handle.
1816 * <p>
1817 * If the constructor's {@code accessible} flag is not set,
1818 * access checking is performed immediately on behalf of the lookup class.
1819 * <p>
1820 * The returned method handle will have
1821 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1822 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1823 * <p>
1824 * If the returned method handle is invoked, the constructor's class will
1825 * be initialized, if it has not already been initialized.
1826 * @param c the reflected constructor
1827 * @return a method handle which can invoke the reflected constructor
1828 * @throws IllegalAccessException if access checking fails
1829 * or if the method's variable arity modifier bit
1830 * is set and {@code asVarargsCollector} fails
1831 * @throws NullPointerException if the argument is null
1832 */
1833 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1834 MemberName ctor = new MemberName(c);
1835 assert(ctor.isConstructor());
1836 @SuppressWarnings("deprecation")
1837 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1838 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1839 }
1840
1841 /**
1842 * Produces a method handle giving read access to a reflected field.
1843 * The type of the method handle will have a return type of the field's
1844 * value type.
1845 * If the field is static, the method handle will take no arguments.
1846 * Otherwise, its single argument will be the instance containing
1847 * the field.
1848 * If the field's {@code accessible} flag is not set,
1849 * access checking is performed immediately on behalf of the lookup class.
1850 * <p>
1851 * If the field is static, and
1852 * if the returned method handle is invoked, the field's class will
1853 * be initialized, if it has not already been initialized.
1854 * @param f the reflected field
1855 * @return a method handle which can load values from the reflected field
1856 * @throws IllegalAccessException if access checking fails
1857 * @throws NullPointerException if the argument is null
1858 */
1859 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1860 return unreflectField(f, false);
1861 }
1862 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1863 MemberName field = new MemberName(f, isSetter);
1864 assert(isSetter
1865 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1866 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1867 @SuppressWarnings("deprecation")
1868 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1869 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1870 }
1871
1872 /**
1873 * Produces a method handle giving write access to a reflected field.
1874 * The type of the method handle will have a void return type.
1875 * If the field is static, the method handle will take a single
1876 * argument, of the field's value type, the value to be stored.
1877 * Otherwise, the two arguments will be the instance containing
1878 * the field, and the value to be stored.
1879 * If the field's {@code accessible} flag is not set,
1880 * access checking is performed immediately on behalf of the lookup class.
1881 * <p>
1882 * If the field is static, and
1883 * if the returned method handle is invoked, the field's class will
1884 * be initialized, if it has not already been initialized.
1885 * @param f the reflected field
1886 * @return a method handle which can store values into the reflected field
1887 * @throws IllegalAccessException if access checking fails
1888 * @throws NullPointerException if the argument is null
1889 */
1890 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1891 return unreflectField(f, true);
1892 }
1893
1894 /**
1895 * Produces a VarHandle giving access to a reflected field {@code f}
1896 * of type {@code T} declared in a class of type {@code R}.
1897 * The VarHandle's variable type is {@code T}.
1898 * If the field is non-static the VarHandle has one coordinate type,
1899 * {@code R}. Otherwise, the field is static, and the VarHandle has no
1900 * coordinate types.
1901 * <p>
1902 * Access checking is performed immediately on behalf of the lookup
1903 * class, regardless of the value of the field's {@code accessible}
1904 * flag.
1905 * <p>
1906 * If the field is static, and if the returned VarHandle is operated
1907 * on, the field's declaring class will be initialized, if it has not
1908 * already been initialized.
1909 * <p>
1910 * Certain access modes of the returned VarHandle are unsupported under
1911 * the following conditions:
1912 * <ul>
1913 * <li>if the field is declared {@code final}, then the write, atomic
1914 * update, numeric atomic update, and bitwise atomic update access
1915 * modes are unsupported.
1916 * <li>if the field type is anything other than {@code byte},
1917 * {@code short}, {@code char}, {@code int}, {@code long},
1918 * {@code float}, or {@code double} then numeric atomic update
1919 * access modes are unsupported.
1920 * <li>if the field type is anything other than {@code boolean},
1921 * {@code byte}, {@code short}, {@code char}, {@code int} or
1922 * {@code long} then bitwise atomic update access modes are
1923 * unsupported.
1924 * </ul>
1925 * <p>
1926 * If the field is declared {@code volatile} then the returned VarHandle
1927 * will override access to the field (effectively ignore the
1928 * {@code volatile} declaration) in accordance to its specified
1929 * access modes.
1930 * <p>
1931 * If the field type is {@code float} or {@code double} then numeric
1932 * and atomic update access modes compare values using their bitwise
1933 * representation (see {@link Float#floatToRawIntBits} and
1934 * {@link Double#doubleToRawLongBits}, respectively).
1935 * @apiNote
1936 * Bitwise comparison of {@code float} values or {@code double} values,
1937 * as performed by the numeric and atomic update access modes, differ
1938 * from the primitive {@code ==} operator and the {@link Float#equals}
1939 * and {@link Double#equals} methods, specifically with respect to
1940 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1941 * Care should be taken when performing a compare and set or a compare
1942 * and exchange operation with such values since the operation may
1943 * unexpectedly fail.
1944 * There are many possible NaN values that are considered to be
1945 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1946 * provided by Java can distinguish between them. Operation failure can
1947 * occur if the expected or witness value is a NaN value and it is
1948 * transformed (perhaps in a platform specific manner) into another NaN
1949 * value, and thus has a different bitwise representation (see
1950 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1951 * details).
1952 * The values {@code -0.0} and {@code +0.0} have different bitwise
1953 * representations but are considered equal when using the primitive
1954 * {@code ==} operator. Operation failure can occur if, for example, a
1955 * numeric algorithm computes an expected value to be say {@code -0.0}
1956 * and previously computed the witness value to be say {@code +0.0}.
1957 * @param f the reflected field, with a field of type {@code T}, and
1958 * a declaring class of type {@code R}
1959 * @return a VarHandle giving access to non-static fields or a static
1960 * field
1961 * @throws IllegalAccessException if access checking fails
1962 * @throws NullPointerException if the argument is null
1963 * @since 9
1964 */
1965 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
1966 MemberName getField = new MemberName(f, false);
1967 MemberName putField = new MemberName(f, true);
1968 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
1969 f.getDeclaringClass(), getField, putField);
1970 }
1971
1972 /**
1973 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1974 * created by this lookup object or a similar one.
1975 * Security and access checks are performed to ensure that this lookup object
1976 * is capable of reproducing the target method handle.
1977 * This means that the cracking may fail if target is a direct method handle
1978 * but was created by an unrelated lookup object.
1979 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1980 * and was created by a lookup object for a different class.
1981 * @param target a direct method handle to crack into symbolic reference components
1982 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1983 * @exception SecurityException if a security manager is present and it
1984 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1985 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1986 * @exception NullPointerException if the target is {@code null}
1987 * @see MethodHandleInfo
1988 * @since 1.8
1989 */
1990 public MethodHandleInfo revealDirect(MethodHandle target) {
1991 MemberName member = target.internalMemberName();
1992 if (member == null || (!member.isResolved() &&
1993 !member.isMethodHandleInvoke() &&
1994 !member.isVarHandleMethodInvoke()))
1995 throw newIllegalArgumentException("not a direct method handle");
1996 Class<?> defc = member.getDeclaringClass();
1997 byte refKind = member.getReferenceKind();
1998 assert(MethodHandleNatives.refKindIsValid(refKind));
1999 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
2000 // Devirtualized method invocation is usually formally virtual.
2001 // To avoid creating extra MemberName objects for this common case,
2002 // we encode this extra degree of freedom using MH.isInvokeSpecial.
2003 refKind = REF_invokeVirtual;
2004 if (refKind == REF_invokeVirtual && defc.isInterface())
2005 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
2006 refKind = REF_invokeInterface;
2007 // Check SM permissions and member access before cracking.
2008 try {
2009 checkAccess(refKind, defc, member);
2010 checkSecurityManager(defc, member);
2011 } catch (IllegalAccessException ex) {
2012 throw new IllegalArgumentException(ex);
2013 }
2014 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2015 Class<?> callerClass = target.internalCallerClass();
2016 if (!hasPrivateAccess() || callerClass != lookupClass())
2017 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2018 }
2019 // Produce the handle to the results.
2020 return new InfoFromMemberName(this, member, refKind);
2021 }
2022
2023 /// Helper methods, all package-private.
2024
2025 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2026 checkSymbolicClass(refc); // do this before attempting to resolve
2027 Objects.requireNonNull(name);
2028 Objects.requireNonNull(type);
2029 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2030 NoSuchFieldException.class);
2031 }
2032
2033 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2034 checkSymbolicClass(refc); // do this before attempting to resolve
2035 Objects.requireNonNull(name);
2036 Objects.requireNonNull(type);
2037 checkMethodName(refKind, name); // NPE check on name
2038 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2039 NoSuchMethodException.class);
2040 }
2041
2042 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2043 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2044 Objects.requireNonNull(member.getName());
2045 Objects.requireNonNull(member.getType());
2046 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2047 ReflectiveOperationException.class);
2048 }
2049
2050 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
2051 Objects.requireNonNull(refc);
2052 Class<?> caller = lookupClassOrNull();
2053 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
2054 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
2055 }
2056
2057 /** Check name for an illegal leading "<" character. */
2058 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
2059 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
2060 throw new NoSuchMethodException("illegal method name: "+name);
2061 }
2062
2063
2064 /**
2065 * Find my trustable caller class if m is a caller sensitive method.
2066 * If this lookup object has private access, then the caller class is the lookupClass.
2067 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
2068 */
2069 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
2070 Class<?> callerClass = null;
2071 if (MethodHandleNatives.isCallerSensitive(m)) {
2072 // Only lookups with private access are allowed to resolve caller-sensitive methods
2073 if (hasPrivateAccess()) {
2074 callerClass = lookupClass;
2075 } else {
2076 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
2077 }
2078 }
2079 return callerClass;
2080 }
2081
2082 /**
2083 * Returns {@code true} if this lookup has {@code PRIVATE} access.
2084 * @return {@code true} if this lookup has {@code PRIVATE} access.
2085 * @since 9
2086 */
2087 public boolean hasPrivateAccess() {
2088 return (allowedModes & PRIVATE) != 0;
2089 }
2090
2091 /**
2092 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
2093 * Determines a trustable caller class to compare with refc, the symbolic reference class.
2094 * If this lookup object has private access, then the caller class is the lookupClass.
2095 */
2096 void checkSecurityManager(Class<?> refc, MemberName m) {
2097 SecurityManager smgr = System.getSecurityManager();
2098 if (smgr == null) return;
2099 if (allowedModes == TRUSTED) return;
2100
2101 // Step 1:
2102 boolean fullPowerLookup = hasPrivateAccess();
2103 if (!fullPowerLookup ||
2104 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
2105 ReflectUtil.checkPackageAccess(refc);
2106 }
2107
2108 if (m == null) { // findClass or accessClass
2109 // Step 2b:
2110 if (!fullPowerLookup) {
2111 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2112 }
2113 return;
2114 }
2115
2116 // Step 2a:
2117 if (m.isPublic()) return;
2118 if (!fullPowerLookup) {
2119 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
2120 }
2121
2122 // Step 3:
2123 Class<?> defc = m.getDeclaringClass();
2124 if (!fullPowerLookup && defc != refc) {
2125 ReflectUtil.checkPackageAccess(defc);
2126 }
2127 }
2128
2129 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2130 boolean wantStatic = (refKind == REF_invokeStatic);
2131 String message;
2132 if (m.isConstructor())
2133 message = "expected a method, not a constructor";
2134 else if (!m.isMethod())
2135 message = "expected a method";
2136 else if (wantStatic != m.isStatic())
2137 message = wantStatic ? "expected a static method" : "expected a non-static method";
2138 else
2139 { checkAccess(refKind, refc, m); return; }
2140 throw m.makeAccessException(message, this);
2141 }
2142
2143 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2144 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2145 String message;
2146 if (wantStatic != m.isStatic())
2147 message = wantStatic ? "expected a static field" : "expected a non-static field";
2148 else
2149 { checkAccess(refKind, refc, m); return; }
2150 throw m.makeAccessException(message, this);
2151 }
2152
2153 /** Check public/protected/private bits on the symbolic reference class and its member. */
2154 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2155 assert(m.referenceKindIsConsistentWith(refKind) &&
2156 MethodHandleNatives.refKindIsValid(refKind) &&
2157 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2158 int allowedModes = this.allowedModes;
2159 if (allowedModes == TRUSTED) return;
2160 int mods = m.getModifiers();
2161 if (Modifier.isProtected(mods) &&
2162 refKind == REF_invokeVirtual &&
2163 m.getDeclaringClass() == Object.class &&
2164 m.getName().equals("clone") &&
2165 refc.isArray()) {
2166 // The JVM does this hack also.
2167 // (See ClassVerifier::verify_invoke_instructions
2168 // and LinkResolver::check_method_accessability.)
2169 // Because the JVM does not allow separate methods on array types,
2170 // there is no separate method for int[].clone.
2171 // All arrays simply inherit Object.clone.
2172 // But for access checking logic, we make Object.clone
2173 // (normally protected) appear to be public.
2174 // Later on, when the DirectMethodHandle is created,
2175 // its leading argument will be restricted to the
2176 // requested array type.
2177 // N.B. The return type is not adjusted, because
2178 // that is *not* the bytecode behavior.
2179 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2180 }
2181 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2182 // cannot "new" a protected ctor in a different package
2183 mods ^= Modifier.PROTECTED;
2184 }
2185 if (Modifier.isFinal(mods) &&
2186 MethodHandleNatives.refKindIsSetter(refKind))
2187 throw m.makeAccessException("unexpected set of a final field", this);
2188 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2189 if ((requestedModes & allowedModes) != 0) {
2190 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2191 mods, lookupClass(), allowedModes))
2192 return;
2193 } else {
2194 // Protected members can also be checked as if they were package-private.
2195 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2196 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2197 return;
2198 }
2199 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2200 }
2201
2202 String accessFailedMessage(Class<?> refc, MemberName m) {
2203 Class<?> defc = m.getDeclaringClass();
2204 int mods = m.getModifiers();
2205 // check the class first:
2206 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2207 (defc == refc ||
2208 Modifier.isPublic(refc.getModifiers())));
2209 if (!classOK && (allowedModes & PACKAGE) != 0) {
2210 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), FULL_POWER_MODES) &&
2211 (defc == refc ||
2212 VerifyAccess.isClassAccessible(refc, lookupClass(), FULL_POWER_MODES)));
2213 }
2214 if (!classOK)
2215 return "class is not public";
2216 if (Modifier.isPublic(mods))
2217 return "access to public member failed"; // (how?, module not readable?)
2218 if (Modifier.isPrivate(mods))
2219 return "member is private";
2220 if (Modifier.isProtected(mods))
2221 return "member is protected";
2222 return "member is private to package";
2223 }
2224
2225 private static final boolean ALLOW_NESTMATE_ACCESS = false; // experiment with protected nestmate access
2226
2227 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2228 int allowedModes = this.allowedModes;
2229 if (allowedModes == TRUSTED) return;
2230 if (!hasPrivateAccess()
2231 || (specialCaller != lookupClass()
2232 // ensure non-abstract methods in superinterfaces can be special-invoked
2233 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))
2234 && !(ALLOW_NESTMATE_ACCESS &&
2235 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
2236 throw new MemberName(specialCaller).
2237 makeAccessException("no private access for invokespecial", this);
2238 }
2239
2240 private boolean restrictProtectedReceiver(MemberName method) {
2241 // The accessing class only has the right to use a protected member
2242 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2243 if (!method.isProtected() || method.isStatic()
2244 || allowedModes == TRUSTED
2245 || method.getDeclaringClass() == lookupClass()
2246 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
2247 || (ALLOW_NESTMATE_ACCESS &&
2248 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
2249 return false;
2250 return true;
2251 }
2252 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2253 assert(!method.isStatic());
2254 // receiver type of mh is too wide; narrow to caller
2255 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2256 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2257 }
2258 MethodType rawType = mh.type();
2259 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
2260 MethodType narrowType = rawType.changeParameterType(0, caller);
2261 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2262 assert(mh.viewAsTypeChecks(narrowType, true));
2263 return mh.copyWith(narrowType, mh.form);
2264 }
2265
2266 /** Check access and get the requested method. */
2267 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2268 final boolean doRestrict = true;
2269 final boolean checkSecurity = true;
2270 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2271 }
2272 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
2273 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2274 final boolean doRestrict = false;
2275 final boolean checkSecurity = true;
2276 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerClass);
2277 }
2278 /** Check access and get the requested method, eliding security manager checks. */
2279 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2280 final boolean doRestrict = true;
2281 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2282 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2283 }
2284 /** Common code for all methods; do not call directly except from immediately above. */
2285 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
2286 boolean checkSecurity,
2287 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
2288
2289 checkMethod(refKind, refc, method);
2290 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2291 if (checkSecurity)
2292 checkSecurityManager(refc, method);
2293 assert(!method.isMethodHandleInvoke());
2294
2295 if (refKind == REF_invokeSpecial &&
2296 refc != lookupClass() &&
2297 !refc.isInterface() &&
2298 refc != lookupClass().getSuperclass() &&
2299 refc.isAssignableFrom(lookupClass())) {
2300 assert(!method.getName().equals("<init>")); // not this code path
2301
2302 // Per JVMS 6.5, desc. of invokespecial instruction:
2303 // If the method is in a superclass of the LC,
2304 // and if our original search was above LC.super,
2305 // repeat the search (symbolic lookup) from LC.super
2306 // and continue with the direct superclass of that class,
2307 // and so forth, until a match is found or no further superclasses exist.
2308 // FIXME: MemberName.resolve should handle this instead.
2309 Class<?> refcAsSuper = lookupClass();
2310 MemberName m2;
2311 do {
2312 refcAsSuper = refcAsSuper.getSuperclass();
2313 m2 = new MemberName(refcAsSuper,
2314 method.getName(),
2315 method.getMethodType(),
2316 REF_invokeSpecial);
2317 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2318 } while (m2 == null && // no method is found yet
2319 refc != refcAsSuper); // search up to refc
2320 if (m2 == null) throw new InternalError(method.toString());
2321 method = m2;
2322 refc = refcAsSuper;
2323 // redo basic checks
2324 checkMethod(refKind, refc, method);
2325 }
2326
2327 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method);
2328 MethodHandle mh = dmh;
2329 // Optionally narrow the receiver argument to refc using restrictReceiver.
2330 if ((doRestrict && refKind == REF_invokeSpecial) ||
2331 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
2332 mh = restrictReceiver(method, dmh, lookupClass());
2333 }
2334 mh = maybeBindCaller(method, mh, callerClass);
2335 mh = mh.setVarargs(method);
2336 return mh;
2337 }
2338 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2339 Class<?> callerClass)
2340 throws IllegalAccessException {
2341 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2342 return mh;
2343 Class<?> hostClass = lookupClass;
2344 if (!hasPrivateAccess()) // caller must have private access
2345 hostClass = callerClass; // callerClass came from a security manager style stack walk
2346 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2347 // Note: caller will apply varargs after this step happens.
2348 return cbmh;
2349 }
2350 /** Check access and get the requested field. */
2351 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2352 final boolean checkSecurity = true;
2353 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2354 }
2355 /** Check access and get the requested field, eliding security manager checks. */
2356 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2357 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2358 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2359 }
2360 /** Common code for all fields; do not call directly except from immediately above. */
2361 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2362 boolean checkSecurity) throws IllegalAccessException {
2363 checkField(refKind, refc, field);
2364 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2365 if (checkSecurity)
2366 checkSecurityManager(refc, field);
2367 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2368 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2369 restrictProtectedReceiver(field));
2370 if (doRestrict)
2371 return restrictReceiver(field, dmh, lookupClass());
2372 return dmh;
2373 }
2374 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2375 Class<?> refc, MemberName getField, MemberName putField)
2376 throws IllegalAccessException {
2377 final boolean checkSecurity = true;
2378 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2379 }
2380 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2381 Class<?> refc, MemberName getField, MemberName putField)
2382 throws IllegalAccessException {
2383 final boolean checkSecurity = false;
2384 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2385 }
2386 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2387 Class<?> refc, MemberName getField, MemberName putField,
2388 boolean checkSecurity) throws IllegalAccessException {
2389 assert getField.isStatic() == putField.isStatic();
2390 assert getField.isGetter() && putField.isSetter();
2391 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2392 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2393
2394 checkField(getRefKind, refc, getField);
2395 if (checkSecurity)
2396 checkSecurityManager(refc, getField);
2397
2398 if (!putField.isFinal()) {
2399 // A VarHandle does not support updates to final fields, any
2400 // such VarHandle to a final field will be read-only and
2401 // therefore the following write-based accessibility checks are
2402 // only required for non-final fields
2403 checkField(putRefKind, refc, putField);
2404 if (checkSecurity)
2405 checkSecurityManager(refc, putField);
2406 }
2407
2408 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2409 restrictProtectedReceiver(getField));
2410 if (doRestrict) {
2411 assert !getField.isStatic();
2412 // receiver type of VarHandle is too wide; narrow to caller
2413 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2414 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2415 }
2416 refc = lookupClass();
2417 }
2418 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2419 }
2420 /** Check access and get the requested constructor. */
2421 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2422 final boolean checkSecurity = true;
2423 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2424 }
2425 /** Check access and get the requested constructor, eliding security manager checks. */
2426 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2427 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2428 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2429 }
2430 /** Common code for all constructors; do not call directly except from immediately above. */
2431 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2432 boolean checkSecurity) throws IllegalAccessException {
2433 assert(ctor.isConstructor());
2434 checkAccess(REF_newInvokeSpecial, refc, ctor);
2435 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2436 if (checkSecurity)
2437 checkSecurityManager(refc, ctor);
2438 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2439 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2440 }
2441
2442 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2443 */
2444 /*non-public*/
2445 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2446 if (!(type instanceof Class || type instanceof MethodType))
2447 throw new InternalError("unresolved MemberName");
2448 MemberName member = new MemberName(refKind, defc, name, type);
2449 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2450 if (mh != null) {
2451 checkSymbolicClass(defc);
2452 return mh;
2453 }
2454 // Treat MethodHandle.invoke and invokeExact specially.
2455 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2456 mh = findVirtualForMH(member.getName(), member.getMethodType());
2457 if (mh != null) {
2458 return mh;
2459 }
2460 }
2461 MemberName resolved = resolveOrFail(refKind, member);
2462 mh = getDirectMethodForConstant(refKind, defc, resolved);
2463 if (mh instanceof DirectMethodHandle
2464 && canBeCached(refKind, defc, resolved)) {
2465 MemberName key = mh.internalMemberName();
2466 if (key != null) {
2467 key = key.asNormalOriginal();
2468 }
2469 if (member.equals(key)) { // better safe than sorry
2470 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2471 }
2472 }
2473 return mh;
2474 }
2475 private
2476 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2477 if (refKind == REF_invokeSpecial) {
2478 return false;
2479 }
2480 if (!Modifier.isPublic(defc.getModifiers()) ||
2481 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2482 !member.isPublic() ||
2483 member.isCallerSensitive()) {
2484 return false;
2485 }
2486 ClassLoader loader = defc.getClassLoader();
2487 if (loader != null) {
2488 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2489 boolean found = false;
2490 while (sysl != null) {
2491 if (loader == sysl) { found = true; break; }
2492 sysl = sysl.getParent();
2493 }
2494 if (!found) {
2495 return false;
2496 }
2497 }
2498 try {
2499 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
2500 new MemberName(refKind, defc, member.getName(), member.getType()));
2501 checkSecurityManager(defc, resolved2);
2502 } catch (ReflectiveOperationException | SecurityException ex) {
2503 return false;
2504 }
2505 return true;
2506 }
2507 private
2508 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2509 throws ReflectiveOperationException {
2510 if (MethodHandleNatives.refKindIsField(refKind)) {
2511 return getDirectFieldNoSecurityManager(refKind, defc, member);
2512 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2513 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2514 } else if (refKind == REF_newInvokeSpecial) {
2515 return getDirectConstructorNoSecurityManager(defc, member);
2516 }
2517 // oops
2518 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2519 }
2520
2521 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2522 }
2523
2524 /**
2525 * Produces a method handle constructing arrays of a desired type.
2526 * The return type of the method handle will be the array type.
2527 * The type of its sole argument will be {@code int}, which specifies the size of the array.
2528 * @param arrayClass an array type
2529 * @return a method handle which can create arrays of the given type
2530 * @throws NullPointerException if the argument is {@code null}
2531 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2532 * @see java.lang.reflect.Array#newInstance(Class, int)
2533 * @since 9
2534 */
2535 public static
2536 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2537 if (!arrayClass.isArray()) {
2538 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2539 }
2540 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2541 bindTo(arrayClass.getComponentType());
2542 return ani.asType(ani.type().changeReturnType(arrayClass));
2543 }
2544
2545 /**
2546 * Produces a method handle returning the length of an array.
2547 * The type of the method handle will have {@code int} as return type,
2548 * and its sole argument will be the array type.
2549 * @param arrayClass an array type
2550 * @return a method handle which can retrieve the length of an array of the given array type
2551 * @throws NullPointerException if the argument is {@code null}
2552 * @throws IllegalArgumentException if arrayClass is not an array type
2553 * @since 9
2554 */
2555 public static
2556 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2557 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2558 }
2559
2560 /**
2561 * Produces a method handle giving read access to elements of an array.
2562 * The type of the method handle will have a return type of the array's
2563 * element type. Its first argument will be the array type,
2564 * and the second will be {@code int}.
2565 * @param arrayClass an array type
2566 * @return a method handle which can load values from the given array type
2567 * @throws NullPointerException if the argument is null
2568 * @throws IllegalArgumentException if arrayClass is not an array type
2569 */
2570 public static
2571 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2572 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2573 }
2574
2575 /**
2576 * Produces a method handle giving write access to elements of an array.
2577 * The type of the method handle will have a void return type.
2578 * Its last argument will be the array's element type.
2579 * The first and second arguments will be the array type and int.
2580 * @param arrayClass the class of an array
2581 * @return a method handle which can store values into the array type
2582 * @throws NullPointerException if the argument is null
2583 * @throws IllegalArgumentException if arrayClass is not an array type
2584 */
2585 public static
2586 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2587 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2588 }
2589
2590 /**
2591 * Produces a VarHandle giving access to elements of an array of type
2592 * {@code arrayClass}. The VarHandle's variable type is the component type
2593 * of {@code arrayClass} and the list of coordinate types is
2594 * {@code (arrayClass, int)}, where the {@code int} coordinate type
2595 * corresponds to an argument that is an index into an array.
2596 * <p>
2597 * Certain access modes of the returned VarHandle are unsupported under
2598 * the following conditions:
2599 * <ul>
2600 * <li>if the component type is anything other than {@code byte},
2601 * {@code short}, {@code char}, {@code int}, {@code long},
2602 * {@code float}, or {@code double} then numeric atomic update access
2603 * modes are unsupported.
2604 * <li>if the field type is anything other than {@code boolean},
2605 * {@code byte}, {@code short}, {@code char}, {@code int} or
2606 * {@code long} then bitwise atomic update access modes are
2607 * unsupported.
2608 * </ul>
2609 * <p>
2610 * If the component type is {@code float} or {@code double} then numeric
2611 * and atomic update access modes compare values using their bitwise
2612 * representation (see {@link Float#floatToRawIntBits} and
2613 * {@link Double#doubleToRawLongBits}, respectively).
2614 * @apiNote
2615 * Bitwise comparison of {@code float} values or {@code double} values,
2616 * as performed by the numeric and atomic update access modes, differ
2617 * from the primitive {@code ==} operator and the {@link Float#equals}
2618 * and {@link Double#equals} methods, specifically with respect to
2619 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2620 * Care should be taken when performing a compare and set or a compare
2621 * and exchange operation with such values since the operation may
2622 * unexpectedly fail.
2623 * There are many possible NaN values that are considered to be
2624 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2625 * provided by Java can distinguish between them. Operation failure can
2626 * occur if the expected or witness value is a NaN value and it is
2627 * transformed (perhaps in a platform specific manner) into another NaN
2628 * value, and thus has a different bitwise representation (see
2629 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2630 * details).
2631 * The values {@code -0.0} and {@code +0.0} have different bitwise
2632 * representations but are considered equal when using the primitive
2633 * {@code ==} operator. Operation failure can occur if, for example, a
2634 * numeric algorithm computes an expected value to be say {@code -0.0}
2635 * and previously computed the witness value to be say {@code +0.0}.
2636 * @param arrayClass the class of an array, of type {@code T[]}
2637 * @return a VarHandle giving access to elements of an array
2638 * @throws NullPointerException if the arrayClass is null
2639 * @throws IllegalArgumentException if arrayClass is not an array type
2640 * @since 9
2641 */
2642 public static
2643 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
2644 return VarHandles.makeArrayElementHandle(arrayClass);
2645 }
2646
2647 /**
2648 * Produces a VarHandle giving access to elements of a {@code byte[]} array
2649 * viewed as if it were a different primitive array type, such as
2650 * {@code int[]} or {@code long[]}.
2651 * The VarHandle's variable type is the component type of
2652 * {@code viewArrayClass} and the list of coordinate types is
2653 * {@code (byte[], int)}, where the {@code int} coordinate type
2654 * corresponds to an argument that is an index into a {@code byte[]} array.
2655 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
2656 * array, composing bytes to or from a value of the component type of
2657 * {@code viewArrayClass} according to the given endianness.
2658 * <p>
2659 * The supported component types (variables types) are {@code short},
2660 * {@code char}, {@code int}, {@code long}, {@code float} and
2661 * {@code double}.
2662 * <p>
2663 * Access of bytes at a given index will result in an
2664 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2665 * or greater than the {@code byte[]} array length minus the size (in bytes)
2666 * of {@code T}.
2667 * <p>
2668 * Access of bytes at an index may be aligned or misaligned for {@code T},
2669 * with respect to the underlying memory address, {@code A} say, associated
2670 * with the array and index.
2671 * If access is misaligned then access for anything other than the
2672 * {@code get} and {@code set} access modes will result in an
2673 * {@code IllegalStateException}. In such cases atomic access is only
2674 * guaranteed with respect to the largest power of two that divides the GCD
2675 * of {@code A} and the size (in bytes) of {@code T}.
2676 * If access is aligned then following access modes are supported and are
2677 * guaranteed to support atomic access:
2678 * <ul>
2679 * <li>read write access modes for all {@code T}, with the exception of
2680 * access modes {@code get} and {@code set} for {@code long} and
2681 * {@code double} on 32-bit platforms.
2682 * <li>atomic update access modes for {@code int}, {@code long},
2683 * {@code float} or {@code double}.
2684 * (Future major platform releases of the JDK may support additional
2685 * types for certain currently unsupported access modes.)
2686 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2687 * (Future major platform releases of the JDK may support additional
2688 * numeric types for certain currently unsupported access modes.)
2689 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2690 * (Future major platform releases of the JDK may support additional
2691 * numeric types for certain currently unsupported access modes.)
2692 * </ul>
2693 * <p>
2694 * Misaligned access, and therefore atomicity guarantees, may be determined
2695 * for {@code byte[]} arrays without operating on a specific array. Given
2696 * an {@code index}, {@code T} and it's corresponding boxed type,
2697 * {@code T_BOX}, misalignment may be determined as follows:
2698 * <pre>{@code
2699 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2700 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
2701 * alignmentOffset(0, sizeOfT);
2702 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
2703 * boolean isMisaligned = misalignedAtIndex != 0;
2704 * }</pre>
2705 * <p>
2706 * If the variable type is {@code float} or {@code double} then atomic
2707 * update access modes compare values using their bitwise representation
2708 * (see {@link Float#floatToRawIntBits} and
2709 * {@link Double#doubleToRawLongBits}, respectively).
2710 * @param viewArrayClass the view array class, with a component type of
2711 * type {@code T}
2712 * @param byteOrder the endianness of the view array elements, as
2713 * stored in the underlying {@code byte} array
2714 * @return a VarHandle giving access to elements of a {@code byte[]} array
2715 * viewed as if elements corresponding to the components type of the view
2716 * array class
2717 * @throws NullPointerException if viewArrayClass or byteOrder is null
2718 * @throws IllegalArgumentException if viewArrayClass is not an array type
2719 * @throws UnsupportedOperationException if the component type of
2720 * viewArrayClass is not supported as a variable type
2721 * @since 9
2722 */
2723 public static
2724 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
2725 ByteOrder byteOrder) throws IllegalArgumentException {
2726 Objects.requireNonNull(byteOrder);
2727 return VarHandles.byteArrayViewHandle(viewArrayClass,
2728 byteOrder == ByteOrder.BIG_ENDIAN);
2729 }
2730
2731 /**
2732 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
2733 * viewed as if it were an array of elements of a different primitive
2734 * component type to that of {@code byte}, such as {@code int[]} or
2735 * {@code long[]}.
2736 * The VarHandle's variable type is the component type of
2737 * {@code viewArrayClass} and the list of coordinate types is
2738 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
2739 * corresponds to an argument that is an index into a {@code byte[]} array.
2740 * The returned VarHandle accesses bytes at an index in a
2741 * {@code ByteBuffer}, composing bytes to or from a value of the component
2742 * type of {@code viewArrayClass} according to the given endianness.
2743 * <p>
2744 * The supported component types (variables types) are {@code short},
2745 * {@code char}, {@code int}, {@code long}, {@code float} and
2746 * {@code double}.
2747 * <p>
2748 * Access will result in a {@code ReadOnlyBufferException} for anything
2749 * other than the read access modes if the {@code ByteBuffer} is read-only.
2750 * <p>
2751 * Access of bytes at a given index will result in an
2752 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2753 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
2754 * {@code T}.
2755 * <p>
2756 * Access of bytes at an index may be aligned or misaligned for {@code T},
2757 * with respect to the underlying memory address, {@code A} say, associated
2758 * with the {@code ByteBuffer} and index.
2759 * If access is misaligned then access for anything other than the
2760 * {@code get} and {@code set} access modes will result in an
2761 * {@code IllegalStateException}. In such cases atomic access is only
2762 * guaranteed with respect to the largest power of two that divides the GCD
2763 * of {@code A} and the size (in bytes) of {@code T}.
2764 * If access is aligned then following access modes are supported and are
2765 * guaranteed to support atomic access:
2766 * <ul>
2767 * <li>read write access modes for all {@code T}, with the exception of
2768 * access modes {@code get} and {@code set} for {@code long} and
2769 * {@code double} on 32-bit platforms.
2770 * <li>atomic update access modes for {@code int}, {@code long},
2771 * {@code float} or {@code double}.
2772 * (Future major platform releases of the JDK may support additional
2773 * types for certain currently unsupported access modes.)
2774 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2775 * (Future major platform releases of the JDK may support additional
2776 * numeric types for certain currently unsupported access modes.)
2777 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2778 * (Future major platform releases of the JDK may support additional
2779 * numeric types for certain currently unsupported access modes.)
2780 * </ul>
2781 * <p>
2782 * Misaligned access, and therefore atomicity guarantees, may be determined
2783 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
2784 * {@code index}, {@code T} and it's corresponding boxed type,
2785 * {@code T_BOX}, as follows:
2786 * <pre>{@code
2787 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2788 * ByteBuffer bb = ...
2789 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
2790 * boolean isMisaligned = misalignedAtIndex != 0;
2791 * }</pre>
2792 * <p>
2793 * If the variable type is {@code float} or {@code double} then atomic
2794 * update access modes compare values using their bitwise representation
2795 * (see {@link Float#floatToRawIntBits} and
2796 * {@link Double#doubleToRawLongBits}, respectively).
2797 * @param viewArrayClass the view array class, with a component type of
2798 * type {@code T}
2799 * @param byteOrder the endianness of the view array elements, as
2800 * stored in the underlying {@code ByteBuffer} (Note this overrides the
2801 * endianness of a {@code ByteBuffer})
2802 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
2803 * viewed as if elements corresponding to the components type of the view
2804 * array class
2805 * @throws NullPointerException if viewArrayClass or byteOrder is null
2806 * @throws IllegalArgumentException if viewArrayClass is not an array type
2807 * @throws UnsupportedOperationException if the component type of
2808 * viewArrayClass is not supported as a variable type
2809 * @since 9
2810 */
2811 public static
2812 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
2813 ByteOrder byteOrder) throws IllegalArgumentException {
2814 Objects.requireNonNull(byteOrder);
2815 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
2816 byteOrder == ByteOrder.BIG_ENDIAN);
2817 }
2818
2819
2820 /// method handle invocation (reflective style)
2821
2822 /**
2823 * Produces a method handle which will invoke any method handle of the
2824 * given {@code type}, with a given number of trailing arguments replaced by
2825 * a single trailing {@code Object[]} array.
2826 * The resulting invoker will be a method handle with the following
2827 * arguments:
2828 * <ul>
2829 * <li>a single {@code MethodHandle} target
2830 * <li>zero or more leading values (counted by {@code leadingArgCount})
2831 * <li>an {@code Object[]} array containing trailing arguments
2832 * </ul>
2833 * <p>
2834 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
2835 * the indicated {@code type}.
2836 * That is, if the target is exactly of the given {@code type}, it will behave
2837 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
2838 * is used to convert the target to the required {@code type}.
2839 * <p>
2840 * The type of the returned invoker will not be the given {@code type}, but rather
2841 * will have all parameters except the first {@code leadingArgCount}
2842 * replaced by a single array of type {@code Object[]}, which will be
2843 * the final parameter.
2844 * <p>
2845 * Before invoking its target, the invoker will spread the final array, apply
2846 * reference casts as necessary, and unbox and widen primitive arguments.
2847 * If, when the invoker is called, the supplied array argument does
2848 * not have the correct number of elements, the invoker will throw
2849 * an {@link IllegalArgumentException} instead of invoking the target.
2850 * <p>
2851 * This method is equivalent to the following code (though it may be more efficient):
2852 * <blockquote><pre>{@code
2853 MethodHandle invoker = MethodHandles.invoker(type);
2854 int spreadArgCount = type.parameterCount() - leadingArgCount;
2855 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
2856 return invoker;
2857 * }</pre></blockquote>
2858 * This method throws no reflective or security exceptions.
2859 * @param type the desired target type
2860 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
2861 * @return a method handle suitable for invoking any method handle of the given type
2862 * @throws NullPointerException if {@code type} is null
2863 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
2864 * the range from 0 to {@code type.parameterCount()} inclusive,
2865 * or if the resulting method handle's type would have
2866 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2867 */
2868 public static
2869 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
2870 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
2871 throw newIllegalArgumentException("bad argument count", leadingArgCount);
2872 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
2873 return type.invokers().spreadInvoker(leadingArgCount);
2874 }
2875
2876 /**
2877 * Produces a special <em>invoker method handle</em> which can be used to
2878 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
2879 * The resulting invoker will have a type which is
2880 * exactly equal to the desired type, except that it will accept
2881 * an additional leading argument of type {@code MethodHandle}.
2882 * <p>
2883 * This method is equivalent to the following code (though it may be more efficient):
2884 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
2885 *
2886 * <p style="font-size:smaller;">
2887 * <em>Discussion:</em>
2888 * Invoker method handles can be useful when working with variable method handles
2889 * of unknown types.
2890 * For example, to emulate an {@code invokeExact} call to a variable method
2891 * handle {@code M}, extract its type {@code T},
2892 * look up the invoker method {@code X} for {@code T},
2893 * and call the invoker method, as {@code X.invoke(T, A...)}.
2894 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
2895 * is unknown.)
2896 * If spreading, collecting, or other argument transformations are required,
2897 * they can be applied once to the invoker {@code X} and reused on many {@code M}
2898 * method handle values, as long as they are compatible with the type of {@code X}.
2899 * <p style="font-size:smaller;">
2900 * <em>(Note: The invoker method is not available via the Core Reflection API.
2901 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2902 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2903 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2904 * <p>
2905 * This method throws no reflective or security exceptions.
2906 * @param type the desired target type
2907 * @return a method handle suitable for invoking any method handle of the given type
2908 * @throws IllegalArgumentException if the resulting method handle's type would have
2909 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2910 */
2911 public static
2912 MethodHandle exactInvoker(MethodType type) {
2913 return type.invokers().exactInvoker();
2914 }
2915
2916 /**
2917 * Produces a special <em>invoker method handle</em> which can be used to
2918 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2919 * The resulting invoker will have a type which is
2920 * exactly equal to the desired type, except that it will accept
2921 * an additional leading argument of type {@code MethodHandle}.
2922 * <p>
2923 * Before invoking its target, if the target differs from the expected type,
2924 * the invoker will apply reference casts as
2925 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
2926 * Similarly, the return value will be converted as necessary.
2927 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
2928 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
2929 * <p>
2930 * This method is equivalent to the following code (though it may be more efficient):
2931 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
2932 * <p style="font-size:smaller;">
2933 * <em>Discussion:</em>
2934 * A {@linkplain MethodType#genericMethodType general method type} is one which
2935 * mentions only {@code Object} arguments and return values.
2936 * An invoker for such a type is capable of calling any method handle
2937 * of the same arity as the general type.
2938 * <p style="font-size:smaller;">
2939 * <em>(Note: The invoker method is not available via the Core Reflection API.
2940 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2941 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2942 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2943 * <p>
2944 * This method throws no reflective or security exceptions.
2945 * @param type the desired target type
2946 * @return a method handle suitable for invoking any method handle convertible to the given type
2947 * @throws IllegalArgumentException if the resulting method handle's type would have
2948 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2949 */
2950 public static
2951 MethodHandle invoker(MethodType type) {
2952 return type.invokers().genericInvoker();
2953 }
2954
2955 /**
2956 * Produces a special <em>invoker method handle</em> which can be used to
2957 * invoke a signature-polymorphic access mode method on any VarHandle whose
2958 * associated access mode type is compatible with the given type.
2959 * The resulting invoker will have a type which is exactly equal to the
2960 * desired given type, except that it will accept an additional leading
2961 * argument of type {@code VarHandle}.
2962 *
2963 * @param accessMode the VarHandle access mode
2964 * @param type the desired target type
2965 * @return a method handle suitable for invoking an access mode method of
2966 * any VarHandle whose access mode type is of the given type.
2967 * @since 9
2968 */
2969 static public
2970 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
2971 return type.invokers().varHandleMethodExactInvoker(accessMode);
2972 }
2973
2974 /**
2975 * Produces a special <em>invoker method handle</em> which can be used to
2976 * invoke a signature-polymorphic access mode method on any VarHandle whose
2977 * associated access mode type is compatible with the given type.
2978 * The resulting invoker will have a type which is exactly equal to the
2979 * desired given type, except that it will accept an additional leading
2980 * argument of type {@code VarHandle}.
2981 * <p>
2982 * Before invoking its target, if the access mode type differs from the
2983 * desired given type, the invoker will apply reference casts as necessary
2984 * and box, unbox, or widen primitive values, as if by
2985 * {@link MethodHandle#asType asType}. Similarly, the return value will be
2986 * converted as necessary.
2987 * <p>
2988 * This method is equivalent to the following code (though it may be more
2989 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
2990 *
2991 * @param accessMode the VarHandle access mode
2992 * @param type the desired target type
2993 * @return a method handle suitable for invoking an access mode method of
2994 * any VarHandle whose access mode type is convertible to the given
2995 * type.
2996 * @since 9
2997 */
2998 static public
2999 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3000 return type.invokers().varHandleMethodInvoker(accessMode);
3001 }
3002
3003 static /*non-public*/
3004 MethodHandle basicInvoker(MethodType type) {
3005 return type.invokers().basicInvoker();
3006 }
3007
3008 /// method handle modification (creation from other method handles)
3009
3010 /**
3011 * Produces a method handle which adapts the type of the
3012 * given method handle to a new type by pairwise argument and return type conversion.
3013 * The original type and new type must have the same number of arguments.
3014 * The resulting method handle is guaranteed to report a type
3015 * which is equal to the desired new type.
3016 * <p>
3017 * If the original type and new type are equal, returns target.
3018 * <p>
3019 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
3020 * and some additional conversions are also applied if those conversions fail.
3021 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
3022 * if possible, before or instead of any conversions done by {@code asType}:
3023 * <ul>
3024 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
3025 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
3026 * (This treatment of interfaces follows the usage of the bytecode verifier.)
3027 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
3028 * the boolean is converted to a byte value, 1 for true, 0 for false.
3029 * (This treatment follows the usage of the bytecode verifier.)
3030 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
3031 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
3032 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
3033 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
3034 * then a Java casting conversion (JLS 5.5) is applied.
3035 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
3036 * widening and/or narrowing.)
3037 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
3038 * conversion will be applied at runtime, possibly followed
3039 * by a Java casting conversion (JLS 5.5) on the primitive value,
3040 * possibly followed by a conversion from byte to boolean by testing
3041 * the low-order bit.
3042 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
3043 * and if the reference is null at runtime, a zero value is introduced.
3044 * </ul>
3045 * @param target the method handle to invoke after arguments are retyped
3046 * @param newType the expected type of the new method handle
3047 * @return a method handle which delegates to the target after performing
3048 * any necessary argument conversions, and arranges for any
3049 * necessary return value conversions
3050 * @throws NullPointerException if either argument is null
3051 * @throws WrongMethodTypeException if the conversion cannot be made
3052 * @see MethodHandle#asType
3053 */
3054 public static
3055 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
3056 explicitCastArgumentsChecks(target, newType);
3057 // use the asTypeCache when possible:
3058 MethodType oldType = target.type();
3059 if (oldType == newType) return target;
3060 if (oldType.explicitCastEquivalentToAsType(newType)) {
3061 return target.asFixedArity().asType(newType);
3062 }
3063 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
3064 }
3065
3066 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
3067 if (target.type().parameterCount() != newType.parameterCount()) {
3068 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
3069 }
3070 }
3071
3072 /**
3073 * Produces a method handle which adapts the calling sequence of the
3074 * given method handle to a new type, by reordering the arguments.
3075 * The resulting method handle is guaranteed to report a type
3076 * which is equal to the desired new type.
3077 * <p>
3078 * The given array controls the reordering.
3079 * Call {@code #I} the number of incoming parameters (the value
3080 * {@code newType.parameterCount()}, and call {@code #O} the number
3081 * of outgoing parameters (the value {@code target.type().parameterCount()}).
3082 * Then the length of the reordering array must be {@code #O},
3083 * and each element must be a non-negative number less than {@code #I}.
3084 * For every {@code N} less than {@code #O}, the {@code N}-th
3085 * outgoing argument will be taken from the {@code I}-th incoming
3086 * argument, where {@code I} is {@code reorder[N]}.
3087 * <p>
3088 * No argument or return value conversions are applied.
3089 * The type of each incoming argument, as determined by {@code newType},
3090 * must be identical to the type of the corresponding outgoing parameter
3091 * or parameters in the target method handle.
3092 * The return type of {@code newType} must be identical to the return
3093 * type of the original target.
3094 * <p>
3095 * The reordering array need not specify an actual permutation.
3096 * An incoming argument will be duplicated if its index appears
3097 * more than once in the array, and an incoming argument will be dropped
3098 * if its index does not appear in the array.
3099 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
3100 * incoming arguments which are not mentioned in the reordering array
3101 * may be of any type, as determined only by {@code newType}.
3102 * <blockquote><pre>{@code
3103 import static java.lang.invoke.MethodHandles.*;
3104 import static java.lang.invoke.MethodType.*;
3105 ...
3106 MethodType intfn1 = methodType(int.class, int.class);
3107 MethodType intfn2 = methodType(int.class, int.class, int.class);
3108 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
3109 assert(sub.type().equals(intfn2));
3110 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
3111 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
3112 assert((int)rsub.invokeExact(1, 100) == 99);
3113 MethodHandle add = ... (int x, int y) -> (x+y) ...;
3114 assert(add.type().equals(intfn2));
3115 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
3116 assert(twice.type().equals(intfn1));
3117 assert((int)twice.invokeExact(21) == 42);
3118 * }</pre></blockquote>
3119 * <p>
3120 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3121 * variable-arity method handle}, even if the original target method handle was.
3122 * @param target the method handle to invoke after arguments are reordered
3123 * @param newType the expected type of the new method handle
3124 * @param reorder an index array which controls the reordering
3125 * @return a method handle which delegates to the target after it
3126 * drops unused arguments and moves and/or duplicates the other arguments
3127 * @throws NullPointerException if any argument is null
3128 * @throws IllegalArgumentException if the index array length is not equal to
3129 * the arity of the target, or if any index array element
3130 * not a valid index for a parameter of {@code newType},
3131 * or if two corresponding parameter types in
3132 * {@code target.type()} and {@code newType} are not identical,
3133 */
3134 public static
3135 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3136 reorder = reorder.clone(); // get a private copy
3137 MethodType oldType = target.type();
3138 permuteArgumentChecks(reorder, newType, oldType);
3139 // first detect dropped arguments and handle them separately
3140 int[] originalReorder = reorder;
3141 BoundMethodHandle result = target.rebind();
3142 LambdaForm form = result.form;
3143 int newArity = newType.parameterCount();
3144 // Normalize the reordering into a real permutation,
3145 // by removing duplicates and adding dropped elements.
3146 // This somewhat improves lambda form caching, as well
3147 // as simplifying the transform by breaking it up into steps.
3148 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3149 if (ddIdx > 0) {
3150 // We found a duplicated entry at reorder[ddIdx].
3151 // Example: (x,y,z)->asList(x,y,z)
3152 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3153 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3154 // The starred element corresponds to the argument
3155 // deleted by the dupArgumentForm transform.
3156 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3157 boolean killFirst = false;
3158 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3159 // Set killFirst if the dup is larger than an intervening position.
3160 // This will remove at least one inversion from the permutation.
3161 if (dupVal > val) killFirst = true;
3162 }
3163 if (!killFirst) {
3164 srcPos = dstPos;
3165 dstPos = ddIdx;
3166 }
3167 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3168 assert (reorder[srcPos] == reorder[dstPos]);
3169 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3170 // contract the reordering by removing the element at dstPos
3171 int tailPos = dstPos + 1;
3172 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3173 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3174 } else {
3175 int dropVal = ~ddIdx, insPos = 0;
3176 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3177 // Find first element of reorder larger than dropVal.
3178 // This is where we will insert the dropVal.
3179 insPos += 1;
3180 }
3181 Class<?> ptype = newType.parameterType(dropVal);
3182 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3183 oldType = oldType.insertParameterTypes(insPos, ptype);
3184 // expand the reordering by inserting an element at insPos
3185 int tailPos = insPos + 1;
3186 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3187 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3188 reorder[insPos] = dropVal;
3189 }
3190 assert (permuteArgumentChecks(reorder, newType, oldType));
3191 }
3192 assert (reorder.length == newArity); // a perfect permutation
3193 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3194 form = form.editor().permuteArgumentsForm(1, reorder);
3195 if (newType == result.type() && form == result.internalForm())
3196 return result;
3197 return result.copyWith(newType, form);
3198 }
3199
3200 /**
3201 * Return an indication of any duplicate or omission in reorder.
3202 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3203 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3204 * Otherwise, return zero.
3205 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3206 */
3207 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3208 final int BIT_LIMIT = 63; // max number of bits in bit mask
3209 if (newArity < BIT_LIMIT) {
3210 long mask = 0;
3211 for (int i = 0; i < reorder.length; i++) {
3212 int arg = reorder[i];
3213 if (arg >= newArity) {
3214 return reorder.length;
3215 }
3216 long bit = 1L << arg;
3217 if ((mask & bit) != 0) {
3218 return i; // >0 indicates a dup
3219 }
3220 mask |= bit;
3221 }
3222 if (mask == (1L << newArity) - 1) {
3223 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
3224 return 0;
3225 }
3226 // find first zero
3227 long zeroBit = Long.lowestOneBit(~mask);
3228 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
3229 assert(zeroPos <= newArity);
3230 if (zeroPos == newArity) {
3231 return 0;
3232 }
3233 return ~zeroPos;
3234 } else {
3235 // same algorithm, different bit set
3236 BitSet mask = new BitSet(newArity);
3237 for (int i = 0; i < reorder.length; i++) {
3238 int arg = reorder[i];
3239 if (arg >= newArity) {
3240 return reorder.length;
3241 }
3242 if (mask.get(arg)) {
3243 return i; // >0 indicates a dup
3244 }
3245 mask.set(arg);
3246 }
3247 int zeroPos = mask.nextClearBit(0);
3248 assert(zeroPos <= newArity);
3249 if (zeroPos == newArity) {
3250 return 0;
3251 }
3252 return ~zeroPos;
3253 }
3254 }
3255
3256 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
3257 if (newType.returnType() != oldType.returnType())
3258 throw newIllegalArgumentException("return types do not match",
3259 oldType, newType);
3260 if (reorder.length == oldType.parameterCount()) {
3261 int limit = newType.parameterCount();
3262 boolean bad = false;
3263 for (int j = 0; j < reorder.length; j++) {
3264 int i = reorder[j];
3265 if (i < 0 || i >= limit) {
3266 bad = true; break;
3267 }
3268 Class<?> src = newType.parameterType(i);
3269 Class<?> dst = oldType.parameterType(j);
3270 if (src != dst)
3271 throw newIllegalArgumentException("parameter types do not match after reorder",
3272 oldType, newType);
3273 }
3274 if (!bad) return true;
3275 }
3276 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3277 }
3278
3279 /**
3280 * Produces a method handle of the requested return type which returns the given
3281 * constant value every time it is invoked.
3282 * <p>
3283 * Before the method handle is returned, the passed-in value is converted to the requested type.
3284 * If the requested type is primitive, widening primitive conversions are attempted,
3285 * else reference conversions are attempted.
3286 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3287 * @param type the return type of the desired method handle
3288 * @param value the value to return
3289 * @return a method handle of the given return type and no arguments, which always returns the given value
3290 * @throws NullPointerException if the {@code type} argument is null
3291 * @throws ClassCastException if the value cannot be converted to the required return type
3292 * @throws IllegalArgumentException if the given type is {@code void.class}
3293 */
3294 public static
3295 MethodHandle constant(Class<?> type, Object value) {
3296 if (type.isPrimitive()) {
3297 if (type == void.class)
3298 throw newIllegalArgumentException("void type");
3299 Wrapper w = Wrapper.forPrimitiveType(type);
3300 value = w.convert(value, type);
3301 if (w.zero().equals(value))
3302 return zero(w, type);
3303 return insertArguments(identity(type), 0, value);
3304 } else {
3305 if (value == null)
3306 return zero(Wrapper.OBJECT, type);
3307 return identity(type).bindTo(value);
3308 }
3309 }
3310
3311 /**
3312 * Produces a method handle which returns its sole argument when invoked.
3313 * @param type the type of the sole parameter and return value of the desired method handle
3314 * @return a unary method handle which accepts and returns the given type
3315 * @throws NullPointerException if the argument is null
3316 * @throws IllegalArgumentException if the given type is {@code void.class}
3317 */
3318 public static
3319 MethodHandle identity(Class<?> type) {
3320 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3321 int pos = btw.ordinal();
3322 MethodHandle ident = IDENTITY_MHS[pos];
3323 if (ident == null) {
3324 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3325 }
3326 if (ident.type().returnType() == type)
3327 return ident;
3328 // something like identity(Foo.class); do not bother to intern these
3329 assert (btw == Wrapper.OBJECT);
3330 return makeIdentity(type);
3331 }
3332
3333 /**
3334 * Produces a constant method handle of the requested return type which
3335 * returns the default value for that type every time it is invoked.
3336 * The resulting constant method handle will have no side effects.
3337 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3338 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3339 * since {@code explicitCastArguments} converts {@code null} to default values.
3340 * @param type the expected return type of the desired method handle
3341 * @return a constant method handle that takes no arguments
3342 * and returns the default value of the given type (or void, if the type is void)
3343 * @throws NullPointerException if the argument is null
3344 * @see MethodHandles#constant
3345 * @see MethodHandles#empty
3346 * @see MethodHandles#explicitCastArguments
3347 * @since 9
3348 */
3349 public static MethodHandle zero(Class<?> type) {
3350 Objects.requireNonNull(type);
3351 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
3352 }
3353
3354 private static MethodHandle identityOrVoid(Class<?> type) {
3355 return type == void.class ? zero(type) : identity(type);
3356 }
3357
3358 /**
3359 * Produces a method handle of the requested type which ignores any arguments, does nothing,
3360 * and returns a suitable default depending on the return type.
3361 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3362 * <p>The returned method handle is equivalent to
3363 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3364 *
3365 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3366 * {@code guardWithTest(pred, target, empty(target.type())}.
3367 * @param type the type of the desired method handle
3368 * @return a constant method handle of the given type, which returns a default value of the given return type
3369 * @throws NullPointerException if the argument is null
3370 * @see MethodHandles#zero
3371 * @see MethodHandles#constant
3372 * @since 9
3373 */
3374 public static MethodHandle empty(MethodType type) {
3375 Objects.requireNonNull(type);
3376 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3377 }
3378
3379 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
3380 private static MethodHandle makeIdentity(Class<?> ptype) {
3381 MethodType mtype = methodType(ptype, ptype);
3382 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3383 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3384 }
3385
3386 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3387 int pos = btw.ordinal();
3388 MethodHandle zero = ZERO_MHS[pos];
3389 if (zero == null) {
3390 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3391 }
3392 if (zero.type().returnType() == rtype)
3393 return zero;
3394 assert(btw == Wrapper.OBJECT);
3395 return makeZero(rtype);
3396 }
3397 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
3398 private static MethodHandle makeZero(Class<?> rtype) {
3399 MethodType mtype = methodType(rtype);
3400 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3401 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3402 }
3403
3404 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3405 // Simulate a CAS, to avoid racy duplication of results.
3406 MethodHandle prev = cache[pos];
3407 if (prev != null) return prev;
3408 return cache[pos] = value;
3409 }
3410
3411 /**
3412 * Provides a target method handle with one or more <em>bound arguments</em>
3413 * in advance of the method handle's invocation.
3414 * The formal parameters to the target corresponding to the bound
3415 * arguments are called <em>bound parameters</em>.
3416 * Returns a new method handle which saves away the bound arguments.
3417 * When it is invoked, it receives arguments for any non-bound parameters,
3418 * binds the saved arguments to their corresponding parameters,
3419 * and calls the original target.
3420 * <p>
3421 * The type of the new method handle will drop the types for the bound
3422 * parameters from the original target type, since the new method handle
3423 * will no longer require those arguments to be supplied by its callers.
3424 * <p>
3425 * Each given argument object must match the corresponding bound parameter type.
3426 * If a bound parameter type is a primitive, the argument object
3427 * must be a wrapper, and will be unboxed to produce the primitive value.
3428 * <p>
3429 * The {@code pos} argument selects which parameters are to be bound.
3430 * It may range between zero and <i>N-L</i> (inclusively),
3431 * where <i>N</i> is the arity of the target method handle
3432 * and <i>L</i> is the length of the values array.
3433 * <p>
3434 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3435 * variable-arity method handle}, even if the original target method handle was.
3436 * @param target the method handle to invoke after the argument is inserted
3437 * @param pos where to insert the argument (zero for the first)
3438 * @param values the series of arguments to insert
3439 * @return a method handle which inserts an additional argument,
3440 * before calling the original method handle
3441 * @throws NullPointerException if the target or the {@code values} array is null
3442 * @see MethodHandle#bindTo
3443 */
3444 public static
3445 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3446 int insCount = values.length;
3447 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3448 if (insCount == 0) return target;
3449 BoundMethodHandle result = target.rebind();
3450 for (int i = 0; i < insCount; i++) {
3451 Object value = values[i];
3452 Class<?> ptype = ptypes[pos+i];
3453 if (ptype.isPrimitive()) {
3454 result = insertArgumentPrimitive(result, pos, ptype, value);
3455 } else {
3456 value = ptype.cast(value); // throw CCE if needed
3457 result = result.bindArgumentL(pos, value);
3458 }
3459 }
3460 return result;
3461 }
3462
3463 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3464 Class<?> ptype, Object value) {
3465 Wrapper w = Wrapper.forPrimitiveType(ptype);
3466 // perform unboxing and/or primitive conversion
3467 value = w.convert(value, ptype);
3468 switch (w) {
3469 case INT: return result.bindArgumentI(pos, (int)value);
3470 case LONG: return result.bindArgumentJ(pos, (long)value);
3471 case FLOAT: return result.bindArgumentF(pos, (float)value);
3472 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3473 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3474 }
3475 }
3476
3477 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3478 MethodType oldType = target.type();
3479 int outargs = oldType.parameterCount();
3480 int inargs = outargs - insCount;
3481 if (inargs < 0)
3482 throw newIllegalArgumentException("too many values to insert");
3483 if (pos < 0 || pos > inargs)
3484 throw newIllegalArgumentException("no argument type to append");
3485 return oldType.ptypes();
3486 }
3487
3488 /**
3489 * Produces a method handle which will discard some dummy arguments
3490 * before calling some other specified <i>target</i> method handle.
3491 * The type of the new method handle will be the same as the target's type,
3492 * except it will also include the dummy argument types,
3493 * at some given position.
3494 * <p>
3495 * The {@code pos} argument may range between zero and <i>N</i>,
3496 * where <i>N</i> is the arity of the target.
3497 * If {@code pos} is zero, the dummy arguments will precede
3498 * the target's real arguments; if {@code pos} is <i>N</i>
3499 * they will come after.
3500 * <p>
3501 * <b>Example:</b>
3502 * <blockquote><pre>{@code
3503 import static java.lang.invoke.MethodHandles.*;
3504 import static java.lang.invoke.MethodType.*;
3505 ...
3506 MethodHandle cat = lookup().findVirtual(String.class,
3507 "concat", methodType(String.class, String.class));
3508 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3509 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3510 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3511 assertEquals(bigType, d0.type());
3512 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3513 * }</pre></blockquote>
3514 * <p>
3515 * This method is also equivalent to the following code:
3516 * <blockquote><pre>
3517 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3518 * </pre></blockquote>
3519 * @param target the method handle to invoke after the arguments are dropped
3520 * @param valueTypes the type(s) of the argument(s) to drop
3521 * @param pos position of first argument to drop (zero for the leftmost)
3522 * @return a method handle which drops arguments of the given types,
3523 * before calling the original method handle
3524 * @throws NullPointerException if the target is null,
3525 * or if the {@code valueTypes} list or any of its elements is null
3526 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3527 * or if {@code pos} is negative or greater than the arity of the target,
3528 * or if the new method handle's type would have too many parameters
3529 */
3530 public static
3531 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3532 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
3533 }
3534
3535 private static List<Class<?>> copyTypes(Object[] array) {
3536 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
3537 }
3538
3539 private static
3540 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3541 MethodType oldType = target.type(); // get NPE
3542 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3543 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3544 if (dropped == 0) return target;
3545 BoundMethodHandle result = target.rebind();
3546 LambdaForm lform = result.form;
3547 int insertFormArg = 1 + pos;
3548 for (Class<?> ptype : valueTypes) {
3549 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3550 }
3551 result = result.copyWith(newType, lform);
3552 return result;
3553 }
3554
3555 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3556 int dropped = valueTypes.size();
3557 MethodType.checkSlotCount(dropped);
3558 int outargs = oldType.parameterCount();
3559 int inargs = outargs + dropped;
3560 if (pos < 0 || pos > outargs)
3561 throw newIllegalArgumentException("no argument type to remove"
3562 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3563 );
3564 return dropped;
3565 }
3566
3567 /**
3568 * Produces a method handle which will discard some dummy arguments
3569 * before calling some other specified <i>target</i> method handle.
3570 * The type of the new method handle will be the same as the target's type,
3571 * except it will also include the dummy argument types,
3572 * at some given position.
3573 * <p>
3574 * The {@code pos} argument may range between zero and <i>N</i>,
3575 * where <i>N</i> is the arity of the target.
3576 * If {@code pos} is zero, the dummy arguments will precede
3577 * the target's real arguments; if {@code pos} is <i>N</i>
3578 * they will come after.
3579 * @apiNote
3580 * <blockquote><pre>{@code
3581 import static java.lang.invoke.MethodHandles.*;
3582 import static java.lang.invoke.MethodType.*;
3583 ...
3584 MethodHandle cat = lookup().findVirtual(String.class,
3585 "concat", methodType(String.class, String.class));
3586 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3587 MethodHandle d0 = dropArguments(cat, 0, String.class);
3588 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3589 MethodHandle d1 = dropArguments(cat, 1, String.class);
3590 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
3591 MethodHandle d2 = dropArguments(cat, 2, String.class);
3592 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
3593 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
3594 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
3595 * }</pre></blockquote>
3596 * <p>
3597 * This method is also equivalent to the following code:
3598 * <blockquote><pre>
3599 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
3600 * </pre></blockquote>
3601 * @param target the method handle to invoke after the arguments are dropped
3602 * @param valueTypes the type(s) of the argument(s) to drop
3603 * @param pos position of first argument to drop (zero for the leftmost)
3604 * @return a method handle which drops arguments of the given types,
3605 * before calling the original method handle
3606 * @throws NullPointerException if the target is null,
3607 * or if the {@code valueTypes} array or any of its elements is null
3608 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3609 * or if {@code pos} is negative or greater than the arity of the target,
3610 * or if the new method handle's type would have
3611 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3612 */
3613 public static
3614 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
3615 return dropArguments0(target, pos, copyTypes(valueTypes));
3616 }
3617
3618 // private version which allows caller some freedom with error handling
3619 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
3620 boolean nullOnFailure) {
3621 newTypes = copyTypes(newTypes.toArray());
3622 List<Class<?>> oldTypes = target.type().parameterList();
3623 int match = oldTypes.size();
3624 if (skip != 0) {
3625 if (skip < 0 || skip > match) {
3626 throw newIllegalArgumentException("illegal skip", skip, target);
3627 }
3628 oldTypes = oldTypes.subList(skip, match);
3629 match -= skip;
3630 }
3631 List<Class<?>> addTypes = newTypes;
3632 int add = addTypes.size();
3633 if (pos != 0) {
3634 if (pos < 0 || pos > add) {
3635 throw newIllegalArgumentException("illegal pos", pos, newTypes);
3636 }
3637 addTypes = addTypes.subList(pos, add);
3638 add -= pos;
3639 assert(addTypes.size() == add);
3640 }
3641 // Do not add types which already match the existing arguments.
3642 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
3643 if (nullOnFailure) {
3644 return null;
3645 }
3646 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
3647 }
3648 addTypes = addTypes.subList(match, add);
3649 add -= match;
3650 assert(addTypes.size() == add);
3651 // newTypes: ( P*[pos], M*[match], A*[add] )
3652 // target: ( S*[skip], M*[match] )
3653 MethodHandle adapter = target;
3654 if (add > 0) {
3655 adapter = dropArguments0(adapter, skip+ match, addTypes);
3656 }
3657 // adapter: (S*[skip], M*[match], A*[add] )
3658 if (pos > 0) {
3659 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
3660 }
3661 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
3662 return adapter;
3663 }
3664
3665 /**
3666 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
3667 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
3668 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
3669 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
3670 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
3671 * {@link #dropArguments(MethodHandle, int, Class[])}.
3672 * <p>
3673 * The resulting handle will have the same return type as the target handle.
3674 * <p>
3675 * In more formal terms, assume these two type lists:<ul>
3676 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
3677 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
3678 * {@code newTypes}.
3679 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
3680 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
3681 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
3682 * sub-list.
3683 * </ul>
3684 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
3685 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
3686 * {@link #dropArguments(MethodHandle, int, Class[])}.
3687 *
3688 * @apiNote
3689 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
3690 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
3691 * <blockquote><pre>{@code
3692 import static java.lang.invoke.MethodHandles.*;
3693 import static java.lang.invoke.MethodType.*;
3694 ...
3695 ...
3696 MethodHandle h0 = constant(boolean.class, true);
3697 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
3698 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
3699 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
3700 if (h1.type().parameterCount() < h2.type().parameterCount())
3701 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
3702 else
3703 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
3704 MethodHandle h3 = guardWithTest(h0, h1, h2);
3705 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
3706 * }</pre></blockquote>
3707 * @param target the method handle to adapt
3708 * @param skip number of targets parameters to disregard (they will be unchanged)
3709 * @param newTypes the list of types to match {@code target}'s parameter type list to
3710 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
3711 * @return a possibly adapted method handle
3712 * @throws NullPointerException if either argument is null
3713 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
3714 * or if {@code skip} is negative or greater than the arity of the target,
3715 * or if {@code pos} is negative or greater than the newTypes list size,
3716 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
3717 * {@code pos}.
3718 * @since 9
3719 */
3720 public static
3721 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
3722 Objects.requireNonNull(target);
3723 Objects.requireNonNull(newTypes);
3724 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
3725 }
3726
3727 /**
3728 * Adapts a target method handle by pre-processing
3729 * one or more of its arguments, each with its own unary filter function,
3730 * and then calling the target with each pre-processed argument
3731 * replaced by the result of its corresponding filter function.
3732 * <p>
3733 * The pre-processing is performed by one or more method handles,
3734 * specified in the elements of the {@code filters} array.
3735 * The first element of the filter array corresponds to the {@code pos}
3736 * argument of the target, and so on in sequence.
3737 * <p>
3738 * Null arguments in the array are treated as identity functions,
3739 * and the corresponding arguments left unchanged.
3740 * (If there are no non-null elements in the array, the original target is returned.)
3741 * Each filter is applied to the corresponding argument of the adapter.
3742 * <p>
3743 * If a filter {@code F} applies to the {@code N}th argument of
3744 * the target, then {@code F} must be a method handle which
3745 * takes exactly one argument. The type of {@code F}'s sole argument
3746 * replaces the corresponding argument type of the target
3747 * in the resulting adapted method handle.
3748 * The return type of {@code F} must be identical to the corresponding
3749 * parameter type of the target.
3750 * <p>
3751 * It is an error if there are elements of {@code filters}
3752 * (null or not)
3753 * which do not correspond to argument positions in the target.
3754 * <p><b>Example:</b>
3755 * <blockquote><pre>{@code
3756 import static java.lang.invoke.MethodHandles.*;
3757 import static java.lang.invoke.MethodType.*;
3758 ...
3759 MethodHandle cat = lookup().findVirtual(String.class,
3760 "concat", methodType(String.class, String.class));
3761 MethodHandle upcase = lookup().findVirtual(String.class,
3762 "toUpperCase", methodType(String.class));
3763 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3764 MethodHandle f0 = filterArguments(cat, 0, upcase);
3765 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
3766 MethodHandle f1 = filterArguments(cat, 1, upcase);
3767 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
3768 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
3769 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
3770 * }</pre></blockquote>
3771 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3772 * denotes the return type of both the {@code target} and resulting adapter.
3773 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
3774 * of the parameters and arguments that precede and follow the filter position
3775 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
3776 * values of the filtered parameters and arguments; they also represent the
3777 * return types of the {@code filter[i]} handles. The latter accept arguments
3778 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
3779 * the resulting adapter.
3780 * <blockquote><pre>{@code
3781 * T target(P... p, A[i]... a[i], B... b);
3782 * A[i] filter[i](V[i]);
3783 * T adapter(P... p, V[i]... v[i], B... b) {
3784 * return target(p..., filter[i](v[i])..., b...);
3785 * }
3786 * }</pre></blockquote>
3787 * <p>
3788 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3789 * variable-arity method handle}, even if the original target method handle was.
3790 *
3791 * @param target the method handle to invoke after arguments are filtered
3792 * @param pos the position of the first argument to filter
3793 * @param filters method handles to call initially on filtered arguments
3794 * @return method handle which incorporates the specified argument filtering logic
3795 * @throws NullPointerException if the target is null
3796 * or if the {@code filters} array is null
3797 * @throws IllegalArgumentException if a non-null element of {@code filters}
3798 * does not match a corresponding argument type of target as described above,
3799 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
3800 * or if the resulting method handle's type would have
3801 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3802 */
3803 public static
3804 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
3805 filterArgumentsCheckArity(target, pos, filters);
3806 MethodHandle adapter = target;
3807 int curPos = pos-1; // pre-incremented
3808 for (MethodHandle filter : filters) {
3809 curPos += 1;
3810 if (filter == null) continue; // ignore null elements of filters
3811 adapter = filterArgument(adapter, curPos, filter);
3812 }
3813 return adapter;
3814 }
3815
3816 /*non-public*/ static
3817 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
3818 filterArgumentChecks(target, pos, filter);
3819 MethodType targetType = target.type();
3820 MethodType filterType = filter.type();
3821 BoundMethodHandle result = target.rebind();
3822 Class<?> newParamType = filterType.parameterType(0);
3823 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
3824 MethodType newType = targetType.changeParameterType(pos, newParamType);
3825 result = result.copyWithExtendL(newType, lform, filter);
3826 return result;
3827 }
3828
3829 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
3830 MethodType targetType = target.type();
3831 int maxPos = targetType.parameterCount();
3832 if (pos + filters.length > maxPos)
3833 throw newIllegalArgumentException("too many filters");
3834 }
3835
3836 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3837 MethodType targetType = target.type();
3838 MethodType filterType = filter.type();
3839 if (filterType.parameterCount() != 1
3840 || filterType.returnType() != targetType.parameterType(pos))
3841 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3842 }
3843
3844 /**
3845 * Adapts a target method handle by pre-processing
3846 * a sub-sequence of its arguments with a filter (another method handle).
3847 * The pre-processed arguments are replaced by the result (if any) of the
3848 * filter function.
3849 * The target is then called on the modified (usually shortened) argument list.
3850 * <p>
3851 * If the filter returns a value, the target must accept that value as
3852 * its argument in position {@code pos}, preceded and/or followed by
3853 * any arguments not passed to the filter.
3854 * If the filter returns void, the target must accept all arguments
3855 * not passed to the filter.
3856 * No arguments are reordered, and a result returned from the filter
3857 * replaces (in order) the whole subsequence of arguments originally
3858 * passed to the adapter.
3859 * <p>
3860 * The argument types (if any) of the filter
3861 * replace zero or one argument types of the target, at position {@code pos},
3862 * in the resulting adapted method handle.
3863 * The return type of the filter (if any) must be identical to the
3864 * argument type of the target at position {@code pos}, and that target argument
3865 * is supplied by the return value of the filter.
3866 * <p>
3867 * In all cases, {@code pos} must be greater than or equal to zero, and
3868 * {@code pos} must also be less than or equal to the target's arity.
3869 * <p><b>Example:</b>
3870 * <blockquote><pre>{@code
3871 import static java.lang.invoke.MethodHandles.*;
3872 import static java.lang.invoke.MethodType.*;
3873 ...
3874 MethodHandle deepToString = publicLookup()
3875 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
3876
3877 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
3878 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
3879
3880 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
3881 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
3882
3883 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
3884 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
3885 assertEquals("[top, [up, down], strange]",
3886 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
3887
3888 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
3889 assertEquals("[top, [up, down], [strange]]",
3890 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
3891
3892 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
3893 assertEquals("[top, [[up, down, strange], charm], bottom]",
3894 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
3895 * }</pre></blockquote>
3896 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3897 * represents the return type of the {@code target} and resulting adapter.
3898 * {@code V}/{@code v} stand for the return type and value of the
3899 * {@code filter}, which are also found in the signature and arguments of
3900 * the {@code target}, respectively, unless {@code V} is {@code void}.
3901 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
3902 * and values preceding and following the collection position, {@code pos},
3903 * in the {@code target}'s signature. They also turn up in the resulting
3904 * adapter's signature and arguments, where they surround
3905 * {@code B}/{@code b}, which represent the parameter types and arguments
3906 * to the {@code filter} (if any).
3907 * <blockquote><pre>{@code
3908 * T target(A...,V,C...);
3909 * V filter(B...);
3910 * T adapter(A... a,B... b,C... c) {
3911 * V v = filter(b...);
3912 * return target(a...,v,c...);
3913 * }
3914 * // and if the filter has no arguments:
3915 * T target2(A...,V,C...);
3916 * V filter2();
3917 * T adapter2(A... a,C... c) {
3918 * V v = filter2();
3919 * return target2(a...,v,c...);
3920 * }
3921 * // and if the filter has a void return:
3922 * T target3(A...,C...);
3923 * void filter3(B...);
3924 * T adapter3(A... a,B... b,C... c) {
3925 * filter3(b...);
3926 * return target3(a...,c...);
3927 * }
3928 * }</pre></blockquote>
3929 * <p>
3930 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
3931 * one which first "folds" the affected arguments, and then drops them, in separate
3932 * steps as follows:
3933 * <blockquote><pre>{@code
3934 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
3935 * mh = MethodHandles.foldArguments(mh, coll); //step 1
3936 * }</pre></blockquote>
3937 * If the target method handle consumes no arguments besides than the result
3938 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
3939 * is equivalent to {@code filterReturnValue(coll, mh)}.
3940 * If the filter method handle {@code coll} consumes one argument and produces
3941 * a non-void result, then {@code collectArguments(mh, N, coll)}
3942 * is equivalent to {@code filterArguments(mh, N, coll)}.
3943 * Other equivalences are possible but would require argument permutation.
3944 * <p>
3945 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3946 * variable-arity method handle}, even if the original target method handle was.
3947 *
3948 * @param target the method handle to invoke after filtering the subsequence of arguments
3949 * @param pos the position of the first adapter argument to pass to the filter,
3950 * and/or the target argument which receives the result of the filter
3951 * @param filter method handle to call on the subsequence of arguments
3952 * @return method handle which incorporates the specified argument subsequence filtering logic
3953 * @throws NullPointerException if either argument is null
3954 * @throws IllegalArgumentException if the return type of {@code filter}
3955 * is non-void and is not the same as the {@code pos} argument of the target,
3956 * or if {@code pos} is not between 0 and the target's arity, inclusive,
3957 * or if the resulting method handle's type would have
3958 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3959 * @see MethodHandles#foldArguments
3960 * @see MethodHandles#filterArguments
3961 * @see MethodHandles#filterReturnValue
3962 */
3963 public static
3964 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
3965 MethodType newType = collectArgumentsChecks(target, pos, filter);
3966 MethodType collectorType = filter.type();
3967 BoundMethodHandle result = target.rebind();
3968 LambdaForm lform;
3969 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
3970 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
3971 if (lform != null) {
3972 return result.copyWith(newType, lform);
3973 }
3974 }
3975 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
3976 return result.copyWithExtendL(newType, lform, filter);
3977 }
3978
3979 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3980 MethodType targetType = target.type();
3981 MethodType filterType = filter.type();
3982 Class<?> rtype = filterType.returnType();
3983 List<Class<?>> filterArgs = filterType.parameterList();
3984 if (rtype == void.class) {
3985 return targetType.insertParameterTypes(pos, filterArgs);
3986 }
3987 if (rtype != targetType.parameterType(pos)) {
3988 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3989 }
3990 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
3991 }
3992
3993 /**
3994 * Adapts a target method handle by post-processing
3995 * its return value (if any) with a filter (another method handle).
3996 * The result of the filter is returned from the adapter.
3997 * <p>
3998 * If the target returns a value, the filter must accept that value as
3999 * its only argument.
4000 * If the target returns void, the filter must accept no arguments.
4001 * <p>
4002 * The return type of the filter
4003 * replaces the return type of the target
4004 * in the resulting adapted method handle.
4005 * The argument type of the filter (if any) must be identical to the
4006 * return type of the target.
4007 * <p><b>Example:</b>
4008 * <blockquote><pre>{@code
4009 import static java.lang.invoke.MethodHandles.*;
4010 import static java.lang.invoke.MethodType.*;
4011 ...
4012 MethodHandle cat = lookup().findVirtual(String.class,
4013 "concat", methodType(String.class, String.class));
4014 MethodHandle length = lookup().findVirtual(String.class,
4015 "length", methodType(int.class));
4016 System.out.println((String) cat.invokeExact("x", "y")); // xy
4017 MethodHandle f0 = filterReturnValue(cat, length);
4018 System.out.println((int) f0.invokeExact("x", "y")); // 2
4019 * }</pre></blockquote>
4020 * <p>Here is pseudocode for the resulting adapter. In the code,
4021 * {@code T}/{@code t} represent the result type and value of the
4022 * {@code target}; {@code V}, the result type of the {@code filter}; and
4023 * {@code A}/{@code a}, the types and values of the parameters and arguments
4024 * of the {@code target} as well as the resulting adapter.
4025 * <blockquote><pre>{@code
4026 * T target(A...);
4027 * V filter(T);
4028 * V adapter(A... a) {
4029 * T t = target(a...);
4030 * return filter(t);
4031 * }
4032 * // and if the target has a void return:
4033 * void target2(A...);
4034 * V filter2();
4035 * V adapter2(A... a) {
4036 * target2(a...);
4037 * return filter2();
4038 * }
4039 * // and if the filter has a void return:
4040 * T target3(A...);
4041 * void filter3(V);
4042 * void adapter3(A... a) {
4043 * T t = target3(a...);
4044 * filter3(t);
4045 * }
4046 * }</pre></blockquote>
4047 * <p>
4048 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4049 * variable-arity method handle}, even if the original target method handle was.
4050 * @param target the method handle to invoke before filtering the return value
4051 * @param filter method handle to call on the return value
4052 * @return method handle which incorporates the specified return value filtering logic
4053 * @throws NullPointerException if either argument is null
4054 * @throws IllegalArgumentException if the argument list of {@code filter}
4055 * does not match the return type of target as described above
4056 */
4057 public static
4058 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
4059 MethodType targetType = target.type();
4060 MethodType filterType = filter.type();
4061 filterReturnValueChecks(targetType, filterType);
4062 BoundMethodHandle result = target.rebind();
4063 BasicType rtype = BasicType.basicType(filterType.returnType());
4064 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
4065 MethodType newType = targetType.changeReturnType(filterType.returnType());
4066 result = result.copyWithExtendL(newType, lform, filter);
4067 return result;
4068 }
4069
4070 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
4071 Class<?> rtype = targetType.returnType();
4072 int filterValues = filterType.parameterCount();
4073 if (filterValues == 0
4074 ? (rtype != void.class)
4075 : (rtype != filterType.parameterType(0) || filterValues != 1))
4076 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4077 }
4078
4079 /**
4080 * Adapts a target method handle by pre-processing
4081 * some of its arguments, and then calling the target with
4082 * the result of the pre-processing, inserted into the original
4083 * sequence of arguments.
4084 * <p>
4085 * The pre-processing is performed by {@code combiner}, a second method handle.
4086 * Of the arguments passed to the adapter, the first {@code N} arguments
4087 * are copied to the combiner, which is then called.
4088 * (Here, {@code N} is defined as the parameter count of the combiner.)
4089 * After this, control passes to the target, with any result
4090 * from the combiner inserted before the original {@code N} incoming
4091 * arguments.
4092 * <p>
4093 * If the combiner returns a value, the first parameter type of the target
4094 * must be identical with the return type of the combiner, and the next
4095 * {@code N} parameter types of the target must exactly match the parameters
4096 * of the combiner.
4097 * <p>
4098 * If the combiner has a void return, no result will be inserted,
4099 * and the first {@code N} parameter types of the target
4100 * must exactly match the parameters of the combiner.
4101 * <p>
4102 * The resulting adapter is the same type as the target, except that the
4103 * first parameter type is dropped,
4104 * if it corresponds to the result of the combiner.
4105 * <p>
4106 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
4107 * that either the combiner or the target does not wish to receive.
4108 * If some of the incoming arguments are destined only for the combiner,
4109 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
4110 * arguments will not need to be live on the stack on entry to the
4111 * target.)
4112 * <p><b>Example:</b>
4113 * <blockquote><pre>{@code
4114 import static java.lang.invoke.MethodHandles.*;
4115 import static java.lang.invoke.MethodType.*;
4116 ...
4117 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4118 "println", methodType(void.class, String.class))
4119 .bindTo(System.out);
4120 MethodHandle cat = lookup().findVirtual(String.class,
4121 "concat", methodType(String.class, String.class));
4122 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4123 MethodHandle catTrace = foldArguments(cat, trace);
4124 // also prints "boo":
4125 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4126 * }</pre></blockquote>
4127 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4128 * represents the result type of the {@code target} and resulting adapter.
4129 * {@code V}/{@code v} represent the type and value of the parameter and argument
4130 * of {@code target} that precedes the folding position; {@code V} also is
4131 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4132 * types and values of the {@code N} parameters and arguments at the folding
4133 * position. {@code B}/{@code b} represent the types and values of the
4134 * {@code target} parameters and arguments that follow the folded parameters
4135 * and arguments.
4136 * <blockquote><pre>{@code
4137 * // there are N arguments in A...
4138 * T target(V, A[N]..., B...);
4139 * V combiner(A...);
4140 * T adapter(A... a, B... b) {
4141 * V v = combiner(a...);
4142 * return target(v, a..., b...);
4143 * }
4144 * // and if the combiner has a void return:
4145 * T target2(A[N]..., B...);
4146 * void combiner2(A...);
4147 * T adapter2(A... a, B... b) {
4148 * combiner2(a...);
4149 * return target2(a..., b...);
4150 * }
4151 * }</pre></blockquote>
4152 * <p>
4153 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4154 * variable-arity method handle}, even if the original target method handle was.
4155 * @param target the method handle to invoke after arguments are combined
4156 * @param combiner method handle to call initially on the incoming arguments
4157 * @return method handle which incorporates the specified argument folding logic
4158 * @throws NullPointerException if either argument is null
4159 * @throws IllegalArgumentException if {@code combiner}'s return type
4160 * is non-void and not the same as the first argument type of
4161 * the target, or if the initial {@code N} argument types
4162 * of the target
4163 * (skipping one matching the {@code combiner}'s return type)
4164 * are not identical with the argument types of {@code combiner}
4165 */
4166 public static
4167 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
4168 return foldArguments(target, 0, combiner);
4169 }
4170
4171 /**
4172 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4173 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4174 * before the folded arguments.
4175 * <p>
4176 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4177 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4178 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4179 * 0.
4180 *
4181 * @apiNote Example:
4182 * <blockquote><pre>{@code
4183 import static java.lang.invoke.MethodHandles.*;
4184 import static java.lang.invoke.MethodType.*;
4185 ...
4186 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4187 "println", methodType(void.class, String.class))
4188 .bindTo(System.out);
4189 MethodHandle cat = lookup().findVirtual(String.class,
4190 "concat", methodType(String.class, String.class));
4191 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4192 MethodHandle catTrace = foldArguments(cat, 1, trace);
4193 // also prints "jum":
4194 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4195 * }</pre></blockquote>
4196 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4197 * represents the result type of the {@code target} and resulting adapter.
4198 * {@code V}/{@code v} represent the type and value of the parameter and argument
4199 * of {@code target} that precedes the folding position; {@code V} also is
4200 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4201 * types and values of the {@code N} parameters and arguments at the folding
4202 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4203 * and values of the {@code target} parameters and arguments that precede and
4204 * follow the folded parameters and arguments starting at {@code pos},
4205 * respectively.
4206 * <blockquote><pre>{@code
4207 * // there are N arguments in A...
4208 * T target(Z..., V, A[N]..., B...);
4209 * V combiner(A...);
4210 * T adapter(Z... z, A... a, B... b) {
4211 * V v = combiner(a...);
4212 * return target(z..., v, a..., b...);
4213 * }
4214 * // and if the combiner has a void return:
4215 * T target2(Z..., A[N]..., B...);
4216 * void combiner2(A...);
4217 * T adapter2(Z... z, A... a, B... b) {
4218 * combiner2(a...);
4219 * return target2(z..., a..., b...);
4220 * }
4221 * }</pre></blockquote>
4222 * <p>
4223 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4224 * variable-arity method handle}, even if the original target method handle was.
4225 *
4226 * @param target the method handle to invoke after arguments are combined
4227 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4228 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4229 * @param combiner method handle to call initially on the incoming arguments
4230 * @return method handle which incorporates the specified argument folding logic
4231 * @throws NullPointerException if either argument is null
4232 * @throws IllegalArgumentException if either of the following two conditions holds:
4233 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4234 * {@code pos} of the target signature;
4235 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
4236 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
4237 *
4238 * @see #foldArguments(MethodHandle, MethodHandle)
4239 * @since 9
4240 */
4241 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4242 MethodType targetType = target.type();
4243 MethodType combinerType = combiner.type();
4244 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4245 BoundMethodHandle result = target.rebind();
4246 boolean dropResult = rtype == void.class;
4247 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4248 MethodType newType = targetType;
4249 if (!dropResult) {
4250 newType = newType.dropParameterTypes(pos, pos + 1);
4251 }
4252 result = result.copyWithExtendL(newType, lform, combiner);
4253 return result;
4254 }
4255
4256 /**
4257 * As {@see foldArguments(MethodHandle, int, MethodHandle)}, but with the
4258 * added capability of selecting the arguments from the targets parameters
4259 * to call the combiner with. This allows us to avoid some simple cases of
4260 * permutations and padding the combiner with dropArguments to select the
4261 * right argument, which may ultimately produce fewer intermediaries.
4262 */
4263 static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner, int ... argPositions) {
4264 MethodType targetType = target.type();
4265 MethodType combinerType = combiner.type();
4266 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType, argPositions);
4267 BoundMethodHandle result = target.rebind();
4268 boolean dropResult = rtype == void.class;
4269 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType(), argPositions);
4270 MethodType newType = targetType;
4271 if (!dropResult) {
4272 newType = newType.dropParameterTypes(pos, pos + 1);
4273 }
4274 result = result.copyWithExtendL(newType, lform, combiner);
4275 return result;
4276 }
4277
4278 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
4279 int foldArgs = combinerType.parameterCount();
4280 Class<?> rtype = combinerType.returnType();
4281 int foldVals = rtype == void.class ? 0 : 1;
4282 int afterInsertPos = foldPos + foldVals;
4283 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
4284 if (ok) {
4285 for (int i = 0; i < foldArgs; i++) {
4286 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
4287 ok = false;
4288 break;
4289 }
4290 }
4291 }
4292 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
4293 ok = false;
4294 if (!ok)
4295 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4296 return rtype;
4297 }
4298
4299 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType, int ... argPos) {
4300 int foldArgs = combinerType.parameterCount();
4301 if (argPos.length != foldArgs) {
4302 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
4303 }
4304 Class<?> rtype = combinerType.returnType();
4305 int foldVals = rtype == void.class ? 0 : 1;
4306 boolean ok = true;
4307 for (int i = 0; i < foldArgs; i++) {
4308 int arg = argPos[i];
4309 if (arg < 0 || arg > targetType.parameterCount()) {
4310 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
4311 }
4312 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
4313 throw newIllegalArgumentException("target argument type at position " + arg
4314 + " must match combiner argument type at index " + i + ": " + targetType
4315 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
4316 }
4317 }
4318 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) {
4319 ok = false;
4320 }
4321 if (!ok)
4322 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4323 return rtype;
4324 }
4325
4326 /**
4327 * Makes a method handle which adapts a target method handle,
4328 * by guarding it with a test, a boolean-valued method handle.
4329 * If the guard fails, a fallback handle is called instead.
4330 * All three method handles must have the same corresponding
4331 * argument and return types, except that the return type
4332 * of the test must be boolean, and the test is allowed
4333 * to have fewer arguments than the other two method handles.
4334 * <p>
4335 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4336 * represents the uniform result type of the three involved handles;
4337 * {@code A}/{@code a}, the types and values of the {@code target}
4338 * parameters and arguments that are consumed by the {@code test}; and
4339 * {@code B}/{@code b}, those types and values of the {@code target}
4340 * parameters and arguments that are not consumed by the {@code test}.
4341 * <blockquote><pre>{@code
4342 * boolean test(A...);
4343 * T target(A...,B...);
4344 * T fallback(A...,B...);
4345 * T adapter(A... a,B... b) {
4346 * if (test(a...))
4347 * return target(a..., b...);
4348 * else
4349 * return fallback(a..., b...);
4350 * }
4351 * }</pre></blockquote>
4352 * Note that the test arguments ({@code a...} in the pseudocode) cannot
4353 * be modified by execution of the test, and so are passed unchanged
4354 * from the caller to the target or fallback as appropriate.
4355 * @param test method handle used for test, must return boolean
4356 * @param target method handle to call if test passes
4357 * @param fallback method handle to call if test fails
4358 * @return method handle which incorporates the specified if/then/else logic
4359 * @throws NullPointerException if any argument is null
4360 * @throws IllegalArgumentException if {@code test} does not return boolean,
4361 * or if all three method types do not match (with the return
4362 * type of {@code test} changed to match that of the target).
4363 */
4364 public static
4365 MethodHandle guardWithTest(MethodHandle test,
4366 MethodHandle target,
4367 MethodHandle fallback) {
4368 MethodType gtype = test.type();
4369 MethodType ttype = target.type();
4370 MethodType ftype = fallback.type();
4371 if (!ttype.equals(ftype))
4372 throw misMatchedTypes("target and fallback types", ttype, ftype);
4373 if (gtype.returnType() != boolean.class)
4374 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
4375 List<Class<?>> targs = ttype.parameterList();
4376 test = dropArgumentsToMatch(test, 0, targs, 0, true);
4377 if (test == null) {
4378 throw misMatchedTypes("target and test types", ttype, gtype);
4379 }
4380 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
4381 }
4382
4383 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
4384 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
4385 }
4386
4387 /**
4388 * Makes a method handle which adapts a target method handle,
4389 * by running it inside an exception handler.
4390 * If the target returns normally, the adapter returns that value.
4391 * If an exception matching the specified type is thrown, the fallback
4392 * handle is called instead on the exception, plus the original arguments.
4393 * <p>
4394 * The target and handler must have the same corresponding
4395 * argument and return types, except that handler may omit trailing arguments
4396 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
4397 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
4398 * <p>
4399 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4400 * represents the return type of the {@code target} and {@code handler},
4401 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
4402 * the types and values of arguments to the resulting handle consumed by
4403 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
4404 * resulting handle discarded by {@code handler}.
4405 * <blockquote><pre>{@code
4406 * T target(A..., B...);
4407 * T handler(ExType, A...);
4408 * T adapter(A... a, B... b) {
4409 * try {
4410 * return target(a..., b...);
4411 * } catch (ExType ex) {
4412 * return handler(ex, a...);
4413 * }
4414 * }
4415 * }</pre></blockquote>
4416 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4417 * be modified by execution of the target, and so are passed unchanged
4418 * from the caller to the handler, if the handler is invoked.
4419 * <p>
4420 * The target and handler must return the same type, even if the handler
4421 * always throws. (This might happen, for instance, because the handler
4422 * is simulating a {@code finally} clause).
4423 * To create such a throwing handler, compose the handler creation logic
4424 * with {@link #throwException throwException},
4425 * in order to create a method handle of the correct return type.
4426 * @param target method handle to call
4427 * @param exType the type of exception which the handler will catch
4428 * @param handler method handle to call if a matching exception is thrown
4429 * @return method handle which incorporates the specified try/catch logic
4430 * @throws NullPointerException if any argument is null
4431 * @throws IllegalArgumentException if {@code handler} does not accept
4432 * the given exception type, or if the method handle types do
4433 * not match in their return types and their
4434 * corresponding parameters
4435 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4436 */
4437 public static
4438 MethodHandle catchException(MethodHandle target,
4439 Class<? extends Throwable> exType,
4440 MethodHandle handler) {
4441 MethodType ttype = target.type();
4442 MethodType htype = handler.type();
4443 if (!Throwable.class.isAssignableFrom(exType))
4444 throw new ClassCastException(exType.getName());
4445 if (htype.parameterCount() < 1 ||
4446 !htype.parameterType(0).isAssignableFrom(exType))
4447 throw newIllegalArgumentException("handler does not accept exception type "+exType);
4448 if (htype.returnType() != ttype.returnType())
4449 throw misMatchedTypes("target and handler return types", ttype, htype);
4450 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4451 if (handler == null) {
4452 throw misMatchedTypes("target and handler types", ttype, htype);
4453 }
4454 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4455 }
4456
4457 /**
4458 * Produces a method handle which will throw exceptions of the given {@code exType}.
4459 * The method handle will accept a single argument of {@code exType},
4460 * and immediately throw it as an exception.
4461 * The method type will nominally specify a return of {@code returnType}.
4462 * The return type may be anything convenient: It doesn't matter to the
4463 * method handle's behavior, since it will never return normally.
4464 * @param returnType the return type of the desired method handle
4465 * @param exType the parameter type of the desired method handle
4466 * @return method handle which can throw the given exceptions
4467 * @throws NullPointerException if either argument is null
4468 */
4469 public static
4470 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4471 if (!Throwable.class.isAssignableFrom(exType))
4472 throw new ClassCastException(exType.getName());
4473 return MethodHandleImpl.throwException(methodType(returnType, exType));
4474 }
4475
4476 /**
4477 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4478 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4479 * delivers the loop's result, which is the return value of the resulting handle.
4480 * <p>
4481 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
4482 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4483 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4484 * terms of method handles, each clause will specify up to four independent actions:<ul>
4485 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
4486 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
4487 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
4488 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4489 * </ul>
4490 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
4491 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
4492 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
4493 * <p>
4494 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4495 * this case. See below for a detailed description.
4496 * <p>
4497 * <em>Parameters optional everywhere:</em>
4498 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
4499 * As an exception, the init functions cannot take any {@code v} parameters,
4500 * because those values are not yet computed when the init functions are executed.
4501 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
4502 * In fact, any clause function may take no arguments at all.
4503 * <p>
4504 * <em>Loop parameters:</em>
4505 * A clause function may take all the iteration variable values it is entitled to, in which case
4506 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
4507 * with their types and values notated as {@code (A...)} and {@code (a...)}.
4508 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
4509 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
4510 * init function is automatically a loop parameter {@code a}.)
4511 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
4512 * These loop parameters act as loop-invariant values visible across the whole loop.
4513 * <p>
4514 * <em>Parameters visible everywhere:</em>
4515 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
4516 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
4517 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
4518 * Most clause functions will not need all of this information, but they will be formally connected to it
4519 * as if by {@link #dropArguments}.
4520 * <a id="astar"></a>
4521 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
4522 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
4523 * In that notation, the general form of an init function parameter list
4524 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
4525 * <p>
4526 * <em>Checking clause structure:</em>
4527 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4528 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4529 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
4530 * met by the inputs to the loop combinator.
4531 * <p>
4532 * <em>Effectively identical sequences:</em>
4533 * <a id="effid"></a>
4534 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
4535 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
4536 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
4537 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
4538 * that longest list.
4539 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
4540 * and the same is true if more sequences of the form {@code (V... A*)} are added.
4541 * <p>
4542 * <em>Step 0: Determine clause structure.</em><ol type="a">
4543 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
4544 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4545 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4546 * four. Padding takes place by appending elements to the array.
4547 * <li>Clauses with all {@code null}s are disregarded.
4548 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4549 * </ol>
4550 * <p>
4551 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
4552 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
4553 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
4554 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
4555 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
4556 * iteration variable type.
4557 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
4558 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
4559 * </ol>
4560 * <p>
4561 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
4562 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
4563 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
4564 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
4565 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
4566 * (These types will checked in step 2, along with all the clause function types.)
4567 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
4568 * <li>All of the collected parameter lists must be effectively identical.
4569 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
4570 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
4571 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
4572 * the "internal parameter list".
4573 * </ul>
4574 * <p>
4575 * <em>Step 1C: Determine loop return type.</em><ol type="a">
4576 * <li>Examine fini function return types, disregarding omitted fini functions.
4577 * <li>If there are no fini functions, the loop return type is {@code void}.
4578 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
4579 * type.
4580 * </ol>
4581 * <p>
4582 * <em>Step 1D: Check other types.</em><ol type="a">
4583 * <li>There must be at least one non-omitted pred function.
4584 * <li>Every non-omitted pred function must have a {@code boolean} return type.
4585 * </ol>
4586 * <p>
4587 * <em>Step 2: Determine parameter lists.</em><ol type="a">
4588 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
4589 * <li>The parameter list for init functions will be adjusted to the external parameter list.
4590 * (Note that their parameter lists are already effectively identical to this list.)
4591 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
4592 * effectively identical to the internal parameter list {@code (V... A...)}.
4593 * </ol>
4594 * <p>
4595 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
4596 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
4597 * type.
4598 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
4599 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
4600 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
4601 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
4602 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
4603 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
4604 * loop return type.
4605 * </ol>
4606 * <p>
4607 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
4608 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
4609 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
4610 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
4611 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
4612 * pad out the end of the list.
4613 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
4614 * </ol>
4615 * <p>
4616 * <em>Final observations.</em><ol type="a">
4617 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
4618 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
4619 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
4620 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
4621 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
4622 * <li>Each pair of init and step functions agrees in their return type {@code V}.
4623 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
4624 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
4625 * </ol>
4626 * <p>
4627 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
4628 * <ul>
4629 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
4630 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
4631 * (Only one {@code Pn} has to be non-{@code null}.)
4632 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
4633 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
4634 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
4635 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
4636 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
4637 * the resulting loop handle's parameter types {@code (A...)}.
4638 * </ul>
4639 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
4640 * which is natural if most of the loop computation happens in the steps. For some loops,
4641 * the burden of computation might be heaviest in the pred functions, and so the pred functions
4642 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
4643 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
4644 * where the init functions will need the extra parameters. For such reasons, the rules for
4645 * determining these parameters are as symmetric as possible, across all clause parts.
4646 * In general, the loop parameters function as common invariant values across the whole
4647 * loop, while the iteration variables function as common variant values, or (if there is
4648 * no step function) as internal loop invariant temporaries.
4649 * <p>
4650 * <em>Loop execution.</em><ol type="a">
4651 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
4652 * every clause function. These locals are loop invariant.
4653 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
4654 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
4655 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
4656 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
4657 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
4658 * (in argument order).
4659 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
4660 * returns {@code false}.
4661 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
4662 * sequence {@code (v...)} of loop variables.
4663 * The updated value is immediately visible to all subsequent function calls.
4664 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
4665 * (of type {@code R}) is returned from the loop as a whole.
4666 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
4667 * except by throwing an exception.
4668 * </ol>
4669 * <p>
4670 * <em>Usage tips.</em>
4671 * <ul>
4672 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
4673 * sometimes a step function only needs to observe the current value of its own variable.
4674 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
4675 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
4676 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
4677 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
4678 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
4679 * <li>If some of the clause functions are virtual methods on an instance, the instance
4680 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
4681 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
4682 * will be the first iteration variable value, and it will be easy to use virtual
4683 * methods as clause parts, since all of them will take a leading instance reference matching that value.
4684 * </ul>
4685 * <p>
4686 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
4687 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
4688 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
4689 * <blockquote><pre>{@code
4690 * V... init...(A...);
4691 * boolean pred...(V..., A...);
4692 * V... step...(V..., A...);
4693 * R fini...(V..., A...);
4694 * R loop(A... a) {
4695 * V... v... = init...(a...);
4696 * for (;;) {
4697 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
4698 * v = s(v..., a...);
4699 * if (!p(v..., a...)) {
4700 * return f(v..., a...);
4701 * }
4702 * }
4703 * }
4704 * }
4705 * }</pre></blockquote>
4706 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
4707 * to their full length, even though individual clause functions may neglect to take them all.
4708 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
4709 *
4710 * @apiNote Example:
4711 * <blockquote><pre>{@code
4712 * // iterative implementation of the factorial function as a loop handle
4713 * static int one(int k) { return 1; }
4714 * static int inc(int i, int acc, int k) { return i + 1; }
4715 * static int mult(int i, int acc, int k) { return i * acc; }
4716 * static boolean pred(int i, int acc, int k) { return i < k; }
4717 * static int fin(int i, int acc, int k) { return acc; }
4718 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4719 * // null initializer for counter, should initialize to 0
4720 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4721 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4722 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4723 * assertEquals(120, loop.invoke(5));
4724 * }</pre></blockquote>
4725 * The same example, dropping arguments and using combinators:
4726 * <blockquote><pre>{@code
4727 * // simplified implementation of the factorial function as a loop handle
4728 * static int inc(int i) { return i + 1; } // drop acc, k
4729 * static int mult(int i, int acc) { return i * acc; } //drop k
4730 * static boolean cmp(int i, int k) { return i < k; }
4731 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
4732 * // null initializer for counter, should initialize to 0
4733 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4734 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
4735 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
4736 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4737 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4738 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4739 * assertEquals(720, loop.invoke(6));
4740 * }</pre></blockquote>
4741 * A similar example, using a helper object to hold a loop parameter:
4742 * <blockquote><pre>{@code
4743 * // instance-based implementation of the factorial function as a loop handle
4744 * static class FacLoop {
4745 * final int k;
4746 * FacLoop(int k) { this.k = k; }
4747 * int inc(int i) { return i + 1; }
4748 * int mult(int i, int acc) { return i * acc; }
4749 * boolean pred(int i) { return i < k; }
4750 * int fin(int i, int acc) { return acc; }
4751 * }
4752 * // assume MH_FacLoop is a handle to the constructor
4753 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4754 * // null initializer for counter, should initialize to 0
4755 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4756 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
4757 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4758 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4759 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
4760 * assertEquals(5040, loop.invoke(7));
4761 * }</pre></blockquote>
4762 *
4763 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
4764 *
4765 * @return a method handle embodying the looping behavior as defined by the arguments.
4766 *
4767 * @throws IllegalArgumentException in case any of the constraints described above is violated.
4768 *
4769 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
4770 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4771 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
4772 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
4773 * @since 9
4774 */
4775 public static MethodHandle loop(MethodHandle[]... clauses) {
4776 // Step 0: determine clause structure.
4777 loopChecks0(clauses);
4778
4779 List<MethodHandle> init = new ArrayList<>();
4780 List<MethodHandle> step = new ArrayList<>();
4781 List<MethodHandle> pred = new ArrayList<>();
4782 List<MethodHandle> fini = new ArrayList<>();
4783
4784 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
4785 init.add(clause[0]); // all clauses have at least length 1
4786 step.add(clause.length <= 1 ? null : clause[1]);
4787 pred.add(clause.length <= 2 ? null : clause[2]);
4788 fini.add(clause.length <= 3 ? null : clause[3]);
4789 });
4790
4791 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
4792 final int nclauses = init.size();
4793
4794 // Step 1A: determine iteration variables (V...).
4795 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
4796 for (int i = 0; i < nclauses; ++i) {
4797 MethodHandle in = init.get(i);
4798 MethodHandle st = step.get(i);
4799 if (in == null && st == null) {
4800 iterationVariableTypes.add(void.class);
4801 } else if (in != null && st != null) {
4802 loopChecks1a(i, in, st);
4803 iterationVariableTypes.add(in.type().returnType());
4804 } else {
4805 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
4806 }
4807 }
4808 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
4809 collect(Collectors.toList());
4810
4811 // Step 1B: determine loop parameters (A...).
4812 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
4813 loopChecks1b(init, commonSuffix);
4814
4815 // Step 1C: determine loop return type.
4816 // Step 1D: check other types.
4817 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
4818 map(MethodType::returnType).findFirst().orElse(void.class);
4819 loopChecks1cd(pred, fini, loopReturnType);
4820
4821 // Step 2: determine parameter lists.
4822 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
4823 commonParameterSequence.addAll(commonSuffix);
4824 loopChecks2(step, pred, fini, commonParameterSequence);
4825
4826 // Step 3: fill in omitted functions.
4827 for (int i = 0; i < nclauses; ++i) {
4828 Class<?> t = iterationVariableTypes.get(i);
4829 if (init.get(i) == null) {
4830 init.set(i, empty(methodType(t, commonSuffix)));
4831 }
4832 if (step.get(i) == null) {
4833 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
4834 }
4835 if (pred.get(i) == null) {
4836 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
4837 }
4838 if (fini.get(i) == null) {
4839 fini.set(i, empty(methodType(t, commonParameterSequence)));
4840 }
4841 }
4842
4843 // Step 4: fill in missing parameter types.
4844 // Also convert all handles to fixed-arity handles.
4845 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
4846 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
4847 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
4848 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
4849
4850 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
4851 allMatch(pl -> pl.equals(commonSuffix));
4852 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
4853 allMatch(pl -> pl.equals(commonParameterSequence));
4854
4855 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
4856 }
4857
4858 private static void loopChecks0(MethodHandle[][] clauses) {
4859 if (clauses == null || clauses.length == 0) {
4860 throw newIllegalArgumentException("null or no clauses passed");
4861 }
4862 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
4863 throw newIllegalArgumentException("null clauses are not allowed");
4864 }
4865 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
4866 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
4867 }
4868 }
4869
4870 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
4871 if (in.type().returnType() != st.type().returnType()) {
4872 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
4873 st.type().returnType());
4874 }
4875 }
4876
4877 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
4878 final List<Class<?>> empty = List.of();
4879 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
4880 // take only those that can contribute to a common suffix because they are longer than the prefix
4881 map(MethodHandle::type).
4882 filter(t -> t.parameterCount() > skipSize).
4883 map(MethodType::parameterList).
4884 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4885 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
4886 }
4887
4888 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
4889 final List<Class<?>> empty = List.of();
4890 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4891 }
4892
4893 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
4894 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
4895 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
4896 return longestParameterList(Arrays.asList(longest1, longest2));
4897 }
4898
4899 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
4900 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
4901 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
4902 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
4903 " (common suffix: " + commonSuffix + ")");
4904 }
4905 }
4906
4907 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
4908 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4909 anyMatch(t -> t != loopReturnType)) {
4910 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
4911 loopReturnType + ")");
4912 }
4913
4914 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
4915 throw newIllegalArgumentException("no predicate found", pred);
4916 }
4917 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4918 anyMatch(t -> t != boolean.class)) {
4919 throw newIllegalArgumentException("predicates must have boolean return type", pred);
4920 }
4921 }
4922
4923 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
4924 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
4925 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
4926 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
4927 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
4928 }
4929 }
4930
4931 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
4932 return hs.stream().map(h -> {
4933 int pc = h.type().parameterCount();
4934 int tpsize = targetParams.size();
4935 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
4936 }).collect(Collectors.toList());
4937 }
4938
4939 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
4940 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
4941 }
4942
4943 /**
4944 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
4945 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
4946 * <p>
4947 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
4948 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
4949 * evaluates to {@code true}).
4950 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
4951 * <p>
4952 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
4953 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
4954 * and updated with the value returned from its invocation. The result of loop execution will be
4955 * the final value of the additional loop-local variable (if present).
4956 * <p>
4957 * The following rules hold for these argument handles:<ul>
4958 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
4959 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
4960 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
4961 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
4962 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
4963 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
4964 * It will constrain the parameter lists of the other loop parts.
4965 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
4966 * list {@code (A...)} is called the <em>external parameter list</em>.
4967 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
4968 * additional state variable of the loop.
4969 * The body must both accept and return a value of this type {@code V}.
4970 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
4971 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
4972 * <a href="MethodHandles.html#effid">effectively identical</a>
4973 * to the external parameter list {@code (A...)}.
4974 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
4975 * {@linkplain #empty default value}.
4976 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
4977 * Its parameter list (either empty or of the form {@code (V A*)}) must be
4978 * effectively identical to the internal parameter list.
4979 * </ul>
4980 * <p>
4981 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
4982 * <li>The loop handle's result type is the result type {@code V} of the body.
4983 * <li>The loop handle's parameter types are the types {@code (A...)},
4984 * from the external parameter list.
4985 * </ul>
4986 * <p>
4987 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4988 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4989 * passed to the loop.
4990 * <blockquote><pre>{@code
4991 * V init(A...);
4992 * boolean pred(V, A...);
4993 * V body(V, A...);
4994 * V whileLoop(A... a...) {
4995 * V v = init(a...);
4996 * while (pred(v, a...)) {
4997 * v = body(v, a...);
4998 * }
4999 * return v;
5000 * }
5001 * }</pre></blockquote>
5002 *
5003 * @apiNote Example:
5004 * <blockquote><pre>{@code
5005 * // implement the zip function for lists as a loop handle
5006 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
5007 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
5008 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
5009 * zip.add(a.next());
5010 * zip.add(b.next());
5011 * return zip;
5012 * }
5013 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
5014 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
5015 * List<String> a = Arrays.asList("a", "b", "c", "d");
5016 * List<String> b = Arrays.asList("e", "f", "g", "h");
5017 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
5018 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
5019 * }</pre></blockquote>
5020 *
5021 *
5022 * @apiNote The implementation of this method can be expressed as follows:
5023 * <blockquote><pre>{@code
5024 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5025 * MethodHandle fini = (body.type().returnType() == void.class
5026 * ? null : identity(body.type().returnType()));
5027 * MethodHandle[]
5028 * checkExit = { null, null, pred, fini },
5029 * varBody = { init, body };
5030 * return loop(checkExit, varBody);
5031 * }
5032 * }</pre></blockquote>
5033 *
5034 * @param init optional initializer, providing the initial value of the loop variable.
5035 * May be {@code null}, implying a default initial value. See above for other constraints.
5036 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5037 * above for other constraints.
5038 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5039 * See above for other constraints.
5040 *
5041 * @return a method handle implementing the {@code while} loop as described by the arguments.
5042 * @throws IllegalArgumentException if the rules for the arguments are violated.
5043 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5044 *
5045 * @see #loop(MethodHandle[][])
5046 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5047 * @since 9
5048 */
5049 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5050 whileLoopChecks(init, pred, body);
5051 MethodHandle fini = identityOrVoid(body.type().returnType());
5052 MethodHandle[] checkExit = { null, null, pred, fini };
5053 MethodHandle[] varBody = { init, body };
5054 return loop(checkExit, varBody);
5055 }
5056
5057 /**
5058 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
5059 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5060 * <p>
5061 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5062 * method will, in each iteration, first execute its body and then evaluate the predicate.
5063 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
5064 * <p>
5065 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5066 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5067 * and updated with the value returned from its invocation. The result of loop execution will be
5068 * the final value of the additional loop-local variable (if present).
5069 * <p>
5070 * The following rules hold for these argument handles:<ul>
5071 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5072 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5073 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5074 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5075 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5076 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5077 * It will constrain the parameter lists of the other loop parts.
5078 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5079 * list {@code (A...)} is called the <em>external parameter list</em>.
5080 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5081 * additional state variable of the loop.
5082 * The body must both accept and return a value of this type {@code V}.
5083 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5084 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5085 * <a href="MethodHandles.html#effid">effectively identical</a>
5086 * to the external parameter list {@code (A...)}.
5087 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5088 * {@linkplain #empty default value}.
5089 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5090 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5091 * effectively identical to the internal parameter list.
5092 * </ul>
5093 * <p>
5094 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5095 * <li>The loop handle's result type is the result type {@code V} of the body.
5096 * <li>The loop handle's parameter types are the types {@code (A...)},
5097 * from the external parameter list.
5098 * </ul>
5099 * <p>
5100 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5101 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5102 * passed to the loop.
5103 * <blockquote><pre>{@code
5104 * V init(A...);
5105 * boolean pred(V, A...);
5106 * V body(V, A...);
5107 * V doWhileLoop(A... a...) {
5108 * V v = init(a...);
5109 * do {
5110 * v = body(v, a...);
5111 * } while (pred(v, a...));
5112 * return v;
5113 * }
5114 * }</pre></blockquote>
5115 *
5116 * @apiNote Example:
5117 * <blockquote><pre>{@code
5118 * // int i = 0; while (i < limit) { ++i; } return i; => limit
5119 * static int zero(int limit) { return 0; }
5120 * static int step(int i, int limit) { return i + 1; }
5121 * static boolean pred(int i, int limit) { return i < limit; }
5122 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
5123 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
5124 * assertEquals(23, loop.invoke(23));
5125 * }</pre></blockquote>
5126 *
5127 *
5128 * @apiNote The implementation of this method can be expressed as follows:
5129 * <blockquote><pre>{@code
5130 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5131 * MethodHandle fini = (body.type().returnType() == void.class
5132 * ? null : identity(body.type().returnType()));
5133 * MethodHandle[] clause = { init, body, pred, fini };
5134 * return loop(clause);
5135 * }
5136 * }</pre></blockquote>
5137 *
5138 * @param init optional initializer, providing the initial value of the loop variable.
5139 * May be {@code null}, implying a default initial value. See above for other constraints.
5140 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5141 * See above for other constraints.
5142 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5143 * above for other constraints.
5144 *
5145 * @return a method handle implementing the {@code while} loop as described by the arguments.
5146 * @throws IllegalArgumentException if the rules for the arguments are violated.
5147 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5148 *
5149 * @see #loop(MethodHandle[][])
5150 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
5151 * @since 9
5152 */
5153 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5154 whileLoopChecks(init, pred, body);
5155 MethodHandle fini = identityOrVoid(body.type().returnType());
5156 MethodHandle[] clause = {init, body, pred, fini };
5157 return loop(clause);
5158 }
5159
5160 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
5161 Objects.requireNonNull(pred);
5162 Objects.requireNonNull(body);
5163 MethodType bodyType = body.type();
5164 Class<?> returnType = bodyType.returnType();
5165 List<Class<?>> innerList = bodyType.parameterList();
5166 List<Class<?>> outerList = innerList;
5167 if (returnType == void.class) {
5168 // OK
5169 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
5170 // leading V argument missing => error
5171 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5172 throw misMatchedTypes("body function", bodyType, expected);
5173 } else {
5174 outerList = innerList.subList(1, innerList.size());
5175 }
5176 MethodType predType = pred.type();
5177 if (predType.returnType() != boolean.class ||
5178 !predType.effectivelyIdenticalParameters(0, innerList)) {
5179 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
5180 }
5181 if (init != null) {
5182 MethodType initType = init.type();
5183 if (initType.returnType() != returnType ||
5184 !initType.effectivelyIdenticalParameters(0, outerList)) {
5185 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5186 }
5187 }
5188 }
5189
5190 /**
5191 * Constructs a loop that runs a given number of iterations.
5192 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5193 * <p>
5194 * The number of iterations is determined by the {@code iterations} handle evaluation result.
5195 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
5196 * It will be initialized to 0 and incremented by 1 in each iteration.
5197 * <p>
5198 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5199 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5200 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5201 * <p>
5202 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5203 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5204 * iteration variable.
5205 * The result of the loop handle execution will be the final {@code V} value of that variable
5206 * (or {@code void} if there is no {@code V} variable).
5207 * <p>
5208 * The following rules hold for the argument handles:<ul>
5209 * <li>The {@code iterations} handle must not be {@code null}, and must return
5210 * the type {@code int}, referred to here as {@code I} in parameter type lists.
5211 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5212 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5213 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5214 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5215 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5216 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5217 * of types called the <em>internal parameter list</em>.
5218 * It will constrain the parameter lists of the other loop parts.
5219 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5220 * with no additional {@code A} types, then the internal parameter list is extended by
5221 * the argument types {@code A...} of the {@code iterations} handle.
5222 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5223 * list {@code (A...)} is called the <em>external parameter list</em>.
5224 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5225 * additional state variable of the loop.
5226 * The body must both accept a leading parameter and return a value of this type {@code V}.
5227 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5228 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5229 * <a href="MethodHandles.html#effid">effectively identical</a>
5230 * to the external parameter list {@code (A...)}.
5231 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5232 * {@linkplain #empty default value}.
5233 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
5234 * effectively identical to the external parameter list {@code (A...)}.
5235 * </ul>
5236 * <p>
5237 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5238 * <li>The loop handle's result type is the result type {@code V} of the body.
5239 * <li>The loop handle's parameter types are the types {@code (A...)},
5240 * from the external parameter list.
5241 * </ul>
5242 * <p>
5243 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5244 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5245 * arguments passed to the loop.
5246 * <blockquote><pre>{@code
5247 * int iterations(A...);
5248 * V init(A...);
5249 * V body(V, int, A...);
5250 * V countedLoop(A... a...) {
5251 * int end = iterations(a...);
5252 * V v = init(a...);
5253 * for (int i = 0; i < end; ++i) {
5254 * v = body(v, i, a...);
5255 * }
5256 * return v;
5257 * }
5258 * }</pre></blockquote>
5259 *
5260 * @apiNote Example with a fully conformant body method:
5261 * <blockquote><pre>{@code
5262 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5263 * // => a variation on a well known theme
5264 * static String step(String v, int counter, String init) { return "na " + v; }
5265 * // assume MH_step is a handle to the method above
5266 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
5267 * MethodHandle start = MethodHandles.identity(String.class);
5268 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
5269 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
5270 * }</pre></blockquote>
5271 *
5272 * @apiNote Example with the simplest possible body method type,
5273 * and passing the number of iterations to the loop invocation:
5274 * <blockquote><pre>{@code
5275 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5276 * // => a variation on a well known theme
5277 * static String step(String v, int counter ) { return "na " + v; }
5278 * // assume MH_step is a handle to the method above
5279 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
5280 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
5281 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
5282 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
5283 * }</pre></blockquote>
5284 *
5285 * @apiNote Example that treats the number of iterations, string to append to, and string to append
5286 * as loop parameters:
5287 * <blockquote><pre>{@code
5288 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5289 * // => a variation on a well known theme
5290 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
5291 * // assume MH_step is a handle to the method above
5292 * MethodHandle count = MethodHandles.identity(int.class);
5293 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
5294 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
5295 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
5296 * }</pre></blockquote>
5297 *
5298 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
5299 * to enforce a loop type:
5300 * <blockquote><pre>{@code
5301 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5302 * // => a variation on a well known theme
5303 * static String step(String v, int counter, String pre) { return pre + " " + v; }
5304 * // assume MH_step is a handle to the method above
5305 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
5306 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
5307 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
5308 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
5309 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
5310 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
5311 * }</pre></blockquote>
5312 *
5313 * @apiNote The implementation of this method can be expressed as follows:
5314 * <blockquote><pre>{@code
5315 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5316 * return countedLoop(empty(iterations.type()), iterations, init, body);
5317 * }
5318 * }</pre></blockquote>
5319 *
5320 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
5321 * result type must be {@code int}. See above for other constraints.
5322 * @param init optional initializer, providing the initial value of the loop variable.
5323 * May be {@code null}, implying a default initial value. See above for other constraints.
5324 * @param body body of the loop, which may not be {@code null}.
5325 * It controls the loop parameters and result type in the standard case (see above for details).
5326 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5327 * and may accept any number of additional types.
5328 * See above for other constraints.
5329 *
5330 * @return a method handle representing the loop.
5331 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
5332 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5333 *
5334 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
5335 * @since 9
5336 */
5337 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5338 return countedLoop(empty(iterations.type()), iterations, init, body);
5339 }
5340
5341 /**
5342 * Constructs a loop that counts over a range of numbers.
5343 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5344 * <p>
5345 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
5346 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
5347 * values of the loop counter.
5348 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
5349 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
5350 * <p>
5351 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5352 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5353 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5354 * <p>
5355 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5356 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5357 * iteration variable.
5358 * The result of the loop handle execution will be the final {@code V} value of that variable
5359 * (or {@code void} if there is no {@code V} variable).
5360 * <p>
5361 * The following rules hold for the argument handles:<ul>
5362 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
5363 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
5364 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5365 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5366 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5367 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5368 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5369 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5370 * of types called the <em>internal parameter list</em>.
5371 * It will constrain the parameter lists of the other loop parts.
5372 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5373 * with no additional {@code A} types, then the internal parameter list is extended by
5374 * the argument types {@code A...} of the {@code end} handle.
5375 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5376 * list {@code (A...)} is called the <em>external parameter list</em>.
5377 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5378 * additional state variable of the loop.
5379 * The body must both accept a leading parameter and return a value of this type {@code V}.
5380 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5381 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5382 * <a href="MethodHandles.html#effid">effectively identical</a>
5383 * to the external parameter list {@code (A...)}.
5384 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5385 * {@linkplain #empty default value}.
5386 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
5387 * effectively identical to the external parameter list {@code (A...)}.
5388 * <li>Likewise, the parameter list of {@code end} must be effectively identical
5389 * to the external parameter list.
5390 * </ul>
5391 * <p>
5392 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5393 * <li>The loop handle's result type is the result type {@code V} of the body.
5394 * <li>The loop handle's parameter types are the types {@code (A...)},
5395 * from the external parameter list.
5396 * </ul>
5397 * <p>
5398 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5399 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5400 * arguments passed to the loop.
5401 * <blockquote><pre>{@code
5402 * int start(A...);
5403 * int end(A...);
5404 * V init(A...);
5405 * V body(V, int, A...);
5406 * V countedLoop(A... a...) {
5407 * int e = end(a...);
5408 * int s = start(a...);
5409 * V v = init(a...);
5410 * for (int i = s; i < e; ++i) {
5411 * v = body(v, i, a...);
5412 * }
5413 * return v;
5414 * }
5415 * }</pre></blockquote>
5416 *
5417 * @apiNote The implementation of this method can be expressed as follows:
5418 * <blockquote><pre>{@code
5419 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5420 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
5421 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
5422 * // the following semantics:
5423 * // MH_increment: (int limit, int counter) -> counter + 1
5424 * // MH_predicate: (int limit, int counter) -> counter < limit
5425 * Class<?> counterType = start.type().returnType(); // int
5426 * Class<?> returnType = body.type().returnType();
5427 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
5428 * if (returnType != void.class) { // ignore the V variable
5429 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5430 * pred = dropArguments(pred, 1, returnType); // ditto
5431 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
5432 * }
5433 * body = dropArguments(body, 0, counterType); // ignore the limit variable
5434 * MethodHandle[]
5435 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5436 * bodyClause = { init, body }, // v = init(); v = body(v, i)
5437 * indexVar = { start, incr }; // i = start(); i = i + 1
5438 * return loop(loopLimit, bodyClause, indexVar);
5439 * }
5440 * }</pre></blockquote>
5441 *
5442 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
5443 * See above for other constraints.
5444 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
5445 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
5446 * @param init optional initializer, providing the initial value of the loop variable.
5447 * May be {@code null}, implying a default initial value. See above for other constraints.
5448 * @param body body of the loop, which may not be {@code null}.
5449 * It controls the loop parameters and result type in the standard case (see above for details).
5450 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5451 * and may accept any number of additional types.
5452 * See above for other constraints.
5453 *
5454 * @return a method handle representing the loop.
5455 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
5456 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5457 *
5458 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
5459 * @since 9
5460 */
5461 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5462 countedLoopChecks(start, end, init, body);
5463 Class<?> counterType = start.type().returnType(); // int, but who's counting?
5464 Class<?> limitType = end.type().returnType(); // yes, int again
5465 Class<?> returnType = body.type().returnType();
5466 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
5467 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
5468 MethodHandle retv = null;
5469 if (returnType != void.class) {
5470 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5471 pred = dropArguments(pred, 1, returnType); // ditto
5472 retv = dropArguments(identity(returnType), 0, counterType);
5473 }
5474 body = dropArguments(body, 0, counterType); // ignore the limit variable
5475 MethodHandle[]
5476 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5477 bodyClause = { init, body }, // v = init(); v = body(v, i)
5478 indexVar = { start, incr }; // i = start(); i = i + 1
5479 return loop(loopLimit, bodyClause, indexVar);
5480 }
5481
5482 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5483 Objects.requireNonNull(start);
5484 Objects.requireNonNull(end);
5485 Objects.requireNonNull(body);
5486 Class<?> counterType = start.type().returnType();
5487 if (counterType != int.class) {
5488 MethodType expected = start.type().changeReturnType(int.class);
5489 throw misMatchedTypes("start function", start.type(), expected);
5490 } else if (end.type().returnType() != counterType) {
5491 MethodType expected = end.type().changeReturnType(counterType);
5492 throw misMatchedTypes("end function", end.type(), expected);
5493 }
5494 MethodType bodyType = body.type();
5495 Class<?> returnType = bodyType.returnType();
5496 List<Class<?>> innerList = bodyType.parameterList();
5497 // strip leading V value if present
5498 int vsize = (returnType == void.class ? 0 : 1);
5499 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
5500 // argument list has no "V" => error
5501 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5502 throw misMatchedTypes("body function", bodyType, expected);
5503 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
5504 // missing I type => error
5505 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
5506 throw misMatchedTypes("body function", bodyType, expected);
5507 }
5508 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
5509 if (outerList.isEmpty()) {
5510 // special case; take lists from end handle
5511 outerList = end.type().parameterList();
5512 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
5513 }
5514 MethodType expected = methodType(counterType, outerList);
5515 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
5516 throw misMatchedTypes("start parameter types", start.type(), expected);
5517 }
5518 if (end.type() != start.type() &&
5519 !end.type().effectivelyIdenticalParameters(0, outerList)) {
5520 throw misMatchedTypes("end parameter types", end.type(), expected);
5521 }
5522 if (init != null) {
5523 MethodType initType = init.type();
5524 if (initType.returnType() != returnType ||
5525 !initType.effectivelyIdenticalParameters(0, outerList)) {
5526 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5527 }
5528 }
5529 }
5530
5531 /**
5532 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
5533 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5534 * <p>
5535 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
5536 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
5537 * <p>
5538 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5539 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5540 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5541 * <p>
5542 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5543 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5544 * iteration variable.
5545 * The result of the loop handle execution will be the final {@code V} value of that variable
5546 * (or {@code void} if there is no {@code V} variable).
5547 * <p>
5548 * The following rules hold for the argument handles:<ul>
5549 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5550 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
5551 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5552 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
5553 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
5554 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
5555 * of types called the <em>internal parameter list</em>.
5556 * It will constrain the parameter lists of the other loop parts.
5557 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
5558 * with no additional {@code A} types, then the internal parameter list is extended by
5559 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
5560 * single type {@code Iterable} is added and constitutes the {@code A...} list.
5561 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
5562 * list {@code (A...)} is called the <em>external parameter list</em>.
5563 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5564 * additional state variable of the loop.
5565 * The body must both accept a leading parameter and return a value of this type {@code V}.
5566 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5567 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5568 * <a href="MethodHandles.html#effid">effectively identical</a>
5569 * to the external parameter list {@code (A...)}.
5570 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5571 * {@linkplain #empty default value}.
5572 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
5573 * type {@code java.util.Iterator} or a subtype thereof.
5574 * The iterator it produces when the loop is executed will be assumed
5575 * to yield values which can be converted to type {@code T}.
5576 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
5577 * effectively identical to the external parameter list {@code (A...)}.
5578 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
5579 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
5580 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
5581 * handle parameter is adjusted to accept the leading {@code A} type, as if by
5582 * the {@link MethodHandle#asType asType} conversion method.
5583 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
5584 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
5585 * </ul>
5586 * <p>
5587 * The type {@code T} may be either a primitive or reference.
5588 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
5589 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
5590 * as if by the {@link MethodHandle#asType asType} conversion method.
5591 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
5592 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
5593 * <p>
5594 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5595 * <li>The loop handle's result type is the result type {@code V} of the body.
5596 * <li>The loop handle's parameter types are the types {@code (A...)},
5597 * from the external parameter list.
5598 * </ul>
5599 * <p>
5600 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5601 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
5602 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
5603 * <blockquote><pre>{@code
5604 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
5605 * V init(A...);
5606 * V body(V,T,A...);
5607 * V iteratedLoop(A... a...) {
5608 * Iterator<T> it = iterator(a...);
5609 * V v = init(a...);
5610 * while (it.hasNext()) {
5611 * T t = it.next();
5612 * v = body(v, t, a...);
5613 * }
5614 * return v;
5615 * }
5616 * }</pre></blockquote>
5617 *
5618 * @apiNote Example:
5619 * <blockquote><pre>{@code
5620 * // get an iterator from a list
5621 * static List<String> reverseStep(List<String> r, String e) {
5622 * r.add(0, e);
5623 * return r;
5624 * }
5625 * static List<String> newArrayList() { return new ArrayList<>(); }
5626 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
5627 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
5628 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
5629 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
5630 * assertEquals(reversedList, (List<String>) loop.invoke(list));
5631 * }</pre></blockquote>
5632 *
5633 * @apiNote The implementation of this method can be expressed approximately as follows:
5634 * <blockquote><pre>{@code
5635 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5636 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
5637 * Class<?> returnType = body.type().returnType();
5638 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5639 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
5640 * MethodHandle retv = null, step = body, startIter = iterator;
5641 * if (returnType != void.class) {
5642 * // the simple thing first: in (I V A...), drop the I to get V
5643 * retv = dropArguments(identity(returnType), 0, Iterator.class);
5644 * // body type signature (V T A...), internal loop types (I V A...)
5645 * step = swapArguments(body, 0, 1); // swap V <-> T
5646 * }
5647 * if (startIter == null) startIter = MH_getIter;
5648 * MethodHandle[]
5649 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
5650 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
5651 * return loop(iterVar, bodyClause);
5652 * }
5653 * }</pre></blockquote>
5654 *
5655 * @param iterator an optional handle to return the iterator to start the loop.
5656 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
5657 * See above for other constraints.
5658 * @param init optional initializer, providing the initial value of the loop variable.
5659 * May be {@code null}, implying a default initial value. See above for other constraints.
5660 * @param body body of the loop, which may not be {@code null}.
5661 * It controls the loop parameters and result type in the standard case (see above for details).
5662 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
5663 * and may accept any number of additional types.
5664 * See above for other constraints.
5665 *
5666 * @return a method handle embodying the iteration loop functionality.
5667 * @throws NullPointerException if the {@code body} handle is {@code null}.
5668 * @throws IllegalArgumentException if any argument violates the above requirements.
5669 *
5670 * @since 9
5671 */
5672 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5673 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
5674 Class<?> returnType = body.type().returnType();
5675 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
5676 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
5677 MethodHandle startIter;
5678 MethodHandle nextVal;
5679 {
5680 MethodType iteratorType;
5681 if (iterator == null) {
5682 // derive argument type from body, if available, else use Iterable
5683 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
5684 iteratorType = startIter.type().changeParameterType(0, iterableType);
5685 } else {
5686 // force return type to the internal iterator class
5687 iteratorType = iterator.type().changeReturnType(Iterator.class);
5688 startIter = iterator;
5689 }
5690 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5691 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
5692
5693 // perform the asType transforms under an exception transformer, as per spec.:
5694 try {
5695 startIter = startIter.asType(iteratorType);
5696 nextVal = nextRaw.asType(nextValType);
5697 } catch (WrongMethodTypeException ex) {
5698 throw new IllegalArgumentException(ex);
5699 }
5700 }
5701
5702 MethodHandle retv = null, step = body;
5703 if (returnType != void.class) {
5704 // the simple thing first: in (I V A...), drop the I to get V
5705 retv = dropArguments(identity(returnType), 0, Iterator.class);
5706 // body type signature (V T A...), internal loop types (I V A...)
5707 step = swapArguments(body, 0, 1); // swap V <-> T
5708 }
5709
5710 MethodHandle[]
5711 iterVar = { startIter, null, hasNext, retv },
5712 bodyClause = { init, filterArgument(step, 0, nextVal) };
5713 return loop(iterVar, bodyClause);
5714 }
5715
5716 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5717 Objects.requireNonNull(body);
5718 MethodType bodyType = body.type();
5719 Class<?> returnType = bodyType.returnType();
5720 List<Class<?>> internalParamList = bodyType.parameterList();
5721 // strip leading V value if present
5722 int vsize = (returnType == void.class ? 0 : 1);
5723 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
5724 // argument list has no "V" => error
5725 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5726 throw misMatchedTypes("body function", bodyType, expected);
5727 } else if (internalParamList.size() <= vsize) {
5728 // missing T type => error
5729 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
5730 throw misMatchedTypes("body function", bodyType, expected);
5731 }
5732 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
5733 Class<?> iterableType = null;
5734 if (iterator != null) {
5735 // special case; if the body handle only declares V and T then
5736 // the external parameter list is obtained from iterator handle
5737 if (externalParamList.isEmpty()) {
5738 externalParamList = iterator.type().parameterList();
5739 }
5740 MethodType itype = iterator.type();
5741 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
5742 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
5743 }
5744 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
5745 MethodType expected = methodType(itype.returnType(), externalParamList);
5746 throw misMatchedTypes("iterator parameters", itype, expected);
5747 }
5748 } else {
5749 if (externalParamList.isEmpty()) {
5750 // special case; if the iterator handle is null and the body handle
5751 // only declares V and T then the external parameter list consists
5752 // of Iterable
5753 externalParamList = Arrays.asList(Iterable.class);
5754 iterableType = Iterable.class;
5755 } else {
5756 // special case; if the iterator handle is null and the external
5757 // parameter list is not empty then the first parameter must be
5758 // assignable to Iterable
5759 iterableType = externalParamList.get(0);
5760 if (!Iterable.class.isAssignableFrom(iterableType)) {
5761 throw newIllegalArgumentException(
5762 "inferred first loop argument must inherit from Iterable: " + iterableType);
5763 }
5764 }
5765 }
5766 if (init != null) {
5767 MethodType initType = init.type();
5768 if (initType.returnType() != returnType ||
5769 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
5770 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
5771 }
5772 }
5773 return iterableType; // help the caller a bit
5774 }
5775
5776 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
5777 // there should be a better way to uncross my wires
5778 int arity = mh.type().parameterCount();
5779 int[] order = new int[arity];
5780 for (int k = 0; k < arity; k++) order[k] = k;
5781 order[i] = j; order[j] = i;
5782 Class<?>[] types = mh.type().parameterArray();
5783 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
5784 MethodType swapType = methodType(mh.type().returnType(), types);
5785 return permuteArguments(mh, swapType, order);
5786 }
5787
5788 /**
5789 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
5790 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
5791 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
5792 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
5793 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
5794 * {@code try-finally} handle.
5795 * <p>
5796 * The {@code cleanup} handle will be passed one or two additional leading arguments.
5797 * The first is the exception thrown during the
5798 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
5799 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
5800 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
5801 * The second argument is not present if the {@code target} handle has a {@code void} return type.
5802 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
5803 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
5804 * <p>
5805 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
5806 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
5807 * two extra leading parameters:<ul>
5808 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
5809 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
5810 * the result from the execution of the {@code target} handle.
5811 * This parameter is not present if the {@code target} returns {@code void}.
5812 * </ul>
5813 * <p>
5814 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
5815 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
5816 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
5817 * the cleanup.
5818 * <blockquote><pre>{@code
5819 * V target(A..., B...);
5820 * V cleanup(Throwable, V, A...);
5821 * V adapter(A... a, B... b) {
5822 * V result = (zero value for V);
5823 * Throwable throwable = null;
5824 * try {
5825 * result = target(a..., b...);
5826 * } catch (Throwable t) {
5827 * throwable = t;
5828 * throw t;
5829 * } finally {
5830 * result = cleanup(throwable, result, a...);
5831 * }
5832 * return result;
5833 * }
5834 * }</pre></blockquote>
5835 * <p>
5836 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5837 * be modified by execution of the target, and so are passed unchanged
5838 * from the caller to the cleanup, if it is invoked.
5839 * <p>
5840 * The target and cleanup must return the same type, even if the cleanup
5841 * always throws.
5842 * To create such a throwing cleanup, compose the cleanup logic
5843 * with {@link #throwException throwException},
5844 * in order to create a method handle of the correct return type.
5845 * <p>
5846 * Note that {@code tryFinally} never converts exceptions into normal returns.
5847 * In rare cases where exceptions must be converted in that way, first wrap
5848 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
5849 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
5850 *
5851 * @param target the handle whose execution is to be wrapped in a {@code try} block.
5852 * @param cleanup the handle that is invoked in the finally block.
5853 *
5854 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
5855 * @throws NullPointerException if any argument is null
5856 * @throws IllegalArgumentException if {@code cleanup} does not accept
5857 * the required leading arguments, or if the method handle types do
5858 * not match in their return types and their
5859 * corresponding trailing parameters
5860 *
5861 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
5862 * @since 9
5863 */
5864 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
5865 List<Class<?>> targetParamTypes = target.type().parameterList();
5866 List<Class<?>> cleanupParamTypes = cleanup.type().parameterList();
5867 Class<?> rtype = target.type().returnType();
5868
5869 tryFinallyChecks(target, cleanup);
5870
5871 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
5872 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5873 // target parameter list.
5874 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
5875
5876 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
5877 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
5878 }
5879
5880 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
5881 Class<?> rtype = target.type().returnType();
5882 if (rtype != cleanup.type().returnType()) {
5883 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
5884 }
5885 MethodType cleanupType = cleanup.type();
5886 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
5887 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
5888 }
5889 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
5890 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
5891 }
5892 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5893 // target parameter list.
5894 int cleanupArgIndex = rtype == void.class ? 1 : 2;
5895 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
5896 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
5897 cleanup.type(), target.type());
5898 }
5899 }
5900
5901 }