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