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 * Returns a {@link Lookup lookup object} which is trusted minimally.
117 * The lookup has the {@code PUBLIC} and {@code UNCONDITIONAL} modes.
118 * It can only be used to create method handles to public members of
119 * public classes in packages that are exported unconditionally.
120 * <p>
121 * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
122 * of this lookup object will be {@link java.lang.Object}.
123 *
124 * @apiNote The use of Object is conventional, and because the lookup modes are
125 * limited, there is no special access provided to the internals of Object, its package
126 * or its module. Consequently, the lookup context of this lookup object will be the
127 * bootstrap class loader, which means it cannot find user classes.
128 *
129 * <p style="font-size:smaller;">
130 * <em>Discussion:</em>
131 * The lookup class can be changed to any other class {@code C} using an expression of the form
132 * {@link Lookup#in publicLookup().in(C.class)}.
133 * but may change the lookup context by virtue of changing the class loader.
134 * A public lookup object is always subject to
135 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
136 * Also, it cannot access
137 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
138 * @return a lookup object which is trusted minimally
139 *
140 * @revised 9
141 * @spec JPMS
142 */
143 public static Lookup publicLookup() {
144 return Lookup.PUBLIC_LOOKUP;
145 }
146
147 /**
148 * Returns a {@link Lookup lookup object} with full capabilities to emulate all
149 * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">
150 * private access</a>, on a target class.
151 * This method checks that a caller, specified as a {@code Lookup} object, is allowed to
152 * do <em>deep reflection</em> on the target class. If {@code m1} is the module containing
153 * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing
154 * the target class, then this check ensures that
155 * <ul>
156 * <li>{@code m1} {@link Module#canRead reads} {@code m2}.</li>
157 * <li>{@code m2} {@link Module#isOpen(String,Module) opens} the package containing
158 * the target class to at least {@code m1}.</li>
159 * <li>The lookup has the {@link Lookup#MODULE MODULE} lookup mode.</li>
160 * </ul>
161 * <p>
162 * If there is a security manager, its {@code checkPermission} method is called to
163 * check {@code ReflectPermission("suppressAccessChecks")}.
164 * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object
165 * was created by code in the caller module (or derived from a lookup object originally
166 * created by the caller). A lookup object with the {@code MODULE} lookup mode can be
167 * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE}
168 * access to the caller.
169 * @param targetClass the target class
170 * @param lookup the caller lookup object
171 * @return a lookup object for the target class, with private access
172 * @throws IllegalArgumentException if {@code targetClass} is a primitve type or array class
173 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
174 * @throws IllegalAccessException if the access check specified above fails
175 * @throws SecurityException if denied by the security manager
176 * @since 9
177 * @spec JPMS
178 * @see Lookup#dropLookupMode
179 */
180 public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException {
181 SecurityManager sm = System.getSecurityManager();
182 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
183 if (targetClass.isPrimitive())
184 throw new IllegalArgumentException(targetClass + " is a primitive class");
185 if (targetClass.isArray())
186 throw new IllegalArgumentException(targetClass + " is an array class");
187 Module targetModule = targetClass.getModule();
188 Module callerModule = lookup.lookupClass().getModule();
189 if (!callerModule.canRead(targetModule))
190 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
191 if (targetModule.isNamed()) {
192 String pn = targetClass.getPackageName();
193 assert pn.length() > 0 : "unnamed package cannot be in named module";
194 if (!targetModule.isOpen(pn, callerModule))
195 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
196 }
197 if ((lookup.lookupModes() & Lookup.MODULE) == 0)
198 throw new IllegalAccessException("lookup does not have MODULE lookup mode");
199 if (!callerModule.isNamed() && targetModule.isNamed()) {
200 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
201 if (logger != null) {
202 logger.logIfOpenedByBackdoor(lookup, targetClass);
203 }
204 }
205 return new Lookup(targetClass);
206 }
207
208 /**
209 * Performs an unchecked "crack" of a
210 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
211 * The result is as if the user had obtained a lookup object capable enough
212 * to crack the target method handle, called
213 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
214 * on the target to obtain its symbolic reference, and then called
215 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
216 * to resolve the symbolic reference to a member.
217 * <p>
218 * If there is a security manager, its {@code checkPermission} method
219 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
220 * @param <T> the desired type of the result, either {@link Member} or a subtype
221 * @param target a direct method handle to crack into symbolic reference components
222 * @param expected a class object representing the desired result type {@code T}
223 * @return a reference to the method, constructor, or field object
224 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
225 * @exception NullPointerException if either argument is {@code null}
226 * @exception IllegalArgumentException if the target is not a direct method handle
227 * @exception ClassCastException if the member is not of the expected type
228 * @since 1.8
229 */
230 public static <T extends Member> T
231 reflectAs(Class<T> expected, MethodHandle target) {
232 SecurityManager smgr = System.getSecurityManager();
233 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
234 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
235 return lookup.revealDirect(target).reflectAs(expected, lookup);
236 }
237 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
238 private static final java.security.Permission ACCESS_PERMISSION =
239 new ReflectPermission("suppressAccessChecks");
240
241 /**
242 * A <em>lookup object</em> is a factory for creating method handles,
243 * when the creation requires access checking.
244 * Method handles do not perform
245 * access checks when they are called, but rather when they are created.
246 * Therefore, method handle access
247 * restrictions must be enforced when a method handle is created.
248 * The caller class against which those restrictions are enforced
249 * is known as the {@linkplain #lookupClass lookup class}.
250 * <p>
251 * A lookup class which needs to create method handles will call
252 * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
253 * When the {@code Lookup} factory object is created, the identity of the lookup class is
254 * determined, and securely stored in the {@code Lookup} object.
255 * The lookup class (or its delegates) may then use factory methods
256 * on the {@code Lookup} object to create method handles for access-checked members.
257 * This includes all methods, constructors, and fields which are allowed to the lookup class,
258 * even private ones.
259 *
260 * <h1><a id="lookups"></a>Lookup Factory Methods</h1>
261 * The factory methods on a {@code Lookup} object correspond to all major
262 * use cases for methods, constructors, and fields.
263 * Each method handle created by a factory method is the functional
264 * equivalent of a particular <em>bytecode behavior</em>.
265 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
266 * Here is a summary of the correspondence between these factory methods and
267 * the behavior of the resulting method handles:
268 * <table class="altrows">
269 * <caption style="display:none">lookup method behaviors</caption>
270 * <thead>
271 * <tr>
272 * <th><a id="equiv"></a>lookup expression</th>
273 * <th>member</th>
274 * <th>bytecode behavior</th>
275 * </tr>
276 * </thead>
277 * <tbody>
278 * <tr>
279 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
280 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
281 * </tr>
282 * <tr>
283 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
284 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
285 * </tr>
286 * <tr>
287 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
288 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
289 * </tr>
290 * <tr>
291 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
292 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
293 * </tr>
294 * <tr>
295 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
296 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
297 * </tr>
298 * <tr>
299 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
300 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
301 * </tr>
302 * <tr>
303 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
304 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
305 * </tr>
306 * <tr>
307 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
308 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
309 * </tr>
310 * <tr>
311 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
312 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
313 * </tr>
314 * <tr>
315 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
316 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
317 * </tr>
318 * <tr>
319 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
320 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
321 * </tr>
322 * <tr>
323 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
324 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
325 * </tr>
326 * <tr>
327 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
328 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
329 * </tr>
330 * <tr>
331 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</td>
332 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
333 * </tr>
334 * </tbody>
335 * </table>
336 *
337 * Here, the type {@code C} is the class or interface being searched for a member,
338 * documented as a parameter named {@code refc} in the lookup methods.
339 * The method type {@code MT} is composed from the return type {@code T}
340 * and the sequence of argument types {@code A*}.
341 * The constructor also has a sequence of argument types {@code A*} and
342 * is deemed to return the newly-created object of type {@code C}.
343 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
344 * The formal parameter {@code this} stands for the self-reference of type {@code C};
345 * if it is present, it is always the leading argument to the method handle invocation.
346 * (In the case of some {@code protected} members, {@code this} may be
347 * restricted in type to the lookup class; see below.)
348 * The name {@code arg} stands for all the other method handle arguments.
349 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
350 * stands for a null reference if the accessed method or field is static,
351 * and {@code this} otherwise.
352 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
353 * for reflective objects corresponding to the given members.
354 * <p>
355 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
356 * as if by {@code ldc CONSTANT_Class}.
357 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
358 * <p>
359 * In cases where the given member is of variable arity (i.e., a method or constructor)
360 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
361 * In all other cases, the returned method handle will be of fixed arity.
362 * <p style="font-size:smaller;">
363 * <em>Discussion:</em>
364 * The equivalence between looked-up method handles and underlying
365 * class members and bytecode behaviors
366 * can break down in a few ways:
367 * <ul style="font-size:smaller;">
368 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
369 * the lookup can still succeed, even when there is no equivalent
370 * Java expression or bytecoded constant.
371 * <li>Likewise, if {@code T} or {@code MT}
372 * is not symbolically accessible from the lookup class's loader,
373 * the lookup can still succeed.
374 * For example, lookups for {@code MethodHandle.invokeExact} and
375 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
376 * <li>If there is a security manager installed, it can forbid the lookup
377 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
378 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
379 * constant is not subject to security manager checks.
380 * <li>If the looked-up method has a
381 * <a href="MethodHandle.html#maxarity">very large arity</a>,
382 * the method handle creation may fail, due to the method handle
383 * type having too many parameters.
384 * </ul>
385 *
386 * <h1><a id="access"></a>Access checking</h1>
387 * Access checks are applied in the factory methods of {@code Lookup},
388 * when a method handle is created.
389 * This is a key difference from the Core Reflection API, since
390 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
391 * performs access checking against every caller, on every call.
392 * <p>
393 * All access checks start from a {@code Lookup} object, which
394 * compares its recorded lookup class against all requests to
395 * create method handles.
396 * A single {@code Lookup} object can be used to create any number
397 * of access-checked method handles, all checked against a single
398 * lookup class.
399 * <p>
400 * A {@code Lookup} object can be shared with other trusted code,
401 * such as a metaobject protocol.
402 * A shared {@code Lookup} object delegates the capability
403 * to create method handles on private members of the lookup class.
404 * Even if privileged code uses the {@code Lookup} object,
405 * the access checking is confined to the privileges of the
406 * original lookup class.
407 * <p>
408 * A lookup can fail, because
409 * the containing class is not accessible to the lookup class, or
410 * because the desired class member is missing, or because the
411 * desired class member is not accessible to the lookup class, or
412 * because the lookup object is not trusted enough to access the member.
413 * In any of these cases, a {@code ReflectiveOperationException} will be
414 * thrown from the attempted lookup. The exact class will be one of
415 * the following:
416 * <ul>
417 * <li>NoSuchMethodException — if a method is requested but does not exist
418 * <li>NoSuchFieldException — if a field is requested but does not exist
419 * <li>IllegalAccessException — if the member exists but an access check fails
420 * </ul>
421 * <p>
422 * In general, the conditions under which a method handle may be
423 * looked up for a method {@code M} are no more restrictive than the conditions
424 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
425 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
426 * a method handle lookup will generally raise a corresponding
427 * checked exception, such as {@code NoSuchMethodException}.
428 * And the effect of invoking the method handle resulting from the lookup
429 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
430 * to executing the compiled, verified, and resolved call to {@code M}.
431 * The same point is true of fields and constructors.
432 * <p style="font-size:smaller;">
433 * <em>Discussion:</em>
434 * Access checks only apply to named and reflected methods,
435 * constructors, and fields.
436 * Other method handle creation methods, such as
437 * {@link MethodHandle#asType MethodHandle.asType},
438 * do not require any access checks, and are used
439 * independently of any {@code Lookup} object.
440 * <p>
441 * If the desired member is {@code protected}, the usual JVM rules apply,
442 * including the requirement that the lookup class must be either be in the
443 * same package as the desired member, or must inherit that member.
444 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
445 * In addition, if the desired member is a non-static field or method
446 * in a different package, the resulting method handle may only be applied
447 * to objects of the lookup class or one of its subclasses.
448 * This requirement is enforced by narrowing the type of the leading
449 * {@code this} parameter from {@code C}
450 * (which will necessarily be a superclass of the lookup class)
451 * to the lookup class itself.
452 * <p>
453 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
454 * that the receiver argument must match both the resolved method <em>and</em>
455 * the current class. Again, this requirement is enforced by narrowing the
456 * type of the leading parameter to the resulting method handle.
457 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
458 * <p>
459 * The JVM represents constructors and static initializer blocks as internal methods
460 * with special names ({@code "<init>"} and {@code "<clinit>"}).
461 * The internal syntax of invocation instructions allows them to refer to such internal
462 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
463 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
464 * <p>
465 * In some cases, access between nested classes is obtained by the Java compiler by creating
466 * an wrapper method to access a private method of another class
467 * in the same top-level declaration.
468 * For example, a nested class {@code C.D}
469 * can access private members within other related classes such as
470 * {@code C}, {@code C.D.E}, or {@code C.B},
471 * but the Java compiler may need to generate wrapper methods in
472 * those related classes. In such cases, a {@code Lookup} object on
473 * {@code C.E} would be unable to those private members.
474 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
475 * which can transform a lookup on {@code C.E} into one on any of those other
476 * classes, without special elevation of privilege.
477 * <p>
478 * The accesses permitted to a given lookup object may be limited,
479 * according to its set of {@link #lookupModes lookupModes},
480 * to a subset of members normally accessible to the lookup class.
481 * For example, the {@link MethodHandles#publicLookup publicLookup}
482 * method produces a lookup object which is only allowed to access
483 * public members in public classes of exported packages.
484 * The caller sensitive method {@link MethodHandles#lookup lookup}
485 * produces a lookup object with full capabilities relative to
486 * its caller class, to emulate all supported bytecode behaviors.
487 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
488 * with fewer access modes than the original lookup object.
489 *
490 * <p style="font-size:smaller;">
491 * <a id="privacc"></a>
492 * <em>Discussion of private access:</em>
493 * We say that a lookup has <em>private access</em>
494 * if its {@linkplain #lookupModes lookup modes}
495 * include the possibility of accessing {@code private} members.
496 * As documented in the relevant methods elsewhere,
497 * only lookups with private access possess the following capabilities:
498 * <ul style="font-size:smaller;">
499 * <li>access private fields, methods, and constructors of the lookup class
500 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
501 * such as {@code Class.forName}
502 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
503 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
504 * for classes accessible to the lookup class
505 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
506 * within the same package member
507 * </ul>
508 * <p style="font-size:smaller;">
509 * Each of these permissions is a consequence of the fact that a lookup object
510 * with private access can be securely traced back to an originating class,
511 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
512 * can be reliably determined and emulated by method handles.
513 *
514 * <h1><a id="secmgr"></a>Security manager interactions</h1>
515 * Although bytecode instructions can only refer to classes in
516 * a related class loader, this API can search for methods in any
517 * class, as long as a reference to its {@code Class} object is
518 * available. Such cross-loader references are also possible with the
519 * Core Reflection API, and are impossible to bytecode instructions
520 * such as {@code invokestatic} or {@code getfield}.
521 * There is a {@linkplain java.lang.SecurityManager security manager API}
522 * to allow applications to check such cross-loader references.
523 * These checks apply to both the {@code MethodHandles.Lookup} API
524 * and the Core Reflection API
525 * (as found on {@link java.lang.Class Class}).
526 * <p>
527 * If a security manager is present, member and class lookups are subject to
528 * additional checks.
529 * From one to three calls are made to the security manager.
530 * Any of these calls can refuse access by throwing a
531 * {@link java.lang.SecurityException SecurityException}.
532 * Define {@code smgr} as the security manager,
533 * {@code lookc} as the lookup class of the current lookup object,
534 * {@code refc} as the containing class in which the member
535 * is being sought, and {@code defc} as the class in which the
536 * member is actually defined.
537 * (If a class or other type is being accessed,
538 * the {@code refc} and {@code defc} values are the class itself.)
539 * The value {@code lookc} is defined as <em>not present</em>
540 * if the current lookup object does not have
541 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
542 * The calls are made according to the following rules:
543 * <ul>
544 * <li><b>Step 1:</b>
545 * If {@code lookc} is not present, or if its class loader is not
546 * the same as or an ancestor of the class loader of {@code refc},
547 * then {@link SecurityManager#checkPackageAccess
548 * smgr.checkPackageAccess(refcPkg)} is called,
549 * where {@code refcPkg} is the package of {@code refc}.
550 * <li><b>Step 2a:</b>
551 * If the retrieved member is not public and
552 * {@code lookc} is not present, then
553 * {@link SecurityManager#checkPermission smgr.checkPermission}
554 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
555 * <li><b>Step 2b:</b>
556 * If the retrieved class has a {@code null} class loader,
557 * and {@code lookc} is not present, then
558 * {@link SecurityManager#checkPermission smgr.checkPermission}
559 * with {@code RuntimePermission("getClassLoader")} is called.
560 * <li><b>Step 3:</b>
561 * If the retrieved member is not public,
562 * and if {@code lookc} is not present,
563 * and if {@code defc} and {@code refc} are different,
564 * then {@link SecurityManager#checkPackageAccess
565 * smgr.checkPackageAccess(defcPkg)} is called,
566 * where {@code defcPkg} is the package of {@code defc}.
567 * </ul>
568 * Security checks are performed after other access checks have passed.
569 * Therefore, the above rules presuppose a member or class that is public,
570 * or else that is being accessed from a lookup class that has
571 * rights to access the member or class.
572 *
573 * <h1><a id="callsens"></a>Caller sensitive methods</h1>
574 * A small number of Java methods have a special property called caller sensitivity.
575 * A <em>caller-sensitive</em> method can behave differently depending on the
576 * identity of its immediate caller.
577 * <p>
578 * If a method handle for a caller-sensitive method is requested,
579 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
580 * but they take account of the lookup class in a special way.
581 * The resulting method handle behaves as if it were called
582 * from an instruction contained in the lookup class,
583 * so that the caller-sensitive method detects the lookup class.
584 * (By contrast, the invoker of the method handle is disregarded.)
585 * Thus, in the case of caller-sensitive methods,
586 * different lookup classes may give rise to
587 * differently behaving method handles.
588 * <p>
589 * In cases where the lookup object is
590 * {@link MethodHandles#publicLookup() publicLookup()},
591 * or some other lookup object without
592 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
593 * the lookup class is disregarded.
594 * In such cases, no caller-sensitive method handle can be created,
595 * access is forbidden, and the lookup fails with an
596 * {@code IllegalAccessException}.
597 * <p style="font-size:smaller;">
598 * <em>Discussion:</em>
599 * For example, the caller-sensitive method
600 * {@link java.lang.Class#forName(String) Class.forName(x)}
601 * can return varying classes or throw varying exceptions,
602 * depending on the class loader of the class that calls it.
603 * A public lookup of {@code Class.forName} will fail, because
604 * there is no reasonable way to determine its bytecode behavior.
605 * <p style="font-size:smaller;">
606 * If an application caches method handles for broad sharing,
607 * it should use {@code publicLookup()} to create them.
608 * If there is a lookup of {@code Class.forName}, it will fail,
609 * and the application must take appropriate action in that case.
610 * It may be that a later lookup, perhaps during the invocation of a
611 * bootstrap method, can incorporate the specific identity
612 * of the caller, making the method accessible.
613 * <p style="font-size:smaller;">
614 * The function {@code MethodHandles.lookup} is caller sensitive
615 * so that there can be a secure foundation for lookups.
616 * Nearly all other methods in the JSR 292 API rely on lookup
617 * objects to check access requests.
618 *
619 * @revised 9
620 */
621 public static final
622 class Lookup {
623 /** The class on behalf of whom the lookup is being performed. */
624 private final Class<?> lookupClass;
625
626 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
627 private final int allowedModes;
628
629 /** A single-bit mask representing {@code public} access,
630 * which may contribute to the result of {@link #lookupModes lookupModes}.
631 * The value, {@code 0x01}, happens to be the same as the value of the
632 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
633 */
634 public static final int PUBLIC = Modifier.PUBLIC;
635
636 /** A single-bit mask representing {@code private} access,
637 * which may contribute to the result of {@link #lookupModes lookupModes}.
638 * The value, {@code 0x02}, happens to be the same as the value of the
639 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
640 */
641 public static final int PRIVATE = Modifier.PRIVATE;
642
643 /** A single-bit mask representing {@code protected} access,
644 * which may contribute to the result of {@link #lookupModes lookupModes}.
645 * The value, {@code 0x04}, happens to be the same as the value of the
646 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
647 */
648 public static final int PROTECTED = Modifier.PROTECTED;
649
650 /** A single-bit mask representing {@code package} access (default access),
651 * which may contribute to the result of {@link #lookupModes lookupModes}.
652 * The value is {@code 0x08}, which does not correspond meaningfully to
653 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
654 */
655 public static final int PACKAGE = Modifier.STATIC;
656
657 /** A single-bit mask representing {@code module} access (default access),
658 * which may contribute to the result of {@link #lookupModes lookupModes}.
659 * The value is {@code 0x10}, which does not correspond meaningfully to
660 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
661 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
662 * with this lookup mode can access all public types in the module of the
663 * lookup class and public types in packages exported by other modules
664 * to the module of the lookup class.
665 * @since 9
666 * @spec JPMS
667 */
668 public static final int MODULE = PACKAGE << 1;
669
670 /** A single-bit mask representing {@code unconditional} access
671 * which may contribute to the result of {@link #lookupModes lookupModes}.
672 * The value is {@code 0x20}, which does not correspond meaningfully to
673 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
674 * A {@code Lookup} with this lookup mode assumes {@linkplain
675 * java.lang.Module#canRead(java.lang.Module) readability}.
676 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
677 * with this lookup mode can access all public members of public types
678 * of all modules where the type is in a package that is {@link
679 * java.lang.Module#isExported(String) exported unconditionally}.
680 * @since 9
681 * @spec JPMS
682 * @see #publicLookup()
683 */
684 public static final int UNCONDITIONAL = PACKAGE << 2;
685
686 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
687 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
688 private static final int TRUSTED = -1;
689
690 private static int fixmods(int mods) {
691 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
692 return (mods != 0) ? mods : (PACKAGE | MODULE | UNCONDITIONAL);
693 }
694
695 /** Tells which class is performing the lookup. It is this class against
696 * which checks are performed for visibility and access permissions.
697 * <p>
698 * The class implies a maximum level of access permission,
699 * but the permissions may be additionally limited by the bitmask
700 * {@link #lookupModes lookupModes}, which controls whether non-public members
701 * can be accessed.
702 * @return the lookup class, on behalf of which this lookup object finds members
703 */
704 public Class<?> lookupClass() {
705 return lookupClass;
706 }
707
708 // This is just for calling out to MethodHandleImpl.
709 private Class<?> lookupClassOrNull() {
710 return (allowedModes == TRUSTED) ? null : lookupClass;
711 }
712
713 /** Tells which access-protection classes of members this lookup object can produce.
714 * The result is a bit-mask of the bits
715 * {@linkplain #PUBLIC PUBLIC (0x01)},
716 * {@linkplain #PRIVATE PRIVATE (0x02)},
717 * {@linkplain #PROTECTED PROTECTED (0x04)},
718 * {@linkplain #PACKAGE PACKAGE (0x08)},
719 * {@linkplain #MODULE MODULE (0x10)},
720 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
721 * <p>
722 * A freshly-created lookup object
723 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
724 * all possible bits set, except {@code UNCONDITIONAL}. The lookup can be used to
725 * access all members of the caller's class, all public types in the caller's module,
726 * and all public types in packages exported by other modules to the caller's module.
727 * A lookup object on a new lookup class
728 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
729 * may have some mode bits set to zero.
730 * Mode bits can also be
731 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
732 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
733 * The purpose of this is to restrict access via the new lookup object,
734 * so that it can access only names which can be reached by the original
735 * lookup object, and also by the new lookup class.
736 * @return the lookup modes, which limit the kinds of access performed by this lookup object
737 * @see #in
738 * @see #dropLookupMode
739 *
740 * @revised 9
741 * @spec JPMS
742 */
743 public int lookupModes() {
744 return allowedModes & ALL_MODES;
745 }
746
747 /** Embody the current class (the lookupClass) as a lookup class
748 * for method handle creation.
749 * Must be called by from a method in this package,
750 * which in turn is called by a method not in this package.
751 */
752 Lookup(Class<?> lookupClass) {
753 this(lookupClass, FULL_POWER_MODES);
754 // make sure we haven't accidentally picked up a privileged class:
755 checkUnprivilegedlookupClass(lookupClass, FULL_POWER_MODES);
756 }
757
758 private Lookup(Class<?> lookupClass, int allowedModes) {
759 this.lookupClass = lookupClass;
760 this.allowedModes = allowedModes;
761 }
762
763 /**
764 * Creates a lookup on the specified new lookup class.
765 * The resulting object will report the specified
766 * class as its own {@link #lookupClass lookupClass}.
767 * <p>
768 * However, the resulting {@code Lookup} object is guaranteed
769 * to have no more access capabilities than the original.
770 * In particular, access capabilities can be lost as follows:<ul>
771 * <li>If the old lookup class is in a {@link Module#isNamed() named} module, and
772 * the new lookup class is in a different module {@code M}, then no members, not
773 * even public members in {@code M}'s exported packages, will be accessible.
774 * The exception to this is when this lookup is {@link #publicLookup()
775 * publicLookup}, in which case {@code PUBLIC} access is not lost.
776 * <li>If the old lookup class is in an unnamed module, and the new lookup class
777 * is a different module then {@link #MODULE MODULE} access is lost.
778 * <li>If the new lookup class differs from the old one then {@code UNCONDITIONAL} is lost.
779 * <li>If the new lookup class is in a different package
780 * than the old one, protected and default (package) members will not be accessible.
781 * <li>If the new lookup class is not within the same package member
782 * as the old one, private members will not be accessible, and protected members
783 * will not be accessible by virtue of inheritance.
784 * (Protected members may continue to be accessible because of package sharing.)
785 * <li>If the new lookup class is not accessible to the old lookup class,
786 * then no members, not even public members, will be accessible.
787 * (In all other cases, public members will continue to be accessible.)
788 * </ul>
789 * <p>
790 * The resulting lookup's capabilities for loading classes
791 * (used during {@link #findClass} invocations)
792 * are determined by the lookup class' loader,
793 * which may change due to this operation.
794 *
795 * @param requestedLookupClass the desired lookup class for the new lookup object
796 * @return a lookup object which reports the desired lookup class, or the same object
797 * if there is no change
798 * @throws NullPointerException if the argument is null
799 *
800 * @revised 9
801 * @spec JPMS
802 */
803 public Lookup in(Class<?> requestedLookupClass) {
804 Objects.requireNonNull(requestedLookupClass);
805 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
806 return new Lookup(requestedLookupClass, FULL_POWER_MODES);
807 if (requestedLookupClass == this.lookupClass)
808 return this; // keep same capabilities
809 int newModes = (allowedModes & FULL_POWER_MODES);
810 if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
811 // Need to drop all access when teleporting from a named module to another
812 // module. The exception is publicLookup where PUBLIC is not lost.
813 if (this.lookupClass.getModule().isNamed()
814 && (this.allowedModes & UNCONDITIONAL) == 0)
815 newModes = 0;
816 else
817 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
818 }
819 if ((newModes & PACKAGE) != 0
820 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
821 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
822 }
823 // Allow nestmate lookups to be created without special privilege:
824 if ((newModes & PRIVATE) != 0
825 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
826 newModes &= ~(PRIVATE|PROTECTED);
827 }
828 if ((newModes & PUBLIC) != 0
829 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
830 // The requested class it not accessible from the lookup class.
831 // No permissions.
832 newModes = 0;
833 }
834
835 checkUnprivilegedlookupClass(requestedLookupClass, newModes);
836 return new Lookup(requestedLookupClass, newModes);
837 }
838
839
840 /**
841 * Creates a lookup on the same lookup class which this lookup object
842 * finds members, but with a lookup mode that has lost the given lookup mode.
843 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
844 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
845 * {@link #PROTECTED PROTECTED} and {@link #UNCONDITIONAL UNCONDITIONAL} are always
846 * dropped and so the resulting lookup mode will never have these access capabilities.
847 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
848 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
849 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
850 * is dropped then the resulting lookup has no access.
851 * @param modeToDrop the lookup mode to drop
852 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
853 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
854 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
855 * @see MethodHandles#privateLookupIn
856 * @since 9
857 */
858 public Lookup dropLookupMode(int modeToDrop) {
859 int oldModes = lookupModes();
860 int newModes = oldModes & ~(modeToDrop | PROTECTED | UNCONDITIONAL);
861 switch (modeToDrop) {
862 case PUBLIC: newModes &= ~(ALL_MODES); break;
863 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
864 case PACKAGE: newModes &= ~(PRIVATE); break;
865 case PROTECTED:
866 case PRIVATE:
867 case UNCONDITIONAL: break;
868 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
869 }
870 if (newModes == oldModes) return this; // return self if no change
871 return new Lookup(lookupClass(), newModes);
872 }
873
874 /**
875 * Defines a class to the same class loader and in the same runtime package and
876 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
877 * {@linkplain #lookupClass() lookup class}.
878 *
879 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
880 * {@link #PACKAGE PACKAGE} access as default (package) members will be
881 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
882 * that the lookup object was created by a caller in the runtime package (or derived
883 * from a lookup originally created by suitably privileged code to a target class in
884 * the runtime package). The lookup modes cannot include {@link #PRIVATE PRIVATE}
885 * access. A lookup with {@code PRIVATE} access can be downgraded to drop this lookup
886 * mode with the {@linkplain #dropLookupMode(int) dropLookupMode} method. </p>
887 *
888 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
889 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
890 * same package as the lookup class. </p>
891 *
892 * <p> This method does not run the class initializer. The class initializer may
893 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
894 * Specification</em>. </p>
895 *
896 * <p> If there is a security manager, its {@code checkPermission} method is first called
897 * to check {@code RuntimePermission("defineClass")}. </p>
898 *
899 * @param bytes the class bytes
900 * @return the {@code Class} object for the class
901 * @throws IllegalArgumentException the bytes are for a class in a different package
902 * to the lookup class
903 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
904 * @throws UnsupportedOperationException if the lookup class has {@code PRIVATE} access
905 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
906 * verified ({@code VerifyError}), is already defined, or another linkage error occurs
907 * @throws SecurityException if denied by the security manager
908 * @throws NullPointerException if {@code bytes} is {@code null}
909 * @since 9
910 * @spec JPMS
911 * @see Lookup#privateLookupIn
912 * @see Lookup#dropLookupMode
913 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
914 */
915 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
916 SecurityManager sm = System.getSecurityManager();
917 if (sm != null)
918 sm.checkPermission(new RuntimePermission("defineClass"));
919 if (hasPrivateAccess())
920 throw new UnsupportedOperationException("PRIVATE access not supported");
921 if ((lookupModes() & PACKAGE) == 0)
922 throw new IllegalAccessException("Lookup does not have PACKAGE access");
923 assert (lookupModes() & (MODULE|PUBLIC)) != 0;
924
925 // parse class bytes to get class name (in internal form)
926 bytes = bytes.clone();
927 String name;
928 try {
929 ClassReader reader = new ClassReader(bytes);
930 name = reader.getClassName();
931 } catch (RuntimeException e) {
932 // ASM exceptions are poorly specified
933 ClassFormatError cfe = new ClassFormatError();
934 cfe.initCause(e);
935 throw cfe;
936 }
937
938 // get package and class name in binary form
939 String cn, pn;
940 int index = name.lastIndexOf('/');
941 if (index == -1) {
942 cn = name;
943 pn = "";
944 } else {
945 cn = name.replace('/', '.');
946 pn = cn.substring(0, index);
947 }
948 if (!pn.equals(lookupClass.getPackageName())) {
949 throw new IllegalArgumentException("Class not in same package as lookup class");
950 }
951
952 // invoke the class loader's defineClass method
953 ClassLoader loader = lookupClass.getClassLoader();
954 ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null;
955 String source = "__Lookup_defineClass__";
956 Class<?> clazz = SharedSecrets.getJavaLangAccess().defineClass(loader, cn, bytes, pd, source);
957 assert clazz.getClassLoader() == lookupClass.getClassLoader()
958 && clazz.getPackageName().equals(lookupClass.getPackageName())
959 && protectionDomain(clazz) == lookupClassProtectionDomain();
960 return clazz;
961 }
962
963 private ProtectionDomain lookupClassProtectionDomain() {
964 ProtectionDomain pd = cachedProtectionDomain;
965 if (pd == null) {
966 cachedProtectionDomain = pd = protectionDomain(lookupClass);
967 }
968 return pd;
969 }
970
971 private ProtectionDomain protectionDomain(Class<?> clazz) {
972 PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain;
973 return AccessController.doPrivileged(pa);
974 }
975
976 // cached protection domain
977 private volatile ProtectionDomain cachedProtectionDomain;
978
979
980 // Make sure outer class is initialized first.
981 static { IMPL_NAMES.getClass(); }
982
983 /** Package-private version of lookup which is trusted. */
984 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
985
986 /** Version of lookup which is trusted minimally.
987 * It can only be used to create method handles to publicly accessible
988 * members in packages that are exported unconditionally.
989 */
990 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, (PUBLIC|UNCONDITIONAL));
991
992 private static void checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes) {
993 String name = lookupClass.getName();
994 if (name.startsWith("java.lang.invoke."))
995 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
996
997 // For caller-sensitive MethodHandles.lookup() disallow lookup from
998 // restricted packages. This a fragile and blunt approach.
999 // TODO replace with a more formal and less fragile mechanism
1000 // that does not bluntly restrict classes under packages within
1001 // java.base from looking up MethodHandles or VarHandles.
1002 if (allowedModes == FULL_POWER_MODES && lookupClass.getClassLoader() == null) {
1003 if ((name.startsWith("java.") &&
1004 !name.equals("java.lang.Thread") &&
1005 !name.startsWith("java.util.concurrent.")) ||
1006 (name.startsWith("sun.") &&
1007 !name.startsWith("sun.invoke."))) {
1008 throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
1009 }
1010 }
1011 }
1012
1013 /**
1014 * Displays the name of the class from which lookups are to be made.
1015 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
1016 * If there are restrictions on the access permitted to this lookup,
1017 * this is indicated by adding a suffix to the class name, consisting
1018 * of a slash and a keyword. The keyword represents the strongest
1019 * allowed access, and is chosen as follows:
1020 * <ul>
1021 * <li>If no access is allowed, the suffix is "/noaccess".
1022 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
1023 * <li>If only public access and unconditional access are allowed, the suffix is "/publicLookup".
1024 * <li>If only public and module access are allowed, the suffix is "/module".
1025 * <li>If only public, module and package access are allowed, the suffix is "/package".
1026 * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
1027 * </ul>
1028 * If none of the above cases apply, it is the case that full
1029 * access (public, module, package, private, and protected) is allowed.
1030 * In this case, no suffix is added.
1031 * This is true only of an object obtained originally from
1032 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
1033 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
1034 * always have restricted access, and will display a suffix.
1035 * <p>
1036 * (It may seem strange that protected access should be
1037 * stronger than private access. Viewed independently from
1038 * package access, protected access is the first to be lost,
1039 * because it requires a direct subclass relationship between
1040 * caller and callee.)
1041 * @see #in
1042 *
1043 * @revised 9
1044 * @spec JPMS
1045 */
1046 @Override
1047 public String toString() {
1048 String cname = lookupClass.getName();
1049 switch (allowedModes) {
1050 case 0: // no privileges
1051 return cname + "/noaccess";
1052 case PUBLIC:
1053 return cname + "/public";
1054 case PUBLIC|UNCONDITIONAL:
1055 return cname + "/publicLookup";
1056 case PUBLIC|MODULE:
1057 return cname + "/module";
1058 case PUBLIC|MODULE|PACKAGE:
1059 return cname + "/package";
1060 case FULL_POWER_MODES & ~PROTECTED:
1061 return cname + "/private";
1062 case FULL_POWER_MODES:
1063 return cname;
1064 case TRUSTED:
1065 return "/trusted"; // internal only; not exported
1066 default: // Should not happen, but it's a bitfield...
1067 cname = cname + "/" + Integer.toHexString(allowedModes);
1068 assert(false) : cname;
1069 return cname;
1070 }
1071 }
1072
1073 /**
1074 * Produces a method handle for a static method.
1075 * The type of the method handle will be that of the method.
1076 * (Since static methods do not take receivers, there is no
1077 * additional receiver argument inserted into the method handle type,
1078 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
1079 * The method and all its argument types must be accessible to the lookup object.
1080 * <p>
1081 * The returned method handle will have
1082 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1083 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1084 * <p>
1085 * If the returned method handle is invoked, the method's class will
1086 * be initialized, if it has not already been initialized.
1087 * <p><b>Example:</b>
1088 * <blockquote><pre>{@code
1089 import static java.lang.invoke.MethodHandles.*;
1090 import static java.lang.invoke.MethodType.*;
1091 ...
1092 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
1093 "asList", methodType(List.class, Object[].class));
1094 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
1095 * }</pre></blockquote>
1096 * @param refc the class from which the method is accessed
1097 * @param name the name of the method
1098 * @param type the type of the method
1099 * @return the desired method handle
1100 * @throws NoSuchMethodException if the method does not exist
1101 * @throws IllegalAccessException if access checking fails,
1102 * or if the method is not {@code static},
1103 * or if the method's variable arity modifier bit
1104 * is set and {@code asVarargsCollector} fails
1105 * @exception SecurityException if a security manager is present and it
1106 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1107 * @throws NullPointerException if any argument is null
1108 */
1109 public
1110 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1111 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
1112 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
1113 }
1114
1115 /**
1116 * Produces a method handle for a virtual method.
1117 * The type of the method handle will be that of the method,
1118 * with the receiver type (usually {@code refc}) prepended.
1119 * The method and all its argument types must be accessible to the lookup object.
1120 * <p>
1121 * When called, the handle will treat the first argument as a receiver
1122 * and dispatch on the receiver's type to determine which method
1123 * implementation to enter.
1124 * (The dispatching action is identical with that performed by an
1125 * {@code invokevirtual} or {@code invokeinterface} instruction.)
1126 * <p>
1127 * The first argument will be of type {@code refc} if the lookup
1128 * class has full privileges to access the member. Otherwise
1129 * the member must be {@code protected} and the first argument
1130 * will be restricted in type to the lookup class.
1131 * <p>
1132 * The returned method handle will have
1133 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1134 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1135 * <p>
1136 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
1137 * instructions and method handles produced by {@code findVirtual},
1138 * if the class is {@code MethodHandle} and the name string is
1139 * {@code invokeExact} or {@code invoke}, the resulting
1140 * method handle is equivalent to one produced by
1141 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
1142 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
1143 * with the same {@code type} argument.
1144 * <p>
1145 * If the class is {@code VarHandle} and the name string corresponds to
1146 * the name of a signature-polymorphic access mode method, the resulting
1147 * method handle is equivalent to one produced by
1148 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
1149 * the access mode corresponding to the name string and with the same
1150 * {@code type} arguments.
1151 * <p>
1152 * <b>Example:</b>
1153 * <blockquote><pre>{@code
1154 import static java.lang.invoke.MethodHandles.*;
1155 import static java.lang.invoke.MethodType.*;
1156 ...
1157 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
1158 "concat", methodType(String.class, String.class));
1159 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1160 "hashCode", methodType(int.class));
1161 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1162 "hashCode", methodType(int.class));
1163 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1164 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1165 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1166 // interface method:
1167 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1168 "subSequence", methodType(CharSequence.class, int.class, int.class));
1169 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1170 // constructor "internal method" must be accessed differently:
1171 MethodType MT_newString = methodType(void.class); //()V for new String()
1172 try { assertEquals("impossible", lookup()
1173 .findVirtual(String.class, "<init>", MT_newString));
1174 } catch (NoSuchMethodException ex) { } // OK
1175 MethodHandle MH_newString = publicLookup()
1176 .findConstructor(String.class, MT_newString);
1177 assertEquals("", (String) MH_newString.invokeExact());
1178 * }</pre></blockquote>
1179 *
1180 * @param refc the class or interface from which the method is accessed
1181 * @param name the name of the method
1182 * @param type the type of the method, with the receiver argument omitted
1183 * @return the desired method handle
1184 * @throws NoSuchMethodException if the method does not exist
1185 * @throws IllegalAccessException if access checking fails,
1186 * or if the method is {@code static},
1187 * or if the method is {@code private} method of interface,
1188 * or if the method's variable arity modifier bit
1189 * is set and {@code asVarargsCollector} fails
1190 * @exception SecurityException if a security manager is present and it
1191 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1192 * @throws NullPointerException if any argument is null
1193 */
1194 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1195 if (refc == MethodHandle.class) {
1196 MethodHandle mh = findVirtualForMH(name, type);
1197 if (mh != null) return mh;
1198 } else if (refc == VarHandle.class) {
1199 MethodHandle mh = findVirtualForVH(name, type);
1200 if (mh != null) return mh;
1201 }
1202 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1203 MemberName method = resolveOrFail(refKind, refc, name, type);
1204 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
1205 }
1206 private MethodHandle findVirtualForMH(String name, MethodType type) {
1207 // these names require special lookups because of the implicit MethodType argument
1208 if ("invoke".equals(name))
1209 return invoker(type);
1210 if ("invokeExact".equals(name))
1211 return exactInvoker(type);
1212 assert(!MemberName.isMethodHandleInvokeName(name));
1213 return null;
1214 }
1215 private MethodHandle findVirtualForVH(String name, MethodType type) {
1216 try {
1217 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1218 } catch (IllegalArgumentException e) {
1219 return null;
1220 }
1221 }
1222
1223 /**
1224 * Produces a method handle which creates an object and initializes it, using
1225 * the constructor of the specified type.
1226 * The parameter types of the method handle will be those of the constructor,
1227 * while the return type will be a reference to the constructor's class.
1228 * The constructor and all its argument types must be accessible to the lookup object.
1229 * <p>
1230 * The requested type must have a return type of {@code void}.
1231 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1232 * <p>
1233 * The returned method handle will have
1234 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1235 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1236 * <p>
1237 * If the returned method handle is invoked, the constructor's class will
1238 * be initialized, if it has not already been initialized.
1239 * <p><b>Example:</b>
1240 * <blockquote><pre>{@code
1241 import static java.lang.invoke.MethodHandles.*;
1242 import static java.lang.invoke.MethodType.*;
1243 ...
1244 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1245 ArrayList.class, methodType(void.class, Collection.class));
1246 Collection orig = Arrays.asList("x", "y");
1247 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1248 assert(orig != copy);
1249 assertEquals(orig, copy);
1250 // a variable-arity constructor:
1251 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1252 ProcessBuilder.class, methodType(void.class, String[].class));
1253 ProcessBuilder pb = (ProcessBuilder)
1254 MH_newProcessBuilder.invoke("x", "y", "z");
1255 assertEquals("[x, y, z]", pb.command().toString());
1256 * }</pre></blockquote>
1257 * @param refc the class or interface from which the method is accessed
1258 * @param type the type of the method, with the receiver argument omitted, and a void return type
1259 * @return the desired method handle
1260 * @throws NoSuchMethodException if the constructor does not exist
1261 * @throws IllegalAccessException if access checking fails
1262 * or if the method's variable arity modifier bit
1263 * is set and {@code asVarargsCollector} fails
1264 * @exception SecurityException if a security manager is present and it
1265 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1266 * @throws NullPointerException if any argument is null
1267 */
1268 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1269 if (refc.isArray()) {
1270 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1271 }
1272 String name = "<init>";
1273 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1274 return getDirectConstructor(refc, ctor);
1275 }
1276
1277 /**
1278 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1279 * initializer of the class is not run.
1280 * <p>
1281 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1282 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1283 * load the requested class, and then determines whether the class is accessible to this lookup object.
1284 *
1285 * @param targetName the fully qualified name of the class to be looked up.
1286 * @return the requested class.
1287 * @exception SecurityException if a security manager is present and it
1288 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1289 * @throws LinkageError if the linkage fails
1290 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1291 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1292 * modes.
1293 * @exception SecurityException if a security manager is present and it
1294 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1295 * @since 9
1296 */
1297 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1298 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1299 return accessClass(targetClass);
1300 }
1301
1302 /**
1303 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1304 * static initializer of the class is not run.
1305 * <p>
1306 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1307 * {@linkplain #lookupModes() lookup modes}.
1308 *
1309 * @param targetClass the class to be access-checked
1310 *
1311 * @return the class that has been access-checked
1312 *
1313 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1314 * modes.
1315 * @exception SecurityException if a security manager is present and it
1316 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1317 * @since 9
1318 */
1319 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1320 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1321 throw new MemberName(targetClass).makeAccessException("access violation", this);
1322 }
1323 checkSecurityManager(targetClass, null);
1324 return targetClass;
1325 }
1326
1327 /**
1328 * Produces an early-bound method handle for a virtual method.
1329 * It will bypass checks for overriding methods on the receiver,
1330 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1331 * instruction from within the explicitly specified {@code specialCaller}.
1332 * The type of the method handle will be that of the method,
1333 * with a suitably restricted receiver type prepended.
1334 * (The receiver type will be {@code specialCaller} or a subtype.)
1335 * The method and all its argument types must be accessible
1336 * to the lookup object.
1337 * <p>
1338 * Before method resolution,
1339 * if the explicitly specified caller class is not identical with the
1340 * lookup class, or if this lookup object does not have
1341 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1342 * privileges, the access fails.
1343 * <p>
1344 * The returned method handle will have
1345 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1346 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1347 * <p style="font-size:smaller;">
1348 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1349 * even though the {@code invokespecial} instruction can refer to them
1350 * in special circumstances. Use {@link #findConstructor findConstructor}
1351 * to access instance initialization methods in a safe manner.)</em>
1352 * <p><b>Example:</b>
1353 * <blockquote><pre>{@code
1354 import static java.lang.invoke.MethodHandles.*;
1355 import static java.lang.invoke.MethodType.*;
1356 ...
1357 static class Listie extends ArrayList {
1358 public String toString() { return "[wee Listie]"; }
1359 static Lookup lookup() { return MethodHandles.lookup(); }
1360 }
1361 ...
1362 // no access to constructor via invokeSpecial:
1363 MethodHandle MH_newListie = Listie.lookup()
1364 .findConstructor(Listie.class, methodType(void.class));
1365 Listie l = (Listie) MH_newListie.invokeExact();
1366 try { assertEquals("impossible", Listie.lookup().findSpecial(
1367 Listie.class, "<init>", methodType(void.class), Listie.class));
1368 } catch (NoSuchMethodException ex) { } // OK
1369 // access to super and self methods via invokeSpecial:
1370 MethodHandle MH_super = Listie.lookup().findSpecial(
1371 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1372 MethodHandle MH_this = Listie.lookup().findSpecial(
1373 Listie.class, "toString" , methodType(String.class), Listie.class);
1374 MethodHandle MH_duper = Listie.lookup().findSpecial(
1375 Object.class, "toString" , methodType(String.class), Listie.class);
1376 assertEquals("[]", (String) MH_super.invokeExact(l));
1377 assertEquals(""+l, (String) MH_this.invokeExact(l));
1378 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1379 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1380 String.class, "toString", methodType(String.class), Listie.class));
1381 } catch (IllegalAccessException ex) { } // OK
1382 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1383 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1384 * }</pre></blockquote>
1385 *
1386 * @param refc the class or interface from which the method is accessed
1387 * @param name the name of the method (which must not be "<init>")
1388 * @param type the type of the method, with the receiver argument omitted
1389 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1390 * @return the desired method handle
1391 * @throws NoSuchMethodException if the method does not exist
1392 * @throws IllegalAccessException if access checking fails,
1393 * or if the method is {@code static},
1394 * or if the method's variable arity modifier bit
1395 * is set and {@code asVarargsCollector} fails
1396 * @exception SecurityException if a security manager is present and it
1397 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1398 * @throws NullPointerException if any argument is null
1399 */
1400 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1401 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1402 checkSpecialCaller(specialCaller, refc);
1403 Lookup specialLookup = this.in(specialCaller);
1404 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1405 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1406 }
1407
1408 /**
1409 * Produces a method handle giving read access to a non-static field.
1410 * The type of the method handle will have a return type of the field's
1411 * value type.
1412 * The method handle's single argument will be the instance containing
1413 * the field.
1414 * Access checking is performed immediately on behalf of the lookup class.
1415 * @param refc the class or interface from which the method is accessed
1416 * @param name the field's name
1417 * @param type the field's type
1418 * @return a method handle which can load values from the field
1419 * @throws NoSuchFieldException if the field does not exist
1420 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1421 * @exception SecurityException if a security manager is present and it
1422 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1423 * @throws NullPointerException if any argument is null
1424 * @see #findVarHandle(Class, String, Class)
1425 */
1426 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1427 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1428 return getDirectField(REF_getField, refc, field);
1429 }
1430
1431 /**
1432 * Produces a method handle giving write access to a non-static field.
1433 * The type of the method handle will have a void return type.
1434 * The method handle will take two arguments, the instance containing
1435 * the field, and the value to be stored.
1436 * The second argument will be of the field's value type.
1437 * Access checking is performed immediately on behalf of the lookup class.
1438 * @param refc the class or interface from which the method is accessed
1439 * @param name the field's name
1440 * @param type the field's type
1441 * @return a method handle which can store values into the field
1442 * @throws NoSuchFieldException if the field does not exist
1443 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1444 * @exception SecurityException if a security manager is present and it
1445 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1446 * @throws NullPointerException if any argument is null
1447 * @see #findVarHandle(Class, String, Class)
1448 */
1449 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1450 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1451 return getDirectField(REF_putField, refc, field);
1452 }
1453
1454 /**
1455 * Produces a VarHandle giving access to a non-static field {@code name}
1456 * of type {@code type} declared in a class of type {@code recv}.
1457 * The VarHandle's variable type is {@code type} and it has one
1458 * coordinate type, {@code recv}.
1459 * <p>
1460 * Access checking is performed immediately on behalf of the lookup
1461 * class.
1462 * <p>
1463 * Certain access modes of the returned VarHandle are unsupported under
1464 * the following conditions:
1465 * <ul>
1466 * <li>if the field is declared {@code final}, then the write, atomic
1467 * update, numeric atomic update, and bitwise atomic update access
1468 * modes are unsupported.
1469 * <li>if the field type is anything other than {@code byte},
1470 * {@code short}, {@code char}, {@code int}, {@code long},
1471 * {@code float}, or {@code double} then numeric atomic update
1472 * access modes are unsupported.
1473 * <li>if the field type is anything other than {@code boolean},
1474 * {@code byte}, {@code short}, {@code char}, {@code int} or
1475 * {@code long} then bitwise atomic update access modes are
1476 * unsupported.
1477 * </ul>
1478 * <p>
1479 * If the field is declared {@code volatile} then the returned VarHandle
1480 * will override access to the field (effectively ignore the
1481 * {@code volatile} declaration) in accordance to its specified
1482 * access modes.
1483 * <p>
1484 * If the field type is {@code float} or {@code double} then numeric
1485 * and atomic update access modes compare values using their bitwise
1486 * representation (see {@link Float#floatToRawIntBits} and
1487 * {@link Double#doubleToRawLongBits}, respectively).
1488 * @apiNote
1489 * Bitwise comparison of {@code float} values or {@code double} values,
1490 * as performed by the numeric and atomic update access modes, differ
1491 * from the primitive {@code ==} operator and the {@link Float#equals}
1492 * and {@link Double#equals} methods, specifically with respect to
1493 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1494 * Care should be taken when performing a compare and set or a compare
1495 * and exchange operation with such values since the operation may
1496 * unexpectedly fail.
1497 * There are many possible NaN values that are considered to be
1498 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1499 * provided by Java can distinguish between them. Operation failure can
1500 * occur if the expected or witness value is a NaN value and it is
1501 * transformed (perhaps in a platform specific manner) into another NaN
1502 * value, and thus has a different bitwise representation (see
1503 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1504 * details).
1505 * The values {@code -0.0} and {@code +0.0} have different bitwise
1506 * representations but are considered equal when using the primitive
1507 * {@code ==} operator. Operation failure can occur if, for example, a
1508 * numeric algorithm computes an expected value to be say {@code -0.0}
1509 * and previously computed the witness value to be say {@code +0.0}.
1510 * @param recv the receiver class, of type {@code R}, that declares the
1511 * non-static field
1512 * @param name the field's name
1513 * @param type the field's type, of type {@code T}
1514 * @return a VarHandle giving access to non-static fields.
1515 * @throws NoSuchFieldException if the field does not exist
1516 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1517 * @exception SecurityException if a security manager is present and it
1518 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1519 * @throws NullPointerException if any argument is null
1520 * @since 9
1521 */
1522 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1523 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1524 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1525 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1526 }
1527
1528 /**
1529 * Produces a method handle giving read access to a static field.
1530 * The type of the method handle will have a return type of the field's
1531 * value type.
1532 * The method handle will take no arguments.
1533 * Access checking is performed immediately on behalf of the lookup class.
1534 * <p>
1535 * If the returned method handle is invoked, the field's class will
1536 * be initialized, if it has not already been initialized.
1537 * @param refc the class or interface from which the method is accessed
1538 * @param name the field's name
1539 * @param type the field's type
1540 * @return a method handle which can load values from the field
1541 * @throws NoSuchFieldException if the field does not exist
1542 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1543 * @exception SecurityException if a security manager is present and it
1544 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1545 * @throws NullPointerException if any argument is null
1546 */
1547 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1548 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1549 return getDirectField(REF_getStatic, refc, field);
1550 }
1551
1552 /**
1553 * Produces a method handle giving write access to a static field.
1554 * The type of the method handle will have a void return type.
1555 * The method handle will take a single
1556 * argument, of the field's value type, the value to be stored.
1557 * Access checking is performed immediately on behalf of the lookup class.
1558 * <p>
1559 * If the returned method handle is invoked, the field's class will
1560 * be initialized, if it has not already been initialized.
1561 * @param refc the class or interface from which the method is accessed
1562 * @param name the field's name
1563 * @param type the field's type
1564 * @return a method handle which can store values into the field
1565 * @throws NoSuchFieldException if the field does not exist
1566 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1567 * @exception SecurityException if a security manager is present and it
1568 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1569 * @throws NullPointerException if any argument is null
1570 */
1571 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1572 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1573 return getDirectField(REF_putStatic, refc, field);
1574 }
1575
1576 /**
1577 * Produces a VarHandle giving access to a static field {@code name} of
1578 * type {@code type} declared in a class of type {@code decl}.
1579 * The VarHandle's variable type is {@code type} and it has no
1580 * coordinate types.
1581 * <p>
1582 * Access checking is performed immediately on behalf of the lookup
1583 * class.
1584 * <p>
1585 * If the returned VarHandle is operated on, the declaring class will be
1586 * initialized, if it has not already been initialized.
1587 * <p>
1588 * Certain access modes of the returned VarHandle are unsupported under
1589 * the following conditions:
1590 * <ul>
1591 * <li>if the field is declared {@code final}, then the write, atomic
1592 * update, numeric atomic update, and bitwise atomic update access
1593 * modes are unsupported.
1594 * <li>if the field type is anything other than {@code byte},
1595 * {@code short}, {@code char}, {@code int}, {@code long},
1596 * {@code float}, or {@code double}, then numeric atomic update
1597 * access modes are unsupported.
1598 * <li>if the field type is anything other than {@code boolean},
1599 * {@code byte}, {@code short}, {@code char}, {@code int} or
1600 * {@code long} then bitwise atomic update access modes are
1601 * unsupported.
1602 * </ul>
1603 * <p>
1604 * If the field is declared {@code volatile} then the returned VarHandle
1605 * will override access to the field (effectively ignore the
1606 * {@code volatile} declaration) in accordance to its specified
1607 * access modes.
1608 * <p>
1609 * If the field type is {@code float} or {@code double} then numeric
1610 * and atomic update access modes compare values using their bitwise
1611 * representation (see {@link Float#floatToRawIntBits} and
1612 * {@link Double#doubleToRawLongBits}, respectively).
1613 * @apiNote
1614 * Bitwise comparison of {@code float} values or {@code double} values,
1615 * as performed by the numeric and atomic update access modes, differ
1616 * from the primitive {@code ==} operator and the {@link Float#equals}
1617 * and {@link Double#equals} methods, specifically with respect to
1618 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1619 * Care should be taken when performing a compare and set or a compare
1620 * and exchange operation with such values since the operation may
1621 * unexpectedly fail.
1622 * There are many possible NaN values that are considered to be
1623 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1624 * provided by Java can distinguish between them. Operation failure can
1625 * occur if the expected or witness value is a NaN value and it is
1626 * transformed (perhaps in a platform specific manner) into another NaN
1627 * value, and thus has a different bitwise representation (see
1628 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1629 * details).
1630 * The values {@code -0.0} and {@code +0.0} have different bitwise
1631 * representations but are considered equal when using the primitive
1632 * {@code ==} operator. Operation failure can occur if, for example, a
1633 * numeric algorithm computes an expected value to be say {@code -0.0}
1634 * and previously computed the witness value to be say {@code +0.0}.
1635 * @param decl the class that declares the static field
1636 * @param name the field's name
1637 * @param type the field's type, of type {@code T}
1638 * @return a VarHandle giving access to a static field
1639 * @throws NoSuchFieldException if the field does not exist
1640 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1641 * @exception SecurityException if a security manager is present and it
1642 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1643 * @throws NullPointerException if any argument is null
1644 * @since 9
1645 */
1646 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1647 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1648 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1649 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1650 }
1651
1652 /**
1653 * Produces an early-bound method handle for a non-static method.
1654 * The receiver must have a supertype {@code defc} in which a method
1655 * of the given name and type is accessible to the lookup class.
1656 * The method and all its argument types must be accessible to the lookup object.
1657 * The type of the method handle will be that of the method,
1658 * without any insertion of an additional receiver parameter.
1659 * The given receiver will be bound into the method handle,
1660 * so that every call to the method handle will invoke the
1661 * requested method on the given receiver.
1662 * <p>
1663 * The returned method handle will have
1664 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1665 * the method's variable arity modifier bit ({@code 0x0080}) is set
1666 * <em>and</em> the trailing array argument is not the only argument.
1667 * (If the trailing array argument is the only argument,
1668 * the given receiver value will be bound to it.)
1669 * <p>
1670 * This is equivalent to the following code:
1671 * <blockquote><pre>{@code
1672 import static java.lang.invoke.MethodHandles.*;
1673 import static java.lang.invoke.MethodType.*;
1674 ...
1675 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1676 MethodHandle mh1 = mh0.bindTo(receiver);
1677 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1678 return mh1;
1679 * }</pre></blockquote>
1680 * where {@code defc} is either {@code receiver.getClass()} or a super
1681 * type of that class, in which the requested method is accessible
1682 * to the lookup class.
1683 * (Note that {@code bindTo} does not preserve variable arity.)
1684 * @param receiver the object from which the method is accessed
1685 * @param name the name of the method
1686 * @param type the type of the method, with the receiver argument omitted
1687 * @return the desired method handle
1688 * @throws NoSuchMethodException if the method does not exist
1689 * @throws IllegalAccessException if access checking fails
1690 * or if the method's variable arity modifier bit
1691 * is set and {@code asVarargsCollector} fails
1692 * @exception SecurityException if a security manager is present and it
1693 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1694 * @throws NullPointerException if any argument is null
1695 * @see MethodHandle#bindTo
1696 * @see #findVirtual
1697 */
1698 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1699 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1700 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1701 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
1702 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
1703 throw new IllegalAccessException("The restricted defining class " +
1704 mh.type().leadingReferenceParameter().getName() +
1705 " is not assignable from receiver class " +
1706 receiver.getClass().getName());
1707 }
1708 return mh.bindArgumentL(0, receiver).setVarargs(method);
1709 }
1710
1711 /**
1712 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1713 * to <i>m</i>, if the lookup class has permission.
1714 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1715 * If <i>m</i> is virtual, overriding is respected on every call.
1716 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1717 * The type of the method handle will be that of the method,
1718 * with the receiver type prepended (but only if it is non-static).
1719 * If the method's {@code accessible} flag is not set,
1720 * access checking is performed immediately on behalf of the lookup class.
1721 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1722 * <p>
1723 * The returned method handle will have
1724 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1725 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1726 * <p>
1727 * If <i>m</i> is static, and
1728 * if the returned method handle is invoked, the method's class will
1729 * be initialized, if it has not already been initialized.
1730 * @param m the reflected method
1731 * @return a method handle which can invoke the reflected method
1732 * @throws IllegalAccessException if access checking fails
1733 * or if the method's variable arity modifier bit
1734 * is set and {@code asVarargsCollector} fails
1735 * @throws NullPointerException if the argument is null
1736 */
1737 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1738 if (m.getDeclaringClass() == MethodHandle.class) {
1739 MethodHandle mh = unreflectForMH(m);
1740 if (mh != null) return mh;
1741 }
1742 if (m.getDeclaringClass() == VarHandle.class) {
1743 MethodHandle mh = unreflectForVH(m);
1744 if (mh != null) return mh;
1745 }
1746 MemberName method = new MemberName(m);
1747 byte refKind = method.getReferenceKind();
1748 if (refKind == REF_invokeSpecial)
1749 refKind = REF_invokeVirtual;
1750 assert(method.isMethod());
1751 @SuppressWarnings("deprecation")
1752 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1753 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1754 }
1755 private MethodHandle unreflectForMH(Method m) {
1756 // these names require special lookups because they throw UnsupportedOperationException
1757 if (MemberName.isMethodHandleInvokeName(m.getName()))
1758 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1759 return null;
1760 }
1761 private MethodHandle unreflectForVH(Method m) {
1762 // these names require special lookups because they throw UnsupportedOperationException
1763 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
1764 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
1765 return null;
1766 }
1767
1768 /**
1769 * Produces a method handle for a reflected method.
1770 * It will bypass checks for overriding methods on the receiver,
1771 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1772 * instruction from within the explicitly specified {@code specialCaller}.
1773 * The type of the method handle will be that of the method,
1774 * with a suitably restricted receiver type prepended.
1775 * (The receiver type will be {@code specialCaller} or a subtype.)
1776 * If the method's {@code accessible} flag is not set,
1777 * access checking is performed immediately on behalf of the lookup class,
1778 * as if {@code invokespecial} instruction were being linked.
1779 * <p>
1780 * Before method resolution,
1781 * if the explicitly specified caller class is not identical with the
1782 * lookup class, or if this lookup object does not have
1783 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1784 * privileges, the access fails.
1785 * <p>
1786 * The returned method handle will have
1787 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1788 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1789 * @param m the reflected method
1790 * @param specialCaller the class nominally calling the method
1791 * @return a method handle which can invoke the reflected method
1792 * @throws IllegalAccessException if access checking fails,
1793 * or if the method is {@code static},
1794 * or if the method's variable arity modifier bit
1795 * is set and {@code asVarargsCollector} fails
1796 * @throws NullPointerException if any argument is null
1797 */
1798 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1799 checkSpecialCaller(specialCaller, null);
1800 Lookup specialLookup = this.in(specialCaller);
1801 MemberName method = new MemberName(m, true);
1802 assert(method.isMethod());
1803 // ignore m.isAccessible: this is a new kind of access
1804 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1805 }
1806
1807 /**
1808 * Produces a method handle for a reflected constructor.
1809 * The type of the method handle will be that of the constructor,
1810 * with the return type changed to the declaring class.
1811 * The method handle will perform a {@code newInstance} operation,
1812 * creating a new instance of the constructor's class on the
1813 * arguments passed to the method handle.
1814 * <p>
1815 * If the constructor's {@code accessible} flag is not set,
1816 * access checking is performed immediately on behalf of the lookup class.
1817 * <p>
1818 * The returned method handle will have
1819 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1820 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1821 * <p>
1822 * If the returned method handle is invoked, the constructor's class will
1823 * be initialized, if it has not already been initialized.
1824 * @param c the reflected constructor
1825 * @return a method handle which can invoke the reflected constructor
1826 * @throws IllegalAccessException if access checking fails
1827 * or if the method's variable arity modifier bit
1828 * is set and {@code asVarargsCollector} fails
1829 * @throws NullPointerException if the argument is null
1830 */
1831 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1832 MemberName ctor = new MemberName(c);
1833 assert(ctor.isConstructor());
1834 @SuppressWarnings("deprecation")
1835 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1836 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1837 }
1838
1839 /**
1840 * Produces a method handle giving read access to a reflected field.
1841 * The type of the method handle will have a return type of the field's
1842 * value type.
1843 * If the field is static, the method handle will take no arguments.
1844 * Otherwise, its single argument will be the instance containing
1845 * the field.
1846 * If the field's {@code accessible} flag is not set,
1847 * access checking is performed immediately on behalf of the lookup class.
1848 * <p>
1849 * If the field is static, and
1850 * if the returned method handle is invoked, the field's class will
1851 * be initialized, if it has not already been initialized.
1852 * @param f the reflected field
1853 * @return a method handle which can load values from the reflected field
1854 * @throws IllegalAccessException if access checking fails
1855 * @throws NullPointerException if the argument is null
1856 */
1857 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1858 return unreflectField(f, false);
1859 }
1860 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1861 MemberName field = new MemberName(f, isSetter);
1862 assert(isSetter
1863 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1864 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1865 @SuppressWarnings("deprecation")
1866 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1867 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1868 }
1869
1870 /**
1871 * Produces a method handle giving write access to a reflected field.
1872 * The type of the method handle will have a void return type.
1873 * If the field is static, the method handle will take a single
1874 * argument, of the field's value type, the value to be stored.
1875 * Otherwise, the two arguments will be the instance containing
1876 * the field, and the value to be stored.
1877 * If the field's {@code accessible} flag is not set,
1878 * access checking is performed immediately on behalf of the lookup class.
1879 * <p>
1880 * If the field is static, and
1881 * if the returned method handle is invoked, the field's class will
1882 * be initialized, if it has not already been initialized.
1883 * @param f the reflected field
1884 * @return a method handle which can store values into the reflected field
1885 * @throws IllegalAccessException if access checking fails
1886 * @throws NullPointerException if the argument is null
1887 */
1888 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1889 return unreflectField(f, true);
1890 }
1891
1892 /**
1893 * Produces a VarHandle giving access to a reflected field {@code f}
1894 * of type {@code T} declared in a class of type {@code R}.
1895 * The VarHandle's variable type is {@code T}.
1896 * If the field is non-static the VarHandle has one coordinate type,
1897 * {@code R}. Otherwise, the field is static, and the VarHandle has no
1898 * coordinate types.
1899 * <p>
1900 * Access checking is performed immediately on behalf of the lookup
1901 * class, regardless of the value of the field's {@code accessible}
1902 * flag.
1903 * <p>
1904 * If the field is static, and if the returned VarHandle is operated
1905 * on, the field's declaring class will be initialized, if it has not
1906 * already been initialized.
1907 * <p>
1908 * Certain access modes of the returned VarHandle are unsupported under
1909 * the following conditions:
1910 * <ul>
1911 * <li>if the field is declared {@code final}, then the write, atomic
1912 * update, numeric atomic update, and bitwise atomic update access
1913 * modes are unsupported.
1914 * <li>if the field type is anything other than {@code byte},
1915 * {@code short}, {@code char}, {@code int}, {@code long},
1916 * {@code float}, or {@code double} then numeric atomic update
1917 * access modes are unsupported.
1918 * <li>if the field type is anything other than {@code boolean},
1919 * {@code byte}, {@code short}, {@code char}, {@code int} or
1920 * {@code long} then bitwise atomic update access modes are
1921 * unsupported.
1922 * </ul>
1923 * <p>
1924 * If the field is declared {@code volatile} then the returned VarHandle
1925 * will override access to the field (effectively ignore the
1926 * {@code volatile} declaration) in accordance to its specified
1927 * access modes.
1928 * <p>
1929 * If the field type is {@code float} or {@code double} then numeric
1930 * and atomic update access modes compare values using their bitwise
1931 * representation (see {@link Float#floatToRawIntBits} and
1932 * {@link Double#doubleToRawLongBits}, respectively).
1933 * @apiNote
1934 * Bitwise comparison of {@code float} values or {@code double} values,
1935 * as performed by the numeric and atomic update access modes, differ
1936 * from the primitive {@code ==} operator and the {@link Float#equals}
1937 * and {@link Double#equals} methods, specifically with respect to
1938 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1939 * Care should be taken when performing a compare and set or a compare
1940 * and exchange operation with such values since the operation may
1941 * unexpectedly fail.
1942 * There are many possible NaN values that are considered to be
1943 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1944 * provided by Java can distinguish between them. Operation failure can
1945 * occur if the expected or witness value is a NaN value and it is
1946 * transformed (perhaps in a platform specific manner) into another NaN
1947 * value, and thus has a different bitwise representation (see
1948 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1949 * details).
1950 * The values {@code -0.0} and {@code +0.0} have different bitwise
1951 * representations but are considered equal when using the primitive
1952 * {@code ==} operator. Operation failure can occur if, for example, a
1953 * numeric algorithm computes an expected value to be say {@code -0.0}
1954 * and previously computed the witness value to be say {@code +0.0}.
1955 * @param f the reflected field, with a field of type {@code T}, and
1956 * a declaring class of type {@code R}
1957 * @return a VarHandle giving access to non-static fields or a static
1958 * field
1959 * @throws IllegalAccessException if access checking fails
1960 * @throws NullPointerException if the argument is null
1961 * @since 9
1962 */
1963 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
1964 MemberName getField = new MemberName(f, false);
1965 MemberName putField = new MemberName(f, true);
1966 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
1967 f.getDeclaringClass(), getField, putField);
1968 }
1969
1970 /**
1971 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1972 * created by this lookup object or a similar one.
1973 * Security and access checks are performed to ensure that this lookup object
1974 * is capable of reproducing the target method handle.
1975 * This means that the cracking may fail if target is a direct method handle
1976 * but was created by an unrelated lookup object.
1977 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1978 * and was created by a lookup object for a different class.
1979 * @param target a direct method handle to crack into symbolic reference components
1980 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1981 * @exception SecurityException if a security manager is present and it
1982 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1983 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1984 * @exception NullPointerException if the target is {@code null}
1985 * @see MethodHandleInfo
1986 * @since 1.8
1987 */
1988 public MethodHandleInfo revealDirect(MethodHandle target) {
1989 MemberName member = target.internalMemberName();
1990 if (member == null || (!member.isResolved() &&
1991 !member.isMethodHandleInvoke() &&
1992 !member.isVarHandleMethodInvoke()))
1993 throw newIllegalArgumentException("not a direct method handle");
1994 Class<?> defc = member.getDeclaringClass();
1995 byte refKind = member.getReferenceKind();
1996 assert(MethodHandleNatives.refKindIsValid(refKind));
1997 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1998 // Devirtualized method invocation is usually formally virtual.
1999 // To avoid creating extra MemberName objects for this common case,
2000 // we encode this extra degree of freedom using MH.isInvokeSpecial.
2001 refKind = REF_invokeVirtual;
2002 if (refKind == REF_invokeVirtual && defc.isInterface())
2003 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
2004 refKind = REF_invokeInterface;
2005 // Check SM permissions and member access before cracking.
2006 try {
2007 checkAccess(refKind, defc, member);
2008 checkSecurityManager(defc, member);
2009 } catch (IllegalAccessException ex) {
2010 throw new IllegalArgumentException(ex);
2011 }
2012 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2013 Class<?> callerClass = target.internalCallerClass();
2014 if (!hasPrivateAccess() || callerClass != lookupClass())
2015 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2016 }
2017 // Produce the handle to the results.
2018 return new InfoFromMemberName(this, member, refKind);
2019 }
2020
2021 /// Helper methods, all package-private.
2022
2023 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2024 checkSymbolicClass(refc); // do this before attempting to resolve
2025 Objects.requireNonNull(name);
2026 Objects.requireNonNull(type);
2027 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2028 NoSuchFieldException.class);
2029 }
2030
2031 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2032 checkSymbolicClass(refc); // do this before attempting to resolve
2033 Objects.requireNonNull(name);
2034 Objects.requireNonNull(type);
2035 checkMethodName(refKind, name); // NPE check on name
2036 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2037 NoSuchMethodException.class);
2038 }
2039
2040 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2041 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2042 Objects.requireNonNull(member.getName());
2043 Objects.requireNonNull(member.getType());
2044 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2045 ReflectiveOperationException.class);
2046 }
2047
2048 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
2049 Objects.requireNonNull(refc);
2050 Class<?> caller = lookupClassOrNull();
2051 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
2052 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
2053 }
2054
2055 /** Check name for an illegal leading "<" character. */
2056 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
2057 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
2058 throw new NoSuchMethodException("illegal method name: "+name);
2059 }
2060
2061
2062 /**
2063 * Find my trustable caller class if m is a caller sensitive method.
2064 * If this lookup object has private access, then the caller class is the lookupClass.
2065 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
2066 */
2067 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
2068 Class<?> callerClass = null;
2069 if (MethodHandleNatives.isCallerSensitive(m)) {
2070 // Only lookups with private access are allowed to resolve caller-sensitive methods
2071 if (hasPrivateAccess()) {
2072 callerClass = lookupClass;
2073 } else {
2074 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
2075 }
2076 }
2077 return callerClass;
2078 }
2079
2080 /**
2081 * Returns {@code true} if this lookup has {@code PRIVATE} access.
2082 * @return {@code true} if this lookup has {@code PRIVATE} access.
2083 * @since 9
2084 */
2085 public boolean hasPrivateAccess() {
2086 return (allowedModes & PRIVATE) != 0;
2087 }
2088
2089 /**
2090 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
2091 * Determines a trustable caller class to compare with refc, the symbolic reference class.
2092 * If this lookup object has private access, then the caller class is the lookupClass.
2093 */
2094 void checkSecurityManager(Class<?> refc, MemberName m) {
2095 SecurityManager smgr = System.getSecurityManager();
2096 if (smgr == null) return;
2097 if (allowedModes == TRUSTED) return;
2098
2099 // Step 1:
2100 boolean fullPowerLookup = hasPrivateAccess();
2101 if (!fullPowerLookup ||
2102 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
2103 ReflectUtil.checkPackageAccess(refc);
2104 }
2105
2106 if (m == null) { // findClass or accessClass
2107 // Step 2b:
2108 if (!fullPowerLookup) {
2109 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2110 }
2111 return;
2112 }
2113
2114 // Step 2a:
2115 if (m.isPublic()) return;
2116 if (!fullPowerLookup) {
2117 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
2118 }
2119
2120 // Step 3:
2121 Class<?> defc = m.getDeclaringClass();
2122 if (!fullPowerLookup && defc != refc) {
2123 ReflectUtil.checkPackageAccess(defc);
2124 }
2125 }
2126
2127 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2128 boolean wantStatic = (refKind == REF_invokeStatic);
2129 String message;
2130 if (m.isConstructor())
2131 message = "expected a method, not a constructor";
2132 else if (!m.isMethod())
2133 message = "expected a method";
2134 else if (wantStatic != m.isStatic())
2135 message = wantStatic ? "expected a static method" : "expected a non-static method";
2136 else
2137 { checkAccess(refKind, refc, m); return; }
2138 throw m.makeAccessException(message, this);
2139 }
2140
2141 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2142 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2143 String message;
2144 if (wantStatic != m.isStatic())
2145 message = wantStatic ? "expected a static field" : "expected a non-static field";
2146 else
2147 { checkAccess(refKind, refc, m); return; }
2148 throw m.makeAccessException(message, this);
2149 }
2150
2151 /** Check public/protected/private bits on the symbolic reference class and its member. */
2152 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2153 assert(m.referenceKindIsConsistentWith(refKind) &&
2154 MethodHandleNatives.refKindIsValid(refKind) &&
2155 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2156 int allowedModes = this.allowedModes;
2157 if (allowedModes == TRUSTED) return;
2158 int mods = m.getModifiers();
2159 if (Modifier.isProtected(mods) &&
2160 refKind == REF_invokeVirtual &&
2161 m.getDeclaringClass() == Object.class &&
2162 m.getName().equals("clone") &&
2163 refc.isArray()) {
2164 // The JVM does this hack also.
2165 // (See ClassVerifier::verify_invoke_instructions
2166 // and LinkResolver::check_method_accessability.)
2167 // Because the JVM does not allow separate methods on array types,
2168 // there is no separate method for int[].clone.
2169 // All arrays simply inherit Object.clone.
2170 // But for access checking logic, we make Object.clone
2171 // (normally protected) appear to be public.
2172 // Later on, when the DirectMethodHandle is created,
2173 // its leading argument will be restricted to the
2174 // requested array type.
2175 // N.B. The return type is not adjusted, because
2176 // that is *not* the bytecode behavior.
2177 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2178 }
2179 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2180 // cannot "new" a protected ctor in a different package
2181 mods ^= Modifier.PROTECTED;
2182 }
2183 if (Modifier.isFinal(mods) &&
2184 MethodHandleNatives.refKindIsSetter(refKind))
2185 throw m.makeAccessException("unexpected set of a final field", this);
2186 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2187 if ((requestedModes & allowedModes) != 0) {
2188 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2189 mods, lookupClass(), allowedModes))
2190 return;
2191 } else {
2192 // Protected members can also be checked as if they were package-private.
2193 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2194 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2195 return;
2196 }
2197 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2198 }
2199
2200 String accessFailedMessage(Class<?> refc, MemberName m) {
2201 Class<?> defc = m.getDeclaringClass();
2202 int mods = m.getModifiers();
2203 // check the class first:
2204 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2205 (defc == refc ||
2206 Modifier.isPublic(refc.getModifiers())));
2207 if (!classOK && (allowedModes & PACKAGE) != 0) {
2208 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), FULL_POWER_MODES) &&
2209 (defc == refc ||
2210 VerifyAccess.isClassAccessible(refc, lookupClass(), FULL_POWER_MODES)));
2211 }
2212 if (!classOK)
2213 return "class is not public";
2214 if (Modifier.isPublic(mods))
2215 return "access to public member failed"; // (how?, module not readable?)
2216 if (Modifier.isPrivate(mods))
2217 return "member is private";
2218 if (Modifier.isProtected(mods))
2219 return "member is protected";
2220 return "member is private to package";
2221 }
2222
2223 private static final boolean ALLOW_NESTMATE_ACCESS = false;
2224
2225 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2226 int allowedModes = this.allowedModes;
2227 if (allowedModes == TRUSTED) return;
2228 if (!hasPrivateAccess()
2229 || (specialCaller != lookupClass()
2230 // ensure non-abstract methods in superinterfaces can be special-invoked
2231 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))
2232 && !(ALLOW_NESTMATE_ACCESS &&
2233 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
2234 throw new MemberName(specialCaller).
2235 makeAccessException("no private access for invokespecial", this);
2236 }
2237
2238 private boolean restrictProtectedReceiver(MemberName method) {
2239 // The accessing class only has the right to use a protected member
2240 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2241 if (!method.isProtected() || method.isStatic()
2242 || allowedModes == TRUSTED
2243 || method.getDeclaringClass() == lookupClass()
2244 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
2245 || (ALLOW_NESTMATE_ACCESS &&
2246 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
2247 return false;
2248 return true;
2249 }
2250 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2251 assert(!method.isStatic());
2252 // receiver type of mh is too wide; narrow to caller
2253 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2254 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2255 }
2256 MethodType rawType = mh.type();
2257 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
2258 MethodType narrowType = rawType.changeParameterType(0, caller);
2259 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2260 assert(mh.viewAsTypeChecks(narrowType, true));
2261 return mh.copyWith(narrowType, mh.form);
2262 }
2263
2264 /** Check access and get the requested method. */
2265 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2266 final boolean doRestrict = true;
2267 final boolean checkSecurity = true;
2268 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2269 }
2270 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
2271 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2272 final boolean doRestrict = false;
2273 final boolean checkSecurity = true;
2274 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerClass);
2275 }
2276 /** Check access and get the requested method, eliding security manager checks. */
2277 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2278 final boolean doRestrict = true;
2279 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2280 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2281 }
2282 /** Common code for all methods; do not call directly except from immediately above. */
2283 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
2284 boolean checkSecurity,
2285 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
2286 checkMethod(refKind, refc, method);
2287 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2288 if (checkSecurity)
2289 checkSecurityManager(refc, method);
2290 assert(!method.isMethodHandleInvoke());
2291
2292 if (refKind == REF_invokeSpecial &&
2293 refc != lookupClass() &&
2294 !refc.isInterface() &&
2295 refc != lookupClass().getSuperclass() &&
2296 refc.isAssignableFrom(lookupClass())) {
2297 assert(!method.getName().equals("<init>")); // not this code path
2298 // Per JVMS 6.5, desc. of invokespecial instruction:
2299 // If the method is in a superclass of the LC,
2300 // and if our original search was above LC.super,
2301 // repeat the search (symbolic lookup) from LC.super
2302 // and continue with the direct superclass of that class,
2303 // and so forth, until a match is found or no further superclasses exist.
2304 // FIXME: MemberName.resolve should handle this instead.
2305 Class<?> refcAsSuper = lookupClass();
2306 MemberName m2;
2307 do {
2308 refcAsSuper = refcAsSuper.getSuperclass();
2309 m2 = new MemberName(refcAsSuper,
2310 method.getName(),
2311 method.getMethodType(),
2312 REF_invokeSpecial);
2313 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2314 } while (m2 == null && // no method is found yet
2315 refc != refcAsSuper); // search up to refc
2316 if (m2 == null) throw new InternalError(method.toString());
2317 method = m2;
2318 refc = refcAsSuper;
2319 // redo basic checks
2320 checkMethod(refKind, refc, method);
2321 }
2322
2323 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method);
2324 MethodHandle mh = dmh;
2325 // Optionally narrow the receiver argument to refc using restrictReceiver.
2326 if ((doRestrict && refKind == REF_invokeSpecial) ||
2327 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
2328 mh = restrictReceiver(method, dmh, lookupClass());
2329 }
2330 mh = maybeBindCaller(method, mh, callerClass);
2331 mh = mh.setVarargs(method);
2332 return mh;
2333 }
2334 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2335 Class<?> callerClass)
2336 throws IllegalAccessException {
2337 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2338 return mh;
2339 Class<?> hostClass = lookupClass;
2340 if (!hasPrivateAccess()) // caller must have private access
2341 hostClass = callerClass; // callerClass came from a security manager style stack walk
2342 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2343 // Note: caller will apply varargs after this step happens.
2344 return cbmh;
2345 }
2346 /** Check access and get the requested field. */
2347 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2348 final boolean checkSecurity = true;
2349 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2350 }
2351 /** Check access and get the requested field, eliding security manager checks. */
2352 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2353 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2354 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2355 }
2356 /** Common code for all fields; do not call directly except from immediately above. */
2357 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2358 boolean checkSecurity) throws IllegalAccessException {
2359 checkField(refKind, refc, field);
2360 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2361 if (checkSecurity)
2362 checkSecurityManager(refc, field);
2363 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2364 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2365 restrictProtectedReceiver(field));
2366 if (doRestrict)
2367 return restrictReceiver(field, dmh, lookupClass());
2368 return dmh;
2369 }
2370 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2371 Class<?> refc, MemberName getField, MemberName putField)
2372 throws IllegalAccessException {
2373 final boolean checkSecurity = true;
2374 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2375 }
2376 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2377 Class<?> refc, MemberName getField, MemberName putField)
2378 throws IllegalAccessException {
2379 final boolean checkSecurity = false;
2380 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2381 }
2382 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2383 Class<?> refc, MemberName getField, MemberName putField,
2384 boolean checkSecurity) throws IllegalAccessException {
2385 assert getField.isStatic() == putField.isStatic();
2386 assert getField.isGetter() && putField.isSetter();
2387 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2388 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2389
2390 checkField(getRefKind, refc, getField);
2391 if (checkSecurity)
2392 checkSecurityManager(refc, getField);
2393
2394 if (!putField.isFinal()) {
2395 // A VarHandle does not support updates to final fields, any
2396 // such VarHandle to a final field will be read-only and
2397 // therefore the following write-based accessibility checks are
2398 // only required for non-final fields
2399 checkField(putRefKind, refc, putField);
2400 if (checkSecurity)
2401 checkSecurityManager(refc, putField);
2402 }
2403
2404 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2405 restrictProtectedReceiver(getField));
2406 if (doRestrict) {
2407 assert !getField.isStatic();
2408 // receiver type of VarHandle is too wide; narrow to caller
2409 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2410 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2411 }
2412 refc = lookupClass();
2413 }
2414 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2415 }
2416 /** Check access and get the requested constructor. */
2417 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2418 final boolean checkSecurity = true;
2419 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2420 }
2421 /** Check access and get the requested constructor, eliding security manager checks. */
2422 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2423 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2424 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2425 }
2426 /** Common code for all constructors; do not call directly except from immediately above. */
2427 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2428 boolean checkSecurity) throws IllegalAccessException {
2429 assert(ctor.isConstructor());
2430 checkAccess(REF_newInvokeSpecial, refc, ctor);
2431 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2432 if (checkSecurity)
2433 checkSecurityManager(refc, ctor);
2434 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2435 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2436 }
2437
2438 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2439 */
2440 /*non-public*/
2441 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2442 if (!(type instanceof Class || type instanceof MethodType))
2443 throw new InternalError("unresolved MemberName");
2444 MemberName member = new MemberName(refKind, defc, name, type);
2445 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2446 if (mh != null) {
2447 checkSymbolicClass(defc);
2448 return mh;
2449 }
2450 // Treat MethodHandle.invoke and invokeExact specially.
2451 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2452 mh = findVirtualForMH(member.getName(), member.getMethodType());
2453 if (mh != null) {
2454 return mh;
2455 }
2456 }
2457 MemberName resolved = resolveOrFail(refKind, member);
2458 mh = getDirectMethodForConstant(refKind, defc, resolved);
2459 if (mh instanceof DirectMethodHandle
2460 && canBeCached(refKind, defc, resolved)) {
2461 MemberName key = mh.internalMemberName();
2462 if (key != null) {
2463 key = key.asNormalOriginal();
2464 }
2465 if (member.equals(key)) { // better safe than sorry
2466 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2467 }
2468 }
2469 return mh;
2470 }
2471 private
2472 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2473 if (refKind == REF_invokeSpecial) {
2474 return false;
2475 }
2476 if (!Modifier.isPublic(defc.getModifiers()) ||
2477 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2478 !member.isPublic() ||
2479 member.isCallerSensitive()) {
2480 return false;
2481 }
2482 ClassLoader loader = defc.getClassLoader();
2483 if (!jdk.internal.misc.VM.isSystemDomainLoader(loader)) {
2484 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2485 boolean found = false;
2486 while (sysl != null) {
2487 if (loader == sysl) { found = true; break; }
2488 sysl = sysl.getParent();
2489 }
2490 if (!found) {
2491 return false;
2492 }
2493 }
2494 try {
2495 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
2496 new MemberName(refKind, defc, member.getName(), member.getType()));
2497 checkSecurityManager(defc, resolved2);
2498 } catch (ReflectiveOperationException | SecurityException ex) {
2499 return false;
2500 }
2501 return true;
2502 }
2503 private
2504 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2505 throws ReflectiveOperationException {
2506 if (MethodHandleNatives.refKindIsField(refKind)) {
2507 return getDirectFieldNoSecurityManager(refKind, defc, member);
2508 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2509 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2510 } else if (refKind == REF_newInvokeSpecial) {
2511 return getDirectConstructorNoSecurityManager(defc, member);
2512 }
2513 // oops
2514 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2515 }
2516
2517 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2518 }
2519
2520 /**
2521 * Produces a method handle constructing arrays of a desired type.
2522 * The return type of the method handle will be the array type.
2523 * The type of its sole argument will be {@code int}, which specifies the size of the array.
2524 * @param arrayClass an array type
2525 * @return a method handle which can create arrays of the given type
2526 * @throws NullPointerException if the argument is {@code null}
2527 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2528 * @see java.lang.reflect.Array#newInstance(Class, int)
2529 * @since 9
2530 */
2531 public static
2532 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2533 if (!arrayClass.isArray()) {
2534 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2535 }
2536 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2537 bindTo(arrayClass.getComponentType());
2538 return ani.asType(ani.type().changeReturnType(arrayClass));
2539 }
2540
2541 /**
2542 * Produces a method handle returning the length of an array.
2543 * The type of the method handle will have {@code int} as return type,
2544 * and its sole argument will be the array type.
2545 * @param arrayClass an array type
2546 * @return a method handle which can retrieve the length of an array of the given array type
2547 * @throws NullPointerException if the argument is {@code null}
2548 * @throws IllegalArgumentException if arrayClass is not an array type
2549 * @since 9
2550 */
2551 public static
2552 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2553 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2554 }
2555
2556 /**
2557 * Produces a method handle giving read access to elements of an array.
2558 * The type of the method handle will have a return type of the array's
2559 * element type. Its first argument will be the array type,
2560 * and the second will be {@code int}.
2561 * @param arrayClass an array type
2562 * @return a method handle which can load values from the given array type
2563 * @throws NullPointerException if the argument is null
2564 * @throws IllegalArgumentException if arrayClass is not an array type
2565 */
2566 public static
2567 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2568 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2569 }
2570
2571 /**
2572 * Produces a method handle giving write access to elements of an array.
2573 * The type of the method handle will have a void return type.
2574 * Its last argument will be the array's element type.
2575 * The first and second arguments will be the array type and int.
2576 * @param arrayClass the class of an array
2577 * @return a method handle which can store values into the array type
2578 * @throws NullPointerException if the argument is null
2579 * @throws IllegalArgumentException if arrayClass is not an array type
2580 */
2581 public static
2582 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2583 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2584 }
2585
2586 /**
2587 * Produces a VarHandle giving access to elements of an array of type
2588 * {@code arrayClass}. The VarHandle's variable type is the component type
2589 * of {@code arrayClass} and the list of coordinate types is
2590 * {@code (arrayClass, int)}, where the {@code int} coordinate type
2591 * corresponds to an argument that is an index into an array.
2592 * <p>
2593 * Certain access modes of the returned VarHandle are unsupported under
2594 * the following conditions:
2595 * <ul>
2596 * <li>if the component type is anything other than {@code byte},
2597 * {@code short}, {@code char}, {@code int}, {@code long},
2598 * {@code float}, or {@code double} then numeric atomic update access
2599 * modes are unsupported.
2600 * <li>if the field type is anything other than {@code boolean},
2601 * {@code byte}, {@code short}, {@code char}, {@code int} or
2602 * {@code long} then bitwise atomic update access modes are
2603 * unsupported.
2604 * </ul>
2605 * <p>
2606 * If the component type is {@code float} or {@code double} then numeric
2607 * and atomic update access modes compare values using their bitwise
2608 * representation (see {@link Float#floatToRawIntBits} and
2609 * {@link Double#doubleToRawLongBits}, respectively).
2610 * @apiNote
2611 * Bitwise comparison of {@code float} values or {@code double} values,
2612 * as performed by the numeric and atomic update access modes, differ
2613 * from the primitive {@code ==} operator and the {@link Float#equals}
2614 * and {@link Double#equals} methods, specifically with respect to
2615 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2616 * Care should be taken when performing a compare and set or a compare
2617 * and exchange operation with such values since the operation may
2618 * unexpectedly fail.
2619 * There are many possible NaN values that are considered to be
2620 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2621 * provided by Java can distinguish between them. Operation failure can
2622 * occur if the expected or witness value is a NaN value and it is
2623 * transformed (perhaps in a platform specific manner) into another NaN
2624 * value, and thus has a different bitwise representation (see
2625 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2626 * details).
2627 * The values {@code -0.0} and {@code +0.0} have different bitwise
2628 * representations but are considered equal when using the primitive
2629 * {@code ==} operator. Operation failure can occur if, for example, a
2630 * numeric algorithm computes an expected value to be say {@code -0.0}
2631 * and previously computed the witness value to be say {@code +0.0}.
2632 * @param arrayClass the class of an array, of type {@code T[]}
2633 * @return a VarHandle giving access to elements of an array
2634 * @throws NullPointerException if the arrayClass is null
2635 * @throws IllegalArgumentException if arrayClass is not an array type
2636 * @since 9
2637 */
2638 public static
2639 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
2640 return VarHandles.makeArrayElementHandle(arrayClass);
2641 }
2642
2643 /**
2644 * Produces a VarHandle giving access to elements of a {@code byte[]} array
2645 * viewed as if it were a different primitive array type, such as
2646 * {@code int[]} or {@code long[]}.
2647 * The VarHandle's variable type is the component type of
2648 * {@code viewArrayClass} and the list of coordinate types is
2649 * {@code (byte[], int)}, where the {@code int} coordinate type
2650 * corresponds to an argument that is an index into a {@code byte[]} array.
2651 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
2652 * array, composing bytes to or from a value of the component type of
2653 * {@code viewArrayClass} according to the given endianness.
2654 * <p>
2655 * The supported component types (variables types) are {@code short},
2656 * {@code char}, {@code int}, {@code long}, {@code float} and
2657 * {@code double}.
2658 * <p>
2659 * Access of bytes at a given index will result in an
2660 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2661 * or greater than the {@code byte[]} array length minus the size (in bytes)
2662 * of {@code T}.
2663 * <p>
2664 * Access of bytes at an index may be aligned or misaligned for {@code T},
2665 * with respect to the underlying memory address, {@code A} say, associated
2666 * with the array and index.
2667 * If access is misaligned then access for anything other than the
2668 * {@code get} and {@code set} access modes will result in an
2669 * {@code IllegalStateException}. In such cases atomic access is only
2670 * guaranteed with respect to the largest power of two that divides the GCD
2671 * of {@code A} and the size (in bytes) of {@code T}.
2672 * If access is aligned then following access modes are supported and are
2673 * guaranteed to support atomic access:
2674 * <ul>
2675 * <li>read write access modes for all {@code T}, with the exception of
2676 * access modes {@code get} and {@code set} for {@code long} and
2677 * {@code double} on 32-bit platforms.
2678 * <li>atomic update access modes for {@code int}, {@code long},
2679 * {@code float} or {@code double}.
2680 * (Future major platform releases of the JDK may support additional
2681 * types for certain currently unsupported access modes.)
2682 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2683 * (Future major platform releases of the JDK may support additional
2684 * numeric types for certain currently unsupported access modes.)
2685 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2686 * (Future major platform releases of the JDK may support additional
2687 * numeric types for certain currently unsupported access modes.)
2688 * </ul>
2689 * <p>
2690 * Misaligned access, and therefore atomicity guarantees, may be determined
2691 * for {@code byte[]} arrays without operating on a specific array. Given
2692 * an {@code index}, {@code T} and it's corresponding boxed type,
2693 * {@code T_BOX}, misalignment may be determined as follows:
2694 * <pre>{@code
2695 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2696 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
2697 * alignmentOffset(0, sizeOfT);
2698 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
2699 * boolean isMisaligned = misalignedAtIndex != 0;
2700 * }</pre>
2701 * <p>
2702 * If the variable type is {@code float} or {@code double} then atomic
2703 * update access modes compare values using their bitwise representation
2704 * (see {@link Float#floatToRawIntBits} and
2705 * {@link Double#doubleToRawLongBits}, respectively).
2706 * @param viewArrayClass the view array class, with a component type of
2707 * type {@code T}
2708 * @param byteOrder the endianness of the view array elements, as
2709 * stored in the underlying {@code byte} array
2710 * @return a VarHandle giving access to elements of a {@code byte[]} array
2711 * viewed as if elements corresponding to the components type of the view
2712 * array class
2713 * @throws NullPointerException if viewArrayClass or byteOrder is null
2714 * @throws IllegalArgumentException if viewArrayClass is not an array type
2715 * @throws UnsupportedOperationException if the component type of
2716 * viewArrayClass is not supported as a variable type
2717 * @since 9
2718 */
2719 public static
2720 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
2721 ByteOrder byteOrder) throws IllegalArgumentException {
2722 Objects.requireNonNull(byteOrder);
2723 return VarHandles.byteArrayViewHandle(viewArrayClass,
2724 byteOrder == ByteOrder.BIG_ENDIAN);
2725 }
2726
2727 /**
2728 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
2729 * viewed as if it were an array of elements of a different primitive
2730 * component type to that of {@code byte}, such as {@code int[]} or
2731 * {@code long[]}.
2732 * The VarHandle's variable type is the component type of
2733 * {@code viewArrayClass} and the list of coordinate types is
2734 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
2735 * corresponds to an argument that is an index into a {@code byte[]} array.
2736 * The returned VarHandle accesses bytes at an index in a
2737 * {@code ByteBuffer}, composing bytes to or from a value of the component
2738 * type of {@code viewArrayClass} according to the given endianness.
2739 * <p>
2740 * The supported component types (variables types) are {@code short},
2741 * {@code char}, {@code int}, {@code long}, {@code float} and
2742 * {@code double}.
2743 * <p>
2744 * Access will result in a {@code ReadOnlyBufferException} for anything
2745 * other than the read access modes if the {@code ByteBuffer} is read-only.
2746 * <p>
2747 * Access of bytes at a given index will result in an
2748 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2749 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
2750 * {@code T}.
2751 * <p>
2752 * Access of bytes at an index may be aligned or misaligned for {@code T},
2753 * with respect to the underlying memory address, {@code A} say, associated
2754 * with the {@code ByteBuffer} and index.
2755 * If access is misaligned then access for anything other than the
2756 * {@code get} and {@code set} access modes will result in an
2757 * {@code IllegalStateException}. In such cases atomic access is only
2758 * guaranteed with respect to the largest power of two that divides the GCD
2759 * of {@code A} and the size (in bytes) of {@code T}.
2760 * If access is aligned then following access modes are supported and are
2761 * guaranteed to support atomic access:
2762 * <ul>
2763 * <li>read write access modes for all {@code T}, with the exception of
2764 * access modes {@code get} and {@code set} for {@code long} and
2765 * {@code double} on 32-bit platforms.
2766 * <li>atomic update access modes for {@code int}, {@code long},
2767 * {@code float} or {@code double}.
2768 * (Future major platform releases of the JDK may support additional
2769 * types for certain currently unsupported access modes.)
2770 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2771 * (Future major platform releases of the JDK may support additional
2772 * numeric types for certain currently unsupported access modes.)
2773 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2774 * (Future major platform releases of the JDK may support additional
2775 * numeric types for certain currently unsupported access modes.)
2776 * </ul>
2777 * <p>
2778 * Misaligned access, and therefore atomicity guarantees, may be determined
2779 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
2780 * {@code index}, {@code T} and it's corresponding boxed type,
2781 * {@code T_BOX}, as follows:
2782 * <pre>{@code
2783 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2784 * ByteBuffer bb = ...
2785 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
2786 * boolean isMisaligned = misalignedAtIndex != 0;
2787 * }</pre>
2788 * <p>
2789 * If the variable type is {@code float} or {@code double} then atomic
2790 * update access modes compare values using their bitwise representation
2791 * (see {@link Float#floatToRawIntBits} and
2792 * {@link Double#doubleToRawLongBits}, respectively).
2793 * @param viewArrayClass the view array class, with a component type of
2794 * type {@code T}
2795 * @param byteOrder the endianness of the view array elements, as
2796 * stored in the underlying {@code ByteBuffer} (Note this overrides the
2797 * endianness of a {@code ByteBuffer})
2798 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
2799 * viewed as if elements corresponding to the components type of the view
2800 * array class
2801 * @throws NullPointerException if viewArrayClass or byteOrder is null
2802 * @throws IllegalArgumentException if viewArrayClass is not an array type
2803 * @throws UnsupportedOperationException if the component type of
2804 * viewArrayClass is not supported as a variable type
2805 * @since 9
2806 */
2807 public static
2808 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
2809 ByteOrder byteOrder) throws IllegalArgumentException {
2810 Objects.requireNonNull(byteOrder);
2811 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
2812 byteOrder == ByteOrder.BIG_ENDIAN);
2813 }
2814
2815
2816 /// method handle invocation (reflective style)
2817
2818 /**
2819 * Produces a method handle which will invoke any method handle of the
2820 * given {@code type}, with a given number of trailing arguments replaced by
2821 * a single trailing {@code Object[]} array.
2822 * The resulting invoker will be a method handle with the following
2823 * arguments:
2824 * <ul>
2825 * <li>a single {@code MethodHandle} target
2826 * <li>zero or more leading values (counted by {@code leadingArgCount})
2827 * <li>an {@code Object[]} array containing trailing arguments
2828 * </ul>
2829 * <p>
2830 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
2831 * the indicated {@code type}.
2832 * That is, if the target is exactly of the given {@code type}, it will behave
2833 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
2834 * is used to convert the target to the required {@code type}.
2835 * <p>
2836 * The type of the returned invoker will not be the given {@code type}, but rather
2837 * will have all parameters except the first {@code leadingArgCount}
2838 * replaced by a single array of type {@code Object[]}, which will be
2839 * the final parameter.
2840 * <p>
2841 * Before invoking its target, the invoker will spread the final array, apply
2842 * reference casts as necessary, and unbox and widen primitive arguments.
2843 * If, when the invoker is called, the supplied array argument does
2844 * not have the correct number of elements, the invoker will throw
2845 * an {@link IllegalArgumentException} instead of invoking the target.
2846 * <p>
2847 * This method is equivalent to the following code (though it may be more efficient):
2848 * <blockquote><pre>{@code
2849 MethodHandle invoker = MethodHandles.invoker(type);
2850 int spreadArgCount = type.parameterCount() - leadingArgCount;
2851 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
2852 return invoker;
2853 * }</pre></blockquote>
2854 * This method throws no reflective or security exceptions.
2855 * @param type the desired target type
2856 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
2857 * @return a method handle suitable for invoking any method handle of the given type
2858 * @throws NullPointerException if {@code type} is null
2859 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
2860 * the range from 0 to {@code type.parameterCount()} inclusive,
2861 * or if the resulting method handle's type would have
2862 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2863 */
2864 public static
2865 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
2866 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
2867 throw newIllegalArgumentException("bad argument count", leadingArgCount);
2868 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
2869 return type.invokers().spreadInvoker(leadingArgCount);
2870 }
2871
2872 /**
2873 * Produces a special <em>invoker method handle</em> which can be used to
2874 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
2875 * The resulting invoker will have a type which is
2876 * exactly equal to the desired type, except that it will accept
2877 * an additional leading argument of type {@code MethodHandle}.
2878 * <p>
2879 * This method is equivalent to the following code (though it may be more efficient):
2880 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
2881 *
2882 * <p style="font-size:smaller;">
2883 * <em>Discussion:</em>
2884 * Invoker method handles can be useful when working with variable method handles
2885 * of unknown types.
2886 * For example, to emulate an {@code invokeExact} call to a variable method
2887 * handle {@code M}, extract its type {@code T},
2888 * look up the invoker method {@code X} for {@code T},
2889 * and call the invoker method, as {@code X.invoke(T, A...)}.
2890 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
2891 * is unknown.)
2892 * If spreading, collecting, or other argument transformations are required,
2893 * they can be applied once to the invoker {@code X} and reused on many {@code M}
2894 * method handle values, as long as they are compatible with the type of {@code X}.
2895 * <p style="font-size:smaller;">
2896 * <em>(Note: The invoker method is not available via the Core Reflection API.
2897 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2898 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2899 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2900 * <p>
2901 * This method throws no reflective or security exceptions.
2902 * @param type the desired target type
2903 * @return a method handle suitable for invoking any method handle of the given type
2904 * @throws IllegalArgumentException if the resulting method handle's type would have
2905 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2906 */
2907 public static
2908 MethodHandle exactInvoker(MethodType type) {
2909 return type.invokers().exactInvoker();
2910 }
2911
2912 /**
2913 * Produces a special <em>invoker method handle</em> which can be used to
2914 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2915 * The resulting invoker will have a type which is
2916 * exactly equal to the desired type, except that it will accept
2917 * an additional leading argument of type {@code MethodHandle}.
2918 * <p>
2919 * Before invoking its target, if the target differs from the expected type,
2920 * the invoker will apply reference casts as
2921 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
2922 * Similarly, the return value will be converted as necessary.
2923 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
2924 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
2925 * <p>
2926 * This method is equivalent to the following code (though it may be more efficient):
2927 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
2928 * <p style="font-size:smaller;">
2929 * <em>Discussion:</em>
2930 * A {@linkplain MethodType#genericMethodType general method type} is one which
2931 * mentions only {@code Object} arguments and return values.
2932 * An invoker for such a type is capable of calling any method handle
2933 * of the same arity as the general type.
2934 * <p style="font-size:smaller;">
2935 * <em>(Note: The invoker method is not available via the Core Reflection API.
2936 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2937 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2938 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2939 * <p>
2940 * This method throws no reflective or security exceptions.
2941 * @param type the desired target type
2942 * @return a method handle suitable for invoking any method handle convertible to the given type
2943 * @throws IllegalArgumentException if the resulting method handle's type would have
2944 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2945 */
2946 public static
2947 MethodHandle invoker(MethodType type) {
2948 return type.invokers().genericInvoker();
2949 }
2950
2951 /**
2952 * Produces a special <em>invoker method handle</em> which can be used to
2953 * invoke a signature-polymorphic access mode method on any VarHandle whose
2954 * associated access mode type is compatible with the given type.
2955 * The resulting invoker will have a type which is exactly equal to the
2956 * desired given type, except that it will accept an additional leading
2957 * argument of type {@code VarHandle}.
2958 *
2959 * @param accessMode the VarHandle access mode
2960 * @param type the desired target type
2961 * @return a method handle suitable for invoking an access mode method of
2962 * any VarHandle whose access mode type is of the given type.
2963 * @since 9
2964 */
2965 static public
2966 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
2967 return type.invokers().varHandleMethodExactInvoker(accessMode);
2968 }
2969
2970 /**
2971 * Produces a special <em>invoker method handle</em> which can be used to
2972 * invoke a signature-polymorphic access mode method on any VarHandle whose
2973 * associated access mode type is compatible with the given type.
2974 * The resulting invoker will have a type which is exactly equal to the
2975 * desired given type, except that it will accept an additional leading
2976 * argument of type {@code VarHandle}.
2977 * <p>
2978 * Before invoking its target, if the access mode type differs from the
2979 * desired given type, the invoker will apply reference casts as necessary
2980 * and box, unbox, or widen primitive values, as if by
2981 * {@link MethodHandle#asType asType}. Similarly, the return value will be
2982 * converted as necessary.
2983 * <p>
2984 * This method is equivalent to the following code (though it may be more
2985 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
2986 *
2987 * @param accessMode the VarHandle access mode
2988 * @param type the desired target type
2989 * @return a method handle suitable for invoking an access mode method of
2990 * any VarHandle whose access mode type is convertible to the given
2991 * type.
2992 * @since 9
2993 */
2994 static public
2995 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
2996 return type.invokers().varHandleMethodInvoker(accessMode);
2997 }
2998
2999 static /*non-public*/
3000 MethodHandle basicInvoker(MethodType type) {
3001 return type.invokers().basicInvoker();
3002 }
3003
3004 /// method handle modification (creation from other method handles)
3005
3006 /**
3007 * Produces a method handle which adapts the type of the
3008 * given method handle to a new type by pairwise argument and return type conversion.
3009 * The original type and new type must have the same number of arguments.
3010 * The resulting method handle is guaranteed to report a type
3011 * which is equal to the desired new type.
3012 * <p>
3013 * If the original type and new type are equal, returns target.
3014 * <p>
3015 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
3016 * and some additional conversions are also applied if those conversions fail.
3017 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
3018 * if possible, before or instead of any conversions done by {@code asType}:
3019 * <ul>
3020 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
3021 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
3022 * (This treatment of interfaces follows the usage of the bytecode verifier.)
3023 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
3024 * the boolean is converted to a byte value, 1 for true, 0 for false.
3025 * (This treatment follows the usage of the bytecode verifier.)
3026 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
3027 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
3028 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
3029 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
3030 * then a Java casting conversion (JLS 5.5) is applied.
3031 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
3032 * widening and/or narrowing.)
3033 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
3034 * conversion will be applied at runtime, possibly followed
3035 * by a Java casting conversion (JLS 5.5) on the primitive value,
3036 * possibly followed by a conversion from byte to boolean by testing
3037 * the low-order bit.
3038 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
3039 * and if the reference is null at runtime, a zero value is introduced.
3040 * </ul>
3041 * @param target the method handle to invoke after arguments are retyped
3042 * @param newType the expected type of the new method handle
3043 * @return a method handle which delegates to the target after performing
3044 * any necessary argument conversions, and arranges for any
3045 * necessary return value conversions
3046 * @throws NullPointerException if either argument is null
3047 * @throws WrongMethodTypeException if the conversion cannot be made
3048 * @see MethodHandle#asType
3049 */
3050 public static
3051 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
3052 explicitCastArgumentsChecks(target, newType);
3053 // use the asTypeCache when possible:
3054 MethodType oldType = target.type();
3055 if (oldType == newType) return target;
3056 if (oldType.explicitCastEquivalentToAsType(newType)) {
3057 return target.asFixedArity().asType(newType);
3058 }
3059 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
3060 }
3061
3062 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
3063 if (target.type().parameterCount() != newType.parameterCount()) {
3064 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
3065 }
3066 }
3067
3068 /**
3069 * Produces a method handle which adapts the calling sequence of the
3070 * given method handle to a new type, by reordering the arguments.
3071 * The resulting method handle is guaranteed to report a type
3072 * which is equal to the desired new type.
3073 * <p>
3074 * The given array controls the reordering.
3075 * Call {@code #I} the number of incoming parameters (the value
3076 * {@code newType.parameterCount()}, and call {@code #O} the number
3077 * of outgoing parameters (the value {@code target.type().parameterCount()}).
3078 * Then the length of the reordering array must be {@code #O},
3079 * and each element must be a non-negative number less than {@code #I}.
3080 * For every {@code N} less than {@code #O}, the {@code N}-th
3081 * outgoing argument will be taken from the {@code I}-th incoming
3082 * argument, where {@code I} is {@code reorder[N]}.
3083 * <p>
3084 * No argument or return value conversions are applied.
3085 * The type of each incoming argument, as determined by {@code newType},
3086 * must be identical to the type of the corresponding outgoing parameter
3087 * or parameters in the target method handle.
3088 * The return type of {@code newType} must be identical to the return
3089 * type of the original target.
3090 * <p>
3091 * The reordering array need not specify an actual permutation.
3092 * An incoming argument will be duplicated if its index appears
3093 * more than once in the array, and an incoming argument will be dropped
3094 * if its index does not appear in the array.
3095 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
3096 * incoming arguments which are not mentioned in the reordering array
3097 * may be of any type, as determined only by {@code newType}.
3098 * <blockquote><pre>{@code
3099 import static java.lang.invoke.MethodHandles.*;
3100 import static java.lang.invoke.MethodType.*;
3101 ...
3102 MethodType intfn1 = methodType(int.class, int.class);
3103 MethodType intfn2 = methodType(int.class, int.class, int.class);
3104 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
3105 assert(sub.type().equals(intfn2));
3106 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
3107 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
3108 assert((int)rsub.invokeExact(1, 100) == 99);
3109 MethodHandle add = ... (int x, int y) -> (x+y) ...;
3110 assert(add.type().equals(intfn2));
3111 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
3112 assert(twice.type().equals(intfn1));
3113 assert((int)twice.invokeExact(21) == 42);
3114 * }</pre></blockquote>
3115 * <p>
3116 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3117 * variable-arity method handle}, even if the original target method handle was.
3118 * @param target the method handle to invoke after arguments are reordered
3119 * @param newType the expected type of the new method handle
3120 * @param reorder an index array which controls the reordering
3121 * @return a method handle which delegates to the target after it
3122 * drops unused arguments and moves and/or duplicates the other arguments
3123 * @throws NullPointerException if any argument is null
3124 * @throws IllegalArgumentException if the index array length is not equal to
3125 * the arity of the target, or if any index array element
3126 * not a valid index for a parameter of {@code newType},
3127 * or if two corresponding parameter types in
3128 * {@code target.type()} and {@code newType} are not identical,
3129 */
3130 public static
3131 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3132 reorder = reorder.clone(); // get a private copy
3133 MethodType oldType = target.type();
3134 permuteArgumentChecks(reorder, newType, oldType);
3135 // first detect dropped arguments and handle them separately
3136 int[] originalReorder = reorder;
3137 BoundMethodHandle result = target.rebind();
3138 LambdaForm form = result.form;
3139 int newArity = newType.parameterCount();
3140 // Normalize the reordering into a real permutation,
3141 // by removing duplicates and adding dropped elements.
3142 // This somewhat improves lambda form caching, as well
3143 // as simplifying the transform by breaking it up into steps.
3144 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3145 if (ddIdx > 0) {
3146 // We found a duplicated entry at reorder[ddIdx].
3147 // Example: (x,y,z)->asList(x,y,z)
3148 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3149 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3150 // The starred element corresponds to the argument
3151 // deleted by the dupArgumentForm transform.
3152 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3153 boolean killFirst = false;
3154 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3155 // Set killFirst if the dup is larger than an intervening position.
3156 // This will remove at least one inversion from the permutation.
3157 if (dupVal > val) killFirst = true;
3158 }
3159 if (!killFirst) {
3160 srcPos = dstPos;
3161 dstPos = ddIdx;
3162 }
3163 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3164 assert (reorder[srcPos] == reorder[dstPos]);
3165 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3166 // contract the reordering by removing the element at dstPos
3167 int tailPos = dstPos + 1;
3168 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3169 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3170 } else {
3171 int dropVal = ~ddIdx, insPos = 0;
3172 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3173 // Find first element of reorder larger than dropVal.
3174 // This is where we will insert the dropVal.
3175 insPos += 1;
3176 }
3177 Class<?> ptype = newType.parameterType(dropVal);
3178 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3179 oldType = oldType.insertParameterTypes(insPos, ptype);
3180 // expand the reordering by inserting an element at insPos
3181 int tailPos = insPos + 1;
3182 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3183 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3184 reorder[insPos] = dropVal;
3185 }
3186 assert (permuteArgumentChecks(reorder, newType, oldType));
3187 }
3188 assert (reorder.length == newArity); // a perfect permutation
3189 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3190 form = form.editor().permuteArgumentsForm(1, reorder);
3191 if (newType == result.type() && form == result.internalForm())
3192 return result;
3193 return result.copyWith(newType, form);
3194 }
3195
3196 /**
3197 * Return an indication of any duplicate or omission in reorder.
3198 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3199 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3200 * Otherwise, return zero.
3201 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3202 */
3203 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3204 final int BIT_LIMIT = 63; // max number of bits in bit mask
3205 if (newArity < BIT_LIMIT) {
3206 long mask = 0;
3207 for (int i = 0; i < reorder.length; i++) {
3208 int arg = reorder[i];
3209 if (arg >= newArity) {
3210 return reorder.length;
3211 }
3212 long bit = 1L << arg;
3213 if ((mask & bit) != 0) {
3214 return i; // >0 indicates a dup
3215 }
3216 mask |= bit;
3217 }
3218 if (mask == (1L << newArity) - 1) {
3219 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
3220 return 0;
3221 }
3222 // find first zero
3223 long zeroBit = Long.lowestOneBit(~mask);
3224 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
3225 assert(zeroPos <= newArity);
3226 if (zeroPos == newArity) {
3227 return 0;
3228 }
3229 return ~zeroPos;
3230 } else {
3231 // same algorithm, different bit set
3232 BitSet mask = new BitSet(newArity);
3233 for (int i = 0; i < reorder.length; i++) {
3234 int arg = reorder[i];
3235 if (arg >= newArity) {
3236 return reorder.length;
3237 }
3238 if (mask.get(arg)) {
3239 return i; // >0 indicates a dup
3240 }
3241 mask.set(arg);
3242 }
3243 int zeroPos = mask.nextClearBit(0);
3244 assert(zeroPos <= newArity);
3245 if (zeroPos == newArity) {
3246 return 0;
3247 }
3248 return ~zeroPos;
3249 }
3250 }
3251
3252 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
3253 if (newType.returnType() != oldType.returnType())
3254 throw newIllegalArgumentException("return types do not match",
3255 oldType, newType);
3256 if (reorder.length == oldType.parameterCount()) {
3257 int limit = newType.parameterCount();
3258 boolean bad = false;
3259 for (int j = 0; j < reorder.length; j++) {
3260 int i = reorder[j];
3261 if (i < 0 || i >= limit) {
3262 bad = true; break;
3263 }
3264 Class<?> src = newType.parameterType(i);
3265 Class<?> dst = oldType.parameterType(j);
3266 if (src != dst)
3267 throw newIllegalArgumentException("parameter types do not match after reorder",
3268 oldType, newType);
3269 }
3270 if (!bad) return true;
3271 }
3272 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3273 }
3274
3275 /**
3276 * Produces a method handle of the requested return type which returns the given
3277 * constant value every time it is invoked.
3278 * <p>
3279 * Before the method handle is returned, the passed-in value is converted to the requested type.
3280 * If the requested type is primitive, widening primitive conversions are attempted,
3281 * else reference conversions are attempted.
3282 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3283 * @param type the return type of the desired method handle
3284 * @param value the value to return
3285 * @return a method handle of the given return type and no arguments, which always returns the given value
3286 * @throws NullPointerException if the {@code type} argument is null
3287 * @throws ClassCastException if the value cannot be converted to the required return type
3288 * @throws IllegalArgumentException if the given type is {@code void.class}
3289 */
3290 public static
3291 MethodHandle constant(Class<?> type, Object value) {
3292 if (type.isPrimitive()) {
3293 if (type == void.class)
3294 throw newIllegalArgumentException("void type");
3295 Wrapper w = Wrapper.forPrimitiveType(type);
3296 value = w.convert(value, type);
3297 if (w.zero().equals(value))
3298 return zero(w, type);
3299 return insertArguments(identity(type), 0, value);
3300 } else {
3301 if (value == null)
3302 return zero(Wrapper.OBJECT, type);
3303 return identity(type).bindTo(value);
3304 }
3305 }
3306
3307 /**
3308 * Produces a method handle which returns its sole argument when invoked.
3309 * @param type the type of the sole parameter and return value of the desired method handle
3310 * @return a unary method handle which accepts and returns the given type
3311 * @throws NullPointerException if the argument is null
3312 * @throws IllegalArgumentException if the given type is {@code void.class}
3313 */
3314 public static
3315 MethodHandle identity(Class<?> type) {
3316 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3317 int pos = btw.ordinal();
3318 MethodHandle ident = IDENTITY_MHS[pos];
3319 if (ident == null) {
3320 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3321 }
3322 if (ident.type().returnType() == type)
3323 return ident;
3324 // something like identity(Foo.class); do not bother to intern these
3325 assert (btw == Wrapper.OBJECT);
3326 return makeIdentity(type);
3327 }
3328
3329 /**
3330 * Produces a constant method handle of the requested return type which
3331 * returns the default value for that type every time it is invoked.
3332 * The resulting constant method handle will have no side effects.
3333 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3334 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3335 * since {@code explicitCastArguments} converts {@code null} to default values.
3336 * @param type the expected return type of the desired method handle
3337 * @return a constant method handle that takes no arguments
3338 * and returns the default value of the given type (or void, if the type is void)
3339 * @throws NullPointerException if the argument is null
3340 * @see MethodHandles#constant
3341 * @see MethodHandles#empty
3342 * @see MethodHandles#explicitCastArguments
3343 * @since 9
3344 */
3345 public static MethodHandle zero(Class<?> type) {
3346 Objects.requireNonNull(type);
3347 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
3348 }
3349
3350 private static MethodHandle identityOrVoid(Class<?> type) {
3351 return type == void.class ? zero(type) : identity(type);
3352 }
3353
3354 /**
3355 * Produces a method handle of the requested type which ignores any arguments, does nothing,
3356 * and returns a suitable default depending on the return type.
3357 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3358 * <p>The returned method handle is equivalent to
3359 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3360 * <p>
3361 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3362 * {@code guardWithTest(pred, target, empty(target.type())}.
3363 * @param type the type of the desired method handle
3364 * @return a constant method handle of the given type, which returns a default value of the given return type
3365 * @throws NullPointerException if the argument is null
3366 * @see MethodHandles#zero
3367 * @see MethodHandles#constant
3368 * @since 9
3369 */
3370 public static MethodHandle empty(MethodType type) {
3371 Objects.requireNonNull(type);
3372 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3373 }
3374
3375 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
3376 private static MethodHandle makeIdentity(Class<?> ptype) {
3377 MethodType mtype = methodType(ptype, ptype);
3378 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3379 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3380 }
3381
3382 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3383 int pos = btw.ordinal();
3384 MethodHandle zero = ZERO_MHS[pos];
3385 if (zero == null) {
3386 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3387 }
3388 if (zero.type().returnType() == rtype)
3389 return zero;
3390 assert(btw == Wrapper.OBJECT);
3391 return makeZero(rtype);
3392 }
3393 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
3394 private static MethodHandle makeZero(Class<?> rtype) {
3395 MethodType mtype = methodType(rtype);
3396 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3397 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3398 }
3399
3400 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3401 // Simulate a CAS, to avoid racy duplication of results.
3402 MethodHandle prev = cache[pos];
3403 if (prev != null) return prev;
3404 return cache[pos] = value;
3405 }
3406
3407 /**
3408 * Provides a target method handle with one or more <em>bound arguments</em>
3409 * in advance of the method handle's invocation.
3410 * The formal parameters to the target corresponding to the bound
3411 * arguments are called <em>bound parameters</em>.
3412 * Returns a new method handle which saves away the bound arguments.
3413 * When it is invoked, it receives arguments for any non-bound parameters,
3414 * binds the saved arguments to their corresponding parameters,
3415 * and calls the original target.
3416 * <p>
3417 * The type of the new method handle will drop the types for the bound
3418 * parameters from the original target type, since the new method handle
3419 * will no longer require those arguments to be supplied by its callers.
3420 * <p>
3421 * Each given argument object must match the corresponding bound parameter type.
3422 * If a bound parameter type is a primitive, the argument object
3423 * must be a wrapper, and will be unboxed to produce the primitive value.
3424 * <p>
3425 * The {@code pos} argument selects which parameters are to be bound.
3426 * It may range between zero and <i>N-L</i> (inclusively),
3427 * where <i>N</i> is the arity of the target method handle
3428 * and <i>L</i> is the length of the values array.
3429 * <p>
3430 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3431 * variable-arity method handle}, even if the original target method handle was.
3432 * @param target the method handle to invoke after the argument is inserted
3433 * @param pos where to insert the argument (zero for the first)
3434 * @param values the series of arguments to insert
3435 * @return a method handle which inserts an additional argument,
3436 * before calling the original method handle
3437 * @throws NullPointerException if the target or the {@code values} array is null
3438 * @see MethodHandle#bindTo
3439 */
3440 public static
3441 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3442 int insCount = values.length;
3443 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3444 if (insCount == 0) return target;
3445 BoundMethodHandle result = target.rebind();
3446 for (int i = 0; i < insCount; i++) {
3447 Object value = values[i];
3448 Class<?> ptype = ptypes[pos+i];
3449 if (ptype.isPrimitive()) {
3450 result = insertArgumentPrimitive(result, pos, ptype, value);
3451 } else {
3452 value = ptype.cast(value); // throw CCE if needed
3453 result = result.bindArgumentL(pos, value);
3454 }
3455 }
3456 return result;
3457 }
3458
3459 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3460 Class<?> ptype, Object value) {
3461 Wrapper w = Wrapper.forPrimitiveType(ptype);
3462 // perform unboxing and/or primitive conversion
3463 value = w.convert(value, ptype);
3464 switch (w) {
3465 case INT: return result.bindArgumentI(pos, (int)value);
3466 case LONG: return result.bindArgumentJ(pos, (long)value);
3467 case FLOAT: return result.bindArgumentF(pos, (float)value);
3468 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3469 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3470 }
3471 }
3472
3473 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3474 MethodType oldType = target.type();
3475 int outargs = oldType.parameterCount();
3476 int inargs = outargs - insCount;
3477 if (inargs < 0)
3478 throw newIllegalArgumentException("too many values to insert");
3479 if (pos < 0 || pos > inargs)
3480 throw newIllegalArgumentException("no argument type to append");
3481 return oldType.ptypes();
3482 }
3483
3484 /**
3485 * Produces a method handle which will discard some dummy arguments
3486 * before calling some other specified <i>target</i> method handle.
3487 * The type of the new method handle will be the same as the target's type,
3488 * except it will also include the dummy argument types,
3489 * at some given position.
3490 * <p>
3491 * The {@code pos} argument may range between zero and <i>N</i>,
3492 * where <i>N</i> is the arity of the target.
3493 * If {@code pos} is zero, the dummy arguments will precede
3494 * the target's real arguments; if {@code pos} is <i>N</i>
3495 * they will come after.
3496 * <p>
3497 * <b>Example:</b>
3498 * <blockquote><pre>{@code
3499 import static java.lang.invoke.MethodHandles.*;
3500 import static java.lang.invoke.MethodType.*;
3501 ...
3502 MethodHandle cat = lookup().findVirtual(String.class,
3503 "concat", methodType(String.class, String.class));
3504 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3505 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3506 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3507 assertEquals(bigType, d0.type());
3508 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3509 * }</pre></blockquote>
3510 * <p>
3511 * This method is also equivalent to the following code:
3512 * <blockquote><pre>
3513 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3514 * </pre></blockquote>
3515 * @param target the method handle to invoke after the arguments are dropped
3516 * @param valueTypes the type(s) of the argument(s) to drop
3517 * @param pos position of first argument to drop (zero for the leftmost)
3518 * @return a method handle which drops arguments of the given types,
3519 * before calling the original method handle
3520 * @throws NullPointerException if the target is null,
3521 * or if the {@code valueTypes} list or any of its elements is null
3522 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3523 * or if {@code pos} is negative or greater than the arity of the target,
3524 * or if the new method handle's type would have too many parameters
3525 */
3526 public static
3527 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3528 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
3529 }
3530
3531 private static List<Class<?>> copyTypes(Object[] array) {
3532 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
3533 }
3534
3535 private static
3536 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3537 MethodType oldType = target.type(); // get NPE
3538 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3539 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3540 if (dropped == 0) return target;
3541 BoundMethodHandle result = target.rebind();
3542 LambdaForm lform = result.form;
3543 int insertFormArg = 1 + pos;
3544 for (Class<?> ptype : valueTypes) {
3545 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3546 }
3547 result = result.copyWith(newType, lform);
3548 return result;
3549 }
3550
3551 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3552 int dropped = valueTypes.size();
3553 MethodType.checkSlotCount(dropped);
3554 int outargs = oldType.parameterCount();
3555 int inargs = outargs + dropped;
3556 if (pos < 0 || pos > outargs)
3557 throw newIllegalArgumentException("no argument type to remove"
3558 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3559 );
3560 return dropped;
3561 }
3562
3563 /**
3564 * Produces a method handle which will discard some dummy arguments
3565 * before calling some other specified <i>target</i> method handle.
3566 * The type of the new method handle will be the same as the target's type,
3567 * except it will also include the dummy argument types,
3568 * at some given position.
3569 * <p>
3570 * The {@code pos} argument may range between zero and <i>N</i>,
3571 * where <i>N</i> is the arity of the target.
3572 * If {@code pos} is zero, the dummy arguments will precede
3573 * the target's real arguments; if {@code pos} is <i>N</i>
3574 * they will come after.
3575 * @apiNote
3576 * <blockquote><pre>{@code
3577 import static java.lang.invoke.MethodHandles.*;
3578 import static java.lang.invoke.MethodType.*;
3579 ...
3580 MethodHandle cat = lookup().findVirtual(String.class,
3581 "concat", methodType(String.class, String.class));
3582 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3583 MethodHandle d0 = dropArguments(cat, 0, String.class);
3584 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3585 MethodHandle d1 = dropArguments(cat, 1, String.class);
3586 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
3587 MethodHandle d2 = dropArguments(cat, 2, String.class);
3588 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
3589 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
3590 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
3591 * }</pre></blockquote>
3592 * <p>
3593 * This method is also equivalent to the following code:
3594 * <blockquote><pre>
3595 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
3596 * </pre></blockquote>
3597 * @param target the method handle to invoke after the arguments are dropped
3598 * @param valueTypes the type(s) of the argument(s) to drop
3599 * @param pos position of first argument to drop (zero for the leftmost)
3600 * @return a method handle which drops arguments of the given types,
3601 * before calling the original method handle
3602 * @throws NullPointerException if the target is null,
3603 * or if the {@code valueTypes} array or any of its elements is null
3604 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3605 * or if {@code pos} is negative or greater than the arity of the target,
3606 * or if the new method handle's type would have
3607 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3608 */
3609 public static
3610 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
3611 return dropArguments0(target, pos, copyTypes(valueTypes));
3612 }
3613
3614 // private version which allows caller some freedom with error handling
3615 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
3616 boolean nullOnFailure) {
3617 newTypes = copyTypes(newTypes.toArray());
3618 List<Class<?>> oldTypes = target.type().parameterList();
3619 int match = oldTypes.size();
3620 if (skip != 0) {
3621 if (skip < 0 || skip > match) {
3622 throw newIllegalArgumentException("illegal skip", skip, target);
3623 }
3624 oldTypes = oldTypes.subList(skip, match);
3625 match -= skip;
3626 }
3627 List<Class<?>> addTypes = newTypes;
3628 int add = addTypes.size();
3629 if (pos != 0) {
3630 if (pos < 0 || pos > add) {
3631 throw newIllegalArgumentException("illegal pos", pos, newTypes);
3632 }
3633 addTypes = addTypes.subList(pos, add);
3634 add -= pos;
3635 assert(addTypes.size() == add);
3636 }
3637 // Do not add types which already match the existing arguments.
3638 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
3639 if (nullOnFailure) {
3640 return null;
3641 }
3642 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
3643 }
3644 addTypes = addTypes.subList(match, add);
3645 add -= match;
3646 assert(addTypes.size() == add);
3647 // newTypes: ( P*[pos], M*[match], A*[add] )
3648 // target: ( S*[skip], M*[match] )
3649 MethodHandle adapter = target;
3650 if (add > 0) {
3651 adapter = dropArguments0(adapter, skip+ match, addTypes);
3652 }
3653 // adapter: (S*[skip], M*[match], A*[add] )
3654 if (pos > 0) {
3655 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
3656 }
3657 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
3658 return adapter;
3659 }
3660
3661 /**
3662 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
3663 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
3664 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
3665 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
3666 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
3667 * {@link #dropArguments(MethodHandle, int, Class[])}.
3668 * <p>
3669 * The resulting handle will have the same return type as the target handle.
3670 * <p>
3671 * In more formal terms, assume these two type lists:<ul>
3672 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
3673 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
3674 * {@code newTypes}.
3675 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
3676 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
3677 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
3678 * sub-list.
3679 * </ul>
3680 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
3681 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
3682 * {@link #dropArguments(MethodHandle, int, Class[])}.
3683 * <p>
3684 * @apiNote
3685 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
3686 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
3687 * <blockquote><pre>{@code
3688 import static java.lang.invoke.MethodHandles.*;
3689 import static java.lang.invoke.MethodType.*;
3690 ...
3691 ...
3692 MethodHandle h0 = constant(boolean.class, true);
3693 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
3694 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
3695 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
3696 if (h1.type().parameterCount() < h2.type().parameterCount())
3697 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
3698 else
3699 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
3700 MethodHandle h3 = guardWithTest(h0, h1, h2);
3701 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
3702 * }</pre></blockquote>
3703 * @param target the method handle to adapt
3704 * @param skip number of targets parameters to disregard (they will be unchanged)
3705 * @param newTypes the list of types to match {@code target}'s parameter type list to
3706 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
3707 * @return a possibly adapted method handle
3708 * @throws NullPointerException if either argument is null
3709 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
3710 * or if {@code skip} is negative or greater than the arity of the target,
3711 * or if {@code pos} is negative or greater than the newTypes list size,
3712 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
3713 * {@code pos}.
3714 * @since 9
3715 */
3716 public static
3717 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
3718 Objects.requireNonNull(target);
3719 Objects.requireNonNull(newTypes);
3720 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
3721 }
3722
3723 /**
3724 * Adapts a target method handle by pre-processing
3725 * one or more of its arguments, each with its own unary filter function,
3726 * and then calling the target with each pre-processed argument
3727 * replaced by the result of its corresponding filter function.
3728 * <p>
3729 * The pre-processing is performed by one or more method handles,
3730 * specified in the elements of the {@code filters} array.
3731 * The first element of the filter array corresponds to the {@code pos}
3732 * argument of the target, and so on in sequence.
3733 * <p>
3734 * Null arguments in the array are treated as identity functions,
3735 * and the corresponding arguments left unchanged.
3736 * (If there are no non-null elements in the array, the original target is returned.)
3737 * Each filter is applied to the corresponding argument of the adapter.
3738 * <p>
3739 * If a filter {@code F} applies to the {@code N}th argument of
3740 * the target, then {@code F} must be a method handle which
3741 * takes exactly one argument. The type of {@code F}'s sole argument
3742 * replaces the corresponding argument type of the target
3743 * in the resulting adapted method handle.
3744 * The return type of {@code F} must be identical to the corresponding
3745 * parameter type of the target.
3746 * <p>
3747 * It is an error if there are elements of {@code filters}
3748 * (null or not)
3749 * which do not correspond to argument positions in the target.
3750 * <p><b>Example:</b>
3751 * <blockquote><pre>{@code
3752 import static java.lang.invoke.MethodHandles.*;
3753 import static java.lang.invoke.MethodType.*;
3754 ...
3755 MethodHandle cat = lookup().findVirtual(String.class,
3756 "concat", methodType(String.class, String.class));
3757 MethodHandle upcase = lookup().findVirtual(String.class,
3758 "toUpperCase", methodType(String.class));
3759 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3760 MethodHandle f0 = filterArguments(cat, 0, upcase);
3761 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
3762 MethodHandle f1 = filterArguments(cat, 1, upcase);
3763 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
3764 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
3765 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
3766 * }</pre></blockquote>
3767 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3768 * denotes the return type of both the {@code target} and resulting adapter.
3769 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
3770 * of the parameters and arguments that precede and follow the filter position
3771 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
3772 * values of the filtered parameters and arguments; they also represent the
3773 * return types of the {@code filter[i]} handles. The latter accept arguments
3774 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
3775 * the resulting adapter.
3776 * <blockquote><pre>{@code
3777 * T target(P... p, A[i]... a[i], B... b);
3778 * A[i] filter[i](V[i]);
3779 * T adapter(P... p, V[i]... v[i], B... b) {
3780 * return target(p..., filter[i](v[i])..., b...);
3781 * }
3782 * }</pre></blockquote>
3783 * <p>
3784 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3785 * variable-arity method handle}, even if the original target method handle was.
3786 *
3787 * @param target the method handle to invoke after arguments are filtered
3788 * @param pos the position of the first argument to filter
3789 * @param filters method handles to call initially on filtered arguments
3790 * @return method handle which incorporates the specified argument filtering logic
3791 * @throws NullPointerException if the target is null
3792 * or if the {@code filters} array is null
3793 * @throws IllegalArgumentException if a non-null element of {@code filters}
3794 * does not match a corresponding argument type of target as described above,
3795 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
3796 * or if the resulting method handle's type would have
3797 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3798 */
3799 public static
3800 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
3801 filterArgumentsCheckArity(target, pos, filters);
3802 MethodHandle adapter = target;
3803 int curPos = pos-1; // pre-incremented
3804 for (MethodHandle filter : filters) {
3805 curPos += 1;
3806 if (filter == null) continue; // ignore null elements of filters
3807 adapter = filterArgument(adapter, curPos, filter);
3808 }
3809 return adapter;
3810 }
3811
3812 /*non-public*/ static
3813 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
3814 filterArgumentChecks(target, pos, filter);
3815 MethodType targetType = target.type();
3816 MethodType filterType = filter.type();
3817 BoundMethodHandle result = target.rebind();
3818 Class<?> newParamType = filterType.parameterType(0);
3819 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
3820 MethodType newType = targetType.changeParameterType(pos, newParamType);
3821 result = result.copyWithExtendL(newType, lform, filter);
3822 return result;
3823 }
3824
3825 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
3826 MethodType targetType = target.type();
3827 int maxPos = targetType.parameterCount();
3828 if (pos + filters.length > maxPos)
3829 throw newIllegalArgumentException("too many filters");
3830 }
3831
3832 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3833 MethodType targetType = target.type();
3834 MethodType filterType = filter.type();
3835 if (filterType.parameterCount() != 1
3836 || filterType.returnType() != targetType.parameterType(pos))
3837 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3838 }
3839
3840 /**
3841 * Adapts a target method handle by pre-processing
3842 * a sub-sequence of its arguments with a filter (another method handle).
3843 * The pre-processed arguments are replaced by the result (if any) of the
3844 * filter function.
3845 * The target is then called on the modified (usually shortened) argument list.
3846 * <p>
3847 * If the filter returns a value, the target must accept that value as
3848 * its argument in position {@code pos}, preceded and/or followed by
3849 * any arguments not passed to the filter.
3850 * If the filter returns void, the target must accept all arguments
3851 * not passed to the filter.
3852 * No arguments are reordered, and a result returned from the filter
3853 * replaces (in order) the whole subsequence of arguments originally
3854 * passed to the adapter.
3855 * <p>
3856 * The argument types (if any) of the filter
3857 * replace zero or one argument types of the target, at position {@code pos},
3858 * in the resulting adapted method handle.
3859 * The return type of the filter (if any) must be identical to the
3860 * argument type of the target at position {@code pos}, and that target argument
3861 * is supplied by the return value of the filter.
3862 * <p>
3863 * In all cases, {@code pos} must be greater than or equal to zero, and
3864 * {@code pos} must also be less than or equal to the target's arity.
3865 * <p><b>Example:</b>
3866 * <blockquote><pre>{@code
3867 import static java.lang.invoke.MethodHandles.*;
3868 import static java.lang.invoke.MethodType.*;
3869 ...
3870 MethodHandle deepToString = publicLookup()
3871 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
3872
3873 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
3874 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
3875
3876 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
3877 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
3878
3879 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
3880 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
3881 assertEquals("[top, [up, down], strange]",
3882 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
3883
3884 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
3885 assertEquals("[top, [up, down], [strange]]",
3886 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
3887
3888 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
3889 assertEquals("[top, [[up, down, strange], charm], bottom]",
3890 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
3891 * }</pre></blockquote>
3892 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3893 * represents the return type of the {@code target} and resulting adapter.
3894 * {@code V}/{@code v} stand for the return type and value of the
3895 * {@code filter}, which are also found in the signature and arguments of
3896 * the {@code target}, respectively, unless {@code V} is {@code void}.
3897 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
3898 * and values preceding and following the collection position, {@code pos},
3899 * in the {@code target}'s signature. They also turn up in the resulting
3900 * adapter's signature and arguments, where they surround
3901 * {@code B}/{@code b}, which represent the parameter types and arguments
3902 * to the {@code filter} (if any).
3903 * <blockquote><pre>{@code
3904 * T target(A...,V,C...);
3905 * V filter(B...);
3906 * T adapter(A... a,B... b,C... c) {
3907 * V v = filter(b...);
3908 * return target(a...,v,c...);
3909 * }
3910 * // and if the filter has no arguments:
3911 * T target2(A...,V,C...);
3912 * V filter2();
3913 * T adapter2(A... a,C... c) {
3914 * V v = filter2();
3915 * return target2(a...,v,c...);
3916 * }
3917 * // and if the filter has a void return:
3918 * T target3(A...,C...);
3919 * void filter3(B...);
3920 * T adapter3(A... a,B... b,C... c) {
3921 * filter3(b...);
3922 * return target3(a...,c...);
3923 * }
3924 * }</pre></blockquote>
3925 * <p>
3926 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
3927 * one which first "folds" the affected arguments, and then drops them, in separate
3928 * steps as follows:
3929 * <blockquote><pre>{@code
3930 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
3931 * mh = MethodHandles.foldArguments(mh, coll); //step 1
3932 * }</pre></blockquote>
3933 * If the target method handle consumes no arguments besides than the result
3934 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
3935 * is equivalent to {@code filterReturnValue(coll, mh)}.
3936 * If the filter method handle {@code coll} consumes one argument and produces
3937 * a non-void result, then {@code collectArguments(mh, N, coll)}
3938 * is equivalent to {@code filterArguments(mh, N, coll)}.
3939 * Other equivalences are possible but would require argument permutation.
3940 * <p>
3941 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3942 * variable-arity method handle}, even if the original target method handle was.
3943 *
3944 * @param target the method handle to invoke after filtering the subsequence of arguments
3945 * @param pos the position of the first adapter argument to pass to the filter,
3946 * and/or the target argument which receives the result of the filter
3947 * @param filter method handle to call on the subsequence of arguments
3948 * @return method handle which incorporates the specified argument subsequence filtering logic
3949 * @throws NullPointerException if either argument is null
3950 * @throws IllegalArgumentException if the return type of {@code filter}
3951 * is non-void and is not the same as the {@code pos} argument of the target,
3952 * or if {@code pos} is not between 0 and the target's arity, inclusive,
3953 * or if the resulting method handle's type would have
3954 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3955 * @see MethodHandles#foldArguments
3956 * @see MethodHandles#filterArguments
3957 * @see MethodHandles#filterReturnValue
3958 */
3959 public static
3960 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
3961 MethodType newType = collectArgumentsChecks(target, pos, filter);
3962 MethodType collectorType = filter.type();
3963 BoundMethodHandle result = target.rebind();
3964 LambdaForm lform;
3965 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
3966 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
3967 if (lform != null) {
3968 return result.copyWith(newType, lform);
3969 }
3970 }
3971 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
3972 return result.copyWithExtendL(newType, lform, filter);
3973 }
3974
3975 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3976 MethodType targetType = target.type();
3977 MethodType filterType = filter.type();
3978 Class<?> rtype = filterType.returnType();
3979 List<Class<?>> filterArgs = filterType.parameterList();
3980 if (rtype == void.class) {
3981 return targetType.insertParameterTypes(pos, filterArgs);
3982 }
3983 if (rtype != targetType.parameterType(pos)) {
3984 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3985 }
3986 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
3987 }
3988
3989 /**
3990 * Adapts a target method handle by post-processing
3991 * its return value (if any) with a filter (another method handle).
3992 * The result of the filter is returned from the adapter.
3993 * <p>
3994 * If the target returns a value, the filter must accept that value as
3995 * its only argument.
3996 * If the target returns void, the filter must accept no arguments.
3997 * <p>
3998 * The return type of the filter
3999 * replaces the return type of the target
4000 * in the resulting adapted method handle.
4001 * The argument type of the filter (if any) must be identical to the
4002 * return type of the target.
4003 * <p><b>Example:</b>
4004 * <blockquote><pre>{@code
4005 import static java.lang.invoke.MethodHandles.*;
4006 import static java.lang.invoke.MethodType.*;
4007 ...
4008 MethodHandle cat = lookup().findVirtual(String.class,
4009 "concat", methodType(String.class, String.class));
4010 MethodHandle length = lookup().findVirtual(String.class,
4011 "length", methodType(int.class));
4012 System.out.println((String) cat.invokeExact("x", "y")); // xy
4013 MethodHandle f0 = filterReturnValue(cat, length);
4014 System.out.println((int) f0.invokeExact("x", "y")); // 2
4015 * }</pre></blockquote>
4016 * <p>Here is pseudocode for the resulting adapter. In the code,
4017 * {@code T}/{@code t} represent the result type and value of the
4018 * {@code target}; {@code V}, the result type of the {@code filter}; and
4019 * {@code A}/{@code a}, the types and values of the parameters and arguments
4020 * of the {@code target} as well as the resulting adapter.
4021 * <blockquote><pre>{@code
4022 * T target(A...);
4023 * V filter(T);
4024 * V adapter(A... a) {
4025 * T t = target(a...);
4026 * return filter(t);
4027 * }
4028 * // and if the target has a void return:
4029 * void target2(A...);
4030 * V filter2();
4031 * V adapter2(A... a) {
4032 * target2(a...);
4033 * return filter2();
4034 * }
4035 * // and if the filter has a void return:
4036 * T target3(A...);
4037 * void filter3(V);
4038 * void adapter3(A... a) {
4039 * T t = target3(a...);
4040 * filter3(t);
4041 * }
4042 * }</pre></blockquote>
4043 * <p>
4044 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4045 * variable-arity method handle}, even if the original target method handle was.
4046 * @param target the method handle to invoke before filtering the return value
4047 * @param filter method handle to call on the return value
4048 * @return method handle which incorporates the specified return value filtering logic
4049 * @throws NullPointerException if either argument is null
4050 * @throws IllegalArgumentException if the argument list of {@code filter}
4051 * does not match the return type of target as described above
4052 */
4053 public static
4054 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
4055 MethodType targetType = target.type();
4056 MethodType filterType = filter.type();
4057 filterReturnValueChecks(targetType, filterType);
4058 BoundMethodHandle result = target.rebind();
4059 BasicType rtype = BasicType.basicType(filterType.returnType());
4060 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
4061 MethodType newType = targetType.changeReturnType(filterType.returnType());
4062 result = result.copyWithExtendL(newType, lform, filter);
4063 return result;
4064 }
4065
4066 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
4067 Class<?> rtype = targetType.returnType();
4068 int filterValues = filterType.parameterCount();
4069 if (filterValues == 0
4070 ? (rtype != void.class)
4071 : (rtype != filterType.parameterType(0) || filterValues != 1))
4072 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4073 }
4074
4075 /**
4076 * Adapts a target method handle by pre-processing
4077 * some of its arguments, and then calling the target with
4078 * the result of the pre-processing, inserted into the original
4079 * sequence of arguments.
4080 * <p>
4081 * The pre-processing is performed by {@code combiner}, a second method handle.
4082 * Of the arguments passed to the adapter, the first {@code N} arguments
4083 * are copied to the combiner, which is then called.
4084 * (Here, {@code N} is defined as the parameter count of the combiner.)
4085 * After this, control passes to the target, with any result
4086 * from the combiner inserted before the original {@code N} incoming
4087 * arguments.
4088 * <p>
4089 * If the combiner returns a value, the first parameter type of the target
4090 * must be identical with the return type of the combiner, and the next
4091 * {@code N} parameter types of the target must exactly match the parameters
4092 * of the combiner.
4093 * <p>
4094 * If the combiner has a void return, no result will be inserted,
4095 * and the first {@code N} parameter types of the target
4096 * must exactly match the parameters of the combiner.
4097 * <p>
4098 * The resulting adapter is the same type as the target, except that the
4099 * first parameter type is dropped,
4100 * if it corresponds to the result of the combiner.
4101 * <p>
4102 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
4103 * that either the combiner or the target does not wish to receive.
4104 * If some of the incoming arguments are destined only for the combiner,
4105 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
4106 * arguments will not need to be live on the stack on entry to the
4107 * target.)
4108 * <p><b>Example:</b>
4109 * <blockquote><pre>{@code
4110 import static java.lang.invoke.MethodHandles.*;
4111 import static java.lang.invoke.MethodType.*;
4112 ...
4113 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4114 "println", methodType(void.class, String.class))
4115 .bindTo(System.out);
4116 MethodHandle cat = lookup().findVirtual(String.class,
4117 "concat", methodType(String.class, String.class));
4118 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4119 MethodHandle catTrace = foldArguments(cat, trace);
4120 // also prints "boo":
4121 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4122 * }</pre></blockquote>
4123 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4124 * represents the result type of the {@code target} and resulting adapter.
4125 * {@code V}/{@code v} represent the type and value of the parameter and argument
4126 * of {@code target} that precedes the folding position; {@code V} also is
4127 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4128 * types and values of the {@code N} parameters and arguments at the folding
4129 * position. {@code B}/{@code b} represent the types and values of the
4130 * {@code target} parameters and arguments that follow the folded parameters
4131 * and arguments.
4132 * <blockquote><pre>{@code
4133 * // there are N arguments in A...
4134 * T target(V, A[N]..., B...);
4135 * V combiner(A...);
4136 * T adapter(A... a, B... b) {
4137 * V v = combiner(a...);
4138 * return target(v, a..., b...);
4139 * }
4140 * // and if the combiner has a void return:
4141 * T target2(A[N]..., B...);
4142 * void combiner2(A...);
4143 * T adapter2(A... a, B... b) {
4144 * combiner2(a...);
4145 * return target2(a..., b...);
4146 * }
4147 * }</pre></blockquote>
4148 * <p>
4149 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4150 * variable-arity method handle}, even if the original target method handle was.
4151 * @param target the method handle to invoke after arguments are combined
4152 * @param combiner method handle to call initially on the incoming arguments
4153 * @return method handle which incorporates the specified argument folding logic
4154 * @throws NullPointerException if either argument is null
4155 * @throws IllegalArgumentException if {@code combiner}'s return type
4156 * is non-void and not the same as the first argument type of
4157 * the target, or if the initial {@code N} argument types
4158 * of the target
4159 * (skipping one matching the {@code combiner}'s return type)
4160 * are not identical with the argument types of {@code combiner}
4161 */
4162 public static
4163 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
4164 return foldArguments(target, 0, combiner);
4165 }
4166
4167 /**
4168 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4169 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4170 * before the folded arguments.
4171 * <p>
4172 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4173 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4174 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4175 * 0.
4176 * <p>
4177 * @apiNote Example:
4178 * <blockquote><pre>{@code
4179 import static java.lang.invoke.MethodHandles.*;
4180 import static java.lang.invoke.MethodType.*;
4181 ...
4182 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4183 "println", methodType(void.class, String.class))
4184 .bindTo(System.out);
4185 MethodHandle cat = lookup().findVirtual(String.class,
4186 "concat", methodType(String.class, String.class));
4187 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4188 MethodHandle catTrace = foldArguments(cat, 1, trace);
4189 // also prints "jum":
4190 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4191 * }</pre></blockquote>
4192 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4193 * represents the result type of the {@code target} and resulting adapter.
4194 * {@code V}/{@code v} represent the type and value of the parameter and argument
4195 * of {@code target} that precedes the folding position; {@code V} also is
4196 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4197 * types and values of the {@code N} parameters and arguments at the folding
4198 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4199 * and values of the {@code target} parameters and arguments that precede and
4200 * follow the folded parameters and arguments starting at {@code pos},
4201 * respectively.
4202 * <blockquote><pre>{@code
4203 * // there are N arguments in A...
4204 * T target(Z..., V, A[N]..., B...);
4205 * V combiner(A...);
4206 * T adapter(Z... z, A... a, B... b) {
4207 * V v = combiner(a...);
4208 * return target(z..., v, a..., b...);
4209 * }
4210 * // and if the combiner has a void return:
4211 * T target2(Z..., A[N]..., B...);
4212 * void combiner2(A...);
4213 * T adapter2(Z... z, A... a, B... b) {
4214 * combiner2(a...);
4215 * return target2(z..., a..., b...);
4216 * }
4217 * }</pre></blockquote>
4218 * <p>
4219 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4220 * variable-arity method handle}, even if the original target method handle was.
4221 *
4222 * @param target the method handle to invoke after arguments are combined
4223 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4224 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4225 * @param combiner method handle to call initially on the incoming arguments
4226 * @return method handle which incorporates the specified argument folding logic
4227 * @throws NullPointerException if either argument is null
4228 * @throws IllegalArgumentException if either of the following two conditions holds:
4229 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4230 * {@code pos} of the target signature;
4231 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
4232 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
4233 *
4234 * @see #foldArguments(MethodHandle, MethodHandle)
4235 * @since 9
4236 */
4237 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4238 MethodType targetType = target.type();
4239 MethodType combinerType = combiner.type();
4240 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4241 BoundMethodHandle result = target.rebind();
4242 boolean dropResult = rtype == void.class;
4243 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4244 MethodType newType = targetType;
4245 if (!dropResult) {
4246 newType = newType.dropParameterTypes(pos, pos + 1);
4247 }
4248 result = result.copyWithExtendL(newType, lform, combiner);
4249 return result;
4250 }
4251
4252 /**
4253 * As {@see foldArguments(MethodHandle, int, MethodHandle)}, but with the
4254 * added capability of selecting the arguments from the targets parameters
4255 * to call the combiner with. This allows us to avoid some simple cases of
4256 * permutations and padding the combiner with dropArguments to select the
4257 * right argument, which may ultimately produce fewer intermediaries.
4258 */
4259 static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner, int ... argPositions) {
4260 MethodType targetType = target.type();
4261 MethodType combinerType = combiner.type();
4262 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType, argPositions);
4263 BoundMethodHandle result = target.rebind();
4264 boolean dropResult = rtype == void.class;
4265 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType(), argPositions);
4266 MethodType newType = targetType;
4267 if (!dropResult) {
4268 newType = newType.dropParameterTypes(pos, pos + 1);
4269 }
4270 result = result.copyWithExtendL(newType, lform, combiner);
4271 return result;
4272 }
4273
4274 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
4275 int foldArgs = combinerType.parameterCount();
4276 Class<?> rtype = combinerType.returnType();
4277 int foldVals = rtype == void.class ? 0 : 1;
4278 int afterInsertPos = foldPos + foldVals;
4279 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
4280 if (ok) {
4281 for (int i = 0; i < foldArgs; i++) {
4282 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
4283 ok = false;
4284 break;
4285 }
4286 }
4287 }
4288 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
4289 ok = false;
4290 if (!ok)
4291 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4292 return rtype;
4293 }
4294
4295 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType, int ... argPos) {
4296 int foldArgs = combinerType.parameterCount();
4297 if (argPos.length != foldArgs) {
4298 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
4299 }
4300 Class<?> rtype = combinerType.returnType();
4301 int foldVals = rtype == void.class ? 0 : 1;
4302 boolean ok = true;
4303 for (int i = 0; i < foldArgs; i++) {
4304 int arg = argPos[i];
4305 if (arg < 0 || arg > targetType.parameterCount()) {
4306 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
4307 }
4308 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
4309 throw newIllegalArgumentException("target argument type at position " + arg
4310 + " must match combiner argument type at index " + i + ": " + targetType
4311 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
4312 }
4313 }
4314 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) {
4315 ok = false;
4316 }
4317 if (!ok)
4318 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4319 return rtype;
4320 }
4321
4322 /**
4323 * Makes a method handle which adapts a target method handle,
4324 * by guarding it with a test, a boolean-valued method handle.
4325 * If the guard fails, a fallback handle is called instead.
4326 * All three method handles must have the same corresponding
4327 * argument and return types, except that the return type
4328 * of the test must be boolean, and the test is allowed
4329 * to have fewer arguments than the other two method handles.
4330 * <p>
4331 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4332 * represents the uniform result type of the three involved handles;
4333 * {@code A}/{@code a}, the types and values of the {@code target}
4334 * parameters and arguments that are consumed by the {@code test}; and
4335 * {@code B}/{@code b}, those types and values of the {@code target}
4336 * parameters and arguments that are not consumed by the {@code test}.
4337 * <blockquote><pre>{@code
4338 * boolean test(A...);
4339 * T target(A...,B...);
4340 * T fallback(A...,B...);
4341 * T adapter(A... a,B... b) {
4342 * if (test(a...))
4343 * return target(a..., b...);
4344 * else
4345 * return fallback(a..., b...);
4346 * }
4347 * }</pre></blockquote>
4348 * Note that the test arguments ({@code a...} in the pseudocode) cannot
4349 * be modified by execution of the test, and so are passed unchanged
4350 * from the caller to the target or fallback as appropriate.
4351 * @param test method handle used for test, must return boolean
4352 * @param target method handle to call if test passes
4353 * @param fallback method handle to call if test fails
4354 * @return method handle which incorporates the specified if/then/else logic
4355 * @throws NullPointerException if any argument is null
4356 * @throws IllegalArgumentException if {@code test} does not return boolean,
4357 * or if all three method types do not match (with the return
4358 * type of {@code test} changed to match that of the target).
4359 */
4360 public static
4361 MethodHandle guardWithTest(MethodHandle test,
4362 MethodHandle target,
4363 MethodHandle fallback) {
4364 MethodType gtype = test.type();
4365 MethodType ttype = target.type();
4366 MethodType ftype = fallback.type();
4367 if (!ttype.equals(ftype))
4368 throw misMatchedTypes("target and fallback types", ttype, ftype);
4369 if (gtype.returnType() != boolean.class)
4370 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
4371 List<Class<?>> targs = ttype.parameterList();
4372 test = dropArgumentsToMatch(test, 0, targs, 0, true);
4373 if (test == null) {
4374 throw misMatchedTypes("target and test types", ttype, gtype);
4375 }
4376 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
4377 }
4378
4379 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
4380 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
4381 }
4382
4383 /**
4384 * Makes a method handle which adapts a target method handle,
4385 * by running it inside an exception handler.
4386 * If the target returns normally, the adapter returns that value.
4387 * If an exception matching the specified type is thrown, the fallback
4388 * handle is called instead on the exception, plus the original arguments.
4389 * <p>
4390 * The target and handler must have the same corresponding
4391 * argument and return types, except that handler may omit trailing arguments
4392 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
4393 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
4394 * <p>
4395 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4396 * represents the return type of the {@code target} and {@code handler},
4397 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
4398 * the types and values of arguments to the resulting handle consumed by
4399 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
4400 * resulting handle discarded by {@code handler}.
4401 * <blockquote><pre>{@code
4402 * T target(A..., B...);
4403 * T handler(ExType, A...);
4404 * T adapter(A... a, B... b) {
4405 * try {
4406 * return target(a..., b...);
4407 * } catch (ExType ex) {
4408 * return handler(ex, a...);
4409 * }
4410 * }
4411 * }</pre></blockquote>
4412 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4413 * be modified by execution of the target, and so are passed unchanged
4414 * from the caller to the handler, if the handler is invoked.
4415 * <p>
4416 * The target and handler must return the same type, even if the handler
4417 * always throws. (This might happen, for instance, because the handler
4418 * is simulating a {@code finally} clause).
4419 * To create such a throwing handler, compose the handler creation logic
4420 * with {@link #throwException throwException},
4421 * in order to create a method handle of the correct return type.
4422 * @param target method handle to call
4423 * @param exType the type of exception which the handler will catch
4424 * @param handler method handle to call if a matching exception is thrown
4425 * @return method handle which incorporates the specified try/catch logic
4426 * @throws NullPointerException if any argument is null
4427 * @throws IllegalArgumentException if {@code handler} does not accept
4428 * the given exception type, or if the method handle types do
4429 * not match in their return types and their
4430 * corresponding parameters
4431 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4432 */
4433 public static
4434 MethodHandle catchException(MethodHandle target,
4435 Class<? extends Throwable> exType,
4436 MethodHandle handler) {
4437 MethodType ttype = target.type();
4438 MethodType htype = handler.type();
4439 if (!Throwable.class.isAssignableFrom(exType))
4440 throw new ClassCastException(exType.getName());
4441 if (htype.parameterCount() < 1 ||
4442 !htype.parameterType(0).isAssignableFrom(exType))
4443 throw newIllegalArgumentException("handler does not accept exception type "+exType);
4444 if (htype.returnType() != ttype.returnType())
4445 throw misMatchedTypes("target and handler return types", ttype, htype);
4446 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4447 if (handler == null) {
4448 throw misMatchedTypes("target and handler types", ttype, htype);
4449 }
4450 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4451 }
4452
4453 /**
4454 * Produces a method handle which will throw exceptions of the given {@code exType}.
4455 * The method handle will accept a single argument of {@code exType},
4456 * and immediately throw it as an exception.
4457 * The method type will nominally specify a return of {@code returnType}.
4458 * The return type may be anything convenient: It doesn't matter to the
4459 * method handle's behavior, since it will never return normally.
4460 * @param returnType the return type of the desired method handle
4461 * @param exType the parameter type of the desired method handle
4462 * @return method handle which can throw the given exceptions
4463 * @throws NullPointerException if either argument is null
4464 */
4465 public static
4466 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4467 if (!Throwable.class.isAssignableFrom(exType))
4468 throw new ClassCastException(exType.getName());
4469 return MethodHandleImpl.throwException(methodType(returnType, exType));
4470 }
4471
4472 /**
4473 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4474 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4475 * delivers the loop's result, which is the return value of the resulting handle.
4476 * <p>
4477 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
4478 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4479 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4480 * terms of method handles, each clause will specify up to four independent actions:<ul>
4481 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
4482 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
4483 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
4484 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4485 * </ul>
4486 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
4487 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
4488 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
4489 * <p>
4490 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4491 * this case. See below for a detailed description.
4492 * <p>
4493 * <em>Parameters optional everywhere:</em>
4494 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
4495 * As an exception, the init functions cannot take any {@code v} parameters,
4496 * because those values are not yet computed when the init functions are executed.
4497 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
4498 * In fact, any clause function may take no arguments at all.
4499 * <p>
4500 * <em>Loop parameters:</em>
4501 * A clause function may take all the iteration variable values it is entitled to, in which case
4502 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
4503 * with their types and values notated as {@code (A...)} and {@code (a...)}.
4504 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
4505 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
4506 * init function is automatically a loop parameter {@code a}.)
4507 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
4508 * These loop parameters act as loop-invariant values visible across the whole loop.
4509 * <p>
4510 * <em>Parameters visible everywhere:</em>
4511 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
4512 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
4513 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
4514 * Most clause functions will not need all of this information, but they will be formally connected to it
4515 * as if by {@link #dropArguments}.
4516 * <a id="astar"></a>
4517 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
4518 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
4519 * In that notation, the general form of an init function parameter list
4520 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
4521 * <p>
4522 * <em>Checking clause structure:</em>
4523 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4524 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4525 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
4526 * met by the inputs to the loop combinator.
4527 * <p>
4528 * <em>Effectively identical sequences:</em>
4529 * <a id="effid"></a>
4530 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
4531 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
4532 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
4533 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
4534 * that longest list.
4535 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
4536 * and the same is true if more sequences of the form {@code (V... A*)} are added.
4537 * <p>
4538 * <em>Step 0: Determine clause structure.</em><ol type="a">
4539 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
4540 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4541 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4542 * four. Padding takes place by appending elements to the array.
4543 * <li>Clauses with all {@code null}s are disregarded.
4544 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4545 * </ol>
4546 * <p>
4547 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
4548 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
4549 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
4550 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
4551 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
4552 * iteration variable type.
4553 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
4554 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
4555 * </ol>
4556 * <p>
4557 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
4558 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
4559 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
4560 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
4561 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
4562 * (These types will checked in step 2, along with all the clause function types.)
4563 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
4564 * <li>All of the collected parameter lists must be effectively identical.
4565 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
4566 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
4567 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
4568 * the "internal parameter list".
4569 * </ul>
4570 * <p>
4571 * <em>Step 1C: Determine loop return type.</em><ol type="a">
4572 * <li>Examine fini function return types, disregarding omitted fini functions.
4573 * <li>If there are no fini functions, the loop return type is {@code void}.
4574 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
4575 * type.
4576 * </ol>
4577 * <p>
4578 * <em>Step 1D: Check other types.</em><ol type="a">
4579 * <li>There must be at least one non-omitted pred function.
4580 * <li>Every non-omitted pred function must have a {@code boolean} return type.
4581 * </ol>
4582 * <p>
4583 * <em>Step 2: Determine parameter lists.</em><ol type="a">
4584 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
4585 * <li>The parameter list for init functions will be adjusted to the external parameter list.
4586 * (Note that their parameter lists are already effectively identical to this list.)
4587 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
4588 * effectively identical to the internal parameter list {@code (V... A...)}.
4589 * </ol>
4590 * <p>
4591 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
4592 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
4593 * type.
4594 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
4595 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
4596 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
4597 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
4598 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
4599 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
4600 * loop return type.
4601 * </ol>
4602 * <p>
4603 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
4604 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
4605 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
4606 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
4607 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
4608 * pad out the end of the list.
4609 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch dropping unused trailing arguments}.
4610 * </ol>
4611 * <p>
4612 * <em>Final observations.</em><ol type="a">
4613 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
4614 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
4615 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
4616 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
4617 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
4618 * <li>Each pair of init and step functions agrees in their return type {@code V}.
4619 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
4620 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
4621 * </ol>
4622 * <p>
4623 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
4624 * <ul>
4625 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
4626 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
4627 * (Only one {@code Pn} has to be non-{@code null}.)
4628 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
4629 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
4630 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
4631 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
4632 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
4633 * the resulting loop handle's parameter types {@code (A...)}.
4634 * </ul>
4635 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
4636 * which is natural if most of the loop computation happens in the steps. For some loops,
4637 * the burden of computation might be heaviest in the pred functions, and so the pred functions
4638 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
4639 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
4640 * where the init functions will need the extra parameters. For such reasons, the rules for
4641 * determining these parameters are as symmetric as possible, across all clause parts.
4642 * In general, the loop parameters function as common invariant values across the whole
4643 * loop, while the iteration variables function as common variant values, or (if there is
4644 * no step function) as internal loop invariant temporaries.
4645 * <p>
4646 * <em>Loop execution.</em><ol type="a">
4647 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
4648 * every clause function. These locals are loop invariant.
4649 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
4650 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
4651 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
4652 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
4653 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
4654 * (in argument order).
4655 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
4656 * returns {@code false}.
4657 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
4658 * sequence {@code (v...)} of loop variables.
4659 * The updated value is immediately visible to all subsequent function calls.
4660 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
4661 * (of type {@code R}) is returned from the loop as a whole.
4662 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
4663 * except by throwing an exception.
4664 * </ol>
4665 * <p>
4666 * <em>Usage tips.</em>
4667 * <ul>
4668 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
4669 * sometimes a step function only needs to observe the current value of its own variable.
4670 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
4671 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
4672 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
4673 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
4674 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
4675 * <li>If some of the clause functions are virtual methods on an instance, the instance
4676 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
4677 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
4678 * will be the first iteration variable value, and it will be easy to use virtual
4679 * methods as clause parts, since all of them will take a leading instance reference matching that value.
4680 * </ul>
4681 * <p>
4682 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
4683 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
4684 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
4685 * <blockquote><pre>{@code
4686 * V... init...(A...);
4687 * boolean pred...(V..., A...);
4688 * V... step...(V..., A...);
4689 * R fini...(V..., A...);
4690 * R loop(A... a) {
4691 * V... v... = init...(a...);
4692 * for (;;) {
4693 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
4694 * v = s(v..., a...);
4695 * if (!p(v..., a...)) {
4696 * return f(v..., a...);
4697 * }
4698 * }
4699 * }
4700 * }
4701 * }</pre></blockquote>
4702 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
4703 * to their full length, even though individual clause functions may neglect to take them all.
4704 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch}.
4705 * <p>
4706 * @apiNote Example:
4707 * <blockquote><pre>{@code
4708 * // iterative implementation of the factorial function as a loop handle
4709 * static int one(int k) { return 1; }
4710 * static int inc(int i, int acc, int k) { return i + 1; }
4711 * static int mult(int i, int acc, int k) { return i * acc; }
4712 * static boolean pred(int i, int acc, int k) { return i < k; }
4713 * static int fin(int i, int acc, int k) { return acc; }
4714 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4715 * // null initializer for counter, should initialize to 0
4716 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4717 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4718 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4719 * assertEquals(120, loop.invoke(5));
4720 * }</pre></blockquote>
4721 * The same example, dropping arguments and using combinators:
4722 * <blockquote><pre>{@code
4723 * // simplified implementation of the factorial function as a loop handle
4724 * static int inc(int i) { return i + 1; } // drop acc, k
4725 * static int mult(int i, int acc) { return i * acc; } //drop k
4726 * static boolean cmp(int i, int k) { return i < k; }
4727 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
4728 * // null initializer for counter, should initialize to 0
4729 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4730 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
4731 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
4732 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4733 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4734 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4735 * assertEquals(720, loop.invoke(6));
4736 * }</pre></blockquote>
4737 * A similar example, using a helper object to hold a loop parameter:
4738 * <blockquote><pre>{@code
4739 * // instance-based implementation of the factorial function as a loop handle
4740 * static class FacLoop {
4741 * final int k;
4742 * FacLoop(int k) { this.k = k; }
4743 * int inc(int i) { return i + 1; }
4744 * int mult(int i, int acc) { return i * acc; }
4745 * boolean pred(int i) { return i < k; }
4746 * int fin(int i, int acc) { return acc; }
4747 * }
4748 * // assume MH_FacLoop is a handle to the constructor
4749 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4750 * // null initializer for counter, should initialize to 0
4751 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4752 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
4753 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4754 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4755 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
4756 * assertEquals(5040, loop.invoke(7));
4757 * }</pre></blockquote>
4758 *
4759 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
4760 *
4761 * @return a method handle embodying the looping behavior as defined by the arguments.
4762 *
4763 * @throws IllegalArgumentException in case any of the constraints described above is violated.
4764 *
4765 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
4766 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4767 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
4768 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
4769 * @since 9
4770 */
4771 public static MethodHandle loop(MethodHandle[]... clauses) {
4772 // Step 0: determine clause structure.
4773 loopChecks0(clauses);
4774
4775 List<MethodHandle> init = new ArrayList<>();
4776 List<MethodHandle> step = new ArrayList<>();
4777 List<MethodHandle> pred = new ArrayList<>();
4778 List<MethodHandle> fini = new ArrayList<>();
4779
4780 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
4781 init.add(clause[0]); // all clauses have at least length 1
4782 step.add(clause.length <= 1 ? null : clause[1]);
4783 pred.add(clause.length <= 2 ? null : clause[2]);
4784 fini.add(clause.length <= 3 ? null : clause[3]);
4785 });
4786
4787 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
4788 final int nclauses = init.size();
4789
4790 // Step 1A: determine iteration variables (V...).
4791 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
4792 for (int i = 0; i < nclauses; ++i) {
4793 MethodHandle in = init.get(i);
4794 MethodHandle st = step.get(i);
4795 if (in == null && st == null) {
4796 iterationVariableTypes.add(void.class);
4797 } else if (in != null && st != null) {
4798 loopChecks1a(i, in, st);
4799 iterationVariableTypes.add(in.type().returnType());
4800 } else {
4801 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
4802 }
4803 }
4804 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
4805 collect(Collectors.toList());
4806
4807 // Step 1B: determine loop parameters (A...).
4808 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
4809 loopChecks1b(init, commonSuffix);
4810
4811 // Step 1C: determine loop return type.
4812 // Step 1D: check other types.
4813 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
4814 map(MethodType::returnType).findFirst().orElse(void.class);
4815 loopChecks1cd(pred, fini, loopReturnType);
4816
4817 // Step 2: determine parameter lists.
4818 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
4819 commonParameterSequence.addAll(commonSuffix);
4820 loopChecks2(step, pred, fini, commonParameterSequence);
4821
4822 // Step 3: fill in omitted functions.
4823 for (int i = 0; i < nclauses; ++i) {
4824 Class<?> t = iterationVariableTypes.get(i);
4825 if (init.get(i) == null) {
4826 init.set(i, empty(methodType(t, commonSuffix)));
4827 }
4828 if (step.get(i) == null) {
4829 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
4830 }
4831 if (pred.get(i) == null) {
4832 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
4833 }
4834 if (fini.get(i) == null) {
4835 fini.set(i, empty(methodType(t, commonParameterSequence)));
4836 }
4837 }
4838
4839 // Step 4: fill in missing parameter types.
4840 // Also convert all handles to fixed-arity handles.
4841 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
4842 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
4843 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
4844 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
4845
4846 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
4847 allMatch(pl -> pl.equals(commonSuffix));
4848 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
4849 allMatch(pl -> pl.equals(commonParameterSequence));
4850
4851 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
4852 }
4853
4854 private static void loopChecks0(MethodHandle[][] clauses) {
4855 if (clauses == null || clauses.length == 0) {
4856 throw newIllegalArgumentException("null or no clauses passed");
4857 }
4858 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
4859 throw newIllegalArgumentException("null clauses are not allowed");
4860 }
4861 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
4862 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
4863 }
4864 }
4865
4866 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
4867 if (in.type().returnType() != st.type().returnType()) {
4868 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
4869 st.type().returnType());
4870 }
4871 }
4872
4873 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
4874 final List<Class<?>> empty = List.of();
4875 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
4876 // take only those that can contribute to a common suffix because they are longer than the prefix
4877 map(MethodHandle::type).
4878 filter(t -> t.parameterCount() > skipSize).
4879 map(MethodType::parameterList).
4880 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4881 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
4882 }
4883
4884 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
4885 final List<Class<?>> empty = List.of();
4886 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4887 }
4888
4889 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
4890 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
4891 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
4892 return longestParameterList(Arrays.asList(longest1, longest2));
4893 }
4894
4895 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
4896 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
4897 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
4898 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
4899 " (common suffix: " + commonSuffix + ")");
4900 }
4901 }
4902
4903 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
4904 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4905 anyMatch(t -> t != loopReturnType)) {
4906 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
4907 loopReturnType + ")");
4908 }
4909
4910 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
4911 throw newIllegalArgumentException("no predicate found", pred);
4912 }
4913 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4914 anyMatch(t -> t != boolean.class)) {
4915 throw newIllegalArgumentException("predicates must have boolean return type", pred);
4916 }
4917 }
4918
4919 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
4920 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
4921 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
4922 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
4923 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
4924 }
4925 }
4926
4927 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
4928 return hs.stream().map(h -> {
4929 int pc = h.type().parameterCount();
4930 int tpsize = targetParams.size();
4931 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
4932 }).collect(Collectors.toList());
4933 }
4934
4935 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
4936 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
4937 }
4938
4939 /**
4940 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
4941 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
4942 * <p>
4943 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
4944 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
4945 * evaluates to {@code true}).
4946 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
4947 * <p>
4948 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
4949 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
4950 * and updated with the value returned from its invocation. The result of loop execution will be
4951 * the final value of the additional loop-local variable (if present).
4952 * <p>
4953 * The following rules hold for these argument handles:<ul>
4954 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
4955 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
4956 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
4957 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
4958 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
4959 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
4960 * It will constrain the parameter lists of the other loop parts.
4961 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
4962 * list {@code (A...)} is called the <em>external parameter list</em>.
4963 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
4964 * additional state variable of the loop.
4965 * The body must both accept and return a value of this type {@code V}.
4966 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
4967 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
4968 * <a href="MethodHandles.html#effid">effectively identical</a>
4969 * to the external parameter list {@code (A...)}.
4970 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
4971 * {@linkplain #empty default value}.
4972 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
4973 * Its parameter list (either empty or of the form {@code (V A*)}) must be
4974 * effectively identical to the internal parameter list.
4975 * </ul>
4976 * <p>
4977 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
4978 * <li>The loop handle's result type is the result type {@code V} of the body.
4979 * <li>The loop handle's parameter types are the types {@code (A...)},
4980 * from the external parameter list.
4981 * </ul>
4982 * <p>
4983 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4984 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4985 * passed to the loop.
4986 * <blockquote><pre>{@code
4987 * V init(A...);
4988 * boolean pred(V, A...);
4989 * V body(V, A...);
4990 * V whileLoop(A... a...) {
4991 * V v = init(a...);
4992 * while (pred(v, a...)) {
4993 * v = body(v, a...);
4994 * }
4995 * return v;
4996 * }
4997 * }</pre></blockquote>
4998 * <p>
4999 * @apiNote Example:
5000 * <blockquote><pre>{@code
5001 * // implement the zip function for lists as a loop handle
5002 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
5003 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
5004 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
5005 * zip.add(a.next());
5006 * zip.add(b.next());
5007 * return zip;
5008 * }
5009 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
5010 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
5011 * List<String> a = Arrays.asList("a", "b", "c", "d");
5012 * List<String> b = Arrays.asList("e", "f", "g", "h");
5013 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
5014 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
5015 * }</pre></blockquote>
5016 *
5017 * <p>
5018 * @apiNote The implementation of this method can be expressed as follows:
5019 * <blockquote><pre>{@code
5020 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5021 * MethodHandle fini = (body.type().returnType() == void.class
5022 * ? null : identity(body.type().returnType()));
5023 * MethodHandle[]
5024 * checkExit = { null, null, pred, fini },
5025 * varBody = { init, body };
5026 * return loop(checkExit, varBody);
5027 * }
5028 * }</pre></blockquote>
5029 *
5030 * @param init optional initializer, providing the initial value of the loop variable.
5031 * May be {@code null}, implying a default initial value. See above for other constraints.
5032 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5033 * above for other constraints.
5034 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5035 * See above for other constraints.
5036 *
5037 * @return a method handle implementing the {@code while} loop as described by the arguments.
5038 * @throws IllegalArgumentException if the rules for the arguments are violated.
5039 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5040 *
5041 * @see #loop(MethodHandle[][])
5042 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5043 * @since 9
5044 */
5045 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5046 whileLoopChecks(init, pred, body);
5047 MethodHandle fini = identityOrVoid(body.type().returnType());
5048 MethodHandle[] checkExit = { null, null, pred, fini };
5049 MethodHandle[] varBody = { init, body };
5050 return loop(checkExit, varBody);
5051 }
5052
5053 /**
5054 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
5055 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5056 * <p>
5057 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5058 * method will, in each iteration, first execute its body and then evaluate the predicate.
5059 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
5060 * <p>
5061 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5062 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5063 * and updated with the value returned from its invocation. The result of loop execution will be
5064 * the final value of the additional loop-local variable (if present).
5065 * <p>
5066 * The following rules hold for these argument handles:<ul>
5067 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5068 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5069 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5070 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5071 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5072 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5073 * It will constrain the parameter lists of the other loop parts.
5074 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5075 * list {@code (A...)} is called the <em>external parameter list</em>.
5076 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5077 * additional state variable of the loop.
5078 * The body must both accept and return a value of this type {@code V}.
5079 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5080 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5081 * <a href="MethodHandles.html#effid">effectively identical</a>
5082 * to the external parameter list {@code (A...)}.
5083 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5084 * {@linkplain #empty default value}.
5085 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5086 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5087 * effectively identical to the internal parameter list.
5088 * </ul>
5089 * <p>
5090 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5091 * <li>The loop handle's result type is the result type {@code V} of the body.
5092 * <li>The loop handle's parameter types are the types {@code (A...)},
5093 * from the external parameter list.
5094 * </ul>
5095 * <p>
5096 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5097 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5098 * passed to the loop.
5099 * <blockquote><pre>{@code
5100 * V init(A...);
5101 * boolean pred(V, A...);
5102 * V body(V, A...);
5103 * V doWhileLoop(A... a...) {
5104 * V v = init(a...);
5105 * do {
5106 * v = body(v, a...);
5107 * } while (pred(v, a...));
5108 * return v;
5109 * }
5110 * }</pre></blockquote>
5111 * <p>
5112 * @apiNote Example:
5113 * <blockquote><pre>{@code
5114 * // int i = 0; while (i < limit) { ++i; } return i; => limit
5115 * static int zero(int limit) { return 0; }
5116 * static int step(int i, int limit) { return i + 1; }
5117 * static boolean pred(int i, int limit) { return i < limit; }
5118 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
5119 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
5120 * assertEquals(23, loop.invoke(23));
5121 * }</pre></blockquote>
5122 *
5123 * <p>
5124 * @apiNote The implementation of this method can be expressed as follows:
5125 * <blockquote><pre>{@code
5126 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5127 * MethodHandle fini = (body.type().returnType() == void.class
5128 * ? null : identity(body.type().returnType()));
5129 * MethodHandle[] clause = { init, body, pred, fini };
5130 * return loop(clause);
5131 * }
5132 * }</pre></blockquote>
5133 *
5134 * @param init optional initializer, providing the initial value of the loop variable.
5135 * May be {@code null}, implying a default initial value. See above for other constraints.
5136 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5137 * See above for other constraints.
5138 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5139 * above for other constraints.
5140 *
5141 * @return a method handle implementing the {@code while} loop as described by the arguments.
5142 * @throws IllegalArgumentException if the rules for the arguments are violated.
5143 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5144 *
5145 * @see #loop(MethodHandle[][])
5146 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
5147 * @since 9
5148 */
5149 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5150 whileLoopChecks(init, pred, body);
5151 MethodHandle fini = identityOrVoid(body.type().returnType());
5152 MethodHandle[] clause = {init, body, pred, fini };
5153 return loop(clause);
5154 }
5155
5156 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
5157 Objects.requireNonNull(pred);
5158 Objects.requireNonNull(body);
5159 MethodType bodyType = body.type();
5160 Class<?> returnType = bodyType.returnType();
5161 List<Class<?>> innerList = bodyType.parameterList();
5162 List<Class<?>> outerList = innerList;
5163 if (returnType == void.class) {
5164 // OK
5165 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
5166 // leading V argument missing => error
5167 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5168 throw misMatchedTypes("body function", bodyType, expected);
5169 } else {
5170 outerList = innerList.subList(1, innerList.size());
5171 }
5172 MethodType predType = pred.type();
5173 if (predType.returnType() != boolean.class ||
5174 !predType.effectivelyIdenticalParameters(0, innerList)) {
5175 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
5176 }
5177 if (init != null) {
5178 MethodType initType = init.type();
5179 if (initType.returnType() != returnType ||
5180 !initType.effectivelyIdenticalParameters(0, outerList)) {
5181 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5182 }
5183 }
5184 }
5185
5186 /**
5187 * Constructs a loop that runs a given number of iterations.
5188 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5189 * <p>
5190 * The number of iterations is determined by the {@code iterations} handle evaluation result.
5191 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
5192 * It will be initialized to 0 and incremented by 1 in each iteration.
5193 * <p>
5194 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5195 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5196 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5197 * <p>
5198 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5199 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5200 * iteration variable.
5201 * The result of the loop handle execution will be the final {@code V} value of that variable
5202 * (or {@code void} if there is no {@code V} variable).
5203 * <p>
5204 * The following rules hold for the argument handles:<ul>
5205 * <li>The {@code iterations} handle must not be {@code null}, and must return
5206 * the type {@code int}, referred to here as {@code I} in parameter type lists.
5207 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5208 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5209 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5210 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5211 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5212 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5213 * of types called the <em>internal parameter list</em>.
5214 * It will constrain the parameter lists of the other loop parts.
5215 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5216 * with no additional {@code A} types, then the internal parameter list is extended by
5217 * the argument types {@code A...} of the {@code iterations} handle.
5218 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5219 * list {@code (A...)} is called the <em>external parameter list</em>.
5220 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5221 * additional state variable of the loop.
5222 * The body must both accept a leading parameter and return a value of this type {@code V}.
5223 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5224 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5225 * <a href="MethodHandles.html#effid">effectively identical</a>
5226 * to the external parameter list {@code (A...)}.
5227 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5228 * {@linkplain #empty default value}.
5229 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
5230 * effectively identical to the external parameter list {@code (A...)}.
5231 * </ul>
5232 * <p>
5233 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5234 * <li>The loop handle's result type is the result type {@code V} of the body.
5235 * <li>The loop handle's parameter types are the types {@code (A...)},
5236 * from the external parameter list.
5237 * </ul>
5238 * <p>
5239 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5240 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5241 * arguments passed to the loop.
5242 * <blockquote><pre>{@code
5243 * int iterations(A...);
5244 * V init(A...);
5245 * V body(V, int, A...);
5246 * V countedLoop(A... a...) {
5247 * int end = iterations(a...);
5248 * V v = init(a...);
5249 * for (int i = 0; i < end; ++i) {
5250 * v = body(v, i, a...);
5251 * }
5252 * return v;
5253 * }
5254 * }</pre></blockquote>
5255 * <p>
5256 * @apiNote Example with a fully conformant body method:
5257 * <blockquote><pre>{@code
5258 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5259 * // => a variation on a well known theme
5260 * static String step(String v, int counter, String init) { return "na " + v; }
5261 * // assume MH_step is a handle to the method above
5262 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
5263 * MethodHandle start = MethodHandles.identity(String.class);
5264 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
5265 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
5266 * }</pre></blockquote>
5267 * <p>
5268 * @apiNote Example with the simplest possible body method type,
5269 * and passing the number of iterations to the loop invocation:
5270 * <blockquote><pre>{@code
5271 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5272 * // => a variation on a well known theme
5273 * static String step(String v, int counter ) { return "na " + v; }
5274 * // assume MH_step is a handle to the method above
5275 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
5276 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
5277 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
5278 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
5279 * }</pre></blockquote>
5280 * <p>
5281 * @apiNote Example that treats the number of iterations, string to append to, and string to append
5282 * as loop parameters:
5283 * <blockquote><pre>{@code
5284 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5285 * // => a variation on a well known theme
5286 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
5287 * // assume MH_step is a handle to the method above
5288 * MethodHandle count = MethodHandles.identity(int.class);
5289 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
5290 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
5291 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
5292 * }</pre></blockquote>
5293 * <p>
5294 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
5295 * to enforce a loop type:
5296 * <blockquote><pre>{@code
5297 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5298 * // => a variation on a well known theme
5299 * static String step(String v, int counter, String pre) { return pre + " " + v; }
5300 * // assume MH_step is a handle to the method above
5301 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
5302 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
5303 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
5304 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
5305 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
5306 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
5307 * }</pre></blockquote>
5308 * <p>
5309 * @apiNote The implementation of this method can be expressed as follows:
5310 * <blockquote><pre>{@code
5311 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5312 * return countedLoop(empty(iterations.type()), iterations, init, body);
5313 * }
5314 * }</pre></blockquote>
5315 *
5316 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
5317 * result type must be {@code int}. See above for other constraints.
5318 * @param init optional initializer, providing the initial value of the loop variable.
5319 * May be {@code null}, implying a default initial value. See above for other constraints.
5320 * @param body body of the loop, which may not be {@code null}.
5321 * It controls the loop parameters and result type in the standard case (see above for details).
5322 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5323 * and may accept any number of additional types.
5324 * See above for other constraints.
5325 *
5326 * @return a method handle representing the loop.
5327 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
5328 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5329 *
5330 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
5331 * @since 9
5332 */
5333 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5334 return countedLoop(empty(iterations.type()), iterations, init, body);
5335 }
5336
5337 /**
5338 * Constructs a loop that counts over a range of numbers.
5339 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5340 * <p>
5341 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
5342 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
5343 * values of the loop counter.
5344 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
5345 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
5346 * <p>
5347 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5348 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5349 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5350 * <p>
5351 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5352 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5353 * iteration variable.
5354 * The result of the loop handle execution will be the final {@code V} value of that variable
5355 * (or {@code void} if there is no {@code V} variable).
5356 * <p>
5357 * The following rules hold for the argument handles:<ul>
5358 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
5359 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
5360 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5361 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5362 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5363 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5364 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5365 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5366 * of types called the <em>internal parameter list</em>.
5367 * It will constrain the parameter lists of the other loop parts.
5368 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5369 * with no additional {@code A} types, then the internal parameter list is extended by
5370 * the argument types {@code A...} of the {@code end} handle.
5371 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5372 * list {@code (A...)} is called the <em>external parameter list</em>.
5373 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5374 * additional state variable of the loop.
5375 * The body must both accept a leading parameter and return a value of this type {@code V}.
5376 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5377 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5378 * <a href="MethodHandles.html#effid">effectively identical</a>
5379 * to the external parameter list {@code (A...)}.
5380 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5381 * {@linkplain #empty default value}.
5382 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
5383 * effectively identical to the external parameter list {@code (A...)}.
5384 * <li>Likewise, the parameter list of {@code end} must be effectively identical
5385 * to the external parameter list.
5386 * </ul>
5387 * <p>
5388 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5389 * <li>The loop handle's result type is the result type {@code V} of the body.
5390 * <li>The loop handle's parameter types are the types {@code (A...)},
5391 * from the external parameter list.
5392 * </ul>
5393 * <p>
5394 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5395 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5396 * arguments passed to the loop.
5397 * <blockquote><pre>{@code
5398 * int start(A...);
5399 * int end(A...);
5400 * V init(A...);
5401 * V body(V, int, A...);
5402 * V countedLoop(A... a...) {
5403 * int e = end(a...);
5404 * int s = start(a...);
5405 * V v = init(a...);
5406 * for (int i = s; i < e; ++i) {
5407 * v = body(v, i, a...);
5408 * }
5409 * return v;
5410 * }
5411 * }</pre></blockquote>
5412 *
5413 * <p>
5414 * @apiNote The implementation of this method can be expressed as follows:
5415 * <blockquote><pre>{@code
5416 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5417 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
5418 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
5419 * // the following semantics:
5420 * // MH_increment: (int limit, int counter) -> counter + 1
5421 * // MH_predicate: (int limit, int counter) -> counter < limit
5422 * Class<?> counterType = start.type().returnType(); // int
5423 * Class<?> returnType = body.type().returnType();
5424 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
5425 * if (returnType != void.class) { // ignore the V variable
5426 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5427 * pred = dropArguments(pred, 1, returnType); // ditto
5428 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
5429 * }
5430 * body = dropArguments(body, 0, counterType); // ignore the limit variable
5431 * MethodHandle[]
5432 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5433 * bodyClause = { init, body }, // v = init(); v = body(v, i)
5434 * indexVar = { start, incr }; // i = start(); i = i + 1
5435 * return loop(loopLimit, bodyClause, indexVar);
5436 * }
5437 * }</pre></blockquote>
5438 *
5439 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
5440 * See above for other constraints.
5441 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
5442 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
5443 * @param init optional initializer, providing the initial value of the loop variable.
5444 * May be {@code null}, implying a default initial value. See above for other constraints.
5445 * @param body body of the loop, which may not be {@code null}.
5446 * It controls the loop parameters and result type in the standard case (see above for details).
5447 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5448 * and may accept any number of additional types.
5449 * See above for other constraints.
5450 *
5451 * @return a method handle representing the loop.
5452 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
5453 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5454 *
5455 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
5456 * @since 9
5457 */
5458 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5459 countedLoopChecks(start, end, init, body);
5460 Class<?> counterType = start.type().returnType(); // int, but who's counting?
5461 Class<?> limitType = end.type().returnType(); // yes, int again
5462 Class<?> returnType = body.type().returnType();
5463 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
5464 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
5465 MethodHandle retv = null;
5466 if (returnType != void.class) {
5467 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5468 pred = dropArguments(pred, 1, returnType); // ditto
5469 retv = dropArguments(identity(returnType), 0, counterType);
5470 }
5471 body = dropArguments(body, 0, counterType); // ignore the limit variable
5472 MethodHandle[]
5473 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5474 bodyClause = { init, body }, // v = init(); v = body(v, i)
5475 indexVar = { start, incr }; // i = start(); i = i + 1
5476 return loop(loopLimit, bodyClause, indexVar);
5477 }
5478
5479 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5480 Objects.requireNonNull(start);
5481 Objects.requireNonNull(end);
5482 Objects.requireNonNull(body);
5483 Class<?> counterType = start.type().returnType();
5484 if (counterType != int.class) {
5485 MethodType expected = start.type().changeReturnType(int.class);
5486 throw misMatchedTypes("start function", start.type(), expected);
5487 } else if (end.type().returnType() != counterType) {
5488 MethodType expected = end.type().changeReturnType(counterType);
5489 throw misMatchedTypes("end function", end.type(), expected);
5490 }
5491 MethodType bodyType = body.type();
5492 Class<?> returnType = bodyType.returnType();
5493 List<Class<?>> innerList = bodyType.parameterList();
5494 // strip leading V value if present
5495 int vsize = (returnType == void.class ? 0 : 1);
5496 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
5497 // argument list has no "V" => error
5498 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5499 throw misMatchedTypes("body function", bodyType, expected);
5500 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
5501 // missing I type => error
5502 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
5503 throw misMatchedTypes("body function", bodyType, expected);
5504 }
5505 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
5506 if (outerList.isEmpty()) {
5507 // special case; take lists from end handle
5508 outerList = end.type().parameterList();
5509 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
5510 }
5511 MethodType expected = methodType(counterType, outerList);
5512 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
5513 throw misMatchedTypes("start parameter types", start.type(), expected);
5514 }
5515 if (end.type() != start.type() &&
5516 !end.type().effectivelyIdenticalParameters(0, outerList)) {
5517 throw misMatchedTypes("end parameter types", end.type(), expected);
5518 }
5519 if (init != null) {
5520 MethodType initType = init.type();
5521 if (initType.returnType() != returnType ||
5522 !initType.effectivelyIdenticalParameters(0, outerList)) {
5523 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5524 }
5525 }
5526 }
5527
5528 /**
5529 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
5530 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5531 * <p>
5532 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
5533 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
5534 * <p>
5535 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5536 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5537 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5538 * <p>
5539 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5540 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5541 * iteration variable.
5542 * The result of the loop handle execution will be the final {@code V} value of that variable
5543 * (or {@code void} if there is no {@code V} variable).
5544 * <p>
5545 * The following rules hold for the argument handles:<ul>
5546 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5547 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
5548 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5549 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
5550 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
5551 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
5552 * of types called the <em>internal parameter list</em>.
5553 * It will constrain the parameter lists of the other loop parts.
5554 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
5555 * with no additional {@code A} types, then the internal parameter list is extended by
5556 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
5557 * single type {@code Iterable} is added and constitutes the {@code A...} list.
5558 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
5559 * list {@code (A...)} is called the <em>external parameter list</em>.
5560 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5561 * additional state variable of the loop.
5562 * The body must both accept a leading parameter and return a value of this type {@code V}.
5563 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5564 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5565 * <a href="MethodHandles.html#effid">effectively identical</a>
5566 * to the external parameter list {@code (A...)}.
5567 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5568 * {@linkplain #empty default value}.
5569 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
5570 * type {@code java.util.Iterator} or a subtype thereof.
5571 * The iterator it produces when the loop is executed will be assumed
5572 * to yield values which can be converted to type {@code T}.
5573 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
5574 * effectively identical to the external parameter list {@code (A...)}.
5575 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
5576 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
5577 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
5578 * handle parameter is adjusted to accept the leading {@code A} type, as if by
5579 * the {@link MethodHandle#asType asType} conversion method.
5580 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
5581 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
5582 * </ul>
5583 * <p>
5584 * The type {@code T} may be either a primitive or reference.
5585 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
5586 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
5587 * as if by the {@link MethodHandle#asType asType} conversion method.
5588 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
5589 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
5590 * <p>
5591 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5592 * <li>The loop handle's result type is the result type {@code V} of the body.
5593 * <li>The loop handle's parameter types are the types {@code (A...)},
5594 * from the external parameter list.
5595 * </ul>
5596 * <p>
5597 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5598 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
5599 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
5600 * <blockquote><pre>{@code
5601 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
5602 * V init(A...);
5603 * V body(V,T,A...);
5604 * V iteratedLoop(A... a...) {
5605 * Iterator<T> it = iterator(a...);
5606 * V v = init(a...);
5607 * while (it.hasNext()) {
5608 * T t = it.next();
5609 * v = body(v, t, a...);
5610 * }
5611 * return v;
5612 * }
5613 * }</pre></blockquote>
5614 * <p>
5615 * @apiNote Example:
5616 * <blockquote><pre>{@code
5617 * // get an iterator from a list
5618 * static List<String> reverseStep(List<String> r, String e) {
5619 * r.add(0, e);
5620 * return r;
5621 * }
5622 * static List<String> newArrayList() { return new ArrayList<>(); }
5623 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
5624 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
5625 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
5626 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
5627 * assertEquals(reversedList, (List<String>) loop.invoke(list));
5628 * }</pre></blockquote>
5629 * <p>
5630 * @apiNote The implementation of this method can be expressed approximately as follows:
5631 * <blockquote><pre>{@code
5632 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5633 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
5634 * Class<?> returnType = body.type().returnType();
5635 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5636 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
5637 * MethodHandle retv = null, step = body, startIter = iterator;
5638 * if (returnType != void.class) {
5639 * // the simple thing first: in (I V A...), drop the I to get V
5640 * retv = dropArguments(identity(returnType), 0, Iterator.class);
5641 * // body type signature (V T A...), internal loop types (I V A...)
5642 * step = swapArguments(body, 0, 1); // swap V <-> T
5643 * }
5644 * if (startIter == null) startIter = MH_getIter;
5645 * MethodHandle[]
5646 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
5647 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
5648 * return loop(iterVar, bodyClause);
5649 * }
5650 * }</pre></blockquote>
5651 *
5652 * @param iterator an optional handle to return the iterator to start the loop.
5653 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
5654 * See above for other constraints.
5655 * @param init optional initializer, providing the initial value of the loop variable.
5656 * May be {@code null}, implying a default initial value. See above for other constraints.
5657 * @param body body of the loop, which may not be {@code null}.
5658 * It controls the loop parameters and result type in the standard case (see above for details).
5659 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
5660 * and may accept any number of additional types.
5661 * See above for other constraints.
5662 *
5663 * @return a method handle embodying the iteration loop functionality.
5664 * @throws NullPointerException if the {@code body} handle is {@code null}.
5665 * @throws IllegalArgumentException if any argument violates the above requirements.
5666 *
5667 * @since 9
5668 */
5669 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5670 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
5671 Class<?> returnType = body.type().returnType();
5672 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
5673 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
5674 MethodHandle startIter;
5675 MethodHandle nextVal;
5676 {
5677 MethodType iteratorType;
5678 if (iterator == null) {
5679 // derive argument type from body, if available, else use Iterable
5680 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
5681 iteratorType = startIter.type().changeParameterType(0, iterableType);
5682 } else {
5683 // force return type to the internal iterator class
5684 iteratorType = iterator.type().changeReturnType(Iterator.class);
5685 startIter = iterator;
5686 }
5687 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5688 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
5689
5690 // perform the asType transforms under an exception transformer, as per spec.:
5691 try {
5692 startIter = startIter.asType(iteratorType);
5693 nextVal = nextRaw.asType(nextValType);
5694 } catch (WrongMethodTypeException ex) {
5695 throw new IllegalArgumentException(ex);
5696 }
5697 }
5698
5699 MethodHandle retv = null, step = body;
5700 if (returnType != void.class) {
5701 // the simple thing first: in (I V A...), drop the I to get V
5702 retv = dropArguments(identity(returnType), 0, Iterator.class);
5703 // body type signature (V T A...), internal loop types (I V A...)
5704 step = swapArguments(body, 0, 1); // swap V <-> T
5705 }
5706
5707 MethodHandle[]
5708 iterVar = { startIter, null, hasNext, retv },
5709 bodyClause = { init, filterArgument(step, 0, nextVal) };
5710 return loop(iterVar, bodyClause);
5711 }
5712
5713 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5714 Objects.requireNonNull(body);
5715 MethodType bodyType = body.type();
5716 Class<?> returnType = bodyType.returnType();
5717 List<Class<?>> internalParamList = bodyType.parameterList();
5718 // strip leading V value if present
5719 int vsize = (returnType == void.class ? 0 : 1);
5720 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
5721 // argument list has no "V" => error
5722 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5723 throw misMatchedTypes("body function", bodyType, expected);
5724 } else if (internalParamList.size() <= vsize) {
5725 // missing T type => error
5726 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
5727 throw misMatchedTypes("body function", bodyType, expected);
5728 }
5729 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
5730 Class<?> iterableType = null;
5731 if (iterator != null) {
5732 // special case; if the body handle only declares V and T then
5733 // the external parameter list is obtained from iterator handle
5734 if (externalParamList.isEmpty()) {
5735 externalParamList = iterator.type().parameterList();
5736 }
5737 MethodType itype = iterator.type();
5738 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
5739 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
5740 }
5741 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
5742 MethodType expected = methodType(itype.returnType(), externalParamList);
5743 throw misMatchedTypes("iterator parameters", itype, expected);
5744 }
5745 } else {
5746 if (externalParamList.isEmpty()) {
5747 // special case; if the iterator handle is null and the body handle
5748 // only declares V and T then the external parameter list consists
5749 // of Iterable
5750 externalParamList = Arrays.asList(Iterable.class);
5751 iterableType = Iterable.class;
5752 } else {
5753 // special case; if the iterator handle is null and the external
5754 // parameter list is not empty then the first parameter must be
5755 // assignable to Iterable
5756 iterableType = externalParamList.get(0);
5757 if (!Iterable.class.isAssignableFrom(iterableType)) {
5758 throw newIllegalArgumentException(
5759 "inferred first loop argument must inherit from Iterable: " + iterableType);
5760 }
5761 }
5762 }
5763 if (init != null) {
5764 MethodType initType = init.type();
5765 if (initType.returnType() != returnType ||
5766 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
5767 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
5768 }
5769 }
5770 return iterableType; // help the caller a bit
5771 }
5772
5773 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
5774 // there should be a better way to uncross my wires
5775 int arity = mh.type().parameterCount();
5776 int[] order = new int[arity];
5777 for (int k = 0; k < arity; k++) order[k] = k;
5778 order[i] = j; order[j] = i;
5779 Class<?>[] types = mh.type().parameterArray();
5780 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
5781 MethodType swapType = methodType(mh.type().returnType(), types);
5782 return permuteArguments(mh, swapType, order);
5783 }
5784
5785 /**
5786 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
5787 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
5788 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
5789 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
5790 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
5791 * {@code try-finally} handle.
5792 * <p>
5793 * The {@code cleanup} handle will be passed one or two additional leading arguments.
5794 * The first is the exception thrown during the
5795 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
5796 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
5797 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
5798 * The second argument is not present if the {@code target} handle has a {@code void} return type.
5799 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
5800 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
5801 * <p>
5802 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
5803 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
5804 * two extra leading parameters:<ul>
5805 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
5806 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
5807 * the result from the execution of the {@code target} handle.
5808 * This parameter is not present if the {@code target} returns {@code void}.
5809 * </ul>
5810 * <p>
5811 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
5812 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
5813 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
5814 * the cleanup.
5815 * <blockquote><pre>{@code
5816 * V target(A..., B...);
5817 * V cleanup(Throwable, V, A...);
5818 * V adapter(A... a, B... b) {
5819 * V result = (zero value for V);
5820 * Throwable throwable = null;
5821 * try {
5822 * result = target(a..., b...);
5823 * } catch (Throwable t) {
5824 * throwable = t;
5825 * throw t;
5826 * } finally {
5827 * result = cleanup(throwable, result, a...);
5828 * }
5829 * return result;
5830 * }
5831 * }</pre></blockquote>
5832 * <p>
5833 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5834 * be modified by execution of the target, and so are passed unchanged
5835 * from the caller to the cleanup, if it is invoked.
5836 * <p>
5837 * The target and cleanup must return the same type, even if the cleanup
5838 * always throws.
5839 * To create such a throwing cleanup, compose the cleanup logic
5840 * with {@link #throwException throwException},
5841 * in order to create a method handle of the correct return type.
5842 * <p>
5843 * Note that {@code tryFinally} never converts exceptions into normal returns.
5844 * In rare cases where exceptions must be converted in that way, first wrap
5845 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
5846 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
5847 *
5848 * @param target the handle whose execution is to be wrapped in a {@code try} block.
5849 * @param cleanup the handle that is invoked in the finally block.
5850 *
5851 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
5852 * @throws NullPointerException if any argument is null
5853 * @throws IllegalArgumentException if {@code cleanup} does not accept
5854 * the required leading arguments, or if the method handle types do
5855 * not match in their return types and their
5856 * corresponding trailing parameters
5857 *
5858 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
5859 * @since 9
5860 */
5861 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
5862 List<Class<?>> targetParamTypes = target.type().parameterList();
5863 List<Class<?>> cleanupParamTypes = cleanup.type().parameterList();
5864 Class<?> rtype = target.type().returnType();
5865
5866 tryFinallyChecks(target, cleanup);
5867
5868 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
5869 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5870 // target parameter list.
5871 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
5872
5873 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
5874 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
5875 }
5876
5877 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
5878 Class<?> rtype = target.type().returnType();
5879 if (rtype != cleanup.type().returnType()) {
5880 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
5881 }
5882 MethodType cleanupType = cleanup.type();
5883 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
5884 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
5885 }
5886 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
5887 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
5888 }
5889 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5890 // target parameter list.
5891 int cleanupArgIndex = rtype == void.class ? 1 : 2;
5892 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
5893 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
5894 cleanup.type(), target.type());
5895 }
5896 }
5897
5898 }