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
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24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.reflect.CallerSensitive;
29 import jdk.internal.reflect.Reflection;
30 import jdk.internal.vm.annotation.ForceInline;
31 import sun.invoke.util.ValueConversions;
32 import sun.invoke.util.VerifyAccess;
33 import sun.invoke.util.Wrapper;
34 import sun.reflect.misc.ReflectUtil;
35 import sun.security.util.SecurityConstants;
36
37 import java.lang.invoke.LambdaForm.BasicType;
38 import java.lang.reflect.Constructor;
39 import java.lang.reflect.Field;
40 import java.lang.reflect.Member;
41 import java.lang.reflect.Method;
42 import java.lang.reflect.Modifier;
43 import java.lang.reflect.Module;
44 import java.lang.reflect.ReflectPermission;
45 import java.nio.ByteOrder;
46 import java.util.ArrayList;
47 import java.util.Arrays;
48 import java.util.BitSet;
49 import java.util.Iterator;
50 import java.util.List;
51 import java.util.Objects;
52 import java.util.concurrent.ConcurrentHashMap;
53 import java.util.stream.Collectors;
54 import java.util.stream.Stream;
55
56 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
57 import static java.lang.invoke.MethodHandleNatives.Constants.*;
58 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
59 import static java.lang.invoke.MethodType.methodType;
60
61 /**
62 * This class consists exclusively of static methods that operate on or return
63 * method handles. They fall into several categories:
64 * <ul>
65 * <li>Lookup methods which help create method handles for methods and fields.
66 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
67 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
68 * </ul>
69 *
70 * @author John Rose, JSR 292 EG
71 * @since 1.7
72 */
73 public class MethodHandles {
74
75 private MethodHandles() { } // do not instantiate
76
77 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
78
79 // See IMPL_LOOKUP below.
80
81 //// Method handle creation from ordinary methods.
82
83 /**
84 * Returns a {@link Lookup lookup object} with
85 * full capabilities to emulate all supported bytecode behaviors of the caller.
86 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
87 * Factory methods on the lookup object can create
88 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
89 * for any member that the caller has access to via bytecodes,
90 * including protected and private fields and methods.
91 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
92 * Do not store it in place where untrusted code can access it.
93 * <p>
94 * This method is caller sensitive, which means that it may return different
95 * values to different callers.
96 * <p>
97 * For any given caller class {@code C}, the lookup object returned by this call
98 * has equivalent capabilities to any lookup object
99 * supplied by the JVM to the bootstrap method of an
100 * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>
101 * executing in the same caller class {@code C}.
102 * @return a lookup object for the caller of this method, with private access
103 */
104 @CallerSensitive
105 @ForceInline // to ensure Reflection.getCallerClass optimization
106 public static Lookup lookup() {
107 return new Lookup(Reflection.getCallerClass());
108 }
109
110 /**
111 * Returns a {@link Lookup lookup object} which is trusted minimally.
112 * The lookup has the {@code PUBLIC} and {@code UNCONDITIONAL} modes.
113 * It can only be used to create method handles to public members of
114 * public classes in packages that are exported unconditionally.
115 * <p>
116 * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
117 * of this lookup object will be {@link java.lang.Object}.
118 *
119 * @apiNote The use of Object is conventional, and because the lookup modes are
120 * limited, there is no special access provided to the internals of Object, its package
121 * or its module. Consequently, the lookup context of this lookup object will be the
122 * bootstrap class loader, which means it cannot find user classes.
123 *
124 * <p style="font-size:smaller;">
125 * <em>Discussion:</em>
126 * The lookup class can be changed to any other class {@code C} using an expression of the form
127 * {@link Lookup#in publicLookup().in(C.class)}.
128 * but may change the lookup context by virtue of changing the class loader.
129 * A public lookup object is always subject to
130 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
131 * Also, it cannot access
132 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
133 * @return a lookup object which is trusted minimally
134 *
135 * @revised 9
136 * @spec JPMS
137 */
138 public static Lookup publicLookup() {
139 return Lookup.PUBLIC_LOOKUP;
140 }
141
142 /**
143 * Returns a {@link Lookup lookup object} with full capabilities to emulate all
144 * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">
145 * private access</a>, on a target class.
146 * This method checks that a caller, specified as a {@code Lookup} object, is allowed to
147 * do <em>deep reflection</em> on the target class. If {@code m1} is the module containing
148 * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing
149 * the target class, then this check ensures that
150 * <ul>
151 * <li>{@code m1} {@link Module#canRead reads} {@code m2}.</li>
152 * <li>{@code m2} {@link Module#isOpen(String,Module) opens} the package containing
153 * the target class to at least {@code m1}.</li>
154 * <li>The lookup has the {@link Lookup#MODULE MODULE} lookup mode.</li>
155 * </ul>
156 * <p>
157 * If there is a security manager, its {@code checkPermission} method is called to
158 * check {@code ReflectPermission("suppressAccessChecks")}.
159 * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object
160 * was created by code in the caller module (or derived from a lookup object originally
161 * created by the caller). A lookup object with the {@code MODULE} lookup mode can be
162 * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE}
163 * access to the caller.
164 * @param targetClass the target class
165 * @param lookup the caller lookup object
166 * @return a lookup object for the target class, with private access
167 * @throws IllegalArgumentException if {@code targetClass} is a primitve type or array class
168 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
169 * @throws IllegalAccessException if the access check specified above fails
170 * @throws SecurityException if denied by the security manager
171 * @since 9
172 * @spec JPMS
173 * @see Lookup#dropLookupMode
174 */
175 public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException {
176 SecurityManager sm = System.getSecurityManager();
177 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
178 if (targetClass.isPrimitive())
179 throw new IllegalArgumentException(targetClass + " is a primitive class");
180 if (targetClass.isArray())
181 throw new IllegalArgumentException(targetClass + " is an array class");
182 Module targetModule = targetClass.getModule();
183 Module callerModule = lookup.lookupClass().getModule();
184 if (!callerModule.canRead(targetModule))
185 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
186 if (targetModule.isNamed()) {
187 String pn = targetClass.getPackageName();
188 assert pn.length() > 0 : "unnamed package cannot be in named module";
189 if (!targetModule.isOpen(pn, callerModule))
190 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
191 }
192 if ((lookup.lookupModes() & Lookup.MODULE) == 0)
193 throw new IllegalAccessException("lookup does not have MODULE lookup mode");
194 return new Lookup(targetClass);
195 }
196
197 /**
198 * Performs an unchecked "crack" of a
199 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
200 * The result is as if the user had obtained a lookup object capable enough
201 * to crack the target method handle, called
202 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
203 * on the target to obtain its symbolic reference, and then called
204 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
205 * to resolve the symbolic reference to a member.
206 * <p>
207 * If there is a security manager, its {@code checkPermission} method
208 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
209 * @param <T> the desired type of the result, either {@link Member} or a subtype
210 * @param target a direct method handle to crack into symbolic reference components
211 * @param expected a class object representing the desired result type {@code T}
212 * @return a reference to the method, constructor, or field object
213 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
214 * @exception NullPointerException if either argument is {@code null}
215 * @exception IllegalArgumentException if the target is not a direct method handle
216 * @exception ClassCastException if the member is not of the expected type
217 * @since 1.8
218 */
219 public static <T extends Member> T
220 reflectAs(Class<T> expected, MethodHandle target) {
221 SecurityManager smgr = System.getSecurityManager();
222 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
223 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
224 return lookup.revealDirect(target).reflectAs(expected, lookup);
225 }
226 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
227 private static final java.security.Permission ACCESS_PERMISSION =
228 new ReflectPermission("suppressAccessChecks");
229
230 /**
231 * A <em>lookup object</em> is a factory for creating method handles,
232 * when the creation requires access checking.
233 * Method handles do not perform
234 * access checks when they are called, but rather when they are created.
235 * Therefore, method handle access
236 * restrictions must be enforced when a method handle is created.
237 * The caller class against which those restrictions are enforced
238 * is known as the {@linkplain #lookupClass lookup class}.
239 * <p>
240 * A lookup class which needs to create method handles will call
241 * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
242 * When the {@code Lookup} factory object is created, the identity of the lookup class is
243 * determined, and securely stored in the {@code Lookup} object.
244 * The lookup class (or its delegates) may then use factory methods
245 * on the {@code Lookup} object to create method handles for access-checked members.
246 * This includes all methods, constructors, and fields which are allowed to the lookup class,
247 * even private ones.
248 *
249 * <h1><a name="lookups"></a>Lookup Factory Methods</h1>
250 * The factory methods on a {@code Lookup} object correspond to all major
251 * use cases for methods, constructors, and fields.
252 * Each method handle created by a factory method is the functional
253 * equivalent of a particular <em>bytecode behavior</em>.
254 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
255 * Here is a summary of the correspondence between these factory methods and
256 * the behavior of the resulting method handles:
257 * <table border=1 cellpadding=5 summary="lookup method behaviors">
258 * <tr>
259 * <th><a name="equiv"></a>lookup expression</th>
260 * <th>member</th>
261 * <th>bytecode behavior</th>
262 * </tr>
263 * <tr>
264 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
265 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
266 * </tr>
267 * <tr>
268 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
269 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
270 * </tr>
271 * <tr>
272 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
273 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
274 * </tr>
275 * <tr>
276 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
277 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
278 * </tr>
279 * <tr>
280 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
281 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
282 * </tr>
283 * <tr>
284 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
285 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
286 * </tr>
287 * <tr>
288 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
289 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
290 * </tr>
291 * <tr>
292 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
293 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
294 * </tr>
295 * <tr>
296 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
297 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
298 * </tr>
299 * <tr>
300 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
301 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
302 * </tr>
303 * <tr>
304 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
305 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
306 * </tr>
307 * <tr>
308 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
309 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
310 * </tr>
311 * <tr>
312 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
313 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
314 * </tr>
315 * <tr>
316 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</td>
317 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
318 * </tr>
319 * </table>
320 *
321 * Here, the type {@code C} is the class or interface being searched for a member,
322 * documented as a parameter named {@code refc} in the lookup methods.
323 * The method type {@code MT} is composed from the return type {@code T}
324 * and the sequence of argument types {@code A*}.
325 * The constructor also has a sequence of argument types {@code A*} and
326 * is deemed to return the newly-created object of type {@code C}.
327 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
328 * The formal parameter {@code this} stands for the self-reference of type {@code C};
329 * if it is present, it is always the leading argument to the method handle invocation.
330 * (In the case of some {@code protected} members, {@code this} may be
331 * restricted in type to the lookup class; see below.)
332 * The name {@code arg} stands for all the other method handle arguments.
333 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
334 * stands for a null reference if the accessed method or field is static,
335 * and {@code this} otherwise.
336 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
337 * for reflective objects corresponding to the given members.
338 * <p>
339 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
340 * as if by {@code ldc CONSTANT_Class}.
341 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
342 * <p>
343 * In cases where the given member is of variable arity (i.e., a method or constructor)
344 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
345 * In all other cases, the returned method handle will be of fixed arity.
346 * <p style="font-size:smaller;">
347 * <em>Discussion:</em>
348 * The equivalence between looked-up method handles and underlying
349 * class members and bytecode behaviors
350 * can break down in a few ways:
351 * <ul style="font-size:smaller;">
352 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
353 * the lookup can still succeed, even when there is no equivalent
354 * Java expression or bytecoded constant.
355 * <li>Likewise, if {@code T} or {@code MT}
356 * is not symbolically accessible from the lookup class's loader,
357 * the lookup can still succeed.
358 * For example, lookups for {@code MethodHandle.invokeExact} and
359 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
360 * <li>If there is a security manager installed, it can forbid the lookup
361 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
362 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
363 * constant is not subject to security manager checks.
364 * <li>If the looked-up method has a
365 * <a href="MethodHandle.html#maxarity">very large arity</a>,
366 * the method handle creation may fail, due to the method handle
367 * type having too many parameters.
368 * </ul>
369 *
370 * <h1><a name="access"></a>Access checking</h1>
371 * Access checks are applied in the factory methods of {@code Lookup},
372 * when a method handle is created.
373 * This is a key difference from the Core Reflection API, since
374 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
375 * performs access checking against every caller, on every call.
376 * <p>
377 * All access checks start from a {@code Lookup} object, which
378 * compares its recorded lookup class against all requests to
379 * create method handles.
380 * A single {@code Lookup} object can be used to create any number
381 * of access-checked method handles, all checked against a single
382 * lookup class.
383 * <p>
384 * A {@code Lookup} object can be shared with other trusted code,
385 * such as a metaobject protocol.
386 * A shared {@code Lookup} object delegates the capability
387 * to create method handles on private members of the lookup class.
388 * Even if privileged code uses the {@code Lookup} object,
389 * the access checking is confined to the privileges of the
390 * original lookup class.
391 * <p>
392 * A lookup can fail, because
393 * the containing class is not accessible to the lookup class, or
394 * because the desired class member is missing, or because the
395 * desired class member is not accessible to the lookup class, or
396 * because the lookup object is not trusted enough to access the member.
397 * In any of these cases, a {@code ReflectiveOperationException} will be
398 * thrown from the attempted lookup. The exact class will be one of
399 * the following:
400 * <ul>
401 * <li>NoSuchMethodException — if a method is requested but does not exist
402 * <li>NoSuchFieldException — if a field is requested but does not exist
403 * <li>IllegalAccessException — if the member exists but an access check fails
404 * </ul>
405 * <p>
406 * In general, the conditions under which a method handle may be
407 * looked up for a method {@code M} are no more restrictive than the conditions
408 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
409 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
410 * a method handle lookup will generally raise a corresponding
411 * checked exception, such as {@code NoSuchMethodException}.
412 * And the effect of invoking the method handle resulting from the lookup
413 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
414 * to executing the compiled, verified, and resolved call to {@code M}.
415 * The same point is true of fields and constructors.
416 * <p style="font-size:smaller;">
417 * <em>Discussion:</em>
418 * Access checks only apply to named and reflected methods,
419 * constructors, and fields.
420 * Other method handle creation methods, such as
421 * {@link MethodHandle#asType MethodHandle.asType},
422 * do not require any access checks, and are used
423 * independently of any {@code Lookup} object.
424 * <p>
425 * If the desired member is {@code protected}, the usual JVM rules apply,
426 * including the requirement that the lookup class must be either be in the
427 * same package as the desired member, or must inherit that member.
428 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
429 * In addition, if the desired member is a non-static field or method
430 * in a different package, the resulting method handle may only be applied
431 * to objects of the lookup class or one of its subclasses.
432 * This requirement is enforced by narrowing the type of the leading
433 * {@code this} parameter from {@code C}
434 * (which will necessarily be a superclass of the lookup class)
435 * to the lookup class itself.
436 * <p>
437 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
438 * that the receiver argument must match both the resolved method <em>and</em>
439 * the current class. Again, this requirement is enforced by narrowing the
440 * type of the leading parameter to the resulting method handle.
441 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
442 * <p>
443 * The JVM represents constructors and static initializer blocks as internal methods
444 * with special names ({@code "<init>"} and {@code "<clinit>"}).
445 * The internal syntax of invocation instructions allows them to refer to such internal
446 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
447 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
448 * <p>
449 * In some cases, access between nested classes is obtained by the Java compiler by creating
450 * an wrapper method to access a private method of another class
451 * in the same top-level declaration.
452 * For example, a nested class {@code C.D}
453 * can access private members within other related classes such as
454 * {@code C}, {@code C.D.E}, or {@code C.B},
455 * but the Java compiler may need to generate wrapper methods in
456 * those related classes. In such cases, a {@code Lookup} object on
457 * {@code C.E} would be unable to those private members.
458 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
459 * which can transform a lookup on {@code C.E} into one on any of those other
460 * classes, without special elevation of privilege.
461 * <p>
462 * The accesses permitted to a given lookup object may be limited,
463 * according to its set of {@link #lookupModes lookupModes},
464 * to a subset of members normally accessible to the lookup class.
465 * For example, the {@link MethodHandles#publicLookup publicLookup}
466 * method produces a lookup object which is only allowed to access
467 * public members in public classes of exported packages.
468 * The caller sensitive method {@link MethodHandles#lookup lookup}
469 * produces a lookup object with full capabilities relative to
470 * its caller class, to emulate all supported bytecode behaviors.
471 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
472 * with fewer access modes than the original lookup object.
473 *
474 * <p style="font-size:smaller;">
475 * <a name="privacc"></a>
476 * <em>Discussion of private access:</em>
477 * We say that a lookup has <em>private access</em>
478 * if its {@linkplain #lookupModes lookup modes}
479 * include the possibility of accessing {@code private} members.
480 * As documented in the relevant methods elsewhere,
481 * only lookups with private access possess the following capabilities:
482 * <ul style="font-size:smaller;">
483 * <li>access private fields, methods, and constructors of the lookup class
484 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
485 * such as {@code Class.forName}
486 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
487 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
488 * for classes accessible to the lookup class
489 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
490 * within the same package member
491 * </ul>
492 * <p style="font-size:smaller;">
493 * Each of these permissions is a consequence of the fact that a lookup object
494 * with private access can be securely traced back to an originating class,
495 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
496 * can be reliably determined and emulated by method handles.
497 *
498 * <h1><a name="secmgr"></a>Security manager interactions</h1>
499 * Although bytecode instructions can only refer to classes in
500 * a related class loader, this API can search for methods in any
501 * class, as long as a reference to its {@code Class} object is
502 * available. Such cross-loader references are also possible with the
503 * Core Reflection API, and are impossible to bytecode instructions
504 * such as {@code invokestatic} or {@code getfield}.
505 * There is a {@linkplain java.lang.SecurityManager security manager API}
506 * to allow applications to check such cross-loader references.
507 * These checks apply to both the {@code MethodHandles.Lookup} API
508 * and the Core Reflection API
509 * (as found on {@link java.lang.Class Class}).
510 * <p>
511 * If a security manager is present, member and class lookups are subject to
512 * additional checks.
513 * From one to three calls are made to the security manager.
514 * Any of these calls can refuse access by throwing a
515 * {@link java.lang.SecurityException SecurityException}.
516 * Define {@code smgr} as the security manager,
517 * {@code lookc} as the lookup class of the current lookup object,
518 * {@code refc} as the containing class in which the member
519 * is being sought, and {@code defc} as the class in which the
520 * member is actually defined.
521 * (If a class or other type is being accessed,
522 * the {@code refc} and {@code defc} values are the class itself.)
523 * The value {@code lookc} is defined as <em>not present</em>
524 * if the current lookup object does not have
525 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
526 * The calls are made according to the following rules:
527 * <ul>
528 * <li><b>Step 1:</b>
529 * If {@code lookc} is not present, or if its class loader is not
530 * the same as or an ancestor of the class loader of {@code refc},
531 * then {@link SecurityManager#checkPackageAccess
532 * smgr.checkPackageAccess(refcPkg)} is called,
533 * where {@code refcPkg} is the package of {@code refc}.
534 * <li><b>Step 2a:</b>
535 * If the retrieved member is not public and
536 * {@code lookc} is not present, then
537 * {@link SecurityManager#checkPermission smgr.checkPermission}
538 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
539 * <li><b>Step 2b:</b>
540 * If the retrieved class has a {@code null} class loader,
541 * and {@code lookc} is not present, then
542 * {@link SecurityManager#checkPermission smgr.checkPermission}
543 * with {@code RuntimePermission("getClassLoader")} is called.
544 * <li><b>Step 3:</b>
545 * If the retrieved member is not public,
546 * and if {@code lookc} is not present,
547 * and if {@code defc} and {@code refc} are different,
548 * then {@link SecurityManager#checkPackageAccess
549 * smgr.checkPackageAccess(defcPkg)} is called,
550 * where {@code defcPkg} is the package of {@code defc}.
551 * </ul>
552 * Security checks are performed after other access checks have passed.
553 * Therefore, the above rules presuppose a member or class that is public,
554 * or else that is being accessed from a lookup class that has
555 * rights to access the member or class.
556 *
557 * <h1><a name="callsens"></a>Caller sensitive methods</h1>
558 * A small number of Java methods have a special property called caller sensitivity.
559 * A <em>caller-sensitive</em> method can behave differently depending on the
560 * identity of its immediate caller.
561 * <p>
562 * If a method handle for a caller-sensitive method is requested,
563 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
564 * but they take account of the lookup class in a special way.
565 * The resulting method handle behaves as if it were called
566 * from an instruction contained in the lookup class,
567 * so that the caller-sensitive method detects the lookup class.
568 * (By contrast, the invoker of the method handle is disregarded.)
569 * Thus, in the case of caller-sensitive methods,
570 * different lookup classes may give rise to
571 * differently behaving method handles.
572 * <p>
573 * In cases where the lookup object is
574 * {@link MethodHandles#publicLookup() publicLookup()},
575 * or some other lookup object without
576 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
577 * the lookup class is disregarded.
578 * In such cases, no caller-sensitive method handle can be created,
579 * access is forbidden, and the lookup fails with an
580 * {@code IllegalAccessException}.
581 * <p style="font-size:smaller;">
582 * <em>Discussion:</em>
583 * For example, the caller-sensitive method
584 * {@link java.lang.Class#forName(String) Class.forName(x)}
585 * can return varying classes or throw varying exceptions,
586 * depending on the class loader of the class that calls it.
587 * A public lookup of {@code Class.forName} will fail, because
588 * there is no reasonable way to determine its bytecode behavior.
589 * <p style="font-size:smaller;">
590 * If an application caches method handles for broad sharing,
591 * it should use {@code publicLookup()} to create them.
592 * If there is a lookup of {@code Class.forName}, it will fail,
593 * and the application must take appropriate action in that case.
594 * It may be that a later lookup, perhaps during the invocation of a
595 * bootstrap method, can incorporate the specific identity
596 * of the caller, making the method accessible.
597 * <p style="font-size:smaller;">
598 * The function {@code MethodHandles.lookup} is caller sensitive
599 * so that there can be a secure foundation for lookups.
600 * Nearly all other methods in the JSR 292 API rely on lookup
601 * objects to check access requests.
602 *
603 * @revised 9
604 */
605 public static final
606 class Lookup {
607 /** The class on behalf of whom the lookup is being performed. */
608 private final Class<?> lookupClass;
609
610 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
611 private final int allowedModes;
612
613 /** A single-bit mask representing {@code public} access,
614 * which may contribute to the result of {@link #lookupModes lookupModes}.
615 * The value, {@code 0x01}, happens to be the same as the value of the
616 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
617 */
618 public static final int PUBLIC = Modifier.PUBLIC;
619
620 /** A single-bit mask representing {@code private} access,
621 * which may contribute to the result of {@link #lookupModes lookupModes}.
622 * The value, {@code 0x02}, happens to be the same as the value of the
623 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
624 */
625 public static final int PRIVATE = Modifier.PRIVATE;
626
627 /** A single-bit mask representing {@code protected} access,
628 * which may contribute to the result of {@link #lookupModes lookupModes}.
629 * The value, {@code 0x04}, happens to be the same as the value of the
630 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
631 */
632 public static final int PROTECTED = Modifier.PROTECTED;
633
634 /** A single-bit mask representing {@code package} access (default access),
635 * which may contribute to the result of {@link #lookupModes lookupModes}.
636 * The value is {@code 0x08}, which does not correspond meaningfully to
637 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
638 */
639 public static final int PACKAGE = Modifier.STATIC;
640
641 /** A single-bit mask representing {@code module} access (default access),
642 * which may contribute to the result of {@link #lookupModes lookupModes}.
643 * The value is {@code 0x10}, which does not correspond meaningfully to
644 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
645 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
646 * with this lookup mode can access all public types in the module of the
647 * lookup class and public types in packages exported by other modules
648 * to the module of the lookup class.
649 * @since 9
650 * @spec JPMS
651 */
652 public static final int MODULE = PACKAGE << 1;
653
654 /** A single-bit mask representing {@code unconditional} access
655 * which may contribute to the result of {@link #lookupModes lookupModes}.
656 * The value is {@code 0x20}, which does not correspond meaningfully to
657 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
658 * A {@code Lookup} with this lookup mode assumes {@linkplain
659 * java.lang.reflect.Module#canRead(java.lang.reflect.Module) readability}.
660 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
661 * with this lookup mode can access all public members of public types
662 * of all modules where the type is in a package that is {@link
663 * java.lang.reflect.Module#isExported(String) exported unconditionally}.
664 * @see #publicLookup()
665 * @since 9
666 */
667 public static final int UNCONDITIONAL = PACKAGE << 2;
668
669 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
670 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
671 private static final int TRUSTED = -1;
672
673 private static int fixmods(int mods) {
674 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
675 return (mods != 0) ? mods : (PACKAGE | MODULE | UNCONDITIONAL);
676 }
677
678 /** Tells which class is performing the lookup. It is this class against
679 * which checks are performed for visibility and access permissions.
680 * <p>
681 * The class implies a maximum level of access permission,
682 * but the permissions may be additionally limited by the bitmask
683 * {@link #lookupModes lookupModes}, which controls whether non-public members
684 * can be accessed.
685 * @return the lookup class, on behalf of which this lookup object finds members
686 */
687 public Class<?> lookupClass() {
688 return lookupClass;
689 }
690
691 // This is just for calling out to MethodHandleImpl.
692 private Class<?> lookupClassOrNull() {
693 return (allowedModes == TRUSTED) ? null : lookupClass;
694 }
695
696 /** Tells which access-protection classes of members this lookup object can produce.
697 * The result is a bit-mask of the bits
698 * {@linkplain #PUBLIC PUBLIC (0x01)},
699 * {@linkplain #PRIVATE PRIVATE (0x02)},
700 * {@linkplain #PROTECTED PROTECTED (0x04)},
701 * {@linkplain #PACKAGE PACKAGE (0x08)},
702 * {@linkplain #MODULE MODULE (0x10)},
703 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
704 * <p>
705 * A freshly-created lookup object
706 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
707 * all possible bits set, except {@code UNCONDITIONAL}. The lookup can be used to
708 * access all members of the caller's class, all public types in the caller's module,
709 * and all public types in packages exported by other modules to the caller's module.
710 * A lookup object on a new lookup class
711 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
712 * may have some mode bits set to zero.
713 * Mode bits can also be
714 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
715 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
716 * The purpose of this is to restrict access via the new lookup object,
717 * so that it can access only names which can be reached by the original
718 * lookup object, and also by the new lookup class.
719 * @return the lookup modes, which limit the kinds of access performed by this lookup object
720 * @see #in
721 * @see #dropLookupMode
722 *
723 * @revised 9
724 * @spec JPMS
725 */
726 public int lookupModes() {
727 return allowedModes & ALL_MODES;
728 }
729
730 /** Embody the current class (the lookupClass) as a lookup class
731 * for method handle creation.
732 * Must be called by from a method in this package,
733 * which in turn is called by a method not in this package.
734 */
735 Lookup(Class<?> lookupClass) {
736 this(lookupClass, FULL_POWER_MODES);
737 // make sure we haven't accidentally picked up a privileged class:
738 checkUnprivilegedlookupClass(lookupClass, FULL_POWER_MODES);
739 }
740
741 private Lookup(Class<?> lookupClass, int allowedModes) {
742 this.lookupClass = lookupClass;
743 this.allowedModes = allowedModes;
744 }
745
746 /**
747 * Creates a lookup on the specified new lookup class.
748 * The resulting object will report the specified
749 * class as its own {@link #lookupClass lookupClass}.
750 * <p>
751 * However, the resulting {@code Lookup} object is guaranteed
752 * to have no more access capabilities than the original.
753 * In particular, access capabilities can be lost as follows:<ul>
754 * <li>If the old lookup class is in a {@link Module#isNamed() named} module, and
755 * the new lookup class is in a different module {@code M}, then no members, not
756 * even public members in {@code M}'s exported packages, will be accessible.
757 * The exception to this is when this lookup is {@link #publicLookup()
758 * publicLookup}, in which case {@code PUBLIC} access is not lost.
759 * <li>If the old lookup class is in an unnamed module, and the new lookup class
760 * is a different module then {@link #MODULE MODULE} access is lost.
761 * <li>If the new lookup class differs from the old one then {@code UNCONDITIONAL} is lost.
762 * <li>If the new lookup class is in a different package
763 * than the old one, protected and default (package) members will not be accessible.
764 * <li>If the new lookup class is not within the same package member
765 * as the old one, private members will not be accessible, and protected members
766 * will not be accessible by virtue of inheritance.
767 * (Protected members may continue to be accessible because of package sharing.)
768 * <li>If the new lookup class is not accessible to the old lookup class,
769 * then no members, not even public members, will be accessible.
770 * (In all other cases, public members will continue to be accessible.)
771 * </ul>
772 * <p>
773 * The resulting lookup's capabilities for loading classes
774 * (used during {@link #findClass} invocations)
775 * are determined by the lookup class' loader,
776 * which may change due to this operation.
777 *
778 * @param requestedLookupClass the desired lookup class for the new lookup object
779 * @return a lookup object which reports the desired lookup class, or the same object
780 * if there is no change
781 * @throws NullPointerException if the argument is null
782 *
783 * @revised 9
784 * @spec JPMS
785 */
786 public Lookup in(Class<?> requestedLookupClass) {
787 Objects.requireNonNull(requestedLookupClass);
788 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
789 return new Lookup(requestedLookupClass, FULL_POWER_MODES);
790 if (requestedLookupClass == this.lookupClass)
791 return this; // keep same capabilities
792 int newModes = (allowedModes & FULL_POWER_MODES);
793 if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
794 // Need to drop all access when teleporting from a named module to another
795 // module. The exception is publicLookup where PUBLIC is not lost.
796 if (this.lookupClass.getModule().isNamed()
797 && (this.allowedModes & UNCONDITIONAL) == 0)
798 newModes = 0;
799 else
800 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
801 }
802 if ((newModes & PACKAGE) != 0
803 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
804 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
805 }
806 // Allow nestmate lookups to be created without special privilege:
807 if ((newModes & PRIVATE) != 0
808 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
809 newModes &= ~(PRIVATE|PROTECTED);
810 }
811 if ((newModes & PUBLIC) != 0
812 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
813 // The requested class it not accessible from the lookup class.
814 // No permissions.
815 newModes = 0;
816 }
817
818 checkUnprivilegedlookupClass(requestedLookupClass, newModes);
819 return new Lookup(requestedLookupClass, newModes);
820 }
821
822
823 /**
824 * Creates a lookup on the same lookup class which this lookup object
825 * finds members, but with a lookup mode that has lost the given lookup mode.
826 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
827 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
828 * {@link #PROTECTED PROTECTED} and {@link #UNCONDITIONAL UNCONDITIONAL} are always
829 * dropped and so the resulting lookup mode will never have these access capabilities.
830 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
831 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
832 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
833 * is dropped then the resulting lookup has no access.
834 * @param modeToDrop the lookup mode to drop
835 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
836 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
837 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
838 * @see MethodHandles#privateLookupIn
839 * @since 9
840 */
841 public Lookup dropLookupMode(int modeToDrop) {
842 int oldModes = lookupModes();
843 int newModes = oldModes & ~(modeToDrop | PROTECTED | UNCONDITIONAL);
844 switch (modeToDrop) {
845 case PUBLIC: newModes &= ~(ALL_MODES); break;
846 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
847 case PACKAGE: newModes &= ~(PRIVATE); break;
848 case PROTECTED:
849 case PRIVATE:
850 case UNCONDITIONAL: break;
851 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
852 }
853 if (newModes == oldModes) return this; // return self if no change
854 return new Lookup(lookupClass(), newModes);
855 }
856
857 // Make sure outer class is initialized first.
858 static { IMPL_NAMES.getClass(); }
859
860 /** Package-private version of lookup which is trusted. */
861 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
862
863 /** Version of lookup which is trusted minimally.
864 * It can only be used to create method handles to publicly accessible
865 * members in packages that are exported unconditionally.
866 */
867 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, (PUBLIC|UNCONDITIONAL));
868
869 private static void checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes) {
870 String name = lookupClass.getName();
871 if (name.startsWith("java.lang.invoke."))
872 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
873
874 // For caller-sensitive MethodHandles.lookup() disallow lookup from
875 // restricted packages. This a fragile and blunt approach.
876 // TODO replace with a more formal and less fragile mechanism
877 // that does not bluntly restrict classes under packages within
878 // java.base from looking up MethodHandles or VarHandles.
879 if (allowedModes == FULL_POWER_MODES && lookupClass.getClassLoader() == null) {
880 if ((name.startsWith("java.") &&
881 !name.equals("java.lang.Thread") &&
882 !name.startsWith("java.util.concurrent.")) ||
883 (name.startsWith("sun.") &&
884 !name.startsWith("sun.invoke."))) {
885 throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
886 }
887 }
888 }
889
890 /**
891 * Displays the name of the class from which lookups are to be made.
892 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
893 * If there are restrictions on the access permitted to this lookup,
894 * this is indicated by adding a suffix to the class name, consisting
895 * of a slash and a keyword. The keyword represents the strongest
896 * allowed access, and is chosen as follows:
897 * <ul>
898 * <li>If no access is allowed, the suffix is "/noaccess".
899 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
900 * <li>If only public access and unconditional access are allowed, the suffix is "/publicLookup".
901 * <li>If only public and module access are allowed, the suffix is "/module".
902 * <li>If only public, module and package access are allowed, the suffix is "/package".
903 * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
904 * </ul>
905 * If none of the above cases apply, it is the case that full
906 * access (public, module, package, private, and protected) is allowed.
907 * In this case, no suffix is added.
908 * This is true only of an object obtained originally from
909 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
910 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
911 * always have restricted access, and will display a suffix.
912 * <p>
913 * (It may seem strange that protected access should be
914 * stronger than private access. Viewed independently from
915 * package access, protected access is the first to be lost,
916 * because it requires a direct subclass relationship between
917 * caller and callee.)
918 * @see #in
919 *
920 * @revised 9
921 * @spec JPMS
922 */
923 @Override
924 public String toString() {
925 String cname = lookupClass.getName();
926 switch (allowedModes) {
927 case 0: // no privileges
928 return cname + "/noaccess";
929 case PUBLIC:
930 return cname + "/public";
931 case PUBLIC|UNCONDITIONAL:
932 return cname + "/publicLookup";
933 case PUBLIC|MODULE:
934 return cname + "/module";
935 case PUBLIC|MODULE|PACKAGE:
936 return cname + "/package";
937 case FULL_POWER_MODES & ~PROTECTED:
938 return cname + "/private";
939 case FULL_POWER_MODES:
940 return cname;
941 case TRUSTED:
942 return "/trusted"; // internal only; not exported
943 default: // Should not happen, but it's a bitfield...
944 cname = cname + "/" + Integer.toHexString(allowedModes);
945 assert(false) : cname;
946 return cname;
947 }
948 }
949
950 /**
951 * Produces a method handle for a static method.
952 * The type of the method handle will be that of the method.
953 * (Since static methods do not take receivers, there is no
954 * additional receiver argument inserted into the method handle type,
955 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
956 * The method and all its argument types must be accessible to the lookup object.
957 * <p>
958 * The returned method handle will have
959 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
960 * the method's variable arity modifier bit ({@code 0x0080}) is set.
961 * <p>
962 * If the returned method handle is invoked, the method's class will
963 * be initialized, if it has not already been initialized.
964 * <p><b>Example:</b>
965 * <blockquote><pre>{@code
966 import static java.lang.invoke.MethodHandles.*;
967 import static java.lang.invoke.MethodType.*;
968 ...
969 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
970 "asList", methodType(List.class, Object[].class));
971 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
972 * }</pre></blockquote>
973 * @param refc the class from which the method is accessed
974 * @param name the name of the method
975 * @param type the type of the method
976 * @return the desired method handle
977 * @throws NoSuchMethodException if the method does not exist
978 * @throws IllegalAccessException if access checking fails,
979 * or if the method is not {@code static},
980 * or if the method's variable arity modifier bit
981 * is set and {@code asVarargsCollector} fails
982 * @exception SecurityException if a security manager is present and it
983 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
984 * @throws NullPointerException if any argument is null
985 */
986 public
987 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
988 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
989 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
990 }
991
992 /**
993 * Produces a method handle for a virtual method.
994 * The type of the method handle will be that of the method,
995 * with the receiver type (usually {@code refc}) prepended.
996 * The method and all its argument types must be accessible to the lookup object.
997 * <p>
998 * When called, the handle will treat the first argument as a receiver
999 * and dispatch on the receiver's type to determine which method
1000 * implementation to enter.
1001 * (The dispatching action is identical with that performed by an
1002 * {@code invokevirtual} or {@code invokeinterface} instruction.)
1003 * <p>
1004 * The first argument will be of type {@code refc} if the lookup
1005 * class has full privileges to access the member. Otherwise
1006 * the member must be {@code protected} and the first argument
1007 * will be restricted in type to the lookup class.
1008 * <p>
1009 * The returned method handle will have
1010 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1011 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1012 * <p>
1013 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
1014 * instructions and method handles produced by {@code findVirtual},
1015 * if the class is {@code MethodHandle} and the name string is
1016 * {@code invokeExact} or {@code invoke}, the resulting
1017 * method handle is equivalent to one produced by
1018 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
1019 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
1020 * with the same {@code type} argument.
1021 * <p>
1022 * If the class is {@code VarHandle} and the name string corresponds to
1023 * the name of a signature-polymorphic access mode method, the resulting
1024 * method handle is equivalent to one produced by
1025 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
1026 * the access mode corresponding to the name string and with the same
1027 * {@code type} arguments.
1028 * <p>
1029 * <b>Example:</b>
1030 * <blockquote><pre>{@code
1031 import static java.lang.invoke.MethodHandles.*;
1032 import static java.lang.invoke.MethodType.*;
1033 ...
1034 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
1035 "concat", methodType(String.class, String.class));
1036 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1037 "hashCode", methodType(int.class));
1038 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1039 "hashCode", methodType(int.class));
1040 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1041 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1042 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1043 // interface method:
1044 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1045 "subSequence", methodType(CharSequence.class, int.class, int.class));
1046 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1047 // constructor "internal method" must be accessed differently:
1048 MethodType MT_newString = methodType(void.class); //()V for new String()
1049 try { assertEquals("impossible", lookup()
1050 .findVirtual(String.class, "<init>", MT_newString));
1051 } catch (NoSuchMethodException ex) { } // OK
1052 MethodHandle MH_newString = publicLookup()
1053 .findConstructor(String.class, MT_newString);
1054 assertEquals("", (String) MH_newString.invokeExact());
1055 * }</pre></blockquote>
1056 *
1057 * @param refc the class or interface from which the method is accessed
1058 * @param name the name of the method
1059 * @param type the type of the method, with the receiver argument omitted
1060 * @return the desired method handle
1061 * @throws NoSuchMethodException if the method does not exist
1062 * @throws IllegalAccessException if access checking fails,
1063 * or if the method is {@code static},
1064 * or if the method is {@code private} method of interface,
1065 * or if the method's variable arity modifier bit
1066 * is set and {@code asVarargsCollector} fails
1067 * @exception SecurityException if a security manager is present and it
1068 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1069 * @throws NullPointerException if any argument is null
1070 */
1071 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1072 if (refc == MethodHandle.class) {
1073 MethodHandle mh = findVirtualForMH(name, type);
1074 if (mh != null) return mh;
1075 } else if (refc == VarHandle.class) {
1076 MethodHandle mh = findVirtualForVH(name, type);
1077 if (mh != null) return mh;
1078 }
1079 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1080 MemberName method = resolveOrFail(refKind, refc, name, type);
1081 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
1082 }
1083 private MethodHandle findVirtualForMH(String name, MethodType type) {
1084 // these names require special lookups because of the implicit MethodType argument
1085 if ("invoke".equals(name))
1086 return invoker(type);
1087 if ("invokeExact".equals(name))
1088 return exactInvoker(type);
1089 assert(!MemberName.isMethodHandleInvokeName(name));
1090 return null;
1091 }
1092 private MethodHandle findVirtualForVH(String name, MethodType type) {
1093 try {
1094 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1095 } catch (IllegalArgumentException e) {
1096 return null;
1097 }
1098 }
1099
1100 /**
1101 * Produces a method handle which creates an object and initializes it, using
1102 * the constructor of the specified type.
1103 * The parameter types of the method handle will be those of the constructor,
1104 * while the return type will be a reference to the constructor's class.
1105 * The constructor and all its argument types must be accessible to the lookup object.
1106 * <p>
1107 * The requested type must have a return type of {@code void}.
1108 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1109 * <p>
1110 * The returned method handle will have
1111 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1112 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1113 * <p>
1114 * If the returned method handle is invoked, the constructor's class will
1115 * be initialized, if it has not already been initialized.
1116 * <p><b>Example:</b>
1117 * <blockquote><pre>{@code
1118 import static java.lang.invoke.MethodHandles.*;
1119 import static java.lang.invoke.MethodType.*;
1120 ...
1121 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1122 ArrayList.class, methodType(void.class, Collection.class));
1123 Collection orig = Arrays.asList("x", "y");
1124 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1125 assert(orig != copy);
1126 assertEquals(orig, copy);
1127 // a variable-arity constructor:
1128 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1129 ProcessBuilder.class, methodType(void.class, String[].class));
1130 ProcessBuilder pb = (ProcessBuilder)
1131 MH_newProcessBuilder.invoke("x", "y", "z");
1132 assertEquals("[x, y, z]", pb.command().toString());
1133 * }</pre></blockquote>
1134 * @param refc the class or interface from which the method is accessed
1135 * @param type the type of the method, with the receiver argument omitted, and a void return type
1136 * @return the desired method handle
1137 * @throws NoSuchMethodException if the constructor does not exist
1138 * @throws IllegalAccessException if access checking fails
1139 * or if the method's variable arity modifier bit
1140 * is set and {@code asVarargsCollector} fails
1141 * @exception SecurityException if a security manager is present and it
1142 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1143 * @throws NullPointerException if any argument is null
1144 */
1145 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1146 if (refc.isArray()) {
1147 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1148 }
1149 String name = "<init>";
1150 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1151 return getDirectConstructor(refc, ctor);
1152 }
1153
1154 /**
1155 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1156 * initializer of the class is not run.
1157 * <p>
1158 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1159 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1160 * load the requested class, and then determines whether the class is accessible to this lookup object.
1161 *
1162 * @param targetName the fully qualified name of the class to be looked up.
1163 * @return the requested class.
1164 * @exception SecurityException if a security manager is present and it
1165 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1166 * @throws LinkageError if the linkage fails
1167 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1168 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1169 * modes.
1170 * @exception SecurityException if a security manager is present and it
1171 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1172 * @since 9
1173 */
1174 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1175 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1176 return accessClass(targetClass);
1177 }
1178
1179 /**
1180 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1181 * static initializer of the class is not run.
1182 * <p>
1183 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1184 * {@linkplain #lookupModes() lookup modes}.
1185 *
1186 * @param targetClass the class to be access-checked
1187 *
1188 * @return the class that has been access-checked
1189 *
1190 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1191 * modes.
1192 * @exception SecurityException if a security manager is present and it
1193 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1194 * @since 9
1195 */
1196 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1197 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1198 throw new MemberName(targetClass).makeAccessException("access violation", this);
1199 }
1200 checkSecurityManager(targetClass, null);
1201 return targetClass;
1202 }
1203
1204 /**
1205 * Produces an early-bound method handle for a virtual method.
1206 * It will bypass checks for overriding methods on the receiver,
1207 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1208 * instruction from within the explicitly specified {@code specialCaller}.
1209 * The type of the method handle will be that of the method,
1210 * with a suitably restricted receiver type prepended.
1211 * (The receiver type will be {@code specialCaller} or a subtype.)
1212 * The method and all its argument types must be accessible
1213 * to the lookup object.
1214 * <p>
1215 * Before method resolution,
1216 * if the explicitly specified caller class is not identical with the
1217 * lookup class, or if this lookup object does not have
1218 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1219 * privileges, the access fails.
1220 * <p>
1221 * The returned method handle will have
1222 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1223 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1224 * <p style="font-size:smaller;">
1225 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1226 * even though the {@code invokespecial} instruction can refer to them
1227 * in special circumstances. Use {@link #findConstructor findConstructor}
1228 * to access instance initialization methods in a safe manner.)</em>
1229 * <p><b>Example:</b>
1230 * <blockquote><pre>{@code
1231 import static java.lang.invoke.MethodHandles.*;
1232 import static java.lang.invoke.MethodType.*;
1233 ...
1234 static class Listie extends ArrayList {
1235 public String toString() { return "[wee Listie]"; }
1236 static Lookup lookup() { return MethodHandles.lookup(); }
1237 }
1238 ...
1239 // no access to constructor via invokeSpecial:
1240 MethodHandle MH_newListie = Listie.lookup()
1241 .findConstructor(Listie.class, methodType(void.class));
1242 Listie l = (Listie) MH_newListie.invokeExact();
1243 try { assertEquals("impossible", Listie.lookup().findSpecial(
1244 Listie.class, "<init>", methodType(void.class), Listie.class));
1245 } catch (NoSuchMethodException ex) { } // OK
1246 // access to super and self methods via invokeSpecial:
1247 MethodHandle MH_super = Listie.lookup().findSpecial(
1248 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1249 MethodHandle MH_this = Listie.lookup().findSpecial(
1250 Listie.class, "toString" , methodType(String.class), Listie.class);
1251 MethodHandle MH_duper = Listie.lookup().findSpecial(
1252 Object.class, "toString" , methodType(String.class), Listie.class);
1253 assertEquals("[]", (String) MH_super.invokeExact(l));
1254 assertEquals(""+l, (String) MH_this.invokeExact(l));
1255 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1256 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1257 String.class, "toString", methodType(String.class), Listie.class));
1258 } catch (IllegalAccessException ex) { } // OK
1259 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1260 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1261 * }</pre></blockquote>
1262 *
1263 * @param refc the class or interface from which the method is accessed
1264 * @param name the name of the method (which must not be "<init>")
1265 * @param type the type of the method, with the receiver argument omitted
1266 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1267 * @return the desired method handle
1268 * @throws NoSuchMethodException if the method does not exist
1269 * @throws IllegalAccessException if access checking fails,
1270 * or if the method is {@code static},
1271 * or if the method's variable arity modifier bit
1272 * is set and {@code asVarargsCollector} fails
1273 * @exception SecurityException if a security manager is present and it
1274 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1275 * @throws NullPointerException if any argument is null
1276 */
1277 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1278 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1279 checkSpecialCaller(specialCaller, refc);
1280 Lookup specialLookup = this.in(specialCaller);
1281 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1282 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1283 }
1284
1285 /**
1286 * Produces a method handle giving read access to a non-static field.
1287 * The type of the method handle will have a return type of the field's
1288 * value type.
1289 * The method handle's single argument will be the instance containing
1290 * the field.
1291 * Access checking is performed immediately on behalf of the lookup class.
1292 * @param refc the class or interface from which the method is accessed
1293 * @param name the field's name
1294 * @param type the field's type
1295 * @return a method handle which can load values from the field
1296 * @throws NoSuchFieldException if the field does not exist
1297 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1298 * @exception SecurityException if a security manager is present and it
1299 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1300 * @throws NullPointerException if any argument is null
1301 * @see #findVarHandle(Class, String, Class)
1302 */
1303 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1304 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1305 return getDirectField(REF_getField, refc, field);
1306 }
1307
1308 /**
1309 * Produces a method handle giving write access to a non-static field.
1310 * The type of the method handle will have a void return type.
1311 * The method handle will take two arguments, the instance containing
1312 * the field, and the value to be stored.
1313 * The second argument will be of the field's value type.
1314 * Access checking is performed immediately on behalf of the lookup class.
1315 * @param refc the class or interface from which the method is accessed
1316 * @param name the field's name
1317 * @param type the field's type
1318 * @return a method handle which can store values into the field
1319 * @throws NoSuchFieldException if the field does not exist
1320 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1321 * @exception SecurityException if a security manager is present and it
1322 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1323 * @throws NullPointerException if any argument is null
1324 * @see #findVarHandle(Class, String, Class)
1325 */
1326 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1327 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1328 return getDirectField(REF_putField, refc, field);
1329 }
1330
1331 /**
1332 * Produces a VarHandle giving access to non-static fields of type
1333 * {@code T} declared by a receiver class of type {@code R}, supporting
1334 * shape {@code (R : T)}.
1335 * <p>
1336 * Access checking is performed immediately on behalf of the lookup
1337 * class.
1338 * <p>
1339 * Certain access modes of the returned VarHandle are unsupported under
1340 * the following conditions:
1341 * <ul>
1342 * <li>if the field is declared {@code final}, then the write, atomic
1343 * update, numeric atomic update, and bitwise atomic update access
1344 * modes are unsupported.
1345 * <li>if the field type is anything other than {@code byte},
1346 * {@code short}, {@code char}, {@code int}, {@code long},
1347 * {@code float}, or {@code double} then numeric atomic update
1348 * access modes are unsupported.
1349 * <li>if the field type is anything other than {@code boolean},
1350 * {@code byte}, {@code short}, {@code char}, {@code int} or
1351 * {@code long} then bitwise atomic update access modes are
1352 * unsupported.
1353 * </ul>
1354 * <p>
1355 * If the field is declared {@code volatile} then the returned VarHandle
1356 * will override access to the field (effectively ignore the
1357 * {@code volatile} declaration) in accordance to it's specified
1358 * access modes.
1359 * <p>
1360 * If the field type is {@code float} or {@code double} then numeric
1361 * and atomic update access modes compare values using their bitwise
1362 * representation (see {@link Float#floatToRawIntBits} and
1363 * {@link Double#doubleToRawLongBits}, respectively).
1364 * @apiNote
1365 * Bitwise comparison of {@code float} values or {@code double} values,
1366 * as performed by the numeric and atomic update access modes, differ
1367 * from the primitive {@code ==} operator and the {@link Float#equals}
1368 * and {@link Double#equals} methods, specifically with respect to
1369 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1370 * Care should be taken when performing a compare and set or a compare
1371 * and exchange operation with such values since the operation may
1372 * unexpectedly fail.
1373 * There are many possible NaN values that are considered to be
1374 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1375 * provided by Java can distinguish between them. Operation failure can
1376 * occur if the expected or witness value is a NaN value and it is
1377 * transformed (perhaps in a platform specific manner) into another NaN
1378 * value, and thus has a different bitwise representation (see
1379 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1380 * details).
1381 * The values {@code -0.0} and {@code +0.0} have different bitwise
1382 * representations but are considered equal when using the primitive
1383 * {@code ==} operator. Operation failure can occur if, for example, a
1384 * numeric algorithm computes an expected value to be say {@code -0.0}
1385 * and previously computed the witness value to be say {@code +0.0}.
1386 * @param recv the receiver class, of type {@code R}, that declares the
1387 * non-static field
1388 * @param name the field's name
1389 * @param type the field's type, of type {@code T}
1390 * @return a VarHandle giving access to non-static fields.
1391 * @throws NoSuchFieldException if the field does not exist
1392 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1393 * @exception SecurityException if a security manager is present and it
1394 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1395 * @throws NullPointerException if any argument is null
1396 * @since 9
1397 */
1398 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1399 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1400 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1401 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1402 }
1403
1404 /**
1405 * Produces a method handle giving read access to a static field.
1406 * The type of the method handle will have a return type of the field's
1407 * value type.
1408 * The method handle will take no arguments.
1409 * Access checking is performed immediately on behalf of the lookup class.
1410 * <p>
1411 * If the returned method handle is invoked, the field's class will
1412 * be initialized, if it has not already been initialized.
1413 * @param refc the class or interface from which the method is accessed
1414 * @param name the field's name
1415 * @param type the field's type
1416 * @return a method handle which can load values from the field
1417 * @throws NoSuchFieldException if the field does not exist
1418 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1419 * @exception SecurityException if a security manager is present and it
1420 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1421 * @throws NullPointerException if any argument is null
1422 */
1423 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1424 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1425 return getDirectField(REF_getStatic, refc, field);
1426 }
1427
1428 /**
1429 * Produces a method handle giving write access to a static field.
1430 * The type of the method handle will have a void return type.
1431 * The method handle will take a single
1432 * argument, of the field's value type, the value to be stored.
1433 * Access checking is performed immediately on behalf of the lookup class.
1434 * <p>
1435 * If the returned method handle is invoked, the field's class will
1436 * be initialized, if it has not already been initialized.
1437 * @param refc the class or interface from which the method is accessed
1438 * @param name the field's name
1439 * @param type the field's type
1440 * @return a method handle which can store values into the field
1441 * @throws NoSuchFieldException if the field does not exist
1442 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1443 * @exception SecurityException if a security manager is present and it
1444 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1445 * @throws NullPointerException if any argument is null
1446 */
1447 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1448 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1449 return getDirectField(REF_putStatic, refc, field);
1450 }
1451
1452 /**
1453 * Produces a VarHandle giving access to a static field of type
1454 * {@code T} declared by a given declaring class, supporting shape
1455 * {@code ((empty) : T)}.
1456 * <p>
1457 * Access checking is performed immediately on behalf of the lookup
1458 * class.
1459 * <p>
1460 * If the returned VarHandle is operated on, the declaring class will be
1461 * initialized, if it has not already been initialized.
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 it's 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 decl the class that declares the static field
1511 * @param name the field's name
1512 * @param type the field's type, of type {@code T}
1513 * @return a VarHandle giving access to a static field
1514 * @throws NoSuchFieldException if the field does not exist
1515 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1516 * @exception SecurityException if a security manager is present and it
1517 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1518 * @throws NullPointerException if any argument is null
1519 * @since 9
1520 */
1521 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1522 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1523 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1524 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1525 }
1526
1527 /**
1528 * Produces an early-bound method handle for a non-static method.
1529 * The receiver must have a supertype {@code defc} in which a method
1530 * of the given name and type is accessible to the lookup class.
1531 * The method and all its argument types must be accessible to the lookup object.
1532 * The type of the method handle will be that of the method,
1533 * without any insertion of an additional receiver parameter.
1534 * The given receiver will be bound into the method handle,
1535 * so that every call to the method handle will invoke the
1536 * requested method on the given receiver.
1537 * <p>
1538 * The returned method handle will have
1539 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1540 * the method's variable arity modifier bit ({@code 0x0080}) is set
1541 * <em>and</em> the trailing array argument is not the only argument.
1542 * (If the trailing array argument is the only argument,
1543 * the given receiver value will be bound to it.)
1544 * <p>
1545 * This is equivalent to the following code:
1546 * <blockquote><pre>{@code
1547 import static java.lang.invoke.MethodHandles.*;
1548 import static java.lang.invoke.MethodType.*;
1549 ...
1550 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1551 MethodHandle mh1 = mh0.bindTo(receiver);
1552 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1553 return mh1;
1554 * }</pre></blockquote>
1555 * where {@code defc} is either {@code receiver.getClass()} or a super
1556 * type of that class, in which the requested method is accessible
1557 * to the lookup class.
1558 * (Note that {@code bindTo} does not preserve variable arity.)
1559 * @param receiver the object from which the method is accessed
1560 * @param name the name of the method
1561 * @param type the type of the method, with the receiver argument omitted
1562 * @return the desired method handle
1563 * @throws NoSuchMethodException if the method does not exist
1564 * @throws IllegalAccessException if access checking fails
1565 * or if the method's variable arity modifier bit
1566 * is set and {@code asVarargsCollector} fails
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 * @see MethodHandle#bindTo
1571 * @see #findVirtual
1572 */
1573 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1574 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1575 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1576 MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1577 return mh.bindArgumentL(0, receiver).setVarargs(method);
1578 }
1579
1580 /**
1581 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1582 * to <i>m</i>, if the lookup class has permission.
1583 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1584 * If <i>m</i> is virtual, overriding is respected on every call.
1585 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1586 * The type of the method handle will be that of the method,
1587 * with the receiver type prepended (but only if it is non-static).
1588 * If the method's {@code accessible} flag is not set,
1589 * access checking is performed immediately on behalf of the lookup class.
1590 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1591 * <p>
1592 * The returned method handle will have
1593 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1594 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1595 * <p>
1596 * If <i>m</i> is static, and
1597 * if the returned method handle is invoked, the method's class will
1598 * be initialized, if it has not already been initialized.
1599 * @param m the reflected method
1600 * @return a method handle which can invoke the reflected method
1601 * @throws IllegalAccessException if access checking fails
1602 * or if the method's variable arity modifier bit
1603 * is set and {@code asVarargsCollector} fails
1604 * @throws NullPointerException if the argument is null
1605 */
1606 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1607 if (m.getDeclaringClass() == MethodHandle.class) {
1608 MethodHandle mh = unreflectForMH(m);
1609 if (mh != null) return mh;
1610 }
1611 if (m.getDeclaringClass() == VarHandle.class) {
1612 MethodHandle mh = unreflectForVH(m);
1613 if (mh != null) return mh;
1614 }
1615 MemberName method = new MemberName(m);
1616 byte refKind = method.getReferenceKind();
1617 if (refKind == REF_invokeSpecial)
1618 refKind = REF_invokeVirtual;
1619 assert(method.isMethod());
1620 @SuppressWarnings("deprecation")
1621 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1622 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1623 }
1624 private MethodHandle unreflectForMH(Method m) {
1625 // these names require special lookups because they throw UnsupportedOperationException
1626 if (MemberName.isMethodHandleInvokeName(m.getName()))
1627 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1628 return null;
1629 }
1630 private MethodHandle unreflectForVH(Method m) {
1631 // these names require special lookups because they throw UnsupportedOperationException
1632 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
1633 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
1634 return null;
1635 }
1636
1637 /**
1638 * Produces a method handle for a reflected method.
1639 * It will bypass checks for overriding methods on the receiver,
1640 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1641 * instruction from within the explicitly specified {@code specialCaller}.
1642 * The type of the method handle will be that of the method,
1643 * with a suitably restricted receiver type prepended.
1644 * (The receiver type will be {@code specialCaller} or a subtype.)
1645 * If the method's {@code accessible} flag is not set,
1646 * access checking is performed immediately on behalf of the lookup class,
1647 * as if {@code invokespecial} instruction were being linked.
1648 * <p>
1649 * Before method resolution,
1650 * if the explicitly specified caller class is not identical with the
1651 * lookup class, or if this lookup object does not have
1652 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1653 * privileges, the access fails.
1654 * <p>
1655 * The returned method handle will have
1656 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1657 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1658 * @param m the reflected method
1659 * @param specialCaller the class nominally calling the method
1660 * @return a method handle which can invoke the reflected method
1661 * @throws IllegalAccessException if access checking fails,
1662 * or if the method is {@code static},
1663 * or if the method's variable arity modifier bit
1664 * is set and {@code asVarargsCollector} fails
1665 * @throws NullPointerException if any argument is null
1666 */
1667 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1668 checkSpecialCaller(specialCaller, null);
1669 Lookup specialLookup = this.in(specialCaller);
1670 MemberName method = new MemberName(m, true);
1671 assert(method.isMethod());
1672 // ignore m.isAccessible: this is a new kind of access
1673 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1674 }
1675
1676 /**
1677 * Produces a method handle for a reflected constructor.
1678 * The type of the method handle will be that of the constructor,
1679 * with the return type changed to the declaring class.
1680 * The method handle will perform a {@code newInstance} operation,
1681 * creating a new instance of the constructor's class on the
1682 * arguments passed to the method handle.
1683 * <p>
1684 * If the constructor's {@code accessible} flag is not set,
1685 * access checking is performed immediately on behalf of the lookup class.
1686 * <p>
1687 * The returned method handle will have
1688 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1689 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1690 * <p>
1691 * If the returned method handle is invoked, the constructor's class will
1692 * be initialized, if it has not already been initialized.
1693 * @param c the reflected constructor
1694 * @return a method handle which can invoke the reflected constructor
1695 * @throws IllegalAccessException if access checking fails
1696 * or if the method's variable arity modifier bit
1697 * is set and {@code asVarargsCollector} fails
1698 * @throws NullPointerException if the argument is null
1699 */
1700 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1701 MemberName ctor = new MemberName(c);
1702 assert(ctor.isConstructor());
1703 @SuppressWarnings("deprecation")
1704 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1705 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1706 }
1707
1708 /**
1709 * Produces a method handle giving read access to a reflected field.
1710 * The type of the method handle will have a return type of the field's
1711 * value type.
1712 * If the field is static, the method handle will take no arguments.
1713 * Otherwise, its single argument will be the instance containing
1714 * the field.
1715 * If the field's {@code accessible} flag is not set,
1716 * access checking is performed immediately on behalf of the lookup class.
1717 * <p>
1718 * If the field is static, and
1719 * if the returned method handle is invoked, the field's class will
1720 * be initialized, if it has not already been initialized.
1721 * @param f the reflected field
1722 * @return a method handle which can load values from the reflected field
1723 * @throws IllegalAccessException if access checking fails
1724 * @throws NullPointerException if the argument is null
1725 */
1726 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1727 return unreflectField(f, false);
1728 }
1729 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1730 MemberName field = new MemberName(f, isSetter);
1731 assert(isSetter
1732 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1733 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1734 @SuppressWarnings("deprecation")
1735 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1736 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1737 }
1738
1739 /**
1740 * Produces a method handle giving write access to a reflected field.
1741 * The type of the method handle will have a void return type.
1742 * If the field is static, the method handle will take a single
1743 * argument, of the field's value type, the value to be stored.
1744 * Otherwise, the two arguments will be the instance containing
1745 * the field, and the value to be stored.
1746 * If the field's {@code accessible} flag is not set,
1747 * access checking is performed immediately on behalf of the lookup class.
1748 * <p>
1749 * If the field is static, and
1750 * if the returned method handle is invoked, the field's class will
1751 * be initialized, if it has not already been initialized.
1752 * @param f the reflected field
1753 * @return a method handle which can store values into the reflected field
1754 * @throws IllegalAccessException if access checking fails
1755 * @throws NullPointerException if the argument is null
1756 */
1757 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1758 return unreflectField(f, true);
1759 }
1760
1761 /**
1762 * Produces a VarHandle that accesses fields of type {@code T} declared
1763 * by a class of type {@code R}, as described by the given reflected
1764 * field.
1765 * If the field is non-static the VarHandle supports a shape of
1766 * {@code (R : T)}, otherwise supports a shape of {@code ((empty) : T)}.
1767 * <p>
1768 * Access checking is performed immediately on behalf of the lookup
1769 * class, regardless of the value of the field's {@code accessible}
1770 * flag.
1771 * <p>
1772 * If the field is static, and if the returned VarHandle is operated
1773 * on, the field's declaring class will be initialized, if it has not
1774 * already been initialized.
1775 * <p>
1776 * Certain access modes of the returned VarHandle are unsupported under
1777 * the following conditions:
1778 * <ul>
1779 * <li>if the field is declared {@code final}, then the write, atomic
1780 * update, numeric atomic update, and bitwise atomic update access
1781 * modes are unsupported.
1782 * <li>if the field type is anything other than {@code byte},
1783 * {@code short}, {@code char}, {@code int}, {@code long},
1784 * {@code float}, or {@code double} then numeric atomic update
1785 * access modes are unsupported.
1786 * <li>if the field type is anything other than {@code boolean},
1787 * {@code byte}, {@code short}, {@code char}, {@code int} or
1788 * {@code long} then bitwise atomic update access modes are
1789 * unsupported.
1790 * </ul>
1791 * <p>
1792 * If the field is declared {@code volatile} then the returned VarHandle
1793 * will override access to the field (effectively ignore the
1794 * {@code volatile} declaration) in accordance to it's specified
1795 * access modes.
1796 * <p>
1797 * If the field type is {@code float} or {@code double} then numeric
1798 * and atomic update access modes compare values using their bitwise
1799 * representation (see {@link Float#floatToRawIntBits} and
1800 * {@link Double#doubleToRawLongBits}, respectively).
1801 * @apiNote
1802 * Bitwise comparison of {@code float} values or {@code double} values,
1803 * as performed by the numeric and atomic update access modes, differ
1804 * from the primitive {@code ==} operator and the {@link Float#equals}
1805 * and {@link Double#equals} methods, specifically with respect to
1806 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1807 * Care should be taken when performing a compare and set or a compare
1808 * and exchange operation with such values since the operation may
1809 * unexpectedly fail.
1810 * There are many possible NaN values that are considered to be
1811 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1812 * provided by Java can distinguish between them. Operation failure can
1813 * occur if the expected or witness value is a NaN value and it is
1814 * transformed (perhaps in a platform specific manner) into another NaN
1815 * value, and thus has a different bitwise representation (see
1816 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1817 * details).
1818 * The values {@code -0.0} and {@code +0.0} have different bitwise
1819 * representations but are considered equal when using the primitive
1820 * {@code ==} operator. Operation failure can occur if, for example, a
1821 * numeric algorithm computes an expected value to be say {@code -0.0}
1822 * and previously computed the witness value to be say {@code +0.0}.
1823 * @param f the reflected field, with a field of type {@code T}, and
1824 * a declaring class of type {@code R}
1825 * @return a VarHandle giving access to non-static fields or a static
1826 * field
1827 * @throws IllegalAccessException if access checking fails
1828 * @throws NullPointerException if the argument is null
1829 * @since 9
1830 */
1831 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
1832 MemberName getField = new MemberName(f, false);
1833 MemberName putField = new MemberName(f, true);
1834 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
1835 f.getDeclaringClass(), getField, putField);
1836 }
1837
1838 /**
1839 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1840 * created by this lookup object or a similar one.
1841 * Security and access checks are performed to ensure that this lookup object
1842 * is capable of reproducing the target method handle.
1843 * This means that the cracking may fail if target is a direct method handle
1844 * but was created by an unrelated lookup object.
1845 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1846 * and was created by a lookup object for a different class.
1847 * @param target a direct method handle to crack into symbolic reference components
1848 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1849 * @exception SecurityException if a security manager is present and it
1850 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1851 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1852 * @exception NullPointerException if the target is {@code null}
1853 * @see MethodHandleInfo
1854 * @since 1.8
1855 */
1856 public MethodHandleInfo revealDirect(MethodHandle target) {
1857 MemberName member = target.internalMemberName();
1858 if (member == null || (!member.isResolved() &&
1859 !member.isMethodHandleInvoke() &&
1860 !member.isVarHandleMethodInvoke()))
1861 throw newIllegalArgumentException("not a direct method handle");
1862 Class<?> defc = member.getDeclaringClass();
1863 byte refKind = member.getReferenceKind();
1864 assert(MethodHandleNatives.refKindIsValid(refKind));
1865 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1866 // Devirtualized method invocation is usually formally virtual.
1867 // To avoid creating extra MemberName objects for this common case,
1868 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1869 refKind = REF_invokeVirtual;
1870 if (refKind == REF_invokeVirtual && defc.isInterface())
1871 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
1872 refKind = REF_invokeInterface;
1873 // Check SM permissions and member access before cracking.
1874 try {
1875 checkAccess(refKind, defc, member);
1876 checkSecurityManager(defc, member);
1877 } catch (IllegalAccessException ex) {
1878 throw new IllegalArgumentException(ex);
1879 }
1880 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
1881 Class<?> callerClass = target.internalCallerClass();
1882 if (!hasPrivateAccess() || callerClass != lookupClass())
1883 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
1884 }
1885 // Produce the handle to the results.
1886 return new InfoFromMemberName(this, member, refKind);
1887 }
1888
1889 /// Helper methods, all package-private.
1890
1891 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1892 checkSymbolicClass(refc); // do this before attempting to resolve
1893 Objects.requireNonNull(name);
1894 Objects.requireNonNull(type);
1895 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1896 NoSuchFieldException.class);
1897 }
1898
1899 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1900 checkSymbolicClass(refc); // do this before attempting to resolve
1901 Objects.requireNonNull(name);
1902 Objects.requireNonNull(type);
1903 checkMethodName(refKind, name); // NPE check on name
1904 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1905 NoSuchMethodException.class);
1906 }
1907
1908 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
1909 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
1910 Objects.requireNonNull(member.getName());
1911 Objects.requireNonNull(member.getType());
1912 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
1913 ReflectiveOperationException.class);
1914 }
1915
1916 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
1917 Objects.requireNonNull(refc);
1918 Class<?> caller = lookupClassOrNull();
1919 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
1920 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
1921 }
1922
1923 /** Check name for an illegal leading "<" character. */
1924 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
1925 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
1926 throw new NoSuchMethodException("illegal method name: "+name);
1927 }
1928
1929
1930 /**
1931 * Find my trustable caller class if m is a caller sensitive method.
1932 * If this lookup object has private access, then the caller class is the lookupClass.
1933 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
1934 */
1935 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
1936 Class<?> callerClass = null;
1937 if (MethodHandleNatives.isCallerSensitive(m)) {
1938 // Only lookups with private access are allowed to resolve caller-sensitive methods
1939 if (hasPrivateAccess()) {
1940 callerClass = lookupClass;
1941 } else {
1942 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
1943 }
1944 }
1945 return callerClass;
1946 }
1947
1948 /**
1949 * Returns {@code true} if this lookup has {@code PRIVATE} access.
1950 * @return {@code true} if this lookup has {@code PRIVATE} acesss.
1951 * @since 9
1952 */
1953 public boolean hasPrivateAccess() {
1954 return (allowedModes & PRIVATE) != 0;
1955 }
1956
1957 /**
1958 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
1959 * Determines a trustable caller class to compare with refc, the symbolic reference class.
1960 * If this lookup object has private access, then the caller class is the lookupClass.
1961 */
1962 void checkSecurityManager(Class<?> refc, MemberName m) {
1963 SecurityManager smgr = System.getSecurityManager();
1964 if (smgr == null) return;
1965 if (allowedModes == TRUSTED) return;
1966
1967 // Step 1:
1968 boolean fullPowerLookup = hasPrivateAccess();
1969 if (!fullPowerLookup ||
1970 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
1971 ReflectUtil.checkPackageAccess(refc);
1972 }
1973
1974 if (m == null) { // findClass or accessClass
1975 // Step 2b:
1976 if (!fullPowerLookup) {
1977 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1978 }
1979 return;
1980 }
1981
1982 // Step 2a:
1983 if (m.isPublic()) return;
1984 if (!fullPowerLookup) {
1985 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
1986 }
1987
1988 // Step 3:
1989 Class<?> defc = m.getDeclaringClass();
1990 if (!fullPowerLookup && defc != refc) {
1991 ReflectUtil.checkPackageAccess(defc);
1992 }
1993 }
1994
1995 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1996 boolean wantStatic = (refKind == REF_invokeStatic);
1997 String message;
1998 if (m.isConstructor())
1999 message = "expected a method, not a constructor";
2000 else if (!m.isMethod())
2001 message = "expected a method";
2002 else if (wantStatic != m.isStatic())
2003 message = wantStatic ? "expected a static method" : "expected a non-static method";
2004 else
2005 { checkAccess(refKind, refc, m); return; }
2006 throw m.makeAccessException(message, this);
2007 }
2008
2009 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2010 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2011 String message;
2012 if (wantStatic != m.isStatic())
2013 message = wantStatic ? "expected a static field" : "expected a non-static field";
2014 else
2015 { checkAccess(refKind, refc, m); return; }
2016 throw m.makeAccessException(message, this);
2017 }
2018
2019 /** Check public/protected/private bits on the symbolic reference class and its member. */
2020 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2021 assert(m.referenceKindIsConsistentWith(refKind) &&
2022 MethodHandleNatives.refKindIsValid(refKind) &&
2023 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2024 int allowedModes = this.allowedModes;
2025 if (allowedModes == TRUSTED) return;
2026 int mods = m.getModifiers();
2027 if (Modifier.isProtected(mods) &&
2028 refKind == REF_invokeVirtual &&
2029 m.getDeclaringClass() == Object.class &&
2030 m.getName().equals("clone") &&
2031 refc.isArray()) {
2032 // The JVM does this hack also.
2033 // (See ClassVerifier::verify_invoke_instructions
2034 // and LinkResolver::check_method_accessability.)
2035 // Because the JVM does not allow separate methods on array types,
2036 // there is no separate method for int[].clone.
2037 // All arrays simply inherit Object.clone.
2038 // But for access checking logic, we make Object.clone
2039 // (normally protected) appear to be public.
2040 // Later on, when the DirectMethodHandle is created,
2041 // its leading argument will be restricted to the
2042 // requested array type.
2043 // N.B. The return type is not adjusted, because
2044 // that is *not* the bytecode behavior.
2045 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2046 }
2047 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2048 // cannot "new" a protected ctor in a different package
2049 mods ^= Modifier.PROTECTED;
2050 }
2051 if (Modifier.isFinal(mods) &&
2052 MethodHandleNatives.refKindIsSetter(refKind))
2053 throw m.makeAccessException("unexpected set of a final field", this);
2054 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2055 if ((requestedModes & allowedModes) != 0) {
2056 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2057 mods, lookupClass(), allowedModes))
2058 return;
2059 } else {
2060 // Protected members can also be checked as if they were package-private.
2061 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2062 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2063 return;
2064 }
2065 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2066 }
2067
2068 String accessFailedMessage(Class<?> refc, MemberName m) {
2069 Class<?> defc = m.getDeclaringClass();
2070 int mods = m.getModifiers();
2071 // check the class first:
2072 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2073 (defc == refc ||
2074 Modifier.isPublic(refc.getModifiers())));
2075 if (!classOK && (allowedModes & PACKAGE) != 0) {
2076 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), FULL_POWER_MODES) &&
2077 (defc == refc ||
2078 VerifyAccess.isClassAccessible(refc, lookupClass(), FULL_POWER_MODES)));
2079 }
2080 if (!classOK)
2081 return "class is not public";
2082 if (Modifier.isPublic(mods))
2083 return "access to public member failed"; // (how?, module not readable?)
2084 if (Modifier.isPrivate(mods))
2085 return "member is private";
2086 if (Modifier.isProtected(mods))
2087 return "member is protected";
2088 return "member is private to package";
2089 }
2090
2091 private static final boolean ALLOW_NESTMATE_ACCESS = false;
2092
2093 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2094 int allowedModes = this.allowedModes;
2095 if (allowedModes == TRUSTED) return;
2096 if (!hasPrivateAccess()
2097 || (specialCaller != lookupClass()
2098 // ensure non-abstract methods in superinterfaces can be special-invoked
2099 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))
2100 && !(ALLOW_NESTMATE_ACCESS &&
2101 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
2102 throw new MemberName(specialCaller).
2103 makeAccessException("no private access for invokespecial", this);
2104 }
2105
2106 private boolean restrictProtectedReceiver(MemberName method) {
2107 // The accessing class only has the right to use a protected member
2108 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2109 if (!method.isProtected() || method.isStatic()
2110 || allowedModes == TRUSTED
2111 || method.getDeclaringClass() == lookupClass()
2112 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
2113 || (ALLOW_NESTMATE_ACCESS &&
2114 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
2115 return false;
2116 return true;
2117 }
2118 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2119 assert(!method.isStatic());
2120 // receiver type of mh is too wide; narrow to caller
2121 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2122 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2123 }
2124 MethodType rawType = mh.type();
2125 if (rawType.parameterType(0) == caller) return mh;
2126 MethodType narrowType = rawType.changeParameterType(0, caller);
2127 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2128 assert(mh.viewAsTypeChecks(narrowType, true));
2129 return mh.copyWith(narrowType, mh.form);
2130 }
2131
2132 /** Check access and get the requested method. */
2133 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2134 final boolean doRestrict = true;
2135 final boolean checkSecurity = true;
2136 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2137 }
2138 /** Check access and get the requested method, eliding receiver narrowing rules. */
2139 private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2140 final boolean doRestrict = false;
2141 final boolean checkSecurity = true;
2142 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2143 }
2144 /** Check access and get the requested method, eliding security manager checks. */
2145 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2146 final boolean doRestrict = true;
2147 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2148 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2149 }
2150 /** Common code for all methods; do not call directly except from immediately above. */
2151 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
2152 boolean checkSecurity,
2153 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
2154 checkMethod(refKind, refc, method);
2155 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2156 if (checkSecurity)
2157 checkSecurityManager(refc, method);
2158 assert(!method.isMethodHandleInvoke());
2159
2160 if (refKind == REF_invokeSpecial &&
2161 refc != lookupClass() &&
2162 !refc.isInterface() &&
2163 refc != lookupClass().getSuperclass() &&
2164 refc.isAssignableFrom(lookupClass())) {
2165 assert(!method.getName().equals("<init>")); // not this code path
2166 // Per JVMS 6.5, desc. of invokespecial instruction:
2167 // If the method is in a superclass of the LC,
2168 // and if our original search was above LC.super,
2169 // repeat the search (symbolic lookup) from LC.super
2170 // and continue with the direct superclass of that class,
2171 // and so forth, until a match is found or no further superclasses exist.
2172 // FIXME: MemberName.resolve should handle this instead.
2173 Class<?> refcAsSuper = lookupClass();
2174 MemberName m2;
2175 do {
2176 refcAsSuper = refcAsSuper.getSuperclass();
2177 m2 = new MemberName(refcAsSuper,
2178 method.getName(),
2179 method.getMethodType(),
2180 REF_invokeSpecial);
2181 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2182 } while (m2 == null && // no method is found yet
2183 refc != refcAsSuper); // search up to refc
2184 if (m2 == null) throw new InternalError(method.toString());
2185 method = m2;
2186 refc = refcAsSuper;
2187 // redo basic checks
2188 checkMethod(refKind, refc, method);
2189 }
2190
2191 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method);
2192 MethodHandle mh = dmh;
2193 // Optionally narrow the receiver argument to refc using restrictReceiver.
2194 if (doRestrict &&
2195 (refKind == REF_invokeSpecial ||
2196 (MethodHandleNatives.refKindHasReceiver(refKind) &&
2197 restrictProtectedReceiver(method)))) {
2198 mh = restrictReceiver(method, dmh, lookupClass());
2199 }
2200 mh = maybeBindCaller(method, mh, callerClass);
2201 mh = mh.setVarargs(method);
2202 return mh;
2203 }
2204 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2205 Class<?> callerClass)
2206 throws IllegalAccessException {
2207 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2208 return mh;
2209 Class<?> hostClass = lookupClass;
2210 if (!hasPrivateAccess()) // caller must have private access
2211 hostClass = callerClass; // callerClass came from a security manager style stack walk
2212 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2213 // Note: caller will apply varargs after this step happens.
2214 return cbmh;
2215 }
2216 /** Check access and get the requested field. */
2217 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2218 final boolean checkSecurity = true;
2219 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2220 }
2221 /** Check access and get the requested field, eliding security manager checks. */
2222 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2223 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2224 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2225 }
2226 /** Common code for all fields; do not call directly except from immediately above. */
2227 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2228 boolean checkSecurity) throws IllegalAccessException {
2229 checkField(refKind, refc, field);
2230 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2231 if (checkSecurity)
2232 checkSecurityManager(refc, field);
2233 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2234 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2235 restrictProtectedReceiver(field));
2236 if (doRestrict)
2237 return restrictReceiver(field, dmh, lookupClass());
2238 return dmh;
2239 }
2240 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2241 Class<?> refc, MemberName getField, MemberName putField)
2242 throws IllegalAccessException {
2243 final boolean checkSecurity = true;
2244 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2245 }
2246 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2247 Class<?> refc, MemberName getField, MemberName putField)
2248 throws IllegalAccessException {
2249 final boolean checkSecurity = false;
2250 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2251 }
2252 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2253 Class<?> refc, MemberName getField, MemberName putField,
2254 boolean checkSecurity) throws IllegalAccessException {
2255 assert getField.isStatic() == putField.isStatic();
2256 assert getField.isGetter() && putField.isSetter();
2257 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2258 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2259
2260 checkField(getRefKind, refc, getField);
2261 if (checkSecurity)
2262 checkSecurityManager(refc, getField);
2263
2264 if (!putField.isFinal()) {
2265 // A VarHandle does not support updates to final fields, any
2266 // such VarHandle to a final field will be read-only and
2267 // therefore the following write-based accessibility checks are
2268 // only required for non-final fields
2269 checkField(putRefKind, refc, putField);
2270 if (checkSecurity)
2271 checkSecurityManager(refc, putField);
2272 }
2273
2274 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2275 restrictProtectedReceiver(getField));
2276 if (doRestrict) {
2277 assert !getField.isStatic();
2278 // receiver type of VarHandle is too wide; narrow to caller
2279 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2280 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2281 }
2282 refc = lookupClass();
2283 }
2284 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2285 }
2286 /** Check access and get the requested constructor. */
2287 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2288 final boolean checkSecurity = true;
2289 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2290 }
2291 /** Check access and get the requested constructor, eliding security manager checks. */
2292 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2293 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2294 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2295 }
2296 /** Common code for all constructors; do not call directly except from immediately above. */
2297 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2298 boolean checkSecurity) throws IllegalAccessException {
2299 assert(ctor.isConstructor());
2300 checkAccess(REF_newInvokeSpecial, refc, ctor);
2301 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2302 if (checkSecurity)
2303 checkSecurityManager(refc, ctor);
2304 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2305 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2306 }
2307
2308 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2309 */
2310 /*non-public*/
2311 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2312 if (!(type instanceof Class || type instanceof MethodType))
2313 throw new InternalError("unresolved MemberName");
2314 MemberName member = new MemberName(refKind, defc, name, type);
2315 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2316 if (mh != null) {
2317 checkSymbolicClass(defc);
2318 return mh;
2319 }
2320 // Treat MethodHandle.invoke and invokeExact specially.
2321 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2322 mh = findVirtualForMH(member.getName(), member.getMethodType());
2323 if (mh != null) {
2324 return mh;
2325 }
2326 }
2327 MemberName resolved = resolveOrFail(refKind, member);
2328 mh = getDirectMethodForConstant(refKind, defc, resolved);
2329 if (mh instanceof DirectMethodHandle
2330 && canBeCached(refKind, defc, resolved)) {
2331 MemberName key = mh.internalMemberName();
2332 if (key != null) {
2333 key = key.asNormalOriginal();
2334 }
2335 if (member.equals(key)) { // better safe than sorry
2336 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2337 }
2338 }
2339 return mh;
2340 }
2341 private
2342 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2343 if (refKind == REF_invokeSpecial) {
2344 return false;
2345 }
2346 if (!Modifier.isPublic(defc.getModifiers()) ||
2347 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2348 !member.isPublic() ||
2349 member.isCallerSensitive()) {
2350 return false;
2351 }
2352 ClassLoader loader = defc.getClassLoader();
2353 if (!jdk.internal.misc.VM.isSystemDomainLoader(loader)) {
2354 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2355 boolean found = false;
2356 while (sysl != null) {
2357 if (loader == sysl) { found = true; break; }
2358 sysl = sysl.getParent();
2359 }
2360 if (!found) {
2361 return false;
2362 }
2363 }
2364 try {
2365 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
2366 new MemberName(refKind, defc, member.getName(), member.getType()));
2367 checkSecurityManager(defc, resolved2);
2368 } catch (ReflectiveOperationException | SecurityException ex) {
2369 return false;
2370 }
2371 return true;
2372 }
2373 private
2374 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2375 throws ReflectiveOperationException {
2376 if (MethodHandleNatives.refKindIsField(refKind)) {
2377 return getDirectFieldNoSecurityManager(refKind, defc, member);
2378 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2379 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2380 } else if (refKind == REF_newInvokeSpecial) {
2381 return getDirectConstructorNoSecurityManager(defc, member);
2382 }
2383 // oops
2384 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2385 }
2386
2387 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2388 }
2389
2390 /**
2391 * Produces a method handle constructing arrays of a desired type.
2392 * The return type of the method handle will be the array type.
2393 * The type of its sole argument will be {@code int}, which specifies the size of the array.
2394 * @param arrayClass an array type
2395 * @return a method handle which can create arrays of the given type
2396 * @throws NullPointerException if the argument is {@code null}
2397 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2398 * @see java.lang.reflect.Array#newInstance(Class, int)
2399 * @since 9
2400 */
2401 public static
2402 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2403 if (!arrayClass.isArray()) {
2404 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2405 }
2406 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2407 bindTo(arrayClass.getComponentType());
2408 return ani.asType(ani.type().changeReturnType(arrayClass));
2409 }
2410
2411 /**
2412 * Produces a method handle returning the length of an array.
2413 * The type of the method handle will have {@code int} as return type,
2414 * and its sole argument will be the array type.
2415 * @param arrayClass an array type
2416 * @return a method handle which can retrieve the length of an array of the given array type
2417 * @throws NullPointerException if the argument is {@code null}
2418 * @throws IllegalArgumentException if arrayClass is not an array type
2419 * @since 9
2420 */
2421 public static
2422 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2423 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2424 }
2425
2426 /**
2427 * Produces a method handle giving read access to elements of an array.
2428 * The type of the method handle will have a return type of the array's
2429 * element type. Its first argument will be the array type,
2430 * and the second will be {@code int}.
2431 * @param arrayClass an array type
2432 * @return a method handle which can load values from the given array type
2433 * @throws NullPointerException if the argument is null
2434 * @throws IllegalArgumentException if arrayClass is not an array type
2435 */
2436 public static
2437 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2438 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2439 }
2440
2441 /**
2442 * Produces a method handle giving write access to elements of an array.
2443 * The type of the method handle will have a void return type.
2444 * Its last argument will be the array's element type.
2445 * The first and second arguments will be the array type and int.
2446 * @param arrayClass the class of an array
2447 * @return a method handle which can store values into the array type
2448 * @throws NullPointerException if the argument is null
2449 * @throws IllegalArgumentException if arrayClass is not an array type
2450 */
2451 public static
2452 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2453 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2454 }
2455
2456 /**
2457 *
2458 * Produces a VarHandle giving access to elements of an array type
2459 * {@code T[]}, supporting shape {@code (T[], int : T)}.
2460 * <p>
2461 * Certain access modes of the returned VarHandle are unsupported under
2462 * the following conditions:
2463 * <ul>
2464 * <li>if the component type is anything other than {@code byte},
2465 * {@code short}, {@code char}, {@code int}, {@code long},
2466 * {@code float}, or {@code double} then numeric atomic update access
2467 * modes are unsupported.
2468 * <li>if the field type is anything other than {@code boolean},
2469 * {@code byte}, {@code short}, {@code char}, {@code int} or
2470 * {@code long} then bitwise atomic update access modes are
2471 * unsupported.
2472 * </ul>
2473 * <p>
2474 * If the component type is {@code float} or {@code double} then numeric
2475 * and atomic update access modes compare values using their bitwise
2476 * representation (see {@link Float#floatToRawIntBits} and
2477 * {@link Double#doubleToRawLongBits}, respectively).
2478 * @apiNote
2479 * Bitwise comparison of {@code float} values or {@code double} values,
2480 * as performed by the numeric and atomic update access modes, differ
2481 * from the primitive {@code ==} operator and the {@link Float#equals}
2482 * and {@link Double#equals} methods, specifically with respect to
2483 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2484 * Care should be taken when performing a compare and set or a compare
2485 * and exchange operation with such values since the operation may
2486 * unexpectedly fail.
2487 * There are many possible NaN values that are considered to be
2488 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2489 * provided by Java can distinguish between them. Operation failure can
2490 * occur if the expected or witness value is a NaN value and it is
2491 * transformed (perhaps in a platform specific manner) into another NaN
2492 * value, and thus has a different bitwise representation (see
2493 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2494 * details).
2495 * The values {@code -0.0} and {@code +0.0} have different bitwise
2496 * representations but are considered equal when using the primitive
2497 * {@code ==} operator. Operation failure can occur if, for example, a
2498 * numeric algorithm computes an expected value to be say {@code -0.0}
2499 * and previously computed the witness value to be say {@code +0.0}.
2500 * @param arrayClass the class of an array, of type {@code T[]}
2501 * @return a VarHandle giving access to elements of an array
2502 * @throws NullPointerException if the arrayClass is null
2503 * @throws IllegalArgumentException if arrayClass is not an array type
2504 * @since 9
2505 */
2506 public static
2507 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
2508 return VarHandles.makeArrayElementHandle(arrayClass);
2509 }
2510
2511 /**
2512 * Produces a VarHandle giving access to elements of a {@code byte[]} array
2513 * viewed as if it were a different primitive array type, such as
2514 * {@code int[]} or {@code long[]}. The shape of the resulting VarHandle is
2515 * {@code (byte[], int : T)}, where the {@code int} coordinate type
2516 * corresponds to an argument that is an index in a {@code byte[]} array,
2517 * and {@code T} is the component type of the given view array class. The
2518 * returned VarHandle accesses bytes at an index in a {@code byte[]} array,
2519 * composing bytes to or from a value of {@code T} according to the given
2520 * endianness.
2521 * <p>
2522 * The supported component types (variables types) are {@code short},
2523 * {@code char}, {@code int}, {@code long}, {@code float} and
2524 * {@code double}.
2525 * <p>
2526 * Access of bytes at a given index will result in an
2527 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2528 * or greater than the {@code byte[]} array length minus the size (in bytes)
2529 * of {@code T}.
2530 * <p>
2531 * Access of bytes at an index may be aligned or misaligned for {@code T},
2532 * with respect to the underlying memory address, {@code A} say, associated
2533 * with the array and index.
2534 * If access is misaligned then access for anything other than the
2535 * {@code get} and {@code set} access modes will result in an
2536 * {@code IllegalStateException}. In such cases atomic access is only
2537 * guaranteed with respect to the largest power of two that divides the GCD
2538 * of {@code A} and the size (in bytes) of {@code T}.
2539 * If access is aligned then following access modes are supported and are
2540 * guaranteed to support atomic access:
2541 * <ul>
2542 * <li>read write access modes for all {@code T}, with the exception of
2543 * access modes {@code get} and {@code set} for {@code long} and
2544 * {@code double} on 32-bit platforms.
2545 * <li>atomic update access modes for {@code int}, {@code long},
2546 * {@code float} or {@code double}.
2547 * (Future major platform releases of the JDK may support additional
2548 * types for certain currently unsupported access modes.)
2549 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2550 * (Future major platform releases of the JDK may support additional
2551 * numeric types for certain currently unsupported access modes.)
2552 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2553 * (Future major platform releases of the JDK may support additional
2554 * numeric types for certain currently unsupported access modes.)
2555 * </ul>
2556 * <p>
2557 * Misaligned access, and therefore atomicity guarantees, may be determined
2558 * for {@code byte[]} arrays without operating on a specific array. Given
2559 * an {@code index}, {@code T} and it's corresponding boxed type,
2560 * {@code T_BOX}, misalignment may be determined as follows:
2561 * <pre>{@code
2562 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2563 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
2564 * alignmentOffset(0, sizeOfT);
2565 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
2566 * boolean isMisaligned = misalignedAtIndex != 0;
2567 * }</pre>
2568 * <p>
2569 * If the variable type is {@code float} or {@code double} then atomic
2570 * update access modes compare values using their bitwise representation
2571 * (see {@link Float#floatToRawIntBits} and
2572 * {@link Double#doubleToRawLongBits}, respectively).
2573 * @param viewArrayClass the view array class, with a component type of
2574 * type {@code T}
2575 * @param byteOrder the endianness of the view array elements, as
2576 * stored in the underlying {@code byte} array
2577 * @return a VarHandle giving access to elements of a {@code byte[]} array
2578 * viewed as if elements corresponding to the components type of the view
2579 * array class
2580 * @throws NullPointerException if viewArrayClass or byteOrder is null
2581 * @throws IllegalArgumentException if viewArrayClass is not an array type
2582 * @throws UnsupportedOperationException if the component type of
2583 * viewArrayClass is not supported as a variable type
2584 * @since 9
2585 */
2586 public static
2587 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
2588 ByteOrder byteOrder) throws IllegalArgumentException {
2589 Objects.requireNonNull(byteOrder);
2590 return VarHandles.byteArrayViewHandle(viewArrayClass,
2591 byteOrder == ByteOrder.BIG_ENDIAN);
2592 }
2593
2594 /**
2595 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
2596 * viewed as if it were an array of elements of a different primitive
2597 * component type to that of {@code byte}, such as {@code int[]} or
2598 * {@code long[]}. The shape of the resulting VarHandle is
2599 * {@code (ByteBuffer, int : T)}, where the {@code int} coordinate type
2600 * corresponds to an argument that is an index in a {@code ByteBuffer}, and
2601 * {@code T} is the component type of the given view array class. The
2602 * returned VarHandle accesses bytes at an index in a {@code ByteBuffer},
2603 * composing bytes to or from a value of {@code T} according to the given
2604 * endianness.
2605 * <p>
2606 * The supported component types (variables types) are {@code short},
2607 * {@code char}, {@code int}, {@code long}, {@code float} and
2608 * {@code double}.
2609 * <p>
2610 * Access will result in a {@code ReadOnlyBufferException} for anything
2611 * other than the read access modes if the {@code ByteBuffer} is read-only.
2612 * <p>
2613 * Access of bytes at a given index will result in an
2614 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2615 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
2616 * {@code T}.
2617 * <p>
2618 * Access of bytes at an index may be aligned or misaligned for {@code T},
2619 * with respect to the underlying memory address, {@code A} say, associated
2620 * with the {@code ByteBuffer} and index.
2621 * If access is misaligned then access for anything other than the
2622 * {@code get} and {@code set} access modes will result in an
2623 * {@code IllegalStateException}. In such cases atomic access is only
2624 * guaranteed with respect to the largest power of two that divides the GCD
2625 * of {@code A} and the size (in bytes) of {@code T}.
2626 * If access is aligned then following access modes are supported and are
2627 * guaranteed to support atomic access:
2628 * <ul>
2629 * <li>read write access modes for all {@code T}, with the exception of
2630 * access modes {@code get} and {@code set} for {@code long} and
2631 * {@code double} on 32-bit platforms.
2632 * <li>atomic update access modes for {@code int}, {@code long},
2633 * {@code float} or {@code double}.
2634 * (Future major platform releases of the JDK may support additional
2635 * types for certain currently unsupported access modes.)
2636 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2637 * (Future major platform releases of the JDK may support additional
2638 * numeric types for certain currently unsupported access modes.)
2639 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2640 * (Future major platform releases of the JDK may support additional
2641 * numeric types for certain currently unsupported access modes.)
2642 * </ul>
2643 * <p>
2644 * Misaligned access, and therefore atomicity guarantees, may be determined
2645 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
2646 * {@code index}, {@code T} and it's corresponding boxed type,
2647 * {@code T_BOX}, as follows:
2648 * <pre>{@code
2649 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2650 * ByteBuffer bb = ...
2651 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
2652 * boolean isMisaligned = misalignedAtIndex != 0;
2653 * }</pre>
2654 * <p>
2655 * If the variable type is {@code float} or {@code double} then atomic
2656 * update access modes compare values using their bitwise representation
2657 * (see {@link Float#floatToRawIntBits} and
2658 * {@link Double#doubleToRawLongBits}, respectively).
2659 * @param viewArrayClass the view array class, with a component type of
2660 * type {@code T}
2661 * @param byteOrder the endianness of the view array elements, as
2662 * stored in the underlying {@code ByteBuffer} (Note this overrides the
2663 * endianness of a {@code ByteBuffer})
2664 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
2665 * viewed as if elements corresponding to the components type of the view
2666 * array class
2667 * @throws NullPointerException if viewArrayClass or byteOrder is null
2668 * @throws IllegalArgumentException if viewArrayClass is not an array type
2669 * @throws UnsupportedOperationException if the component type of
2670 * viewArrayClass is not supported as a variable type
2671 * @since 9
2672 */
2673 public static
2674 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
2675 ByteOrder byteOrder) throws IllegalArgumentException {
2676 Objects.requireNonNull(byteOrder);
2677 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
2678 byteOrder == ByteOrder.BIG_ENDIAN);
2679 }
2680
2681
2682 /// method handle invocation (reflective style)
2683
2684 /**
2685 * Produces a method handle which will invoke any method handle of the
2686 * given {@code type}, with a given number of trailing arguments replaced by
2687 * a single trailing {@code Object[]} array.
2688 * The resulting invoker will be a method handle with the following
2689 * arguments:
2690 * <ul>
2691 * <li>a single {@code MethodHandle} target
2692 * <li>zero or more leading values (counted by {@code leadingArgCount})
2693 * <li>an {@code Object[]} array containing trailing arguments
2694 * </ul>
2695 * <p>
2696 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
2697 * the indicated {@code type}.
2698 * That is, if the target is exactly of the given {@code type}, it will behave
2699 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
2700 * is used to convert the target to the required {@code type}.
2701 * <p>
2702 * The type of the returned invoker will not be the given {@code type}, but rather
2703 * will have all parameters except the first {@code leadingArgCount}
2704 * replaced by a single array of type {@code Object[]}, which will be
2705 * the final parameter.
2706 * <p>
2707 * Before invoking its target, the invoker will spread the final array, apply
2708 * reference casts as necessary, and unbox and widen primitive arguments.
2709 * If, when the invoker is called, the supplied array argument does
2710 * not have the correct number of elements, the invoker will throw
2711 * an {@link IllegalArgumentException} instead of invoking the target.
2712 * <p>
2713 * This method is equivalent to the following code (though it may be more efficient):
2714 * <blockquote><pre>{@code
2715 MethodHandle invoker = MethodHandles.invoker(type);
2716 int spreadArgCount = type.parameterCount() - leadingArgCount;
2717 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
2718 return invoker;
2719 * }</pre></blockquote>
2720 * This method throws no reflective or security exceptions.
2721 * @param type the desired target type
2722 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
2723 * @return a method handle suitable for invoking any method handle of the given type
2724 * @throws NullPointerException if {@code type} is null
2725 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
2726 * the range from 0 to {@code type.parameterCount()} inclusive,
2727 * or if the resulting method handle's type would have
2728 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2729 */
2730 public static
2731 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
2732 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
2733 throw newIllegalArgumentException("bad argument count", leadingArgCount);
2734 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
2735 return type.invokers().spreadInvoker(leadingArgCount);
2736 }
2737
2738 /**
2739 * Produces a special <em>invoker method handle</em> which can be used to
2740 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
2741 * The resulting invoker will have a type which is
2742 * exactly equal to the desired type, except that it will accept
2743 * an additional leading argument of type {@code MethodHandle}.
2744 * <p>
2745 * This method is equivalent to the following code (though it may be more efficient):
2746 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
2747 *
2748 * <p style="font-size:smaller;">
2749 * <em>Discussion:</em>
2750 * Invoker method handles can be useful when working with variable method handles
2751 * of unknown types.
2752 * For example, to emulate an {@code invokeExact} call to a variable method
2753 * handle {@code M}, extract its type {@code T},
2754 * look up the invoker method {@code X} for {@code T},
2755 * and call the invoker method, as {@code X.invoke(T, A...)}.
2756 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
2757 * is unknown.)
2758 * If spreading, collecting, or other argument transformations are required,
2759 * they can be applied once to the invoker {@code X} and reused on many {@code M}
2760 * method handle values, as long as they are compatible with the type of {@code X}.
2761 * <p style="font-size:smaller;">
2762 * <em>(Note: The invoker method is not available via the Core Reflection API.
2763 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2764 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2765 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2766 * <p>
2767 * This method throws no reflective or security exceptions.
2768 * @param type the desired target type
2769 * @return a method handle suitable for invoking any method handle of the given type
2770 * @throws IllegalArgumentException if the resulting method handle's type would have
2771 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2772 */
2773 public static
2774 MethodHandle exactInvoker(MethodType type) {
2775 return type.invokers().exactInvoker();
2776 }
2777
2778 /**
2779 * Produces a special <em>invoker method handle</em> which can be used to
2780 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2781 * The resulting invoker will have a type which is
2782 * exactly equal to the desired type, except that it will accept
2783 * an additional leading argument of type {@code MethodHandle}.
2784 * <p>
2785 * Before invoking its target, if the target differs from the expected type,
2786 * the invoker will apply reference casts as
2787 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
2788 * Similarly, the return value will be converted as necessary.
2789 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
2790 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
2791 * <p>
2792 * This method is equivalent to the following code (though it may be more efficient):
2793 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
2794 * <p style="font-size:smaller;">
2795 * <em>Discussion:</em>
2796 * A {@linkplain MethodType#genericMethodType general method type} is one which
2797 * mentions only {@code Object} arguments and return values.
2798 * An invoker for such a type is capable of calling any method handle
2799 * of the same arity as the general type.
2800 * <p style="font-size:smaller;">
2801 * <em>(Note: The invoker method is not available via the Core Reflection API.
2802 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2803 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2804 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2805 * <p>
2806 * This method throws no reflective or security exceptions.
2807 * @param type the desired target type
2808 * @return a method handle suitable for invoking any method handle convertible to the given type
2809 * @throws IllegalArgumentException if the resulting method handle's type would have
2810 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2811 */
2812 public static
2813 MethodHandle invoker(MethodType type) {
2814 return type.invokers().genericInvoker();
2815 }
2816
2817 /**
2818 * Produces a special <em>invoker method handle</em> which can be used to
2819 * invoke a signature-polymorphic access mode method on any VarHandle whose
2820 * associated access mode type is compatible with the given type.
2821 * The resulting invoker will have a type which is exactly equal to the
2822 * desired given type, except that it will accept an additional leading
2823 * argument of type {@code VarHandle}.
2824 *
2825 * @param accessMode the VarHandle access mode
2826 * @param type the desired target type
2827 * @return a method handle suitable for invoking an access mode method of
2828 * any VarHandle whose access mode type is of the given type.
2829 * @since 9
2830 */
2831 static public
2832 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
2833 return type.invokers().varHandleMethodExactInvoker(accessMode);
2834 }
2835
2836 /**
2837 * Produces a special <em>invoker method handle</em> which can be used to
2838 * invoke a signature-polymorphic access mode method on any VarHandle whose
2839 * associated access mode type is compatible with the given type.
2840 * The resulting invoker will have a type which is exactly equal to the
2841 * desired given type, except that it will accept an additional leading
2842 * argument of type {@code VarHandle}.
2843 * <p>
2844 * Before invoking its target, if the access mode type differs from the
2845 * desired given type, the invoker will apply reference casts as necessary
2846 * and box, unbox, or widen primitive values, as if by
2847 * {@link MethodHandle#asType asType}. Similarly, the return value will be
2848 * converted as necessary.
2849 * <p>
2850 * This method is equivalent to the following code (though it may be more
2851 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
2852 *
2853 * @param accessMode the VarHandle access mode
2854 * @param type the desired target type
2855 * @return a method handle suitable for invoking an access mode method of
2856 * any VarHandle whose access mode type is convertible to the given
2857 * type.
2858 * @since 9
2859 */
2860 static public
2861 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
2862 return type.invokers().varHandleMethodInvoker(accessMode);
2863 }
2864
2865 static /*non-public*/
2866 MethodHandle basicInvoker(MethodType type) {
2867 return type.invokers().basicInvoker();
2868 }
2869
2870 /// method handle modification (creation from other method handles)
2871
2872 /**
2873 * Produces a method handle which adapts the type of the
2874 * given method handle to a new type by pairwise argument and return type conversion.
2875 * The original type and new type must have the same number of arguments.
2876 * The resulting method handle is guaranteed to report a type
2877 * which is equal to the desired new type.
2878 * <p>
2879 * If the original type and new type are equal, returns target.
2880 * <p>
2881 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
2882 * and some additional conversions are also applied if those conversions fail.
2883 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
2884 * if possible, before or instead of any conversions done by {@code asType}:
2885 * <ul>
2886 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
2887 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
2888 * (This treatment of interfaces follows the usage of the bytecode verifier.)
2889 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
2890 * the boolean is converted to a byte value, 1 for true, 0 for false.
2891 * (This treatment follows the usage of the bytecode verifier.)
2892 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
2893 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
2894 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
2895 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
2896 * then a Java casting conversion (JLS 5.5) is applied.
2897 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
2898 * widening and/or narrowing.)
2899 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
2900 * conversion will be applied at runtime, possibly followed
2901 * by a Java casting conversion (JLS 5.5) on the primitive value,
2902 * possibly followed by a conversion from byte to boolean by testing
2903 * the low-order bit.
2904 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
2905 * and if the reference is null at runtime, a zero value is introduced.
2906 * </ul>
2907 * @param target the method handle to invoke after arguments are retyped
2908 * @param newType the expected type of the new method handle
2909 * @return a method handle which delegates to the target after performing
2910 * any necessary argument conversions, and arranges for any
2911 * necessary return value conversions
2912 * @throws NullPointerException if either argument is null
2913 * @throws WrongMethodTypeException if the conversion cannot be made
2914 * @see MethodHandle#asType
2915 */
2916 public static
2917 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
2918 explicitCastArgumentsChecks(target, newType);
2919 // use the asTypeCache when possible:
2920 MethodType oldType = target.type();
2921 if (oldType == newType) return target;
2922 if (oldType.explicitCastEquivalentToAsType(newType)) {
2923 return target.asFixedArity().asType(newType);
2924 }
2925 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
2926 }
2927
2928 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
2929 if (target.type().parameterCount() != newType.parameterCount()) {
2930 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
2931 }
2932 }
2933
2934 /**
2935 * Produces a method handle which adapts the calling sequence of the
2936 * given method handle to a new type, by reordering the arguments.
2937 * The resulting method handle is guaranteed to report a type
2938 * which is equal to the desired new type.
2939 * <p>
2940 * The given array controls the reordering.
2941 * Call {@code #I} the number of incoming parameters (the value
2942 * {@code newType.parameterCount()}, and call {@code #O} the number
2943 * of outgoing parameters (the value {@code target.type().parameterCount()}).
2944 * Then the length of the reordering array must be {@code #O},
2945 * and each element must be a non-negative number less than {@code #I}.
2946 * For every {@code N} less than {@code #O}, the {@code N}-th
2947 * outgoing argument will be taken from the {@code I}-th incoming
2948 * argument, where {@code I} is {@code reorder[N]}.
2949 * <p>
2950 * No argument or return value conversions are applied.
2951 * The type of each incoming argument, as determined by {@code newType},
2952 * must be identical to the type of the corresponding outgoing parameter
2953 * or parameters in the target method handle.
2954 * The return type of {@code newType} must be identical to the return
2955 * type of the original target.
2956 * <p>
2957 * The reordering array need not specify an actual permutation.
2958 * An incoming argument will be duplicated if its index appears
2959 * more than once in the array, and an incoming argument will be dropped
2960 * if its index does not appear in the array.
2961 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
2962 * incoming arguments which are not mentioned in the reordering array
2963 * may be of any type, as determined only by {@code newType}.
2964 * <blockquote><pre>{@code
2965 import static java.lang.invoke.MethodHandles.*;
2966 import static java.lang.invoke.MethodType.*;
2967 ...
2968 MethodType intfn1 = methodType(int.class, int.class);
2969 MethodType intfn2 = methodType(int.class, int.class, int.class);
2970 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
2971 assert(sub.type().equals(intfn2));
2972 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
2973 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
2974 assert((int)rsub.invokeExact(1, 100) == 99);
2975 MethodHandle add = ... (int x, int y) -> (x+y) ...;
2976 assert(add.type().equals(intfn2));
2977 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
2978 assert(twice.type().equals(intfn1));
2979 assert((int)twice.invokeExact(21) == 42);
2980 * }</pre></blockquote>
2981 * <p>
2982 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
2983 * variable-arity method handle}, even if the original target method handle was.
2984 * @param target the method handle to invoke after arguments are reordered
2985 * @param newType the expected type of the new method handle
2986 * @param reorder an index array which controls the reordering
2987 * @return a method handle which delegates to the target after it
2988 * drops unused arguments and moves and/or duplicates the other arguments
2989 * @throws NullPointerException if any argument is null
2990 * @throws IllegalArgumentException if the index array length is not equal to
2991 * the arity of the target, or if any index array element
2992 * not a valid index for a parameter of {@code newType},
2993 * or if two corresponding parameter types in
2994 * {@code target.type()} and {@code newType} are not identical,
2995 */
2996 public static
2997 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
2998 reorder = reorder.clone(); // get a private copy
2999 MethodType oldType = target.type();
3000 permuteArgumentChecks(reorder, newType, oldType);
3001 // first detect dropped arguments and handle them separately
3002 int[] originalReorder = reorder;
3003 BoundMethodHandle result = target.rebind();
3004 LambdaForm form = result.form;
3005 int newArity = newType.parameterCount();
3006 // Normalize the reordering into a real permutation,
3007 // by removing duplicates and adding dropped elements.
3008 // This somewhat improves lambda form caching, as well
3009 // as simplifying the transform by breaking it up into steps.
3010 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3011 if (ddIdx > 0) {
3012 // We found a duplicated entry at reorder[ddIdx].
3013 // Example: (x,y,z)->asList(x,y,z)
3014 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3015 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3016 // The starred element corresponds to the argument
3017 // deleted by the dupArgumentForm transform.
3018 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3019 boolean killFirst = false;
3020 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3021 // Set killFirst if the dup is larger than an intervening position.
3022 // This will remove at least one inversion from the permutation.
3023 if (dupVal > val) killFirst = true;
3024 }
3025 if (!killFirst) {
3026 srcPos = dstPos;
3027 dstPos = ddIdx;
3028 }
3029 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3030 assert (reorder[srcPos] == reorder[dstPos]);
3031 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3032 // contract the reordering by removing the element at dstPos
3033 int tailPos = dstPos + 1;
3034 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3035 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3036 } else {
3037 int dropVal = ~ddIdx, insPos = 0;
3038 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3039 // Find first element of reorder larger than dropVal.
3040 // This is where we will insert the dropVal.
3041 insPos += 1;
3042 }
3043 Class<?> ptype = newType.parameterType(dropVal);
3044 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3045 oldType = oldType.insertParameterTypes(insPos, ptype);
3046 // expand the reordering by inserting an element at insPos
3047 int tailPos = insPos + 1;
3048 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3049 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3050 reorder[insPos] = dropVal;
3051 }
3052 assert (permuteArgumentChecks(reorder, newType, oldType));
3053 }
3054 assert (reorder.length == newArity); // a perfect permutation
3055 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3056 form = form.editor().permuteArgumentsForm(1, reorder);
3057 if (newType == result.type() && form == result.internalForm())
3058 return result;
3059 return result.copyWith(newType, form);
3060 }
3061
3062 /**
3063 * Return an indication of any duplicate or omission in reorder.
3064 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3065 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3066 * Otherwise, return zero.
3067 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3068 */
3069 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3070 final int BIT_LIMIT = 63; // max number of bits in bit mask
3071 if (newArity < BIT_LIMIT) {
3072 long mask = 0;
3073 for (int i = 0; i < reorder.length; i++) {
3074 int arg = reorder[i];
3075 if (arg >= newArity) {
3076 return reorder.length;
3077 }
3078 long bit = 1L << arg;
3079 if ((mask & bit) != 0) {
3080 return i; // >0 indicates a dup
3081 }
3082 mask |= bit;
3083 }
3084 if (mask == (1L << newArity) - 1) {
3085 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
3086 return 0;
3087 }
3088 // find first zero
3089 long zeroBit = Long.lowestOneBit(~mask);
3090 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
3091 assert(zeroPos <= newArity);
3092 if (zeroPos == newArity) {
3093 return 0;
3094 }
3095 return ~zeroPos;
3096 } else {
3097 // same algorithm, different bit set
3098 BitSet mask = new BitSet(newArity);
3099 for (int i = 0; i < reorder.length; i++) {
3100 int arg = reorder[i];
3101 if (arg >= newArity) {
3102 return reorder.length;
3103 }
3104 if (mask.get(arg)) {
3105 return i; // >0 indicates a dup
3106 }
3107 mask.set(arg);
3108 }
3109 int zeroPos = mask.nextClearBit(0);
3110 assert(zeroPos <= newArity);
3111 if (zeroPos == newArity) {
3112 return 0;
3113 }
3114 return ~zeroPos;
3115 }
3116 }
3117
3118 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
3119 if (newType.returnType() != oldType.returnType())
3120 throw newIllegalArgumentException("return types do not match",
3121 oldType, newType);
3122 if (reorder.length == oldType.parameterCount()) {
3123 int limit = newType.parameterCount();
3124 boolean bad = false;
3125 for (int j = 0; j < reorder.length; j++) {
3126 int i = reorder[j];
3127 if (i < 0 || i >= limit) {
3128 bad = true; break;
3129 }
3130 Class<?> src = newType.parameterType(i);
3131 Class<?> dst = oldType.parameterType(j);
3132 if (src != dst)
3133 throw newIllegalArgumentException("parameter types do not match after reorder",
3134 oldType, newType);
3135 }
3136 if (!bad) return true;
3137 }
3138 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3139 }
3140
3141 /**
3142 * Produces a method handle of the requested return type which returns the given
3143 * constant value every time it is invoked.
3144 * <p>
3145 * Before the method handle is returned, the passed-in value is converted to the requested type.
3146 * If the requested type is primitive, widening primitive conversions are attempted,
3147 * else reference conversions are attempted.
3148 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3149 * @param type the return type of the desired method handle
3150 * @param value the value to return
3151 * @return a method handle of the given return type and no arguments, which always returns the given value
3152 * @throws NullPointerException if the {@code type} argument is null
3153 * @throws ClassCastException if the value cannot be converted to the required return type
3154 * @throws IllegalArgumentException if the given type is {@code void.class}
3155 */
3156 public static
3157 MethodHandle constant(Class<?> type, Object value) {
3158 if (type.isPrimitive()) {
3159 if (type == void.class)
3160 throw newIllegalArgumentException("void type");
3161 Wrapper w = Wrapper.forPrimitiveType(type);
3162 value = w.convert(value, type);
3163 if (w.zero().equals(value))
3164 return zero(w, type);
3165 return insertArguments(identity(type), 0, value);
3166 } else {
3167 if (value == null)
3168 return zero(Wrapper.OBJECT, type);
3169 return identity(type).bindTo(value);
3170 }
3171 }
3172
3173 /**
3174 * Produces a method handle which returns its sole argument when invoked.
3175 * @param type the type of the sole parameter and return value of the desired method handle
3176 * @return a unary method handle which accepts and returns the given type
3177 * @throws NullPointerException if the argument is null
3178 * @throws IllegalArgumentException if the given type is {@code void.class}
3179 */
3180 public static
3181 MethodHandle identity(Class<?> type) {
3182 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3183 int pos = btw.ordinal();
3184 MethodHandle ident = IDENTITY_MHS[pos];
3185 if (ident == null) {
3186 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3187 }
3188 if (ident.type().returnType() == type)
3189 return ident;
3190 // something like identity(Foo.class); do not bother to intern these
3191 assert (btw == Wrapper.OBJECT);
3192 return makeIdentity(type);
3193 }
3194
3195 /**
3196 * Produces a constant method handle of the requested return type which
3197 * returns the default value for that type every time it is invoked.
3198 * The resulting constant method handle will have no side effects.
3199 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3200 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3201 * since {@code explicitCastArguments} converts {@code null} to default values.
3202 * @param type the expected return type of the desired method handle
3203 * @return a constant method handle that takes no arguments
3204 * and returns the default value of the given type (or void, if the type is void)
3205 * @throws NullPointerException if the argument is null
3206 * @see MethodHandles#constant
3207 * @see MethodHandles#empty
3208 * @see MethodHandles#explicitCastArguments
3209 * @since 9
3210 */
3211 public static MethodHandle zero(Class<?> type) {
3212 Objects.requireNonNull(type);
3213 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
3214 }
3215
3216 private static MethodHandle identityOrVoid(Class<?> type) {
3217 return type == void.class ? zero(type) : identity(type);
3218 }
3219
3220 /**
3221 * Produces a method handle of the requested type which ignores any arguments, does nothing,
3222 * and returns a suitable default depending on the return type.
3223 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3224 * <p>The returned method handle is equivalent to
3225 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3226 * <p>
3227 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3228 * {@code guardWithTest(pred, target, empty(target.type())}.
3229 * @param type the type of the desired method handle
3230 * @return a constant method handle of the given type, which returns a default value of the given return type
3231 * @throws NullPointerException if the argument is null
3232 * @see MethodHandles#zero
3233 * @see MethodHandles#constant
3234 * @since 9
3235 */
3236 public static MethodHandle empty(MethodType type) {
3237 Objects.requireNonNull(type);
3238 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3239 }
3240
3241 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
3242 private static MethodHandle makeIdentity(Class<?> ptype) {
3243 MethodType mtype = methodType(ptype, ptype);
3244 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3245 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3246 }
3247
3248 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3249 int pos = btw.ordinal();
3250 MethodHandle zero = ZERO_MHS[pos];
3251 if (zero == null) {
3252 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3253 }
3254 if (zero.type().returnType() == rtype)
3255 return zero;
3256 assert(btw == Wrapper.OBJECT);
3257 return makeZero(rtype);
3258 }
3259 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
3260 private static MethodHandle makeZero(Class<?> rtype) {
3261 MethodType mtype = methodType(rtype);
3262 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3263 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3264 }
3265
3266 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3267 // Simulate a CAS, to avoid racy duplication of results.
3268 MethodHandle prev = cache[pos];
3269 if (prev != null) return prev;
3270 return cache[pos] = value;
3271 }
3272
3273 /**
3274 * Provides a target method handle with one or more <em>bound arguments</em>
3275 * in advance of the method handle's invocation.
3276 * The formal parameters to the target corresponding to the bound
3277 * arguments are called <em>bound parameters</em>.
3278 * Returns a new method handle which saves away the bound arguments.
3279 * When it is invoked, it receives arguments for any non-bound parameters,
3280 * binds the saved arguments to their corresponding parameters,
3281 * and calls the original target.
3282 * <p>
3283 * The type of the new method handle will drop the types for the bound
3284 * parameters from the original target type, since the new method handle
3285 * will no longer require those arguments to be supplied by its callers.
3286 * <p>
3287 * Each given argument object must match the corresponding bound parameter type.
3288 * If a bound parameter type is a primitive, the argument object
3289 * must be a wrapper, and will be unboxed to produce the primitive value.
3290 * <p>
3291 * The {@code pos} argument selects which parameters are to be bound.
3292 * It may range between zero and <i>N-L</i> (inclusively),
3293 * where <i>N</i> is the arity of the target method handle
3294 * and <i>L</i> is the length of the values array.
3295 * <p>
3296 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3297 * variable-arity method handle}, even if the original target method handle was.
3298 * @param target the method handle to invoke after the argument is inserted
3299 * @param pos where to insert the argument (zero for the first)
3300 * @param values the series of arguments to insert
3301 * @return a method handle which inserts an additional argument,
3302 * before calling the original method handle
3303 * @throws NullPointerException if the target or the {@code values} array is null
3304 * @see MethodHandle#bindTo
3305 */
3306 public static
3307 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3308 int insCount = values.length;
3309 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3310 if (insCount == 0) return target;
3311 BoundMethodHandle result = target.rebind();
3312 for (int i = 0; i < insCount; i++) {
3313 Object value = values[i];
3314 Class<?> ptype = ptypes[pos+i];
3315 if (ptype.isPrimitive()) {
3316 result = insertArgumentPrimitive(result, pos, ptype, value);
3317 } else {
3318 value = ptype.cast(value); // throw CCE if needed
3319 result = result.bindArgumentL(pos, value);
3320 }
3321 }
3322 return result;
3323 }
3324
3325 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3326 Class<?> ptype, Object value) {
3327 Wrapper w = Wrapper.forPrimitiveType(ptype);
3328 // perform unboxing and/or primitive conversion
3329 value = w.convert(value, ptype);
3330 switch (w) {
3331 case INT: return result.bindArgumentI(pos, (int)value);
3332 case LONG: return result.bindArgumentJ(pos, (long)value);
3333 case FLOAT: return result.bindArgumentF(pos, (float)value);
3334 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3335 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3336 }
3337 }
3338
3339 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3340 MethodType oldType = target.type();
3341 int outargs = oldType.parameterCount();
3342 int inargs = outargs - insCount;
3343 if (inargs < 0)
3344 throw newIllegalArgumentException("too many values to insert");
3345 if (pos < 0 || pos > inargs)
3346 throw newIllegalArgumentException("no argument type to append");
3347 return oldType.ptypes();
3348 }
3349
3350 /**
3351 * Produces a method handle which will discard some dummy arguments
3352 * before calling some other specified <i>target</i> method handle.
3353 * The type of the new method handle will be the same as the target's type,
3354 * except it will also include the dummy argument types,
3355 * at some given position.
3356 * <p>
3357 * The {@code pos} argument may range between zero and <i>N</i>,
3358 * where <i>N</i> is the arity of the target.
3359 * If {@code pos} is zero, the dummy arguments will precede
3360 * the target's real arguments; if {@code pos} is <i>N</i>
3361 * they will come after.
3362 * <p>
3363 * <b>Example:</b>
3364 * <blockquote><pre>{@code
3365 import static java.lang.invoke.MethodHandles.*;
3366 import static java.lang.invoke.MethodType.*;
3367 ...
3368 MethodHandle cat = lookup().findVirtual(String.class,
3369 "concat", methodType(String.class, String.class));
3370 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3371 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3372 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3373 assertEquals(bigType, d0.type());
3374 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3375 * }</pre></blockquote>
3376 * <p>
3377 * This method is also equivalent to the following code:
3378 * <blockquote><pre>
3379 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3380 * </pre></blockquote>
3381 * @param target the method handle to invoke after the arguments are dropped
3382 * @param valueTypes the type(s) of the argument(s) to drop
3383 * @param pos position of first argument to drop (zero for the leftmost)
3384 * @return a method handle which drops arguments of the given types,
3385 * before calling the original method handle
3386 * @throws NullPointerException if the target is null,
3387 * or if the {@code valueTypes} list or any of its elements is null
3388 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3389 * or if {@code pos} is negative or greater than the arity of the target,
3390 * or if the new method handle's type would have too many parameters
3391 */
3392 public static
3393 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3394 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
3395 }
3396
3397 private static List<Class<?>> copyTypes(Object[] array) {
3398 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
3399 }
3400
3401 private static
3402 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3403 MethodType oldType = target.type(); // get NPE
3404 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3405 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3406 if (dropped == 0) return target;
3407 BoundMethodHandle result = target.rebind();
3408 LambdaForm lform = result.form;
3409 int insertFormArg = 1 + pos;
3410 for (Class<?> ptype : valueTypes) {
3411 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3412 }
3413 result = result.copyWith(newType, lform);
3414 return result;
3415 }
3416
3417 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3418 int dropped = valueTypes.size();
3419 MethodType.checkSlotCount(dropped);
3420 int outargs = oldType.parameterCount();
3421 int inargs = outargs + dropped;
3422 if (pos < 0 || pos > outargs)
3423 throw newIllegalArgumentException("no argument type to remove"
3424 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3425 );
3426 return dropped;
3427 }
3428
3429 /**
3430 * Produces a method handle which will discard some dummy arguments
3431 * before calling some other specified <i>target</i> method handle.
3432 * The type of the new method handle will be the same as the target's type,
3433 * except it will also include the dummy argument types,
3434 * at some given position.
3435 * <p>
3436 * The {@code pos} argument may range between zero and <i>N</i>,
3437 * where <i>N</i> is the arity of the target.
3438 * If {@code pos} is zero, the dummy arguments will precede
3439 * the target's real arguments; if {@code pos} is <i>N</i>
3440 * they will come after.
3441 * @apiNote
3442 * <blockquote><pre>{@code
3443 import static java.lang.invoke.MethodHandles.*;
3444 import static java.lang.invoke.MethodType.*;
3445 ...
3446 MethodHandle cat = lookup().findVirtual(String.class,
3447 "concat", methodType(String.class, String.class));
3448 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3449 MethodHandle d0 = dropArguments(cat, 0, String.class);
3450 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3451 MethodHandle d1 = dropArguments(cat, 1, String.class);
3452 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
3453 MethodHandle d2 = dropArguments(cat, 2, String.class);
3454 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
3455 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
3456 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
3457 * }</pre></blockquote>
3458 * <p>
3459 * This method is also equivalent to the following code:
3460 * <blockquote><pre>
3461 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
3462 * </pre></blockquote>
3463 * @param target the method handle to invoke after the arguments are dropped
3464 * @param valueTypes the type(s) of the argument(s) to drop
3465 * @param pos position of first argument to drop (zero for the leftmost)
3466 * @return a method handle which drops arguments of the given types,
3467 * before calling the original method handle
3468 * @throws NullPointerException if the target is null,
3469 * or if the {@code valueTypes} array or any of its elements is null
3470 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3471 * or if {@code pos} is negative or greater than the arity of the target,
3472 * or if the new method handle's type would have
3473 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3474 */
3475 public static
3476 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
3477 return dropArguments0(target, pos, copyTypes(valueTypes));
3478 }
3479
3480 // private version which allows caller some freedom with error handling
3481 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
3482 boolean nullOnFailure) {
3483 newTypes = copyTypes(newTypes.toArray());
3484 List<Class<?>> oldTypes = target.type().parameterList();
3485 int match = oldTypes.size();
3486 if (skip != 0) {
3487 if (skip < 0 || skip > match) {
3488 throw newIllegalArgumentException("illegal skip", skip, target);
3489 }
3490 oldTypes = oldTypes.subList(skip, match);
3491 match -= skip;
3492 }
3493 List<Class<?>> addTypes = newTypes;
3494 int add = addTypes.size();
3495 if (pos != 0) {
3496 if (pos < 0 || pos > add) {
3497 throw newIllegalArgumentException("illegal pos", pos, newTypes);
3498 }
3499 addTypes = addTypes.subList(pos, add);
3500 add -= pos;
3501 assert(addTypes.size() == add);
3502 }
3503 // Do not add types which already match the existing arguments.
3504 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
3505 if (nullOnFailure) {
3506 return null;
3507 }
3508 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
3509 }
3510 addTypes = addTypes.subList(match, add);
3511 add -= match;
3512 assert(addTypes.size() == add);
3513 // newTypes: ( P*[pos], M*[match], A*[add] )
3514 // target: ( S*[skip], M*[match] )
3515 MethodHandle adapter = target;
3516 if (add > 0) {
3517 adapter = dropArguments0(adapter, skip+ match, addTypes);
3518 }
3519 // adapter: (S*[skip], M*[match], A*[add] )
3520 if (pos > 0) {
3521 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
3522 }
3523 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
3524 return adapter;
3525 }
3526
3527 /**
3528 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
3529 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
3530 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
3531 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
3532 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
3533 * {@link #dropArguments(MethodHandle, int, Class[])}.
3534 * <p>
3535 * The resulting handle will have the same return type as the target handle.
3536 * <p>
3537 * In more formal terms, assume these two type lists:<ul>
3538 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
3539 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
3540 * {@code newTypes}.
3541 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
3542 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
3543 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
3544 * sub-list.
3545 * </ul>
3546 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
3547 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
3548 * {@link #dropArguments(MethodHandle, int, Class[])}.
3549 * <p>
3550 * @apiNote
3551 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
3552 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
3553 * <blockquote><pre>{@code
3554 import static java.lang.invoke.MethodHandles.*;
3555 import static java.lang.invoke.MethodType.*;
3556 ...
3557 ...
3558 MethodHandle h0 = constant(boolean.class, true);
3559 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
3560 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
3561 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
3562 if (h1.type().parameterCount() < h2.type().parameterCount())
3563 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
3564 else
3565 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
3566 MethodHandle h3 = guardWithTest(h0, h1, h2);
3567 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
3568 * }</pre></blockquote>
3569 * @param target the method handle to adapt
3570 * @param skip number of targets parameters to disregard (they will be unchanged)
3571 * @param newTypes the list of types to match {@code target}'s parameter type list to
3572 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
3573 * @return a possibly adapted method handle
3574 * @throws NullPointerException if either argument is null
3575 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
3576 * or if {@code skip} is negative or greater than the arity of the target,
3577 * or if {@code pos} is negative or greater than the newTypes list size,
3578 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
3579 * {@code pos}.
3580 * @since 9
3581 */
3582 public static
3583 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
3584 Objects.requireNonNull(target);
3585 Objects.requireNonNull(newTypes);
3586 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
3587 }
3588
3589 /**
3590 * Adapts a target method handle by pre-processing
3591 * one or more of its arguments, each with its own unary filter function,
3592 * and then calling the target with each pre-processed argument
3593 * replaced by the result of its corresponding filter function.
3594 * <p>
3595 * The pre-processing is performed by one or more method handles,
3596 * specified in the elements of the {@code filters} array.
3597 * The first element of the filter array corresponds to the {@code pos}
3598 * argument of the target, and so on in sequence.
3599 * <p>
3600 * Null arguments in the array are treated as identity functions,
3601 * and the corresponding arguments left unchanged.
3602 * (If there are no non-null elements in the array, the original target is returned.)
3603 * Each filter is applied to the corresponding argument of the adapter.
3604 * <p>
3605 * If a filter {@code F} applies to the {@code N}th argument of
3606 * the target, then {@code F} must be a method handle which
3607 * takes exactly one argument. The type of {@code F}'s sole argument
3608 * replaces the corresponding argument type of the target
3609 * in the resulting adapted method handle.
3610 * The return type of {@code F} must be identical to the corresponding
3611 * parameter type of the target.
3612 * <p>
3613 * It is an error if there are elements of {@code filters}
3614 * (null or not)
3615 * which do not correspond to argument positions in the target.
3616 * <p><b>Example:</b>
3617 * <blockquote><pre>{@code
3618 import static java.lang.invoke.MethodHandles.*;
3619 import static java.lang.invoke.MethodType.*;
3620 ...
3621 MethodHandle cat = lookup().findVirtual(String.class,
3622 "concat", methodType(String.class, String.class));
3623 MethodHandle upcase = lookup().findVirtual(String.class,
3624 "toUpperCase", methodType(String.class));
3625 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3626 MethodHandle f0 = filterArguments(cat, 0, upcase);
3627 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
3628 MethodHandle f1 = filterArguments(cat, 1, upcase);
3629 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
3630 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
3631 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
3632 * }</pre></blockquote>
3633 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3634 * denotes the return type of both the {@code target} and resulting adapter.
3635 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
3636 * of the parameters and arguments that precede and follow the filter position
3637 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
3638 * values of the filtered parameters and arguments; they also represent the
3639 * return types of the {@code filter[i]} handles. The latter accept arguments
3640 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
3641 * the resulting adapter.
3642 * <blockquote><pre>{@code
3643 * T target(P... p, A[i]... a[i], B... b);
3644 * A[i] filter[i](V[i]);
3645 * T adapter(P... p, V[i]... v[i], B... b) {
3646 * return target(p..., filter[i](v[i])..., b...);
3647 * }
3648 * }</pre></blockquote>
3649 * <p>
3650 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3651 * variable-arity method handle}, even if the original target method handle was.
3652 *
3653 * @param target the method handle to invoke after arguments are filtered
3654 * @param pos the position of the first argument to filter
3655 * @param filters method handles to call initially on filtered arguments
3656 * @return method handle which incorporates the specified argument filtering logic
3657 * @throws NullPointerException if the target is null
3658 * or if the {@code filters} array is null
3659 * @throws IllegalArgumentException if a non-null element of {@code filters}
3660 * does not match a corresponding argument type of target as described above,
3661 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
3662 * or if the resulting method handle's type would have
3663 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3664 */
3665 public static
3666 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
3667 filterArgumentsCheckArity(target, pos, filters);
3668 MethodHandle adapter = target;
3669 int curPos = pos-1; // pre-incremented
3670 for (MethodHandle filter : filters) {
3671 curPos += 1;
3672 if (filter == null) continue; // ignore null elements of filters
3673 adapter = filterArgument(adapter, curPos, filter);
3674 }
3675 return adapter;
3676 }
3677
3678 /*non-public*/ static
3679 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
3680 filterArgumentChecks(target, pos, filter);
3681 MethodType targetType = target.type();
3682 MethodType filterType = filter.type();
3683 BoundMethodHandle result = target.rebind();
3684 Class<?> newParamType = filterType.parameterType(0);
3685 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
3686 MethodType newType = targetType.changeParameterType(pos, newParamType);
3687 result = result.copyWithExtendL(newType, lform, filter);
3688 return result;
3689 }
3690
3691 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
3692 MethodType targetType = target.type();
3693 int maxPos = targetType.parameterCount();
3694 if (pos + filters.length > maxPos)
3695 throw newIllegalArgumentException("too many filters");
3696 }
3697
3698 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3699 MethodType targetType = target.type();
3700 MethodType filterType = filter.type();
3701 if (filterType.parameterCount() != 1
3702 || filterType.returnType() != targetType.parameterType(pos))
3703 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3704 }
3705
3706 /**
3707 * Adapts a target method handle by pre-processing
3708 * a sub-sequence of its arguments with a filter (another method handle).
3709 * The pre-processed arguments are replaced by the result (if any) of the
3710 * filter function.
3711 * The target is then called on the modified (usually shortened) argument list.
3712 * <p>
3713 * If the filter returns a value, the target must accept that value as
3714 * its argument in position {@code pos}, preceded and/or followed by
3715 * any arguments not passed to the filter.
3716 * If the filter returns void, the target must accept all arguments
3717 * not passed to the filter.
3718 * No arguments are reordered, and a result returned from the filter
3719 * replaces (in order) the whole subsequence of arguments originally
3720 * passed to the adapter.
3721 * <p>
3722 * The argument types (if any) of the filter
3723 * replace zero or one argument types of the target, at position {@code pos},
3724 * in the resulting adapted method handle.
3725 * The return type of the filter (if any) must be identical to the
3726 * argument type of the target at position {@code pos}, and that target argument
3727 * is supplied by the return value of the filter.
3728 * <p>
3729 * In all cases, {@code pos} must be greater than or equal to zero, and
3730 * {@code pos} must also be less than or equal to the target's arity.
3731 * <p><b>Example:</b>
3732 * <blockquote><pre>{@code
3733 import static java.lang.invoke.MethodHandles.*;
3734 import static java.lang.invoke.MethodType.*;
3735 ...
3736 MethodHandle deepToString = publicLookup()
3737 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
3738
3739 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
3740 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
3741
3742 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
3743 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
3744
3745 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
3746 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
3747 assertEquals("[top, [up, down], strange]",
3748 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
3749
3750 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
3751 assertEquals("[top, [up, down], [strange]]",
3752 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
3753
3754 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
3755 assertEquals("[top, [[up, down, strange], charm], bottom]",
3756 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
3757 * }</pre></blockquote>
3758 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3759 * represents the return type of the {@code target} and resulting adapter.
3760 * {@code V}/{@code v} stand for the return type and value of the
3761 * {@code filter}, which are also found in the signature and arguments of
3762 * the {@code target}, respectively, unless {@code V} is {@code void}.
3763 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
3764 * and values preceding and following the collection position, {@code pos},
3765 * in the {@code target}'s signature. They also turn up in the resulting
3766 * adapter's signature and arguments, where they surround
3767 * {@code B}/{@code b}, which represent the parameter types and arguments
3768 * to the {@code filter} (if any).
3769 * <blockquote><pre>{@code
3770 * T target(A...,V,C...);
3771 * V filter(B...);
3772 * T adapter(A... a,B... b,C... c) {
3773 * V v = filter(b...);
3774 * return target(a...,v,c...);
3775 * }
3776 * // and if the filter has no arguments:
3777 * T target2(A...,V,C...);
3778 * V filter2();
3779 * T adapter2(A... a,C... c) {
3780 * V v = filter2();
3781 * return target2(a...,v,c...);
3782 * }
3783 * // and if the filter has a void return:
3784 * T target3(A...,C...);
3785 * void filter3(B...);
3786 * T adapter3(A... a,B... b,C... c) {
3787 * filter3(b...);
3788 * return target3(a...,c...);
3789 * }
3790 * }</pre></blockquote>
3791 * <p>
3792 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
3793 * one which first "folds" the affected arguments, and then drops them, in separate
3794 * steps as follows:
3795 * <blockquote><pre>{@code
3796 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
3797 * mh = MethodHandles.foldArguments(mh, coll); //step 1
3798 * }</pre></blockquote>
3799 * If the target method handle consumes no arguments besides than the result
3800 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
3801 * is equivalent to {@code filterReturnValue(coll, mh)}.
3802 * If the filter method handle {@code coll} consumes one argument and produces
3803 * a non-void result, then {@code collectArguments(mh, N, coll)}
3804 * is equivalent to {@code filterArguments(mh, N, coll)}.
3805 * Other equivalences are possible but would require argument permutation.
3806 * <p>
3807 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3808 * variable-arity method handle}, even if the original target method handle was.
3809 *
3810 * @param target the method handle to invoke after filtering the subsequence of arguments
3811 * @param pos the position of the first adapter argument to pass to the filter,
3812 * and/or the target argument which receives the result of the filter
3813 * @param filter method handle to call on the subsequence of arguments
3814 * @return method handle which incorporates the specified argument subsequence filtering logic
3815 * @throws NullPointerException if either argument is null
3816 * @throws IllegalArgumentException if the return type of {@code filter}
3817 * is non-void and is not the same as the {@code pos} argument of the target,
3818 * or if {@code pos} is not between 0 and the target's arity, inclusive,
3819 * or if the resulting method handle's type would have
3820 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3821 * @see MethodHandles#foldArguments
3822 * @see MethodHandles#filterArguments
3823 * @see MethodHandles#filterReturnValue
3824 */
3825 public static
3826 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
3827 MethodType newType = collectArgumentsChecks(target, pos, filter);
3828 MethodType collectorType = filter.type();
3829 BoundMethodHandle result = target.rebind();
3830 LambdaForm lform;
3831 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
3832 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
3833 if (lform != null) {
3834 return result.copyWith(newType, lform);
3835 }
3836 }
3837 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
3838 return result.copyWithExtendL(newType, lform, filter);
3839 }
3840
3841 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3842 MethodType targetType = target.type();
3843 MethodType filterType = filter.type();
3844 Class<?> rtype = filterType.returnType();
3845 List<Class<?>> filterArgs = filterType.parameterList();
3846 if (rtype == void.class) {
3847 return targetType.insertParameterTypes(pos, filterArgs);
3848 }
3849 if (rtype != targetType.parameterType(pos)) {
3850 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3851 }
3852 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
3853 }
3854
3855 /**
3856 * Adapts a target method handle by post-processing
3857 * its return value (if any) with a filter (another method handle).
3858 * The result of the filter is returned from the adapter.
3859 * <p>
3860 * If the target returns a value, the filter must accept that value as
3861 * its only argument.
3862 * If the target returns void, the filter must accept no arguments.
3863 * <p>
3864 * The return type of the filter
3865 * replaces the return type of the target
3866 * in the resulting adapted method handle.
3867 * The argument type of the filter (if any) must be identical to the
3868 * return type of the target.
3869 * <p><b>Example:</b>
3870 * <blockquote><pre>{@code
3871 import static java.lang.invoke.MethodHandles.*;
3872 import static java.lang.invoke.MethodType.*;
3873 ...
3874 MethodHandle cat = lookup().findVirtual(String.class,
3875 "concat", methodType(String.class, String.class));
3876 MethodHandle length = lookup().findVirtual(String.class,
3877 "length", methodType(int.class));
3878 System.out.println((String) cat.invokeExact("x", "y")); // xy
3879 MethodHandle f0 = filterReturnValue(cat, length);
3880 System.out.println((int) f0.invokeExact("x", "y")); // 2
3881 * }</pre></blockquote>
3882 * <p>Here is pseudocode for the resulting adapter. In the code,
3883 * {@code T}/{@code t} represent the result type and value of the
3884 * {@code target}; {@code V}, the result type of the {@code filter}; and
3885 * {@code A}/{@code a}, the types and values of the parameters and arguments
3886 * of the {@code target} as well as the resulting adapter.
3887 * <blockquote><pre>{@code
3888 * T target(A...);
3889 * V filter(T);
3890 * V adapter(A... a) {
3891 * T t = target(a...);
3892 * return filter(t);
3893 * }
3894 * // and if the target has a void return:
3895 * void target2(A...);
3896 * V filter2();
3897 * V adapter2(A... a) {
3898 * target2(a...);
3899 * return filter2();
3900 * }
3901 * // and if the filter has a void return:
3902 * T target3(A...);
3903 * void filter3(V);
3904 * void adapter3(A... a) {
3905 * T t = target3(a...);
3906 * filter3(t);
3907 * }
3908 * }</pre></blockquote>
3909 * <p>
3910 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3911 * variable-arity method handle}, even if the original target method handle was.
3912 * @param target the method handle to invoke before filtering the return value
3913 * @param filter method handle to call on the return value
3914 * @return method handle which incorporates the specified return value filtering logic
3915 * @throws NullPointerException if either argument is null
3916 * @throws IllegalArgumentException if the argument list of {@code filter}
3917 * does not match the return type of target as described above
3918 */
3919 public static
3920 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
3921 MethodType targetType = target.type();
3922 MethodType filterType = filter.type();
3923 filterReturnValueChecks(targetType, filterType);
3924 BoundMethodHandle result = target.rebind();
3925 BasicType rtype = BasicType.basicType(filterType.returnType());
3926 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
3927 MethodType newType = targetType.changeReturnType(filterType.returnType());
3928 result = result.copyWithExtendL(newType, lform, filter);
3929 return result;
3930 }
3931
3932 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
3933 Class<?> rtype = targetType.returnType();
3934 int filterValues = filterType.parameterCount();
3935 if (filterValues == 0
3936 ? (rtype != void.class)
3937 : (rtype != filterType.parameterType(0) || filterValues != 1))
3938 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3939 }
3940
3941 /**
3942 * Adapts a target method handle by pre-processing
3943 * some of its arguments, and then calling the target with
3944 * the result of the pre-processing, inserted into the original
3945 * sequence of arguments.
3946 * <p>
3947 * The pre-processing is performed by {@code combiner}, a second method handle.
3948 * Of the arguments passed to the adapter, the first {@code N} arguments
3949 * are copied to the combiner, which is then called.
3950 * (Here, {@code N} is defined as the parameter count of the combiner.)
3951 * After this, control passes to the target, with any result
3952 * from the combiner inserted before the original {@code N} incoming
3953 * arguments.
3954 * <p>
3955 * If the combiner returns a value, the first parameter type of the target
3956 * must be identical with the return type of the combiner, and the next
3957 * {@code N} parameter types of the target must exactly match the parameters
3958 * of the combiner.
3959 * <p>
3960 * If the combiner has a void return, no result will be inserted,
3961 * and the first {@code N} parameter types of the target
3962 * must exactly match the parameters of the combiner.
3963 * <p>
3964 * The resulting adapter is the same type as the target, except that the
3965 * first parameter type is dropped,
3966 * if it corresponds to the result of the combiner.
3967 * <p>
3968 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
3969 * that either the combiner or the target does not wish to receive.
3970 * If some of the incoming arguments are destined only for the combiner,
3971 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
3972 * arguments will not need to be live on the stack on entry to the
3973 * target.)
3974 * <p><b>Example:</b>
3975 * <blockquote><pre>{@code
3976 import static java.lang.invoke.MethodHandles.*;
3977 import static java.lang.invoke.MethodType.*;
3978 ...
3979 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
3980 "println", methodType(void.class, String.class))
3981 .bindTo(System.out);
3982 MethodHandle cat = lookup().findVirtual(String.class,
3983 "concat", methodType(String.class, String.class));
3984 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
3985 MethodHandle catTrace = foldArguments(cat, trace);
3986 // also prints "boo":
3987 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
3988 * }</pre></blockquote>
3989 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3990 * represents the result type of the {@code target} and resulting adapter.
3991 * {@code V}/{@code v} represent the type and value of the parameter and argument
3992 * of {@code target} that precedes the folding position; {@code V} also is
3993 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
3994 * types and values of the {@code N} parameters and arguments at the folding
3995 * position. {@code B}/{@code b} represent the types and values of the
3996 * {@code target} parameters and arguments that follow the folded parameters
3997 * and arguments.
3998 * <blockquote><pre>{@code
3999 * // there are N arguments in A...
4000 * T target(V, A[N]..., B...);
4001 * V combiner(A...);
4002 * T adapter(A... a, B... b) {
4003 * V v = combiner(a...);
4004 * return target(v, a..., b...);
4005 * }
4006 * // and if the combiner has a void return:
4007 * T target2(A[N]..., B...);
4008 * void combiner2(A...);
4009 * T adapter2(A... a, B... b) {
4010 * combiner2(a...);
4011 * return target2(a..., b...);
4012 * }
4013 * }</pre></blockquote>
4014 * <p>
4015 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4016 * variable-arity method handle}, even if the original target method handle was.
4017 * @param target the method handle to invoke after arguments are combined
4018 * @param combiner method handle to call initially on the incoming arguments
4019 * @return method handle which incorporates the specified argument folding logic
4020 * @throws NullPointerException if either argument is null
4021 * @throws IllegalArgumentException if {@code combiner}'s return type
4022 * is non-void and not the same as the first argument type of
4023 * the target, or if the initial {@code N} argument types
4024 * of the target
4025 * (skipping one matching the {@code combiner}'s return type)
4026 * are not identical with the argument types of {@code combiner}
4027 */
4028 public static
4029 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
4030 return foldArguments(target, 0, combiner);
4031 }
4032
4033 /**
4034 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4035 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4036 * before the folded arguments.
4037 * <p>
4038 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4039 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4040 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4041 * 0.
4042 * <p>
4043 * @apiNote Example:
4044 * <blockquote><pre>{@code
4045 import static java.lang.invoke.MethodHandles.*;
4046 import static java.lang.invoke.MethodType.*;
4047 ...
4048 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4049 "println", methodType(void.class, String.class))
4050 .bindTo(System.out);
4051 MethodHandle cat = lookup().findVirtual(String.class,
4052 "concat", methodType(String.class, String.class));
4053 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4054 MethodHandle catTrace = foldArguments(cat, 1, trace);
4055 // also prints "jum":
4056 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4057 * }</pre></blockquote>
4058 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4059 * represents the result type of the {@code target} and resulting adapter.
4060 * {@code V}/{@code v} represent the type and value of the parameter and argument
4061 * of {@code target} that precedes the folding position; {@code V} also is
4062 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4063 * types and values of the {@code N} parameters and arguments at the folding
4064 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4065 * and values of the {@code target} parameters and arguments that precede and
4066 * follow the folded parameters and arguments starting at {@code pos},
4067 * respectively.
4068 * <blockquote><pre>{@code
4069 * // there are N arguments in A...
4070 * T target(Z..., V, A[N]..., B...);
4071 * V combiner(A...);
4072 * T adapter(Z... z, A... a, B... b) {
4073 * V v = combiner(a...);
4074 * return target(z..., v, a..., b...);
4075 * }
4076 * // and if the combiner has a void return:
4077 * T target2(Z..., A[N]..., B...);
4078 * void combiner2(A...);
4079 * T adapter2(Z... z, A... a, B... b) {
4080 * combiner2(a...);
4081 * return target2(z..., a..., b...);
4082 * }
4083 * }</pre></blockquote>
4084 * <p>
4085 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4086 * variable-arity method handle}, even if the original target method handle was.
4087 *
4088 * @param target the method handle to invoke after arguments are combined
4089 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4090 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4091 * @param combiner method handle to call initially on the incoming arguments
4092 * @return method handle which incorporates the specified argument folding logic
4093 * @throws NullPointerException if either argument is null
4094 * @throws IllegalArgumentException if either of the following two conditions holds:
4095 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4096 * {@code pos} of the target signature;
4097 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
4098 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
4099 *
4100 * @see #foldArguments(MethodHandle, MethodHandle)
4101 * @since 9
4102 */
4103 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4104 MethodType targetType = target.type();
4105 MethodType combinerType = combiner.type();
4106 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4107 BoundMethodHandle result = target.rebind();
4108 boolean dropResult = rtype == void.class;
4109 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4110 MethodType newType = targetType;
4111 if (!dropResult) {
4112 newType = newType.dropParameterTypes(pos, pos + 1);
4113 }
4114 result = result.copyWithExtendL(newType, lform, combiner);
4115 return result;
4116 }
4117
4118 /**
4119 * As {@see foldArguments(MethodHandle, int, MethodHandle)}, but with the
4120 * added capability of selecting the arguments from the targets parameters
4121 * to call the combiner with. This allows us to avoid some simple cases of
4122 * permutations and padding the combiner with dropArguments to select the
4123 * right argument, which may ultimately produce fewer intermediaries.
4124 */
4125 static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner, int ... argPositions) {
4126 MethodType targetType = target.type();
4127 MethodType combinerType = combiner.type();
4128 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType, argPositions);
4129 BoundMethodHandle result = target.rebind();
4130 boolean dropResult = rtype == void.class;
4131 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType(), argPositions);
4132 MethodType newType = targetType;
4133 if (!dropResult) {
4134 newType = newType.dropParameterTypes(pos, pos + 1);
4135 }
4136 result = result.copyWithExtendL(newType, lform, combiner);
4137 return result;
4138 }
4139
4140 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
4141 int foldArgs = combinerType.parameterCount();
4142 Class<?> rtype = combinerType.returnType();
4143 int foldVals = rtype == void.class ? 0 : 1;
4144 int afterInsertPos = foldPos + foldVals;
4145 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
4146 if (ok) {
4147 for (int i = 0; i < foldArgs; i++) {
4148 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
4149 ok = false;
4150 break;
4151 }
4152 }
4153 }
4154 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
4155 ok = false;
4156 if (!ok)
4157 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4158 return rtype;
4159 }
4160
4161 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType, int ... argPos) {
4162 int foldArgs = combinerType.parameterCount();
4163 if (argPos.length != foldArgs) {
4164 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
4165 }
4166 Class<?> rtype = combinerType.returnType();
4167 int foldVals = rtype == void.class ? 0 : 1;
4168 boolean ok = true;
4169 for (int i = 0; i < foldArgs; i++) {
4170 int arg = argPos[i];
4171 if (arg < 0 || arg > targetType.parameterCount()) {
4172 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
4173 }
4174 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
4175 throw newIllegalArgumentException("target argument type at position " + arg
4176 + " must match combiner argument type at index " + i + ": " + targetType
4177 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
4178 }
4179 }
4180 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) {
4181 ok = false;
4182 }
4183 if (!ok)
4184 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4185 return rtype;
4186 }
4187
4188 /**
4189 * Makes a method handle which adapts a target method handle,
4190 * by guarding it with a test, a boolean-valued method handle.
4191 * If the guard fails, a fallback handle is called instead.
4192 * All three method handles must have the same corresponding
4193 * argument and return types, except that the return type
4194 * of the test must be boolean, and the test is allowed
4195 * to have fewer arguments than the other two method handles.
4196 * <p>
4197 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4198 * represents the uniform result type of the three involved handles;
4199 * {@code A}/{@code a}, the types and values of the {@code target}
4200 * parameters and arguments that are consumed by the {@code test}; and
4201 * {@code B}/{@code b}, those types and values of the {@code target}
4202 * parameters and arguments that are not consumed by the {@code test}.
4203 * <blockquote><pre>{@code
4204 * boolean test(A...);
4205 * T target(A...,B...);
4206 * T fallback(A...,B...);
4207 * T adapter(A... a,B... b) {
4208 * if (test(a...))
4209 * return target(a..., b...);
4210 * else
4211 * return fallback(a..., b...);
4212 * }
4213 * }</pre></blockquote>
4214 * Note that the test arguments ({@code a...} in the pseudocode) cannot
4215 * be modified by execution of the test, and so are passed unchanged
4216 * from the caller to the target or fallback as appropriate.
4217 * @param test method handle used for test, must return boolean
4218 * @param target method handle to call if test passes
4219 * @param fallback method handle to call if test fails
4220 * @return method handle which incorporates the specified if/then/else logic
4221 * @throws NullPointerException if any argument is null
4222 * @throws IllegalArgumentException if {@code test} does not return boolean,
4223 * or if all three method types do not match (with the return
4224 * type of {@code test} changed to match that of the target).
4225 */
4226 public static
4227 MethodHandle guardWithTest(MethodHandle test,
4228 MethodHandle target,
4229 MethodHandle fallback) {
4230 MethodType gtype = test.type();
4231 MethodType ttype = target.type();
4232 MethodType ftype = fallback.type();
4233 if (!ttype.equals(ftype))
4234 throw misMatchedTypes("target and fallback types", ttype, ftype);
4235 if (gtype.returnType() != boolean.class)
4236 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
4237 List<Class<?>> targs = ttype.parameterList();
4238 test = dropArgumentsToMatch(test, 0, targs, 0, true);
4239 if (test == null) {
4240 throw misMatchedTypes("target and test types", ttype, gtype);
4241 }
4242 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
4243 }
4244
4245 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
4246 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
4247 }
4248
4249 /**
4250 * Makes a method handle which adapts a target method handle,
4251 * by running it inside an exception handler.
4252 * If the target returns normally, the adapter returns that value.
4253 * If an exception matching the specified type is thrown, the fallback
4254 * handle is called instead on the exception, plus the original arguments.
4255 * <p>
4256 * The target and handler must have the same corresponding
4257 * argument and return types, except that handler may omit trailing arguments
4258 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
4259 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
4260 * <p>
4261 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4262 * represents the return type of the {@code target} and {@code handler},
4263 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
4264 * the types and values of arguments to the resulting handle consumed by
4265 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
4266 * resulting handle discarded by {@code handler}.
4267 * <blockquote><pre>{@code
4268 * T target(A..., B...);
4269 * T handler(ExType, A...);
4270 * T adapter(A... a, B... b) {
4271 * try {
4272 * return target(a..., b...);
4273 * } catch (ExType ex) {
4274 * return handler(ex, a...);
4275 * }
4276 * }
4277 * }</pre></blockquote>
4278 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4279 * be modified by execution of the target, and so are passed unchanged
4280 * from the caller to the handler, if the handler is invoked.
4281 * <p>
4282 * The target and handler must return the same type, even if the handler
4283 * always throws. (This might happen, for instance, because the handler
4284 * is simulating a {@code finally} clause).
4285 * To create such a throwing handler, compose the handler creation logic
4286 * with {@link #throwException throwException},
4287 * in order to create a method handle of the correct return type.
4288 * @param target method handle to call
4289 * @param exType the type of exception which the handler will catch
4290 * @param handler method handle to call if a matching exception is thrown
4291 * @return method handle which incorporates the specified try/catch logic
4292 * @throws NullPointerException if any argument is null
4293 * @throws IllegalArgumentException if {@code handler} does not accept
4294 * the given exception type, or if the method handle types do
4295 * not match in their return types and their
4296 * corresponding parameters
4297 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4298 */
4299 public static
4300 MethodHandle catchException(MethodHandle target,
4301 Class<? extends Throwable> exType,
4302 MethodHandle handler) {
4303 MethodType ttype = target.type();
4304 MethodType htype = handler.type();
4305 if (!Throwable.class.isAssignableFrom(exType))
4306 throw new ClassCastException(exType.getName());
4307 if (htype.parameterCount() < 1 ||
4308 !htype.parameterType(0).isAssignableFrom(exType))
4309 throw newIllegalArgumentException("handler does not accept exception type "+exType);
4310 if (htype.returnType() != ttype.returnType())
4311 throw misMatchedTypes("target and handler return types", ttype, htype);
4312 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4313 if (handler == null) {
4314 throw misMatchedTypes("target and handler types", ttype, htype);
4315 }
4316 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4317 }
4318
4319 /**
4320 * Produces a method handle which will throw exceptions of the given {@code exType}.
4321 * The method handle will accept a single argument of {@code exType},
4322 * and immediately throw it as an exception.
4323 * The method type will nominally specify a return of {@code returnType}.
4324 * The return type may be anything convenient: It doesn't matter to the
4325 * method handle's behavior, since it will never return normally.
4326 * @param returnType the return type of the desired method handle
4327 * @param exType the parameter type of the desired method handle
4328 * @return method handle which can throw the given exceptions
4329 * @throws NullPointerException if either argument is null
4330 */
4331 public static
4332 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4333 if (!Throwable.class.isAssignableFrom(exType))
4334 throw new ClassCastException(exType.getName());
4335 return MethodHandleImpl.throwException(methodType(returnType, exType));
4336 }
4337
4338 /**
4339 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4340 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4341 * delivers the loop's result, which is the return value of the resulting handle.
4342 * <p>
4343 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
4344 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4345 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4346 * terms of method handles, each clause will specify up to four independent actions:<ul>
4347 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
4348 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
4349 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
4350 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4351 * </ul>
4352 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
4353 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
4354 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
4355 * <p>
4356 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4357 * this case. See below for a detailed description.
4358 * <p>
4359 * <em>Parameters optional everywhere:</em>
4360 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
4361 * As an exception, the init functions cannot take any {@code v} parameters,
4362 * because those values are not yet computed when the init functions are executed.
4363 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
4364 * In fact, any clause function may take no arguments at all.
4365 * <p>
4366 * <em>Loop parameters:</em>
4367 * A clause function may take all the iteration variable values it is entitled to, in which case
4368 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
4369 * with their types and values notated as {@code (A...)} and {@code (a...)}.
4370 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
4371 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
4372 * init function is automatically a loop parameter {@code a}.)
4373 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
4374 * These loop parameters act as loop-invariant values visible across the whole loop.
4375 * <p>
4376 * <em>Parameters visible everywhere:</em>
4377 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
4378 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
4379 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
4380 * Most clause functions will not need all of this information, but they will be formally connected to it
4381 * as if by {@link #dropArguments}.
4382 * <a name="astar"></a>
4383 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
4384 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
4385 * In that notation, the general form of an init function parameter list
4386 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
4387 * <p>
4388 * <em>Checking clause structure:</em>
4389 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4390 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4391 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
4392 * met by the inputs to the loop combinator.
4393 * <p>
4394 * <em>Effectively identical sequences:</em>
4395 * <a name="effid"></a>
4396 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
4397 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
4398 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
4399 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
4400 * that longest list.
4401 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
4402 * and the same is true if more sequences of the form {@code (V... A*)} are added.
4403 * <p>
4404 * <em>Step 0: Determine clause structure.</em><ol type="a">
4405 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
4406 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4407 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4408 * four. Padding takes place by appending elements to the array.
4409 * <li>Clauses with all {@code null}s are disregarded.
4410 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4411 * </ol>
4412 * <p>
4413 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
4414 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
4415 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
4416 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
4417 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
4418 * iteration variable type.
4419 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
4420 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
4421 * </ol>
4422 * <p>
4423 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
4424 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
4425 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
4426 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
4427 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
4428 * (These types will checked in step 2, along with all the clause function types.)
4429 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
4430 * <li>All of the collected parameter lists must be effectively identical.
4431 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
4432 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
4433 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
4434 * the "internal parameter list".
4435 * </ul>
4436 * <p>
4437 * <em>Step 1C: Determine loop return type.</em><ol type="a">
4438 * <li>Examine fini function return types, disregarding omitted fini functions.
4439 * <li>If there are no fini functions, the loop return type is {@code void}.
4440 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
4441 * type.
4442 * </ol>
4443 * <p>
4444 * <em>Step 1D: Check other types.</em><ol type="a">
4445 * <li>There must be at least one non-omitted pred function.
4446 * <li>Every non-omitted pred function must have a {@code boolean} return type.
4447 * </ol>
4448 * <p>
4449 * <em>Step 2: Determine parameter lists.</em><ol type="a">
4450 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
4451 * <li>The parameter list for init functions will be adjusted to the external parameter list.
4452 * (Note that their parameter lists are already effectively identical to this list.)
4453 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
4454 * effectively identical to the internal parameter list {@code (V... A...)}.
4455 * </ol>
4456 * <p>
4457 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
4458 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
4459 * type.
4460 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
4461 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
4462 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
4463 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
4464 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
4465 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
4466 * loop return type.
4467 * </ol>
4468 * <p>
4469 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
4470 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
4471 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
4472 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
4473 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
4474 * pad out the end of the list.
4475 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch dropping unused trailing arguments}.
4476 * </ol>
4477 * <p>
4478 * <em>Final observations.</em><ol type="a">
4479 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
4480 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
4481 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
4482 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
4483 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
4484 * <li>Each pair of init and step functions agrees in their return type {@code V}.
4485 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
4486 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
4487 * </ol>
4488 * <p>
4489 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
4490 * <ul>
4491 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
4492 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
4493 * (Only one {@code Pn} has to be non-{@code null}.)
4494 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
4495 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
4496 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
4497 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
4498 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
4499 * the resulting loop handle's parameter types {@code (A...)}.
4500 * </ul>
4501 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
4502 * which is natural if most of the loop computation happens in the steps. For some loops,
4503 * the burden of computation might be heaviest in the pred functions, and so the pred functions
4504 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
4505 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
4506 * where the init functions will need the extra parameters. For such reasons, the rules for
4507 * determining these parameters are as symmetric as possible, across all clause parts.
4508 * In general, the loop parameters function as common invariant values across the whole
4509 * loop, while the iteration variables function as common variant values, or (if there is
4510 * no step function) as internal loop invariant temporaries.
4511 * <p>
4512 * <em>Loop execution.</em><ol type="a">
4513 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
4514 * every clause function. These locals are loop invariant.
4515 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
4516 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
4517 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
4518 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
4519 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
4520 * (in argument order).
4521 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
4522 * returns {@code false}.
4523 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
4524 * sequence {@code (v...)} of loop variables.
4525 * The updated value is immediately visible to all subsequent function calls.
4526 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
4527 * (of type {@code R}) is returned from the loop as a whole.
4528 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
4529 * except by throwing an exception.
4530 * </ol>
4531 * <p>
4532 * <em>Usage tips.</em>
4533 * <ul>
4534 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
4535 * sometimes a step function only needs to observe the current value of its own variable.
4536 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
4537 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
4538 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
4539 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
4540 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
4541 * <li>If some of the clause functions are virtual methods on an instance, the instance
4542 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
4543 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
4544 * will be the first iteration variable value, and it will be easy to use virtual
4545 * methods as clause parts, since all of them will take a leading instance reference matching that value.
4546 * </ul>
4547 * <p>
4548 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
4549 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
4550 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
4551 * <blockquote><pre>{@code
4552 * V... init...(A...);
4553 * boolean pred...(V..., A...);
4554 * V... step...(V..., A...);
4555 * R fini...(V..., A...);
4556 * R loop(A... a) {
4557 * V... v... = init...(a...);
4558 * for (;;) {
4559 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
4560 * v = s(v..., a...);
4561 * if (!p(v..., a...)) {
4562 * return f(v..., a...);
4563 * }
4564 * }
4565 * }
4566 * }
4567 * }</pre></blockquote>
4568 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
4569 * to their full length, even though individual clause functions may neglect to take them all.
4570 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch}.
4571 * <p>
4572 * @apiNote Example:
4573 * <blockquote><pre>{@code
4574 * // iterative implementation of the factorial function as a loop handle
4575 * static int one(int k) { return 1; }
4576 * static int inc(int i, int acc, int k) { return i + 1; }
4577 * static int mult(int i, int acc, int k) { return i * acc; }
4578 * static boolean pred(int i, int acc, int k) { return i < k; }
4579 * static int fin(int i, int acc, int k) { return acc; }
4580 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4581 * // null initializer for counter, should initialize to 0
4582 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4583 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4584 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4585 * assertEquals(120, loop.invoke(5));
4586 * }</pre></blockquote>
4587 * The same example, dropping arguments and using combinators:
4588 * <blockquote><pre>{@code
4589 * // simplified implementation of the factorial function as a loop handle
4590 * static int inc(int i) { return i + 1; } // drop acc, k
4591 * static int mult(int i, int acc) { return i * acc; } //drop k
4592 * static boolean cmp(int i, int k) { return i < k; }
4593 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
4594 * // null initializer for counter, should initialize to 0
4595 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4596 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
4597 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
4598 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4599 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4600 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4601 * assertEquals(720, loop.invoke(6));
4602 * }</pre></blockquote>
4603 * A similar example, using a helper object to hold a loop parameter:
4604 * <blockquote><pre>{@code
4605 * // instance-based implementation of the factorial function as a loop handle
4606 * static class FacLoop {
4607 * final int k;
4608 * FacLoop(int k) { this.k = k; }
4609 * int inc(int i) { return i + 1; }
4610 * int mult(int i, int acc) { return i * acc; }
4611 * boolean pred(int i) { return i < k; }
4612 * int fin(int i, int acc) { return acc; }
4613 * }
4614 * // assume MH_FacLoop is a handle to the constructor
4615 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4616 * // null initializer for counter, should initialize to 0
4617 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4618 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
4619 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4620 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4621 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
4622 * assertEquals(5040, loop.invoke(7));
4623 * }</pre></blockquote>
4624 *
4625 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
4626 *
4627 * @return a method handle embodying the looping behavior as defined by the arguments.
4628 *
4629 * @throws IllegalArgumentException in case any of the constraints described above is violated.
4630 *
4631 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
4632 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4633 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
4634 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
4635 * @since 9
4636 */
4637 public static MethodHandle loop(MethodHandle[]... clauses) {
4638 // Step 0: determine clause structure.
4639 loopChecks0(clauses);
4640
4641 List<MethodHandle> init = new ArrayList<>();
4642 List<MethodHandle> step = new ArrayList<>();
4643 List<MethodHandle> pred = new ArrayList<>();
4644 List<MethodHandle> fini = new ArrayList<>();
4645
4646 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
4647 init.add(clause[0]); // all clauses have at least length 1
4648 step.add(clause.length <= 1 ? null : clause[1]);
4649 pred.add(clause.length <= 2 ? null : clause[2]);
4650 fini.add(clause.length <= 3 ? null : clause[3]);
4651 });
4652
4653 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
4654 final int nclauses = init.size();
4655
4656 // Step 1A: determine iteration variables (V...).
4657 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
4658 for (int i = 0; i < nclauses; ++i) {
4659 MethodHandle in = init.get(i);
4660 MethodHandle st = step.get(i);
4661 if (in == null && st == null) {
4662 iterationVariableTypes.add(void.class);
4663 } else if (in != null && st != null) {
4664 loopChecks1a(i, in, st);
4665 iterationVariableTypes.add(in.type().returnType());
4666 } else {
4667 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
4668 }
4669 }
4670 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
4671 collect(Collectors.toList());
4672
4673 // Step 1B: determine loop parameters (A...).
4674 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
4675 loopChecks1b(init, commonSuffix);
4676
4677 // Step 1C: determine loop return type.
4678 // Step 1D: check other types.
4679 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
4680 map(MethodType::returnType).findFirst().orElse(void.class);
4681 loopChecks1cd(pred, fini, loopReturnType);
4682
4683 // Step 2: determine parameter lists.
4684 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
4685 commonParameterSequence.addAll(commonSuffix);
4686 loopChecks2(step, pred, fini, commonParameterSequence);
4687
4688 // Step 3: fill in omitted functions.
4689 for (int i = 0; i < nclauses; ++i) {
4690 Class<?> t = iterationVariableTypes.get(i);
4691 if (init.get(i) == null) {
4692 init.set(i, empty(methodType(t, commonSuffix)));
4693 }
4694 if (step.get(i) == null) {
4695 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
4696 }
4697 if (pred.get(i) == null) {
4698 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
4699 }
4700 if (fini.get(i) == null) {
4701 fini.set(i, empty(methodType(t, commonParameterSequence)));
4702 }
4703 }
4704
4705 // Step 4: fill in missing parameter types.
4706 // Also convert all handles to fixed-arity handles.
4707 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
4708 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
4709 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
4710 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
4711
4712 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
4713 allMatch(pl -> pl.equals(commonSuffix));
4714 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
4715 allMatch(pl -> pl.equals(commonParameterSequence));
4716
4717 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
4718 }
4719
4720 private static void loopChecks0(MethodHandle[][] clauses) {
4721 if (clauses == null || clauses.length == 0) {
4722 throw newIllegalArgumentException("null or no clauses passed");
4723 }
4724 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
4725 throw newIllegalArgumentException("null clauses are not allowed");
4726 }
4727 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
4728 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
4729 }
4730 }
4731
4732 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
4733 if (in.type().returnType() != st.type().returnType()) {
4734 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
4735 st.type().returnType());
4736 }
4737 }
4738
4739 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
4740 final List<Class<?>> empty = List.of();
4741 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
4742 // take only those that can contribute to a common suffix because they are longer than the prefix
4743 map(MethodHandle::type).
4744 filter(t -> t.parameterCount() > skipSize).
4745 map(MethodType::parameterList).
4746 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4747 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
4748 }
4749
4750 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
4751 final List<Class<?>> empty = List.of();
4752 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4753 }
4754
4755 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
4756 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
4757 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
4758 return longestParameterList(Arrays.asList(longest1, longest2));
4759 }
4760
4761 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
4762 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
4763 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
4764 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
4765 " (common suffix: " + commonSuffix + ")");
4766 }
4767 }
4768
4769 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
4770 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4771 anyMatch(t -> t != loopReturnType)) {
4772 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
4773 loopReturnType + ")");
4774 }
4775
4776 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
4777 throw newIllegalArgumentException("no predicate found", pred);
4778 }
4779 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4780 anyMatch(t -> t != boolean.class)) {
4781 throw newIllegalArgumentException("predicates must have boolean return type", pred);
4782 }
4783 }
4784
4785 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
4786 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
4787 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
4788 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
4789 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
4790 }
4791 }
4792
4793 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
4794 return hs.stream().map(h -> {
4795 int pc = h.type().parameterCount();
4796 int tpsize = targetParams.size();
4797 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
4798 }).collect(Collectors.toList());
4799 }
4800
4801 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
4802 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
4803 }
4804
4805 /**
4806 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
4807 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
4808 * <p>
4809 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
4810 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
4811 * evaluates to {@code true}).
4812 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
4813 * <p>
4814 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
4815 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
4816 * and updated with the value returned from its invocation. The result of loop execution will be
4817 * the final value of the additional loop-local variable (if present).
4818 * <p>
4819 * The following rules hold for these argument handles:<ul>
4820 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
4821 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
4822 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
4823 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
4824 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
4825 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
4826 * It will constrain the parameter lists of the other loop parts.
4827 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
4828 * list {@code (A...)} is called the <em>external parameter list</em>.
4829 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
4830 * additional state variable of the loop.
4831 * The body must both accept and return a value of this type {@code V}.
4832 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
4833 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
4834 * <a href="MethodHandles.html#effid">effectively identical</a>
4835 * to the external parameter list {@code (A...)}.
4836 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
4837 * {@linkplain #empty default value}.
4838 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
4839 * Its parameter list (either empty or of the form {@code (V A*)}) must be
4840 * effectively identical to the internal parameter list.
4841 * </ul>
4842 * <p>
4843 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
4844 * <li>The loop handle's result type is the result type {@code V} of the body.
4845 * <li>The loop handle's parameter types are the types {@code (A...)},
4846 * from the external parameter list.
4847 * </ul>
4848 * <p>
4849 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4850 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4851 * passed to the loop.
4852 * <blockquote><pre>{@code
4853 * V init(A...);
4854 * boolean pred(V, A...);
4855 * V body(V, A...);
4856 * V whileLoop(A... a...) {
4857 * V v = init(a...);
4858 * while (pred(v, a...)) {
4859 * v = body(v, a...);
4860 * }
4861 * return v;
4862 * }
4863 * }</pre></blockquote>
4864 * <p>
4865 * @apiNote Example:
4866 * <blockquote><pre>{@code
4867 * // implement the zip function for lists as a loop handle
4868 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
4869 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
4870 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
4871 * zip.add(a.next());
4872 * zip.add(b.next());
4873 * return zip;
4874 * }
4875 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
4876 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
4877 * List<String> a = Arrays.asList("a", "b", "c", "d");
4878 * List<String> b = Arrays.asList("e", "f", "g", "h");
4879 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
4880 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
4881 * }</pre></blockquote>
4882 *
4883 * <p>
4884 * @apiNote The implementation of this method can be expressed as follows:
4885 * <blockquote><pre>{@code
4886 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
4887 * MethodHandle fini = (body.type().returnType() == void.class
4888 * ? null : identity(body.type().returnType()));
4889 * MethodHandle[]
4890 * checkExit = { null, null, pred, fini },
4891 * varBody = { init, body };
4892 * return loop(checkExit, varBody);
4893 * }
4894 * }</pre></blockquote>
4895 *
4896 * @param init optional initializer, providing the initial value of the loop variable.
4897 * May be {@code null}, implying a default initial value. See above for other constraints.
4898 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
4899 * above for other constraints.
4900 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
4901 * See above for other constraints.
4902 *
4903 * @return a method handle implementing the {@code while} loop as described by the arguments.
4904 * @throws IllegalArgumentException if the rules for the arguments are violated.
4905 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
4906 *
4907 * @see #loop(MethodHandle[][])
4908 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4909 * @since 9
4910 */
4911 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
4912 whileLoopChecks(init, pred, body);
4913 MethodHandle fini = identityOrVoid(body.type().returnType());
4914 MethodHandle[] checkExit = { null, null, pred, fini };
4915 MethodHandle[] varBody = { init, body };
4916 return loop(checkExit, varBody);
4917 }
4918
4919 /**
4920 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
4921 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
4922 * <p>
4923 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
4924 * method will, in each iteration, first execute its body and then evaluate the predicate.
4925 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
4926 * <p>
4927 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
4928 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
4929 * and updated with the value returned from its invocation. The result of loop execution will be
4930 * the final value of the additional loop-local variable (if present).
4931 * <p>
4932 * The following rules hold for these argument handles:<ul>
4933 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
4934 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
4935 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
4936 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
4937 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
4938 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
4939 * It will constrain the parameter lists of the other loop parts.
4940 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
4941 * list {@code (A...)} is called the <em>external parameter list</em>.
4942 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
4943 * additional state variable of the loop.
4944 * The body must both accept and return a value of this type {@code V}.
4945 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
4946 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
4947 * <a href="MethodHandles.html#effid">effectively identical</a>
4948 * to the external parameter list {@code (A...)}.
4949 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
4950 * {@linkplain #empty default value}.
4951 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
4952 * Its parameter list (either empty or of the form {@code (V A*)}) must be
4953 * effectively identical to the internal parameter list.
4954 * </ul>
4955 * <p>
4956 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
4957 * <li>The loop handle's result type is the result type {@code V} of the body.
4958 * <li>The loop handle's parameter types are the types {@code (A...)},
4959 * from the external parameter list.
4960 * </ul>
4961 * <p>
4962 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4963 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4964 * passed to the loop.
4965 * <blockquote><pre>{@code
4966 * V init(A...);
4967 * boolean pred(V, A...);
4968 * V body(V, A...);
4969 * V doWhileLoop(A... a...) {
4970 * V v = init(a...);
4971 * do {
4972 * v = body(v, a...);
4973 * } while (pred(v, a...));
4974 * return v;
4975 * }
4976 * }</pre></blockquote>
4977 * <p>
4978 * @apiNote Example:
4979 * <blockquote><pre>{@code
4980 * // int i = 0; while (i < limit) { ++i; } return i; => limit
4981 * static int zero(int limit) { return 0; }
4982 * static int step(int i, int limit) { return i + 1; }
4983 * static boolean pred(int i, int limit) { return i < limit; }
4984 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
4985 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
4986 * assertEquals(23, loop.invoke(23));
4987 * }</pre></blockquote>
4988 *
4989 * <p>
4990 * @apiNote The implementation of this method can be expressed as follows:
4991 * <blockquote><pre>{@code
4992 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
4993 * MethodHandle fini = (body.type().returnType() == void.class
4994 * ? null : identity(body.type().returnType()));
4995 * MethodHandle[] clause = { init, body, pred, fini };
4996 * return loop(clause);
4997 * }
4998 * }</pre></blockquote>
4999 *
5000 * @param init optional initializer, providing the initial value of the loop variable.
5001 * May be {@code null}, implying a default initial value. See above for other constraints.
5002 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5003 * See above for other constraints.
5004 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5005 * above for other constraints.
5006 *
5007 * @return a method handle implementing the {@code while} loop as described by the arguments.
5008 * @throws IllegalArgumentException if the rules for the arguments are violated.
5009 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5010 *
5011 * @see #loop(MethodHandle[][])
5012 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
5013 * @since 9
5014 */
5015 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5016 whileLoopChecks(init, pred, body);
5017 MethodHandle fini = identityOrVoid(body.type().returnType());
5018 MethodHandle[] clause = {init, body, pred, fini };
5019 return loop(clause);
5020 }
5021
5022 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
5023 Objects.requireNonNull(pred);
5024 Objects.requireNonNull(body);
5025 MethodType bodyType = body.type();
5026 Class<?> returnType = bodyType.returnType();
5027 List<Class<?>> innerList = bodyType.parameterList();
5028 List<Class<?>> outerList = innerList;
5029 if (returnType == void.class) {
5030 // OK
5031 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
5032 // leading V argument missing => error
5033 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5034 throw misMatchedTypes("body function", bodyType, expected);
5035 } else {
5036 outerList = innerList.subList(1, innerList.size());
5037 }
5038 MethodType predType = pred.type();
5039 if (predType.returnType() != boolean.class ||
5040 !predType.effectivelyIdenticalParameters(0, innerList)) {
5041 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
5042 }
5043 if (init != null) {
5044 MethodType initType = init.type();
5045 if (initType.returnType() != returnType ||
5046 !initType.effectivelyIdenticalParameters(0, outerList)) {
5047 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5048 }
5049 }
5050 }
5051
5052 /**
5053 * Constructs a loop that runs a given number of iterations.
5054 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5055 * <p>
5056 * The number of iterations is determined by the {@code iterations} handle evaluation result.
5057 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
5058 * It will be initialized to 0 and incremented by 1 in each iteration.
5059 * <p>
5060 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5061 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5062 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5063 * <p>
5064 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5065 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5066 * iteration variable.
5067 * The result of the loop handle execution will be the final {@code V} value of that variable
5068 * (or {@code void} if there is no {@code V} variable).
5069 * <p>
5070 * The following rules hold for the argument handles:<ul>
5071 * <li>The {@code iterations} handle must not be {@code null}, and must return
5072 * the type {@code int}, referred to here as {@code I} in parameter type lists.
5073 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5074 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5075 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5076 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5077 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5078 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5079 * of types called the <em>internal parameter list</em>.
5080 * It will constrain the parameter lists of the other loop parts.
5081 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5082 * with no additional {@code A} types, then the internal parameter list is extended by
5083 * the argument types {@code A...} of the {@code iterations} handle.
5084 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5085 * list {@code (A...)} is called the <em>external parameter list</em>.
5086 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5087 * additional state variable of the loop.
5088 * The body must both accept a leading parameter and return a value of this type {@code V}.
5089 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5090 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5091 * <a href="MethodHandles.html#effid">effectively identical</a>
5092 * to the external parameter list {@code (A...)}.
5093 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5094 * {@linkplain #empty default value}.
5095 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
5096 * effectively identical to the external parameter list {@code (A...)}.
5097 * </ul>
5098 * <p>
5099 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5100 * <li>The loop handle's result type is the result type {@code V} of the body.
5101 * <li>The loop handle's parameter types are the types {@code (A...)},
5102 * from the external parameter list.
5103 * </ul>
5104 * <p>
5105 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5106 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5107 * arguments passed to the loop.
5108 * <blockquote><pre>{@code
5109 * int iterations(A...);
5110 * V init(A...);
5111 * V body(V, int, A...);
5112 * V countedLoop(A... a...) {
5113 * int end = iterations(a...);
5114 * V v = init(a...);
5115 * for (int i = 0; i < end; ++i) {
5116 * v = body(v, i, a...);
5117 * }
5118 * return v;
5119 * }
5120 * }</pre></blockquote>
5121 * <p>
5122 * @apiNote Example with a fully conformant body method:
5123 * <blockquote><pre>{@code
5124 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5125 * // => a variation on a well known theme
5126 * static String step(String v, int counter, String init) { return "na " + v; }
5127 * // assume MH_step is a handle to the method above
5128 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
5129 * MethodHandle start = MethodHandles.identity(String.class);
5130 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
5131 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
5132 * }</pre></blockquote>
5133 * <p>
5134 * @apiNote Example with the simplest possible body method type,
5135 * and passing the number of iterations to the loop invocation:
5136 * <blockquote><pre>{@code
5137 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5138 * // => a variation on a well known theme
5139 * static String step(String v, int counter ) { return "na " + v; }
5140 * // assume MH_step is a handle to the method above
5141 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
5142 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
5143 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
5144 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
5145 * }</pre></blockquote>
5146 * <p>
5147 * @apiNote Example that treats the number of iterations, string to append to, and string to append
5148 * as loop parameters:
5149 * <blockquote><pre>{@code
5150 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5151 * // => a variation on a well known theme
5152 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
5153 * // assume MH_step is a handle to the method above
5154 * MethodHandle count = MethodHandles.identity(int.class);
5155 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
5156 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
5157 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
5158 * }</pre></blockquote>
5159 * <p>
5160 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
5161 * to enforce a loop type:
5162 * <blockquote><pre>{@code
5163 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5164 * // => a variation on a well known theme
5165 * static String step(String v, int counter, String pre) { return pre + " " + v; }
5166 * // assume MH_step is a handle to the method above
5167 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
5168 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
5169 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
5170 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
5171 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
5172 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
5173 * }</pre></blockquote>
5174 * <p>
5175 * @apiNote The implementation of this method can be expressed as follows:
5176 * <blockquote><pre>{@code
5177 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5178 * return countedLoop(empty(iterations.type()), iterations, init, body);
5179 * }
5180 * }</pre></blockquote>
5181 *
5182 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
5183 * result type must be {@code int}. See above for other constraints.
5184 * @param init optional initializer, providing the initial value of the loop variable.
5185 * May be {@code null}, implying a default initial value. See above for other constraints.
5186 * @param body body of the loop, which may not be {@code null}.
5187 * It controls the loop parameters and result type in the standard case (see above for details).
5188 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5189 * and may accept any number of additional types.
5190 * See above for other constraints.
5191 *
5192 * @return a method handle representing the loop.
5193 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
5194 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5195 *
5196 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
5197 * @since 9
5198 */
5199 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5200 return countedLoop(empty(iterations.type()), iterations, init, body);
5201 }
5202
5203 /**
5204 * Constructs a loop that counts over a range of numbers.
5205 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5206 * <p>
5207 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
5208 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
5209 * values of the loop counter.
5210 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
5211 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
5212 * <p>
5213 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5214 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5215 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5216 * <p>
5217 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5218 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5219 * iteration variable.
5220 * The result of the loop handle execution will be the final {@code V} value of that variable
5221 * (or {@code void} if there is no {@code V} variable).
5222 * <p>
5223 * The following rules hold for the argument handles:<ul>
5224 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
5225 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
5226 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5227 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5228 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5229 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5230 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5231 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5232 * of types called the <em>internal parameter list</em>.
5233 * It will constrain the parameter lists of the other loop parts.
5234 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5235 * with no additional {@code A} types, then the internal parameter list is extended by
5236 * the argument types {@code A...} of the {@code end} handle.
5237 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5238 * list {@code (A...)} is called the <em>external parameter list</em>.
5239 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5240 * additional state variable of the loop.
5241 * The body must both accept a leading parameter and return a value of this type {@code V}.
5242 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5243 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5244 * <a href="MethodHandles.html#effid">effectively identical</a>
5245 * to the external parameter list {@code (A...)}.
5246 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5247 * {@linkplain #empty default value}.
5248 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
5249 * effectively identical to the external parameter list {@code (A...)}.
5250 * <li>Likewise, the parameter list of {@code end} must be effectively identical
5251 * to the external parameter list.
5252 * </ul>
5253 * <p>
5254 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5255 * <li>The loop handle's result type is the result type {@code V} of the body.
5256 * <li>The loop handle's parameter types are the types {@code (A...)},
5257 * from the external parameter list.
5258 * </ul>
5259 * <p>
5260 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5261 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5262 * arguments passed to the loop.
5263 * <blockquote><pre>{@code
5264 * int start(A...);
5265 * int end(A...);
5266 * V init(A...);
5267 * V body(V, int, A...);
5268 * V countedLoop(A... a...) {
5269 * int e = end(a...);
5270 * int s = start(a...);
5271 * V v = init(a...);
5272 * for (int i = s; i < e; ++i) {
5273 * v = body(v, i, a...);
5274 * }
5275 * return v;
5276 * }
5277 * }</pre></blockquote>
5278 *
5279 * <p>
5280 * @apiNote The implementation of this method can be expressed as follows:
5281 * <blockquote><pre>{@code
5282 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5283 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
5284 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
5285 * // the following semantics:
5286 * // MH_increment: (int limit, int counter) -> counter + 1
5287 * // MH_predicate: (int limit, int counter) -> counter < limit
5288 * Class<?> counterType = start.type().returnType(); // int
5289 * Class<?> returnType = body.type().returnType();
5290 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
5291 * if (returnType != void.class) { // ignore the V variable
5292 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5293 * pred = dropArguments(pred, 1, returnType); // ditto
5294 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
5295 * }
5296 * body = dropArguments(body, 0, counterType); // ignore the limit variable
5297 * MethodHandle[]
5298 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5299 * bodyClause = { init, body }, // v = init(); v = body(v, i)
5300 * indexVar = { start, incr }; // i = start(); i = i + 1
5301 * return loop(loopLimit, bodyClause, indexVar);
5302 * }
5303 * }</pre></blockquote>
5304 *
5305 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
5306 * See above for other constraints.
5307 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
5308 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
5309 * @param init optional initializer, providing the initial value of the loop variable.
5310 * May be {@code null}, implying a default initial value. See above for other constraints.
5311 * @param body body of the loop, which may not be {@code null}.
5312 * It controls the loop parameters and result type in the standard case (see above for details).
5313 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5314 * and may accept any number of additional types.
5315 * See above for other constraints.
5316 *
5317 * @return a method handle representing the loop.
5318 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
5319 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5320 *
5321 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
5322 * @since 9
5323 */
5324 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5325 countedLoopChecks(start, end, init, body);
5326 Class<?> counterType = start.type().returnType(); // int, but who's counting?
5327 Class<?> limitType = end.type().returnType(); // yes, int again
5328 Class<?> returnType = body.type().returnType();
5329 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
5330 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
5331 MethodHandle retv = null;
5332 if (returnType != void.class) {
5333 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5334 pred = dropArguments(pred, 1, returnType); // ditto
5335 retv = dropArguments(identity(returnType), 0, counterType);
5336 }
5337 body = dropArguments(body, 0, counterType); // ignore the limit variable
5338 MethodHandle[]
5339 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5340 bodyClause = { init, body }, // v = init(); v = body(v, i)
5341 indexVar = { start, incr }; // i = start(); i = i + 1
5342 return loop(loopLimit, bodyClause, indexVar);
5343 }
5344
5345 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5346 Objects.requireNonNull(start);
5347 Objects.requireNonNull(end);
5348 Objects.requireNonNull(body);
5349 Class<?> counterType = start.type().returnType();
5350 if (counterType != int.class) {
5351 MethodType expected = start.type().changeReturnType(int.class);
5352 throw misMatchedTypes("start function", start.type(), expected);
5353 } else if (end.type().returnType() != counterType) {
5354 MethodType expected = end.type().changeReturnType(counterType);
5355 throw misMatchedTypes("end function", end.type(), expected);
5356 }
5357 MethodType bodyType = body.type();
5358 Class<?> returnType = bodyType.returnType();
5359 List<Class<?>> innerList = bodyType.parameterList();
5360 // strip leading V value if present
5361 int vsize = (returnType == void.class ? 0 : 1);
5362 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
5363 // argument list has no "V" => error
5364 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5365 throw misMatchedTypes("body function", bodyType, expected);
5366 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
5367 // missing I type => error
5368 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
5369 throw misMatchedTypes("body function", bodyType, expected);
5370 }
5371 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
5372 if (outerList.isEmpty()) {
5373 // special case; take lists from end handle
5374 outerList = end.type().parameterList();
5375 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
5376 }
5377 MethodType expected = methodType(counterType, outerList);
5378 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
5379 throw misMatchedTypes("start parameter types", start.type(), expected);
5380 }
5381 if (end.type() != start.type() &&
5382 !end.type().effectivelyIdenticalParameters(0, outerList)) {
5383 throw misMatchedTypes("end parameter types", end.type(), expected);
5384 }
5385 if (init != null) {
5386 MethodType initType = init.type();
5387 if (initType.returnType() != returnType ||
5388 !initType.effectivelyIdenticalParameters(0, outerList)) {
5389 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5390 }
5391 }
5392 }
5393
5394 /**
5395 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
5396 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5397 * <p>
5398 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
5399 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
5400 * <p>
5401 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5402 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5403 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5404 * <p>
5405 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5406 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5407 * iteration variable.
5408 * The result of the loop handle execution will be the final {@code V} value of that variable
5409 * (or {@code void} if there is no {@code V} variable).
5410 * <p>
5411 * The following rules hold for the argument handles:<ul>
5412 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5413 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
5414 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5415 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
5416 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
5417 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
5418 * of types called the <em>internal parameter list</em>.
5419 * It will constrain the parameter lists of the other loop parts.
5420 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
5421 * with no additional {@code A} types, then the internal parameter list is extended by
5422 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
5423 * single type {@code Iterable} is added and constitutes the {@code A...} list.
5424 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
5425 * list {@code (A...)} is called the <em>external parameter list</em>.
5426 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5427 * additional state variable of the loop.
5428 * The body must both accept a leading parameter and return a value of this type {@code V}.
5429 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5430 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5431 * <a href="MethodHandles.html#effid">effectively identical</a>
5432 * to the external parameter list {@code (A...)}.
5433 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5434 * {@linkplain #empty default value}.
5435 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
5436 * type {@code java.util.Iterator} or a subtype thereof.
5437 * The iterator it produces when the loop is executed will be assumed
5438 * to yield values which can be converted to type {@code T}.
5439 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
5440 * effectively identical to the external parameter list {@code (A...)}.
5441 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
5442 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
5443 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
5444 * handle parameter is adjusted to accept the leading {@code A} type, as if by
5445 * the {@link MethodHandle#asType asType} conversion method.
5446 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
5447 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
5448 * </ul>
5449 * <p>
5450 * The type {@code T} may be either a primitive or reference.
5451 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
5452 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
5453 * as if by the {@link MethodHandle#asType asType} conversion method.
5454 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
5455 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
5456 * <p>
5457 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5458 * <li>The loop handle's result type is the result type {@code V} of the body.
5459 * <li>The loop handle's parameter types are the types {@code (A...)},
5460 * from the external parameter list.
5461 * </ul>
5462 * <p>
5463 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5464 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
5465 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
5466 * <blockquote><pre>{@code
5467 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
5468 * V init(A...);
5469 * V body(V,T,A...);
5470 * V iteratedLoop(A... a...) {
5471 * Iterator<T> it = iterator(a...);
5472 * V v = init(a...);
5473 * while (it.hasNext()) {
5474 * T t = it.next();
5475 * v = body(v, t, a...);
5476 * }
5477 * return v;
5478 * }
5479 * }</pre></blockquote>
5480 * <p>
5481 * @apiNote Example:
5482 * <blockquote><pre>{@code
5483 * // get an iterator from a list
5484 * static List<String> reverseStep(List<String> r, String e) {
5485 * r.add(0, e);
5486 * return r;
5487 * }
5488 * static List<String> newArrayList() { return new ArrayList<>(); }
5489 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
5490 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
5491 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
5492 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
5493 * assertEquals(reversedList, (List<String>) loop.invoke(list));
5494 * }</pre></blockquote>
5495 * <p>
5496 * @apiNote The implementation of this method can be expressed approximately as follows:
5497 * <blockquote><pre>{@code
5498 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5499 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
5500 * Class<?> returnType = body.type().returnType();
5501 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5502 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
5503 * MethodHandle retv = null, step = body, startIter = iterator;
5504 * if (returnType != void.class) {
5505 * // the simple thing first: in (I V A...), drop the I to get V
5506 * retv = dropArguments(identity(returnType), 0, Iterator.class);
5507 * // body type signature (V T A...), internal loop types (I V A...)
5508 * step = swapArguments(body, 0, 1); // swap V <-> T
5509 * }
5510 * if (startIter == null) startIter = MH_getIter;
5511 * MethodHandle[]
5512 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
5513 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
5514 * return loop(iterVar, bodyClause);
5515 * }
5516 * }</pre></blockquote>
5517 *
5518 * @param iterator an optional handle to return the iterator to start the loop.
5519 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
5520 * See above for other constraints.
5521 * @param init optional initializer, providing the initial value of the loop variable.
5522 * May be {@code null}, implying a default initial value. See above for other constraints.
5523 * @param body body of the loop, which may not be {@code null}.
5524 * It controls the loop parameters and result type in the standard case (see above for details).
5525 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
5526 * and may accept any number of additional types.
5527 * See above for other constraints.
5528 *
5529 * @return a method handle embodying the iteration loop functionality.
5530 * @throws NullPointerException if the {@code body} handle is {@code null}.
5531 * @throws IllegalArgumentException if any argument violates the above requirements.
5532 *
5533 * @since 9
5534 */
5535 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5536 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
5537 Class<?> returnType = body.type().returnType();
5538 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
5539 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
5540 MethodHandle startIter;
5541 MethodHandle nextVal;
5542 {
5543 MethodType iteratorType;
5544 if (iterator == null) {
5545 // derive argument type from body, if available, else use Iterable
5546 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
5547 iteratorType = startIter.type().changeParameterType(0, iterableType);
5548 } else {
5549 // force return type to the internal iterator class
5550 iteratorType = iterator.type().changeReturnType(Iterator.class);
5551 startIter = iterator;
5552 }
5553 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5554 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
5555
5556 // perform the asType transforms under an exception transformer, as per spec.:
5557 try {
5558 startIter = startIter.asType(iteratorType);
5559 nextVal = nextRaw.asType(nextValType);
5560 } catch (WrongMethodTypeException ex) {
5561 throw new IllegalArgumentException(ex);
5562 }
5563 }
5564
5565 MethodHandle retv = null, step = body;
5566 if (returnType != void.class) {
5567 // the simple thing first: in (I V A...), drop the I to get V
5568 retv = dropArguments(identity(returnType), 0, Iterator.class);
5569 // body type signature (V T A...), internal loop types (I V A...)
5570 step = swapArguments(body, 0, 1); // swap V <-> T
5571 }
5572
5573 MethodHandle[]
5574 iterVar = { startIter, null, hasNext, retv },
5575 bodyClause = { init, filterArgument(step, 0, nextVal) };
5576 return loop(iterVar, bodyClause);
5577 }
5578
5579 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5580 Objects.requireNonNull(body);
5581 MethodType bodyType = body.type();
5582 Class<?> returnType = bodyType.returnType();
5583 List<Class<?>> internalParamList = bodyType.parameterList();
5584 // strip leading V value if present
5585 int vsize = (returnType == void.class ? 0 : 1);
5586 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
5587 // argument list has no "V" => error
5588 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5589 throw misMatchedTypes("body function", bodyType, expected);
5590 } else if (internalParamList.size() <= vsize) {
5591 // missing T type => error
5592 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
5593 throw misMatchedTypes("body function", bodyType, expected);
5594 }
5595 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
5596 Class<?> iterableType = null;
5597 if (iterator != null) {
5598 // special case; if the body handle only declares V and T then
5599 // the external parameter list is obtained from iterator handle
5600 if (externalParamList.isEmpty()) {
5601 externalParamList = iterator.type().parameterList();
5602 }
5603 MethodType itype = iterator.type();
5604 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
5605 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
5606 }
5607 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
5608 MethodType expected = methodType(itype.returnType(), externalParamList);
5609 throw misMatchedTypes("iterator parameters", itype, expected);
5610 }
5611 } else {
5612 if (externalParamList.isEmpty()) {
5613 // special case; if the iterator handle is null and the body handle
5614 // only declares V and T then the external parameter list consists
5615 // of Iterable
5616 externalParamList = Arrays.asList(Iterable.class);
5617 iterableType = Iterable.class;
5618 } else {
5619 // special case; if the iterator handle is null and the external
5620 // parameter list is not empty then the first parameter must be
5621 // assignable to Iterable
5622 iterableType = externalParamList.get(0);
5623 if (!Iterable.class.isAssignableFrom(iterableType)) {
5624 throw newIllegalArgumentException(
5625 "inferred first loop argument must inherit from Iterable: " + iterableType);
5626 }
5627 }
5628 }
5629 if (init != null) {
5630 MethodType initType = init.type();
5631 if (initType.returnType() != returnType ||
5632 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
5633 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
5634 }
5635 }
5636 return iterableType; // help the caller a bit
5637 }
5638
5639 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
5640 // there should be a better way to uncross my wires
5641 int arity = mh.type().parameterCount();
5642 int[] order = new int[arity];
5643 for (int k = 0; k < arity; k++) order[k] = k;
5644 order[i] = j; order[j] = i;
5645 Class<?>[] types = mh.type().parameterArray();
5646 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
5647 MethodType swapType = methodType(mh.type().returnType(), types);
5648 return permuteArguments(mh, swapType, order);
5649 }
5650
5651 /**
5652 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
5653 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
5654 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
5655 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
5656 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
5657 * {@code try-finally} handle.
5658 * <p>
5659 * The {@code cleanup} handle will be passed one or two additional leading arguments.
5660 * The first is the exception thrown during the
5661 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
5662 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
5663 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
5664 * The second argument is not present if the {@code target} handle has a {@code void} return type.
5665 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
5666 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
5667 * <p>
5668 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
5669 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
5670 * two extra leading parameters:<ul>
5671 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
5672 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
5673 * the result from the execution of the {@code target} handle.
5674 * This parameter is not present if the {@code target} returns {@code void}.
5675 * </ul>
5676 * <p>
5677 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
5678 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
5679 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
5680 * the cleanup.
5681 * <blockquote><pre>{@code
5682 * V target(A..., B...);
5683 * V cleanup(Throwable, V, A...);
5684 * V adapter(A... a, B... b) {
5685 * V result = (zero value for V);
5686 * Throwable throwable = null;
5687 * try {
5688 * result = target(a..., b...);
5689 * } catch (Throwable t) {
5690 * throwable = t;
5691 * throw t;
5692 * } finally {
5693 * result = cleanup(throwable, result, a...);
5694 * }
5695 * return result;
5696 * }
5697 * }</pre></blockquote>
5698 * <p>
5699 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5700 * be modified by execution of the target, and so are passed unchanged
5701 * from the caller to the cleanup, if it is invoked.
5702 * <p>
5703 * The target and cleanup must return the same type, even if the cleanup
5704 * always throws.
5705 * To create such a throwing cleanup, compose the cleanup logic
5706 * with {@link #throwException throwException},
5707 * in order to create a method handle of the correct return type.
5708 * <p>
5709 * Note that {@code tryFinally} never converts exceptions into normal returns.
5710 * In rare cases where exceptions must be converted in that way, first wrap
5711 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
5712 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
5713 *
5714 * @param target the handle whose execution is to be wrapped in a {@code try} block.
5715 * @param cleanup the handle that is invoked in the finally block.
5716 *
5717 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
5718 * @throws NullPointerException if any argument is null
5719 * @throws IllegalArgumentException if {@code cleanup} does not accept
5720 * the required leading arguments, or if the method handle types do
5721 * not match in their return types and their
5722 * corresponding trailing parameters
5723 *
5724 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
5725 * @since 9
5726 */
5727 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
5728 List<Class<?>> targetParamTypes = target.type().parameterList();
5729 List<Class<?>> cleanupParamTypes = cleanup.type().parameterList();
5730 Class<?> rtype = target.type().returnType();
5731
5732 tryFinallyChecks(target, cleanup);
5733
5734 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
5735 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5736 // target parameter list.
5737 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
5738
5739 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
5740 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
5741 }
5742
5743 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
5744 Class<?> rtype = target.type().returnType();
5745 if (rtype != cleanup.type().returnType()) {
5746 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
5747 }
5748 MethodType cleanupType = cleanup.type();
5749 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
5750 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
5751 }
5752 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
5753 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
5754 }
5755 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5756 // target parameter list.
5757 int cleanupArgIndex = rtype == void.class ? 1 : 2;
5758 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
5759 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
5760 cleanup.type(), target.type());
5761 }
5762 }
5763
5764 }