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26 package java.lang.invoke;
28 import java.lang.reflect.*;
29 import java.util.List;
30 import java.util.ArrayList;
31 import java.util.Arrays;
33 import sun.invoke.util.ValueConversions;
34 import sun.invoke.util.VerifyAccess;
35 import sun.invoke.util.Wrapper;
36 import static java.lang.invoke.MethodHandleStatics.*;
37 import static java.lang.invoke.MethodHandleNatives.Constants.*;
38 import java.util.concurrent.ConcurrentHashMap;
41 * This class consists exclusively of static methods that operate on or return
42 * method handles. They fall into several categories:
44 * <li>Lookup methods which help create method handles for methods and fields.
45 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
46 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
49 * @author John Rose, JSR 292 EG
52 public class MethodHandles {
54 private MethodHandles() { } // do not instantiate
56 private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
57 static { MethodHandleImpl.initStatics(); }
58 // See IMPL_LOOKUP below.
60 //// Method handle creation from ordinary methods.
63 * Returns a {@link Lookup lookup object} with
64 * full capabilities to emulate all supported bytecode behaviors of the caller.
65 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
66 * Factory methods on the lookup object can create
67 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
68 * for any member that the caller has access to via bytecodes,
69 * including protected and private fields and methods.
70 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
71 * Do not store it in place where untrusted code can access it.
73 * This method is caller sensitive, which means that it may return different
74 * values to different callers.
76 * For any given caller class {@code C}, the lookup object returned by this call
77 * has equivalent capabilities to any lookup object
78 * supplied by the JVM to the bootstrap method of an
79 * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>
80 * executing in the same caller class {@code C}.
81 * @return a lookup object for the caller of this method, with private access
84 public static Lookup lookup() {
85 throw new IllegalStateException("Implement me!");
86 // return new Lookup(Reflection.getCallerClass());
90 * Returns a {@link Lookup lookup object} which is trusted minimally.
91 * It can only be used to create method handles to
92 * publicly accessible fields and methods.
94 * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
95 * of this lookup object will be {@link java.lang.Object}.
97 * <p style="font-size:smaller;">
98 * <em>Discussion:</em>
99 * The lookup class can be changed to any other class {@code C} using an expression of the form
100 * {@link Lookup#in publicLookup().in(C.class)}.
101 * Since all classes have equal access to public names,
102 * such a change would confer no new access rights.
103 * A public lookup object is always subject to
104 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
105 * Also, it cannot access
106 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
107 * @return a lookup object which is trusted minimally
109 public static Lookup publicLookup() {
110 return Lookup.PUBLIC_LOOKUP;
114 * Performs an unchecked "crack" of a
115 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
116 * The result is as if the user had obtained a lookup object capable enough
117 * to crack the target method handle, called
118 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
119 * on the target to obtain its symbolic reference, and then called
120 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
121 * to resolve the symbolic reference to a member.
123 * If there is a security manager, its {@code checkPermission} method
124 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
125 * @param <T> the desired type of the result, either {@link Member} or a subtype
126 * @param target a direct method handle to crack into symbolic reference components
127 * @param expected a class object representing the desired result type {@code T}
128 * @return a reference to the method, constructor, or field object
129 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
130 * @exception NullPointerException if either argument is {@code null}
131 * @exception IllegalArgumentException if the target is not a direct method handle
132 * @exception ClassCastException if the member is not of the expected type
135 public static <T extends Member> T
136 reflectAs(Class<T> expected, MethodHandle target) {
137 // SecurityManager smgr = System.getSecurityManager();
138 // if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
139 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
140 return lookup.revealDirect(target).reflectAs(expected, lookup);
142 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
143 // static final private java.security.Permission ACCESS_PERMISSION =
144 // new ReflectPermission("suppressAccessChecks");
146 static Lookup findFor(Class<?> clazz) {
148 if (o instanceof Class) {
149 return new Lookup(clazz, Lookup.ALL_MODES);
151 throw new IllegalArgumentException("Expecting class: " + o);
155 * A <em>lookup object</em> is a factory for creating method handles,
156 * when the creation requires access checking.
157 * Method handles do not perform
158 * access checks when they are called, but rather when they are created.
159 * Therefore, method handle access
160 * restrictions must be enforced when a method handle is created.
161 * The caller class against which those restrictions are enforced
162 * is known as the {@linkplain #lookupClass lookup class}.
164 * A lookup class which needs to create method handles will call
165 * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
166 * When the {@code Lookup} factory object is created, the identity of the lookup class is
167 * determined, and securely stored in the {@code Lookup} object.
168 * The lookup class (or its delegates) may then use factory methods
169 * on the {@code Lookup} object to create method handles for access-checked members.
170 * This includes all methods, constructors, and fields which are allowed to the lookup class,
173 * <h1><a name="lookups"></a>Lookup Factory Methods</h1>
174 * The factory methods on a {@code Lookup} object correspond to all major
175 * use cases for methods, constructors, and fields.
176 * Each method handle created by a factory method is the functional
177 * equivalent of a particular <em>bytecode behavior</em>.
178 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
179 * Here is a summary of the correspondence between these factory methods and
180 * the behavior the resulting method handles:
181 * <table border=1 cellpadding=5 summary="lookup method behaviors">
183 * <th><a name="equiv"></a>lookup expression</th>
185 * <th>bytecode behavior</th>
188 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
189 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
192 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
193 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
196 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
197 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
200 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
201 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
204 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
205 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
208 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
209 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
212 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
213 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
216 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
217 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
220 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
221 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
224 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
225 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
228 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
229 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
232 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
233 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
236 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
237 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
241 * Here, the type {@code C} is the class or interface being searched for a member,
242 * documented as a parameter named {@code refc} in the lookup methods.
243 * The method type {@code MT} is composed from the return type {@code T}
244 * and the sequence of argument types {@code A*}.
245 * The constructor also has a sequence of argument types {@code A*} and
246 * is deemed to return the newly-created object of type {@code C}.
247 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
248 * The formal parameter {@code this} stands for the self-reference of type {@code C};
249 * if it is present, it is always the leading argument to the method handle invocation.
250 * (In the case of some {@code protected} members, {@code this} may be
251 * restricted in type to the lookup class; see below.)
252 * The name {@code arg} stands for all the other method handle arguments.
253 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
254 * stands for a null reference if the accessed method or field is static,
255 * and {@code this} otherwise.
256 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
257 * for reflective objects corresponding to the given members.
259 * In cases where the given member is of variable arity (i.e., a method or constructor)
260 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
261 * In all other cases, the returned method handle will be of fixed arity.
262 * <p style="font-size:smaller;">
263 * <em>Discussion:</em>
264 * The equivalence between looked-up method handles and underlying
265 * class members and bytecode behaviors
266 * can break down in a few ways:
267 * <ul style="font-size:smaller;">
268 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
269 * the lookup can still succeed, even when there is no equivalent
270 * Java expression or bytecoded constant.
271 * <li>Likewise, if {@code T} or {@code MT}
272 * is not symbolically accessible from the lookup class's loader,
273 * the lookup can still succeed.
274 * For example, lookups for {@code MethodHandle.invokeExact} and
275 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
276 * <li>If there is a security manager installed, it can forbid the lookup
277 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
278 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
279 * constant is not subject to security manager checks.
280 * <li>If the looked-up method has a
281 * <a href="MethodHandle.html#maxarity">very large arity</a>,
282 * the method handle creation may fail, due to the method handle
283 * type having too many parameters.
286 * <h1><a name="access"></a>Access checking</h1>
287 * Access checks are applied in the factory methods of {@code Lookup},
288 * when a method handle is created.
289 * This is a key difference from the Core Reflection API, since
290 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
291 * performs access checking against every caller, on every call.
293 * All access checks start from a {@code Lookup} object, which
294 * compares its recorded lookup class against all requests to
295 * create method handles.
296 * A single {@code Lookup} object can be used to create any number
297 * of access-checked method handles, all checked against a single
300 * A {@code Lookup} object can be shared with other trusted code,
301 * such as a metaobject protocol.
302 * A shared {@code Lookup} object delegates the capability
303 * to create method handles on private members of the lookup class.
304 * Even if privileged code uses the {@code Lookup} object,
305 * the access checking is confined to the privileges of the
306 * original lookup class.
308 * A lookup can fail, because
309 * the containing class is not accessible to the lookup class, or
310 * because the desired class member is missing, or because the
311 * desired class member is not accessible to the lookup class, or
312 * because the lookup object is not trusted enough to access the member.
313 * In any of these cases, a {@code ReflectiveOperationException} will be
314 * thrown from the attempted lookup. The exact class will be one of
317 * <li>NoSuchMethodException — if a method is requested but does not exist
318 * <li>NoSuchFieldException — if a field is requested but does not exist
319 * <li>IllegalAccessException — if the member exists but an access check fails
322 * In general, the conditions under which a method handle may be
323 * looked up for a method {@code M} are no more restrictive than the conditions
324 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
325 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
326 * a method handle lookup will generally raise a corresponding
327 * checked exception, such as {@code NoSuchMethodException}.
328 * And the effect of invoking the method handle resulting from the lookup
329 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
330 * to executing the compiled, verified, and resolved call to {@code M}.
331 * The same point is true of fields and constructors.
332 * <p style="font-size:smaller;">
333 * <em>Discussion:</em>
334 * Access checks only apply to named and reflected methods,
335 * constructors, and fields.
336 * Other method handle creation methods, such as
337 * {@link MethodHandle#asType MethodHandle.asType},
338 * do not require any access checks, and are used
339 * independently of any {@code Lookup} object.
341 * If the desired member is {@code protected}, the usual JVM rules apply,
342 * including the requirement that the lookup class must be either be in the
343 * same package as the desired member, or must inherit that member.
344 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
345 * In addition, if the desired member is a non-static field or method
346 * in a different package, the resulting method handle may only be applied
347 * to objects of the lookup class or one of its subclasses.
348 * This requirement is enforced by narrowing the type of the leading
349 * {@code this} parameter from {@code C}
350 * (which will necessarily be a superclass of the lookup class)
351 * to the lookup class itself.
353 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
354 * that the receiver argument must match both the resolved method <em>and</em>
355 * the current class. Again, this requirement is enforced by narrowing the
356 * type of the leading parameter to the resulting method handle.
357 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
359 * The JVM represents constructors and static initializer blocks as internal methods
360 * with special names ({@code "<init>"} and {@code "<clinit>"}).
361 * The internal syntax of invocation instructions allows them to refer to such internal
362 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
363 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
365 * In some cases, access between nested classes is obtained by the Java compiler by creating
366 * an wrapper method to access a private method of another class
367 * in the same top-level declaration.
368 * For example, a nested class {@code C.D}
369 * can access private members within other related classes such as
370 * {@code C}, {@code C.D.E}, or {@code C.B},
371 * but the Java compiler may need to generate wrapper methods in
372 * those related classes. In such cases, a {@code Lookup} object on
373 * {@code C.E} would be unable to those private members.
374 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
375 * which can transform a lookup on {@code C.E} into one on any of those other
376 * classes, without special elevation of privilege.
378 * The accesses permitted to a given lookup object may be limited,
379 * according to its set of {@link #lookupModes lookupModes},
380 * to a subset of members normally accessible to the lookup class.
381 * For example, the {@link MethodHandles#publicLookup publicLookup}
382 * method produces a lookup object which is only allowed to access
383 * public members in public classes.
384 * The caller sensitive method {@link MethodHandles#lookup lookup}
385 * produces a lookup object with full capabilities relative to
386 * its caller class, to emulate all supported bytecode behaviors.
387 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
388 * with fewer access modes than the original lookup object.
390 * <p style="font-size:smaller;">
391 * <a name="privacc"></a>
392 * <em>Discussion of private access:</em>
393 * We say that a lookup has <em>private access</em>
394 * if its {@linkplain #lookupModes lookup modes}
395 * include the possibility of accessing {@code private} members.
396 * As documented in the relevant methods elsewhere,
397 * only lookups with private access possess the following capabilities:
398 * <ul style="font-size:smaller;">
399 * <li>access private fields, methods, and constructors of the lookup class
400 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
401 * such as {@code Class.forName}
402 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
403 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
404 * for classes accessible to the lookup class
405 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
406 * within the same package member
408 * <p style="font-size:smaller;">
409 * Each of these permissions is a consequence of the fact that a lookup object
410 * with private access can be securely traced back to an originating class,
411 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
412 * can be reliably determined and emulated by method handles.
414 * <h1><a name="secmgr"></a>Security manager interactions</h1>
415 * Although bytecode instructions can only refer to classes in
416 * a related class loader, this API can search for methods in any
417 * class, as long as a reference to its {@code Class} object is
418 * available. Such cross-loader references are also possible with the
419 * Core Reflection API, and are impossible to bytecode instructions
420 * such as {@code invokestatic} or {@code getfield}.
421 * There is a {@linkplain java.lang.SecurityManager security manager API}
422 * to allow applications to check such cross-loader references.
423 * These checks apply to both the {@code MethodHandles.Lookup} API
424 * and the Core Reflection API
425 * (as found on {@link java.lang.Class Class}).
427 * If a security manager is present, member lookups are subject to
429 * From one to three calls are made to the security manager.
430 * Any of these calls can refuse access by throwing a
431 * {@link java.lang.SecurityException SecurityException}.
432 * Define {@code smgr} as the security manager,
433 * {@code lookc} as the lookup class of the current lookup object,
434 * {@code refc} as the containing class in which the member
435 * is being sought, and {@code defc} as the class in which the
436 * member is actually defined.
437 * The value {@code lookc} is defined as <em>not present</em>
438 * if the current lookup object does not have
439 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
440 * The calls are made according to the following rules:
443 * If {@code lookc} is not present, or if its class loader is not
444 * the same as or an ancestor of the class loader of {@code refc},
445 * then {@link SecurityManager#checkPackageAccess
446 * smgr.checkPackageAccess(refcPkg)} is called,
447 * where {@code refcPkg} is the package of {@code refc}.
449 * If the retrieved member is not public and
450 * {@code lookc} is not present, then
451 * {@link SecurityManager#checkPermission smgr.checkPermission}
452 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
454 * If the retrieved member is not public,
455 * and if {@code lookc} is not present,
456 * and if {@code defc} and {@code refc} are different,
457 * then {@link SecurityManager#checkPackageAccess
458 * smgr.checkPackageAccess(defcPkg)} is called,
459 * where {@code defcPkg} is the package of {@code defc}.
461 * Security checks are performed after other access checks have passed.
462 * Therefore, the above rules presuppose a member that is public,
463 * or else that is being accessed from a lookup class that has
464 * rights to access the member.
466 * <h1><a name="callsens"></a>Caller sensitive methods</h1>
467 * A small number of Java methods have a special property called caller sensitivity.
468 * A <em>caller-sensitive</em> method can behave differently depending on the
469 * identity of its immediate caller.
471 * If a method handle for a caller-sensitive method is requested,
472 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
473 * but they take account of the lookup class in a special way.
474 * The resulting method handle behaves as if it were called
475 * from an instruction contained in the lookup class,
476 * so that the caller-sensitive method detects the lookup class.
477 * (By contrast, the invoker of the method handle is disregarded.)
478 * Thus, in the case of caller-sensitive methods,
479 * different lookup classes may give rise to
480 * differently behaving method handles.
482 * In cases where the lookup object is
483 * {@link MethodHandles#publicLookup() publicLookup()},
484 * or some other lookup object without
485 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
486 * the lookup class is disregarded.
487 * In such cases, no caller-sensitive method handle can be created,
488 * access is forbidden, and the lookup fails with an
489 * {@code IllegalAccessException}.
490 * <p style="font-size:smaller;">
491 * <em>Discussion:</em>
492 * For example, the caller-sensitive method
493 * {@link java.lang.Class#forName(String) Class.forName(x)}
494 * can return varying classes or throw varying exceptions,
495 * depending on the class loader of the class that calls it.
496 * A public lookup of {@code Class.forName} will fail, because
497 * there is no reasonable way to determine its bytecode behavior.
498 * <p style="font-size:smaller;">
499 * If an application caches method handles for broad sharing,
500 * it should use {@code publicLookup()} to create them.
501 * If there is a lookup of {@code Class.forName}, it will fail,
502 * and the application must take appropriate action in that case.
503 * It may be that a later lookup, perhaps during the invocation of a
504 * bootstrap method, can incorporate the specific identity
505 * of the caller, making the method accessible.
506 * <p style="font-size:smaller;">
507 * The function {@code MethodHandles.lookup} is caller sensitive
508 * so that there can be a secure foundation for lookups.
509 * Nearly all other methods in the JSR 292 API rely on lookup
510 * objects to check access requests.
514 /** The class on behalf of whom the lookup is being performed. */
515 private final Class<?> lookupClass;
517 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
518 private final int allowedModes;
520 /** A single-bit mask representing {@code public} access,
521 * which may contribute to the result of {@link #lookupModes lookupModes}.
522 * The value, {@code 0x01}, happens to be the same as the value of the
523 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
525 public static final int PUBLIC = Modifier.PUBLIC;
527 /** A single-bit mask representing {@code private} access,
528 * which may contribute to the result of {@link #lookupModes lookupModes}.
529 * The value, {@code 0x02}, happens to be the same as the value of the
530 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
532 public static final int PRIVATE = Modifier.PRIVATE;
534 /** A single-bit mask representing {@code protected} access,
535 * which may contribute to the result of {@link #lookupModes lookupModes}.
536 * The value, {@code 0x04}, happens to be the same as the value of the
537 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
539 public static final int PROTECTED = Modifier.PROTECTED;
541 /** A single-bit mask representing {@code package} access (default access),
542 * which may contribute to the result of {@link #lookupModes lookupModes}.
543 * The value is {@code 0x08}, which does not correspond meaningfully to
544 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
546 public static final int PACKAGE = Modifier.STATIC;
548 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE);
549 private static final int TRUSTED = -1;
551 private static int fixmods(int mods) {
552 mods &= (ALL_MODES - PACKAGE);
553 return (mods != 0) ? mods : PACKAGE;
556 /** Tells which class is performing the lookup. It is this class against
557 * which checks are performed for visibility and access permissions.
559 * The class implies a maximum level of access permission,
560 * but the permissions may be additionally limited by the bitmask
561 * {@link #lookupModes lookupModes}, which controls whether non-public members
563 * @return the lookup class, on behalf of which this lookup object finds members
565 public Class<?> lookupClass() {
569 // This is just for calling out to MethodHandleImpl.
570 private Class<?> lookupClassOrNull() {
571 return (allowedModes == TRUSTED) ? null : lookupClass;
574 /** Tells which access-protection classes of members this lookup object can produce.
575 * The result is a bit-mask of the bits
576 * {@linkplain #PUBLIC PUBLIC (0x01)},
577 * {@linkplain #PRIVATE PRIVATE (0x02)},
578 * {@linkplain #PROTECTED PROTECTED (0x04)},
579 * and {@linkplain #PACKAGE PACKAGE (0x08)}.
581 * A freshly-created lookup object
582 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
583 * has all possible bits set, since the caller class can access all its own members.
584 * A lookup object on a new lookup class
585 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
586 * may have some mode bits set to zero.
587 * The purpose of this is to restrict access via the new lookup object,
588 * so that it can access only names which can be reached by the original
589 * lookup object, and also by the new lookup class.
590 * @return the lookup modes, which limit the kinds of access performed by this lookup object
592 public int lookupModes() {
593 return allowedModes & ALL_MODES;
596 /** Embody the current class (the lookupClass) as a lookup class
597 * for method handle creation.
598 * Must be called by from a method in this package,
599 * which in turn is called by a method not in this package.
601 Lookup(Class<?> lookupClass) {
602 this(lookupClass, ALL_MODES);
603 // make sure we haven't accidentally picked up a privileged class:
604 checkUnprivilegedlookupClass(lookupClass, ALL_MODES);
607 private Lookup(Class<?> lookupClass, int allowedModes) {
608 this.lookupClass = lookupClass;
609 this.allowedModes = allowedModes;
613 * Creates a lookup on the specified new lookup class.
614 * The resulting object will report the specified
615 * class as its own {@link #lookupClass lookupClass}.
617 * However, the resulting {@code Lookup} object is guaranteed
618 * to have no more access capabilities than the original.
619 * In particular, access capabilities can be lost as follows:<ul>
620 * <li>If the new lookup class differs from the old one,
621 * protected members will not be accessible by virtue of inheritance.
622 * (Protected members may continue to be accessible because of package sharing.)
623 * <li>If the new lookup class is in a different package
624 * than the old one, protected and default (package) members will not be accessible.
625 * <li>If the new lookup class is not within the same package member
626 * as the old one, private members will not be accessible.
627 * <li>If the new lookup class is not accessible to the old lookup class,
628 * then no members, not even public members, will be accessible.
629 * (In all other cases, public members will continue to be accessible.)
632 * @param requestedLookupClass the desired lookup class for the new lookup object
633 * @return a lookup object which reports the desired lookup class
634 * @throws NullPointerException if the argument is null
636 public Lookup in(Class<?> requestedLookupClass) {
637 requestedLookupClass.getClass(); // null check
638 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
639 return new Lookup(requestedLookupClass, ALL_MODES);
640 if (requestedLookupClass == this.lookupClass)
641 return this; // keep same capabilities
642 int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
643 if ((newModes & PACKAGE) != 0
644 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
645 newModes &= ~(PACKAGE|PRIVATE);
647 // Allow nestmate lookups to be created without special privilege:
648 if ((newModes & PRIVATE) != 0
649 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
650 newModes &= ~PRIVATE;
652 if ((newModes & PUBLIC) != 0
653 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
654 // The requested class it not accessible from the lookup class.
658 checkUnprivilegedlookupClass(requestedLookupClass, newModes);
659 return new Lookup(requestedLookupClass, newModes);
662 // Make sure outer class is initialized first.
663 static { IMPL_NAMES.getClass(); }
665 /** Version of lookup which is trusted minimally.
666 * It can only be used to create method handles to
667 * publicly accessible members.
669 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC);
671 /** Package-private version of lookup which is trusted. */
672 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
674 private static void checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes) {
675 String name = lookupClass.getName();
676 if (name.startsWith("java.lang.invoke."))
677 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
679 // For caller-sensitive MethodHandles.lookup()
680 // disallow lookup more restricted packages
681 if (allowedModes == ALL_MODES && lookupClass.getClassLoader() == null) {
682 if (name.startsWith("java.") ||
683 (name.startsWith("sun.") && !name.startsWith("sun.invoke."))) {
684 throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
690 * Displays the name of the class from which lookups are to be made.
691 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
692 * If there are restrictions on the access permitted to this lookup,
693 * this is indicated by adding a suffix to the class name, consisting
694 * of a slash and a keyword. The keyword represents the strongest
695 * allowed access, and is chosen as follows:
697 * <li>If no access is allowed, the suffix is "/noaccess".
698 * <li>If only public access is allowed, the suffix is "/public".
699 * <li>If only public and package access are allowed, the suffix is "/package".
700 * <li>If only public, package, and private access are allowed, the suffix is "/private".
702 * If none of the above cases apply, it is the case that full
703 * access (public, package, private, and protected) is allowed.
704 * In this case, no suffix is added.
705 * This is true only of an object obtained originally from
706 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
707 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
708 * always have restricted access, and will display a suffix.
710 * (It may seem strange that protected access should be
711 * stronger than private access. Viewed independently from
712 * package access, protected access is the first to be lost,
713 * because it requires a direct subclass relationship between
714 * caller and callee.)
718 public String toString() {
719 String cname = lookupClass.getName();
720 switch (allowedModes) {
721 case 0: // no privileges
722 return cname + "/noaccess";
724 return cname + "/public";
726 return cname + "/package";
727 case ALL_MODES & ~PROTECTED:
728 return cname + "/private";
732 return "/trusted"; // internal only; not exported
733 default: // Should not happen, but it's a bitfield...
734 cname = cname + "/" + Integer.toHexString(allowedModes);
735 assert(false) : cname;
741 * Produces a method handle for a static method.
742 * The type of the method handle will be that of the method.
743 * (Since static methods do not take receivers, there is no
744 * additional receiver argument inserted into the method handle type,
745 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
746 * The method and all its argument types must be accessible to the lookup object.
748 * The returned method handle will have
749 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
750 * the method's variable arity modifier bit ({@code 0x0080}) is set.
752 * If the returned method handle is invoked, the method's class will
753 * be initialized, if it has not already been initialized.
755 * <blockquote><pre>{@code
756 import static java.lang.invoke.MethodHandles.*;
757 import static java.lang.invoke.MethodType.*;
759 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
760 "asList", methodType(List.class, Object[].class));
761 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
762 * }</pre></blockquote>
763 * @param refc the class from which the method is accessed
764 * @param name the name of the method
765 * @param type the type of the method
766 * @return the desired method handle
767 * @throws NoSuchMethodException if the method does not exist
768 * @throws IllegalAccessException if access checking fails,
769 * or if the method is not {@code static},
770 * or if the method's variable arity modifier bit
771 * is set and {@code asVarargsCollector} fails
772 * @exception SecurityException if a security manager is present and it
773 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
774 * @throws NullPointerException if any argument is null
777 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
778 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
779 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
783 * Produces a method handle for a virtual method.
784 * The type of the method handle will be that of the method,
785 * with the receiver type (usually {@code refc}) prepended.
786 * The method and all its argument types must be accessible to the lookup object.
788 * When called, the handle will treat the first argument as a receiver
789 * and dispatch on the receiver's type to determine which method
790 * implementation to enter.
791 * (The dispatching action is identical with that performed by an
792 * {@code invokevirtual} or {@code invokeinterface} instruction.)
794 * The first argument will be of type {@code refc} if the lookup
795 * class has full privileges to access the member. Otherwise
796 * the member must be {@code protected} and the first argument
797 * will be restricted in type to the lookup class.
799 * The returned method handle will have
800 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
801 * the method's variable arity modifier bit ({@code 0x0080}) is set.
803 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
804 * instructions and method handles produced by {@code findVirtual},
805 * if the class is {@code MethodHandle} and the name string is
806 * {@code invokeExact} or {@code invoke}, the resulting
807 * method handle is equivalent to one produced by
808 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
809 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
810 * with the same {@code type} argument.
813 * <blockquote><pre>{@code
814 import static java.lang.invoke.MethodHandles.*;
815 import static java.lang.invoke.MethodType.*;
817 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
818 "concat", methodType(String.class, String.class));
819 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
820 "hashCode", methodType(int.class));
821 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
822 "hashCode", methodType(int.class));
823 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
824 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
825 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
827 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
828 "subSequence", methodType(CharSequence.class, int.class, int.class));
829 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
830 // constructor "internal method" must be accessed differently:
831 MethodType MT_newString = methodType(void.class); //()V for new String()
832 try { assertEquals("impossible", lookup()
833 .findVirtual(String.class, "<init>", MT_newString));
834 } catch (NoSuchMethodException ex) { } // OK
835 MethodHandle MH_newString = publicLookup()
836 .findConstructor(String.class, MT_newString);
837 assertEquals("", (String) MH_newString.invokeExact());
838 * }</pre></blockquote>
840 * @param refc the class or interface from which the method is accessed
841 * @param name the name of the method
842 * @param type the type of the method, with the receiver argument omitted
843 * @return the desired method handle
844 * @throws NoSuchMethodException if the method does not exist
845 * @throws IllegalAccessException if access checking fails,
846 * or if the method is {@code static}
847 * or if the method's variable arity modifier bit
848 * is set and {@code asVarargsCollector} fails
849 * @exception SecurityException if a security manager is present and it
850 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
851 * @throws NullPointerException if any argument is null
853 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
854 if (refc == MethodHandle.class) {
855 MethodHandle mh = findVirtualForMH(name, type);
856 if (mh != null) return mh;
858 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
859 MemberName method = resolveOrFail(refKind, refc, name, type);
860 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
862 private MethodHandle findVirtualForMH(String name, MethodType type) {
863 // these names require special lookups because of the implicit MethodType argument
864 if ("invoke".equals(name))
865 return invoker(type);
866 if ("invokeExact".equals(name))
867 return exactInvoker(type);
868 assert(!MemberName.isMethodHandleInvokeName(name));
873 * Produces a method handle which creates an object and initializes it, using
874 * the constructor of the specified type.
875 * The parameter types of the method handle will be those of the constructor,
876 * while the return type will be a reference to the constructor's class.
877 * The constructor and all its argument types must be accessible to the lookup object.
879 * The requested type must have a return type of {@code void}.
880 * (This is consistent with the JVM's treatment of constructor type descriptors.)
882 * The returned method handle will have
883 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
884 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
886 * If the returned method handle is invoked, the constructor's class will
887 * be initialized, if it has not already been initialized.
889 * <blockquote><pre>{@code
890 import static java.lang.invoke.MethodHandles.*;
891 import static java.lang.invoke.MethodType.*;
893 MethodHandle MH_newArrayList = publicLookup().findConstructor(
894 ArrayList.class, methodType(void.class, Collection.class));
895 Collection orig = Arrays.asList("x", "y");
896 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
897 assert(orig != copy);
898 assertEquals(orig, copy);
899 // a variable-arity constructor:
900 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
901 ProcessBuilder.class, methodType(void.class, String[].class));
902 ProcessBuilder pb = (ProcessBuilder)
903 MH_newProcessBuilder.invoke("x", "y", "z");
904 assertEquals("[x, y, z]", pb.command().toString());
905 * }</pre></blockquote>
906 * @param refc the class or interface from which the method is accessed
907 * @param type the type of the method, with the receiver argument omitted, and a void return type
908 * @return the desired method handle
909 * @throws NoSuchMethodException if the constructor does not exist
910 * @throws IllegalAccessException if access checking fails
911 * or if the method's variable arity modifier bit
912 * is set and {@code asVarargsCollector} fails
913 * @exception SecurityException if a security manager is present and it
914 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
915 * @throws NullPointerException if any argument is null
917 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
918 String name = "<init>";
919 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
920 return getDirectConstructor(refc, ctor);
924 * Produces an early-bound method handle for a virtual method.
925 * It will bypass checks for overriding methods on the receiver,
926 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
927 * instruction from within the explicitly specified {@code specialCaller}.
928 * The type of the method handle will be that of the method,
929 * with a suitably restricted receiver type prepended.
930 * (The receiver type will be {@code specialCaller} or a subtype.)
931 * The method and all its argument types must be accessible
932 * to the lookup object.
934 * Before method resolution,
935 * if the explicitly specified caller class is not identical with the
936 * lookup class, or if this lookup object does not have
937 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
938 * privileges, the access fails.
940 * The returned method handle will have
941 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
942 * the method's variable arity modifier bit ({@code 0x0080}) is set.
943 * <p style="font-size:smaller;">
944 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
945 * even though the {@code invokespecial} instruction can refer to them
946 * in special circumstances. Use {@link #findConstructor findConstructor}
947 * to access instance initialization methods in a safe manner.)</em>
949 * <blockquote><pre>{@code
950 import static java.lang.invoke.MethodHandles.*;
951 import static java.lang.invoke.MethodType.*;
953 static class Listie extends ArrayList {
954 public String toString() { return "[wee Listie]"; }
955 static Lookup lookup() { return MethodHandles.lookup(); }
958 // no access to constructor via invokeSpecial:
959 MethodHandle MH_newListie = Listie.lookup()
960 .findConstructor(Listie.class, methodType(void.class));
961 Listie l = (Listie) MH_newListie.invokeExact();
962 try { assertEquals("impossible", Listie.lookup().findSpecial(
963 Listie.class, "<init>", methodType(void.class), Listie.class));
964 } catch (NoSuchMethodException ex) { } // OK
965 // access to super and self methods via invokeSpecial:
966 MethodHandle MH_super = Listie.lookup().findSpecial(
967 ArrayList.class, "toString" , methodType(String.class), Listie.class);
968 MethodHandle MH_this = Listie.lookup().findSpecial(
969 Listie.class, "toString" , methodType(String.class), Listie.class);
970 MethodHandle MH_duper = Listie.lookup().findSpecial(
971 Object.class, "toString" , methodType(String.class), Listie.class);
972 assertEquals("[]", (String) MH_super.invokeExact(l));
973 assertEquals(""+l, (String) MH_this.invokeExact(l));
974 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
975 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
976 String.class, "toString", methodType(String.class), Listie.class));
977 } catch (IllegalAccessException ex) { } // OK
978 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
979 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
980 * }</pre></blockquote>
982 * @param refc the class or interface from which the method is accessed
983 * @param name the name of the method (which must not be "<init>")
984 * @param type the type of the method, with the receiver argument omitted
985 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
986 * @return the desired method handle
987 * @throws NoSuchMethodException if the method does not exist
988 * @throws IllegalAccessException if access checking fails
989 * or if the method's variable arity modifier bit
990 * is set and {@code asVarargsCollector} fails
991 * @exception SecurityException if a security manager is present and it
992 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
993 * @throws NullPointerException if any argument is null
995 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
996 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
997 checkSpecialCaller(specialCaller);
998 Lookup specialLookup = this.in(specialCaller);
999 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1000 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1004 * Produces a method handle giving read access to a non-static field.
1005 * The type of the method handle will have a return type of the field's
1007 * The method handle's single argument will be the instance containing
1009 * Access checking is performed immediately on behalf of the lookup class.
1010 * @param refc the class or interface from which the method is accessed
1011 * @param name the field's name
1012 * @param type the field's type
1013 * @return a method handle which can load values from the field
1014 * @throws NoSuchFieldException if the field does not exist
1015 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1016 * @exception SecurityException if a security manager is present and it
1017 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1018 * @throws NullPointerException if any argument is null
1020 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1021 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1022 return getDirectField(REF_getField, refc, field);
1026 * Produces a method handle giving write access to a non-static field.
1027 * The type of the method handle will have a void return type.
1028 * The method handle will take two arguments, the instance containing
1029 * the field, and the value to be stored.
1030 * The second argument will be of the field's value type.
1031 * Access checking is performed immediately on behalf of the lookup class.
1032 * @param refc the class or interface from which the method is accessed
1033 * @param name the field's name
1034 * @param type the field's type
1035 * @return a method handle which can store values into the field
1036 * @throws NoSuchFieldException if the field does not exist
1037 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1038 * @exception SecurityException if a security manager is present and it
1039 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1040 * @throws NullPointerException if any argument is null
1042 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1043 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1044 return getDirectField(REF_putField, refc, field);
1048 * Produces a method handle giving read access to a static field.
1049 * The type of the method handle will have a return type of the field's
1051 * The method handle will take no arguments.
1052 * Access checking is performed immediately on behalf of the lookup class.
1054 * If the returned method handle is invoked, the field's class will
1055 * be initialized, if it has not already been initialized.
1056 * @param refc the class or interface from which the method is accessed
1057 * @param name the field's name
1058 * @param type the field's type
1059 * @return a method handle which can load values from the field
1060 * @throws NoSuchFieldException if the field does not exist
1061 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1062 * @exception SecurityException if a security manager is present and it
1063 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1064 * @throws NullPointerException if any argument is null
1066 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1067 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1068 return getDirectField(REF_getStatic, refc, field);
1072 * Produces a method handle giving write access to a static field.
1073 * The type of the method handle will have a void return type.
1074 * The method handle will take a single
1075 * argument, of the field's value type, the value to be stored.
1076 * Access checking is performed immediately on behalf of the lookup class.
1078 * If the returned method handle is invoked, the field's class will
1079 * be initialized, if it has not already been initialized.
1080 * @param refc the class or interface from which the method is accessed
1081 * @param name the field's name
1082 * @param type the field's type
1083 * @return a method handle which can store values into the field
1084 * @throws NoSuchFieldException if the field does not exist
1085 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1086 * @exception SecurityException if a security manager is present and it
1087 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1088 * @throws NullPointerException if any argument is null
1090 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1091 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1092 return getDirectField(REF_putStatic, refc, field);
1096 * Produces an early-bound method handle for a non-static method.
1097 * The receiver must have a supertype {@code defc} in which a method
1098 * of the given name and type is accessible to the lookup class.
1099 * The method and all its argument types must be accessible to the lookup object.
1100 * The type of the method handle will be that of the method,
1101 * without any insertion of an additional receiver parameter.
1102 * The given receiver will be bound into the method handle,
1103 * so that every call to the method handle will invoke the
1104 * requested method on the given receiver.
1106 * The returned method handle will have
1107 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1108 * the method's variable arity modifier bit ({@code 0x0080}) is set
1109 * <em>and</em> the trailing array argument is not the only argument.
1110 * (If the trailing array argument is the only argument,
1111 * the given receiver value will be bound to it.)
1113 * This is equivalent to the following code:
1114 * <blockquote><pre>{@code
1115 import static java.lang.invoke.MethodHandles.*;
1116 import static java.lang.invoke.MethodType.*;
1118 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1119 MethodHandle mh1 = mh0.bindTo(receiver);
1120 MethodType mt1 = mh1.type();
1121 if (mh0.isVarargsCollector())
1122 mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
1124 * }</pre></blockquote>
1125 * where {@code defc} is either {@code receiver.getClass()} or a super
1126 * type of that class, in which the requested method is accessible
1127 * to the lookup class.
1128 * (Note that {@code bindTo} does not preserve variable arity.)
1129 * @param receiver the object from which the method is accessed
1130 * @param name the name of the method
1131 * @param type the type of the method, with the receiver argument omitted
1132 * @return the desired method handle
1133 * @throws NoSuchMethodException if the method does not exist
1134 * @throws IllegalAccessException if access checking fails
1135 * or if the method's variable arity modifier bit
1136 * is set and {@code asVarargsCollector} fails
1137 * @exception SecurityException if a security manager is present and it
1138 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1139 * @throws NullPointerException if any argument is null
1140 * @see MethodHandle#bindTo
1143 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1144 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1145 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1146 MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1147 return mh.bindReceiver(receiver).setVarargs(method);
1151 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1152 * to <i>m</i>, if the lookup class has permission.
1153 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1154 * If <i>m</i> is virtual, overriding is respected on every call.
1155 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1156 * The type of the method handle will be that of the method,
1157 * with the receiver type prepended (but only if it is non-static).
1158 * If the method's {@code accessible} flag is not set,
1159 * access checking is performed immediately on behalf of the lookup class.
1160 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1162 * The returned method handle will have
1163 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1164 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1166 * If <i>m</i> is static, and
1167 * if the returned method handle is invoked, the method's class will
1168 * be initialized, if it has not already been initialized.
1169 * @param m the reflected method
1170 * @return a method handle which can invoke the reflected method
1171 * @throws IllegalAccessException if access checking fails
1172 * or if the method's variable arity modifier bit
1173 * is set and {@code asVarargsCollector} fails
1174 * @throws NullPointerException if the argument is null
1176 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1177 if (m.getDeclaringClass() == MethodHandle.class) {
1178 MethodHandle mh = unreflectForMH(m);
1179 if (mh != null) return mh;
1181 MemberName method = new MemberName(m);
1182 byte refKind = method.getReferenceKind();
1183 if (refKind == REF_invokeSpecial)
1184 refKind = REF_invokeVirtual;
1185 assert(method.isMethod());
1186 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1187 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1189 private MethodHandle unreflectForMH(Method m) {
1190 // these names require special lookups because they throw UnsupportedOperationException
1191 if (MemberName.isMethodHandleInvokeName(m.getName()))
1192 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1197 * Produces a method handle for a reflected method.
1198 * It will bypass checks for overriding methods on the receiver,
1199 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1200 * instruction from within the explicitly specified {@code specialCaller}.
1201 * The type of the method handle will be that of the method,
1202 * with a suitably restricted receiver type prepended.
1203 * (The receiver type will be {@code specialCaller} or a subtype.)
1204 * If the method's {@code accessible} flag is not set,
1205 * access checking is performed immediately on behalf of the lookup class,
1206 * as if {@code invokespecial} instruction were being linked.
1208 * Before method resolution,
1209 * if the explicitly specified caller class is not identical with the
1210 * lookup class, or if this lookup object does not have
1211 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1212 * privileges, the access fails.
1214 * The returned method handle will have
1215 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1216 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1217 * @param m the reflected method
1218 * @param specialCaller the class nominally calling the method
1219 * @return a method handle which can invoke the reflected method
1220 * @throws IllegalAccessException if access checking fails
1221 * or if the method's variable arity modifier bit
1222 * is set and {@code asVarargsCollector} fails
1223 * @throws NullPointerException if any argument is null
1225 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1226 checkSpecialCaller(specialCaller);
1227 Lookup specialLookup = this.in(specialCaller);
1228 MemberName method = new MemberName(m, true);
1229 assert(method.isMethod());
1230 // ignore m.isAccessible: this is a new kind of access
1231 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1235 * Produces a method handle for a reflected constructor.
1236 * The type of the method handle will be that of the constructor,
1237 * with the return type changed to the declaring class.
1238 * The method handle will perform a {@code newInstance} operation,
1239 * creating a new instance of the constructor's class on the
1240 * arguments passed to the method handle.
1242 * If the constructor's {@code accessible} flag is not set,
1243 * access checking is performed immediately on behalf of the lookup class.
1245 * The returned method handle will have
1246 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1247 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1249 * If the returned method handle is invoked, the constructor's class will
1250 * be initialized, if it has not already been initialized.
1251 * @param c the reflected constructor
1252 * @return a method handle which can invoke the reflected constructor
1253 * @throws IllegalAccessException if access checking fails
1254 * or if the method's variable arity modifier bit
1255 * is set and {@code asVarargsCollector} fails
1256 * @throws NullPointerException if the argument is null
1258 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1259 MemberName ctor = new MemberName(c);
1260 assert(ctor.isConstructor());
1261 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1262 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1266 * Produces a method handle giving read access to a reflected field.
1267 * The type of the method handle will have a return type of the field's
1269 * If the field is static, the method handle will take no arguments.
1270 * Otherwise, its single argument will be the instance containing
1272 * If the field's {@code accessible} flag is not set,
1273 * access checking is performed immediately on behalf of the lookup class.
1275 * If the field is static, and
1276 * if the returned method handle is invoked, the field's class will
1277 * be initialized, if it has not already been initialized.
1278 * @param f the reflected field
1279 * @return a method handle which can load values from the reflected field
1280 * @throws IllegalAccessException if access checking fails
1281 * @throws NullPointerException if the argument is null
1283 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1284 return unreflectField(f, false);
1286 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1287 MemberName field = new MemberName(f, isSetter);
1289 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1290 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1291 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1292 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1296 * Produces a method handle giving write access to a reflected field.
1297 * The type of the method handle will have a void return type.
1298 * If the field is static, the method handle will take a single
1299 * argument, of the field's value type, the value to be stored.
1300 * Otherwise, the two arguments will be the instance containing
1301 * the field, and the value to be stored.
1302 * If the field's {@code accessible} flag is not set,
1303 * access checking is performed immediately on behalf of the lookup class.
1305 * If the field is static, and
1306 * if the returned method handle is invoked, the field's class will
1307 * be initialized, if it has not already been initialized.
1308 * @param f the reflected field
1309 * @return a method handle which can store values into the reflected field
1310 * @throws IllegalAccessException if access checking fails
1311 * @throws NullPointerException if the argument is null
1313 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1314 return unreflectField(f, true);
1318 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1319 * created by this lookup object or a similar one.
1320 * Security and access checks are performed to ensure that this lookup object
1321 * is capable of reproducing the target method handle.
1322 * This means that the cracking may fail if target is a direct method handle
1323 * but was created by an unrelated lookup object.
1324 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1325 * and was created by a lookup object for a different class.
1326 * @param target a direct method handle to crack into symbolic reference components
1327 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1328 * @exception SecurityException if a security manager is present and it
1329 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1330 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1331 * @exception NullPointerException if the target is {@code null}
1332 * @see MethodHandleInfo
1335 public MethodHandleInfo revealDirect(MethodHandle target) {
1336 MemberName member = target.internalMemberName();
1337 if (member == null || (!member.isResolved() && !member.isMethodHandleInvoke()))
1338 throw newIllegalArgumentException("not a direct method handle");
1339 Class<?> defc = member.getDeclaringClass();
1340 byte refKind = member.getReferenceKind();
1341 assert(MethodHandleNatives.refKindIsValid(refKind));
1342 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1343 // Devirtualized method invocation is usually formally virtual.
1344 // To avoid creating extra MemberName objects for this common case,
1345 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1346 refKind = REF_invokeVirtual;
1347 if (refKind == REF_invokeVirtual && defc.isInterface())
1348 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
1349 refKind = REF_invokeInterface;
1350 // Check SM permissions and member access before cracking.
1352 checkAccess(refKind, defc, member);
1353 checkSecurityManager(defc, member);
1354 } catch (IllegalAccessException ex) {
1355 throw new IllegalArgumentException(ex);
1357 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
1358 Class<?> callerClass = target.internalCallerClass();
1359 if (!hasPrivateAccess() || callerClass != lookupClass())
1360 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
1362 // Produce the handle to the results.
1363 return new InfoFromMemberName(this, member, refKind);
1366 /// Helper methods, all package-private.
1368 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1369 checkSymbolicClass(refc); // do this before attempting to resolve
1370 name.getClass(); // NPE
1371 type.getClass(); // NPE
1372 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1373 NoSuchFieldException.class);
1376 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1377 checkSymbolicClass(refc); // do this before attempting to resolve
1378 name.getClass(); // NPE
1379 type.getClass(); // NPE
1380 checkMethodName(refKind, name); // NPE check on name
1381 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1382 NoSuchMethodException.class);
1385 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
1386 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
1387 member.getName().getClass(); // NPE
1388 member.getType().getClass(); // NPE
1389 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
1390 ReflectiveOperationException.class);
1393 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
1394 refc.getClass(); // NPE
1395 Class<?> caller = lookupClassOrNull();
1396 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
1397 throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this);
1400 /** Check name for an illegal leading "<" character. */
1401 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
1402 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
1403 throw new NoSuchMethodException("illegal method name: "+name);
1408 * Find my trustable caller class if m is a caller sensitive method.
1409 * If this lookup object has private access, then the caller class is the lookupClass.
1410 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
1412 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
1413 Class<?> callerClass = null;
1414 if (MethodHandleNatives.isCallerSensitive(m)) {
1415 // Only lookups with private access are allowed to resolve caller-sensitive methods
1416 if (hasPrivateAccess()) {
1417 callerClass = lookupClass;
1419 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
1425 private boolean hasPrivateAccess() {
1426 return (allowedModes & PRIVATE) != 0;
1430 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
1431 * Determines a trustable caller class to compare with refc, the symbolic reference class.
1432 * If this lookup object has private access, then the caller class is the lookupClass.
1434 void checkSecurityManager(Class<?> refc, MemberName m) {
1435 // SecurityManager smgr = System.getSecurityManager();
1436 // if (smgr == null) return;
1437 // if (allowedModes == TRUSTED) return;
1440 // boolean fullPowerLookup = hasPrivateAccess();
1441 // if (!fullPowerLookup ||
1442 // !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
1443 // ReflectUtil.checkPackageAccess(refc);
1447 // if (m.isPublic()) return;
1448 // if (!fullPowerLookup) {
1449 // smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
1453 // Class<?> defc = m.getDeclaringClass();
1454 // if (!fullPowerLookup && defc != refc) {
1455 // ReflectUtil.checkPackageAccess(defc);
1459 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1460 boolean wantStatic = (refKind == REF_invokeStatic);
1462 if (m.isConstructor())
1463 message = "expected a method, not a constructor";
1464 else if (!m.isMethod())
1465 message = "expected a method";
1466 else if (wantStatic != m.isStatic())
1467 message = wantStatic ? "expected a static method" : "expected a non-static method";
1469 { checkAccess(refKind, refc, m); return; }
1470 throw m.makeAccessException(message, this);
1473 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1474 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
1476 if (wantStatic != m.isStatic())
1477 message = wantStatic ? "expected a static field" : "expected a non-static field";
1479 { checkAccess(refKind, refc, m); return; }
1480 throw m.makeAccessException(message, this);
1483 /** Check public/protected/private bits on the symbolic reference class and its member. */
1484 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1485 assert(m.referenceKindIsConsistentWith(refKind) &&
1486 MethodHandleNatives.refKindIsValid(refKind) &&
1487 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
1488 int allowedModes = this.allowedModes;
1489 if (allowedModes == TRUSTED) return;
1490 int mods = m.getModifiers();
1491 if (Modifier.isProtected(mods) &&
1492 refKind == REF_invokeVirtual &&
1493 m.getDeclaringClass() == Object.class &&
1494 m.getName().equals("clone") &&
1496 // The JVM does this hack also.
1497 // (See ClassVerifier::verify_invoke_instructions
1498 // and LinkResolver::check_method_accessability.)
1499 // Because the JVM does not allow separate methods on array types,
1500 // there is no separate method for int[].clone.
1501 // All arrays simply inherit Object.clone.
1502 // But for access checking logic, we make Object.clone
1503 // (normally protected) appear to be public.
1504 // Later on, when the DirectMethodHandle is created,
1505 // its leading argument will be restricted to the
1506 // requested array type.
1507 // N.B. The return type is not adjusted, because
1508 // that is *not* the bytecode behavior.
1509 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
1511 if (Modifier.isFinal(mods) &&
1512 MethodHandleNatives.refKindIsSetter(refKind))
1513 throw m.makeAccessException("unexpected set of a final field", this);
1514 if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0)
1515 return; // common case
1516 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
1517 if ((requestedModes & allowedModes) != 0) {
1518 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
1519 mods, lookupClass(), allowedModes))
1522 // Protected members can also be checked as if they were package-private.
1523 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
1524 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
1527 throw m.makeAccessException(accessFailedMessage(refc, m), this);
1530 String accessFailedMessage(Class<?> refc, MemberName m) {
1531 Class<?> defc = m.getDeclaringClass();
1532 int mods = m.getModifiers();
1533 // check the class first:
1534 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
1536 Modifier.isPublic(refc.getModifiers())));
1537 if (!classOK && (allowedModes & PACKAGE) != 0) {
1538 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
1540 VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
1543 return "class is not public";
1544 if (Modifier.isPublic(mods))
1545 return "access to public member failed"; // (how?)
1546 if (Modifier.isPrivate(mods))
1547 return "member is private";
1548 if (Modifier.isProtected(mods))
1549 return "member is protected";
1550 return "member is private to package";
1553 private static final boolean ALLOW_NESTMATE_ACCESS = false;
1555 private void checkSpecialCaller(Class<?> specialCaller) throws IllegalAccessException {
1556 int allowedModes = this.allowedModes;
1557 if (allowedModes == TRUSTED) return;
1558 if (!hasPrivateAccess()
1559 || (specialCaller != lookupClass()
1560 && !(ALLOW_NESTMATE_ACCESS &&
1561 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
1562 throw new MemberName(specialCaller).
1563 makeAccessException("no private access for invokespecial", this);
1566 private boolean restrictProtectedReceiver(MemberName method) {
1567 // The accessing class only has the right to use a protected member
1568 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
1569 if (!method.isProtected() || method.isStatic()
1570 || allowedModes == TRUSTED
1571 || method.getDeclaringClass() == lookupClass()
1572 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
1573 || (ALLOW_NESTMATE_ACCESS &&
1574 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
1578 private MethodHandle restrictReceiver(MemberName method, MethodHandle mh, Class<?> caller) throws IllegalAccessException {
1579 assert(!method.isStatic());
1580 // receiver type of mh is too wide; narrow to caller
1581 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
1582 throw method.makeAccessException("caller class must be a subclass below the method", caller);
1584 MethodType rawType = mh.type();
1585 if (rawType.parameterType(0) == caller) return mh;
1586 MethodType narrowType = rawType.changeParameterType(0, caller);
1587 return mh.viewAsType(narrowType);
1590 /** Check access and get the requested method. */
1591 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1592 final boolean doRestrict = true;
1593 final boolean checkSecurity = true;
1594 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1596 /** Check access and get the requested method, eliding receiver narrowing rules. */
1597 private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1598 final boolean doRestrict = false;
1599 final boolean checkSecurity = true;
1600 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1602 /** Check access and get the requested method, eliding security manager checks. */
1603 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1604 final boolean doRestrict = true;
1605 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1606 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1608 /** Common code for all methods; do not call directly except from immediately above. */
1609 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
1610 boolean checkSecurity,
1611 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
1612 checkMethod(refKind, refc, method);
1613 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1615 checkSecurityManager(refc, method);
1616 assert(!method.isMethodHandleInvoke());
1618 Class<?> refcAsSuper;
1619 if (refKind == REF_invokeSpecial &&
1620 refc != lookupClass() &&
1621 !refc.isInterface() &&
1622 refc != (refcAsSuper = lookupClass().getSuperclass()) &&
1623 refc.isAssignableFrom(lookupClass())) {
1624 assert(!method.getName().equals("<init>")); // not this code path
1625 // Per JVMS 6.5, desc. of invokespecial instruction:
1626 // If the method is in a superclass of the LC,
1627 // and if our original search was above LC.super,
1628 // repeat the search (symbolic lookup) from LC.super.
1629 // FIXME: MemberName.resolve should handle this instead.
1630 MemberName m2 = new MemberName(refcAsSuper,
1632 method.getMethodType(),
1634 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
1635 if (m2 == null) throw new InternalError(method.toString());
1638 // redo basic checks
1639 checkMethod(refKind, refc, method);
1642 MethodHandle mh = DirectMethodHandle.make(refKind, refc, method);
1643 mh = maybeBindCaller(method, mh, callerClass);
1644 mh = mh.setVarargs(method);
1645 // Optionally narrow the receiver argument to refc using restrictReceiver.
1647 (refKind == REF_invokeSpecial ||
1648 (MethodHandleNatives.refKindHasReceiver(refKind) &&
1649 restrictProtectedReceiver(method))))
1650 mh = restrictReceiver(method, mh, lookupClass());
1653 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
1654 Class<?> callerClass)
1655 throws IllegalAccessException {
1656 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
1658 Class<?> hostClass = lookupClass;
1659 if (!hasPrivateAccess()) // caller must have private access
1660 hostClass = callerClass; // callerClass came from a security manager style stack walk
1661 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
1662 // Note: caller will apply varargs after this step happens.
1665 /** Check access and get the requested field. */
1666 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1667 final boolean checkSecurity = true;
1668 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1670 /** Check access and get the requested field, eliding security manager checks. */
1671 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1672 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1673 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1675 /** Common code for all fields; do not call directly except from immediately above. */
1676 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
1677 boolean checkSecurity) throws IllegalAccessException {
1678 checkField(refKind, refc, field);
1679 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1681 checkSecurityManager(refc, field);
1682 MethodHandle mh = DirectMethodHandle.make(refc, field);
1683 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
1684 restrictProtectedReceiver(field));
1686 mh = restrictReceiver(field, mh, lookupClass());
1689 /** Check access and get the requested constructor. */
1690 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1691 final boolean checkSecurity = true;
1692 return getDirectConstructorCommon(refc, ctor, checkSecurity);
1694 /** Check access and get the requested constructor, eliding security manager checks. */
1695 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1696 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1697 return getDirectConstructorCommon(refc, ctor, checkSecurity);
1699 /** Common code for all constructors; do not call directly except from immediately above. */
1700 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
1701 boolean checkSecurity) throws IllegalAccessException {
1702 assert(ctor.isConstructor());
1703 checkAccess(REF_newInvokeSpecial, refc, ctor);
1704 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1706 checkSecurityManager(refc, ctor);
1707 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
1708 return DirectMethodHandle.make(ctor).setVarargs(ctor);
1711 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
1714 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
1715 if (!(type instanceof Class || type instanceof MethodType))
1716 throw new InternalError("unresolved MemberName");
1717 MemberName member = new MemberName(refKind, defc, name, type);
1718 MethodHandle mh = LOOKASIDE_TABLE.get(member);
1720 checkSymbolicClass(defc);
1723 // Treat MethodHandle.invoke and invokeExact specially.
1724 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
1725 mh = findVirtualForMH(member.getName(), member.getMethodType());
1730 MemberName resolved = resolveOrFail(refKind, member);
1731 mh = getDirectMethodForConstant(refKind, defc, resolved);
1732 if (mh instanceof DirectMethodHandle
1733 && canBeCached(refKind, defc, resolved)) {
1734 MemberName key = mh.internalMemberName();
1736 key = key.asNormalOriginal();
1738 if (member.equals(key)) { // better safe than sorry
1739 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
1745 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
1746 if (refKind == REF_invokeSpecial) {
1749 if (!Modifier.isPublic(defc.getModifiers()) ||
1750 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
1751 !member.isPublic() ||
1752 member.isCallerSensitive()) {
1755 ClassLoader loader = defc.getClassLoader();
1756 // if (!sun.misc.VM.isSystemDomainLoader(loader)) {
1757 // ClassLoader sysl = ClassLoader.getSystemClassLoader();
1758 // boolean found = false;
1759 // while (sysl != null) {
1760 // if (loader == sysl) { found = true; break; }
1761 // sysl = sysl.getParent();
1768 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
1769 new MemberName(refKind, defc, member.getName(), member.getType()));
1770 checkSecurityManager(defc, resolved2);
1771 } catch (ReflectiveOperationException | SecurityException ex) {
1777 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
1778 throws ReflectiveOperationException {
1779 if (MethodHandleNatives.refKindIsField(refKind)) {
1780 return getDirectFieldNoSecurityManager(refKind, defc, member);
1781 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
1782 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
1783 } else if (refKind == REF_newInvokeSpecial) {
1784 return getDirectConstructorNoSecurityManager(defc, member);
1787 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
1790 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
1794 * Produces a method handle giving read access to elements of an array.
1795 * The type of the method handle will have a return type of the array's
1796 * element type. Its first argument will be the array type,
1797 * and the second will be {@code int}.
1798 * @param arrayClass an array type
1799 * @return a method handle which can load values from the given array type
1800 * @throws NullPointerException if the argument is null
1801 * @throws IllegalArgumentException if arrayClass is not an array type
1804 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
1805 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, false);
1809 * Produces a method handle giving write access to elements of an array.
1810 * The type of the method handle will have a void return type.
1811 * Its last argument will be the array's element type.
1812 * The first and second arguments will be the array type and int.
1813 * @param arrayClass the class of an array
1814 * @return a method handle which can store values into the array type
1815 * @throws NullPointerException if the argument is null
1816 * @throws IllegalArgumentException if arrayClass is not an array type
1819 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
1820 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, true);
1823 /// method handle invocation (reflective style)
1826 * Produces a method handle which will invoke any method handle of the
1827 * given {@code type}, with a given number of trailing arguments replaced by
1828 * a single trailing {@code Object[]} array.
1829 * The resulting invoker will be a method handle with the following
1832 * <li>a single {@code MethodHandle} target
1833 * <li>zero or more leading values (counted by {@code leadingArgCount})
1834 * <li>an {@code Object[]} array containing trailing arguments
1837 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
1838 * the indicated {@code type}.
1839 * That is, if the target is exactly of the given {@code type}, it will behave
1840 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
1841 * is used to convert the target to the required {@code type}.
1843 * The type of the returned invoker will not be the given {@code type}, but rather
1844 * will have all parameters except the first {@code leadingArgCount}
1845 * replaced by a single array of type {@code Object[]}, which will be
1846 * the final parameter.
1848 * Before invoking its target, the invoker will spread the final array, apply
1849 * reference casts as necessary, and unbox and widen primitive arguments.
1850 * If, when the invoker is called, the supplied array argument does
1851 * not have the correct number of elements, the invoker will throw
1852 * an {@link IllegalArgumentException} instead of invoking the target.
1854 * This method is equivalent to the following code (though it may be more efficient):
1855 * <blockquote><pre>{@code
1856 MethodHandle invoker = MethodHandles.invoker(type);
1857 int spreadArgCount = type.parameterCount() - leadingArgCount;
1858 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
1860 * }</pre></blockquote>
1861 * This method throws no reflective or security exceptions.
1862 * @param type the desired target type
1863 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
1864 * @return a method handle suitable for invoking any method handle of the given type
1865 * @throws NullPointerException if {@code type} is null
1866 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
1867 * the range from 0 to {@code type.parameterCount()} inclusive,
1868 * or if the resulting method handle's type would have
1869 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1872 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
1873 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
1874 throw new IllegalArgumentException("bad argument count "+leadingArgCount);
1875 return type.invokers().spreadInvoker(leadingArgCount);
1879 * Produces a special <em>invoker method handle</em> which can be used to
1880 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
1881 * The resulting invoker will have a type which is
1882 * exactly equal to the desired type, except that it will accept
1883 * an additional leading argument of type {@code MethodHandle}.
1885 * This method is equivalent to the following code (though it may be more efficient):
1886 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
1888 * <p style="font-size:smaller;">
1889 * <em>Discussion:</em>
1890 * Invoker method handles can be useful when working with variable method handles
1892 * For example, to emulate an {@code invokeExact} call to a variable method
1893 * handle {@code M}, extract its type {@code T},
1894 * look up the invoker method {@code X} for {@code T},
1895 * and call the invoker method, as {@code X.invoke(T, A...)}.
1896 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
1898 * If spreading, collecting, or other argument transformations are required,
1899 * they can be applied once to the invoker {@code X} and reused on many {@code M}
1900 * method handle values, as long as they are compatible with the type of {@code X}.
1901 * <p style="font-size:smaller;">
1902 * <em>(Note: The invoker method is not available via the Core Reflection API.
1903 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1904 * on the declared {@code invokeExact} or {@code invoke} method will raise an
1905 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1907 * This method throws no reflective or security exceptions.
1908 * @param type the desired target type
1909 * @return a method handle suitable for invoking any method handle of the given type
1910 * @throws IllegalArgumentException if the resulting method handle's type would have
1911 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1914 MethodHandle exactInvoker(MethodType type) {
1915 return type.invokers().exactInvoker();
1919 * Produces a special <em>invoker method handle</em> which can be used to
1920 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
1921 * The resulting invoker will have a type which is
1922 * exactly equal to the desired type, except that it will accept
1923 * an additional leading argument of type {@code MethodHandle}.
1925 * Before invoking its target, if the target differs from the expected type,
1926 * the invoker will apply reference casts as
1927 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
1928 * Similarly, the return value will be converted as necessary.
1929 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
1930 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
1932 * This method is equivalent to the following code (though it may be more efficient):
1933 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
1934 * <p style="font-size:smaller;">
1935 * <em>Discussion:</em>
1936 * A {@linkplain MethodType#genericMethodType general method type} is one which
1937 * mentions only {@code Object} arguments and return values.
1938 * An invoker for such a type is capable of calling any method handle
1939 * of the same arity as the general type.
1940 * <p style="font-size:smaller;">
1941 * <em>(Note: The invoker method is not available via the Core Reflection API.
1942 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1943 * on the declared {@code invokeExact} or {@code invoke} method will raise an
1944 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1946 * This method throws no reflective or security exceptions.
1947 * @param type the desired target type
1948 * @return a method handle suitable for invoking any method handle convertible to the given type
1949 * @throws IllegalArgumentException if the resulting method handle's type would have
1950 * <a href="MethodHandle.html#maxarity">too many parameters</a>
1953 MethodHandle invoker(MethodType type) {
1954 return type.invokers().generalInvoker();
1957 static /*non-public*/
1958 MethodHandle basicInvoker(MethodType type) {
1959 return type.form().basicInvoker();
1962 /// method handle modification (creation from other method handles)
1965 * Produces a method handle which adapts the type of the
1966 * given method handle to a new type by pairwise argument and return type conversion.
1967 * The original type and new type must have the same number of arguments.
1968 * The resulting method handle is guaranteed to report a type
1969 * which is equal to the desired new type.
1971 * If the original type and new type are equal, returns target.
1973 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
1974 * and some additional conversions are also applied if those conversions fail.
1975 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
1976 * if possible, before or instead of any conversions done by {@code asType}:
1978 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
1979 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
1980 * (This treatment of interfaces follows the usage of the bytecode verifier.)
1981 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
1982 * the boolean is converted to a byte value, 1 for true, 0 for false.
1983 * (This treatment follows the usage of the bytecode verifier.)
1984 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
1985 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
1986 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
1987 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
1988 * then a Java casting conversion (JLS 5.5) is applied.
1989 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
1990 * widening and/or narrowing.)
1991 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
1992 * conversion will be applied at runtime, possibly followed
1993 * by a Java casting conversion (JLS 5.5) on the primitive value,
1994 * possibly followed by a conversion from byte to boolean by testing
1995 * the low-order bit.
1996 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
1997 * and if the reference is null at runtime, a zero value is introduced.
1999 * @param target the method handle to invoke after arguments are retyped
2000 * @param newType the expected type of the new method handle
2001 * @return a method handle which delegates to the target after performing
2002 * any necessary argument conversions, and arranges for any
2003 * necessary return value conversions
2004 * @throws NullPointerException if either argument is null
2005 * @throws WrongMethodTypeException if the conversion cannot be made
2006 * @see MethodHandle#asType
2009 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
2010 if (!target.type().isCastableTo(newType)) {
2011 throw new WrongMethodTypeException("cannot explicitly cast "+target+" to "+newType);
2013 return MethodHandleImpl.makePairwiseConvert(target, newType, 2);
2017 * Produces a method handle which adapts the calling sequence of the
2018 * given method handle to a new type, by reordering the arguments.
2019 * The resulting method handle is guaranteed to report a type
2020 * which is equal to the desired new type.
2022 * The given array controls the reordering.
2023 * Call {@code #I} the number of incoming parameters (the value
2024 * {@code newType.parameterCount()}, and call {@code #O} the number
2025 * of outgoing parameters (the value {@code target.type().parameterCount()}).
2026 * Then the length of the reordering array must be {@code #O},
2027 * and each element must be a non-negative number less than {@code #I}.
2028 * For every {@code N} less than {@code #O}, the {@code N}-th
2029 * outgoing argument will be taken from the {@code I}-th incoming
2030 * argument, where {@code I} is {@code reorder[N]}.
2032 * No argument or return value conversions are applied.
2033 * The type of each incoming argument, as determined by {@code newType},
2034 * must be identical to the type of the corresponding outgoing parameter
2035 * or parameters in the target method handle.
2036 * The return type of {@code newType} must be identical to the return
2037 * type of the original target.
2039 * The reordering array need not specify an actual permutation.
2040 * An incoming argument will be duplicated if its index appears
2041 * more than once in the array, and an incoming argument will be dropped
2042 * if its index does not appear in the array.
2043 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
2044 * incoming arguments which are not mentioned in the reordering array
2045 * are may be any type, as determined only by {@code newType}.
2046 * <blockquote><pre>{@code
2047 import static java.lang.invoke.MethodHandles.*;
2048 import static java.lang.invoke.MethodType.*;
2050 MethodType intfn1 = methodType(int.class, int.class);
2051 MethodType intfn2 = methodType(int.class, int.class, int.class);
2052 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
2053 assert(sub.type().equals(intfn2));
2054 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
2055 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
2056 assert((int)rsub.invokeExact(1, 100) == 99);
2057 MethodHandle add = ... (int x, int y) -> (x+y) ...;
2058 assert(add.type().equals(intfn2));
2059 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
2060 assert(twice.type().equals(intfn1));
2061 assert((int)twice.invokeExact(21) == 42);
2062 * }</pre></blockquote>
2063 * @param target the method handle to invoke after arguments are reordered
2064 * @param newType the expected type of the new method handle
2065 * @param reorder an index array which controls the reordering
2066 * @return a method handle which delegates to the target after it
2067 * drops unused arguments and moves and/or duplicates the other arguments
2068 * @throws NullPointerException if any argument is null
2069 * @throws IllegalArgumentException if the index array length is not equal to
2070 * the arity of the target, or if any index array element
2071 * not a valid index for a parameter of {@code newType},
2072 * or if two corresponding parameter types in
2073 * {@code target.type()} and {@code newType} are not identical,
2076 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
2077 checkReorder(reorder, newType, target.type());
2078 return target.permuteArguments(newType, reorder);
2081 private static void checkReorder(int[] reorder, MethodType newType, MethodType oldType) {
2082 if (newType.returnType() != oldType.returnType())
2083 throw newIllegalArgumentException("return types do not match",
2085 if (reorder.length == oldType.parameterCount()) {
2086 int limit = newType.parameterCount();
2087 boolean bad = false;
2088 for (int j = 0; j < reorder.length; j++) {
2090 if (i < 0 || i >= limit) {
2093 Class<?> src = newType.parameterType(i);
2094 Class<?> dst = oldType.parameterType(j);
2096 throw newIllegalArgumentException("parameter types do not match after reorder",
2101 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
2105 * Produces a method handle of the requested return type which returns the given
2106 * constant value every time it is invoked.
2108 * Before the method handle is returned, the passed-in value is converted to the requested type.
2109 * If the requested type is primitive, widening primitive conversions are attempted,
2110 * else reference conversions are attempted.
2111 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
2112 * @param type the return type of the desired method handle
2113 * @param value the value to return
2114 * @return a method handle of the given return type and no arguments, which always returns the given value
2115 * @throws NullPointerException if the {@code type} argument is null
2116 * @throws ClassCastException if the value cannot be converted to the required return type
2117 * @throws IllegalArgumentException if the given type is {@code void.class}
2120 MethodHandle constant(Class<?> type, Object value) {
2121 if (type.isPrimitive()) {
2122 if (type == void.class)
2123 throw newIllegalArgumentException("void type");
2124 Wrapper w = Wrapper.forPrimitiveType(type);
2125 return insertArguments(identity(type), 0, w.convert(value, type));
2127 return identity(type).bindTo(type.cast(value));
2132 * Produces a method handle which returns its sole argument when invoked.
2133 * @param type the type of the sole parameter and return value of the desired method handle
2134 * @return a unary method handle which accepts and returns the given type
2135 * @throws NullPointerException if the argument is null
2136 * @throws IllegalArgumentException if the given type is {@code void.class}
2139 MethodHandle identity(Class<?> type) {
2140 if (type == void.class)
2141 throw newIllegalArgumentException("void type");
2142 else if (type == Object.class)
2143 return ValueConversions.identity();
2144 else if (type.isPrimitive())
2145 return ValueConversions.identity(Wrapper.forPrimitiveType(type));
2147 return MethodHandleImpl.makeReferenceIdentity(type);
2151 * Provides a target method handle with one or more <em>bound arguments</em>
2152 * in advance of the method handle's invocation.
2153 * The formal parameters to the target corresponding to the bound
2154 * arguments are called <em>bound parameters</em>.
2155 * Returns a new method handle which saves away the bound arguments.
2156 * When it is invoked, it receives arguments for any non-bound parameters,
2157 * binds the saved arguments to their corresponding parameters,
2158 * and calls the original target.
2160 * The type of the new method handle will drop the types for the bound
2161 * parameters from the original target type, since the new method handle
2162 * will no longer require those arguments to be supplied by its callers.
2164 * Each given argument object must match the corresponding bound parameter type.
2165 * If a bound parameter type is a primitive, the argument object
2166 * must be a wrapper, and will be unboxed to produce the primitive value.
2168 * The {@code pos} argument selects which parameters are to be bound.
2169 * It may range between zero and <i>N-L</i> (inclusively),
2170 * where <i>N</i> is the arity of the target method handle
2171 * and <i>L</i> is the length of the values array.
2172 * @param target the method handle to invoke after the argument is inserted
2173 * @param pos where to insert the argument (zero for the first)
2174 * @param values the series of arguments to insert
2175 * @return a method handle which inserts an additional argument,
2176 * before calling the original method handle
2177 * @throws NullPointerException if the target or the {@code values} array is null
2178 * @see MethodHandle#bindTo
2181 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
2182 int insCount = values.length;
2183 MethodType oldType = target.type();
2184 int outargs = oldType.parameterCount();
2185 int inargs = outargs - insCount;
2187 throw newIllegalArgumentException("too many values to insert");
2188 if (pos < 0 || pos > inargs)
2189 throw newIllegalArgumentException("no argument type to append");
2190 MethodHandle result = target;
2191 for (int i = 0; i < insCount; i++) {
2192 Object value = values[i];
2193 Class<?> ptype = oldType.parameterType(pos+i);
2194 if (ptype.isPrimitive()) {
2196 Wrapper w = Wrapper.forPrimitiveType(ptype);
2198 case LONG: btype = 'J'; break;
2199 case FLOAT: btype = 'F'; break;
2200 case DOUBLE: btype = 'D'; break;
2202 // perform unboxing and/or primitive conversion
2203 value = w.convert(value, ptype);
2204 result = result.bindArgument(pos, btype, value);
2207 value = ptype.cast(value); // throw CCE if needed
2209 result = result.bindReceiver(value);
2211 result = result.bindArgument(pos, 'L', value);
2218 * Produces a method handle which will discard some dummy arguments
2219 * before calling some other specified <i>target</i> method handle.
2220 * The type of the new method handle will be the same as the target's type,
2221 * except it will also include the dummy argument types,
2222 * at some given position.
2224 * The {@code pos} argument may range between zero and <i>N</i>,
2225 * where <i>N</i> is the arity of the target.
2226 * If {@code pos} is zero, the dummy arguments will precede
2227 * the target's real arguments; if {@code pos} is <i>N</i>
2228 * they will come after.
2231 * <blockquote><pre>{@code
2232 import static java.lang.invoke.MethodHandles.*;
2233 import static java.lang.invoke.MethodType.*;
2235 MethodHandle cat = lookup().findVirtual(String.class,
2236 "concat", methodType(String.class, String.class));
2237 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2238 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
2239 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
2240 assertEquals(bigType, d0.type());
2241 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
2242 * }</pre></blockquote>
2244 * This method is also equivalent to the following code:
2246 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
2247 * </pre></blockquote>
2248 * @param target the method handle to invoke after the arguments are dropped
2249 * @param valueTypes the type(s) of the argument(s) to drop
2250 * @param pos position of first argument to drop (zero for the leftmost)
2251 * @return a method handle which drops arguments of the given types,
2252 * before calling the original method handle
2253 * @throws NullPointerException if the target is null,
2254 * or if the {@code valueTypes} list or any of its elements is null
2255 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
2256 * or if {@code pos} is negative or greater than the arity of the target,
2257 * or if the new method handle's type would have too many parameters
2260 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
2261 MethodType oldType = target.type(); // get NPE
2262 int dropped = valueTypes.size();
2263 MethodType.checkSlotCount(dropped);
2264 if (dropped == 0) return target;
2265 int outargs = oldType.parameterCount();
2266 int inargs = outargs + dropped;
2267 if (pos < 0 || pos >= inargs)
2268 throw newIllegalArgumentException("no argument type to remove");
2269 ArrayList<Class<?>> ptypes = new ArrayList<>(oldType.parameterList());
2270 ptypes.addAll(pos, valueTypes);
2271 MethodType newType = MethodType.methodType(oldType.returnType(), ptypes);
2272 return target.dropArguments(newType, pos, dropped);
2276 * Produces a method handle which will discard some dummy arguments
2277 * before calling some other specified <i>target</i> method handle.
2278 * The type of the new method handle will be the same as the target's type,
2279 * except it will also include the dummy argument types,
2280 * at some given position.
2282 * The {@code pos} argument may range between zero and <i>N</i>,
2283 * where <i>N</i> is the arity of the target.
2284 * If {@code pos} is zero, the dummy arguments will precede
2285 * the target's real arguments; if {@code pos} is <i>N</i>
2286 * they will come after.
2289 * <blockquote><pre>{@code
2290 import static java.lang.invoke.MethodHandles.*;
2291 import static java.lang.invoke.MethodType.*;
2293 MethodHandle cat = lookup().findVirtual(String.class,
2294 "concat", methodType(String.class, String.class));
2295 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2296 MethodHandle d0 = dropArguments(cat, 0, String.class);
2297 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
2298 MethodHandle d1 = dropArguments(cat, 1, String.class);
2299 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
2300 MethodHandle d2 = dropArguments(cat, 2, String.class);
2301 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
2302 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
2303 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
2304 * }</pre></blockquote>
2306 * This method is also equivalent to the following code:
2308 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
2309 * </pre></blockquote>
2310 * @param target the method handle to invoke after the arguments are dropped
2311 * @param valueTypes the type(s) of the argument(s) to drop
2312 * @param pos position of first argument to drop (zero for the leftmost)
2313 * @return a method handle which drops arguments of the given types,
2314 * before calling the original method handle
2315 * @throws NullPointerException if the target is null,
2316 * or if the {@code valueTypes} array or any of its elements is null
2317 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
2318 * or if {@code pos} is negative or greater than the arity of the target,
2319 * or if the new method handle's type would have
2320 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2323 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
2324 return dropArguments(target, pos, Arrays.asList(valueTypes));
2328 * Adapts a target method handle by pre-processing
2329 * one or more of its arguments, each with its own unary filter function,
2330 * and then calling the target with each pre-processed argument
2331 * replaced by the result of its corresponding filter function.
2333 * The pre-processing is performed by one or more method handles,
2334 * specified in the elements of the {@code filters} array.
2335 * The first element of the filter array corresponds to the {@code pos}
2336 * argument of the target, and so on in sequence.
2338 * Null arguments in the array are treated as identity functions,
2339 * and the corresponding arguments left unchanged.
2340 * (If there are no non-null elements in the array, the original target is returned.)
2341 * Each filter is applied to the corresponding argument of the adapter.
2343 * If a filter {@code F} applies to the {@code N}th argument of
2344 * the target, then {@code F} must be a method handle which
2345 * takes exactly one argument. The type of {@code F}'s sole argument
2346 * replaces the corresponding argument type of the target
2347 * in the resulting adapted method handle.
2348 * The return type of {@code F} must be identical to the corresponding
2349 * parameter type of the target.
2351 * It is an error if there are elements of {@code filters}
2353 * which do not correspond to argument positions in the target.
2354 * <p><b>Example:</b>
2355 * <blockquote><pre>{@code
2356 import static java.lang.invoke.MethodHandles.*;
2357 import static java.lang.invoke.MethodType.*;
2359 MethodHandle cat = lookup().findVirtual(String.class,
2360 "concat", methodType(String.class, String.class));
2361 MethodHandle upcase = lookup().findVirtual(String.class,
2362 "toUpperCase", methodType(String.class));
2363 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2364 MethodHandle f0 = filterArguments(cat, 0, upcase);
2365 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
2366 MethodHandle f1 = filterArguments(cat, 1, upcase);
2367 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
2368 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
2369 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
2370 * }</pre></blockquote>
2371 * <p> Here is pseudocode for the resulting adapter:
2372 * <blockquote><pre>{@code
2373 * V target(P... p, A[i]... a[i], B... b);
2374 * A[i] filter[i](V[i]);
2375 * T adapter(P... p, V[i]... v[i], B... b) {
2376 * return target(p..., f[i](v[i])..., b...);
2378 * }</pre></blockquote>
2380 * @param target the method handle to invoke after arguments are filtered
2381 * @param pos the position of the first argument to filter
2382 * @param filters method handles to call initially on filtered arguments
2383 * @return method handle which incorporates the specified argument filtering logic
2384 * @throws NullPointerException if the target is null
2385 * or if the {@code filters} array is null
2386 * @throws IllegalArgumentException if a non-null element of {@code filters}
2387 * does not match a corresponding argument type of target as described above,
2388 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
2389 * or if the resulting method handle's type would have
2390 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2393 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
2394 MethodType targetType = target.type();
2395 MethodHandle adapter = target;
2396 MethodType adapterType = null;
2397 assert((adapterType = targetType) != null);
2398 int maxPos = targetType.parameterCount();
2399 if (pos + filters.length > maxPos)
2400 throw newIllegalArgumentException("too many filters");
2401 int curPos = pos-1; // pre-incremented
2402 for (MethodHandle filter : filters) {
2404 if (filter == null) continue; // ignore null elements of filters
2405 adapter = filterArgument(adapter, curPos, filter);
2406 assert((adapterType = adapterType.changeParameterType(curPos, filter.type().parameterType(0))) != null);
2408 assert(adapterType.equals(adapter.type()));
2412 /*non-public*/ static
2413 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
2414 MethodType targetType = target.type();
2415 MethodType filterType = filter.type();
2416 if (filterType.parameterCount() != 1
2417 || filterType.returnType() != targetType.parameterType(pos))
2418 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2419 return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
2423 * Adapts a target method handle by pre-processing
2424 * a sub-sequence of its arguments with a filter (another method handle).
2425 * The pre-processed arguments are replaced by the result (if any) of the
2427 * The target is then called on the modified (usually shortened) argument list.
2429 * If the filter returns a value, the target must accept that value as
2430 * its argument in position {@code pos}, preceded and/or followed by
2431 * any arguments not passed to the filter.
2432 * If the filter returns void, the target must accept all arguments
2433 * not passed to the filter.
2434 * No arguments are reordered, and a result returned from the filter
2435 * replaces (in order) the whole subsequence of arguments originally
2436 * passed to the adapter.
2438 * The argument types (if any) of the filter
2439 * replace zero or one argument types of the target, at position {@code pos},
2440 * in the resulting adapted method handle.
2441 * The return type of the filter (if any) must be identical to the
2442 * argument type of the target at position {@code pos}, and that target argument
2443 * is supplied by the return value of the filter.
2445 * In all cases, {@code pos} must be greater than or equal to zero, and
2446 * {@code pos} must also be less than or equal to the target's arity.
2447 * <p><b>Example:</b>
2448 * <blockquote><pre>{@code
2449 import static java.lang.invoke.MethodHandles.*;
2450 import static java.lang.invoke.MethodType.*;
2452 MethodHandle deepToString = publicLookup()
2453 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
2455 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
2456 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
2458 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
2459 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
2461 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
2462 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
2463 assertEquals("[top, [up, down], strange]",
2464 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
2466 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
2467 assertEquals("[top, [up, down], [strange]]",
2468 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
2470 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
2471 assertEquals("[top, [[up, down, strange], charm], bottom]",
2472 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
2473 * }</pre></blockquote>
2474 * <p> Here is pseudocode for the resulting adapter:
2475 * <blockquote><pre>{@code
2476 * T target(A...,V,C...);
2478 * T adapter(A... a,B... b,C... c) {
2479 * V v = filter(b...);
2480 * return target(a...,v,c...);
2482 * // and if the filter has no arguments:
2483 * T target2(A...,V,C...);
2485 * T adapter2(A... a,C... c) {
2487 * return target2(a...,v,c...);
2489 * // and if the filter has a void return:
2490 * T target3(A...,C...);
2491 * void filter3(B...);
2492 * void adapter3(A... a,B... b,C... c) {
2494 * return target3(a...,c...);
2496 * }</pre></blockquote>
2498 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
2499 * one which first "folds" the affected arguments, and then drops them, in separate
2501 * <blockquote><pre>{@code
2502 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
2503 * mh = MethodHandles.foldArguments(mh, coll); //step 1
2504 * }</pre></blockquote>
2505 * If the target method handle consumes no arguments besides than the result
2506 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
2507 * is equivalent to {@code filterReturnValue(coll, mh)}.
2508 * If the filter method handle {@code coll} consumes one argument and produces
2509 * a non-void result, then {@code collectArguments(mh, N, coll)}
2510 * is equivalent to {@code filterArguments(mh, N, coll)}.
2511 * Other equivalences are possible but would require argument permutation.
2513 * @param target the method handle to invoke after filtering the subsequence of arguments
2514 * @param pos the position of the first adapter argument to pass to the filter,
2515 * and/or the target argument which receives the result of the filter
2516 * @param filter method handle to call on the subsequence of arguments
2517 * @return method handle which incorporates the specified argument subsequence filtering logic
2518 * @throws NullPointerException if either argument is null
2519 * @throws IllegalArgumentException if the return type of {@code filter}
2520 * is non-void and is not the same as the {@code pos} argument of the target,
2521 * or if {@code pos} is not between 0 and the target's arity, inclusive,
2522 * or if the resulting method handle's type would have
2523 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2524 * @see MethodHandles#foldArguments
2525 * @see MethodHandles#filterArguments
2526 * @see MethodHandles#filterReturnValue
2529 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
2530 MethodType targetType = target.type();
2531 MethodType filterType = filter.type();
2532 if (filterType.returnType() != void.class &&
2533 filterType.returnType() != targetType.parameterType(pos))
2534 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2535 return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
2539 * Adapts a target method handle by post-processing
2540 * its return value (if any) with a filter (another method handle).
2541 * The result of the filter is returned from the adapter.
2543 * If the target returns a value, the filter must accept that value as
2544 * its only argument.
2545 * If the target returns void, the filter must accept no arguments.
2547 * The return type of the filter
2548 * replaces the return type of the target
2549 * in the resulting adapted method handle.
2550 * The argument type of the filter (if any) must be identical to the
2551 * return type of the target.
2552 * <p><b>Example:</b>
2553 * <blockquote><pre>{@code
2554 import static java.lang.invoke.MethodHandles.*;
2555 import static java.lang.invoke.MethodType.*;
2557 MethodHandle cat = lookup().findVirtual(String.class,
2558 "concat", methodType(String.class, String.class));
2559 MethodHandle length = lookup().findVirtual(String.class,
2560 "length", methodType(int.class));
2561 System.out.println((String) cat.invokeExact("x", "y")); // xy
2562 MethodHandle f0 = filterReturnValue(cat, length);
2563 System.out.println((int) f0.invokeExact("x", "y")); // 2
2564 * }</pre></blockquote>
2565 * <p> Here is pseudocode for the resulting adapter:
2566 * <blockquote><pre>{@code
2569 * T adapter(A... a) {
2570 * V v = target(a...);
2573 * // and if the target has a void return:
2574 * void target2(A...);
2576 * T adapter2(A... a) {
2580 * // and if the filter has a void return:
2583 * void adapter3(A... a) {
2584 * V v = target3(a...);
2587 * }</pre></blockquote>
2588 * @param target the method handle to invoke before filtering the return value
2589 * @param filter method handle to call on the return value
2590 * @return method handle which incorporates the specified return value filtering logic
2591 * @throws NullPointerException if either argument is null
2592 * @throws IllegalArgumentException if the argument list of {@code filter}
2593 * does not match the return type of target as described above
2596 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
2597 MethodType targetType = target.type();
2598 MethodType filterType = filter.type();
2599 Class<?> rtype = targetType.returnType();
2600 int filterValues = filterType.parameterCount();
2601 if (filterValues == 0
2602 ? (rtype != void.class)
2603 : (rtype != filterType.parameterType(0)))
2604 throw newIllegalArgumentException("target and filter types do not match", target, filter);
2605 // result = fold( lambda(retval, arg...) { filter(retval) },
2606 // lambda( arg...) { target(arg...) } )
2607 return MethodHandleImpl.makeCollectArguments(filter, target, 0, false);
2611 * Adapts a target method handle by pre-processing
2612 * some of its arguments, and then calling the target with
2613 * the result of the pre-processing, inserted into the original
2614 * sequence of arguments.
2616 * The pre-processing is performed by {@code combiner}, a second method handle.
2617 * Of the arguments passed to the adapter, the first {@code N} arguments
2618 * are copied to the combiner, which is then called.
2619 * (Here, {@code N} is defined as the parameter count of the combiner.)
2620 * After this, control passes to the target, with any result
2621 * from the combiner inserted before the original {@code N} incoming
2624 * If the combiner returns a value, the first parameter type of the target
2625 * must be identical with the return type of the combiner, and the next
2626 * {@code N} parameter types of the target must exactly match the parameters
2629 * If the combiner has a void return, no result will be inserted,
2630 * and the first {@code N} parameter types of the target
2631 * must exactly match the parameters of the combiner.
2633 * The resulting adapter is the same type as the target, except that the
2634 * first parameter type is dropped,
2635 * if it corresponds to the result of the combiner.
2637 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
2638 * that either the combiner or the target does not wish to receive.
2639 * If some of the incoming arguments are destined only for the combiner,
2640 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
2641 * arguments will not need to be live on the stack on entry to the
2643 * <p><b>Example:</b>
2644 * <blockquote><pre>{@code
2645 import static java.lang.invoke.MethodHandles.*;
2646 import static java.lang.invoke.MethodType.*;
2648 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
2649 "println", methodType(void.class, String.class))
2650 .bindTo(System.out);
2651 MethodHandle cat = lookup().findVirtual(String.class,
2652 "concat", methodType(String.class, String.class));
2653 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
2654 MethodHandle catTrace = foldArguments(cat, trace);
2655 // also prints "boo":
2656 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
2657 * }</pre></blockquote>
2658 * <p> Here is pseudocode for the resulting adapter:
2659 * <blockquote><pre>{@code
2660 * // there are N arguments in A...
2661 * T target(V, A[N]..., B...);
2663 * T adapter(A... a, B... b) {
2664 * V v = combiner(a...);
2665 * return target(v, a..., b...);
2667 * // and if the combiner has a void return:
2668 * T target2(A[N]..., B...);
2669 * void combiner2(A...);
2670 * T adapter2(A... a, B... b) {
2672 * return target2(a..., b...);
2674 * }</pre></blockquote>
2675 * @param target the method handle to invoke after arguments are combined
2676 * @param combiner method handle to call initially on the incoming arguments
2677 * @return method handle which incorporates the specified argument folding logic
2678 * @throws NullPointerException if either argument is null
2679 * @throws IllegalArgumentException if {@code combiner}'s return type
2680 * is non-void and not the same as the first argument type of
2681 * the target, or if the initial {@code N} argument types
2683 * (skipping one matching the {@code combiner}'s return type)
2684 * are not identical with the argument types of {@code combiner}
2687 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
2689 MethodType targetType = target.type();
2690 MethodType combinerType = combiner.type();
2692 int foldArgs = combinerType.parameterCount();
2693 int foldVals = combinerType.returnType() == void.class ? 0 : 1;
2694 int afterInsertPos = foldPos + foldVals;
2695 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
2696 if (ok && !(combinerType.parameterList()
2697 .equals(targetType.parameterList().subList(afterInsertPos,
2698 afterInsertPos + foldArgs))))
2700 if (ok && foldVals != 0 && !combinerType.returnType().equals(targetType.parameterType(0)))
2703 throw misMatchedTypes("target and combiner types", targetType, combinerType);
2704 MethodType newType = targetType.dropParameterTypes(foldPos, afterInsertPos);
2705 return MethodHandleImpl.makeCollectArguments(target, combiner, foldPos, true);
2709 * Makes a method handle which adapts a target method handle,
2710 * by guarding it with a test, a boolean-valued method handle.
2711 * If the guard fails, a fallback handle is called instead.
2712 * All three method handles must have the same corresponding
2713 * argument and return types, except that the return type
2714 * of the test must be boolean, and the test is allowed
2715 * to have fewer arguments than the other two method handles.
2716 * <p> Here is pseudocode for the resulting adapter:
2717 * <blockquote><pre>{@code
2718 * boolean test(A...);
2719 * T target(A...,B...);
2720 * T fallback(A...,B...);
2721 * T adapter(A... a,B... b) {
2723 * return target(a..., b...);
2725 * return fallback(a..., b...);
2727 * }</pre></blockquote>
2728 * Note that the test arguments ({@code a...} in the pseudocode) cannot
2729 * be modified by execution of the test, and so are passed unchanged
2730 * from the caller to the target or fallback as appropriate.
2731 * @param test method handle used for test, must return boolean
2732 * @param target method handle to call if test passes
2733 * @param fallback method handle to call if test fails
2734 * @return method handle which incorporates the specified if/then/else logic
2735 * @throws NullPointerException if any argument is null
2736 * @throws IllegalArgumentException if {@code test} does not return boolean,
2737 * or if all three method types do not match (with the return
2738 * type of {@code test} changed to match that of the target).
2741 MethodHandle guardWithTest(MethodHandle test,
2742 MethodHandle target,
2743 MethodHandle fallback) {
2744 MethodType gtype = test.type();
2745 MethodType ttype = target.type();
2746 MethodType ftype = fallback.type();
2747 if (!ttype.equals(ftype))
2748 throw misMatchedTypes("target and fallback types", ttype, ftype);
2749 if (gtype.returnType() != boolean.class)
2750 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
2751 List<Class<?>> targs = ttype.parameterList();
2752 List<Class<?>> gargs = gtype.parameterList();
2753 if (!targs.equals(gargs)) {
2754 int gpc = gargs.size(), tpc = targs.size();
2755 if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs))
2756 throw misMatchedTypes("target and test types", ttype, gtype);
2757 test = dropArguments(test, gpc, targs.subList(gpc, tpc));
2758 gtype = test.type();
2760 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
2763 static RuntimeException misMatchedTypes(String what, MethodType t1, MethodType t2) {
2764 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
2768 * Makes a method handle which adapts a target method handle,
2769 * by running it inside an exception handler.
2770 * If the target returns normally, the adapter returns that value.
2771 * If an exception matching the specified type is thrown, the fallback
2772 * handle is called instead on the exception, plus the original arguments.
2774 * The target and handler must have the same corresponding
2775 * argument and return types, except that handler may omit trailing arguments
2776 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
2777 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
2778 * <p> Here is pseudocode for the resulting adapter:
2779 * <blockquote><pre>{@code
2780 * T target(A..., B...);
2781 * T handler(ExType, A...);
2782 * T adapter(A... a, B... b) {
2784 * return target(a..., b...);
2785 * } catch (ExType ex) {
2786 * return handler(ex, a...);
2789 * }</pre></blockquote>
2790 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
2791 * be modified by execution of the target, and so are passed unchanged
2792 * from the caller to the handler, if the handler is invoked.
2794 * The target and handler must return the same type, even if the handler
2795 * always throws. (This might happen, for instance, because the handler
2796 * is simulating a {@code finally} clause).
2797 * To create such a throwing handler, compose the handler creation logic
2798 * with {@link #throwException throwException},
2799 * in order to create a method handle of the correct return type.
2800 * @param target method handle to call
2801 * @param exType the type of exception which the handler will catch
2802 * @param handler method handle to call if a matching exception is thrown
2803 * @return method handle which incorporates the specified try/catch logic
2804 * @throws NullPointerException if any argument is null
2805 * @throws IllegalArgumentException if {@code handler} does not accept
2806 * the given exception type, or if the method handle types do
2807 * not match in their return types and their
2808 * corresponding parameters
2811 MethodHandle catchException(MethodHandle target,
2812 Class<? extends Throwable> exType,
2813 MethodHandle handler) {
2814 MethodType ttype = target.type();
2815 MethodType htype = handler.type();
2816 if (htype.parameterCount() < 1 ||
2817 !htype.parameterType(0).isAssignableFrom(exType))
2818 throw newIllegalArgumentException("handler does not accept exception type "+exType);
2819 if (htype.returnType() != ttype.returnType())
2820 throw misMatchedTypes("target and handler return types", ttype, htype);
2821 List<Class<?>> targs = ttype.parameterList();
2822 List<Class<?>> hargs = htype.parameterList();
2823 hargs = hargs.subList(1, hargs.size()); // omit leading parameter from handler
2824 if (!targs.equals(hargs)) {
2825 int hpc = hargs.size(), tpc = targs.size();
2826 if (hpc >= tpc || !targs.subList(0, hpc).equals(hargs))
2827 throw misMatchedTypes("target and handler types", ttype, htype);
2828 handler = dropArguments(handler, 1+hpc, targs.subList(hpc, tpc));
2829 htype = handler.type();
2831 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
2835 * Produces a method handle which will throw exceptions of the given {@code exType}.
2836 * The method handle will accept a single argument of {@code exType},
2837 * and immediately throw it as an exception.
2838 * The method type will nominally specify a return of {@code returnType}.
2839 * The return type may be anything convenient: It doesn't matter to the
2840 * method handle's behavior, since it will never return normally.
2841 * @param returnType the return type of the desired method handle
2842 * @param exType the parameter type of the desired method handle
2843 * @return method handle which can throw the given exceptions
2844 * @throws NullPointerException if either argument is null
2847 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
2848 if (!Throwable.class.isAssignableFrom(exType))
2849 throw new ClassCastException(exType.getName());
2850 return MethodHandleImpl.throwException(MethodType.methodType(returnType, exType));