diff -r adf468d05745 -r 1c545d70a157 jdk/src/share/classes/java/dyn/MethodHandleProvider.java --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/jdk/src/share/classes/java/dyn/MethodHandleProvider.java Wed Sep 08 18:40:11 2010 -0700 @@ -0,0 +1,80 @@ +/* + * Copyright (c) 2009, 2010, Oracle and/or its affiliates. All rights reserved. + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. + * + * This code is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License version 2 only, as + * published by the Free Software Foundation. Oracle designates this + * particular file as subject to the "Classpath" exception as provided + * by Oracle in the LICENSE file that accompanied this code. + * + * This code is distributed in the hope that it will be useful, but WITHOUT + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License + * version 2 for more details (a copy is included in the LICENSE file that + * accompanied this code). + * + * You should have received a copy of the GNU General Public License version + * 2 along with this work; if not, write to the Free Software Foundation, + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. + * + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA + * or visit www.oracle.com if you need additional information or have any + * questions. + */ + +package java.dyn; + +/** + * An interface for an object to provide a target {@linkplain MethodHandle method handle} to a {@code invokedynamic} instruction. + * There are many function-like objects in various Java APIs. + * This interface provides a standard way for such function-like objects to be bound + * to a dynamic call site, by providing a view of their behavior in the form of a low-level method handle. + *

+ * The type {@link MethodHandle} is a concrete class whose implementation + * hierarchy (if any) may be tightly coupled to the underlying JVM implementation. + * It cannot also serve as a base type for user-defined functional APIs. + * For this reason, {@code MethodHandle} cannot be subclassed to add new + * behavior to method handles. But this interface can be used to provide + * a link between a user-defined function and the {@code invokedynamic} + * instruction and the method handle API. + */ +public interface MethodHandleProvider { + /** Produce a method handle which will serve as a behavioral proxy for the current object. + * The type and invocation behavior of the proxy method handle are user-defined, + * and should have some relation to the intended meaning of the original object itself. + *

+ * The current object may have a changeable behavior. + * For example, {@link CallSite} has a {@code setTarget} method which changes its invocation. + * In such a case, it is incorrect for {@code asMethodHandle} to return + * a method handle whose behavior may diverge from that of the current object. + * Rather, the returned method handle must stably and permanently access + * the behavior of the current object, even if that behavior is changeable. + *

+ * The reference identity of the proxy method handle is not guaranteed to + * have any particular relation to the reference identity of the object. + * In particular, several objects with the same intended meaning could + * share a common method handle, or the same object could return different + * method handles at different times. In the latter case, the different + * method handles should have the same type and invocation behavior, + * and be usable from any thread at any time. + * In particular, if a MethodHandleProvider is bound to an invokedynamic + * call site, the proxy method handle extracted at the time of binding + * will be used for an unlimited time, until the call site is rebound. + *

+ * The type {@link MethodHandle} itself implements {@code MethodHandleProvider}, and + * for this method simply returns {@code this}. + */ + public MethodHandle asMethodHandle(); + + /** Produce a method handle of a given type which will serve as a behavioral proxy for the current object. + * As for the no-argument version {@link #asMethodHandle()}, the invocation behavior of the + * proxy method handle is user-defined. But the type must be the given type, + * or else a {@link WrongMethodTypeException} must be thrown. + *

+ * If the current object somehow represents a variadic or overloaded behavior, + * the method handle returned for a given type might represent only a subset of + * the current object's repertoire of behaviors, which correspond to that type. + */ + public MethodHandle asMethodHandle(MethodType type) throws WrongMethodTypeException; +}