| /* |
| * Copyright (c) 2010, 2013, 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 |
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| * questions. |
| */ |
| |
| package java.lang.invoke; |
| |
| /** |
| * A {@code ConstantCallSite} is a {@link CallSite} whose target is permanent, and can never be changed. |
| * An {@code invokedynamic} instruction linked to a {@code ConstantCallSite} is permanently |
| * bound to the call site's target. |
| * @author John Rose, JSR 292 EG |
| * @since 1.7 |
| */ |
| public class ConstantCallSite extends CallSite { |
| private final boolean isFrozen; |
| |
| /** |
| * Creates a call site with a permanent target. |
| * @param target the target to be permanently associated with this call site |
| * @throws NullPointerException if the proposed target is null |
| */ |
| public ConstantCallSite(MethodHandle target) { |
| super(target); |
| isFrozen = true; |
| } |
| |
| /** |
| * Creates a call site with a permanent target, possibly bound to the call site itself. |
| * <p> |
| * During construction of the call site, the {@code createTargetHook} is invoked to |
| * produce the actual target, as if by a call of the form |
| * {@code (MethodHandle) createTargetHook.invoke(this)}. |
| * <p> |
| * Note that user code cannot perform such an action directly in a subclass constructor, |
| * since the target must be fixed before the {@code ConstantCallSite} constructor returns. |
| * <p> |
| * The hook is said to bind the call site to a target method handle, |
| * and a typical action would be {@code someTarget.bindTo(this)}. |
| * However, the hook is free to take any action whatever, |
| * including ignoring the call site and returning a constant target. |
| * <p> |
| * The result returned by the hook must be a method handle of exactly |
| * the same type as the call site. |
| * <p> |
| * While the hook is being called, the new {@code ConstantCallSite} |
| * object is in a partially constructed state. |
| * In this state, |
| * a call to {@code getTarget}, or any other attempt to use the target, |
| * will result in an {@code IllegalStateException}. |
| * It is legal at all times to obtain the call site's type using the {@code type} method. |
| * |
| * @param targetType the type of the method handle to be permanently associated with this call site |
| * @param createTargetHook a method handle to invoke (on the call site) to produce the call site's target |
| * @throws WrongMethodTypeException if the hook cannot be invoked on the required arguments, |
| * or if the target returned by the hook is not of the given {@code targetType} |
| * @throws NullPointerException if the hook returns a null value |
| * @throws ClassCastException if the hook returns something other than a {@code MethodHandle} |
| * @throws Throwable anything else thrown by the hook function |
| */ |
| protected ConstantCallSite(MethodType targetType, MethodHandle createTargetHook) throws Throwable { |
| super(targetType, createTargetHook); |
| isFrozen = true; |
| } |
| |
| /** |
| * Returns the target method of the call site, which behaves |
| * like a {@code final} field of the {@code ConstantCallSite}. |
| * That is, the target is always the original value passed |
| * to the constructor call which created this instance. |
| * |
| * @return the immutable linkage state of this call site, a constant method handle |
| * @throws IllegalStateException if the {@code ConstantCallSite} constructor has not completed |
| */ |
| @Override public final MethodHandle getTarget() { |
| if (!isFrozen) throw new IllegalStateException(); |
| return target; |
| } |
| |
| /** |
| * Always throws an {@link UnsupportedOperationException}. |
| * This kind of call site cannot change its target. |
| * @param ignore a new target proposed for the call site, which is ignored |
| * @throws UnsupportedOperationException because this kind of call site cannot change its target |
| */ |
| @Override public final void setTarget(MethodHandle ignore) { |
| throw new UnsupportedOperationException(); |
| } |
| |
| /** |
| * Returns this call site's permanent target. |
| * Since that target will never change, this is a correct implementation |
| * of {@link CallSite#dynamicInvoker CallSite.dynamicInvoker}. |
| * @return the immutable linkage state of this call site, a constant method handle |
| * @throws IllegalStateException if the {@code ConstantCallSite} constructor has not completed |
| */ |
| @Override |
| public final MethodHandle dynamicInvoker() { |
| return getTarget(); |
| } |
| } |