/*

 * Copyright (c) 2010, 2011, 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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 */

/**

 * 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

 */

public class ConstantCallSite extends CallSite {

    /**

     * 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);

    }

    /**

     * Returns the target method of the call site, which behaves

     * like a {@code final} field of the {@code ConstantCallSite}.

     * That is, the 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 UnsupportedOperationException because this kind of call site cannot change its target

     */

    @Override public final MethodHandle getTarget() {

        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("ConstantCallSite");

    }

    /**

     * 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

     */

    @Override

    public final MethodHandle dynamicInvoker() {

        return getTarget();

    }

}