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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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).
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package java.dyn;

/**
 * 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();
    }
}