1 /*

     2  * Copyright (c) 2010, 2011, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.  Oracle designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Oracle in the LICENSE file that accompanied this code.

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

    16  *

    17  * You should have received a copy of the GNU General Public License version

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    22  * or visit www.oracle.com if you need additional information or have any

    23  * questions.

    24  */

    25 

    26 package java.dyn;

    27 

    28 /**

    29  * A {@code ConstantCallSite} is a {@link CallSite} whose target is permanent, and can never be changed.

    30  * An {@code invokedynamic} instruction linked to a {@code ConstantCallSite} is permanently

    31  * bound to the call site's target.

    32  * @author John Rose, JSR 292 EG

    33  */

    34 public class ConstantCallSite extends CallSite {

    35     /**

    36      * Creates a call site with a permanent target.

    37      * @param target the target to be permanently associated with this call site

    38      * @throws NullPointerException if the proposed target is null

    39      */

    40     public ConstantCallSite(MethodHandle target) {

    41         super(target);

    42     }

    43 

    44     /**

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

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

    47      * That is, the the target is always the original value passed

    48      * to the constructor call which created this instance.

    49      *

    50      * @return the immutable linkage state of this call site, a constant method handle

    51      * @throws UnsupportedOperationException because this kind of call site cannot change its target

    52      */

    53     @Override public final MethodHandle getTarget() {

    54         return target;

    55     }

    56 

    57     /**

    58      * Always throws an {@link UnsupportedOperationException}.

    59      * This kind of call site cannot change its target.

    60      * @param ignore a new target proposed for the call site, which is ignored

    61      * @throws UnsupportedOperationException because this kind of call site cannot change its target

    62      */

    63     @Override public final void setTarget(MethodHandle ignore) {

    64         throw new UnsupportedOperationException("ConstantCallSite");

    65     }

    66 

    67     /**

    68      * Returns this call site's permanent target.

    69      * Since that target will never change, this is a correct implementation

    70      * of {@link CallSite#dynamicInvoker CallSite.dynamicInvoker}.

    71      * @return the immutable linkage state of this call site, a constant method handle

    72      */

    73     @Override

    74     public final MethodHandle dynamicInvoker() {

    75         return getTarget();

    76     }

    77 }