001 /*
002 * Copyright (C) 2009 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017 package com.google.common.util.concurrent;
018
019 import com.google.common.base.Preconditions;
020
021 import java.util.concurrent.Executor;
022
023 /**
024 * A {@link ListenableFuture} which forwards all its method calls to another
025 * future. Subclasses should override one or more methods to modify the behavior
026 * of the backing future as desired per the <a
027 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
028 *
029 * <p>Most subclasses can just use {@link SimpleForwardingListenableFuture}.
030 *
031 * @param <V> The result type returned by this Future's {@code get} method
032 *
033 * @author Shardul Deo
034 * @since 4.0
035 */
036 public abstract class ForwardingListenableFuture<V> extends ForwardingFuture<V>
037 implements ListenableFuture<V> {
038
039 /** Constructor for use by subclasses. */
040 protected ForwardingListenableFuture() {}
041
042 @Override
043 protected abstract ListenableFuture<V> delegate();
044
045 @Override
046 public void addListener(Runnable listener, Executor exec) {
047 delegate().addListener(listener, exec);
048 }
049
050 /*
051 * TODO(cpovirk): Use standard Javadoc form for SimpleForwarding* class and
052 * constructor
053 */
054 /**
055 * A simplified version of {@link ForwardingListenableFuture} where subclasses
056 * can pass in an already constructed {@link ListenableFuture}
057 * as the delegate.
058 *
059 * @since 9.0
060 */
061 public abstract static class SimpleForwardingListenableFuture<V>
062 extends ForwardingListenableFuture<V> {
063 private final ListenableFuture<V> delegate;
064
065 protected SimpleForwardingListenableFuture(ListenableFuture<V> delegate) {
066 this.delegate = Preconditions.checkNotNull(delegate);
067 }
068
069 @Override
070 protected final ListenableFuture<V> delegate() {
071 return delegate;
072 }
073 }
074 }