1/* 2 * Copyright (C) 2009 The Guava Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17package com.google.common.util.concurrent; 18 19import com.google.common.base.Preconditions; 20 21import java.util.concurrent.Executor; 22 23/** 24 * A {@link ListenableFuture} which forwards all its method calls to another 25 * future. Subclasses should override one or more methods to modify the behavior 26 * of the backing future as desired per the <a 27 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. 28 * 29 * <p>Most subclasses can just use {@link SimpleForwardingListenableFuture}. 30 * 31 * @param <V> The result type returned by this Future's {@code get} method 32 * 33 * @author Shardul Deo 34 * @since 4.0 35 */ 36public abstract class ForwardingListenableFuture<V> extends ForwardingFuture<V> 37 implements ListenableFuture<V> { 38 39 /** Constructor for use by subclasses. */ 40 protected ForwardingListenableFuture() {} 41 42 @Override 43 protected abstract ListenableFuture<V> delegate(); 44 45 @Override 46 public void addListener(Runnable listener, Executor exec) { 47 delegate().addListener(listener, exec); 48 } 49 50 /* 51 * TODO(cpovirk): Use standard Javadoc form for SimpleForwarding* class and 52 * constructor 53 */ 54 /** 55 * A simplified version of {@link ForwardingListenableFuture} where subclasses 56 * can pass in an already constructed {@link ListenableFuture} 57 * as the delegate. 58 * 59 * @since 9.0 60 */ 61 public abstract static class SimpleForwardingListenableFuture<V> 62 extends ForwardingListenableFuture<V> { 63 private final ListenableFuture<V> delegate; 64 65 protected SimpleForwardingListenableFuture(ListenableFuture<V> delegate) { 66 this.delegate = Preconditions.checkNotNull(delegate); 67 } 68 69 @Override 70 protected final ListenableFuture<V> delegate() { 71 return delegate; 72 } 73 } 74} 75