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.annotations.Beta; 020 import com.google.common.base.Preconditions; 021 022 import java.util.concurrent.Executor; 023 024 /** 025 * A {@link ListenableFuture} which forwards all its method calls to another 026 * future. Subclasses should override one or more methods to modify the behavior 027 * of the backing future as desired per the <a 028 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. 029 * 030 * <p>Most subclasses can just use {@link SimpleForwardingListenableFuture}. 031 * 032 * @param <V> The result type returned by this Future's {@code get} method 033 * 034 * @author Shardul Deo 035 * @since 4 036 */ 037 @Beta 038 public abstract class ForwardingListenableFuture<V> extends ForwardingFuture<V> 039 implements ListenableFuture<V> { 040 041 /** Constructor for use by subclasses. */ 042 protected ForwardingListenableFuture() {} 043 044 @Override 045 protected abstract ListenableFuture<V> delegate(); 046 047 @Override 048 public void addListener(Runnable listener, Executor exec) { 049 delegate().addListener(listener, exec); 050 } 051 052 // TODO(cpovirk): Use Standard Javadoc form for SimpleForwarding* 053 /** 054 * A simplified version of {@link ForwardingListenableFuture} where subclasses 055 * can pass in an already constructed {@link ListenableFuture} 056 * as the delegate. 057 * 058 * @since 9 059 */ 060 @Beta 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 }