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