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
017package com.google.common.util.concurrent;
018
019import com.google.common.base.Preconditions;
020import com.google.common.collect.ForwardingObject;
021
022import java.util.concurrent.ExecutionException;
023import java.util.concurrent.Future;
024import java.util.concurrent.TimeUnit;
025import java.util.concurrent.TimeoutException;
026
027/**
028 * A {@link Future} which forwards all its method calls to another future.
029 * Subclasses should override one or more methods to modify the behavior of
030 * the backing future as desired per the <a
031 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
032 *
033 * <p>Most subclasses can just use {@link SimpleForwardingFuture}.
034 * 
035 * @author Sven Mawson
036 * @since 1.0
037 */
038public abstract class ForwardingFuture<V> extends ForwardingObject
039    implements Future<V> {
040
041  /** Constructor for use by subclasses. */
042  protected ForwardingFuture() {}
043
044  @Override protected abstract Future<V> delegate();
045
046  @Override
047  public boolean cancel(boolean mayInterruptIfRunning) {
048    return delegate().cancel(mayInterruptIfRunning);
049  }
050
051  @Override
052  public boolean isCancelled() {
053    return delegate().isCancelled();
054  }
055
056  @Override
057  public boolean isDone() {
058    return delegate().isDone();
059  }
060
061  @Override
062  public V get() throws InterruptedException, ExecutionException {
063    return delegate().get();
064  }
065
066  @Override
067  public V get(long timeout, TimeUnit unit)
068      throws InterruptedException, ExecutionException, TimeoutException {
069    return delegate().get(timeout, unit);
070  }
071
072  /*
073   * TODO(cpovirk): Use standard Javadoc form for SimpleForwarding* class and
074   * constructor
075   */
076  /**
077   * A simplified version of {@link ForwardingFuture} where subclasses
078   * can pass in an already constructed {@link Future} as the delegate.
079   * 
080   * @since 9.0
081   */
082  public abstract static class SimpleForwardingFuture<V> 
083      extends ForwardingFuture<V> {
084    private final Future<V> delegate;
085
086    protected SimpleForwardingFuture(Future<V> delegate) {
087      this.delegate = Preconditions.checkNotNull(delegate);
088    }
089
090    @Override
091    protected final Future<V> delegate() {
092      return delegate;
093    }
094    
095  }
096}