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.annotations.Beta;
020import com.google.common.base.Preconditions;
021import com.google.common.collect.ForwardingObject;
022
023import java.util.concurrent.ExecutionException;
024import java.util.concurrent.Future;
025import java.util.concurrent.TimeUnit;
026import java.util.concurrent.TimeoutException;
027
028/**
029 * A {@link Future} which forwards all its method calls to another future.
030 * Subclasses should override one or more methods to modify the behavior of
031 * the backing future as desired per the <a
032 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
033 *
034 * <p>Most subclasses can just use {@link SimpleForwardingFuture}.
035 * 
036 * @author Sven Mawson
037 * @since 1
038 */
039public abstract class ForwardingFuture<V> extends ForwardingObject
040    implements Future<V> {
041
042  /** Constructor for use by subclasses. */
043  protected ForwardingFuture() {}
044
045  @Override protected abstract Future<V> delegate();
046
047  @Override
048  public boolean cancel(boolean mayInterruptIfRunning) {
049    return delegate().cancel(mayInterruptIfRunning);
050  }
051
052  @Override
053  public boolean isCancelled() {
054    return delegate().isCancelled();
055  }
056
057  @Override
058  public boolean isDone() {
059    return delegate().isDone();
060  }
061
062  @Override
063  public V get() throws InterruptedException, ExecutionException {
064    return delegate().get();
065  }
066
067  @Override
068  public V get(long timeout, TimeUnit unit)
069      throws InterruptedException, ExecutionException, TimeoutException {
070    return delegate().get(timeout, unit);
071  }
072
073  // TODO(cpovirk): Use Standard Javadoc form for SimpleForwarding*
074  /**
075   * A simplified version of {@link ForwardingFuture} where subclasses
076   * can pass in an already constructed {@link Future} as the delegate.
077   * 
078   * @since 9
079   */
080  @Beta
081  public abstract static class SimpleForwardingFuture<V> 
082      extends ForwardingFuture<V> {
083    private final Future<V> delegate;
084
085    protected SimpleForwardingFuture(Future<V> delegate) {
086      this.delegate = Preconditions.checkNotNull(delegate);
087    }
088
089    @Override
090    protected final Future<V> delegate() {
091      return delegate;
092    }
093    
094  }
095}