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;
20import com.google.common.collect.ForwardingObject;
21
22import java.util.concurrent.ExecutionException;
23import java.util.concurrent.Future;
24import java.util.concurrent.TimeUnit;
25import java.util.concurrent.TimeoutException;
26
27/**
28 * A {@link Future} which forwards all its method calls to another future.
29 * Subclasses should override one or more methods to modify the behavior of
30 * the backing future as desired per the <a
31 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
32 *
33 * <p>Most subclasses can just use {@link SimpleForwardingFuture}.
34 *
35 * @author Sven Mawson
36 * @since 1.0
37 */
38public abstract class ForwardingFuture<V> extends ForwardingObject
39    implements Future<V> {
40
41  /** Constructor for use by subclasses. */
42  protected ForwardingFuture() {}
43
44  @Override protected abstract Future<V> delegate();
45
46  @Override
47  public boolean cancel(boolean mayInterruptIfRunning) {
48    return delegate().cancel(mayInterruptIfRunning);
49  }
50
51  @Override
52  public boolean isCancelled() {
53    return delegate().isCancelled();
54  }
55
56  @Override
57  public boolean isDone() {
58    return delegate().isDone();
59  }
60
61  @Override
62  public V get() throws InterruptedException, ExecutionException {
63    return delegate().get();
64  }
65
66  @Override
67  public V get(long timeout, TimeUnit unit)
68      throws InterruptedException, ExecutionException, TimeoutException {
69    return delegate().get(timeout, unit);
70  }
71
72  /*
73   * TODO(cpovirk): Use standard Javadoc form for SimpleForwarding* class and
74   * constructor
75   */
76  /**
77   * A simplified version of {@link ForwardingFuture} where subclasses
78   * can pass in an already constructed {@link Future} as the delegate.
79   *
80   * @since 9.0
81   */
82  public abstract static class SimpleForwardingFuture<V>
83      extends ForwardingFuture<V> {
84    private final Future<V> delegate;
85
86    protected SimpleForwardingFuture(Future<V> delegate) {
87      this.delegate = Preconditions.checkNotNull(delegate);
88    }
89
90    @Override
91    protected final Future<V> delegate() {
92      return delegate;
93    }
94
95  }
96}
97