1 /*
2 * Copyright (C) 2009 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
5 * in compliance with the License. You may obtain a copy of the License at
6 *
7 * http://www.apache.org/licenses/LICENSE-2.0
8 *
9 * Unless required by applicable law or agreed to in writing, software distributed under the License
10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
11 * or implied. See the License for the specific language governing permissions and limitations under
12 * the License.
13 */
14
15 package com.google.common.util.concurrent;
16
17 import com.google.common.annotations.GwtCompatible;
18 import com.google.common.base.Preconditions;
19 import com.google.errorprone.annotations.CanIgnoreReturnValue;
20 import java.util.concurrent.Executor;
21 import org.checkerframework.checker.nullness.qual.Nullable;
22
23 /**
24 * A {@link ListenableFuture} which forwards all its method calls to another future. Subclasses
25 * should override one or more methods to modify the behavior of the backing future as desired per
26 * the <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
27 *
28 * <p>Most subclasses can just use {@link SimpleForwardingListenableFuture}.
29 *
30 * @author Shardul Deo
31 * @since 4.0
32 */
33 @CanIgnoreReturnValue // TODO(cpovirk): Consider being more strict.
34 @GwtCompatible
35 @ElementTypesAreNonnullByDefault
36 public abstract class ForwardingListenableFuture<V extends @Nullable Object>
37 extends ForwardingFuture<V> implements ListenableFuture<V> {
38
39 /** Constructor for use by subclasses. */
40 protected ForwardingListenableFuture() {}
41
42 @Override
43 protected abstract ListenableFuture<? extends V> delegate();
44
45 @Override
46 public void addListener(Runnable listener, Executor exec) {
47 delegate().addListener(listener, exec);
48 }
49
50 // TODO(cpovirk): Use standard Javadoc form for SimpleForwarding* class and constructor
51 /**
52 * A simplified version of {@link ForwardingListenableFuture} where subclasses can pass in an
53 * already constructed {@link ListenableFuture} as the delegate.
54 *
55 * @since 9.0
56 */
57 public abstract static class SimpleForwardingListenableFuture<V extends @Nullable Object>
58 extends ForwardingListenableFuture<V> {
59 private final ListenableFuture<V> delegate;
60
61 protected SimpleForwardingListenableFuture(ListenableFuture<V> delegate) {
62 this.delegate = Preconditions.checkNotNull(delegate);
63 }
64
65 @Override
66 protected final ListenableFuture<V> delegate() {
67 return delegate;
68 }
69 }
70 }