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