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;
025import org.jspecify.annotations.Nullable;
026
027/**
028 * A {@link Future} which forwards all its method calls to another future. Subclasses should
029 * override one or more methods to modify the behavior of the backing future as desired per the <a
030 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
031 *
032 * <p><b>Warning:</b> The methods of {@code ForwardingFuture} forward <b>indiscriminately</b> to the
033 * methods of the delegate. For example, overriding {@link #get(long, TimeUnit)} alone <b>will
034 * not</b> change the behavior of {@link #get()}, which can lead to unexpected behavior. In this
035 * case, you should override {@code get()} as well.
036 *
037 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
038 * default} methods. Instead, it inherits their default implementations. When those implementations
039 * invoke methods, they invoke methods on the {@code ForwardingFuture}.
040 *
041 * <p>Most subclasses can just use {@link SimpleForwardingFuture}.
042 *
043 * @author Sven Mawson
044 * @since 1.0
045 */
046@GwtCompatible
047public abstract class ForwardingFuture<V extends @Nullable Object> extends ForwardingObject
048    implements Future<V> {
049  /** Constructor for use by subclasses. */
050  protected ForwardingFuture() {}
051
052  @Override
053  protected abstract Future<? extends V> delegate();
054
055  @Override
056  @CanIgnoreReturnValue
057  public boolean cancel(boolean mayInterruptIfRunning) {
058    return delegate().cancel(mayInterruptIfRunning);
059  }
060
061  @Override
062  public boolean isCancelled() {
063    return delegate().isCancelled();
064  }
065
066  @Override
067  public boolean isDone() {
068    return delegate().isDone();
069  }
070
071  @Override
072  @CanIgnoreReturnValue
073  @ParametricNullness
074  public V get() throws InterruptedException, ExecutionException {
075    return delegate().get();
076  }
077
078  @Override
079  @CanIgnoreReturnValue
080  @ParametricNullness
081  public V get(long timeout, TimeUnit unit)
082      throws InterruptedException, ExecutionException, TimeoutException {
083    return delegate().get(timeout, unit);
084  }
085
086  // TODO(cpovirk): Use standard Javadoc form for SimpleForwarding* class and constructor
087  /**
088   * A simplified version of {@link ForwardingFuture} where subclasses can pass in an already
089   * constructed {@link Future} as the delegate.
090   *
091   * @since 9.0
092   */
093  public abstract static class SimpleForwardingFuture<V extends @Nullable Object>
094      extends ForwardingFuture<V> {
095    private final Future<V> delegate;
096
097    /** Constructor for use by subclasses. */
098    protected SimpleForwardingFuture(Future<V> delegate) {
099      this.delegate = Preconditions.checkNotNull(delegate);
100    }
101
102    @Override
103    protected final Future<V> delegate() {
104      return delegate;
105    }
106  }
107}