/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.util.concurrent;

import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Preconditions;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.concurrent.Executor;

A ListenableFuture which forwards all its method calls to another future. Subclasses should override one or more methods to modify the behavior of the backing future as desired per the decorator pattern.
Most subclasses can just use SimpleForwardingListenableFuture. 
Author:
Shardul Deo
Since:
4.0/**
 * A {@link ListenableFuture} which forwards all its method calls to another future. Subclasses
 * should override one or more methods to modify the behavior of the backing future as desired per
 * the <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *
 * <p>Most subclasses can just use {@link SimpleForwardingListenableFuture}.
 *
 * @author Shardul Deo
 * @since 4.0
 */
@CanIgnoreReturnValue // TODO(cpovirk): Consider being more strict.
@GwtCompatible
public abstract class ForwardingListenableFuture<V> extends ForwardingFuture<V>
    implements ListenableFuture<V> {

  
Constructor for use by subclasses. /** Constructor for use by subclasses. */
  protected ForwardingListenableFuture() {}

  @Override
  protected abstract ListenableFuture<? extends V> delegate();

  @Override
  public void addListener(Runnable listener, Executor exec) {
    delegate().addListener(listener, exec);
  }

  // TODO(cpovirk): Use standard Javadoc form for SimpleForwarding* class and constructor
  
A simplified version of ForwardingListenableFuture where subclasses can pass in an already constructed ListenableFuture as the delegate. 
Since:
9.0/**
   * A simplified version of {@link ForwardingListenableFuture} where subclasses can pass in an
   * already constructed {@link ListenableFuture} as the delegate.
   *
   * @since 9.0
   */
  public abstract static class SimpleForwardingListenableFuture<V>
      extends ForwardingListenableFuture<V> {
    private final ListenableFuture<V> delegate;

    protected SimpleForwardingListenableFuture(ListenableFuture<V> delegate) {
      this.delegate = Preconditions.checkNotNull(delegate);
    }

    @Override
    protected final ListenableFuture<V> delegate() {
      return delegate;
    }
  }
}