    001    /*
    002     * Copyright (C) 2009 The Guava Authors
    003     *
    004     * Licensed under the Apache License, Version 2.0 (the "License");
    005     * you may not use this file except in compliance with the License.
    006     * You may obtain a copy of the License at
    007     *
    008     * http://www.apache.org/licenses/LICENSE-2.0
    009     *
    010     * Unless required by applicable law or agreed to in writing, software
    011     * distributed under the License is distributed on an "AS IS" BASIS,
    012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    013     * See the License for the specific language governing permissions and
    014     * limitations under the License.
    015     */
    016
    017    package com.google.common.util.concurrent;
    018
    019    import com.google.common.base.Preconditions;
    020
    021    import java.util.concurrent.Executor;
    022
    023    /**
    024     * A {@link ListenableFuture} which forwards all its method calls to another
    025     * future. Subclasses should override one or more methods to modify the behavior
    026     * of the backing future as desired per the <a
    027     * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
    028     *
    029     * <p>Most subclasses can just use {@link SimpleForwardingListenableFuture}.
    030     *
    031     * @param <V> The result type returned by this Future's {@code get} method
    032     *
    033     * @author Shardul Deo
    034     * @since 4.0
    035     */
    036    public abstract class ForwardingListenableFuture<V> extends ForwardingFuture<V>
    037        implements ListenableFuture<V> {
    038
    039      /** Constructor for use by subclasses. */
    040      protected ForwardingListenableFuture() {}
    041
    042      @Override
    043      protected abstract ListenableFuture<V> delegate();
    044
    045      @Override
    046      public void addListener(Runnable listener, Executor exec) {
    047        delegate().addListener(listener, exec);
    048      }
    049
    050      /*
    051       * TODO(cpovirk): Use standard Javadoc form for SimpleForwarding* class and
    052       * constructor
    053       */
    054      /**
    055       * A simplified version of {@link ForwardingListenableFuture} where subclasses
    056       * can pass in an already constructed {@link ListenableFuture}
    057       * as the delegate.
    058       *
    059       * @since 9.0
    060       */
    061      public abstract static class SimpleForwardingListenableFuture<V>
    062          extends ForwardingListenableFuture<V> {
    063        private final ListenableFuture<V> delegate;
    064
    065        protected SimpleForwardingListenableFuture(ListenableFuture<V> delegate) {
    066          this.delegate = Preconditions.checkNotNull(delegate);
    067        }
    068
    069        @Override
    070        protected final ListenableFuture<V> delegate() {
    071          return delegate;
    072        }
    073      }
    074    }