    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    import com.google.common.collect.ForwardingObject;
    021
    022    import java.util.concurrent.ExecutionException;
    023    import java.util.concurrent.Future;
    024    import java.util.concurrent.TimeUnit;
    025    import java.util.concurrent.TimeoutException;
    026
    027    /**
    028     * A {@link Future} which forwards all its method calls to another future.
    029     * Subclasses should override one or more methods to modify the behavior of
    030     * the backing future as desired per the <a
    031     * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
    032     *
    033     * <p>Most subclasses can just use {@link SimpleForwardingFuture}.
    034     *
    035     * @author Sven Mawson
    036     * @since 1.0
    037     */
    038    public abstract class ForwardingFuture<V> extends ForwardingObject
    039        implements Future<V> {
    040
    041      /** Constructor for use by subclasses. */
    042      protected ForwardingFuture() {}
    043
    044      @Override protected abstract Future<V> delegate();
    045
    046      @Override
    047      public boolean cancel(boolean mayInterruptIfRunning) {
    048        return delegate().cancel(mayInterruptIfRunning);
    049      }
    050
    051      @Override
    052      public boolean isCancelled() {
    053        return delegate().isCancelled();
    054      }
    055
    056      @Override
    057      public boolean isDone() {
    058        return delegate().isDone();
    059      }
    060
    061      @Override
    062      public V get() throws InterruptedException, ExecutionException {
    063        return delegate().get();
    064      }
    065
    066      @Override
    067      public V get(long timeout, TimeUnit unit)
    068          throws InterruptedException, ExecutionException, TimeoutException {
    069        return delegate().get(timeout, unit);
    070      }
    071
    072      /*
    073       * TODO(cpovirk): Use standard Javadoc form for SimpleForwarding* class and
    074       * constructor
    075       */
    076      /**
    077       * A simplified version of {@link ForwardingFuture} where subclasses
    078       * can pass in an already constructed {@link Future} as the delegate.
    079       *
    080       * @since 9.0
    081       */
    082      public abstract static class SimpleForwardingFuture<V>
    083          extends ForwardingFuture<V> {
    084        private final Future<V> delegate;
    085
    086        protected SimpleForwardingFuture(Future<V> delegate) {
    087          this.delegate = Preconditions.checkNotNull(delegate);
    088        }
    089
    090        @Override
    091        protected final Future<V> delegate() {
    092          return delegate;
    093        }
    094
    095      }
    096    }