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.annotations.Beta;
020    import com.google.common.base.Preconditions;
021    import com.google.common.collect.ForwardingObject;
022    
023    import java.util.concurrent.ExecutionException;
024    import java.util.concurrent.Future;
025    import java.util.concurrent.TimeUnit;
026    import java.util.concurrent.TimeoutException;
027    
028    /**
029     * A {@link Future} which forwards all its method calls to another future.
030     * Subclasses should override one or more methods to modify the behavior of
031     * the backing future as desired per the <a
032     * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
033     *
034     * <p>Most subclasses can just use {@link SimpleForwardingFuture}.
035     * 
036     * @author Sven Mawson
037     * @since 1
038     */
039    public abstract class ForwardingFuture<V> extends ForwardingObject
040        implements Future<V> {
041    
042      /** Constructor for use by subclasses. */
043      protected ForwardingFuture() {}
044    
045      @Override protected abstract Future<V> delegate();
046    
047      @Override
048      public boolean cancel(boolean mayInterruptIfRunning) {
049        return delegate().cancel(mayInterruptIfRunning);
050      }
051    
052      @Override
053      public boolean isCancelled() {
054        return delegate().isCancelled();
055      }
056    
057      @Override
058      public boolean isDone() {
059        return delegate().isDone();
060      }
061    
062      @Override
063      public V get() throws InterruptedException, ExecutionException {
064        return delegate().get();
065      }
066    
067      @Override
068      public V get(long timeout, TimeUnit unit)
069          throws InterruptedException, ExecutionException, TimeoutException {
070        return delegate().get(timeout, unit);
071      }
072    
073      // TODO(cpovirk): Use Standard Javadoc form for SimpleForwarding*
074      /**
075       * A simplified version of {@link ForwardingFuture} where subclasses
076       * can pass in an already constructed {@link Future} as the delegate.
077       * 
078       * @since 9
079       */
080      @Beta
081      public abstract static class SimpleForwardingFuture<V> 
082          extends ForwardingFuture<V> {
083        private final Future<V> delegate;
084    
085        protected SimpleForwardingFuture(Future<V> delegate) {
086          this.delegate = Preconditions.checkNotNull(delegate);
087        }
088    
089        @Override
090        protected final Future<V> delegate() {
091          return delegate;
092        }
093        
094      }
095    }