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  /*
   * Copyright (C) 2007 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.collect;
 
 
A queue which forwards all its method calls to another queue. Subclasses should override one or more methods to modify the behavior of the backing queue as desired per the decorator pattern.

Warning: The methods of ForwardingQueue forward indiscriminately to the methods of the delegate. For example, overriding ForwardingCollection.add(java.lang.Object) alone will not change the behavior of offer(java.lang.Object) which can lead to unexpected behavior. In this case, you should override offer as well, either providing your own implementation, or delegating to the provided standardOffer method.

The standard methods are not guaranteed to be thread-safe, even when all of the methods that they depend on are thread-safe.

Author(s):
Mike Bostock
Louis Wasserman
Since:
2.0 (imported from Google Collections Library)
 
 public abstract class ForwardingQueue<E> extends ForwardingCollection<E>
     implements Queue<E> {

  
Constructor for use by subclasses.
 
   protected ForwardingQueue() {}
 
   @Override protected abstract Queue<E> delegate();
 
   @Override
   public boolean offer(E o) {
     return delegate().offer(o);
   }
 
   @Override
   public E poll() {
     return delegate().poll();
   }
 
   @Override
   public E remove() {
     return delegate().remove();
   }
 
   @Override
   public E peek() {
     return delegate().peek();
   }
 
   @Override
   public E element() {
     return delegate().element();
   }

  
A sensible definition of offer(java.lang.Object) in terms of ForwardingCollection.add(java.lang.Object). If you override ForwardingCollection.add(java.lang.Object), you may wish to override offer(java.lang.Object) to forward to this implementation.

Since:
7.0
 
   @Beta protected boolean standardOffer(E e) {
     try {
       return add(e);
     } catch (IllegalStateException caught) {
       return false;
     }
   }

  
A sensible definition of peek() in terms of element(). If you override element(), you may wish to override peek() to forward to this implementation.

Since:
7.0
  @Beta protected E standardPeek() {
    try {
      return element();
    } catch (NoSuchElementException caught) {
      return null;
    }
  }

  
A sensible definition of poll() in terms of remove(). If you override remove(), you may wish to override poll() to forward to this implementation.

Since:
7.0
  @Beta protected E standardPoll() {
    try {
      return remove();
    } catch (NoSuchElementException caught) {
      return null;
    }
  }
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