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/*
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.qpid.junit.extensions.util;
import java.util.EmptyStackException;
import java.util.NoSuchElementException;
import java.util.Queue;
import java.util.Stack;
/**
* The Stack class in java.util (most unhelpfully) does not implement the Queue interface. This is an adaption of that
* class as a queue.
*
* <p><table id="crc"><caption>CRC Card</caption>
* <tr><th> Responsibilities <th> Collaborations
* <tr><td> Turn a stack into a queue.
* </table>
*
* @todo Need to override the add method, and iterator and consider other methods too. They work like LIFO but
* really wany FIFO behaviour accross the whole data structure.
*
* @author Rupert Smith
*/
public class StackQueue<E> extends Stack<E> implements Queue<E>
{
/**
* Retrieves, but does not remove, the head of this queue.
*
* @return The element at the top of the stack.
*/
public E element()
{
try
{
return super.peek();
}
catch (EmptyStackException e)
{
NoSuchElementException t = new NoSuchElementException();
t.initCause(e);
throw t;
}
}
/**
* Inserts the specified element into this queue, if possible.
*
* @param o The data element to push onto the stack.
*
* @return True if it was added to the stack, false otherwise (this implementation always returns true).
*/
public boolean offer(E o)
{
push(o);
return true;
}
/**
* Retrieves, but does not remove, the head of this queue, returning null if this queue is empty.
*
* @return The top element from the stack, or null if the stack is empty.
*/
public E peek()
{
try
{
return super.peek();
}
catch (EmptyStackException e)
{
return null;
}
}
/**
* Retrieves and removes the head of this queue, or null if this queue is empty.
*
* @return The top element from the stack, or null if the stack is empty.
*/
public E poll()
{
try
{
return super.pop();
}
catch (EmptyStackException e)
{
return null;
}
}
/**
* Retrieves and removes the head of this queue.
*
* @return The top element from the stack, or null if the stack is empty.
*
* @throws NoSuchElementException If the stack is empty so no element can be removed from it.
*/
public E remove()
{
try
{
return super.pop();
}
catch (EmptyStackException e)
{
NoSuchElementException t = new NoSuchElementException();
t.initCause(e);
throw t;
}
}
}
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