Queue


1   /*
2    * All content copyright (c) 2003-2006 Terracotta, Inc., except as may otherwise be noted in a separate copyright notice.  All rights reserved.
3    */
4   package com.tc.util.concurrent;
5   
6   import java.util.NoSuchElementException  ;
7   
8   /**
9    * A generic queue interface similar to the java.util.Queue interface in the JDK 1.5 API NOTE: the interface is not
10   * complete with respect to the JDK version. Feel free to complete it if you'd like
11   * 
12   * @author orion
13   */
14  public interface Queue {
15    /**
16     * @return true iff this queue is empty (ie. contains no elements)
17     */
18    boolean isEmpty();
19  
20    /**
21     * Retrieves and removes the head of this queue, or null if this queue is empty.
22     * 
23     * @return the head of this queue, or null if this queue is empty.
24     */
25    Object   element();
26  
27    /**
28     * Inserts the specified element into this queue, if possible
29     * 
30     * @param o the element to insert.
31     * @return true if it was possible to add the element to this queue, else false
32     */
33    boolean offer(Object   o);
34  
35    /**
36     * Retrieves, but does not remove, the head of this queue, returning null if this queue is empty.
37     * 
38     * @return the head of this queue, or null if this queue is empty.
39     */
40    Object   peek();
41  
42    /**
43     * Retrieves and removes the head of this queue, or null if this queue is empty.
44     * 
45     * @return the head of this queue, or null if this queue is empty.
46     */
47    Object   poll();
48  
49    /**
50     * Retrieves and removes the head of this queue. This method differs from the poll method in that it throws an
51     * exception if this queue is empty.
52     * 
53     * @return the head of this queue.
54     * @throws NoSuchElementException if this queue is empty.
55     */
56    Object   remove();
57  }
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