PriorityQueue


1   /* 
2    * Copyright 1999-2004 The Apache Software Foundation
3    * Licensed  under the  Apache License,  Version 2.0  (the "License");
4    * you may not use  this file  except in  compliance with the License.
5    * You may obtain a copy of the License at 
6    * 
7    *   http://www.apache.org/licenses/LICENSE-2.0
8    * 
9    * Unless required by applicable law or agreed to in writing, software
10   * distributed  under the  License is distributed on an "AS IS" BASIS,
11   * WITHOUT  WARRANTIES OR CONDITIONS  OF ANY KIND, either  express  or
12   * implied.
13   * 
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  package org.apache.avalon.cornerstone.blocks.scheduler;
19  
20  import java.util.NoSuchElementException  ;
21  
22  /**
23   * Iterface for priority queues.
24   * This interface does not dictate whether it is min or max heap.
25   *
26   * @author <a HREF="mailto:dev@avalon.apache.org">Avalon Development Team</a>
27   * @version CVS $Revision: 1.1 $ $Date: 2004/03/16 12:49:52 $
28   * @since 4.0
29   */
30  public interface PriorityQueue
31  {
32      /**
33       * Clear all elements from queue.
34       */
35      void clear();
36  
37      /**
38       * Test if queue is empty.
39       *
40       * @return true if queue is empty else false.
41       */
42      boolean isEmpty();
43  
44      /**
45       * Insert an element into queue.
46       *
47       * @param element the element to be inserted
48       */
49      void insert( Object   element );
50  
51      /**
52       * Return element on top of heap but don't remove it.
53       *
54       * @return the element at top of heap
55       * @throws NoSuchElementException if isEmpty() == true
56       */
57      Object   peek() throws NoSuchElementException  ;
58  
59      /**
60       * Return element on top of heap and remove it.
61       *
62       * @return the element at top of heap
63       * @throws NoSuchElementException if isEmpty() == true
64       */
65      Object   pop() throws NoSuchElementException  ;
66  }
67  
68
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