OrderedMap


1   /*
2    *  Copyright 2001-2004 The Apache Software Foundation
3    *
4    *  Licensed under the Apache License, Version 2.0 (the "License");
5    *  you may not use this file except in compliance with the License.
6    *  You may obtain a copy of the License at
7    *
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    *
10   *  Unless required by applicable law or agreed to in writing, software
11   *  distributed under the License is distributed on an "AS IS" BASIS,
12   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   *  See the License for the specific language governing permissions and
14   *  limitations under the License.
15   */
16  package org.apache.commons.collections;
17  
18  /**
19   * Defines a map that maintains order and allows both forward and backward
20   * iteration through that order.
21   * 
22   * @since Commons Collections 3.0
23   * @version $Revision: 1.6 $ $Date: 2004/02/18 01:15:42 $
24   *
25   * @author Stephen Colebourne
26   */
27  public interface OrderedMap extends IterableMap {
28      
29      /**
30       * Obtains an <code>OrderedMapIterator</code> over the map.
31       * <p>
32       * A ordered map iterator is an efficient way of iterating over maps
33       * in both directions.
34       * <pre>
35       * BidiMap map = new TreeBidiMap();
36       * MapIterator it = map.mapIterator();
37       * while (it.hasNext()) {
38       *   Object key = it.next();
39       *   Object value = it.getValue();
40       *   it.setValue("newValue");
41       *   Object previousKey = it.previous();
42       * }
43       * </pre>
44       * 
45       * @return a map iterator
46       */
47      OrderedMapIterator orderedMapIterator();
48      
49      /**
50       * Gets the first key currently in this map.
51       *
52       * @return the first key currently in this map
53       * @throws java.util.NoSuchElementException if this map is empty
54       */
55      public Object   firstKey();
56  
57      /**
58       * Gets the last key currently in this map.
59       *
60       * @return the last key currently in this map
61       * @throws java.util.NoSuchElementException if this map is empty
62       */
63      public Object   lastKey();
64      
65      /**
66       * Gets the next key after the one specified.
67       *
68       * @param key  the key to search for next from
69       * @return the next key, null if no match or at end
70       */
71      public Object   nextKey(Object   key);
72  
73      /**
74       * Gets the previous key before the one specified.
75       *
76       * @param key  the key to search for previous from
77       * @return the previous key, null if no match or at start
78       */
79      public Object   previousKey(Object   key);
80      
81  }
82
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