HashMapUtils


1   /*
2    * Copyright 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.myfaces.util;
17  
18  import java.util.HashMap  ;
19  import java.util.Map  ;
20  
21  
22  /**
23   * @author Anton Koinov (latest modification by $Author: matze $)
24   * @version $Revision: 1.3 $ $Date: 2004/10/13 11:51:01 $
25   */
26  public class HashMapUtils
27  {
28      //~ Constructors -------------------------------------------------------------------------------
29  
30      protected HashMapUtils()
31      {
32          // block public access
33      }
34  
35      //~ Methods ------------------------------------------------------------------------------------
36  
37      /**
38       * Calculates initial capacity needed to hold <code>size</code> elements in
39       * a HashMap or Hashtable without forcing an expensive increase in internal
40       * capacity. Capacity is based on the default load factor of .75.
41       * <p>
42       * Usage: <code>Map map = new HashMap(HashMapUtils.calcCapacity(10));<code>
43       * </p>
44       * @param size the number of items that will be put into a HashMap
45       * @return initial capacity needed
46       */
47      public static final int calcCapacity(int size)
48      {
49          return ((size * 4) + 3) / 3;
50      }
51  
52      /**
53       * Creates a new <code>HashMap</code> that has all of the elements
54       * of <code>map1</code> and <code>map2</code> (on key collision, the latter
55       * override the former).
56       *
57       * @param map1 the fist hashmap to merge
58       * @param map2 the second hashmap to merge
59       * @return new hashmap
60       */
61      public static HashMap   merge(Map   map1, Map   map2)
62      {
63          HashMap   retval = new HashMap  (calcCapacity(map1.size() + map2.size()));
64  
65          retval.putAll(map1);
66          retval.putAll(map2);
67  
68          return retval;
69      }
70  }
71
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