MultiHashMap


1   package com.jdon.util;
2   
3   
4   import java.util.HashMap  ;
5   import java.util.Set  ;
6   
7   /**
8    * MultiHashMap is a extension java.util.HashMap.It is usde if following condition.<br>
9    * Sometime, a value shoud be determinated by key and subkey.
10   */
11  public class MultiHashMap extends HashMap  {
12  
13      public MultiHashMap() {
14          super();
15      }
16  
17      /**
18       * Associates the specified value with the specified key and subKey in this map.
19       * If the map previously contained a mapping for this key and subKey , the old value is replaced.
20       * @param key Is a Primary key.
21       * @param subKey  with which the specified value is to be associated.
22       * @param value to be associated with the specified key and subKey
23       * @return previous value associated with specified key and subKey, or null if there was no mapping for key and subKey.
24       * A null return can also indicate that the HashMap previously associated null with the specified key and subKey.
25       */
26      public Object   put(Object   key,Object   subKey,Object   value){
27          HashMap   a = (HashMap  )super.get(key);
28          if(a==null){
29              a = new HashMap  ();
30              super.put(key,a);
31          }
32          return a.put(subKey,value);
33      }
34  
35      /**
36       * Returns the value to which this map maps the specified key and subKey. Returns null if the map contains no mapping
37       * for this key and subKey. A return value of null does not necessarily indicate that the map contains no mapping
38       * for the key and subKey; it's also possible that the map explicitly maps the key to null.
39       * The containsKey operation may be used to distinguish these two cases.
40       * @param key  whose associated value is to be returned.
41       * @param subKey whose associated value is to be returned
42       * @return the value to which this map maps the specified key.
43       */
44      public Object   get(Object   key,Object   subKey){
45          HashMap   a = (HashMap  )super.get(key);
46          if(a!=null){
47              Object   b=a.get(subKey);
48              return b;
49          }
50          return null;
51      }
52      
53      public Set   getSubKeys(Object   key){
54          HashMap   a = (HashMap  )super.get(key);
55          if(a==null) return null;
56          return a.keySet();        
57      }
58      
59      
60  }
61
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