Java Doc for MultiKeyMap.java in  » Library » Apache-common-Collections » org » apache » commons » collections » map » Java Source Code / Java DocumentationJava Source Code and Java Documentation

This class is the most efficient way to uses multiple keys to map to a value. The best way to use this class is via the additional map-style methods. These provide get, containsKey, put and remove for individual keys which operate without extra object creation.

The additional methods are the main interface of this map. As such, you will not normally hold this map in a variable of type Map.

The normal map methods take in and return a MultiKey . If you try to use put() with any other object type a ClassCastException is thrown. If you try to use null as the key in put() a NullPointerException is thrown.

This map is implemented as a decorator of a AbstractHashedMap which enables extra behaviour to be added easily.

• MultiKeyMap.decorate(new LinkedMap()) creates an ordered map.
• MultiKeyMap.decorate(new LRUMap()) creates an least recently used map.
• MultiKeyMap.decorate(new ReferenceMap()) creates a garbage collector sensitive map.

As an example, consider a least recently used cache that uses a String airline code and a Locale to lookup the airline's name:

 private MultiKeyMap cache = MultiKeyMap.decorate(new LRUMap(50));
 public String getAirlineName(String code, String locale) {
 String name = (String) cache.get(code, locale);
 if (name == null) {
 name = getAirlineNameFromDB(code, locale);
 cache.put(code, locale, name);
 }
 return name;
 }
 

Note that MultiKeyMap is not synchronized and is not thread-safe. If you wish to use this map from multiple threads concurrently, you must use appropriate synchronization. This class may throw exceptions when accessed by concurrent threads without synchronization.
since:
   Commons Collections 3.1
version:
   $Revision: 348007 $ $Date: 2005-11-21 22:52:57 +0000 (Mon, 21 Nov 2005) $
author:
   Stephen Colebourne

This method removes all the mappings where the MultiKey has one or more keys, and the first matches that specified.
Parameters:
  key1 - the first key true if any elements were removed

This method removes all the mappings where the MultiKey has two or more keys, and the first two match those specified.
Parameters:
  key1 - the first key
Parameters:
  key2 - the second key true if any elements were removed

This method removes all the mappings where the MultiKey has three or more keys, and the first three match those specified.
Parameters:
  key1 - the first key
Parameters:
  key2 - the second key
Parameters:
  key3 - the third key true if any elements were removed

This method removes all the mappings where the MultiKey has four or more keys, and the first four match those specified.
Parameters:
  key1 - the first key
Parameters:
  key2 - the second key
Parameters:
  key3 - the third key
Parameters:
  key4 - the fourth key true if any elements were removed