jpaul.DataStructs
Class MapWithDefault<K,V>

java.lang.Object
  jpaul.DataStructs.MapWrapper<K,V>
      jpaul.DataStructs.MapWithDefault<K,V>

All Implemented Interfaces:

java.util.Map<K,V>

public class MapWithDefault<K,V>
extends MapWrapper<K,V>

MapWithDefault is a map that returns default values for unassigned keys. Notice the difference with the usual implementations of Map, that return null for unassigned keys. A boolean flag in the constructor choose between two possible behaviours for the get method.

• with memory: for any unassigned key, in addition to returning a default value, get will store this value in the map. Therefore, if you execute another get for the same key (without any relevant put in between, you will get the same object.
• without memory: for unassigned keys, get just returns a default value. It does not mutate the map.

Version:

$Id: MapWithDefault.java,v 1.6 2006/03/14 02:29:31 salcianu Exp $

Author:

Alexandru Salcianu - salcianu@alum.mit.edu

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map

java.util.Map.Entry<K,V>

Field Summary

Fields inherited from class jpaul.DataStructs.MapWrapper

map

Constructor Summary

MapWithDefault(Factory<V> defValFact, boolean withMemory)
Creates a MapWithDefault, backed by a LinkedHashMap.

MapWithDefault(java.util.Map<K,V> map, Factory<V> defValFact, boolean withMemory)
Creates a MapWithDefault.

Method Summary

V	get(java.lang.Object key) Returns the value to which this map maps the specified key.
V	getNoDefault(java.lang.Object key) Returns the value assigned to key, if any.

Methods inherited from class jpaul.DataStructs.MapWrapper

clear, containsKey, containsValue, entrySet, equals, hashCode, isEmpty, keySet, put, putAll, remove, size, values

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

MapWithDefault

public MapWithDefault(Factory<V> defValFact,
                      boolean withMemory)

Creates a MapWithDefault, backed by a LinkedHashMap.

Parameters:

defValFact - Factory that provides the default values for previously unassigned keys.

withMemory - Selects one of the two behaviours described above.

MapWithDefault

public MapWithDefault(java.util.Map<K,V> map,
                      Factory<V> defValFact,
                      boolean withMemory)

Creates a MapWithDefault.

Parameters:

map - Underlying map.

defValFact - Factory that provides the default values for previously unassigned keys.

withMemory - Selects one of the two behaviours described above.

Method Detail

get

public V get(java.lang.Object key)

Returns the value to which this map maps the specified key. Unlike the common implementations of Map, if the key is not mapped to anything, a freshly-generated value will be returned instead. In addition, for maps with memory, the previously unassigned key will be mapped to the freshly-generated value (note that in this case, get mutates the map).

Specified by:

get in interface java.util.Map<K,V>

Overrides:

get in class MapWrapper<K,V>

getNoDefault

public V getNoDefault(java.lang.Object key)

Returns the value assigned to key, if any. Otherwise, returns null (unlike get, no default element is generated, and the map is never mutated by this method.