org.apache.commons.collections.map
Class DefaultedMap

java.lang.Object
  extended by org.apache.commons.collections.map.AbstractMapDecorator
      extended by org.apache.commons.collections.map.DefaultedMap
All Implemented Interfaces:
java.io.Serializable, java.util.Map

public class DefaultedMap
extends AbstractMapDecorator
implements java.util.Map, java.io.Serializable

Decorates another Map returning a default value if the map does not contain the requested key.

When the get(Object) method is called with a key that does not exist in the map, this map will return the default value specified in the constructor/factory. Only the get method is altered, so the Map.containsKey(Object) can be used to determine if a key really is in the map or not.

The defaulted value is not added to the map. Compare this behaviour with LazyMap, which does add the value to the map (via a Transformer).

For instance:

 Map map = new DefaultedMap("NULL");
 Object obj = map.get("Surname");
 // obj == "NULL"
 
After the above code is executed the map is still empty.

Note that DefaultedMap is not synchronized and is not thread-safe. If you wish to use this map from multiple threads concurrently, you must use appropriate synchronization. The simplest approach is to wrap this map using Collections.synchronizedMap(Map). This class may throw exceptions when accessed by concurrent threads without synchronization.

Since:
Commons Collections 3.2
Version:
$Revision: 1.7 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
Author:
Stephen Colebourne, Rafael U.C. Afonso
See Also:
LazyMap, Serialized Form

Nested Class Summary
 
Nested classes/interfaces inherited from interface java.util.Map
java.util.Map.Entry
 
Field Summary
protected  java.lang.Object value
          The transformer to use if the map does not contain a key
 
Fields inherited from class org.apache.commons.collections.map.AbstractMapDecorator
map
 
Constructor Summary
protected DefaultedMap(java.util.Map map, java.lang.Object value)
          Constructor that wraps (not copies).
  DefaultedMap(java.lang.Object defaultValue)
          Constructs a new empty DefaultedMap that decorates a HashMap.
 
Method Summary
static java.util.Map decorate(java.util.Map map, Factory factory)
          Factory method to create a defaulting map.
static java.util.Map decorate(java.util.Map map, java.lang.Object defaultValue)
          Factory method to create a defaulting map.
static java.util.Map decorate(java.util.Map map, Transformer factory)
          Factory method to create a defaulting map.
 java.lang.Object get(java.lang.Object key)
           
 
Methods inherited from class org.apache.commons.collections.map.AbstractMapDecorator
clear, containsKey, containsValue, entrySet, equals, getMap, hashCode, isEmpty, keySet, put, putAll, remove, size, toString, values
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
 
Methods inherited from interface java.util.Map
clear, containsKey, containsValue, entrySet, equals, hashCode, isEmpty, keySet, put, putAll, remove, size, values
 

Field Detail

value

protected final java.lang.Object value
The transformer to use if the map does not contain a key

Constructor Detail

DefaultedMap

public DefaultedMap(java.lang.Object defaultValue)
Constructs a new empty DefaultedMap that decorates a HashMap.

The object passed in will be returned by the map whenever an unknown key is requested.

Parameters:
defaultValue - the default value to return when the key is not found

DefaultedMap

protected DefaultedMap(java.util.Map map,
                       java.lang.Object value)
Constructor that wraps (not copies).

Parameters:
map - the map to decorate, must not be null
value - the value to use
Throws:
java.lang.IllegalArgumentException - if map or transformer is null
Method Detail

decorate

public static java.util.Map decorate(java.util.Map map,
                                     java.lang.Object defaultValue)
Factory method to create a defaulting map.

The value specified is returned when a missing key is found.

Parameters:
map - the map to decorate, must not be null
defaultValue - the default value to return when the key is not found
Throws:
java.lang.IllegalArgumentException - if map is null

decorate

public static java.util.Map decorate(java.util.Map map,
                                     Factory factory)
Factory method to create a defaulting map.

The factory specified is called when a missing key is found. The result will be returned as the result of the map get(key) method.

Parameters:
map - the map to decorate, must not be null
factory - the factory to use, must not be null
Throws:
java.lang.IllegalArgumentException - if map or factory is null

decorate

public static java.util.Map decorate(java.util.Map map,
                                     Transformer factory)
Factory method to create a defaulting map.

The transformer specified is called when a missing key is found. The key is passed to the transformer as the input, and the result will be returned as the result of the map get(key) method.

Parameters:
map - the map to decorate, must not be null
factory - the factory to use, must not be null
Throws:
java.lang.IllegalArgumentException - if map or factory is null

get

public java.lang.Object get(java.lang.Object key)
Specified by:
get in interface java.util.Map
Overrides:
get in class AbstractMapDecorator


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