org.apache.commons.collections.map

Class DefaultedMap

Implemented Interfaces:
Map, Serializable

public class DefaultedMap
extends AbstractMapDecorator
implements Map, 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 java.util.Collections.synchronizedMap(Map). This class may throw exceptions when accessed by concurrent threads without synchronization.

Version:
$Revision: 1.7 $ $Date: 2005-11-21 22:52:57 +0000 (Mon, 21 Nov 2005) $
Authors:
Stephen Colebourne
Rafael U.C. Afonso
Since:
Commons Collections 3.2
See Also:
LazyMap

Field Summary

protected 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

DefaultedMap(Map map, Object value)
Constructor that wraps (not copies).
DefaultedMap(Object defaultValue)
Constructs a new empty DefaultedMap that decorates a HashMap.

Method Summary

static Map
decorate(Map map, Object defaultValue)
Factory method to create a defaulting map.
static Map
decorate(Map map, Factory factory)
Factory method to create a defaulting map.
static Map
decorate(Map map, Transformer factory)
Factory method to create a defaulting map.
Object
get(Object key)

Methods inherited from class org.apache.commons.collections.map.AbstractMapDecorator

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

Field Details

value

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

Constructor Details

DefaultedMap

protected DefaultedMap(Map map,
                       Object value)
Constructor that wraps (not copies).
Parameters:
map - the map to decorate, must not be null
value - the value to use

DefaultedMap

public DefaultedMap(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

Method Details

decorate

public static Map decorate(Map map,
                           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

decorate

public static Map decorate(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

decorate

public static Map decorate(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

get

public Object get(Object key)
Overrides:
get in interface AbstractMapDecorator

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