org.apache.commons.collections.map

Class DefaultedMap

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 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.

Since: Commons Collections 3.2

Version: $Revision: 1.7 $ $Date: 2005-11-21 22:52:57 +0000 (Mon, 21 Nov 2005) $

Author: Stephen Colebourne Rafael U.C. Afonso

See Also: LazyMap

Field Summary
protected Objectvalue
The transformer to use if the map does not contain a key
Constructor Summary
DefaultedMap(Object defaultValue)
Constructs a new empty DefaultedMap that decorates a HashMap.
protected DefaultedMap(Map map, Object value)
Constructor that wraps (not copies).
Method Summary
static Mapdecorate(Map map, Object defaultValue)
Factory method to create a defaulting map.
static Mapdecorate(Map map, Factory factory)
Factory method to create a defaulting map.
static Mapdecorate(Map map, Transformer factory)
Factory method to create a defaulting map.
Objectget(Object key)

Field Detail

value

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

Constructor Detail

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

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

Throws: IllegalArgumentException if map or transformer is null

Method Detail

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

Throws: IllegalArgumentException if map is null

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

Throws: IllegalArgumentException if map or factory is 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

Throws: IllegalArgumentException if map or factory is null

get

public Object get(Object key)
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