org.apache.commons.collections.map
Class DefaultedMap

java.lang.Object
  org.apache.commons.collections.map.AbstractMapDecorator
      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