org.apache.commons.collections.map

Class LazyMap

public class LazyMap extends AbstractMapDecorator implements Map, Serializable

Decorates another Map to create objects in the map on demand.

When the get method is called with a key that does not exist in the map, the factory is used to create the object. The created object will be added to the map using the requested key.

For instance:

 Factory factory = new Factory() {
     public Object create() {
         return new Date();
     }
 }
 Map lazy = Lazy.map(new HashMap(), factory);
 Object obj = lazy.get("NOW");
 
After the above code is executed, obj will contain a new Date instance. Furthermore, that Date instance is mapped to the "NOW" key in the map.

Note that LazyMap 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.

This class is Serializable from Commons Collections 3.1.

Since: Commons Collections 3.0

Version: $Revision: 348007 $ $Date: 2005-11-21 22:52:57 +0000 (Mon, 21 Nov 2005) $

Author: Stephen Colebourne Paul Jack

Field Summary
protected Transformerfactory
The factory to use to construct elements
Constructor Summary
protected LazyMap(Map map, Factory factory)
Constructor that wraps (not copies).
protected LazyMap(Map map, Transformer factory)
Constructor that wraps (not copies).
Method Summary
static Mapdecorate(Map map, Factory factory)
Factory method to create a lazily instantiated map.
static Mapdecorate(Map map, Transformer factory)
Factory method to create a lazily instantiated map.
Objectget(Object key)

Field Detail

factory

protected final Transformer factory
The factory to use to construct elements

Constructor Detail

LazyMap

protected LazyMap(Map map, Factory factory)
Constructor that wraps (not copies).

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

LazyMap

protected LazyMap(Map map, Transformer factory)
Constructor that wraps (not copies).

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

Method Detail

decorate

public static Map decorate(Map map, Factory factory)
Factory method to create a lazily instantiated map.

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 lazily instantiated map.

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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