org.apache.commons.collections.map

Class LazyMap

java.lang.Object

org.apache.commons.collections.map.AbstractMapDecorator

org.apache.commons.collections.map.LazyMap

All Implemented Interfaces:

java.io.Serializable, java.util.Map

Direct Known Subclasses:

LazySortedMap

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

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

When the get(Object) 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 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

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map

java.util.Map.Entry<K,V>

Method Summary

Modifier and Type	Method and Description
static java.util.Map	decorate(java.util.Map map, Factory factory) Factory method to create a lazily instantiated map.
static java.util.Map	decorate(java.util.Map map, Transformer factory) Factory method to create a lazily instantiated map.
java.lang.Object	get(java.lang.Object key)

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

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

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Map

clear, compute, computeIfAbsent, computeIfPresent, containsKey, containsValue, entrySet, equals, forEach, getOrDefault, hashCode, isEmpty, keySet, merge, put, putAll, putIfAbsent, remove, remove, replace, replace, replaceAll, size, values

Method Detail

decorate

public static java.util.Map decorate(java.util.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:

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 lazily instantiated map.

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