Package org.apache.commons.collections.map

Class LazyMap

  • All Implemented Interfaces:
    Serializable, Map
    Direct Known Subclasses:
    LazySortedMap
    public class LazyMap
extends AbstractMapDecorator
implements Map, 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
    Version:
    $Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
    Author:
    Stephen Colebourne, Paul Jack
    See Also:
    Serialized Form

    • 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