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:
    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

- - ### Nested Class Summary

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

      `Map.Entry`

  - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected Transformer` | `factory` The factory to use to construct elements

    - ### Fields inherited from class org.apache.commons.collections.map.AbstractMapDecorator

      `map`

  - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `LazyMap(Map map, Factory factory)` Constructor that wraps (not copies).
    `protected` | `LazyMap(Map map, Transformer factory)` Constructor that wraps (not copies).

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `static Map` | `decorate(Map map, Factory factory)` Factory method to create a lazily instantiated map.
    `static Map` | `decorate(Map map, Transformer factory)` Factory method to create a lazily instantiated map.
    `Object` | `get(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

    - #### 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)

      Specified by:
        `get` in interface `Map`
      Overrides:
        `get` in class `AbstractMapDecorator`

Copyright © 2001–2015 The Apache Software Foundation. All rights reserved.