Package org.apache.commons.collections.map

Class DefaultedMap

  • All Implemented Interfaces:
    Serializable, Map
    public class DefaultedMap
extends AbstractMapDecorator
implements Map, 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 14:33:15 +0200 (Thu, 10 Apr 2008) $
    Author:
    Stephen Colebourne, Rafael U.C. Afonso
    See Also:
    LazyMap, Serialized Form

    • Field Detail

      • value

        protected final Object value
        The transformer to use if the map does not contain a key

    • Constructor Detail

      • DefaultedMap

        public DefaultedMap​(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​(Map map,
                       Object value)
        Constructor that wraps (not copies).
        Parameters:
        map - the map to decorate, must not be null
        value - the value to use
        Throws:
        IllegalArgumentException - if map or transformer is null

    • Method Detail

      • decorate

        public static Map decorate​(Map map,
                           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:
        IllegalArgumentException - if map is null

      • decorate

        public static Map decorate​(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:
        IllegalArgumentException - if map or factory is null

      • decorate

        public static Map decorate​(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:
        IllegalArgumentException - if map or factory is null