Package org.apache.commons.collections.map

Class DefaultedMap

java.lang.Object
org.apache.commons.collections.map.AbstractMapDecorator
org.apache.commons.collections.map.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:

  • Field Details

    • value

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

  • Constructor Details

    • 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 Details

    • 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

    • get

      public Object get(Object key)
      Specified by:
      get in interface Map
      Overrides:
      get in class AbstractMapDecorator