Package org.apache.commons.collections.map

Class DefaultedMap

  • All Implemented Interfaces:
    java.io.Serializable, java.util.Map
    public class DefaultedMap
extends AbstractMapDecorator
implements java.util.Map, java.io.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
    See Also:
    LazyMap, Serialized Form

    • Nested Class Summary

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

        java.util.Map.Entry<K extends java.lang.Object,​V extends java.lang.Object>

    • Constructor Summary

      Constructors 
      Constructor Description
      DefaultedMap​(java.lang.Object defaultValue)
      Constructs a new empty DefaultedMap that decorates a HashMap.

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      static java.util.Map decorate​(java.util.Map map, java.lang.Object defaultValue)
      Factory method to create a defaulting map.
      static java.util.Map decorate​(java.util.Map map, Factory factory)
      Factory method to create a defaulting map.
      static java.util.Map decorate​(java.util.Map map, Transformer factory)
      Factory method to create a defaulting map.
      java.lang.Object get​(java.lang.Object key)  

      • 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

    • Constructor Detail

      • DefaultedMap

        public DefaultedMap​(java.lang.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

    • Method Detail

      • decorate

        public static java.util.Map decorate​(java.util.Map map,
                                     java.lang.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:
        java.lang.IllegalArgumentException - if map is null

      • decorate

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