Package org.apache.commons.collections4.map

Class DefaultedMap<K,​V>

  • Type Parameters:
    K - the type of the keys in this map
    V - the type of the values in this map
    All Implemented Interfaces:
    Serializable, Map<K,​V>, Get<K,​V>, IterableGet<K,​V>, IterableMap<K,​V>, Put<K,​V>
    public class DefaultedMap<K,​V>
extends AbstractMapDecorator<K,​V>
implements 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:
    3.2
    See Also:
    LazyMap, Serialized Form

    • Constructor Detail

      • DefaultedMap

        public DefaultedMap​(V 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

        public DefaultedMap​(Transformer<? super K,​? extends V> defaultValueTransformer)
        Constructs a new empty DefaultedMap that decorates a HashMap.
        Parameters:
        defaultValueTransformer - transformer to use to generate missing values.

      • DefaultedMap

        protected DefaultedMap​(Map<K,​V> map,
                       Transformer<? super K,​? extends V> defaultValueTransformer)
        Constructor that wraps (not copies).
        Parameters:
        map - the map to decorate, must not be null
        defaultValueTransformer - the value transformer to use
        Throws:
        NullPointerException - if map or transformer is null

    • Method Detail

      • defaultedMap

        public static <K,​V> DefaultedMap<K,​V> defaultedMap​(Map<K,​V> map,
                                                               V defaultValue)
        Factory method to create a defaulting map.

        The value specified is returned when a missing key is found.

        Type Parameters:
        K - the key type
        V - the value type
        Parameters:
        map - the map to decorate, must not be null
        defaultValue - the default value to return when the key is not found
        Returns:
        a new defaulting map
        Throws:
        NullPointerException - if map is null
        Since:
        4.0

      • defaultedMap

        public static <K,​V> DefaultedMap<K,​V> defaultedMap​(Map<K,​V> map,
                                                               Factory<? extends V> 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.

        Type Parameters:
        K - the key type
        V - the value type
        Parameters:
        map - the map to decorate, must not be null
        factory - the factory to use to create entries, must not be null
        Returns:
        a new defaulting map
        Throws:
        NullPointerException - if map or factory is null
        Since:
        4.0

      • defaultedMap

        public static <K,​V> Map<K,​V> defaultedMap​(Map<K,​V> map,
                                                      Transformer<? super K,​? extends V> transformer)
        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.

        Type Parameters:
        K - the key type
        V - the value type
        Parameters:
        map - the map to decorate, must not be null
        transformer - the transformer to use as a factory to create entries, must not be null
        Returns:
        a new defaulting map
        Throws:
        NullPointerException - if map or factory is null
        Since:
        4.0

      • get

        public V get​(Object key)
        Specified by:
        get in interface Get<K,​V>
        Specified by:
        get in interface Map<K,​V>
        Overrides:
        get in class AbstractMapDecorator<K,​V>
        Parameters:
        key - the key whose associated value is to be returned
        Returns:
        the value to which the specified key is mapped, or null if this map contains no mapping for the key
        See Also:
        Map.get(Object)