org.apache.commons.collections4.map
Class DefaultedMap<K,V>

java.lang.Object
  org.apache.commons.collections4.map.AbstractIterableMap<K,V>
      org.apache.commons.collections4.map.AbstractMapDecorator<K,V>
          org.apache.commons.collections4.map.DefaultedMap<K,V>

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"
 

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

Version:

$Id: DefaultedMap.java 1479407 2013-05-05 22:07:53Z tn $

See Also:

LazyMap, Serialized Form

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:

IllegalArgumentException - if map or transformer is null

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:

IllegalArgumentException - 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:

IllegalArgumentException - 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:

IllegalArgumentException - if map or factory is null

Since:

4.0

get

public V get(Object key)

Specified by:

get in interface Map<K,V>

Specified by:

get in interface Get<K,V>

Overrides:

get in class AbstractMapDecorator<K,V>

See Also:

Map.get(Object)