public class DefaultedMap extends AbstractMapDecorator implements Map, Serializable
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.
LazyMap,
Serialized Form| Modifier and Type | Field and Description |
|---|---|
protected Object |
value
The transformer to use if the map does not contain a key
|
map| Modifier | Constructor and Description |
|---|---|
protected |
DefaultedMap(Map map,
Object value)
Constructor that wraps (not copies).
|
|
DefaultedMap(Object defaultValue)
Constructs a new empty
DefaultedMap that decorates
a HashMap. |
| Modifier and Type | Method and Description |
|---|---|
static Map |
decorate(Map map,
Factory factory)
Factory method to create a defaulting map.
|
static Map |
decorate(Map map,
Object defaultValue)
Factory method to create a defaulting map.
|
static Map |
decorate(Map map,
Transformer factory)
Factory method to create a defaulting map.
|
Object |
get(Object key) |
clear, containsKey, containsValue, entrySet, equals, getMap, hashCode, isEmpty, keySet, put, putAll, remove, size, toString, valuesprotected final Object value
public DefaultedMap(Object defaultValue)
DefaultedMap that decorates
a HashMap.
The object passed in will be returned by the map whenever an unknown key is requested.
defaultValue - the default value to return when the key is not foundprotected DefaultedMap(Map map, Object value)
map - the map to decorate, must not be nullvalue - the value to useIllegalArgumentException - if map or transformer is nullpublic static Map decorate(Map map, Object defaultValue)
The value specified is returned when a missing key is found.
map - the map to decorate, must not be nulldefaultValue - the default value to return when the key is not foundIllegalArgumentException - if map is nullpublic static Map decorate(Map map, Factory factory)
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.
map - the map to decorate, must not be nullfactory - the factory to use, must not be nullIllegalArgumentException - if map or factory is nullpublic static Map decorate(Map map, Transformer factory)
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.
map - the map to decorate, must not be nullfactory - the factory to use, must not be nullIllegalArgumentException - if map or factory is nullCopyright © 2001–2015 The Apache Software Foundation. All rights reserved.