org.apache.commons.collections.map
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 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 java.util.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: 2005-11-21 22:52:57 +0000 (Mon, 21 Nov 2005) $
See Also: LazyMap
Field Summary | |
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protected Object | value The transformer to use if the map does not contain a key |
Constructor Summary | |
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DefaultedMap(Object defaultValue)
Constructs a new empty DefaultedMap that decorates
a HashMap .
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protected | DefaultedMap(Map map, Object value)
Constructor that wraps (not copies).
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Method Summary | |
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static Map | decorate(Map map, Object defaultValue)
Factory method to create a defaulting map.
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static Map | decorate(Map map, Factory factory)
Factory method to create a defaulting map.
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static Map | decorate(Map map, Transformer factory)
Factory method to create a defaulting map.
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Object | get(Object key) |
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
Parameters: map the map to decorate, must not be null value the value to use
Throws: IllegalArgumentException if map or transformer is null
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
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
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