org.apache.commons.collections
public interface BidiMap extends IterableMap
This extended Map
represents a mapping where a key may
lookup a value and a value may lookup a key with equal ease.
This interface extends Map
and so may be used anywhere a map
is required. The interface provides an inverse map view, enabling
full access to both directions of the BidiMap
.
Implementations should allow a value to be looked up from a key and a key to be looked up from a value with equal performance.
This map enforces the restriction that there is a 1:1 relation between keys and values, meaning that multiple keys cannot map to the same value. This is required so that "inverting" the map results in a map without duplicate keys. See the BidiMap method description for more information.
Since: Commons Collections 3.0
Version: $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $
Method Summary | |
---|---|
Object | getKey(Object value)
Gets the key that is currently mapped to the specified value.
|
BidiMap | inverseBidiMap()
Gets a view of this map where the keys and values are reversed.
|
MapIterator | mapIterator()
Obtains a MapIterator over the map.
|
Object | put(Object key, Object value)
Puts the key-value pair into the map, replacing any previous pair.
|
Object | removeValue(Object value)
Removes the key-value pair that is currently mapped to the specified
value (optional operation).
|
If the value is not contained in the map, null
is returned.
Implementations should seek to make this method perform equally as well
as get(Object)
.
Parameters: value the value to find the key for
Returns: the mapped key, or null
if not found
Throws: ClassCastException (optional) if the map limits the type of the value and the specified value is inappropriate NullPointerException (optional) if the map limits the values to non-null and null was specified
Changes to one map will be visible in the other and vice versa.
This enables both directions of the map to be accessed as a Map
.
Implementations should seek to avoid creating a new object every time this
method is called. See AbstractMap.values()
etc. Calling this
method on the inverse map should return the original.
Returns: an inverted bidirectional map
MapIterator
over the map.
A map iterator is an efficient way of iterating over maps. It does not require that the map is stored using Map Entry objects which can increase performance.
BidiMap map = new DualHashBidiMap(); MapIterator it = map.mapIterator(); while (it.hasNext()) { Object key = it.next(); Object value = it.getValue(); it.setValue("newValue"); }
Returns: a map iterator
When adding a key-value pair, the value may already exist in the map against a different key. That mapping is removed, to ensure that the value only occurs once in the inverse map.
BidiMap map1 = new DualHashBidiMap(); map.put("A","B"); // contains A mapped to B, as per Map map.put("A","C"); // contains A mapped to C, as per Map BidiMap map2 = new DualHashBidiMap(); map.put("A","B"); // contains A mapped to B, as per Map map.put("C","B"); // contains C mapped to B, key A is removed
Parameters: key the key to store value the value to store
Returns: the previous value mapped to this key
Throws: UnsupportedOperationException if the put
method is not supported ClassCastException (optional) if the map limits the type of the
value and the specified value is inappropriate IllegalArgumentException (optional) if the map limits the values
in some way and the value was invalid NullPointerException (optional) if the map limits the values to
non-null and null was specified
If the value is not contained in the map, null
is returned.
Implementations should seek to make this method perform equally as well
as remove(Object)
.
Parameters: value the value to find the key-value pair for
Returns: the key that was removed, null
if nothing removed
Throws: ClassCastException (optional) if the map limits the type of the value and the specified value is inappropriate NullPointerException (optional) if the map limits the values to non-null and null was specified UnsupportedOperationException if this method is not supported by the implementation