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org.apache.commons.collections

Interface BidiMap

All Superinterfaces:
Map, IterableMap


public interface BidiMap
implements IterableMap

Defines a map that allows bidirectional lookup between key and values.

This extended Map represents a mapping where a key may lookup a value and a value may lookup a key with equal ease. Th 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.

Since:
Commons Collections 3.0
Author:
Stephen Colebourne

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).

Method Details

getKey

public Object getKey(Object value)

Gets the key that is currently mapped to the specified value.

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:
- (optional) if the map limits the type of the value and the specified value is inappropriate
- (optional) if the map limits the values to non-null and null was specified

inverseBidiMap

public BidiMap inverseBidiMap()

Gets a view of this map where the keys and values are reversed.

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

public MapIterator mapIterator()

Obtains a 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

put

public Object put(Object key, Object value)

Puts the key-value pair into the map, replacing any previous pair.

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:
- if the put method is not supported
- (optional) if the map limits the type of the value and the specified value is inappropriate
- (optional) if the map limits the values in some way and the value was invalid
- (optional) if the map limits the values to non-null and null was specified

removeValue

public 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 remove(Object).

Parameters:
value - the value to find the key-value pair for
Returns:
the key that was removed, null if nothing removed
Throws:
- (optional) if the map limits the type of the value and the specified value is inappropriate
- (optional) if the map limits the values to non-null and null was specified
- if this method is not supported by the implementation