public interface

BidiMap

implements IterableMap
org.apache.commons.collections.BidiMap
Known Indirect Subclasses

Class Overview

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. 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 put(K, V) method description for more information.

Summary

Public Methods
abstract Object getKey(Object value)
Gets the key that is currently mapped to the specified value.
abstract BidiMap inverseBidiMap()
Gets a view of this map where the keys and values are reversed.
abstract MapIterator mapIterator()
Obtains a MapIterator over the map.
abstract Object put(Object key, Object value)
Puts the key-value pair into the map, replacing any previous pair.
abstract Object removeValue(Object value)
Removes the key-value pair that is currently mapped to the specified value (optional operation).
[Expand]
Inherited Methods
From interface java.util.Map
From interface org.apache.commons.collections.IterableMap

Public Methods

public abstract 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
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

public abstract 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

public abstract 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

public abstract 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
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

public abstract 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
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