Package org.apache.commons.collections4

Interface BidiMap<K,V>

Type Parameters:
K - the type of the keys in the map
V - the type of the values in the map
All Superinterfaces:
Get<K,V>, IterableGet<K,V>, IterableMap<K,V>, Map<K,V>, Put<K,V>
All Known Subinterfaces:
OrderedBidiMap<K,V>, SortedBidiMap<K,V>
All Known Implementing Classes:
AbstractBidiMapDecorator, AbstractDualBidiMap, AbstractOrderedBidiMapDecorator, AbstractSortedBidiMapDecorator, DualHashBidiMap, DualLinkedHashBidiMap, DualTreeBidiMap, TreeBidiMap, UnmodifiableBidiMap, UnmodifiableOrderedBidiMap, UnmodifiableSortedBidiMap
public interface BidiMap<K,V> extends IterableMap<K,V>
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.

Since:
3.0

  • Method Details

    • getKey

      K 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

    • inverseBidiMap

      BidiMap<V,K> 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

    • put

      V put(K key, V 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
      Specified by:
      put in interface Map<K,V>
      Specified by:
      put in interface Put<K,V>
      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
      See Also:

    • removeValue

      K 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

    • values

      Set<V> values()
      Returns a Set view of the values contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress (except through the iterator's own remove operation), the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.
      Specified by:
      values in interface Get<K,V>
      Specified by:
      values in interface Map<K,V>
      Returns:
      a set view of the values contained in this map
      See Also: