org.knowceans.map
Class BijectiveHashMap<X,Y>

java.lang.Object
  java.util.AbstractMap<K,V>
      java.util.HashMap<X,Y>
          org.knowceans.map.BijectiveHashMap<X,Y>

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable, java.util.Map<X,Y>, IBijectiveMap<X,Y>

public class BijectiveHashMap<X,Y>
extends java.util.HashMap<X,Y>
implements IBijectiveMap<X,Y>

BijectiveHashMap is a HashMap that bijectively assigns unique keys to unique values and vice versa. The inverse mapping is done by a HashMap that maps values to keys. With getInverse(), a key can be found from the value without the search overhead of a value search. The bijective property constrains all input to obey unique keys AND unique values, while permitting the null element.

In relational terms, this class implements a 1:1 relation.

As the underlying HashMap has constant-time, O(1), get() and put() complexity, it can be used to identify numerical dimensions, such as the rows and columns of a matrix, much more conveniently than by array lookups (which would require array search for the inverse), however with some additive overhead over array index lookups.

Author:

heinrich

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class java.util.AbstractMap

java.util.AbstractMap.SimpleEntry<K,V>, java.util.AbstractMap.SimpleImmutableEntry<K,V>

Nested classes/interfaces inherited from interface java.util.Map

java.util.Map.Entry<K,V>

Constructor Summary

BijectiveHashMap()

BijectiveHashMap(int initialCapacity)

BijectiveHashMap(java.util.Map<? extends X,? extends Y> t)

Method Summary

void	clear()
java.util.HashMap<Y,X>	getInverse()
X	getInverse(Y val) gets key for a value.
java.util.Set<Y>	getValues() returns the keys of the inverse map.
static void	main(java.lang.String[] args)
Y	put(X key, Y val) put key-value pair into the map.
Y	remove(java.lang.Object key) removes the key and its value from the map.
java.util.Collection<Y>	values()

Methods inherited from class java.util.HashMap

clone, containsKey, containsValue, entrySet, get, isEmpty, keySet, putAll, size

Methods inherited from class java.util.AbstractMap

equals, hashCode, toString

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Map

containsKey, containsValue, entrySet, equals, get, hashCode, isEmpty, keySet, putAll, size

Constructor Detail

BijectiveHashMap

public BijectiveHashMap()

BijectiveHashMap

public BijectiveHashMap(java.util.Map<? extends X,? extends Y> t)

BijectiveHashMap

public BijectiveHashMap(int initialCapacity)

Method Detail

main

public static void main(java.lang.String[] args)

clear

public void clear()

Specified by:

clear in interface java.util.Map<X,Y>

Overrides:

clear in class java.util.HashMap<X,Y>

put

public Y put(X key,
             Y val)

put key-value pair into the map. If the key exists, it is replaced, along with the value it points to. If the value exists, it is replaced, along with the key it pointed to. The method returns the old value that the key pointed to. This is somewhat asymmetric because if a key gets overwritten, there is no reaction. Thus, check before calling the method.

Specified by:

put in interface java.util.Map<X,Y>

Overrides:

put in class java.util.HashMap<X,Y>

remove

public Y remove(java.lang.Object key)

removes the key and its value from the map. In the inverse map, the value is removed. Returns the value

Specified by:

remove in interface java.util.Map<X,Y>

Overrides:

remove in class java.util.HashMap<X,Y>

getInverse

public X getInverse(Y val)

gets key for a value.

Specified by:

getInverse in interface IBijectiveMap<X,Y>

Parameters:

val -

Returns:

getInverse

public java.util.HashMap<Y,X> getInverse()

Specified by:

getInverse in interface IBijectiveMap<X,Y>

Returns:

the complete inverse HashMap

getValues

public java.util.Set<Y> getValues()

returns the keys of the inverse map. Use this preferably over values().

Returns:

values

public java.util.Collection<Y> values()

Specified by:

values in interface java.util.Map<X,Y>

Overrides:

values in class java.util.HashMap<X,Y>