org.apache.commons.collections.bidimap
Class TreeBidiMap<K extends Comparable,V extends Comparable>

java.lang.Object
  org.apache.commons.collections.bidimap.TreeBidiMap<K,V>

All Implemented Interfaces:

Map<K,V>, BidiMap<K,V>, IterableMap<K,V>, OrderedBidiMap<K,V>, OrderedMap<K,V>

public class TreeBidiMap<K extends Comparable,V extends Comparable>
extends Object
implements OrderedBidiMap<K,V>

Red-Black tree-based implementation of BidiMap where all objects added implement the Comparable interface.

This class guarantees that the map will be in both ascending key order and ascending value order, sorted according to the natural order for the key's and value's classes.

This Map is intended for applications that need to be able to look up a key-value pairing by either key or value, and need to do so with equal efficiency.

While that goal could be accomplished by taking a pair of TreeMaps and redirecting requests to the appropriate TreeMap (e.g., containsKey would be directed to the TreeMap that maps values to keys, containsValue would be directed to the TreeMap that maps keys to values), there are problems with that implementation. If the data contained in the TreeMaps is large, the cost of redundant storage becomes significant. The DualTreeBidiMap and DualHashBidiMap implementations use this approach.

This solution keeps minimizes the data storage by holding data only once. The red-black algorithm is based on java util TreeMap, but has been modified to simultaneously map a tree node by key and by value. This doubles the cost of put operations (but so does using two TreeMaps), and nearly doubles the cost of remove operations (there is a savings in that the lookup of the node to be removed only has to be performed once). And since only one node contains the key and value, storage is significantly less than that required by two TreeMaps.

The Map.Entry instances returned by the appropriate methods will not allow setValue() and will throw an UnsupportedOperationException on attempts to call that method.

Since:

Commons Collections 3.0 (previously DoubleOrderedMap v2.0)

Version:

$Revision: 1.1.1.1 $ $Date: 2005/05/23 04:33:47 $

Author:

Marc Johnson, Matt Hall, John Watkinson, Stephen Colebourne

Nested Class Summary

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

Map.Entry<K,V>

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

Map.Entry<K,V>

Constructor Summary

TreeBidiMap()
Constructs a new empty TreeBidiMap.

TreeBidiMap(Map map)
Constructs a new TreeBidiMap by copying an existing Map.

Method Summary

void	clear() Removes all mappings from this map.
boolean	containsKey(Object key) Checks whether this map contains the a mapping for the specified key.
boolean	containsValue(Object value) Checks whether this map contains the a mapping for the specified value.
Set<Map.Entry<K,V>>	entrySet() Returns a set view of the entries contained in this map in key order.
boolean	equals(Object obj) Compares for equals as per the API.
K	firstKey() Gets the first (lowest) key currently in this map.
V	get(Object key) Gets the value to which this map maps the specified key.
K	getKey(V value) Returns the key to which this map maps the specified value.
int	hashCode() Gets the hash code value for this map as per the API.
BidiMap<V,K>	inverseBidiMap() Gets the inverse map for comparison.
OrderedBidiMap<V,K>	inverseOrderedBidiMap() Gets the inverse map for comparison.
boolean	isEmpty() Checks whether the map is empty or not.
Set<K>	keySet() Returns a set view of the keys contained in this map in key order.
K	lastKey() Gets the last (highest) key currently in this map.
MapIterator<K,V>	mapIterator() Gets an iterator over the map entries.
K	nextKey(K key) Gets the next key after the one specified.
OrderedMapIterator<K,V>	orderedMapIterator() Gets an ordered iterator over the map entries.
K	previousKey(K key) Gets the previous key before the one specified.
V	put(K key, V value) Puts the key-value pair into the map, replacing any previous pair.
void	putAll(Map<? extends K,? extends V> map) Puts all the mappings from the specified map into this map.
V	remove(Object key) Removes the mapping for this key from this map if present.
K	removeValue(V value) Removes the mapping for this value from this map if present.
int	size() Returns the number of key-value mappings in this map.
String	toString() Returns a string version of this Map in standard format.
Collection<V>	values() Returns a set view of the values contained in this map in key order.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

TreeBidiMap

public TreeBidiMap()

Constructs a new empty TreeBidiMap.

TreeBidiMap

public TreeBidiMap(Map map)

Constructs a new TreeBidiMap by copying an existing Map.

Parameters:

map - the map to copy

Throws:

ClassCastException - if the keys/values in the map are not Comparable or are not mutually comparable

NullPointerException - if any key or value in the map is null

Method Detail

size

public int size()

Returns the number of key-value mappings in this map.

Specified by:

size in interface Map<K extends Comparable,V extends Comparable>

Returns:

the number of key-value mappings in this map

isEmpty

public boolean isEmpty()

Checks whether the map is empty or not.

Specified by:

isEmpty in interface Map<K extends Comparable,V extends Comparable>

Returns:

true if the map is empty

containsKey

public boolean containsKey(Object key)

Checks whether this map contains the a mapping for the specified key.

The key must implement Comparable.

Specified by:

containsKey in interface Map<K extends Comparable,V extends Comparable>

Parameters:

key - key whose presence in this map is to be tested

Returns:

true if this map contains a mapping for the specified key

Throws:

ClassCastException - if the key is of an inappropriate type

NullPointerException - if the key is null

containsValue

public boolean containsValue(Object value)

Checks whether this map contains the a mapping for the specified value.

The value must implement Comparable.

Specified by:

containsValue in interface Map<K extends Comparable,V extends Comparable>

Parameters:

value - value whose presence in this map is to be tested

Returns:

true if this map contains a mapping for the specified value

Throws:

ClassCastException - if the value is of an inappropriate type

NullPointerException - if the value is null

get

public V get(Object key)

Gets the value to which this map maps the specified key. Returns null if the map contains no mapping for this key.

The key must implement Comparable.

Specified by:

get in interface Map<K extends Comparable,V extends Comparable>

Parameters:

key - key whose associated value is to be returned

Returns:

the value to which this map maps the specified key, or null if the map contains no mapping for this key

Throws:

ClassCastException - if the key is of an inappropriate type

NullPointerException - if the key is null

put

public 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 TreeBidiMap();
  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 TreeBidiMap();
  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
 

Both key and value must implement Comparable.

Specified by:

put in interface Map<K extends Comparable,V extends Comparable>

Specified by:

put in interface BidiMap<K extends Comparable,V extends Comparable>

Parameters:

key - key with which the specified value is to be associated

value - value to be associated with the specified key

Returns:

the previous value for the key

Throws:

ClassCastException - if the key is of an inappropriate type

NullPointerException - if the key is null

putAll

public void putAll(Map<? extends K,? extends V> map)

Puts all the mappings from the specified map into this map.

All keys and values must implement Comparable.

Specified by:

putAll in interface Map<K extends Comparable,V extends Comparable>

Parameters:

map - the map to copy from

remove

public V remove(Object key)

Removes the mapping for this key from this map if present.

The key must implement Comparable.

Specified by:

remove in interface Map<K extends Comparable,V extends Comparable>

Parameters:

key - key whose mapping is to be removed from the map.

Returns:

previous value associated with specified key, or null if there was no mapping for key.

Throws:

ClassCastException - if the key is of an inappropriate type

NullPointerException - if the key is null

clear

public void clear()

Removes all mappings from this map.

Specified by:

clear in interface Map<K extends Comparable,V extends Comparable>

getKey

public K getKey(V value)

Returns the key to which this map maps the specified value. Returns null if the map contains no mapping for this value.

The value must implement Comparable.

Specified by:

getKey in interface BidiMap<K extends Comparable,V extends Comparable>

Parameters:

value - value whose associated key is to be returned.

Returns:

the key to which this map maps the specified value, or null if the map contains no mapping for this value.

Throws:

ClassCastException - if the value is of an inappropriate type

NullPointerException - if the value is null

removeValue

public K removeValue(V value)

Removes the mapping for this value from this map if present.

The value must implement Comparable.

Specified by:

removeValue in interface BidiMap<K extends Comparable,V extends Comparable>

Parameters:

value - value whose mapping is to be removed from the map

Returns:

previous key associated with specified value, or null if there was no mapping for value.

Throws:

ClassCastException - if the value is of an inappropriate type

NullPointerException - if the value is null

firstKey

public K firstKey()

Gets the first (lowest) key currently in this map.

Specified by:

firstKey in interface OrderedMap<K extends Comparable,V extends Comparable>

Returns:

the first (lowest) key currently in this sorted map

Throws:

NoSuchElementException - if this map is empty

lastKey

public K lastKey()

Gets the last (highest) key currently in this map.

Specified by:

lastKey in interface OrderedMap<K extends Comparable,V extends Comparable>

Returns:

the last (highest) key currently in this sorted map

Throws:

NoSuchElementException - if this map is empty

nextKey

public K nextKey(K key)

Gets the next key after the one specified.

The key must implement Comparable.

Specified by:

nextKey in interface OrderedMap<K extends Comparable,V extends Comparable>

Parameters:

key - the key to search for next from

Returns:

the next key, null if no match or at end

previousKey

public K previousKey(K key)

Gets the previous key before the one specified.

The key must implement Comparable.

Specified by:

previousKey in interface OrderedMap<K extends Comparable,V extends Comparable>

Parameters:

key - the key to search for previous from

Returns:

the previous key, null if no match or at start

keySet

public Set<K> keySet()

Returns a set view of the keys contained in this map in key order.

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, the results of the iteration are undefined.

The set supports element removal, which removes the corresponding mapping from the map. It does not support the add or addAll operations.

Specified by:

keySet in interface Map<K extends Comparable,V extends Comparable>

Returns:

a set view of the keys contained in this map.

values

public Collection<V> values()

Returns a set view of the values contained in this map in key order. The returned object can be cast to a Set.

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, the results of the iteration are undefined.

The set supports element removal, which removes the corresponding mapping from the map. It does not support the add or addAll operations.

Specified by:

values in interface Map<K extends Comparable,V extends Comparable>

Returns:

a set view of the values contained in this map.

entrySet

public Set<Map.Entry<K,V>> entrySet()

Returns a set view of the entries contained in this map in key order. For simple iteration through the map, the MapIterator is quicker.

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, the results of the iteration are undefined.

The set supports element removal, which removes the corresponding mapping from the map. It does not support the add or addAll operations. The returned MapEntry objects do not support setValue.

Specified by:

entrySet in interface Map<K extends Comparable,V extends Comparable>

Returns:

a set view of the values contained in this map.

mapIterator

public MapIterator<K,V> mapIterator()

Gets an iterator over the map entries.

For this map, this iterator is the fastest way to iterate over the entries.

Specified by:

mapIterator in interface BidiMap<K extends Comparable,V extends Comparable>

Specified by:

mapIterator in interface IterableMap<K extends Comparable,V extends Comparable>

Returns:

an iterator

orderedMapIterator

public OrderedMapIterator<K,V> orderedMapIterator()

Gets an ordered iterator over the map entries.

This iterator allows both forward and reverse iteration over the entries.

Specified by:

orderedMapIterator in interface OrderedMap<K extends Comparable,V extends Comparable>

Returns:

an iterator

inverseBidiMap

public BidiMap<V,K> inverseBidiMap()

Gets the inverse map for comparison.

Specified by:

inverseBidiMap in interface BidiMap<K extends Comparable,V extends Comparable>

Specified by:

inverseBidiMap in interface OrderedBidiMap<K extends Comparable,V extends Comparable>

Returns:

the inverse map

inverseOrderedBidiMap

public OrderedBidiMap<V,K> inverseOrderedBidiMap()

Gets the inverse map for comparison.

Specified by:

inverseOrderedBidiMap in interface OrderedBidiMap<K extends Comparable,V extends Comparable>

Returns:

the inverse map

equals

public boolean equals(Object obj)

Compares for equals as per the API.

Specified by:

equals in interface Map<K extends Comparable,V extends Comparable>

Overrides:

equals in class Object

Parameters:

obj - the object to compare to

Returns:

true if equal

hashCode

public int hashCode()

Gets the hash code value for this map as per the API.

Specified by:

hashCode in interface Map<K extends Comparable,V extends Comparable>

Overrides:

hashCode in class Object

Returns:

the hash code value for this map

toString

public String toString()

Returns a string version of this Map in standard format.

Overrides:

toString in class Object

Returns:

a standard format string version of the map