org.apache.commons.collections.bidimap

Class TreeBidiMap

public class TreeBidiMap extends Object implements OrderedBidiMap

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: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $

Author: Marc Johnson Stephen Colebourne

Constructor Summary
TreeBidiMap()
Constructs a new empty TreeBidiMap.
TreeBidiMap(Map map)
Constructs a new TreeBidiMap by copying an existing Map.
Method Summary
voidclear()
Removes all mappings from this map.
booleancontainsKey(Object key)
Checks whether this map contains the a mapping for the specified key.
booleancontainsValue(Object value)
Checks whether this map contains the a mapping for the specified value.
SetentrySet()
Returns a set view of the entries contained in this map in key order.
booleanequals(Object obj)
Compares for equals as per the API.
ObjectfirstKey()
Gets the first (lowest) key currently in this map.
Objectget(Object key)
Gets the value to which this map maps the specified key.
ObjectgetKey(Object value)
Returns the key to which this map maps the specified value.
inthashCode()
Gets the hash code value for this map as per the API.
BidiMapinverseBidiMap()
Gets the inverse map for comparison.
OrderedBidiMapinverseOrderedBidiMap()
Gets the inverse map for comparison.
booleanisEmpty()
Checks whether the map is empty or not.
SetkeySet()
Returns a set view of the keys contained in this map in key order.
ObjectlastKey()
Gets the last (highest) key currently in this map.
MapIteratormapIterator()
Gets an iterator over the map entries.
ObjectnextKey(Object key)
Gets the next key after the one specified.
OrderedMapIteratororderedMapIterator()
Gets an ordered iterator over the map entries.
ObjectpreviousKey(Object key)
Gets the previous key before the one specified.
Objectput(Object key, Object value)
Puts the key-value pair into the map, replacing any previous pair.
voidputAll(Map map)
Puts all the mappings from the specified map into this map.
Objectremove(Object key)
Removes the mapping for this key from this map if present.
ObjectremoveValue(Object value)
Removes the mapping for this value from this map if present.
intsize()
Returns the number of key-value mappings in this map.
StringtoString()
Returns a string version of this Map in standard format.
Collectionvalues()
Returns a set view of the values contained in this map in key order.

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

clear

public void clear()
Removes all mappings from this map.

containsKey

public boolean containsKey(Object key)
Checks whether this map contains the a mapping for the specified key.

The key must implement 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.

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

entrySet

public Set 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.

Returns: a set view of the values contained in this map.

equals

public boolean equals(Object obj)
Compares for equals as per the API.

Parameters: obj the object to compare to

Returns: true if equal

firstKey

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

Returns: the first (lowest) key currently in this sorted map

Throws: NoSuchElementException if this map is empty

get

public Object 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.

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

getKey

public Object getKey(Object 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.

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

hashCode

public int hashCode()
Gets the hash code value for this map as per the API.

Returns: the hash code value for this map

inverseBidiMap

public BidiMap inverseBidiMap()
Gets the inverse map for comparison.

Returns: the inverse map

inverseOrderedBidiMap

public OrderedBidiMap inverseOrderedBidiMap()
Gets the inverse map for comparison.

Returns: the inverse map

isEmpty

public boolean isEmpty()
Checks whether the map is empty or not.

Returns: true if the map is empty

keySet

public Set 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.

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

lastKey

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

Returns: the last (highest) key currently in this sorted map

Throws: NoSuchElementException if this map is empty

mapIterator

public MapIterator mapIterator()
Gets an iterator over the map entries.

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

Returns: an iterator

nextKey

public Object nextKey(Object key)
Gets the next key after the one specified.

The key must implement Comparable.

Parameters: key the key to search for next from

Returns: the next key, null if no match or at end

orderedMapIterator

public OrderedMapIterator orderedMapIterator()
Gets an ordered iterator over the map entries.

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

Returns: an iterator

previousKey

public Object previousKey(Object key)
Gets the previous key before the one specified.

The key must implement Comparable.

Parameters: key the key to search for previous from

Returns: the previous key, null if no match or at start

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 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.

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

All keys and values must implement Comparable.

Parameters: map the map to copy from

remove

public Object remove(Object key)
Removes the mapping for this key from this map if present.

The key must implement 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

removeValue

public Object removeValue(Object value)
Removes the mapping for this value from this map if present.

The value must implement 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

size

public int size()
Returns the number of key-value mappings in this map.

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

toString

public String toString()
Returns a string version of this Map in standard format.

Returns: a standard format string version of the map

values

public Collection 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.

Returns: a set view of the values contained in this map.

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