org.apache.commons.collections.bidimap

Class TreeBidiMap

Implemented Interfaces:
BidiMap, IterableMap, Map, OrderedBidiMap, OrderedMap

public class TreeBidiMap
extends java.lang.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.

Version:
$Revision: 1.14 $ $Date: 2004/05/26 21:58:02 $
Authors:
Marc Johnson
Stephen Colebourne
Since:
Commons Collections 3.0 (previously DoubleOrderedMap v2.0)

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
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.
Object
firstKey()
Gets the first (lowest) key currently in this map.
Object
get(Object key)
Gets the value to which this map maps the specified key.
Object
getKey(Object 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
inverseBidiMap()
Gets the inverse map for comparison.
OrderedBidiMap
inverseOrderedBidiMap()
Gets the inverse map for comparison.
boolean
isEmpty()
Checks whether the map is empty or not.
Set
keySet()
Returns a set view of the keys contained in this map in key order.
Object
lastKey()
Gets the last (highest) key currently in this map.
MapIterator
mapIterator()
Gets an iterator over the map entries.
Object
nextKey(Object key)
Gets the next key after the one specified.
OrderedMapIterator
orderedMapIterator()
Gets an ordered iterator over the map entries.
Object
previousKey(Object key)
Gets the previous key before the one specified.
Object
put(Object key, Object value)
Puts the key-value pair into the map, replacing any previous pair.
void
putAll(Map map)
Puts all the mappings from the specified map into this map.
Object
remove(Object key)
Removes the mapping for this key from this map if present.
Object
removeValue(Object 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
values()
Returns a set view of the values contained in this map in key order.

Constructor Details

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

Method Details

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

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

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.
Specified by:
firstKey in interface OrderedMap
Returns:
the first (lowest) key currently in this sorted map

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

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.

Specified by:
getKey in interface BidiMap
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.

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.
Specified by:
inverseBidiMap in interface OrderedBidiMap
inverseBidiMap in interface BidiMap
Returns:
the inverse map

inverseOrderedBidiMap

public OrderedBidiMap inverseOrderedBidiMap()
Gets the inverse map for comparison.
Specified by:
inverseOrderedBidiMap in interface OrderedBidiMap
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.
Specified by:
lastKey in interface OrderedMap
Returns:
the last (highest) key currently in this sorted map

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.

Specified by:
mapIterator in interface BidiMap
mapIterator in interface IterableMap
Returns:
an iterator

nextKey

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

The key must implement Comparable.

Specified by:
nextKey in interface OrderedMap
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.

Specified by:
orderedMapIterator in interface OrderedMap
Returns:
an iterator

previousKey

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

The key must implement Comparable.

Specified by:
previousKey in interface OrderedMap
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.

Specified by:
put in interface BidiMap
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

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.

removeValue

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

The value must implement Comparable.

Specified by:
removeValue in interface BidiMap
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.

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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