public class

TreeBidiMap

extends Object
implements OrderedBidiMap
java.lang.Object
   ↳ org.apache.commons.collections.bidimap.TreeBidiMap

Class Overview

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.

Summary

Public Constructors
TreeBidiMap()
Constructs a new empty TreeBidiMap.
TreeBidiMap(Map map)
Constructs a new TreeBidiMap by copying an existing Map.
Public Methods
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.
[Expand]
Inherited Methods
From class java.lang.Object
From interface java.util.Map
From interface org.apache.commons.collections.BidiMap
From interface org.apache.commons.collections.IterableMap
From interface org.apache.commons.collections.OrderedBidiMap
From interface org.apache.commons.collections.OrderedMap

Public Constructors

public TreeBidiMap ()

Constructs a new empty 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

Public Methods

public void clear ()

Removes all mappings from this map.

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

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

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.

public boolean equals (Object obj)

Compares for equals as per the API.

Parameters
obj the object to compare to
Returns
  • true if equal

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

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

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

public int hashCode ()

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

Returns
  • the hash code value for this map

public BidiMap inverseBidiMap ()

Gets the inverse map for comparison.

Returns
  • the inverse map

public OrderedBidiMap inverseOrderedBidiMap ()

Gets the inverse map for comparison.

Returns
  • the inverse map

public boolean isEmpty ()

Checks whether the map is empty or not.

Returns
  • true if the map is empty

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.

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

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

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

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

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

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

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

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

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

public int size ()

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

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

public String toString ()

Returns a string version of this Map in standard format.

Returns
  • a standard format string version of the map

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.