org.apache.commons.collections.bidimap
Class TreeBidiMap
java.lang.Object
|
+--org.apache.commons.collections.bidimap.TreeBidiMap
All Implemented Interfaces:
OrderedBidiMap
public class
TreeBidiMapextends java.lang.Object
implements
OrderedBidiMap Red-Black tree-based implementation of BidiMap.
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.
- Commons Collections 3.0 (previously DoubleOrderedMap v2.0)
- Marc Johnson
- Stephen Colebourne
TreeBidiMap
public TreeBidiMap()
Constructs a new empty TreeBidiMap.
TreeBidiMap
public TreeBidiMap(final Map map)
Constructs a new TreeBidiMap by copying an existing Map.
- map - the map to copy
- if the keys/values in the map are
not Comparable or are not mutually comparable
- if any key or value in the map is null
clear
public void clear()
Removes all mappings from this map.
containsKey
public boolean containsKey(final Object key)
Checks whether this map contains the a mapping for the specified key.
- key - key whose presence in this map is to be tested
- true if this map contains a mapping for the specified key
- if the key is of an inappropriate type
- if the key is null
containsValue
public boolean containsValue(final Object value)
Checks whether this map contains the a mapping for the specified value.
- value - value whose presence in this map is to be tested
- true if this map contains a mapping for the specified value
- if the value is of an inappropriate type
- 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.
- a set view of the values contained in this map.
equals
public boolean equals(Object obj)
Compares for equals as per the API.
- obj - the object to compare to
- true if equal
firstKey
public Object firstKey()
Gets the first (lowest) key currently in this map.
- the first (lowest) key currently in this sorted map
- if this map is empty
get
public Object get(final Object key)
Gets the value to which this map maps the specified key.
Returns null if the map contains no mapping for this key.
- key - key whose associated value is to be returned
- the value to which this map maps the specified key,
or null if the map contains no mapping for this key
- if the key is of an inappropriate type
- if the key is null
getKey
public Object getKey(final Object value)
Returns the key to which this map maps the specified value.
Returns null if the map contains no mapping for this value.
- value - value whose associated key is to be returned.
- the key to which this map maps the specified value,
or null if the map contains no mapping for this value.
- if the value is of an inappropriate type
- if the value is null
hashCode
public int hashCode()
Gets the hash code value for this map as per the API.
- the hash code value for this map
inverseBidiMap
public BidiMap inverseBidiMap()
Gets the inverse map for comparison.
- the inverse map
inverseOrderedBidiMap
public OrderedBidiMap inverseOrderedBidiMap()
Gets the inverse map for comparison.
- the inverse map
isEmpty
public boolean isEmpty()
Checks whether the map is empty or not.
- 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.
- a set view of the keys contained in this map.
lastKey
public Object lastKey()
Gets the last (highest) key currently in this map.
- the last (highest) key currently in this sorted map
- 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.
- an iterator
nextKey
public Object nextKey(Object key)
Gets the next key after the one specified.
- key - the key to search for next from
- 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.
- an iterator
previousKey
public Object previousKey(Object key)
Gets the previous key before the one specified.
- key - the key to search for previous from
- the previous key, null if no match or at start
put
public Object put(final Object key, final 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
- key - key with which the specified value is to be associated
- value - value to be associated with the specified key
- the previous value for the key
- if the key is of an inappropriate type
- if the key is null
putAll
public void putAll(Map map)
Puts all the mappings from the specified map into this map.
- map - the map to copy from
remove
public Object remove(final Object key)
Removes the mapping for this key from this map if present.
- key - key whose mapping is to be removed from the map.
- previous value associated with specified key,
or null if there was no mapping for key.
- if the key is of an inappropriate type
- if the key is null
removeValue
public Object removeValue(final Object value)
Removes the mapping for this value from this map if present
- value - value whose mapping is to be removed from the map
- previous key associated with specified value,
or null if there was no mapping for value.
- if the value is of an inappropriate type
- if the value is null
size
public int size()
Returns the number of key-value mappings in this map.
- the number of key-value mappings in this map
toString
public String toString()
Returns a string version of this Map in standard format.
- 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.
- a set view of the values contained in this map.