public class TreeBidiMap extends Object implements OrderedBidiMap
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.
| Constructor and Description |
|---|
TreeBidiMap()
Constructs a new empty TreeBidiMap.
|
TreeBidiMap(Map map)
Constructs a new TreeBidiMap by copying an existing Map.
|
| Modifier and Type | Method and Description |
|---|---|
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.
|
public TreeBidiMap()
public TreeBidiMap(Map map)
map - the map to copyClassCastException - if the keys/values in the map are
not Comparable or are not mutually comparableNullPointerException - if any key or value in the map is nullpublic int size()
public boolean isEmpty()
public boolean containsKey(Object key)
The key must implement Comparable.
containsKey in interface Mapkey - key whose presence in this map is to be testedClassCastException - if the key is of an inappropriate typeNullPointerException - if the key is nullpublic boolean containsValue(Object value)
The value must implement Comparable.
containsValue in interface Mapvalue - value whose presence in this map is to be testedClassCastException - if the value is of an inappropriate typeNullPointerException - if the value is nullpublic Object get(Object key)
The key must implement Comparable.
get in interface Mapkey - key whose associated value is to be returnedClassCastException - if the key is of an inappropriate typeNullPointerException - if the key is nullpublic Object put(Object key, Object value)
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.
put in interface Mapput in interface BidiMapkey - key with which the specified value is to be associatedvalue - value to be associated with the specified keyClassCastException - if the key is of an inappropriate typeNullPointerException - if the key is nullpublic void putAll(Map map)
All keys and values must implement Comparable.
public Object remove(Object key)
The key must implement Comparable.
remove in interface Mapkey - key whose mapping is to be removed from the map.ClassCastException - if the key is of an inappropriate typeNullPointerException - if the key is nullpublic Object getKey(Object value)
The value must implement Comparable.
getKey in interface BidiMapvalue - value whose associated key is to be returned.ClassCastException - if the value is of an inappropriate typeNullPointerException - if the value is nullpublic Object removeValue(Object value)
The value must implement Comparable.
removeValue in interface BidiMapvalue - value whose mapping is to be removed from the mapClassCastException - if the value is of an inappropriate typeNullPointerException - if the value is nullpublic Object firstKey()
firstKey in interface OrderedMapNoSuchElementException - if this map is emptypublic Object lastKey()
lastKey in interface OrderedMapNoSuchElementException - if this map is emptypublic Object nextKey(Object key)
The key must implement Comparable.
nextKey in interface OrderedMapkey - the key to search for next frompublic Object previousKey(Object key)
The key must implement Comparable.
previousKey in interface OrderedMapkey - the key to search for previous frompublic Set keySet()
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.
public Collection values()
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.
public Set entrySet()
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.
public MapIterator mapIterator()
For this map, this iterator is the fastest way to iterate over the entries.
mapIterator in interface BidiMapmapIterator in interface IterableMappublic OrderedMapIterator orderedMapIterator()
This iterator allows both forward and reverse iteration over the entries.
orderedMapIterator in interface OrderedMappublic BidiMap inverseBidiMap()
inverseBidiMap in interface BidiMapinverseBidiMap in interface OrderedBidiMappublic OrderedBidiMap inverseOrderedBidiMap()
inverseOrderedBidiMap in interface OrderedBidiMappublic boolean equals(Object obj)
public int hashCode()
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