org.apache.commons.collections.bidimap
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.
Since: Commons Collections 3.0 (previously DoubleOrderedMap v2.0)
Version: $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $
Constructor Summary | |
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TreeBidiMap()
Constructs a new empty TreeBidiMap. | |
TreeBidiMap(Map map)
Constructs a new TreeBidiMap by copying an existing Map.
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Method Summary | |
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void | clear()
Removes all mappings from this map. |
boolean | containsKey(Object key)
Checks whether this map contains the a mapping for the specified key.
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boolean | containsValue(Object value)
Checks whether this map contains the a mapping for the specified value.
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Set | entrySet()
Returns a set view of the entries contained in this map in key order.
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boolean | equals(Object obj)
Compares for equals as per the API.
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Object | firstKey()
Gets the first (lowest) key currently in this map.
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Object | get(Object key)
Gets the value to which this map maps the specified key.
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Object | getKey(Object value)
Returns the key to which this map maps the specified value.
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int | hashCode()
Gets the hash code value for this map as per the API.
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BidiMap | inverseBidiMap()
Gets the inverse map for comparison.
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OrderedBidiMap | inverseOrderedBidiMap()
Gets the inverse map for comparison.
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boolean | isEmpty()
Checks whether the map is empty or not.
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Set | keySet()
Returns a set view of the keys contained in this map in key order.
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Object | lastKey()
Gets the last (highest) key currently in this map.
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MapIterator | mapIterator()
Gets an iterator over the map entries.
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Object | nextKey(Object key)
Gets the next key after the one specified.
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OrderedMapIterator | orderedMapIterator()
Gets an ordered iterator over the map entries.
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Object | previousKey(Object key)
Gets the previous key before the one specified.
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Object | put(Object key, Object value)
Puts the key-value pair into the map, replacing any previous pair.
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void | putAll(Map map)
Puts all the mappings from the specified map into this map.
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Object | remove(Object key)
Removes the mapping for this key from this map if present.
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Object | removeValue(Object value)
Removes the mapping for this value from this map if present.
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int | size()
Returns the number of key-value mappings in this map.
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String | toString()
Returns a string version of this Map in standard format.
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Collection | values()
Returns a set view of the values contained in this map in key order.
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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
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
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
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.
Parameters: obj the object to compare to
Returns: true if equal
Returns: the first (lowest) key currently in this sorted map
Throws: NoSuchElementException if this map is empty
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
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
Returns: the hash code value for this map
Returns: the inverse map
Returns: the inverse map
Returns: true if the map is empty
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.
Returns: the last (highest) key currently in this sorted map
Throws: NoSuchElementException if this map is empty
For this map, this iterator is the fastest way to iterate over the entries.
Returns: an iterator
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
This iterator allows both forward and reverse iteration over the entries.
Returns: an iterator
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
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
All keys and values must implement Comparable
.
Parameters: map the map to copy from
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
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
Returns: the number of key-value mappings in this map
Returns: a standard format string version of the map
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.