| java.lang.Object
 java.util.AbstractMap
org.apache.commons.collections.DoubleOrderedMap
| DoubleOrderedMap | | final public class DoubleOrderedMap extends AbstractMap (Code) | | Red-Black tree-based implementation of Map. 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,
particularly when trying to keep the two TreeMaps synchronized with
each other. And if the data contained in the TreeMaps is large, the
cost of redundant storage becomes significant. (See also the new
org.apache.commons.collections.bidimap.DualTreeBidiMap DualTreeBidiMap and
org.apache.commons.collections.bidimap.DualHashBidiMap DualHashBidiMap implementations.)
This solution keeps the data properly synchronized and minimizes
the data storage. The red-black algorithm is based on TreeMap's,
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.
There are some limitations placed on data kept in this Map. The
biggest one is this:
When performing a put operation, neither the key nor the value may
already exist in the Map. In the java.util Map implementations
(HashMap, TreeMap), you can perform a put with an already mapped
key, and neither cares about duplicate values at all ... but this
implementation's put method with throw an IllegalArgumentException
if either the key or the value is already in the Map.
Obviously, that same restriction (and consequence of failing to
heed that restriction) applies to the putAll method.
The Map.Entry instances returned by the appropriate methods will
not allow setValue() and will throw an
UnsupportedOperationException on attempts to call that method.
New methods are added to take advantage of the fact that values are
kept sorted independently of their keys:
Object getKeyForValue(Object value) is the opposite of get; it
takes a value and returns its key, if any.
Object removeValue(Object value) finds and removes the specified
value and returns the now un-used key.
Set entrySetByValue() returns the Map.Entry's in a Set whose
iterator will iterate over the Map.Entry's in ascending order by
their corresponding values.
Set keySetByValue() returns the keys in a Set whose iterator will
iterate over the keys in ascending order by their corresponding
values.
Collection valuesByValue() returns the values in a Collection whose
iterator will iterate over the values in ascending order.
See Also: BidiMap
See Also: org.apache.commons.collections.bidimap.DualTreeBidiMap
See Also: org.apache.commons.collections.bidimap.DualHashBidiMap
since:
Commons Collections 2.0
version:
$Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $
author:
Marc Johnson |
| Method Summary | |
| public void | clear()
| | public boolean | containsKey(Object key)
Returns true if this map contains a mapping for the specified
key.
Parameters:
key - key whose presence in this map is to be tested. | | public boolean | containsValue(Object value)
Returns true if this map maps one or more keys to the
specified value.
Parameters:
value - value whose presence in this map is to be tested. | | public Set | entrySet()
Returns a set view of the mappings contained in this map. | | public Set | entrySetByValue()
Returns a set view of the mappings contained in this map. | | public Object | get(Object key)
Returns the value to which this map maps the specified
key. | | public Object | getKeyForValue(Object value)
Returns the key to which this map maps the specified value.
Returns null if the map contains no mapping for this value.
Parameters:
value - value whose associated key is to be returned. | | public Set | keySet()
Returns a set view of the keys contained in this map. | | public Set | keySetByValue()
Returns a set view of the keys contained in this map. | | public Object | put(Object key, Object value)
Associates the specified value with the specified key in this
map.
Parameters:
key - key with which the specified value is to beassociated.
Parameters:
value - value to be associated with the specified key. | | public Object | remove(Object key)
Removes the mapping for this key from this map if present
Parameters:
key - key whose mapping is to be removed from the map. | | public Object | removeValue(Object value)
Removes the mapping for this value from this map if present
Parameters:
value - value whose mapping is to be removed from the map. | | public int | size()
Returns the number of key-value mappings in this map. | | public Collection | values()
Returns a collection view of the values contained in this
map. | | public Collection | valuesByValue()
Returns a collection view of the values contained in this
map. |
| DoubleOrderedMap | | public DoubleOrderedMap()(Code) | | Construct a new DoubleOrderedMap
|
| clear | | public void clear()(Code) | | Removes all mappings from this map
|
| containsValue | | public boolean containsValue(Object value)(Code) | | Returns true if this map maps one or more keys to the
specified value.
Parameters:
value - value whose presence in this map is to be tested. true if this map maps one or more keys to the specifiedvalue. |
| entrySet | | public Set entrySet()(Code) | | Returns a set view of the mappings contained in this map. Each
element in the returned set is a Map.Entry. 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, via the Iterator.remove, Set.remove, removeAll,
retainAll and clear operations.
It does not support the add or addAll operations.
The setValue method is not supported on the Map Entry.
a set view of the mappings contained in this map. |
| entrySetByValue | | public Set entrySetByValue()(Code) | | Returns a set view of the mappings contained in this map. Each
element in the returned set is a Map.Entry. 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, via the Iterator.remove,
Set.remove, removeAll, retainAll and clear operations. It does
not support the add or addAll operations.
The difference between this method and entrySet is that
entrySet's iterator() method returns an iterator that iterates
over the mappings in ascending order by key. This method's
iterator method iterates over the mappings in ascending order
by value.
a set view of the mappings contained in this map. |
| get | | public Object get(Object key) throws ClassCastException, NullPointerException(Code) | | Returns the value to which this map maps the specified
key. Returns null if the map contains no mapping for this key.
Parameters:
key - key whose associated value is to be returned. the value to which this map maps the specified key, ornull if the map contains no mapping for this key.
throws:
ClassCastException - if the key is of an inappropriatetype for this map.
throws:
NullPointerException - if the key is null |
| getKeyForValue | | public Object getKeyForValue(Object value) throws ClassCastException, NullPointerException(Code) | | Returns the key to which this map maps the specified value.
Returns null if the map contains no mapping for this value.
Parameters:
value - value whose associated key is to be returned. the key to which this map maps the specified value, ornull if the map contains no mapping for this value.
throws:
ClassCastException - if the value is of aninappropriate type for this map.
throws:
NullPointerException - if the value is null |
| keySet | | public Set keySet()(Code) | | Returns a set view of the keys contained in this 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, via the
Iterator.remove, Set.remove, removeAll, retainAll, and clear
operations. It does not support the add or addAll operations.
a set view of the keys contained in this map. |
| keySetByValue | | public Set keySetByValue()(Code) | | Returns a set view of the keys contained in this 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, via the
Iterator.remove, Set.remove, removeAll, retainAll, and clear
operations. It does not support the add or addAll
operations.
The difference between this method and keySet is that keySet's
iterator() method returns an iterator that iterates over the
keys in ascending order by key. This method's iterator method
iterates over the keys in ascending order by value.
a set view of the keys contained in this map. |
| remove | | public Object remove(Object key)(Code) | | Removes the mapping for this key from this map if present
Parameters:
key - key whose mapping is to be removed from the map. previous value associated with specified key, or nullif there was no mapping for key. |
| removeValue | | public Object removeValue(Object value)(Code) | | Removes the mapping for this value from this map if present
Parameters:
value - value whose mapping is to be removed from the map. previous key associated with specified value, or nullif there was no mapping for value. |
| size | | public int size()(Code) | | Returns the number of key-value mappings in this map. If the
map contains more than Integer.MAXVALUE elements, returns
Integer.MAXVALUE.
the number of key-value mappings in this map. |
| values | | public Collection values()(Code) | | Returns a collection view of the values contained in this
map. The collection is backed by the map, so changes to the map
are reflected in the collection, and vice-versa. If the map is
modified while an iteration over the collection is in progress,
the results of the iteration are undefined. The collection
supports element removal, which removes the corresponding
mapping from the map, via the Iterator.remove,
Collection.remove, removeAll, retainAll and clear operations.
It does not support the add or addAll operations.
a collection view of the values contained in this map. |
| valuesByValue | | public Collection valuesByValue()(Code) | | Returns a collection view of the values contained in this
map. The collection is backed by the map, so changes to the map
are reflected in the collection, and vice-versa. If the map is
modified while an iteration over the collection is in progress,
the results of the iteration are undefined. The collection
supports element removal, which removes the corresponding
mapping from the map, via the Iterator.remove,
Collection.remove, removeAll, retainAll and clear operations.
It does not support the add or addAll operations.
The difference between this method and values is that values's
iterator() method returns an iterator that iterates over the
values in ascending order by key. This method's iterator method
iterates over the values in ascending order by key.
a collection view of the values contained in this map. |
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