| java.lang.Object | ||
| ↳ | java.util.AbstractMap<K, V> | |
| ↳ | org.apache.commons.collections.DoubleOrderedMap | |
This class is deprecated.
Replaced by TreeBidiMap in bidimap subpackage. Due to be removed in v4.0.
Class Overview
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
DualTreeBidiMap and
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.
Summary
| Public Constructors | |||||||||||
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Construct a new DoubleOrderedMap
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Constructs a new DoubleOrderedMap from an existing Map, with keys and
values sorted
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| Public Methods | |||||||||||
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Removes all mappings from this map
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Returns true if this map contains a mapping for the specified
key.
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Returns true if this map maps one or more keys to the
specified value.
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Returns a set view of the mappings contained in this map.
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Returns a set view of the mappings contained in this map.
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Returns the value to which this map maps the specified
key.
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Returns the key to which this map maps the specified value.
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Returns a set view of the keys contained in this map.
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Returns a set view of the keys contained in this map.
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Associates the specified value with the specified key in this
map.
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Removes the mapping for this key from this map if present
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Removes the mapping for this value from this map if present
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Returns the number of key-value mappings in this map.
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Returns a collection view of the values contained in this
map.
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Returns a collection view of the values contained in this
map.
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[Expand]
Inherited Methods | |||||||||||
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From class
java.util.AbstractMap
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From class
java.lang.Object
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From interface
java.util.Map
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Public Constructors
public DoubleOrderedMap ()
Construct a new DoubleOrderedMap
public DoubleOrderedMap (Map map)
Constructs a new DoubleOrderedMap from an existing Map, with keys and values sorted
Parameters
| map | the map whose mappings are to be placed in this map. |
|---|
Throws
| ClassCastException | if the keys in the map are not Comparable, or are not mutually comparable; also if the values in the map are not Comparable, or are not mutually Comparable |
|---|---|
| NullPointerException | if any key or value in the map is null |
| IllegalArgumentException | if there are duplicate keys or duplicate values in the map |
Public Methods
public void clear ()
Removes all mappings from this map
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. |
|---|
Returns
- true if this map contains a mapping for the specified key.
Throws
| ClassCastException | if the key is of an inappropriate type for this map. |
|---|---|
| NullPointerException | if the key is null |
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. |
|---|
Returns
- true if this map maps one or more keys to the specified value.
public Set entrySet ()
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.
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. 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.
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. Returns null if the map contains no mapping for this key.
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 for this map. |
|---|---|
| NullPointerException | if the key is null |
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. |
|---|
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 for this map. |
|---|---|
| NullPointerException | if the value is null |
public Set keySet ()
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.
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. 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.
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 be associated. |
|---|---|
| value | value to be associated with the specified key. |
Returns
- null
Throws
| ClassCastException | if the class of the specified key or value prevents it from being stored in this map. |
|---|---|
| NullPointerException | if the specified key or value is null |
| IllegalArgumentException | if the key duplicates an existing key, or if the value duplicates an existing value |
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. |
|---|
Returns
- previous value associated with specified key, or null if there was no mapping for key.
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. |
|---|
Returns
- previous key associated with specified value, or null if there was no mapping for value.
public int size ()
Returns the number of key-value mappings in this map. If the map contains more than Integer.MAXVALUE elements, returns Integer.MAXVALUE.
Returns
- the number of key-value mappings in this map.
public Collection values ()
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.
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. 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.
Returns
- a collection view of the values contained in this map.