Package org.apache.commons.collections4.bidimap

Class TreeBidiMap<K extends Comparable<K>,​V extends Comparable<V>>

  • Type Parameters:
    K - the type of the keys in this map
    V - the type of the values in this map
    All Implemented Interfaces:
    Serializable, Map<K,​V>, BidiMap<K,​V>, Get<K,​V>, IterableGet<K,​V>, IterableMap<K,​V>, OrderedBidiMap<K,​V>, OrderedMap<K,​V>, Put<K,​V>
    public class TreeBidiMap<K extends Comparable<K>,​V extends Comparable<V>>
extends Object
implements OrderedBidiMap<K,​V>, Serializable
    Red-Black tree-based implementation of BidiMap where all objects added implement the 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 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:
    3.0 (previously DoubleOrderedMap v2.0)
    See Also:
    Serialized Form

    • Constructor Detail

      • TreeBidiMap

        public TreeBidiMap()
        Constructs a new empty TreeBidiMap.

      • TreeBidiMap

        public TreeBidiMap​(Map<? extends K,​? extends V> map)
        Constructs a new TreeBidiMap by copying an existing Map.
        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

    • Method Detail

      • get

        public V get​(Object key)
        Gets the value to which this map maps the specified key. Returns null if the map contains no mapping for this key.

        The key must implement Comparable.

        Specified by:
        get in interface Get<K extends Comparable<K>,​V extends Comparable<V>>
        Specified by:
        get in interface Map<K extends Comparable<K>,​V extends Comparable<V>>
        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
        See Also:
        Map.get(Object)

      • put

        public V put​(K key,
             V 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

        Both key and value must implement Comparable.

        Specified by:
        put in interface BidiMap<K extends Comparable<K>,​V extends Comparable<V>>
        Specified by:
        put in interface Map<K extends Comparable<K>,​V extends Comparable<V>>
        Specified by:
        put in interface Put<K extends Comparable<K>,​V extends Comparable<V>>
        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
        See Also:
        Map.put(Object, Object)

      • getKey

        public K getKey​(Object value)
        Returns the key to which this map maps the specified value. Returns null if the map contains no mapping for this value.

        The value must implement Comparable.

        Specified by:
        getKey in interface BidiMap<K extends Comparable<K>,​V extends Comparable<V>>
        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

      • removeValue

        public K removeValue​(Object value)
        Removes the mapping for this value from this map if present.

        The value must implement Comparable.

        Specified by:
        removeValue in interface BidiMap<K extends Comparable<K>,​V extends Comparable<V>>
        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

      • nextKey

        public K nextKey​(K key)
        Gets the next key after the one specified.

        The key must implement Comparable.

        Specified by:
        nextKey in interface OrderedMap<K extends Comparable<K>,​V extends Comparable<V>>
        Parameters:
        key - the key to search for next from
        Returns:
        the next key, null if no match or at end

      • previousKey

        public K previousKey​(K key)
        Gets the previous key before the one specified.

        The key must implement Comparable.

        Specified by:
        previousKey in interface OrderedMap<K extends Comparable<K>,​V extends Comparable<V>>
        Parameters:
        key - the key to search for previous from
        Returns:
        the previous key, null if no match or at start

      • keySet

        public Set<K> 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.

        Specified by:
        keySet in interface Get<K extends Comparable<K>,​V extends Comparable<V>>
        Specified by:
        keySet in interface Map<K extends Comparable<K>,​V extends Comparable<V>>
        Returns:
        a set view of the keys contained in this map.
        See Also:
        Map.keySet()

      • values

        public Set<V> 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.

        Specified by:
        values in interface BidiMap<K extends Comparable<K>,​V extends Comparable<V>>
        Specified by:
        values in interface Get<K extends Comparable<K>,​V extends Comparable<V>>
        Specified by:
        values in interface Map<K extends Comparable<K>,​V extends Comparable<V>>
        Returns:
        a set view of the values contained in this map.
        See Also:
        Map.values()

      • entrySet

        public Set<Map.Entry<K,​V>> 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.

        Specified by:
        entrySet in interface Get<K extends Comparable<K>,​V extends Comparable<V>>
        Specified by:
        entrySet in interface Map<K extends Comparable<K>,​V extends Comparable<V>>
        Returns:
        a set view of the values contained in this map.
        See Also:
        Map.entrySet()

      • mapIterator

        public OrderedMapIterator<K,​V> mapIterator()
        Description copied from interface: IterableGet
        Obtains a MapIterator over the map.

        A map iterator is an efficient way of iterating over maps. There is no need to access the entry set or use Map Entry objects. 

         IterableMap<String,Integer> map = new HashedMap<String,Integer>();
 MapIterator<String,Integer> it = map.mapIterator();
 while (it.hasNext()) {
   String key = it.next();
   Integer value = it.getValue();
   it.setValue(value + 1);
 }
        Specified by:
        mapIterator in interface IterableGet<K extends Comparable<K>,​V extends Comparable<V>>
        Specified by:
        mapIterator in interface OrderedMap<K extends Comparable<K>,​V extends Comparable<V>>
        Returns:
        a map iterator

      • equals

        public boolean equals​(Object obj)
        Compares for equals as per the API.
        Specified by:
        equals in interface Map<K extends Comparable<K>,​V extends Comparable<V>>
        Overrides:
        equals in class Object
        Parameters:
        obj - the object to compare to
        Returns:
        true if equal

      • hashCode

        public int hashCode()
        Gets the hash code value for this map as per the API.
        Specified by:
        hashCode in interface Map<K extends Comparable<K>,​V extends Comparable<V>>
        Overrides:
        hashCode in class Object
        Returns:
        the hash code value for this map

      • toString

        public String toString()
        Returns a string version of this Map in standard format.
        Overrides:
        toString in class Object
        Returns:
        a standard format string version of the map