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package org.apache.commons.collections;

Defines a map that allows bidirectional lookup between key and values.

This extended Map represents a mapping where a key may
lookup a value and a value may lookup a key with equal ease.
This interface extends Map and so may be used anywhere a map
is required. The interface provides an inverse map view, enabling
full access to both directions of the BidiMap.

Implementations should allow a value to be looked up from a key and
a key to be looked up from a value with equal performance.
 This map enforces the restriction that there is a 1:1 relation between keys and values, meaning that multiple keys cannot map to the same value. This is required so that "inverting" the map results in a map without duplicate keys. See the put method description for more information. 
Author:
Stephen Colebourne
Since:
Commons Collections 3.0
Version:
$Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $/**
 * Defines a map that allows bidirectional lookup between key and values.
 * <p>
 * This extended <code>Map</code> represents a mapping where a key may
 * lookup a value and a value may lookup a key with equal ease.
 * This interface extends <code>Map</code> and so may be used anywhere a map
 * is required. The interface provides an inverse map view, enabling
 * full access to both directions of the <code>BidiMap</code>.
 * <p>
 * Implementations should allow a value to be looked up from a key and
 * a key to be looked up from a value with equal performance.
 * <p>
 * This map enforces the restriction that there is a 1:1 relation between
 * keys and values, meaning that multiple keys cannot map to the same value. 
 * This is required so that "inverting" the map results in a map without 
 * duplicate keys. See the {@link #put} method description for more information.
 * 
 * @since Commons Collections 3.0
 * @version $Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
 *
 * @author Stephen Colebourne
 */
public interface BidiMap extends IterableMap {

    
Obtains a MapIterator over the map.

A map iterator is an efficient way of iterating over maps.
It does not require that the map is stored using Map Entry objects
which can increase performance.
BidiMap map = new DualHashBidiMap();
MapIterator it = map.mapIterator();
while (it.hasNext()) {
  Object key = it.next();
  Object value = it.getValue();
  it.setValue("newValue");
}

Returns:
a map iterator/**
     * Obtains a <code>MapIterator</code> over the map.
     * <p>
     * A map iterator is an efficient way of iterating over maps.
     * It does not require that the map is stored using Map Entry objects
     * which can increase performance.
     * <pre>
     * BidiMap map = new DualHashBidiMap();
     * MapIterator it = map.mapIterator();
     * while (it.hasNext()) {
     *   Object key = it.next();
     *   Object value = it.getValue();
     *   it.setValue("newValue");
     * }
     * </pre>
     * 
     * @return a map iterator
     */
    MapIterator mapIterator();
    
    
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 DualHashBidiMap();
 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 DualHashBidiMap();
 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

Params:
key –  the key to store
value –  the value to store
Throws:
UnsupportedOperationException – if the put method is not supported
ClassCastException – (optional) if the map limits the type of the 
 value and the specified value is inappropriate
IllegalArgumentException – (optional) if the map limits the values
 in some way and the value was invalid
NullPointerException – (optional) if the map limits the values to
 non-null and null was specified
Returns:
the previous value mapped to this key/**
     * Puts the key-value pair into the map, replacing any previous pair.
     * <p>
     * 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.
     * <pre>
     *  BidiMap map1 = new DualHashBidiMap();
     *  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 DualHashBidiMap();
     *  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
     * </pre>
     *
     * @param key  the key to store
     * @param value  the value to store
     * @return the previous value mapped to this key
     * 
     * @throws UnsupportedOperationException if the <code>put</code> method is not supported
     * @throws ClassCastException (optional) if the map limits the type of the 
     *  value and the specified value is inappropriate
     * @throws IllegalArgumentException (optional) if the map limits the values
     *  in some way and the value was invalid
     * @throws NullPointerException (optional) if the map limits the values to
     *  non-null and null was specified
     */
    Object put(Object key, Object value);
    
    
Gets the key that is currently mapped to the specified value.

If the value is not contained in the map, null is returned.

Implementations should seek to make this method perform equally as well
as get(Object).
Params:
value –  the value to find the key for
Throws:
ClassCastException – (optional) if the map limits the type of the 
 value and the specified value is inappropriate
NullPointerException – (optional) if the map limits the values to
 non-null and null was specified
Returns:
the mapped key, or null if not found/**
     * Gets the key that is currently mapped to the specified value.
     * <p>
     * If the value is not contained in the map, <code>null</code> is returned.
     * <p>
     * Implementations should seek to make this method perform equally as well
     * as <code>get(Object)</code>.
     *
     * @param value  the value to find the key for
     * @return the mapped key, or <code>null</code> if not found
     * 
     * @throws ClassCastException (optional) if the map limits the type of the 
     *  value and the specified value is inappropriate
     * @throws NullPointerException (optional) if the map limits the values to
     *  non-null and null was specified
     */
    Object getKey(Object value);
    
    
Removes the key-value pair that is currently mapped to the specified
value (optional operation).

If the value is not contained in the map, null is returned.

Implementations should seek to make this method perform equally as well
as remove(Object).
Params:
value –  the value to find the key-value pair for
Throws:
ClassCastException – (optional) if the map limits the type of the 
 value and the specified value is inappropriate
NullPointerException – (optional) if the map limits the values to
 non-null and null was specified
UnsupportedOperationException – if this method is not supported
 by the implementation
Returns:
the key that was removed, null if nothing removed/**
     * Removes the key-value pair that is currently mapped to the specified
     * value (optional operation).
     * <p>
     * If the value is not contained in the map, <code>null</code> is returned.
     * <p>
     * Implementations should seek to make this method perform equally as well
     * as <code>remove(Object)</code>.
     *
     * @param value  the value to find the key-value pair for
     * @return the key that was removed, <code>null</code> if nothing removed
     * 
     * @throws ClassCastException (optional) if the map limits the type of the 
     *  value and the specified value is inappropriate
     * @throws NullPointerException (optional) if the map limits the values to
     *  non-null and null was specified
     * @throws UnsupportedOperationException if this method is not supported
     *  by the implementation
     */
    Object removeValue(Object value);
    
    
Gets a view of this map where the keys and values are reversed.

Changes to one map will be visible in the other and vice versa.
This enables both directions of the map to be accessed as a Map.

Implementations should seek to avoid creating a new object every time this
method is called. See AbstractMap.values() etc. Calling this
method on the inverse map should return the original.
Returns:
an inverted bidirectional map/**
     * Gets a view of this map where the keys and values are reversed.
     * <p>
     * Changes to one map will be visible in the other and vice versa.
     * This enables both directions of the map to be accessed as a <code>Map</code>.
     * <p>
     * Implementations should seek to avoid creating a new object every time this
     * method is called. See <code>AbstractMap.values()</code> etc. Calling this
     * method on the inverse map should return the original.
     *
     * @return an inverted bidirectional map
     */
    BidiMap inverseBidiMap();
    
}