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package org.apache.commons.collections;

/**
 * Defines a map that allows bidirectional lookup between key and values
 * and retains and provides access to an ordering.
 * 
 * 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.
 * 
 * @since Commons Collections 3.0
 * @version $Revision: 1.3 $ $Date: 2004/01/14 21:43:05 $
 *
 * @author Stephen Colebourne
 */
public interface OrderedBidiMap extends BidiMap, OrderedMap {

    /**
     * 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 equally.
     * 

     * 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.
     * 

     * Implementations must return an OrderedBidiMap instance,
     * usually by forwarding to inverseOrderedBidiMap().
     *
     * @return an inverted bidirectional map
     */
    public BidiMap inverseBidiMap();
    
    /**
     * 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 equally.
     * 
     * 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.
     *
     * @return an inverted bidirectional map
     */
    public OrderedBidiMap inverseOrderedBidiMap();
    
}