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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
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 {@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");
* }
*
*
* @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
*
*
* @param key the key to store
* @param value the value to store
* @return the previous value mapped to this key
*
* @throws UnsupportedOperationException if the put 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).
*
* @param value the value to find the key for
* @return the mapped key, or null 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).
*
* @param value the value to find the key-value pair for
* @return the key that was removed, null 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.
*
* @return an inverted bidirectional map
*/
BidiMap inverseBidiMap();
}