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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.collections4;

import java.util.Set;

/**
 * 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. * * @param the type of the keys in the map * @param the type of the values in the map * * @since 3.0 * @version $Id: BidiMap.java 1612021 2014-07-20 04:51:05Z ggregory $ */ public interface BidiMap extends IterableMap { /** * 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 */ V put(K key, V 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 */ K 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 */ K 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(); /** * Returns a {@link Set} view of the values 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 (except through the iterator's own * {@code remove} operation), the results of the iteration are undefined. * The set supports element removal, which removes the corresponding * mapping from the map, via the {@code Iterator.remove}, * {@code Collection.remove}, {@code removeAll}, * {@code retainAll} and {@code clear} operations. It does not * support the {@code add} or {@code addAll} operations. * * @return a set view of the values contained in this map */ Set values(); }





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