    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.collections4;
    018
    019import java.util.Set;
    020
    021/**
    022 * Defines a map that allows bidirectional lookup between key and values.
    023 * <p>
    024 * This extended <code>Map</code> represents a mapping where a key may
    025 * lookup a value and a value may lookup a key with equal ease.
    026 * This interface extends <code>Map</code> and so may be used anywhere a map
    027 * is required. The interface provides an inverse map view, enabling
    028 * full access to both directions of the <code>BidiMap</code>.
    029 * </p>
    030 * <p>
    031 * Implementations should allow a value to be looked up from a key and
    032 * a key to be looked up from a value with equal performance.
    033 * </p>
    034 * <p>
    035 * This map enforces the restriction that there is a 1:1 relation between
    036 * keys and values, meaning that multiple keys cannot map to the same value.
    037 * This is required so that "inverting" the map results in a map without
    038 * duplicate keys. See the {@link #put} method description for more information.
    039 * </p>
    040 *
    041 * @param <K> the type of the keys in the map
    042 * @param <V> the type of the values in the map
    043 *
    044 * @since 3.0
    045 */
    046public interface BidiMap<K, V> extends IterableMap<K, V> {
    047
    048    /**
    049     * Puts the key-value pair into the map, replacing any previous pair.
    050     * <p>
    051     * When adding a key-value pair, the value may already exist in the map
    052     * against a different key. That mapping is removed, to ensure that the
    053     * value only occurs once in the inverse map.
    054     * </p>
    055     * <pre>
    056     *  BidiMap map1 = new DualHashBidiMap();
    057     *  map.put("A","B");  // contains A mapped to B, as per Map
    058     *  map.put("A","C");  // contains A mapped to C, as per Map
    059     *
    060     *  BidiMap map2 = new DualHashBidiMap();
    061     *  map.put("A","B");  // contains A mapped to B, as per Map
    062     *  map.put("C","B");  // contains C mapped to B, key A is removed
    063     * </pre>
    064     *
    065     * @param key  the key to store
    066     * @param value  the value to store
    067     * @return the previous value mapped to this key
    068     *
    069     * @throws UnsupportedOperationException if the <code>put</code> method is not supported
    070     * @throws ClassCastException (optional) if the map limits the type of the
    071     *  value and the specified value is inappropriate
    072     * @throws IllegalArgumentException (optional) if the map limits the values
    073     *  in some way and the value was invalid
    074     * @throws NullPointerException (optional) if the map limits the values to
    075     *  non-null and null was specified
    076     */
    077    @Override
    078    V put(K key, V value);
    079
    080    /**
    081     * Gets the key that is currently mapped to the specified value.
    082     * <p>
    083     * If the value is not contained in the map, <code>null</code> is returned.
    084     * </p>
    085     * <p>
    086     * Implementations should seek to make this method perform equally as well
    087     * as <code>get(Object)</code>.
    088     * </p>
    089     *
    090     * @param value  the value to find the key for
    091     * @return the mapped key, or <code>null</code> if not found
    092     *
    093     * @throws ClassCastException (optional) if the map limits the type of the
    094     *  value and the specified value is inappropriate
    095     * @throws NullPointerException (optional) if the map limits the values to
    096     *  non-null and null was specified
    097     */
    098    K getKey(Object value);
    099
    100    /**
    101     * Removes the key-value pair that is currently mapped to the specified
    102     * value (optional operation).
    103     * <p>
    104     * If the value is not contained in the map, <code>null</code> is returned.
    105     * </p>
    106     * <p>
    107     * Implementations should seek to make this method perform equally as well
    108     * as <code>remove(Object)</code>.
    109     * </p>
    110     *
    111     * @param value  the value to find the key-value pair for
    112     * @return the key that was removed, <code>null</code> if nothing removed
    113     *
    114     * @throws ClassCastException (optional) if the map limits the type of the
    115     *  value and the specified value is inappropriate
    116     * @throws NullPointerException (optional) if the map limits the values to
    117     *  non-null and null was specified
    118     * @throws UnsupportedOperationException if this method is not supported
    119     *  by the implementation
    120     */
    121    K removeValue(Object value);
    122
    123    /**
    124     * Gets a view of this map where the keys and values are reversed.
    125     * <p>
    126     * Changes to one map will be visible in the other and vice versa.
    127     * This enables both directions of the map to be accessed as a <code>Map</code>.
    128     * </p>
    129     * <p>
    130     * Implementations should seek to avoid creating a new object every time this
    131     * method is called. See <code>AbstractMap.values()</code> etc. Calling this
    132     * method on the inverse map should return the original.
    133     * </p>
    134     *
    135     * @return an inverted bidirectional map
    136     */
    137    BidiMap<V, K> inverseBidiMap();
    138
    139    /**
    140     * Returns a {@link Set} view of the values contained in this map.
    141     * The set is backed by the map, so changes to the map are reflected
    142     * in the set, and vice-versa.  If the map is modified while an iteration
    143     * over the set is in progress (except through the iterator's own
    144     * {@code remove} operation), the results of the iteration are undefined.
    145     * The set supports element removal, which removes the corresponding
    146     * mapping from the map, via the {@code Iterator.remove},
    147     * {@code Collection.remove}, {@code removeAll},
    148     * {@code retainAll} and {@code clear} operations.  It does not
    149     * support the {@code add} or {@code addAll} operations.
    150     *
    151     * @return a set view of the values contained in this map
    152     */
    153    @Override
    154    Set<V> values();
    155}