1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.collections4;
18
19 import java.util.Set;
20
21 /**
22 * Defines a map that allows bidirectional lookup between key and values.
23 * <p>
24 * This extended {@code Map} represents a mapping where a key may
25 * lookup a value and a value may lookup a key with equal ease.
26 * This interface extends {@code Map} and so may be used anywhere a map
27 * is required. The interface provides an inverse map view, enabling
28 * full access to both directions of the {@code BidiMap}.
29 * </p>
30 * <p>
31 * Implementations should allow a value to be looked up from a key and
32 * a key to be looked up from a value with equal performance.
33 * </p>
34 * <p>
35 * This map enforces the restriction that there is a 1:1 relation between
36 * keys and values, meaning that multiple keys cannot map to the same value.
37 * This is required so that "inverting" the map results in a map without
38 * duplicate keys. See the {@link #put} method description for more information.
39 * </p>
40 *
41 * @param <K> the type of the keys in the map
42 * @param <V> the type of the values in the map
43 *
44 * @since 3.0
45 */
46 public interface BidiMap<K, V> extends IterableMap<K, V> {
47
48 /**
49 * Gets the key that is currently mapped to the specified value.
50 * <p>
51 * If the value is not contained in the map, {@code null} is returned.
52 * </p>
53 * <p>
54 * Implementations should seek to make this method perform equally as well
55 * as {@code get(Object)}.
56 * </p>
57 *
58 * @param value the value to find the key for
59 * @return the mapped key, or {@code null} if not found
60 *
61 * @throws ClassCastException (optional) if the map limits the type of the
62 * value and the specified value is inappropriate
63 * @throws NullPointerException (optional) if the map limits the values to
64 * non-null and null was specified
65 */
66 K getKey(Object value);
67
68 /**
69 * Gets a view of this map where the keys and values are reversed.
70 * <p>
71 * Changes to one map will be visible in the other and vice versa.
72 * This enables both directions of the map to be accessed as a {@code Map}.
73 * </p>
74 * <p>
75 * Implementations should seek to avoid creating a new object every time this
76 * method is called. See {@code AbstractMap.values()} etc. Calling this
77 * method on the inverse map should return the original.
78 * </p>
79 *
80 * @return an inverted bidirectional map
81 */
82 BidiMap<V, K> inverseBidiMap();
83
84 /**
85 * Puts the key-value pair into the map, replacing any previous pair.
86 * <p>
87 * When adding a key-value pair, the value may already exist in the map
88 * against a different key. That mapping is removed, to ensure that the
89 * value only occurs once in the inverse map.
90 * </p>
91 * <pre>
92 * BidiMap map1 = new DualHashBidiMap();
93 * map.put("A","B"); // contains A mapped to B, as per Map
94 * map.put("A","C"); // contains A mapped to C, as per Map
95 *
96 * BidiMap map2 = new DualHashBidiMap();
97 * map.put("A","B"); // contains A mapped to B, as per Map
98 * map.put("C","B"); // contains C mapped to B, key A is removed
99 * </pre>
100 *
101 * @param key the key to store
102 * @param value the value to store
103 * @return the previous value mapped to this key
104 *
105 * @throws UnsupportedOperationException if the {@code put} method is not supported
106 * @throws ClassCastException (optional) if the map limits the type of the
107 * value and the specified value is inappropriate
108 * @throws IllegalArgumentException (optional) if the map limits the values
109 * in some way and the value was invalid
110 * @throws NullPointerException (optional) if the map limits the values to
111 * non-null and null was specified
112 */
113 @Override
114 V put(K key, V value);
115
116 /**
117 * Removes the key-value pair that is currently mapped to the specified
118 * value (optional operation).
119 * <p>
120 * If the value is not contained in the map, {@code null} is returned.
121 * </p>
122 * <p>
123 * Implementations should seek to make this method perform equally as well
124 * as {@code remove(Object)}.
125 * </p>
126 *
127 * @param value the value to find the key-value pair for
128 * @return the key that was removed, {@code null} if nothing removed
129 *
130 * @throws ClassCastException (optional) if the map limits the type of the
131 * value and the specified value is inappropriate
132 * @throws NullPointerException (optional) if the map limits the values to
133 * non-null and null was specified
134 * @throws UnsupportedOperationException if this method is not supported
135 * by the implementation
136 */
137 K removeValue(Object value);
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 }