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.bidimap;
18
19 import java.io.IOException;
20 import java.io.ObjectInputStream;
21 import java.io.ObjectOutputStream;
22 import java.io.Serializable;
23 import java.util.HashMap;
24 import java.util.Map;
25
26 import org.apache.commons.collections4.BidiMap;
27
28 /**
29 * Implementation of {@link BidiMap} that uses two {@link HashMap} instances.
30 * <p>
31 * Two {@link HashMap} instances are used in this class.
32 * This provides fast lookups at the expense of storing two sets of map entries.
33 * Commons Collections would welcome the addition of a direct hash-based
34 * implementation of the {@link BidiMap} interface.
35 * </p>
36 * <p>
37 * NOTE: From Commons Collections 3.1, all subclasses will use {@link HashMap}
38 * and the flawed {@code createMap} method is ignored.
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 class DualHashBidiMap<K, V> extends AbstractDualBidiMap<K, V> implements Serializable {
47
48 /** Ensure serialization compatibility */
49 private static final long serialVersionUID = 721969328361808L;
50
51 /**
52 * Creates an empty {@code HashBidiMap}.
53 */
54 public DualHashBidiMap() {
55 super(new HashMap<>(), new HashMap<>());
56 }
57
58 /**
59 * Constructs a {@code HashBidiMap} and copies the mappings from
60 * specified {@code Map}.
61 *
62 * @param map the map whose mappings are to be placed in this map
63 */
64 public DualHashBidiMap(final Map<? extends K, ? extends V> map) {
65 super(new HashMap<>(), new HashMap<>());
66 putAll(map);
67 }
68
69 /**
70 * Constructs a {@code HashBidiMap} that decorates the specified maps.
71 *
72 * @param normalMap the normal direction map
73 * @param reverseMap the reverse direction map
74 * @param inverseBidiMap the inverse BidiMap
75 */
76 protected DualHashBidiMap(final Map<K, V> normalMap, final Map<V, K> reverseMap,
77 final BidiMap<V, K> inverseBidiMap) {
78 super(normalMap, reverseMap, inverseBidiMap);
79 }
80
81 /**
82 * Creates a new instance of this object.
83 *
84 * @param normalMap the normal direction map
85 * @param reverseMap the reverse direction map
86 * @param inverseBidiMap the inverse BidiMap
87 * @return new bidi map
88 */
89 @Override
90 protected BidiMap<V, K> createBidiMap(final Map<V, K> normalMap, final Map<K, V> reverseMap,
91 final BidiMap<K, V> inverseBidiMap) {
92 return new DualHashBidiMap<>(normalMap, reverseMap, inverseBidiMap);
93 }
94
95 private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
96 in.defaultReadObject();
97 normalMap = new HashMap<>();
98 reverseMap = new HashMap<>();
99 @SuppressWarnings("unchecked") // will fail at runtime if stream is incorrect
100 final Map<K, V> map = (Map<K, V>) in.readObject();
101 putAll(map);
102 }
103
104 // Serialization
105 private void writeObject(final ObjectOutputStream out) throws IOException {
106 out.defaultWriteObject();
107 out.writeObject(normalMap);
108 }
109
110 }