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.LinkedHashMap;
24 import java.util.Map;
25
26 import org.apache.commons.collections4.BidiMap;
27
28 /**
29 * Implements {@link BidiMap} with two {@link LinkedHashMap} instances.
30 * <p>
31 * Two {@link LinkedHashMap} instances are used in this class.
32 * This provides fast lookups at the expense of storing two sets of map entries and two linked lists.
33 * </p>
34 *
35 * @param <K> the type of the keys in the map
36 * @param <V> the type of the values in the map
37 * @since 4.0
38 */
39 public class DualLinkedHashBidiMap<K, V> extends AbstractDualBidiMap<K, V> implements Serializable {
40
41 /** Ensure serialization compatibility */
42 private static final long serialVersionUID = 721969328361810L;
43
44 /**
45 * Creates an empty {@code HashBidiMap}.
46 */
47 public DualLinkedHashBidiMap() {
48 super(new LinkedHashMap<>(), new LinkedHashMap<>());
49 }
50
51 /**
52 * Constructs a {@code LinkedHashBidiMap} and copies the mappings from
53 * specified {@link Map}.
54 *
55 * @param map the map whose mappings are to be placed in this map
56 */
57 public DualLinkedHashBidiMap(final Map<? extends K, ? extends V> map) {
58 super(new LinkedHashMap<>(), new LinkedHashMap<>());
59 putAll(map);
60 }
61
62 /**
63 * Constructs a {@code LinkedHashBidiMap} that decorates the specified maps.
64 *
65 * @param normalMap the normal direction map
66 * @param reverseMap the reverse direction map
67 * @param inverseBidiMap the inverse BidiMap
68 */
69 protected DualLinkedHashBidiMap(final Map<K, V> normalMap, final Map<V, K> reverseMap,
70 final BidiMap<V, K> inverseBidiMap) {
71 super(normalMap, reverseMap, inverseBidiMap);
72 }
73
74 /**
75 * Creates a new instance of this object.
76 *
77 * @param normalMap the normal direction map
78 * @param reverseMap the reverse direction map
79 * @param inverseBidiMap the inverse BidiMap
80 * @return new bidi map
81 */
82 @Override
83 protected BidiMap<V, K> createBidiMap(final Map<V, K> normalMap, final Map<K, V> reverseMap,
84 final BidiMap<K, V> inverseBidiMap) {
85 return new DualLinkedHashBidiMap<>(normalMap, reverseMap, inverseBidiMap);
86 }
87
88 /**
89 * Deserializes an instance from an ObjectInputStream.
90 *
91 * @param in The source ObjectInputStream.
92 * @throws IOException Any of the usual Input/Output related exceptions.
93 * @throws ClassNotFoundException A class of a serialized object cannot be found.
94 */
95 private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
96 in.defaultReadObject();
97 normalMap = new LinkedHashMap<>();
98 reverseMap = new LinkedHashMap<>();
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 /**
105 * Serializes this object to an ObjectOutputStream.
106 *
107 * @param out the target ObjectOutputStream.
108 * @throws IOException thrown when an I/O errors occur writing to the target stream.
109 */
110 private void writeObject(final ObjectOutputStream out) throws IOException {
111 out.defaultWriteObject();
112 out.writeObject(normalMap);
113 }
114 }