EnumHashBiMap.java revision 1d580d0f6ee4f21eb309ba7b509d2c6d671c4044 
1/*
2 * Copyright (C) 2007 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.collect;
18
19import com.google.common.annotations.GwtCompatible;
20import com.google.common.annotations.GwtIncompatible;
21
22import java.io.IOException;
23import java.io.ObjectInputStream;
24import java.io.ObjectOutputStream;
25import java.util.EnumMap;
26import java.util.HashMap;
27import java.util.Map;
28
29import javax.annotation.Nullable;
30
31/**
32 * A {@code BiMap} backed by an {@code EnumMap} instance for keys-to-values, and
33 * a {@code HashMap} instance for values-to-keys. Null keys are not permitted,
34 * but null values are. An {@code EnumHashBiMap} and its inverse are both
35 * serializable.
36 *
37 * @author Mike Bostock
38 * @since 2.0 (imported from Google Collections Library)
39 */
40@GwtCompatible(emulated = true)
41public final class EnumHashBiMap<K extends Enum<K>, V>
42    extends AbstractBiMap<K, V> {
43  private transient Class<K> keyType;
44
45  /**
46   * Returns a new, empty {@code EnumHashBiMap} using the specified key type.
47   *
48   * @param keyType the key type
49   */
50  public static <K extends Enum<K>, V> EnumHashBiMap<K, V>
51      create(Class<K> keyType) {
52    return new EnumHashBiMap<K, V>(keyType);
53  }
54
55  /**
56   * Constructs a new bimap with the same mappings as the specified map. If the
57   * specified map is an {@code EnumHashBiMap} or an {@link EnumBiMap}, the new
58   * bimap has the same key type as the input bimap. Otherwise, the specified
59   * map must contain at least one mapping, in order to determine the key type.
60   *
61   * @param map the map whose mappings are to be placed in this map
62   * @throws IllegalArgumentException if map is not an {@code EnumBiMap} or an
63   *     {@code EnumHashBiMap} instance and contains no mappings
64   */
65  public static <K extends Enum<K>, V> EnumHashBiMap<K, V>
66      create(Map<K, ? extends V> map) {
67    EnumHashBiMap<K, V> bimap = create(EnumBiMap.inferKeyType(map));
68    bimap.putAll(map);
69    return bimap;
70  }
71
72  private EnumHashBiMap(Class<K> keyType) {
73    super(WellBehavedMap.wrap(
74        new EnumMap<K, V>(keyType)),
75        Maps.<V, K>newHashMapWithExpectedSize(
76            keyType.getEnumConstants().length));
77    this.keyType = keyType;
78  }
79
80  // Overriding these two methods to show that values may be null (but not keys)
81
82  @Override public V put(K key, @Nullable V value) {
83    return super.put(key, value);
84  }
85
86  @Override public V forcePut(K key, @Nullable V value) {
87    return super.forcePut(key, value);
88  }
89
90  /** Returns the associated key type. */
91  public Class<K> keyType() {
92    return keyType;
93  }
94
95  /**
96   * @serialData the key class, number of entries, first key, first value,
97   *     second key, second value, and so on.
98   */
99  @GwtIncompatible("java.io.ObjectOutputStream")
100  private void writeObject(ObjectOutputStream stream) throws IOException {
101    stream.defaultWriteObject();
102    stream.writeObject(keyType);
103    Serialization.writeMap(this, stream);
104  }
105
106  @SuppressWarnings("unchecked") // reading field populated by writeObject
107  @GwtIncompatible("java.io.ObjectInputStream")
108  private void readObject(ObjectInputStream stream)
109      throws IOException, ClassNotFoundException {
110    stream.defaultReadObject();
111    keyType = (Class<K>) stream.readObject();
112    setDelegates(WellBehavedMap.wrap(new EnumMap<K, V>(keyType)),
113        new HashMap<V, K>(keyType.getEnumConstants().length * 3 / 2));
114    Serialization.populateMap(this, stream);
115  }
116
117  @GwtIncompatible("only needed in emulated source.")
118  private static final long serialVersionUID = 0;
119}
120