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 
17 package com.google.common.collect;
18 
19 import static com.google.common.base.Preconditions.checkNotNull;
20 
21 import com.google.common.annotations.GwtCompatible;
22 import com.google.common.annotations.GwtIncompatible;
23 import com.google.errorprone.annotations.CanIgnoreReturnValue;
24 import java.io.IOException;
25 import java.io.ObjectInputStream;
26 import java.io.ObjectOutputStream;
27 import java.util.EnumMap;
28 import java.util.HashMap;
29 import java.util.Map;
30 import org.checkerframework.checker.nullness.compatqual.NullableDecl;
31 
32 /**
33  * A {@code BiMap} backed by an {@code EnumMap} instance for keys-to-values, and a {@code HashMap}
34  * instance for values-to-keys. Null keys are not permitted, but null values are. An {@code
35  * EnumHashBiMap} and its inverse are both serializable.
36  *
37  * <p>See the Guava User Guide article on <a href=
38  * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#bimap"> {@code BiMap}</a>.
39  *
40  * @author Mike Bostock
41  * @since 2.0
42  */
43 @GwtCompatible(emulated = true)
44 public final class EnumHashBiMap<K extends Enum<K>, V> extends AbstractBiMap<K, V> {
45   private transient Class<K> keyType;
46 
47   /**
48    * Returns a new, empty {@code EnumHashBiMap} using the specified key type.
49    *
50    * @param keyType the key type
51    */
create(Class<K> keyType)52   public static <K extends Enum<K>, V> EnumHashBiMap<K, V> create(Class<K> keyType) {
53     return new EnumHashBiMap<>(keyType);
54   }
55 
56   /**
57    * Constructs a new bimap with the same mappings as the specified map. If the specified map is an
58    * {@code EnumHashBiMap} or an {@link EnumBiMap}, the new bimap has the same key type as the input
59    * bimap. Otherwise, the specified map must contain at least one mapping, in order to determine
60    * the key type.
61    *
62    * @param map the map whose mappings are to be placed in this map
63    * @throws IllegalArgumentException if map is not an {@code EnumBiMap} or an {@code EnumHashBiMap}
64    *     instance and contains no mappings
65    */
create(Map<K, ? extends V> map)66   public static <K extends Enum<K>, V> EnumHashBiMap<K, V> create(Map<K, ? extends V> map) {
67     EnumHashBiMap<K, V> bimap = create(EnumBiMap.inferKeyType(map));
68     bimap.putAll(map);
69     return bimap;
70   }
71 
EnumHashBiMap(Class<K> keyType)72   private EnumHashBiMap(Class<K> keyType) {
73     super(
74         new EnumMap<K, V>(keyType),
75         Maps.<V, K>newHashMapWithExpectedSize(keyType.getEnumConstants().length));
76     this.keyType = keyType;
77   }
78 
79   // Overriding these 3 methods to show that values may be null (but not keys)
80 
81   @Override
checkKey(K key)82   K checkKey(K key) {
83     return checkNotNull(key);
84   }
85 
86   @CanIgnoreReturnValue
87   @Override
put(K key, @NullableDecl V value)88   public V put(K key, @NullableDecl V value) {
89     return super.put(key, value);
90   }
91 
92   @CanIgnoreReturnValue
93   @Override
forcePut(K key, @NullableDecl V value)94   public V forcePut(K key, @NullableDecl V value) {
95     return super.forcePut(key, value);
96   }
97 
98   /** Returns the associated key type. */
keyType()99   public Class<K> keyType() {
100     return keyType;
101   }
102 
103   /**
104    * @serialData the key class, number of entries, first key, first value, second key, second value,
105    *     and so on.
106    */
107   @GwtIncompatible // java.io.ObjectOutputStream
writeObject(ObjectOutputStream stream)108   private void writeObject(ObjectOutputStream stream) throws IOException {
109     stream.defaultWriteObject();
110     stream.writeObject(keyType);
111     Serialization.writeMap(this, stream);
112   }
113 
114   @SuppressWarnings("unchecked") // reading field populated by writeObject
115   @GwtIncompatible // java.io.ObjectInputStream
readObject(ObjectInputStream stream)116   private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
117     stream.defaultReadObject();
118     keyType = (Class<K>) stream.readObject();
119     setDelegates(
120         new EnumMap<K, V>(keyType), new HashMap<V, K>(keyType.getEnumConstants().length * 3 / 2));
121     Serialization.populateMap(this, stream);
122   }
123 
124   @GwtIncompatible // only needed in emulated source.
125   private static final long serialVersionUID = 0;
126 }
127