1/*
2 * Copyright (C) 2009 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 static com.google.common.base.Preconditions.checkNotNull;
20
21import java.util.Collections;
22
23/**
24 * GWT emulation of {@link SingletonImmutableBiMap}.
25 *
26 * @author Hayward Chan
27 */
28final class SingletonImmutableBiMap<K, V> extends ImmutableBiMap<K, V> {
29
30  // These references are used both by the custom field serializer, and by the
31  // GWT compiler to infer the keys and values of the map that needs to be
32  // serialized.
33  //
34  // Although they are non-final, they are package private and the reference is
35  // never modified after a map is constructed.
36  K singleKey;
37  V singleValue;
38
39  transient SingletonImmutableBiMap<V, K> inverse;
40
41  SingletonImmutableBiMap(K key, V value) {
42    super(Collections.singletonMap(checkNotNull(key), checkNotNull(value)));
43    this.singleKey = key;
44    this.singleValue = value;
45  }
46
47  private SingletonImmutableBiMap(
48      K key, V value, SingletonImmutableBiMap<V, K> inverse) {
49    super(Collections.singletonMap(checkNotNull(key), checkNotNull(value)));
50    this.singleKey = key;
51    this.singleValue = value;
52    this.inverse = inverse;
53  }
54
55  @Override
56  public ImmutableBiMap<V, K> inverse() {
57    ImmutableBiMap<V, K> result = inverse;
58    if (result == null) {
59      return inverse = new SingletonImmutableBiMap<V, K>(singleValue, singleKey, this);
60    } else {
61      return result;
62    }
63  }
64
65  @Override
66  public ImmutableSet<V> values() {
67    return ImmutableSet.of(singleValue);
68  }
69}
70