1/*
2 * Copyright (C) 2008 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;
20
21import javax.annotation.Nullable;
22
23/**
24 * Bimap with no mappings.
25 *
26 * @author Jared Levy
27 */
28@GwtCompatible(emulated = true)
29@SuppressWarnings("serial") // uses writeReplace(), not default serialization
30final class EmptyImmutableBiMap extends ImmutableBiMap<Object, Object> {
31  static final EmptyImmutableBiMap INSTANCE = new EmptyImmutableBiMap();
32
33  private EmptyImmutableBiMap() {}
34
35  @Override public ImmutableBiMap<Object, Object> inverse() {
36    return this;
37  }
38
39  @Override
40  public int size() {
41    return 0;
42  }
43
44  @Override
45  public boolean isEmpty() {
46    return true;
47  }
48
49  @Override
50  public Object get(@Nullable Object key) {
51    return null;
52  }
53
54  @Override
55  public ImmutableSet<Entry<Object, Object>> entrySet() {
56    return ImmutableSet.of();
57  }
58
59  @Override
60  ImmutableSet<Entry<Object, Object>> createEntrySet() {
61    throw new AssertionError("should never be called");
62  }
63
64  @Override
65  public ImmutableSetMultimap<Object, Object> asMultimap() {
66    return ImmutableSetMultimap.of();
67  }
68
69  @Override
70  public ImmutableSet<Object> keySet() {
71    return ImmutableSet.of();
72  }
73
74  @Override
75  boolean isPartialView() {
76    return false;
77  }
78
79  Object readResolve() {
80    return INSTANCE; // preserve singleton property
81  }
82}
83