ImmutableEnumSet.java revision 7dd252788645e940eada959bdde927426e2531c9 
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 com.google.common.annotations.GwtCompatible;
20
21import java.io.Serializable;
22import java.util.Collection;
23import java.util.EnumSet;
24
25/**
26 * Implementation of {@link ImmutableSet} backed by a non-empty {@link
27 * java.util.EnumSet}.
28 *
29 * @author Jared Levy
30 */
31@GwtCompatible(serializable = true, emulated = true)
32@SuppressWarnings("serial")
33// we're overriding default serialization
34final class ImmutableEnumSet<E extends Enum<E>> extends ImmutableSet<E> {
35  static <E extends Enum<E>> ImmutableSet<E> asImmutable(EnumSet<E> set) {
36    switch (set.size()) {
37      case 0:
38        return ImmutableSet.of();
39      case 1:
40        return ImmutableSet.of(Iterables.getOnlyElement(set));
41      default:
42        return new ImmutableEnumSet<E>(set);
43    }
44  }
45
46  /*
47   * Notes on EnumSet and <E extends Enum<E>>:
48   *
49   * This class isn't an arbitrary ForwardingImmutableSet because we need to
50   * know that calling {@code clone()} during deserialization will return an
51   * object that no one else has a reference to, allowing us to guarantee
52   * immutability. Hence, we support only {@link EnumSet}.
53   */
54  private final transient EnumSet<E> delegate;
55
56  private ImmutableEnumSet(EnumSet<E> delegate) {
57    this.delegate = delegate;
58  }
59
60  @Override
61  boolean isPartialView() {
62    return false;
63  }
64
65  @Override
66  public UnmodifiableIterator<E> iterator() {
67    return Iterators.unmodifiableIterator(delegate.iterator());
68  }
69
70  public int size() {
71    return delegate.size();
72  }
73
74  @Override
75  public boolean contains(Object object) {
76    return delegate.contains(object);
77  }
78
79  @Override
80  public boolean containsAll(Collection<?> collection) {
81    return delegate.containsAll(collection);
82  }
83
84  @Override
85  public boolean isEmpty() {
86    return delegate.isEmpty();
87  }
88
89  @Override
90  public Object[] toArray() {
91    return delegate.toArray();
92  }
93
94  @Override
95  public <T> T[] toArray(T[] array) {
96    return delegate.toArray(array);
97  }
98
99  @Override
100  public boolean equals(Object object) {
101    return object == this || delegate.equals(object);
102  }
103
104  private transient int hashCode;
105
106  @Override
107  public int hashCode() {
108    int result = hashCode;
109    return (result == 0) ? hashCode = delegate.hashCode() : result;
110  }
111
112  @Override
113  public String toString() {
114    return delegate.toString();
115  }
116
117  // All callers of the constructor are restricted to <E extends Enum<E>>.
118  @Override
119  Object writeReplace() {
120    return new EnumSerializedForm<E>(delegate);
121  }
122
123  /*
124   * This class is used to serialize ImmutableEnumSet instances.
125   */
126  private static class EnumSerializedForm<E extends Enum<E>> implements Serializable {
127    final EnumSet<E> delegate;
128
129    EnumSerializedForm(EnumSet<E> delegate) {
130      this.delegate = delegate;
131    }
132
133    Object readResolve() {
134      // EJ2 #76: Write readObject() methods defensively.
135      return new ImmutableEnumSet<E>(delegate.clone());
136    }
137
138    private static final long serialVersionUID = 0;
139  }
140}
141