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 com.google.common.annotations.GwtCompatible;
22import com.google.common.base.Preconditions;
23
24import java.util.List;
25
26import javax.annotation.Nullable;
27
28/**
29 * Implementation of {@link ImmutableList} with exactly one element.
30 *
31 * @author Hayward Chan
32 */
33@GwtCompatible(serializable = true, emulated = true)
34@SuppressWarnings("serial") // uses writeReplace(), not default serialization
35final class SingletonImmutableList<E> extends ImmutableList<E> {
36
37  final transient E element;
38
39  SingletonImmutableList(E element) {
40    this.element = checkNotNull(element);
41  }
42
43  @Override
44  public E get(int index) {
45    Preconditions.checkElementIndex(index, 1);
46    return element;
47  }
48
49  @Override public int indexOf(@Nullable Object object) {
50    return element.equals(object) ? 0 : -1;
51  }
52
53  @Override public UnmodifiableIterator<E> iterator() {
54    return Iterators.singletonIterator(element);
55  }
56
57  @Override public int lastIndexOf(@Nullable Object object) {
58    return indexOf(object);
59  }
60
61  @Override
62  public int size() {
63    return 1;
64  }
65
66  @Override public ImmutableList<E> subList(int fromIndex, int toIndex) {
67    Preconditions.checkPositionIndexes(fromIndex, toIndex, 1);
68    return (fromIndex == toIndex) ? ImmutableList.<E>of() : this;
69  }
70
71  @Override public ImmutableList<E> reverse() {
72    return this;
73  }
74
75  @Override public boolean contains(@Nullable Object object) {
76    return element.equals(object);
77  }
78
79  @Override public boolean equals(@Nullable Object object) {
80    if (object == this) {
81      return true;
82    }
83    if (object instanceof List) {
84      List<?> that = (List<?>) object;
85      return that.size() == 1 && element.equals(that.get(0));
86    }
87    return false;
88  }
89
90  @Override public int hashCode() {
91    // not caching hash code since it could change if the element is mutable
92    // in a way that modifies its hash code.
93    return 31 + element.hashCode();
94  }
95
96  @Override public String toString() {
97    String elementToString = element.toString();
98    return new StringBuilder(elementToString.length() + 2)
99        .append('[')
100        .append(elementToString)
101        .append(']')
102        .toString();
103  }
104
105  @Override public boolean isEmpty() {
106    return false;
107  }
108
109  @Override boolean isPartialView() {
110    return false;
111  }
112
113  @Override
114  int copyIntoArray(Object[] dst, int offset) {
115    dst[offset] = element;
116    return offset + 1;
117  }
118}
119