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; 25import java.util.NoSuchElementException; 26 27import javax.annotation.Nullable; 28 29/** 30 * Implementation of {@link ImmutableList} with exactly one element. 31 * 32 * @author Hayward Chan 33 */ 34@GwtCompatible(serializable = true, emulated = true) 35@SuppressWarnings("serial") // uses writeReplace(), not default serialization 36final class SingletonImmutableList<E> extends ImmutableList<E> { 37 38 final transient E element; 39 40 SingletonImmutableList(E element) { 41 this.element = checkNotNull(element); 42 } 43 44 @Override 45 public E get(int index) { 46 Preconditions.checkElementIndex(index, 1); 47 return element; 48 } 49 50 @Override public int indexOf(@Nullable Object object) { 51 return element.equals(object) ? 0 : -1; 52 } 53 54 @Override public UnmodifiableIterator<E> iterator() { 55 return Iterators.singletonIterator(element); 56 } 57 58 @Override public int lastIndexOf(@Nullable Object object) { 59 return element.equals(object) ? 0 : -1; 60 } 61 62 @Override public UnmodifiableListIterator<E> listIterator(final int start) { 63 Preconditions.checkPositionIndex(start, 1); 64 return new UnmodifiableListIterator<E>() { 65 66 boolean hasNext = start == 0; 67 68 @Override public boolean hasNext() { 69 return hasNext; 70 } 71 72 @Override public boolean hasPrevious() { 73 return !hasNext; 74 } 75 76 @Override public E next() { 77 if (!hasNext) { 78 throw new NoSuchElementException(); 79 } 80 hasNext = false; 81 return element; 82 } 83 84 @Override public int nextIndex() { 85 return hasNext ? 0 : 1; 86 } 87 88 @Override public E previous() { 89 if (hasNext) { 90 throw new NoSuchElementException(); 91 } 92 hasNext = true; 93 return element; 94 } 95 96 @Override public int previousIndex() { 97 return hasNext ? -1 : 0; 98 } 99 }; 100 } 101 102 @Override 103 public int size() { 104 return 1; 105 } 106 107 @Override public ImmutableList<E> subList(int fromIndex, int toIndex) { 108 Preconditions.checkPositionIndexes(fromIndex, toIndex, 1); 109 return (fromIndex == toIndex) ? ImmutableList.<E>of() : this; 110 } 111 112 @Override public ImmutableList<E> reverse() { 113 return this; 114 } 115 116 @Override public boolean contains(@Nullable Object object) { 117 return element.equals(object); 118 } 119 120 @Override public boolean equals(Object object) { 121 if (object == this) { 122 return true; 123 } 124 if (object instanceof List) { 125 List<?> that = (List<?>) object; 126 return that.size() == 1 && element.equals(that.get(0)); 127 } 128 return false; 129 } 130 131 @Override public int hashCode() { 132 // not caching hash code since it could change if the element is mutable 133 // in a way that modifies its hash code. 134 return 31 + element.hashCode(); 135 } 136 137 @Override public String toString() { 138 String elementToString = element.toString(); 139 return new StringBuilder(elementToString.length() + 2) 140 .append('[') 141 .append(elementToString) 142 .append(']') 143 .toString(); 144 } 145 146 @Override public boolean isEmpty() { 147 return false; 148 } 149 150 @Override boolean isPartialView() { 151 return false; 152 } 153 154 @Override public Object[] toArray() { 155 return new Object[] { element }; 156 } 157 158 @Override public <T> T[] toArray(T[] array) { 159 if (array.length == 0) { 160 array = ObjectArrays.newArray(array, 1); 161 } else if (array.length > 1) { 162 array[1] = null; 163 } 164 // Writes will produce ArrayStoreException when the toArray() doc requires. 165 Object[] objectArray = array; 166 objectArray[0] = element; 167 return array; 168 } 169} 170