1 /* 2 * Copyright (C) 2009 Google Inc. 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 17 package com.google.common.collect; 18 19 import com.google.common.annotations.GwtCompatible; 20 import com.google.common.base.Preconditions; 21 22 import java.util.Collections; 23 import java.util.List; 24 import java.util.ListIterator; 25 26 import javax.annotation.Nullable; 27 28 import static com.google.common.base.Preconditions.checkNotNull; 29 30 /** 31 * Implementation of {@link ImmutableList} with exactly one element. 32 * 33 * @author Hayward Chan 34 */ 35 @GwtCompatible(serializable = true) 36 @SuppressWarnings("serial") // uses writeReplace(), not default serialization 37 final class SingletonImmutableList<E> extends ImmutableList<E> { 38 final transient E element; 39 40 SingletonImmutableList(E element) { 41 this.element = checkNotNull(element); 42 } 43 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 element.equals(object) ? 0 : -1; 59 } 60 61 public ListIterator<E> listIterator() { 62 return listIterator(0); 63 } 64 65 public ListIterator<E> listIterator(final int start) { 66 // suboptimal but not worth optimizing. 67 return Collections.singletonList(element).listIterator(start); 68 } 69 70 public int size() { 71 return 1; 72 } 73 74 @Override public ImmutableList<E> subList(int fromIndex, int toIndex) { 75 Preconditions.checkPositionIndexes(fromIndex, toIndex, 1); 76 return (fromIndex == toIndex) ? ImmutableList.<E>of() : this; 77 } 78 79 @Override public boolean contains(@Nullable Object object) { 80 return element.equals(object); 81 } 82 83 @Override public boolean equals(Object object) { 84 if (object == this) { 85 return true; 86 } 87 if (object instanceof List) { 88 List<?> that = (List<?>) object; 89 return that.size() == 1 && element.equals(that.get(0)); 90 } 91 return false; 92 } 93 94 @Override public int hashCode() { 95 // not caching hash code since it could change if the element is mutable 96 // in a way that modifies its hash code. 97 return 31 + element.hashCode(); 98 } 99 100 @Override public boolean isEmpty() { 101 return false; 102 } 103 104 @Override public Object[] toArray() { 105 return new Object[] { element }; 106 } 107 108 @Override public <T> T[] toArray(T[] array) { 109 if (array.length == 0) { 110 array = ObjectArrays.newArray(array, 1); 111 } else if (array.length > 1) { 112 array[1] = null; 113 } 114 // Writes will produce ArrayStoreException when the toArray() doc requires. 115 Object[] objectArray = array; 116 objectArray[0] = element; 117 return array; 118 } 119 } 120
