1 /* 2 * Copyright (C) 2007 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.Set; 23 24 import javax.annotation.Nullable; 25 26 /** 27 * Implementation of {@link ImmutableSet} with exactly one element. 28 * 29 * @author Kevin Bourrillion 30 * @author Nick Kralevich 31 */ 32 @GwtCompatible(serializable = true) 33 @SuppressWarnings("serial") // uses writeReplace(), not default serialization 34 final class SingletonImmutableSet<E> extends ImmutableSet<E> { 35 final transient E element; 36 37 // Non-volatile because: 38 // - Integer is immutable and thus thread-safe; 39 // - no problems if one thread overwrites the cachedHashCode from another. 40 private transient Integer cachedHashCode; 41 SingletonImmutableSet(E element)42 SingletonImmutableSet(E element) { 43 this.element = Preconditions.checkNotNull(element); 44 } 45 SingletonImmutableSet(E element, int hashCode)46 SingletonImmutableSet(E element, int hashCode) { 47 // Guaranteed to be non-null by the presence of the pre-computed hash code. 48 this.element = element; 49 cachedHashCode = hashCode; 50 } 51 size()52 public int size() { 53 return 1; 54 } 55 isEmpty()56 @Override public boolean isEmpty() { 57 return false; 58 } 59 contains(Object target)60 @Override public boolean contains(Object target) { 61 return element.equals(target); 62 } 63 iterator()64 @Override public UnmodifiableIterator<E> iterator() { 65 return Iterators.singletonIterator(element); 66 } 67 toArray()68 @Override public Object[] toArray() { 69 return new Object[] { element }; 70 } 71 72 @SuppressWarnings({"unchecked"}) toArray(T[] array)73 @Override public <T> T[] toArray(T[] array) { 74 if (array.length == 0) { 75 array = ObjectArrays.newArray(array, 1); 76 } else if (array.length > 1) { 77 array[1] = null; 78 } 79 // Writes will produce ArrayStoreException when the toArray() doc requires. 80 Object[] objectArray = array; 81 objectArray[0] = element; 82 return array; 83 } 84 equals(@ullable Object object)85 @Override public boolean equals(@Nullable Object object) { 86 if (object == this) { 87 return true; 88 } 89 if (object instanceof Set) { 90 Set<?> that = (Set<?>) object; 91 return that.size() == 1 && element.equals(that.iterator().next()); 92 } 93 return false; 94 } 95 hashCode()96 @Override public final int hashCode() { 97 Integer code = cachedHashCode; 98 if (code == null) { 99 return cachedHashCode = element.hashCode(); 100 } 101 return code; 102 } 103 isHashCodeFast()104 @Override boolean isHashCodeFast() { 105 return false; 106 } 107 toString()108 @Override public String toString() { 109 String elementToString = element.toString(); 110 return new StringBuilder(elementToString.length() + 2) 111 .append('[') 112 .append(elementToString) 113 .append(']') 114 .toString(); 115 } 116 } 117