1 /* 2 * Copyright (C) 2007 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 17 package com.google.common.collect; 18 19 import com.google.common.annotations.GwtCompatible; 20 import com.google.common.annotations.GwtIncompatible; 21 import com.google.common.annotations.J2ktIncompatible; 22 import com.google.common.base.Preconditions; 23 import javax.annotation.CheckForNull; 24 import org.checkerframework.checker.nullness.qual.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, emulated = true) 33 @SuppressWarnings("serial") // uses writeReplace(), not default serialization 34 @ElementTypesAreNonnullByDefault 35 final class SingletonImmutableSet<E> extends ImmutableSet<E> { 36 // We deliberately avoid caching the asList and hashCode here, to ensure that with 37 // compressed oops, a SingletonImmutableSet packs all the way down to the optimal 16 bytes. 38 39 final transient E element; 40 SingletonImmutableSet(E element)41 SingletonImmutableSet(E element) { 42 this.element = Preconditions.checkNotNull(element); 43 } 44 45 @Override size()46 public int size() { 47 return 1; 48 } 49 50 @Override contains(@heckForNull Object target)51 public boolean contains(@CheckForNull Object target) { 52 return element.equals(target); 53 } 54 55 @Override iterator()56 public UnmodifiableIterator<E> iterator() { 57 return Iterators.singletonIterator(element); 58 } 59 60 @Override asList()61 public ImmutableList<E> asList() { 62 return ImmutableList.of(element); 63 } 64 65 @Override isPartialView()66 boolean isPartialView() { 67 return false; 68 } 69 70 @Override copyIntoArray(@ullable Object[] dst, int offset)71 int copyIntoArray(@Nullable Object[] dst, int offset) { 72 dst[offset] = element; 73 return offset + 1; 74 } 75 76 @Override hashCode()77 public final int hashCode() { 78 return element.hashCode(); 79 } 80 81 @Override toString()82 public String toString() { 83 return '[' + element.toString() + ']'; 84 } 85 86 // redeclare to help optimizers with b/310253115 87 @SuppressWarnings("RedundantOverride") 88 @Override 89 @J2ktIncompatible // serialization 90 @GwtIncompatible // serialization writeReplace()91 Object writeReplace() { 92 return super.writeReplace(); 93 } 94 } 95