1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 18 package java.util; 19 20 import java.io.Serializable; 21 22 /** 23 * LinkedHashSet is a variant of HashSet. Its entries are kept in a 24 * doubly-linked list. The iteration order is the order in which entries were 25 * inserted. 26 * <p> 27 * Null elements are allowed, and all the optional Set operations are supported. 28 * <p> 29 * Like HashSet, LinkedHashSet is not thread safe, so access by multiple threads 30 * must be synchronized by an external mechanism such as 31 * {@link Collections#synchronizedSet(Set)}. 32 * 33 * @since 1.4 34 */ 35 public class LinkedHashSet<E> extends HashSet<E> implements Set<E>, Cloneable, 36 Serializable { 37 38 private static final long serialVersionUID = -2851667679971038690L; 39 40 /** 41 * Constructs a new empty instance of {@code LinkedHashSet}. 42 */ 43 public LinkedHashSet() { 44 super(new LinkedHashMap<E, HashSet<E>>()); 45 } 46 47 /** 48 * Constructs a new instance of {@code LinkedHashSet} with the specified 49 * capacity. 50 * 51 * @param capacity 52 * the initial capacity of this {@code LinkedHashSet}. 53 */ 54 public LinkedHashSet(int capacity) { 55 super(new LinkedHashMap<E, HashSet<E>>(capacity)); 56 } 57 58 /** 59 * Constructs a new instance of {@code LinkedHashSet} with the specified 60 * capacity and load factor. 61 * 62 * @param capacity 63 * the initial capacity. 64 * @param loadFactor 65 * the initial load factor. 66 */ 67 public LinkedHashSet(int capacity, float loadFactor) { 68 super(new LinkedHashMap<E, HashSet<E>>(capacity, loadFactor)); 69 } 70 71 /** 72 * Constructs a new instance of {@code LinkedHashSet} containing the unique 73 * elements in the specified collection. 74 * 75 * @param collection 76 * the collection of elements to add. 77 */ 78 public LinkedHashSet(Collection<? extends E> collection) { 79 super(new LinkedHashMap<E, HashSet<E>>(collection.size() < 6 ? 11 80 : collection.size() * 2)); 81 for (E e : collection) { 82 add(e); 83 } 84 } 85 86 /* overrides method in HashMap */ 87 @Override 88 HashMap<E, HashSet<E>> createBackingMap(int capacity, float loadFactor) { 89 return new LinkedHashMap<E, HashSet<E>>(capacity, loadFactor); 90 } 91 } 92