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
18package java.util;
19
20import 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 */
35public 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