|
1 /* |
|
2 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved. |
|
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
|
4 * |
|
5 * This code is free software; you can redistribute it and/or modify it |
|
6 * under the terms of the GNU General Public License version 2 only, as |
|
7 * published by the Free Software Foundation. Oracle designates this |
|
8 * particular file as subject to the "Classpath" exception as provided |
|
9 * by Oracle in the LICENSE file that accompanied this code. |
|
10 * |
|
11 * This code is distributed in the hope that it will be useful, but WITHOUT |
|
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
|
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
|
14 * version 2 for more details (a copy is included in the LICENSE file that |
|
15 * accompanied this code). |
|
16 * |
|
17 * You should have received a copy of the GNU General Public License version |
|
18 * 2 along with this work; if not, write to the Free Software Foundation, |
|
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
|
20 * |
|
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
|
22 * or visit www.oracle.com if you need additional information or have any |
|
23 * questions. |
|
24 */ |
|
25 |
|
26 package java.util; |
|
27 |
|
28 /** |
|
29 * <p>Hash table and linked list implementation of the <tt>Set</tt> interface, |
|
30 * with predictable iteration order. This implementation differs from |
|
31 * <tt>HashSet</tt> in that it maintains a doubly-linked list running through |
|
32 * all of its entries. This linked list defines the iteration ordering, |
|
33 * which is the order in which elements were inserted into the set |
|
34 * (<i>insertion-order</i>). Note that insertion order is <i>not</i> affected |
|
35 * if an element is <i>re-inserted</i> into the set. (An element <tt>e</tt> |
|
36 * is reinserted into a set <tt>s</tt> if <tt>s.add(e)</tt> is invoked when |
|
37 * <tt>s.contains(e)</tt> would return <tt>true</tt> immediately prior to |
|
38 * the invocation.) |
|
39 * |
|
40 * <p>This implementation spares its clients from the unspecified, generally |
|
41 * chaotic ordering provided by {@link HashSet}, without incurring the |
|
42 * increased cost associated with {@link TreeSet}. It can be used to |
|
43 * produce a copy of a set that has the same order as the original, regardless |
|
44 * of the original set's implementation: |
|
45 * <pre> |
|
46 * void foo(Set s) { |
|
47 * Set copy = new LinkedHashSet(s); |
|
48 * ... |
|
49 * } |
|
50 * </pre> |
|
51 * This technique is particularly useful if a module takes a set on input, |
|
52 * copies it, and later returns results whose order is determined by that of |
|
53 * the copy. (Clients generally appreciate having things returned in the same |
|
54 * order they were presented.) |
|
55 * |
|
56 * <p>This class provides all of the optional <tt>Set</tt> operations, and |
|
57 * permits null elements. Like <tt>HashSet</tt>, it provides constant-time |
|
58 * performance for the basic operations (<tt>add</tt>, <tt>contains</tt> and |
|
59 * <tt>remove</tt>), assuming the hash function disperses elements |
|
60 * properly among the buckets. Performance is likely to be just slightly |
|
61 * below that of <tt>HashSet</tt>, due to the added expense of maintaining the |
|
62 * linked list, with one exception: Iteration over a <tt>LinkedHashSet</tt> |
|
63 * requires time proportional to the <i>size</i> of the set, regardless of |
|
64 * its capacity. Iteration over a <tt>HashSet</tt> is likely to be more |
|
65 * expensive, requiring time proportional to its <i>capacity</i>. |
|
66 * |
|
67 * <p>A linked hash set has two parameters that affect its performance: |
|
68 * <i>initial capacity</i> and <i>load factor</i>. They are defined precisely |
|
69 * as for <tt>HashSet</tt>. Note, however, that the penalty for choosing an |
|
70 * excessively high value for initial capacity is less severe for this class |
|
71 * than for <tt>HashSet</tt>, as iteration times for this class are unaffected |
|
72 * by capacity. |
|
73 * |
|
74 * <p><strong>Note that this implementation is not synchronized.</strong> |
|
75 * If multiple threads access a linked hash set concurrently, and at least |
|
76 * one of the threads modifies the set, it <em>must</em> be synchronized |
|
77 * externally. This is typically accomplished by synchronizing on some |
|
78 * object that naturally encapsulates the set. |
|
79 * |
|
80 * If no such object exists, the set should be "wrapped" using the |
|
81 * {@link Collections#synchronizedSet Collections.synchronizedSet} |
|
82 * method. This is best done at creation time, to prevent accidental |
|
83 * unsynchronized access to the set: <pre> |
|
84 * Set s = Collections.synchronizedSet(new LinkedHashSet(...));</pre> |
|
85 * |
|
86 * <p>The iterators returned by this class's <tt>iterator</tt> method are |
|
87 * <em>fail-fast</em>: if the set is modified at any time after the iterator |
|
88 * is created, in any way except through the iterator's own <tt>remove</tt> |
|
89 * method, the iterator will throw a {@link ConcurrentModificationException}. |
|
90 * Thus, in the face of concurrent modification, the iterator fails quickly |
|
91 * and cleanly, rather than risking arbitrary, non-deterministic behavior at |
|
92 * an undetermined time in the future. |
|
93 * |
|
94 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed |
|
95 * as it is, generally speaking, impossible to make any hard guarantees in the |
|
96 * presence of unsynchronized concurrent modification. Fail-fast iterators |
|
97 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. |
|
98 * Therefore, it would be wrong to write a program that depended on this |
|
99 * exception for its correctness: <i>the fail-fast behavior of iterators |
|
100 * should be used only to detect bugs.</i> |
|
101 * |
|
102 * <p>This class is a member of the |
|
103 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
|
104 * Java Collections Framework</a>. |
|
105 * |
|
106 * @param <E> the type of elements maintained by this set |
|
107 * |
|
108 * @author Josh Bloch |
|
109 * @see Object#hashCode() |
|
110 * @see Collection |
|
111 * @see Set |
|
112 * @see HashSet |
|
113 * @see TreeSet |
|
114 * @see Hashtable |
|
115 * @since 1.4 |
|
116 */ |
|
117 |
|
118 public class LinkedHashSet<E> |
|
119 extends HashSet<E> |
|
120 implements Set<E>, Cloneable, java.io.Serializable { |
|
121 |
|
122 private static final long serialVersionUID = -2851667679971038690L; |
|
123 |
|
124 /** |
|
125 * Constructs a new, empty linked hash set with the specified initial |
|
126 * capacity and load factor. |
|
127 * |
|
128 * @param initialCapacity the initial capacity of the linked hash set |
|
129 * @param loadFactor the load factor of the linked hash set |
|
130 * @throws IllegalArgumentException if the initial capacity is less |
|
131 * than zero, or if the load factor is nonpositive |
|
132 */ |
|
133 public LinkedHashSet(int initialCapacity, float loadFactor) { |
|
134 super(initialCapacity, loadFactor, true); |
|
135 } |
|
136 |
|
137 /** |
|
138 * Constructs a new, empty linked hash set with the specified initial |
|
139 * capacity and the default load factor (0.75). |
|
140 * |
|
141 * @param initialCapacity the initial capacity of the LinkedHashSet |
|
142 * @throws IllegalArgumentException if the initial capacity is less |
|
143 * than zero |
|
144 */ |
|
145 public LinkedHashSet(int initialCapacity) { |
|
146 super(initialCapacity, .75f, true); |
|
147 } |
|
148 |
|
149 /** |
|
150 * Constructs a new, empty linked hash set with the default initial |
|
151 * capacity (16) and load factor (0.75). |
|
152 */ |
|
153 public LinkedHashSet() { |
|
154 super(16, .75f, true); |
|
155 } |
|
156 |
|
157 /** |
|
158 * Constructs a new linked hash set with the same elements as the |
|
159 * specified collection. The linked hash set is created with an initial |
|
160 * capacity sufficient to hold the elements in the specified collection |
|
161 * and the default load factor (0.75). |
|
162 * |
|
163 * @param c the collection whose elements are to be placed into |
|
164 * this set |
|
165 * @throws NullPointerException if the specified collection is null |
|
166 */ |
|
167 public LinkedHashSet(Collection<? extends E> c) { |
|
168 super(Math.max(2*c.size(), 11), .75f, true); |
|
169 addAll(c); |
|
170 } |
|
171 |
|
172 /** |
|
173 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em> |
|
174 * and <em>fail-fast</em> {@code Spliterator} over the elements in this set. |
|
175 * |
|
176 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED}, |
|
177 * {@link Spliterator#DISTINCT}, and {@code ORDERED}. Implementations |
|
178 * should document the reporting of additional characteristic values. |
|
179 * |
|
180 * @implNote |
|
181 * The implementation creates a |
|
182 * <em><a href="Spliterator.html#binding">late-binding</a></em> spliterator |
|
183 * from the set's {@code Iterator}. The spliterator inherits the |
|
184 * <em>fail-fast</em> properties of the set's iterator. |
|
185 * The created {@code Spliterator} additionally reports |
|
186 * {@link Spliterator#SUBSIZED}. |
|
187 * |
|
188 * @return a {@code Spliterator} over the elements in this set |
|
189 * @since 1.8 |
|
190 */ |
|
191 @Override |
|
192 public Spliterator<E> spliterator() { |
|
193 return Spliterators.spliterator(this, Spliterator.DISTINCT | Spliterator.ORDERED); |
|
194 } |
|
195 } |