Java tutorial
/* * Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.util; /** * <p>Hash table and linked list implementation of the {@code Set} interface, * with predictable iteration order. This implementation differs from * {@code HashSet} in that it maintains a doubly-linked list running through * all of its entries. This linked list defines the iteration ordering, * which is the order in which elements were inserted into the set * (<i>insertion-order</i>). Note that insertion order is <i>not</i> affected * if an element is <i>re-inserted</i> into the set. (An element {@code e} * is reinserted into a set {@code s} if {@code s.add(e)} is invoked when * {@code s.contains(e)} would return {@code true} immediately prior to * the invocation.) * * <p>This implementation spares its clients from the unspecified, generally * chaotic ordering provided by {@link HashSet}, without incurring the * increased cost associated with {@link TreeSet}. It can be used to * produce a copy of a set that has the same order as the original, regardless * of the original set's implementation: * <pre> * void foo(Set s) { * Set copy = new LinkedHashSet(s); * ... * } * </pre> * This technique is particularly useful if a module takes a set on input, * copies it, and later returns results whose order is determined by that of * the copy. (Clients generally appreciate having things returned in the same * order they were presented.) * * <p>This class provides all of the optional {@code Set} operations, and * permits null elements. Like {@code HashSet}, it provides constant-time * performance for the basic operations ({@code add}, {@code contains} and * {@code remove}), assuming the hash function disperses elements * properly among the buckets. Performance is likely to be just slightly * below that of {@code HashSet}, due to the added expense of maintaining the * linked list, with one exception: Iteration over a {@code LinkedHashSet} * requires time proportional to the <i>size</i> of the set, regardless of * its capacity. Iteration over a {@code HashSet} is likely to be more * expensive, requiring time proportional to its <i>capacity</i>. * * <p>A linked hash set has two parameters that affect its performance: * <i>initial capacity</i> and <i>load factor</i>. They are defined precisely * as for {@code HashSet}. Note, however, that the penalty for choosing an * excessively high value for initial capacity is less severe for this class * than for {@code HashSet}, as iteration times for this class are unaffected * by capacity. * * <p><strong>Note that this implementation is not synchronized.</strong> * If multiple threads access a linked hash set concurrently, and at least * one of the threads modifies the set, it <em>must</em> be synchronized * externally. This is typically accomplished by synchronizing on some * object that naturally encapsulates the set. * * If no such object exists, the set should be "wrapped" using the * {@link Collections#synchronizedSet Collections.synchronizedSet} * method. This is best done at creation time, to prevent accidental * unsynchronized access to the set: <pre> * Set s = Collections.synchronizedSet(new LinkedHashSet(...));</pre> * * <p>The iterators returned by this class's {@code iterator} method are * <em>fail-fast</em>: if the set is modified at any time after the iterator * is created, in any way except through the iterator's own {@code remove} * method, the iterator will throw a {@link ConcurrentModificationException}. * Thus, in the face of concurrent modification, the iterator fails quickly * and cleanly, rather than risking arbitrary, non-deterministic behavior at * an undetermined time in the future. * * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed * as it is, generally speaking, impossible to make any hard guarantees in the * presence of unsynchronized concurrent modification. Fail-fast iterators * throw {@code ConcurrentModificationException} on a best-effort basis. * Therefore, it would be wrong to write a program that depended on this * exception for its correctness: <i>the fail-fast behavior of iterators * should be used only to detect bugs.</i> * * <p>This class is a member of the * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> * Java Collections Framework</a>. * * @param <E> the type of elements maintained by this set * * @author Josh Bloch * @see Object#hashCode() * @see Collection * @see Set * @see HashSet * @see TreeSet * @see Hashtable * @since 1.4 */ public class LinkedHashSet<E> extends HashSet<E> implements Set<E>, Cloneable, java.io.Serializable { private static final long serialVersionUID = -2851667679971038690L; /** * Constructs a new, empty linked hash set with the specified initial * capacity and load factor. * * @param initialCapacity the initial capacity of the linked hash set * @param loadFactor the load factor of the linked hash set * @throws IllegalArgumentException if the initial capacity is less * than zero, or if the load factor is nonpositive */ public LinkedHashSet(int initialCapacity, float loadFactor) { super(initialCapacity, loadFactor, true); } /** * Constructs a new, empty linked hash set with the specified initial * capacity and the default load factor (0.75). * * @param initialCapacity the initial capacity of the LinkedHashSet * @throws IllegalArgumentException if the initial capacity is less * than zero */ public LinkedHashSet(int initialCapacity) { super(initialCapacity, .75f, true); } /** * Constructs a new, empty linked hash set with the default initial * capacity (16) and load factor (0.75). */ public LinkedHashSet() { super(16, .75f, true); } /** * Constructs a new linked hash set with the same elements as the * specified collection. The linked hash set is created with an initial * capacity sufficient to hold the elements in the specified collection * and the default load factor (0.75). * * @param c the collection whose elements are to be placed into * this set * @throws NullPointerException if the specified collection is null */ public LinkedHashSet(Collection<? extends E> c) { super(Math.max(2 * c.size(), 11), .75f, true); addAll(c); } /** * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em> * and <em>fail-fast</em> {@code Spliterator} over the elements in this set. * * <p>The {@code Spliterator} reports {@link Spliterator#SIZED}, * {@link Spliterator#DISTINCT}, and {@code ORDERED}. Implementations * should document the reporting of additional characteristic values. * * @implNote * The implementation creates a * <em><a href="Spliterator.html#binding">late-binding</a></em> spliterator * from the set's {@code Iterator}. The spliterator inherits the * <em>fail-fast</em> properties of the set's iterator. * The created {@code Spliterator} additionally reports * {@link Spliterator#SUBSIZED}. * * @return a {@code Spliterator} over the elements in this set * @since 1.8 */ @Override public Spliterator<E> spliterator() { return Spliterators.spliterator(this, Spliterator.DISTINCT | Spliterator.ORDERED); } }