1 /* LinkedHashSet.java -- a set backed by a LinkedHashMap, for linked 2 list traversal. 3 Copyright (C) 2001, 2004, 2005, 2007 Free Software Foundation, Inc. 4 5 This file is part of GNU Classpath. 6 7 GNU Classpath is free software; you can redistribute it and/or modify 8 it under the terms of the GNU General Public License as published by 9 the Free Software Foundation; either version 2, or (at your option) 10 any later version. 11 12 GNU Classpath is distributed in the hope that it will be useful, but 13 WITHOUT ANY WARRANTY; without even the implied warranty of 14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 15 General Public License for more details. 16 17 You should have received a copy of the GNU General Public License 18 along with GNU Classpath; see the file COPYING. If not, write to the 19 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 20 02110-1301 USA. 21 22 Linking this library statically or dynamically with other modules is 23 making a combined work based on this library. Thus, the terms and 24 conditions of the GNU General Public License cover the whole 25 combination. 26 27 As a special exception, the copyright holders of this library give you 28 permission to link this library with independent modules to produce an 29 executable, regardless of the license terms of these independent 30 modules, and to copy and distribute the resulting executable under 31 terms of your choice, provided that you also meet, for each linked 32 independent module, the terms and conditions of the license of that 33 module. An independent module is a module which is not derived from 34 or based on this library. If you modify this library, you may extend 35 this exception to your version of the library, but you are not 36 obligated to do so. If you do not wish to do so, delete this 37 exception statement from your version. */ 38 39 40 package java.util; 41 42 import java.io.Serializable; 43 44 /** 45 * This class provides a hashtable-backed implementation of the 46 * Set interface, with predictable traversal order. 47 * <p> 48 * 49 * It uses a hash-bucket approach; that is, hash collisions are handled 50 * by linking the new node off of the pre-existing node (or list of 51 * nodes). In this manner, techniques such as linear probing (which 52 * can cause primary clustering) and rehashing (which does not fit very 53 * well with Java's method of precomputing hash codes) are avoided. In 54 * addition, this maintains a doubly-linked list which tracks insertion 55 * order. Note that the insertion order is not modified if an 56 * <code>add</code> simply reinserts an element in the set. 57 * <p> 58 * 59 * One of the nice features of tracking insertion order is that you can 60 * copy a set, and regardless of the implementation of the original, 61 * produce the same results when iterating over the copy. This is possible 62 * without needing the overhead of <code>TreeSet</code>. 63 * <p> 64 * 65 * Under ideal circumstances (no collisions), LinkedHashSet offers O(1) 66 * performance on most operations. In the worst case (all elements map 67 * to the same hash code -- very unlikely), most operations are O(n). 68 * <p> 69 * 70 * LinkedHashSet accepts the null entry. It is not synchronized, so if 71 * you need multi-threaded access, consider using:<br> 72 * <code>Set s = Collections.synchronizedSet(new LinkedHashSet(...));</code> 73 * <p> 74 * 75 * The iterators are <i>fail-fast</i>, meaning that any structural 76 * modification, except for <code>remove()</code> called on the iterator 77 * itself, cause the iterator to throw a 78 * {@link ConcurrentModificationException} rather than exhibit 79 * non-deterministic behavior. 80 * 81 * @author Eric Blake (ebb9@email.byu.edu) 82 * @see Object#hashCode() 83 * @see Collection 84 * @see Set 85 * @see HashSet 86 * @see TreeSet 87 * @see Collections#synchronizedSet(Set) 88 * @since 1.4 89 * @status updated to 1.4 90 */ 91 public class LinkedHashSet<T> extends HashSet<T> 92 implements Set<T>, Cloneable, Serializable 93 { 94 /** 95 * Compatible with JDK 1.4. 96 */ 97 private static final long serialVersionUID = -2851667679971038690L; 98 99 /** 100 * Construct a new, empty HashSet whose backing HashMap has the default 101 * capacity (11) and loadFactor (0.75). 102 */ LinkedHashSet()103 public LinkedHashSet() 104 { 105 super(); 106 } 107 108 /** 109 * Construct a new, empty HashSet whose backing HashMap has the supplied 110 * capacity and the default load factor (0.75). 111 * 112 * @param initialCapacity the initial capacity of the backing HashMap 113 * @throws IllegalArgumentException if the capacity is negative 114 */ LinkedHashSet(int initialCapacity)115 public LinkedHashSet(int initialCapacity) 116 { 117 super(initialCapacity); 118 } 119 120 /** 121 * Construct a new, empty HashSet whose backing HashMap has the supplied 122 * capacity and load factor. 123 * 124 * @param initialCapacity the initial capacity of the backing HashMap 125 * @param loadFactor the load factor of the backing HashMap 126 * @throws IllegalArgumentException if either argument is negative, or 127 * if loadFactor is POSITIVE_INFINITY or NaN 128 */ LinkedHashSet(int initialCapacity, float loadFactor)129 public LinkedHashSet(int initialCapacity, float loadFactor) 130 { 131 super(initialCapacity, loadFactor); 132 } 133 134 /** 135 * Construct a new HashSet with the same elements as are in the supplied 136 * collection (eliminating any duplicates, of course). The backing storage 137 * has twice the size of the collection, or the default size of 11, 138 * whichever is greater; and the default load factor (0.75). 139 * 140 * @param c a collection of initial set elements 141 * @throws NullPointerException if c is null 142 */ LinkedHashSet(Collection<? extends T> c)143 public LinkedHashSet(Collection<? extends T> c) 144 { 145 super(c); 146 } 147 148 /** 149 * Helper method which initializes the backing Map. 150 * 151 * @param capacity the initial capacity 152 * @param load the initial load factor 153 * @return the backing HashMap 154 */ init(int capacity, float load)155 HashMap<T, String> init(int capacity, float load) 156 { 157 return new LinkedHashMap<T, String>(capacity, load); 158 } 159 } 160