001 /* LinkedHashSet.java -- a set backed by a LinkedHashMap, for linked 002 list traversal. 003 Copyright (C) 2001, 2004, 2005, 2007 Free Software Foundation, Inc. 004 005 This file is part of GNU Classpath. 006 007 GNU Classpath is free software; you can redistribute it and/or modify 008 it under the terms of the GNU General Public License as published by 009 the Free Software Foundation; either version 2, or (at your option) 010 any later version. 011 012 GNU Classpath is distributed in the hope that it will be useful, but 013 WITHOUT ANY WARRANTY; without even the implied warranty of 014 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 015 General Public License for more details. 016 017 You should have received a copy of the GNU General Public License 018 along with GNU Classpath; see the file COPYING. If not, write to the 019 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 020 02110-1301 USA. 021 022 Linking this library statically or dynamically with other modules is 023 making a combined work based on this library. Thus, the terms and 024 conditions of the GNU General Public License cover the whole 025 combination. 026 027 As a special exception, the copyright holders of this library give you 028 permission to link this library with independent modules to produce an 029 executable, regardless of the license terms of these independent 030 modules, and to copy and distribute the resulting executable under 031 terms of your choice, provided that you also meet, for each linked 032 independent module, the terms and conditions of the license of that 033 module. An independent module is a module which is not derived from 034 or based on this library. If you modify this library, you may extend 035 this exception to your version of the library, but you are not 036 obligated to do so. If you do not wish to do so, delete this 037 exception statement from your version. */ 038 039 040 package java.util; 041 042 import java.io.Serializable; 043 044 /** 045 * This class provides a hashtable-backed implementation of the 046 * Set interface, with predictable traversal order. 047 * <p> 048 * 049 * It uses a hash-bucket approach; that is, hash collisions are handled 050 * by linking the new node off of the pre-existing node (or list of 051 * nodes). In this manner, techniques such as linear probing (which 052 * can cause primary clustering) and rehashing (which does not fit very 053 * well with Java's method of precomputing hash codes) are avoided. In 054 * addition, this maintains a doubly-linked list which tracks insertion 055 * order. Note that the insertion order is not modified if an 056 * <code>add</code> simply reinserts an element in the set. 057 * <p> 058 * 059 * One of the nice features of tracking insertion order is that you can 060 * copy a set, and regardless of the implementation of the original, 061 * produce the same results when iterating over the copy. This is possible 062 * without needing the overhead of <code>TreeSet</code>. 063 * <p> 064 * 065 * Under ideal circumstances (no collisions), LinkedHashSet offers O(1) 066 * performance on most operations. In the worst case (all elements map 067 * to the same hash code -- very unlikely), most operations are O(n). 068 * <p> 069 * 070 * LinkedHashSet accepts the null entry. It is not synchronized, so if 071 * you need multi-threaded access, consider using:<br> 072 * <code>Set s = Collections.synchronizedSet(new LinkedHashSet(...));</code> 073 * <p> 074 * 075 * The iterators are <i>fail-fast</i>, meaning that any structural 076 * modification, except for <code>remove()</code> called on the iterator 077 * itself, cause the iterator to throw a 078 * {@link ConcurrentModificationException} rather than exhibit 079 * non-deterministic behavior. 080 * 081 * @author Eric Blake (ebb9@email.byu.edu) 082 * @see Object#hashCode() 083 * @see Collection 084 * @see Set 085 * @see HashSet 086 * @see TreeSet 087 * @see Collections#synchronizedSet(Set) 088 * @since 1.4 089 * @status updated to 1.4 090 */ 091 public class LinkedHashSet<T> extends HashSet<T> 092 implements Set<T>, Cloneable, Serializable 093 { 094 /** 095 * Compatible with JDK 1.4. 096 */ 097 private static final long serialVersionUID = -2851667679971038690L; 098 099 /** 100 * Construct a new, empty HashSet whose backing HashMap has the default 101 * capacity (11) and loadFactor (0.75). 102 */ 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 */ 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 */ 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 */ 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 */ 155 HashMap<T, String> init(int capacity, float load) 156 { 157 return new LinkedHashMap<T, String>(capacity, load); 158 } 159 }