libjava/java/util/LinkedHashSet.java

   1 /* LinkedHashSet.java -- a set backed by a LinkedHashMap, for linked
   2    list traversal.
   3    Copyright (C) 2001, 2005  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., 59 Temple Place, Suite 330, Boston, MA
  20 02111-1307 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 extends HashSet
  92   implements Set, 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 loadFacor (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 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 init(int capacity, float load)
 156   {
 157     return new LinkedHashMap(capacity, load);
 158   }
 159
 160 }