libjava/java/util/HashSet.java

   1 /* HashSet.java -- a class providing a HashMap-backed Set
   2    Copyright (C) 1998, 1999, 2001, 2004, 2005  Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38
  39 package java.util;
  40
  41 import java.io.IOException;
  42 import java.io.ObjectInputStream;
  43 import java.io.ObjectOutputStream;
  44 import java.io.Serializable;
  45
  46 /**
  47  * This class provides a HashMap-backed implementation of the Set interface.
  48  * <p>
  49  *
  50  * Most operations are O(1), assuming no hash collisions.  In the worst
  51  * case (where all hashes collide), operations are O(n). Setting the
  52  * initial capacity too low will force many resizing operations, but
  53  * setting the initial capacity too high (or loadfactor too low) leads
  54  * to wasted memory and slower iteration.
  55  * <p>
  56  *
  57  * HashSet accepts the null key and null values.  It is not synchronized,
  58  * so if you need multi-threaded access, consider using:<br>
  59  * <code>Set s = Collections.synchronizedSet(new HashSet(...));</code>
  60  * <p>
  61  *
  62  * The iterators are <i>fail-fast</i>, meaning that any structural
  63  * modification, except for <code>remove()</code> called on the iterator
  64  * itself, cause the iterator to throw a
  65  * {@link ConcurrentModificationException} rather than exhibit
  66  * non-deterministic behavior.
  67  *
  68  * @author Jon Zeppieri
  69  * @author Eric Blake (ebb9@email.byu.edu)
  70  * @see Collection
  71  * @see Set
  72  * @see TreeSet
  73  * @see Collections#synchronizedSet(Set)
  74  * @see HashMap
  75  * @see LinkedHashSet
  76  * @since 1.2
  77  * @status updated to 1.4
  78  */
  79 public class HashSet extends AbstractSet
  80   implements Set, Cloneable, Serializable
  81 {
  82   /**
  83    * Compatible with JDK 1.2.
  84    */
  85   private static final long serialVersionUID = -5024744406713321676L;
  86
  87   /**
  88    * The HashMap which backs this Set.
  89    */
  90   private transient HashMap map;
  91
  92   /**
  93    * Construct a new, empty HashSet whose backing HashMap has the default
  94    * capacity (11) and loadFacor (0.75).
  95    */
  96   public HashSet()
  97   {
  98     this(HashMap.DEFAULT_CAPACITY, HashMap.DEFAULT_LOAD_FACTOR);
  99   }
 100
 101   /**
 102    * Construct a new, empty HashSet whose backing HashMap has the supplied
 103    * capacity and the default load factor (0.75).
 104    *
 105    * @param initialCapacity the initial capacity of the backing HashMap
 106    * @throws IllegalArgumentException if the capacity is negative
 107    */
 108   public HashSet(int initialCapacity)
 109   {
 110     this(initialCapacity, HashMap.DEFAULT_LOAD_FACTOR);
 111   }
 112
 113   /**
 114    * Construct a new, empty HashSet whose backing HashMap has the supplied
 115    * capacity and load factor.
 116    *
 117    * @param initialCapacity the initial capacity of the backing HashMap
 118    * @param loadFactor the load factor of the backing HashMap
 119    * @throws IllegalArgumentException if either argument is negative, or
 120    *         if loadFactor is POSITIVE_INFINITY or NaN
 121    */
 122   public HashSet(int initialCapacity, float loadFactor)
 123   {
 124     map = init(initialCapacity, loadFactor);
 125   }
 126
 127   /**
 128    * Construct a new HashSet with the same elements as are in the supplied
 129    * collection (eliminating any duplicates, of course). The backing storage
 130    * has twice the size of the collection, or the default size of 11,
 131    * whichever is greater; and the default load factor (0.75).
 132    *
 133    * @param c a collection of initial set elements
 134    * @throws NullPointerException if c is null
 135    */
 136   public HashSet(Collection c)
 137   {
 138     this(Math.max(2 * c.size(), HashMap.DEFAULT_CAPACITY));
 139     addAll(c);
 140   }
 141
 142   /**
 143    * Adds the given Object to the set if it is not already in the Set.
 144    * This set permits a null element.
 145    *
 146    * @param o the Object to add to this Set
 147    * @return true if the set did not already contain o
 148    */
 149   public boolean add(Object o)
 150   {
 151     return map.put(o, "") == null;
 152   }
 153
 154   /**
 155    * Empties this Set of all elements; this takes constant time.
 156    */
 157   public void clear()
 158   {
 159     map.clear();
 160   }
 161
 162   /**
 163    * Returns a shallow copy of this Set. The Set itself is cloned; its
 164    * elements are not.
 165    *
 166    * @return a shallow clone of the set
 167    */
 168   public Object clone()
 169   {
 170     HashSet copy = null;
 171     try
 172       {
 173         copy = (HashSet) super.clone();
 174       }
 175     catch (CloneNotSupportedException x)
 176       {
 177         // Impossible to get here.
 178       }
 179     copy.map = (HashMap) map.clone();
 180     return copy;
 181   }
 182
 183   /**
 184    * Returns true if the supplied element is in this Set.
 185    *
 186    * @param o the Object to look for
 187    * @return true if it is in the set
 188    */
 189   public boolean contains(Object o)
 190   {
 191     return map.containsKey(o);
 192   }
 193
 194   /**
 195    * Returns true if this set has no elements in it.
 196    *
 197    * @return <code>size() == 0</code>.
 198    */
 199   public boolean isEmpty()
 200   {
 201     return map.size == 0;
 202   }
 203
 204   /**
 205    * Returns an Iterator over the elements of this Set, which visits the
 206    * elements in no particular order.  For this class, the Iterator allows
 207    * removal of elements. The iterator is fail-fast, and will throw a
 208    * ConcurrentModificationException if the set is modified externally.
 209    *
 210    * @return a set iterator
 211    * @see ConcurrentModificationException
 212    */
 213   public Iterator iterator()
 214   {
 215     // Avoid creating intermediate keySet() object by using non-public API.
 216     return map.iterator(HashMap.KEYS);
 217   }
 218
 219   /**
 220    * Removes the supplied Object from this Set if it is in the Set.
 221    *
 222    * @param o the object to remove
 223    * @return true if an element was removed
 224    */
 225   public boolean remove(Object o)
 226   {
 227     return (map.remove(o) != null);
 228   }
 229
 230   /**
 231    * Returns the number of elements in this Set (its cardinality).
 232    *
 233    * @return the size of the set
 234    */
 235   public int size()
 236   {
 237     return map.size;
 238   }
 239
 240   /**
 241    * Helper method which initializes the backing Map. Overridden by
 242    * LinkedHashSet for correct semantics.
 243    *
 244    * @param capacity the initial capacity
 245    * @param load the initial load factor
 246    * @return the backing HashMap
 247    */
 248   HashMap init(int capacity, float load)
 249   {
 250     return new HashMap(capacity, load);
 251   }
 252
 253   /**
 254    * Serializes this object to the given stream.
 255    *
 256    * @param s the stream to write to
 257    * @throws IOException if the underlying stream fails
 258    * @serialData the <i>capacity</i> (int) and <i>loadFactor</i> (float)
 259    *             of the backing store, followed by the set size (int),
 260    *             then a listing of its elements (Object) in no order
 261    */
 262   private void writeObject(ObjectOutputStream s) throws IOException
 263   {
 264     s.defaultWriteObject();
 265     // Avoid creating intermediate keySet() object by using non-public API.
 266     Iterator it = map.iterator(HashMap.KEYS);
 267     s.writeInt(map.buckets.length);
 268     s.writeFloat(map.loadFactor);
 269     s.writeInt(map.size);
 270     while (it.hasNext())
 271       s.writeObject(it.next());
 272   }
 273
 274   /**
 275    * Deserializes this object from the given stream.
 276    *
 277    * @param s the stream to read from
 278    * @throws ClassNotFoundException if the underlying stream fails
 279    * @throws IOException if the underlying stream fails
 280    * @serialData the <i>capacity</i> (int) and <i>loadFactor</i> (float)
 281    *             of the backing store, followed by the set size (int),
 282    *             then a listing of its elements (Object) in no order
 283    */
 284   private void readObject(ObjectInputStream s)
 285     throws IOException, ClassNotFoundException
 286   {
 287     s.defaultReadObject();
 288
 289     map = init(s.readInt(), s.readFloat());
 290     for (int size = s.readInt(); size > 0; size--)
 291       map.put(s.readObject(), "");
 292   }
 293 }