libjava/java/util/AbstractSet.java

   1 /* AbstractSet.java -- Abstract implementation of most of Set
   2    Copyright (C) 1998, 2000, 2001, 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 /**
  42  * An abstract implementation of Set to make it easier to create your own
  43  * implementations. In order to create a Set, subclass AbstractSet and
  44  * implement the same methods that are required for AbstractCollection
  45  * (although these methods must of course meet the requirements that Set puts
  46  * on them - specifically, no element may be in the set more than once). This
  47  * class simply provides implementations of equals() and hashCode() to fulfil
  48  * the requirements placed on them by the Set interface.
  49  *
  50  * @author Original author unknown
  51  * @author Eric Blake (ebb9@email.byu.edu)
  52  * @see Collection
  53  * @see AbstractCollection
  54  * @see Set
  55  * @see HashSet
  56  * @see TreeSet
  57  * @see LinkedHashSet
  58  * @since 1.2
  59  * @status updated to 1.4
  60  */
  61 public abstract class AbstractSet extends AbstractCollection implements Set
  62 {
  63   /**
  64    * The main constructor, for use by subclasses.
  65    */
  66   protected AbstractSet()
  67   {
  68   }
  69
  70   /**
  71    * Tests whether the given object is equal to this Set. This implementation
  72    * first checks whether this set <em>is</em> the given object, and returns
  73    * true if so. Otherwise, if o is a Set and is the same size as this one, it
  74    * returns the result of calling containsAll on the given Set. Otherwise, it
  75    * returns false.
  76    *
  77    * @param o the Object to be tested for equality with this Set
  78    * @return true if the given object is equal to this Set
  79    */
  80   public boolean equals(Object o)
  81   {
  82     return (o == this ||
  83             (o instanceof Set && ((Set) o).size() == size()
  84              && containsAll((Collection) o)));
  85   }
  86
  87   /**
  88    * Returns a hash code for this Set. The hash code of a Set is the sum of the
  89    * hash codes of all its elements, except that the hash code of null is
  90    * defined to be zero. This implementation obtains an Iterator over the Set,
  91    * and sums the results.
  92    *
  93    * @return a hash code for this Set
  94    */
  95   public int hashCode()
  96   {
  97     Iterator itr = iterator();
  98     int hash = 0;
  99     int pos = size();
 100     while (--pos >= 0)
 101       hash += hashCode(itr.next());
 102     return hash;
 103   }
 104
 105   /**
 106    * Removes from this set all elements in the given collection (optional
 107    * operation). This implementation uses <code>size()</code> to determine
 108    * the smaller collection.  Then, if this set is smaller, it iterates
 109    * over the set, calling Iterator.remove if the collection contains
 110    * the element.  If this set is larger, it iterates over the collection,
 111    * calling Set.remove for all elements in the collection. Note that
 112    * this operation will fail if a remove methods is not supported.
 113    *
 114    * @param c the collection of elements to remove
 115    * @return true if the set was modified as a result
 116    * @throws UnsupportedOperationException if remove is not supported
 117    * @throws NullPointerException if the collection is null
 118    * @see AbstractCollection#remove(Object)
 119    * @see Collection#contains(Object)
 120    * @see Iterator#remove()
 121    */
 122   public boolean removeAll(Collection c)
 123   {
 124     int oldsize = size();
 125     int count = c.size();
 126     Iterator i;
 127     if (oldsize < count)
 128       {
 129         for (i = iterator(), count = oldsize; count > 0; count--)
 130           if (c.contains(i.next()))
 131             i.remove();
 132       }
 133     else
 134       for (i = c.iterator(); count > 0; count--)
 135         remove(i.next());
 136     return oldsize != size();
 137   }
 138
 139 }