Source for java.util.AbstractSet

   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., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 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: }