Source for java.util.AbstractSet

   1: /* AbstractSet.java -- Abstract implementation of most of Set
   2:    Copyright (C) 1998, 2000, 2001, 2004, 2005
   3:    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., 51 Franklin Street, Fifth Floor, Boston, MA
  20: 02110-1301 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: /**
  43:  * An abstract implementation of Set to make it easier to create your own
  44:  * implementations. In order to create a Set, subclass AbstractSet and
  45:  * implement the same methods that are required for AbstractCollection
  46:  * (although these methods must of course meet the requirements that Set puts
  47:  * on them - specifically, no element may be in the set more than once). This
  48:  * class simply provides implementations of equals() and hashCode() to fulfil
  49:  * the requirements placed on them by the Set interface.
  50:  *
  51:  * @author Original author unknown
  52:  * @author Eric Blake (ebb9@email.byu.edu)
  53:  * @see Collection
  54:  * @see AbstractCollection
  55:  * @see Set
  56:  * @see HashSet
  57:  * @see TreeSet
  58:  * @see LinkedHashSet
  59:  * @since 1.2
  60:  * @status updated to 1.4
  61:  */
  62: public abstract class AbstractSet<E>
  63:   extends AbstractCollection<E>
  64:   implements Set<E>
  65: {
  66:   /**
  67:    * The main constructor, for use by subclasses.
  68:    */
  69:   protected AbstractSet()
  70:   {
  71:   }
  72: 
  73:   /**
  74:    * Tests whether the given object is equal to this Set. This implementation
  75:    * first checks whether this set <em>is</em> the given object, and returns
  76:    * true if so. Otherwise, if o is a Set and is the same size as this one, it
  77:    * returns the result of calling containsAll on the given Set. Otherwise, it
  78:    * returns false.
  79:    *
  80:    * @param o the Object to be tested for equality with this Set
  81:    * @return true if the given object is equal to this Set
  82:    */
  83:   public boolean equals(Object o)
  84:   {
  85:     return (o == this
  86:         || (o instanceof Set && ((Set) o).size() == size()
  87:         && containsAll((Collection) o)));
  88:   }
  89: 
  90:   /**
  91:    * Returns a hash code for this Set. The hash code of a Set is the sum of the
  92:    * hash codes of all its elements, except that the hash code of null is
  93:    * defined to be zero. This implementation obtains an Iterator over the Set,
  94:    * and sums the results.
  95:    *
  96:    * @return a hash code for this Set
  97:    */
  98:   public int hashCode()
  99:   {
 100:     Iterator<E> itr = iterator();
 101:     int hash = 0;
 102:     int pos = size();
 103:     while (--pos >= 0)
 104:       hash += hashCode(itr.next());
 105:     return hash;
 106:   }
 107: 
 108:   /**
 109:    * Removes from this set all elements in the given collection (optional
 110:    * operation). This implementation uses <code>size()</code> to determine
 111:    * the smaller collection.  Then, if this set is smaller, it iterates
 112:    * over the set, calling Iterator.remove if the collection contains
 113:    * the element.  If this set is larger, it iterates over the collection,
 114:    * calling Set.remove for all elements in the collection. Note that
 115:    * this operation will fail if a remove methods is not supported.
 116:    *
 117:    * @param c the collection of elements to remove
 118:    * @return true if the set was modified as a result
 119:    * @throws UnsupportedOperationException if remove is not supported
 120:    * @throws NullPointerException if the collection is null
 121:    * @see AbstractCollection#remove(Object)
 122:    * @see Collection#contains(Object)
 123:    * @see Iterator#remove()
 124:    */
 125:   public boolean removeAll(Collection<?> c)
 126:   {
 127:     int oldsize = size();
 128:     int count = c.size();
 129:     if (oldsize < count)
 130:       {
 131:     Iterator<E> i;
 132:     for (i = iterator(), count = oldsize; count > 0; count--)
 133:       {
 134:         if (c.contains(i.next()))
 135:           i.remove();
 136:       }
 137:       }
 138:     else
 139:       {
 140:     Iterator<?> i;
 141:     for (i = c.iterator(); count > 0; count--)
 142:       remove(i.next());
 143:       }
 144:     return oldsize != size();
 145:   }
 146: }