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+/* AbstractSet.java -- Abstract implementation of most of Set
+   Copyright (C) 1998, 2000, 2001, 2004, 2005
+   Free Software Foundation, Inc.
+
+This file is part of GNU Classpath.
+
+GNU Classpath is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+
+GNU Classpath is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Classpath; see the file COPYING.  If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 USA.
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library.  Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module.  An independent module is a module which is not derived from
+or based on this library.  If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so.  If you do not wish to do so, delete this
+exception statement from your version. */
+
+
+package java.util;
+
+/**
+ * An abstract implementation of Set to make it easier to create your own
+ * implementations. In order to create a Set, subclass AbstractSet and
+ * implement the same methods that are required for AbstractCollection
+ * (although these methods must of course meet the requirements that Set puts
+ * on them - specifically, no element may be in the set more than once). This
+ * class simply provides implementations of equals() and hashCode() to fulfil
+ * the requirements placed on them by the Set interface.
+ *
+ * @author Original author unknown
+ * @author Eric Blake (ebb9@email.byu.edu)
+ * @see Collection
+ * @see AbstractCollection
+ * @see Set
+ * @see HashSet
+ * @see TreeSet
+ * @see LinkedHashSet
+ * @since 1.2
+ * @status updated to 1.4
+ */
+public abstract class AbstractSet<E>
+  extends AbstractCollection<E>
+  implements Set<E>
+{
+  /**
+   * The main constructor, for use by subclasses.
+   */
+  protected AbstractSet()
+  {
+  }
+
+  /**
+   * Tests whether the given object is equal to this Set. This implementation
+   * first checks whether this set <em>is</em> the given object, and returns
+   * true if so. Otherwise, if o is a Set and is the same size as this one, it
+   * returns the result of calling containsAll on the given Set. Otherwise, it
+   * returns false.
+   *
+   * @param o the Object to be tested for equality with this Set
+   * @return true if the given object is equal to this Set
+   */
+  public boolean equals(Object o)
+  {
+    return (o == this
+            || (o instanceof Set && ((Set) o).size() == size()
+                && containsAll((Collection) o)));
+  }
+
+  /**
+   * Returns a hash code for this Set. The hash code of a Set is the sum of the
+   * hash codes of all its elements, except that the hash code of null is
+   * defined to be zero. This implementation obtains an Iterator over the Set,
+   * and sums the results.
+   *
+   * @return a hash code for this Set
+   */
+  public int hashCode()
+  {
+    Iterator<E> itr = iterator();
+    int hash = 0;
+    int pos = size();
+    while (--pos >= 0)
+      hash += hashCode(itr.next());
+    return hash;
+  }
+
+  /**
+   * Removes from this set all elements in the given collection (optional
+   * operation). This implementation uses <code>size()</code> to determine
+   * the smaller collection.  Then, if this set is smaller, it iterates
+   * over the set, calling Iterator.remove if the collection contains
+   * the element.  If this set is larger, it iterates over the collection,
+   * calling Set.remove for all elements in the collection. Note that
+   * this operation will fail if a remove methods is not supported.
+   *
+   * @param c the collection of elements to remove
+   * @return true if the set was modified as a result
+   * @throws UnsupportedOperationException if remove is not supported
+   * @throws NullPointerException if the collection is null
+   * @see AbstractCollection#remove(Object)
+   * @see Collection#contains(Object)
+   * @see Iterator#remove()
+   */
+  public boolean removeAll(Collection<?> c)
+  {
+    int oldsize = size();
+    int count = c.size();
+    if (oldsize < count)
+      {
+        Iterator<E> i;
+        for (i = iterator(), count = oldsize; count > 0; count--)
+          {
+            if (c.contains(i.next()))
+              i.remove();
+          }
+      }
+    else
+      {
+        Iterator<?> i;
+        for (i = c.iterator(); count > 0; count--)
+          remove(i.next());
+      }
+    return oldsize != size();
+  }
+}