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+/* AbstractSet.java -- Abstract implementation of most of Set
+   Copyright (C) 1998 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., 59 Temple Place, Suite 330, Boston, MA
+02111-1307 USA.
+
+As a special exception, if you link this library with other files to
+produce an executable, this library does not by itself cause the
+resulting executable to be covered by the GNU General Public License.
+This exception does not however invalidate any other reasons why the
+executable file might be covered by the GNU General Public License. */
+
+
+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.
+ */
+public abstract class AbstractSet extends AbstractCollection implements Set {
+
+  /**
+   * 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) {
+    if (o == this) {
+      return true;
+    } else if (o instanceof Set && ((Set)o).size() == size()) {
+      throw new Error ("FIXME: compiler error - AbstractSet.equals");
+      /*  FIXME: this is the correct implementation, but a compiler
+	  error prevents us from building it.
+	  return containsAll((Collection)o);  */
+    } else {
+      return false;
+    }
+  }
+
+  /**
+   * 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() {
+    int hash = 0;
+    Iterator i = iterator();
+    while (i.hasNext()) {
+      try {
+        hash += i.next().hashCode();
+      } catch (NullPointerException e) {
+      }
+    }
+    return hash;
+  }
+}