public void deleteGroup( int id )
	   {
	     try
	     {
	       PreparedStatement ps = con.prepareStatement( "DELETE FROM groups WHERE id=?" );
	       ps.setInt( 1, id );
	       ps.executeUpdate();
	       ps.close();
	     }
	     catch( SQLException e )
	     { 
	       e.printStackTrace(); 
	     }
	   }