public void actionPerformed(ActionEvent e)
   {
      JButton b = (JButton)e.getSource();
      if (b == roll)
      {
         if (player.getCanRoll()) player.rollDice();
      }

      if (b == upgrade)
      {
         if (player.getCanUpgrade()) player.upgrade();
         else JOptionPane.showMessageDialog(null,"You have no properties to upgrade.","Nothing to upgrade!", JOptionPane.ERROR_MESSAGE);
      }

      if (b == fine)
      {
         if (player.getCanPayFine()) player.getOutOfJail();
         else JOptionPane.showMessageDialog(null,"You're not in jail.","No fines to pay!", JOptionPane.ERROR_MESSAGE);
      }

      if (b == end)
      {
         if (player.getCanRoll()) JOptionPane.showMessageDialog(null,"You haven't finished rolling.","Keep rolling!", JOptionPane.ERROR_MESSAGE);
         else if (player.endTurn())
         {
            playerNode = players.getNext(playerNode);
            takeATurn((Player)playerNode.getData());
         } 
      }
   }