//i get the problem but how to change it :(


private void tableSaleKeyPressed(java.awt.event.KeyEvent evt) { //this line is auto generated so cannot change


        tableSale.getModel().addTableModelListener( new TableModelListener() {

        @Override
        public void tableChanged(TableModelEvent evt) {
            if (evt.getType() == TableModelEvent.UPDATE) {

                int row = evt.getFirstRow();
                int column = evt.getColumn();
                if (column == 6 ) {
                    TableModel model = tableSale.getModel();

                    double cost = ( model.getValueAt(row, 3)==null)?0:((double)model.getValueAt(row, 3));
                    double quantity = ( model.getValueAt(row, 4)==null)?0:((double) model.getValueAt(row, 4));
                    double discount = ( model.getValueAt(row, 5)==null)?0:((double) model.getValueAt(row, 5));


                    double total = new Double ((quantity * cost)-discount);
                    System.out.println("pppppppp"+total);
                    model.setValueAt(total, row, 6);

                }
            }
        }
    });
    }