@Override
    public Object getValueAt(int rowIndex, int columnIndex) {
        InvoiceItem item = (InvoiceItem) data.toArray()[rowIndex];
        double price = item.getPrice();
        switch (columnIndex) {
            case 0:
                return item.getArticlename();
            case 1:
                return item.getTaxes();
            case 2:
                return item.getAmount();
            case 3:
                return price;
            case 4:
//                return price * item.getAmount() * (1 + (item.getArticle().getTaxes() / 100));
                return price * item.getAmount();

            default:
                return "Error";
        }
    }