How to Calculate Purch Totals in purchase order's Totals Form

How to Calculate Purch Totals in purchase order's Totals Form

class KK_PurchTotals
{     
    /// <summary>
    /// Runs the class with the specified arguments.
    /// </summary>
    /// <param name = "_args">The specified arguments.</param>
    public static void main(Args _args)
    {
        PurchTotals purchTotals;
        PurchTable  purchTable  = PurchTable::find('00000225');
        DiscAmount  discAmount;

        purchTotals = PurchTotals::newPurchTable(purchTable);
        purchTotals.calc();
        discAmount = purchTotals.purchTotalAmount();

        setPrefix('Purchase Order');
        info(strFmt('%1 - Total Value: %2', purchTable.PurchId, discAmount));
    }

}