display method to get invoice ID in purchtable

I have to get PO number and invoice number in the report and hoping to make display method on purchtable  table  so wanted to create  a display over there 

 invoiceid is in vendinvoicejour table and purchtable.purchid==vendinvoicejour.purchid

so created this wanted to know isit correct ????

display public   VendInvoiceId getinvoiveid()

{

       VendInvoicejour           vendInvoicejour;

       //declare the invoice table

          ;

    if (this.PurchStatus == PurchStatus::Invoiced || this.existInvoice() || this.isInvoiceMatched())

//if the status is invoiced  or already invoiced or invoice matched  then only fetch he invoice id 

    {

        return vendInvoicejour.invoiceid;

    }

         return vendInvoicejour.invoiceid;

}