Factory Design pattern

problem Without Factory :

• A lot new Keyword, need to add  a lot code in future.
• Client know all the invoice type.

public interface IInvoice

{

    void print();

}    

public class InvoiceWithoutHeader : IInvoice

{

    public void print()

    {

        Console.WriteLine("Invoice Without Header");

    }

}

public class InvoiceWithHeader : IInvoice

{

    public void print()

    {

        Console.WriteLine("Invoice With Header");

    }

}

public class FactoryInvoice

{

      public static IInvoice GetInvoice(int invoiceType)

      {

        IInvoice result = null;

        switch (invoiceType)

        {

            case 1:

                result = new InvoiceWithHeader();

                break;

            case 2:

                result = new InvoiceWithoutHeader();

                break;

            default:

                break;

        }

        return result;

       }

}

static void Main(string[] args)

{

            IInvoice invoice;

            invoice = FactoryInvoice.GetInvoice(1);

            invoice.print();

            IInvoice invoice2;

            invoice2 = FactoryInvoice.GetInvoice(2);

            invoice2.print();

            Console.ReadLine();

}