The code for the InvoiceApp class

import java.util.Scanner;

public class InvoiceApp
{
    public static Invoice invoice = new Invoice();

    public static void main(String args[])
    {
        System.out.println("Welcome to the invoice application.\n");
        getLineItems();
        displayInvoice();
    }

    public static void getLineItems()
    {
        Scanner sc = new Scanner(System.in);
        String choice = "y";
        while (choice.equalsIgnoreCase("y"))
        {
            // get the input from the user
            String productCode = Validator.getString(sc,
                "Enter product code: ");
            int quantity = Validator.getInt(sc,
                "Enter quantity:     ", 0, 1000);
            Product product = ProductDB.getProduct(productCode);
            invoice.addItem(new LineItem(product, quantity));

            // see if the user wants to continue
            choice = Validator.getString(sc, "Another line item?
                (y/n): ");
            System.out.println();
        }
     }

    public static void displayInvoice()
    {
        System.out.println(
            "Code\tDescription\t\t\tPrice\tQty\tTotal");
        System.out.println(
            "----\t-----------\t\t\t-----\t---\t-----");
        for (LineItem lineItem : invoice.getLineItems())
        {
            Product product = lineItem.getProduct();
            String s = product.getCode()
                + "\t" + product.getDescription()
                + "\t" + product.getFormattedPrice()
                + "\t" + lineItem.getQuantity()
                + "\t" + lineItem.getFormattedTotal();
            System.out.println(s);
        }
        System.out.println("\n\t\t\t\t\tInvoice total:\t"
            + invoice.getFormattedTotal() + "\n");
    }
}