Do you have five items you want to sell?

import javax.swing.JOptionPane; // To get windows panels

public class RetailSales 
{
  public static void main (String [] args)
  {
     // name of strings
    String OnlineSales = "Welcome to the online retailer choose"
                       + "choose the items you want to purchase";
    String MoreItemsToCalculate;
    String ProductNumber;
    
    // name of integers
    int TotalSaleItems = 0;
    int AmmountOfItems = 0;
    
    // Name of doubles
    double RetailTotal = 0.0;  // Retail Total goes here
    double Total = 0.0; // Total locally for switch
    
    //Price for products 
    final double ProductOne = 2.98;
    final double ProductTwo = 4.50;
    final double ProductThree = 3.98;
    final double ProductFour = 4.49;
    final double ProductFive = 6.87;

    
    // condition to while statement
    MoreItemsToCalculate = JOptionPane.showInputDialog 
    ("Welcome to our online retailer, are you ready to check out? ");
    MoreItemsToCalculate = MoreItemsToCalculate.toUpperCase();
    
    while (MoreItemsToCalculate.equals ("YES"))
    {
        ProductNumber = JOptionPane.showInputDialog
                ("Please select an item from the list \n" + 
                "Product 1, $2.98 \n" +
                "Product 2, $4.50 \n" +
                "Product 3, $3.98 \n" +
                "Product 4, $4.49 \n" +
                "Product 5, $6.87 \n");
        
        // check if the user cancelled out of program
        if (ProductNumber == null)
            {
                JOptionPane.showMessageDialog (null, "You have clicked on the cancel button, hope to see you soon.");
                System.exit (0); // exits loop
            }
        
        // check if there the input is empty
        else
            if (ProductNumber == (""))
            { 
                JOptionPane.showMessageDialog (null, "You must make an entry  in the input box");
                System.exit (0); // exits loop
            }
            
        // check if its a valid input type for product list   
        else
            if (Integer.parseInt (ProductNumber) < 1 | Integer.parseInt (ProductNumber) > 5)
            {
                JOptionPane.showMessageDialog (null, ProductNumber + "Is not a valid product number, try again");
                System.exit(0); // exits loop
            }              
        
        // Switch satement only allows intergers to be used
        switch(Integer.parseInt(ProductNumber)) 
        {
            case 1:
                AmmountOfItems = Integer.parseInt(JOptionPane.showInputDialog 
                       ("How many of this Items do you have?" ));
                Total = AmmountOfItems * ProductOne;
                TotalSaleItems = AmmountOfItems;  //keeps track of number of items
                RetailTotal = Total;              //keeps track of Retail Total
                break;
                   
            case 2:
                AmmountOfItems = Integer.parseInt(JOptionPane.showInputDialog 
                       ("How many of this Items do you have?" ));
                Total = AmmountOfItems * ProductTwo;
                TotalSaleItems = AmmountOfItems + TotalSaleItems;
                RetailTotal = Total + RetailTotal;
                break;
                
            case 3:
                AmmountOfItems = Integer.parseInt(JOptionPane.showInputDialog 
                       ("How many of this Items do you have?" ));
                Total = AmmountOfItems * ProductThree;
                TotalSaleItems = AmmountOfItems + TotalSaleItems;
                RetailTotal = Total + RetailTotal;
                break;
                
            case 4:
                AmmountOfItems = Integer.parseInt(JOptionPane.showInputDialog 
                       ("How many of this Items do you have?" ));
                Total = AmmountOfItems * ProductFour;
                TotalSaleItems = AmmountOfItems + TotalSaleItems;
                RetailTotal = Total + RetailTotal;
                break;
                
            case 5:
                AmmountOfItems = Integer.parseInt(JOptionPane.showInputDialog 
                       ("How many of this Items do you have?" ));
                Total = AmmountOfItems * ProductFive;
                TotalSaleItems = AmmountOfItems + TotalSaleItems;
                RetailTotal = Total + RetailTotal;
                break;
            default:
                JOptionPane.showMessageDialog
                        (null, ProductNumber + "- is not a valid product number try again.");     
        } //end of switch statement 
            
        
        MoreItemsToCalculate = JOptionPane.showInputDialog ("Do you want to add any more items?" );
        MoreItemsToCalculate = MoreItemsToCalculate.toUpperCase();
            
    } //end of while statement
        
        // displays the totals to screen
        JOptionPane.showMessageDialog (null, "Thank you for shopping with us\n\n"+
                                             "Total items: " + TotalSaleItems + "\n" +
                                             "Total: " + RetailTotal +"\n");
        System.exit(0); // exits loop
    
            
    
  }// end of main method 
}// end of RetailSales class