Beginner programmer here and I am lost on a project for a class. I have to develop a Java application that calculates the monthly paychecks for a numbe of different types of employees. The employee types are created in a subclass array based on parent base class Employee. The initial code is provided for each class and for a driver class.
This is what I have so far:
The program is supposed to ask me what kind of employee I am, for my first name, last name, ssn, and depending on my employee type my salary, etc. I have no idea what I am doing, could someone please take a look and let me know where my goofs are or if I am on the right path. Thus far it does not keep my information so I think my loop is goofed, and it does not print out the information I supplied.
This is what happens when I run the program and enter 1 for salaried employee, it pops up with the box for the information, I imput all that it asks for then it ask me what kind of employee I am again, when I press cancel I get this:

 ----jGRASP exec: java PayrollSystemTest1

Exception in thread "main" java.lang.NumberFormatException: null
    at java.lang.Integer.parseInt(Integer.java:454)
    at java.lang.Integer.parseInt(Integer.java:527)
    at PayrollSystemTest1.main(PayrollSystemTest1.java:47)

 ----jGRASP wedge2: exit code for process is 1.
 ----jGRASP: operation complete.

Thanks for any help.

//PayrollSystemTest.java
//Employee hierarchy test program.
import javax.swing.*;
public class PayrollSystemTest1

{
   public static void main( String args[])

   {

     SalariedEmployee salariedEmployee=   
         new SalariedEmployee("John", "Smith", "111-11-1111", 800.00);
      HourlyEmployee hourlyEmployee=
         new HourlyEmployee("Karen", "Price", "222-22-2222", 16.75, 40);
      CommissionEmployee commissionEmployee=
         new CommissionEmployee("Sue", "Jones", "333-33-3333", 10000, .06);
      BasePlusCommissionEmployee basePlusCommissionEmployee=
         new BasePlusCommissionEmployee("Bob", "Lewis", "444-44-4444", 5000, .04, 300);

     //create four-element Employee array
     Employee employees[] = new Employee[4];


     //declarations
     String first = " ";
     String last = " ";
     String ssn = " ";
     String salaryString;
     double salary = 0;
     String wageString;
     double wage = 0;
     String hoursString;
     int hours = 0;
     String salesString;
     double sales = 0;
     String rateString;
     double rate =0;
     String empTypeString = " ";
     int empType = 0;
     int count = 0;

     for (count = 0; count < 5; count++)

     {
         empTypeString = JOptionPane.showInputDialog
         (null, "Please enter the type of employee you are: \n\nEnter the number that is your employee type\n1. Salaried\n2. Hourly\n3. Commission\n 4. Base Pay Plus Commission", JOptionPane.QUESTION_MESSAGE);
         empType = Integer.parseInt(empTypeString);

         switch(empType)

      {
         case 1:
            first = JOptionPane.showInputDialog
            (null, "Please enter your first name: ", "First Name", JOptionPane.QUESTION_MESSAGE);
            last = JOptionPane.showInputDialog
            (null, "Please enter your last name: ", "Last Name", JOptionPane.QUESTION_MESSAGE);
            ssn = JOptionPane.showInputDialog
            (null, "Please enter your Social Security Number: ", JOptionPane.QUESTION_MESSAGE);
            salaryString = JOptionPane.showInputDialog
            (null, "Please enter your weekly salary: ", "Salary", JOptionPane.QUESTION_MESSAGE);
            salary = Double.parseDouble(salaryString);
            break;

         case 2:
            first = JOptionPane.showInputDialog
            (null, "Please enter your first name: ", "First Name", JOptionPane.QUESTION_MESSAGE);
            last = JOptionPane.showInputDialog
            (null, "Please enter your last name: ", "Last Name", JOptionPane.QUESTION_MESSAGE);
            ssn = JOptionPane.showInputDialog
            (null, "Please enter your Social Security Number: ", JOptionPane.QUESTION_MESSAGE);
            wageString = JOptionPane.showInputDialog
            (null, "Please enter your hourly wage: ", "Hourly Wage", JOptionPane.QUESTION_MESSAGE);
            wage = Double.parseDouble(wageString);
            hoursString = JOptionPane.showInputDialog
            (null, "Please enter the hours worked: ", JOptionPane.QUESTION_MESSAGE);
            hours = Integer.parseInt(hoursString);
            break;

         case 3:
            first = JOptionPane.showInputDialog
            (null, "Please enter your first name: ", "First Name", JOptionPane.QUESTION_MESSAGE);
            last = JOptionPane.showInputDialog
            (null, "Please enter your last name: ", "Last Name", JOptionPane.QUESTION_MESSAGE);
            ssn = JOptionPane.showInputDialog
            (null, "Please enter your Social Security Number: ", JOptionPane.QUESTION_MESSAGE);
            salesString = JOptionPane.showInputDialog
            (null, "Please enter your gross weekly sales: ", "GrossSales",JOptionPane.QUESTION_MESSAGE);
            sales = Double.parseDouble(salesString);
            rateString = JOptionPane.showInputDialog
            (null, "Plese enter the % of commission you receive: ", "Commission Rate", JOptionPane.QUESTION_MESSAGE);
            rate = Double.parseDouble(rateString);            
            break;

          case 4:
            first = JOptionPane.showInputDialog
            (null, "Please enter your first name: ", "First Name", JOptionPane.QUESTION_MESSAGE);
            last = JOptionPane.showInputDialog
            (null, "Please enter your last name: ", "Last Name", JOptionPane.QUESTION_MESSAGE);
            ssn = JOptionPane.showInputDialog
            (null, "Please enter your Social Security Number: ", JOptionPane.QUESTION_MESSAGE);
            salesString = JOptionPane.showInputDialog
            (null, "Please enter your gross weekly sales: ", "GrossSales",JOptionPane.QUESTION_MESSAGE);
            sales = Double.parseDouble(salesString);
            rateString = JOptionPane.showInputDialog
            (null, "Please enter the % of commission you receive: ", "Commission Rate", JOptionPane.QUESTION_MESSAGE);
            rate = Double.parseDouble(rateString);   
            salaryString = JOptionPane.showInputDialog
            (null, "Please enter your base pay: ", "Base Pay", JOptionPane.QUESTION_MESSAGE);
            salary = Double.parseDouble(salaryString);
            break;

         default:
            JOptionPane.showInputDialog
            (null, "That is invalid", JOptionPane.ERROR_MESSAGE);


      }   
         switch (count)
         {
            case 1: 
            employees[0] = new SalariedEmployee(first, last, ssn, salary);
            break;

            case 2: 
            employees[1] = new HourlyEmployee(first, last, ssn, wage, hours);
            break;

            case 3: 
            employees[2] = new CommissionEmployee(first, last, ssn, sales, rate);
            break;

            case 4: 
            employees[3] = new BasePlusCommissionEmployee(first, last, ssn, sales, rate, salary);
            break;

         }       
     }


     //initialize array with Employees
     employees[0] = salariedEmployee;
     employees[1] = hourlyEmployee;
     employees[2] = commissionEmployee;
     employees[3] = basePlusCommissionEmployee;

     System.out.println( "Employees processed polymorphically: \n" );

     //generically process each element in array employees 
     for (Employee currentEmployee : employees)

     {
         System.out.println( currentEmployee); //invokes toString
         // determine whether element is a BasePlusCommissionEmployee
         if (currentEmployee instanceof BasePlusCommissionEmployee)
         {
            //downcast Employee referene to
            //BasePlusCommissionEmployee reference
            BasePlusCommissionEmployee  employee = 
               (BasePlusCommissionEmployee) currentEmployee;

               double oldBaseSalary = employee.getBaseSalary();
               employee.setBaseSalary ( 1.10 * oldBaseSalary);
               System.out.printf(
                  "new base salary with 10%% increase is: $%,.2f\n",
                   employee.getBaseSalary() );
          }//end if

          System.out.printf(
              "earned $%, .2f\n\n", currentEmployee.earnings() );
          }//end for

          //get type name of each object in employees array
          for (int j=0; j<employees.length; j++)
            System.out.printf ( "Employee %d is a %s\n", j,
               employees [j].getClass().getName() );



    }// end main
}// end class PayrollSystemTest

Line 6 of the error message tells you that it was trying to parse the user input on line 47, and failed to parse it as an int.
Did the input dialog appear OK? What did you enter in it?

The dialog did not appear at all. I input a number 1 for the employee field, my first and last name, a number for the ssn and the salary. It did then went back to the "imput a employee field". I am wondering if it went back through it again because of the loop?!

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