(Payroll System Modification) Modify the payroll system of Figs. 1—6 to include private in...

(Payroll System Modification) Modify the payroll system of Figs. 1—6 to include private instance variable birthDate in class Employee. Use class Date of Fig. to represent an employee's birthday. Add get methods to class Date. Assume that payroll is processed once per month. Create an array of Employee variables to store references to the various employee objects. In a loop, calculate the payroll for each Employee (polymorphically), and add a $100.00 bonus to the person's payroll amount if the current month is the one in which the Employee's birthday occurs.

Fig. 1 Employee abstract superclass.

Fig. 2 SalariedEmployee concrete class extends abstract class Employee.

Fig. 3 HourlyEmployee class extends Employee.

Fig. 4 CommissionEmployee class extends Employee.

Fig. 5 BasePlusCommissionEmployee class extends CommissionEmployee.

Fig. 6 Employee hierarchy test program.