(Payroll System Modification) Modify the payroll system of Figs. 10.4–10.9 to include private instance variable birthDate in class Employee. Use class Date of Fig. 8.7 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.

(Project: Shape Hierarchy) Implement the Shape hierarchy shown in Fig. 9.3. Each TwoDimensionalShape should contain method getArea to calculate the area of the two-dimensional shape. Each ThreeDimensionalShape should have methods getArea and getVolume to calculate the surface area and volume, respectively, of the three-dimensional shape. Create a program that uses an array of Shape references to objects of each concrete class in the hierarchy. The program should print a text description of the object to which each array element refers. Also, in the loop that processes all the shapes in the array, determine whether each shape is a TwoDimensionalShape or a ThreeDimensionalShape. If it’s a TwoDimensionalShape, display its area. If it’s a ThreeDimensionalShape, display its area and volume.

(Payroll System Modification) Modify the payroll system of Figs. 10.4–10.9 to include an additional Employee subclass PieceWorker that represents an employee whose pay is based on the number of pieces of merchandise produced. Class PieceWorker should contain private instance variables wage (to store the employee’s wage per piece) and pieces (to store the number of pieces produced). Provide a concrete implementation of method earnings in class PieceWorker that calculates the employee’s earnings by multiplying the number of pieces produced by the wage per piece. Create an array of Employee variables to store references to objects of each concrete class in the new Employee hierarchy. For each Employee, display its String representation and earnings.

(Accounts Payable System Modification) In this exercise, we modify the accounts payable application of Figs. 10.11–10.15 to include the complete functionality of the payroll application of Figs. 10.4–10.9. The application should still process two Invoice objects, but now should process one object of each of the four Employee subclasses. If the object currently being processed is a BasePlusCommissionEmployee, the application should increase the BasePlusCommissionEmployee’s base salary by 10%. Finally, the application should output the payment amount for each object. Complete the following steps to create the new application:

(Accounts Payable System Modification) It’s possible to include the functionality of the payroll application (Figs. 10.4–10.9) in the accounts payable application without modifying Employee subclasses SalariedEmployee, HourlyEmployee, CommissionEmployee or BasePlusCommissionEmplyee. To do so, you can modify class Employee (Fig. 10.4) to implement interface Payable and declare method getPaymentAmount to invoke method earnings. Method getPaymentAmount would then be inherited by the subclasses in the Employee hierarchy. When getPaymentAmount is called for a particular subclass object, it polymorphically invokes the appropriate earnings method for that subclass. Reimplement Exercise 10.11 using the original Employee hierarchy from the payroll application of Figs. 10.4–10.9. Modify class Employee as described in this exercise, and do not modify any of class Employee’s subclasses.