Case Study - Employee

1. Case Study - Employee • In this case study, we will design a class hierarchy for the employees of a firm using inheritance. • In this design, we will see how to create classes and how to set up inheritance relations among these classes. • We will use abstract classes. • We will use polymorphic references, and polymorphic method invocation. COP 3330 Object Oriented Programming

2. Case Study – Problem Definition • A firm has employees. • An employee can be a volunteer or a paid employee. • Each employee has a name and an address. • We should be able to get a string representation of an employee. • Each employee should be associated with an earning method to evaluate his/her monthly earnings (whether 0 or not, this method must be available). • A volunteer is not paid (his/her earnings is zero). • A paid employee has to have a social security number. • A paid employee can be an executive, a monthly-employee, or a hourly-employee. • A monthly-employee has a monthly salary. • An executive has a monthly salary and a bonus for that month. • A hourly-employee earnings depends on how many hours he/she worked on that month (there is a wage per hour for him/her). COP 3330 Object Oriented Programming

3. A Class Hierarchy Employee Volunteer PaidEmployee Executive MonthlyEmployee HourlyEmployee • The inheritance relations among classes. • Now let us look at the details of each class. COP 3330 Object Oriented Programming

4. Class Details Employee class: • This class has to have two fields: name and address • Its constructor must initialize these fields. • Its toString should return a string representation of these fields. • It should enforce that its subclasses have to have an earnings method.This means that it has to have an abstract earnings method. This class must be an abstract class. Volunteer class: • This class will be a sub-class of Employee class. • Since we do not need another information about a volunteer, we do not need to define new fields in this class. • Its toString should return a string representation indicating that this employee is a volunteer. • Its earnings method should return 0 since a volunteer is not paid. • Since earnings method is implemented in this class, it can be a normal class. COP 3330 Object Oriented Programming

5. Class Details (cont.) PaidEmployee class: • This class will be a sub-class of Employee class. • Since we need a social security number for a paid employee, this class should define a new field: socialSecurityNumber. • Its toString should return a string representation of these three fields.. • Since this method does not implement earnings method, it should be abstract. Executive class: • This class will be a sub-class of PaidEmployee class. • Since we need a monthly salary and a bonus for an executive, this class should define the fields: salary and bonus. • Its toString should return a string representation indicating that this employee is an executive. • Its earnings method should return the summation of salary and bonus. • Since we may change the bonus of an executive, this class should include setBonus method. • Since earnings method is implemented in this class, it can be a normal class. COP 3330 Object Oriented Programming

6. Class Details (cont.) MonthlyEmployee class: • This class will be a sub-class of PaidEmployee class. • Since we need a monthly salary for a monthly-employee, this class should define the field: salary. • Its toString should return a string representation indicating that this employee is a monthly-employee. • Its earnings method should return the salary. • Since earnings method is implemented in this class, it can be a normal class. HourlyEmployee class: • This class will be a sub-class of PaidEmployee class. • This class should define the fields: wage and hours. • Its toString should return a string representation indicating that this employee is a hourly-employee. • Its earnings method should return the multiplication of wage and hours. • Since we may add hours for a hourly-employee, this class should include addHours method. • Since earnings method is implemented in this class, it can be a normal class. COP 3330 Object Oriented Programming

7. Other Classes Personnel class: • This class will declare an Employee array to hold all employees of a firm. • It should also include payday method to print paychecks for employees. EmployeeTest class: • A driver class. • It will create a Personnel object, and will call payday method with this object. COP 3330 Object Oriented Programming

8. Employee Class public abstract class Employee { protected String eName; protected String eAddress; // Set up an employee using the specified information public Employee(String name, String address) { eName=name; eAddress=address; } // Return a string containg the basic employee information public String toString() { return ( "Name: " + eName + "\n" + "Address: " + eAddress ) ; } // All subclasses of Employee class must define earnings method public abstract double earnings() ; } COP 3330 Object Oriented Programming

9. Volunteer Class public class Volunteer extends Employee { // Set up a volunteer using the specified information public Volunteer(String name, String address) { super(name,address); } // Return a string containing the paid employee information public String toString() { return ( "Volunteer\n" + super.toString()); } // Volunteers are not paid public double earnings() { return 0.0; } } COP 3330 Object Oriented Programming

10. PaidEmployee Class public abstract class PaidEmployee extends Employee { protected String socialSecurityNumber; // Set up a paid employee using the specified information public PaidEmployee(String name, String address, String ssn) { super(name,address); socialSecurityNumber=ssn; } // Return a string containing the paid employee information public String toString() { return ( super.toString() + "\nSSN: " + socialSecurityNumber) ; } } COP 3330 Object Oriented Programming

11. Executive Class public class Executive extends PaidEmployee { private double salary; private double bonus; // Set up an executive using the specified information public Executive(String name, String address, String ssn, double salary) { super(name,address,ssn); this.salary=salary; bonus=0.0; } // Set up the bonus for the executive public void setBonus(double bonus) { this.bonus=bonus; } // Return a string containing the Executive information public String toString() { return ( "Executive\n" + super.toString() + "\nSalary: " + salary + "\nBonus: " + bonus); } // Executives earn a monthly salary plus a bonus public double earnings() { return salary+bonus; } } COP 3330 Object Oriented Programming

12. MonthlyEmployee Class public class MonthlyEmployee extends PaidEmployee { private double salary; // Set up a monthly employee using the specified information public MonthlyEmployee(String name, String address, String ssn, double salary) { super(name,address,ssn); this.salary=salary; } // Return a string containing the monthly employee information public String toString() { return ( "Monthly Employee\n" + super.toString() + "\nSalary: " + salary ); } // Monthly employees earn a monthly salary public double earnings() { return salary; } } COP 3330 Object Oriented Programming

13. HourlyEmployee Class public class HourlyEmployee extends PaidEmployee { private double wage; // wage per hour private int hours; // hours worked for the month // Set up a hourly employee using the specified information public HourlyEmployee(String name,String address,String ssn,double wage){ super(name,address,ssn); this.wage=wage; hours=0; } // Add hours public void addHours(int hours) { this.hours += hours; } // Return a string containing the hourly employee information public String toString() { return ( "Hourly Employee\n" + super.toString() + "\nWage Per Hour: " + wage + "\nHours Worked: " + hours); } // Get hourly employee's earnings public double earnings() { return wage*hours; } } COP 3330 Object Oriented Programming

14. Personnel Class public class Personnel { Employee[] employeeList; // Holds polymorphic references, it can hold objects of sublasses of Employee // Set up the employee list public Personnel() { employeeList = new Employee[5]; employeeList[0] = new Volunteer("Sam Clark","123 Alafaya Trail"); employeeList[1] = new Executive("Bill Brown","124 Alafaya Trail","666-66-6666",7500); employeeList[2] = new MonthlyEmployee("John Goodman","125 Alafaya Trail","777-77-7777",5000); employeeList[3] = new MonthlyEmployee("Jill Woody","126 Alafaya Trail","888-88-8888",4000); employeeList[4] = new HourlyEmployee("Tom Jones","127 Alafaya Trail","999-99-9999",9.50); ((Executive)employeeList[1]).setBonus(1200); // Downcasting ((HourlyEmployee)employeeList[4]).addHours(150); ((HourlyEmployee)employeeList[4]).addHours(60); } COP 3330 Object Oriented Programming

15. Personnel Class (cont.) // Pays all employees public void payday() { double amount; for (int i=0; i<employeeList.length; i++) { System.out.println(employeeList[i]); amount=employeeList[i].earnings(); // polymorphic method invocation if (amount==0.0) System.out.println("Thanks!"); else System.out.println("Paid: " + amount); System.out.println("----------------------------------------"); } } } COP 3330 Object Oriented Programming

16. EmployeeTest Class public class EmployeeTest { // Creates the personnel of a firm and pays them public static void main (String[] args) { Personnel staff = new Personnel(); staff.payday(); } } COP 3330 Object Oriented Programming

17. Output of The Program COP 3330 Object Oriented Programming