Polymorphism - Object Oriented Programming - Lecture Slides, Slides of Object Oriented Programming

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Object-Oriented Programming

(OOP)

Lecture No. 30

Polymorphism – Case Study

A Simple Payroll Application

Problem Statement

• Develop a simple payroll application.

There are three kinds of employees in the

system: salaried employee, hourly

employee, and commissioned employee.

The system takes as input an array

containing employee objects, calculates

salary polymorphically, and generates

report.

OO Model

Employee

SalariedEmp HourlyEmp CommEmp

getName calcSalary

sales commRate

hours hourlyRate

salary

calcSalary calcSalary

calcSalary

name taxRate

String

String operator = operator <<

pStr

Class Employee

class Employee {

private: String name; double taxRate; public: Employee( String&, double ); String getName(); virtual double calcSalary() = 0;

}

… Class Employee

Employee::Employee( String& n,

double tr ): name(n){ taxRate = tr;

}

String Employee::getName() {

return name;

}

Class SalariedEmp

class SalariedEmp : public Employee

{

private:

double salary;

public:

SalariedEmp(String&,double,double); virtual double calcSalary();

}

… Class SalariedEmp

SalariedEmp::SalariedEmp(String& n,

double tr, double sal) : Employee( n, tr ) { salary = sal;

}

double SalariedEmp::calcSalary() {

double tax = salary * taxRate; return salary – tax;

}

Class HourlyEmp

class HourlyEmp : public Employee {

private:

int hours; double hourlyRate;

public:

HourlyEmp(string&,double,int,double); virtual double calcSalary();

}

… Class HourlyEmp

HourlyEmp ::HourlyEmp( String& n,

double tr, int h, double hr )

: Employee( n, tr ) { hours = h; hourlyRate = hr;

}

… Class HourlyEmp

double HourlyEmp::calcSalary()

{

double grossPay, tax;

grossPay = hours * hourlyRate; tax = grossPay * taxRate;

return grossPay – tax;

}

Class CommEmp

class CommEmp : public Employee

{

private:

double sales; double commRate;

public:

CommEmp( String&, double, double, double ); virtual double calcSalary();

}

… Class CommEmp

CommEmp::CommEmp( String& n,

double tr, double s, double cr ) : Employee( n, tr ) {

sales = s; commRate = cr;

}

… Class CommEmp

double CommEmp::calcSalary()

{

double grossPay = sales * commRate;

double tax = grossPay * taxRate;

return grossPay – tax;

}

A Sample Payroll

int main() {

Employee* emp[10]; emp[0] = new SalariedEmp( “Aamir”, 0.05, 15000 ); emp[1] = new HourlyEmp( “Faakhir”, 0.06, 160, 50 ); emp[2] = new CommEmp( “Fuaad”, 0.04, 150000, 10 ); … generatePayroll( emp, 10 ); return 0;

}

…A Sample Payroll

void generatePayroll(Employee* emp[], int size) {

cout << “Name\tNet Salary\n\n”;

for (int i = 0; i < size; i++) { cout << emp[i]->getName() << ‘\t’ << emp[i]->calcSalary() << ‘\n’; }

}

Sample Output

Name Net Salary

Aamir 14250

Fakhir 7520

Fuaad 14400

…

Never Treat Arrays

Polymorphically

Shape Hierarchy Revisited

Shape

Line Circle Triangle

draw

calcArea

draw

calcArea

draw

calcArea

draw

calcArea

Shape Hierarchy

class Shape {

…

public:

Shape(); virtual void draw(){ cout << “Shape\n”; } virtual int calcArea() { return 0; }

};

… Shape Hierarchy

class Line : public Shape {

…

public:

Line(Point p1, Point p2); void draw(){ cout << “Line\n”; }

}

drawShapes()

void drawShapes( Shape _shape[],

int size ) { for (int i = 0; i < size; i++) {

_shape[i].draw(); }

}

Polymorphism & Arrays

int main() {

Shape _shape[ 10 ]; _shape[ 0 ] = Shape(); _shape[ 1 ] = Shape();

… drawShapes( _shape, 10 ); return 0;

}

Sample Output

Shape

Shape

Shape

…

…Polymorphism & Arrays

int main() {

Point p1(10, 10), p2(20, 20), … Line _line[ 10 ]; _line[ 0 ] = Line( p1, p2 ); _line[ 1 ] = Line( p3, p4 ); … drawShapes( _line, 10 ); return 0;

}