Inheritance

1. Inheritance

2. Derived Class • Given a particular class, it is easy to create a another class (derived class) which is only a little bit different. • E.g., given Insect class, you can create derived classes named BumbleBee class and Grasshopper class. • A class derived from another class (parent) inherits all the public methods of the parent class.

3. Derived Class • Insect Class (6 legs, 4 wings, can fly) • Bumble Bee Class (derived class) • Grasshopper Class(derived class) • Bumble Bee has all Insect characteristics + others—e.g., ability to sting • Grasshopper has all Insect characteristics + others—e.g., ability to jump

4. Derived Class • Account class (ID No., owner, deposit, withdraw) • Savings class (derived class) • Checking class (derived class) • Saving has all Account characteristics + interest rate • Checking has all Account characteristics + minimum balance

5. Derived Class • class Person(ID No., name, address, phone) • derived class Faculty (+ department) • derived class Student (+ major, advisor) • derived class Staff (+ department, supervisor) Person Student Staff Faculty

6. Derived Class • class Shape (position, outlined) • derived class Circle (+ radius) • derived class Rectangle (+ width, height) • derived class Triangle (+ sideA, sideB, sideC) Shape Rectangle Triangle Circle

7. Derived Class • Derived class is a more specialized version of a base class. • Inherits from parent class all data and functions in its public section

8. Advantages of Derived Class • Developing more complicated classes from existing class, which has been tested • Reuse of class resource • Organization of related classes

9. Shape Class (base class) class Shape {private: int topLeftX; // top-left position int topLeftY; bool outline; // bordered or not public: Shape(); int getX(); int getY(); bool getOutline(); void display(); };

10. Circle Class (derived class) class Circle: public Shape {private: double radius; public: Circle(); Circle(double r); Circle(int x, int y, bool ol, double r); double getRadius(); double area(); double circumference(); void display(); // overwriting // getX(), getY(), and getOutline() are // inherited from Shape };

11. Rectangle Class (derived class) class Rectangle: public Shape {private: double width, double height; public: Rectangle(); Rectangle(double w, double h); Rectangle(int x, int y, bool ol, double w, double h); double getWidth(); double getHeight(); double area(); double perimeter(); void display(); // overwriting // getX(), getY(), and getOutline() are // inherited from Shape };

12. Using Derived Classes #include <iostream> #include “shape.h”#include “circle.h” #include “recangle.h” using namespace std; int main(){ Circle c1(1.0); cout << “Circle\n”; cout << “ x-pos: “ << c1.getX() << endl; cout << “ y-pos: “ << c1.getY() << endl; cout << “ area: “ << c1.area() << endl; cout << “ circumference: “ << c2.circumference() << endl;

13. Using Derived Classes Circle c2(10, 20, true, 1.0); Rectangle r2(30, 40, false, 2.0, 3.0); cout << “Circle: “;c2.display() << endl; cout << “Rectangle: “; r2.display() << endl;

14. Implementation for Shape #include “shape.h” void Shape::display(){ cout << “X: “ << topleftX << endl; cout << “Y: “ << topleftY << endl; }

15. Implementation for Circle #include “circle.” Circle::Circle(int x, int y, int ol, double r): Shape(x, y, ol){ // Shape(x, y, ol) has been invoked // at this point radius = r; }

16. Implementation for Circle void Circle::display(){ Shape::display(); cout << “Radius: “ << radius << endl; }

17. Implementation for Rectangle void Rectangle::display(){ Shape::display(); cout << “Width: “ << width << endl << “Height: “ << height << endl; }

18. Utility Function int2str() // converts int to string #include <sstream> using std::stringstream; string int2str(int num) { stringstream ss; ss << num; return ss.str(); }

19. Using Function int2str() // converts int n = 11; int nsqr = n * n; string message; message = “Square of “ + int2str(n) + “ is “ + int2str(nsqr);

20. Polymorphism

21. What Is Polymorphism? • Given:void display(Shape x){x.print();} • In Main():Shape s;Circle c;Rectangle r;display (s);display (c);display(r); Is there a way to let the function decide which print() to use?

22. What Is Polymorphism? • A Circle is a Shape. • A Rectangle is a Shape. • (But Shape is not a Circle. Shape is not a Rectangle.) • Polymorphism – or Dynamic Binding • Automatically choosing appropriate version of a function depending on the type of object.

23. Example of Polymorphism • Suppose an array of Shape object is created. • Array elements must of same type. • We can have an array of pointers to Shape objects.Shape *list[5]; 1 2 3 4 5 list

24. Example of Polymorphism #include <iostream> #include “shape.h” #include “circle.h” #include “rectangle.h” using namespace std; int main(){ Shape *list[5] = {new Shape(10, 11, true), new Circle(20, 21, true, 1.0), new Rectangle(30, 31, false, 2.0, 3.0) }; for (int i = 0; i < 3; i++){ cout << list[i].toString() << endl; }

25. Example of Polymorphism The output is: Each call to toString() function is from the Shape class.

26. Example of Polymorphism To allow polymorphism (dynamic binding): class Shape {private: int topLeftX; // top-left position int topLeftY; bool outline; // bordered or not public: Shape(); int getX(); int getY(); bool getOutline(); virtual string toString(); };

27. Example of Polymorphism class Circle: public Shape {private: double radius; public: Circle(); Circle(double r); Circle(int x, int y, boolol, double r); double getRadius(); double area(); double circumference(); string toString(); // This is also virtual };

28. Example of Polymorphism #include <iostream> #include “shape.h” #include “circle.h” #include “rectangle.h” using namespace std; int main(){ Shape *list[5] = {new Shape(10, 11, true), new Circle(20, 21, true, 1.0), new Rectangle(30, 31, false, 2.0, 3.0) }; for (int i = 0; i < 3; i++){ cout << list[i].toString() << endl; }

29. Example of Polymorphism The output is: From toString() in Shape class From toString() in Circle class From toString() in Rectangle class

30. Example of Polymorphism • Polymorphism – dynamic binding • When an object’s function is called, the version which is appropriate to the object’s class is dynamically bound.