Understanding Inheritance in Object-Oriented Programming

1. Object Oriented Programming ParadigmLesson 07 Mr. Muhammad Hanif Lecturer Information Technology MBBS Campus Dadu University of SIndh

2. Inheritance

3. Inheritance • Inheritance is a form of software reuse where a new class is created to absorb an existing class’s data and behaviors, and enhance them with new capabilities • Basic idea • The new class, the derived class, inherits the members of the existing class, known as the base class

4. Inheritance • Inheritance: It is a process of creating new classes, called derived classes from existing or base classes. • The derived class inherits all the capabilities of the base class but can add additions to its own. • Base class will remain unchanged. • Inheritance provides code reusability, i-e debugged code is used in class and reused in derived class in different situation.

5. Inheritance

6. Derived Class and Base Class • C++ • Base and Drive Classes • Java • Sub Classand Super Class

7. Introduction (continued) • A direct base class is the base class from which a derived class explicitly inherits. • An indirect base class is inherited from two or more levels up in the class hierarchy. • In single inheritance, a class is derived from one base class. • With multiple inheritance, a derived class inherits from multiple base classes.

8. Class Hierarchy (Members of University Community)

9. Access Specifiers • public:: Accessible within the class as well as from outside the class. • Note, base-class objects are NOT objects of their derived classes. • private:: The members declared as "private" can be accessed only within the same class and not from outside the class. • protected:: The members declared as "protected" cannot be accessed from outside the class, but can be accessed from a derived class. • This is used when inheritance is applied to the members of a class.

10. Access Specifiers

11. Derived Class • Member functions of derived class cannot directly access private members of base class • Example:– • Manager member functions in previous example cannot read manager’s own name! • Because data members of a class are by default private

12. Protected Class • A base class’s protectedmembers can be accessed by • members and friends of the base class, and • members and friends of any class derived from the base class. • Derived-class member functions can refer to publicand protectedmembers of the base class. • By simply using their names

13. Public, Protected, Private Inheritance class A { public: int i; protected: int j; private: int k; }; Class B : public A { // … }; Class C : protected A { // … }; Class D : private A { // … }; • Class A declares 3 variables • i is public to all users of class A • j is protected. It can only be used by methods in class A or its derived classes • k is private. It can only be used by methods in class A • Class B inherits publicly from A • i is again public to all users of class B • j is again protected. It can be used by methods in class B or its derived classes • Class C uses protected inheritance from A • i is now protected in C, so the only users of class C that can access i are the methods of class C • j is again protected. It can be used by methods in class C or its derived classes • Class D uses private inheritance from A • i and j are private in D, so users of D cannot access them, only methods of D itself

14. Inheritance • Single Inheritance is method in which a derived class has only one base class. • In the example the derived class "Cube" has only one base class "Value“.

15. Inheritance in_basic.cpp #include <iostream.h> class Value { protected: int val; public: void set_values(int a) {val=a;} }; class Cube: public Value { public: int cube() {return(val*val*val);} }; int main() { Cube cub; cub.set_values(5); cout<<"The cube of 5 is: "<<cub.cube() <<endl; } The Cube of 5 is: 125

16. Inheritance • Multiple Inheritance is a method by which a class is derived from more than one base class. • In the example the derived class "Area" is derived from two base classes "Square" and "CShow".

17. Inheritance in_mult.cpp #include <iostream.h> class Square { protected: int l; public: void set_values (int x) { l=x;} }; class CShow { public: void show(int i); }; void CShow::show (int i) { cout << "The area of the square is" << i << endl; } class Area: public Square, public CShow { public: int area() { return (l *l); } }; int main () { Area r; r.set_values (5); r.show(r.area()); } The area of the square is:: 25

18. Multiple Inheritance