Object Oriented Programming (OOP) - CS304 Power Point Slides Lecture 25

8/13/2019 Object Oriented Programming (OOP) - CS304 Power Point Slides Lecture 25

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Object-Oriented Programming

(OOP)Lecture No. 25


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Overriding Member Functions ofBase Class

Derived class can override themember functions of its baseclass

To override a function the derived

class simply provides a functionwith the same signature as that ofits base class


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Overriding

Parent

...

Func1

Child...

Func1


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Overridingclass Parent {public:

void Func1();void Func1(int);

};

class Child: public Parent {

public:void Func1();

};


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Overloading vs. Overriding

Overloading is done within thescope of one class

Overriding is done in scope ofparent and child

Overriding within the scope of

single class is error due toduplicate declaration


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Overriding

class Parent {public:

void Func1();void Func1(); //Error};


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Derive class can override

member function of base classsuch that the working of functionis totally changed


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Example

class Person{public:

void Walk();};class ParalyzedPerson: public Person{

public:void Walk();

};


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Derive class can overridemember function of base class

such that the working of functionis similar to formerimplementation


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Example

class Person{char *name;

public:

Person(char *=NULL);const char *GetName() const;void Print(){

cout


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Exampleclass Student : public Person{

char * major; public:

Student(char * aName, char* aMajor);

void Print(){cout


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Example

int main(){Student a(Ahmad,

Computer Science); a.Print();

return 0;}


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Output

Output:

Name: AhmedMajor: Computer Science


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Derive class can overridemember function of base classsuch that the working of functionis based on former

implementation


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char * major; public:Student(char * aName, char* m);

void Print(){Print();//Print of Personcout


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Example



return 0;}


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Output

There will be no output as thecompiler will call the print of the

child class from print of child classrecursively There is no ending condition


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char * major; public:Student(char * aName, char* m);

void Print(){Person::Print();cout


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Example



return 0;}


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Output

Output:



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The pointer must be used withcare when working withoverridden member functions


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Exampleint main(){

Student a(Ahmad, ComputerScuence);

Student *sPtr = &a;sPtr->Print();

Person *pPtr = sPtr; pPtr->Print();

return 0;}


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Example

Output:


Name: Ahmed


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The member function is calledaccording to static type

The static type of pPtr is Person The static type of sPtr is Student


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Hierarchy of Inheritance We represent the classes

involved in inheritance relation intree like hierarchy


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Example

GrandParent

Parent1 Parent2

Child1 Child2


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Direct Base Class

A direct base class is explicitly listedin a derived class's header with acolon (:)

class Child1:public Parent1...


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Indirect Base Class An indirect base class is not explicitly

listed in a derived class's header witha colon (:) It is inherited from two or more levels

up the hierarchy of inheritance

class GrandParent{};

class Parent1: public GrandParent {};class Child1:public Parent1{};

Object Oriented Programming (OOP) - CS304 Power Point Slides Lecture 25

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