Hierarchy of Inheritance - Object Oriented Programming - Lecture Slides, Slides of Object Oriented Programming

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Object-Oriented Programming

(OOP)

Lecture No. 26

Hierarchy of Inheritance

• We represent the classes involved in inheritance relation in tree like hierarchy

Example

GrandParent

Parent1 Parent

Child1 (^) Child

Direct Base Class

• A direct base class is explicitly listed in a derived class's header with a colon (:)

class Child1:public Parent

...

Indirect Base Class

• An indirect base class is not explicitly listed in a derived class's header with a colon (:)
• It is inherited from two or more levels up the hierarchy of inheritance

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

Base Initialization

• The child can only perform the initialization of direct base class through base class initialization list
• The child can not perform the initialization of an indirect base class through base class initialization list

Example

class GrandParent{

int gpData;

public:

GrandParent() : gpData(0){...} GrandParent(int i) : gpData(i){...} void Print() const;

};

Example

class Parent1: public GrandParent{

int pData;

public:

Parent1() : GrandParent(), pData(0) {…}

};

Example

class Child1 : public Parent1 {

public:

Child1() : Parent1() {...} Child1(int i) : GrandParent (i) //Error {...} void Print() const;

};

Overriding

• Child class can override the function of GrandParent class

Example

GrandParent Print()

Parent

Child Print()

Example

void GrandParent::Print() {

cout << “GrandParent::Print” << endl;

}

void Child1::Print() {

cout << “Child1::Print” << endl;

}

Example

int main(){

Child1 obj; obj.Print(); obj.Parent1::Print(); obj.GrandParent::Print(); return 0;

}

Output

• Output is as follows

Child1::Print

GrandParent::Print

GrandParent::Print

Types of Inheritance

• There are three types of inheritance - Public - Protected - Private
• Use keyword public, private or protected to specify the type of inheritance

Public Inheritance

Member access in

Base Class Derived Class

Public Public

Protected Protected

Private Hidden

class Child: public Parent {…};

Protected Inheritance

Member access in

Base Class Derived Class

Public Protected

Protected Protected

Private Hidden

class Child: protected Parent {…};

Private Inheritance

Member access in

Base Class Derived Class

Public Private

Protected Private

Private Hidden

class Child: private Parent {…};

Private Inheritance

• If the user does not specifies the type of inheritance then the default type is private inheritance

class Child: private Parent {…}

is equivalent to

class Child: Parent {…}

Private Inheritance

• We use private inheritance when we want to reuse code of some class
• Private Inheritance is used to model “Implemented in terms of” relationship

Example

class Collection {

...

public:

void AddElement(int); bool SearchElement(int); bool SearchElementAgain(int); bool DeleteElement(int);

};

Example

• If element is not found in the Collection the function SearchElement will return false
• SearchElementAgain finds the second instance of element in the collection

Class Set

class Set: private Collection {

private:

...

public:

void AddMember(int); bool IsMember(int); bool DeleteMember(int);

};

Class Set

void Set::AddMember(int i){

if (! IsMember(i) ) AddElement(i);

}

bool Set::IsMember(int i){

return SearchElement(i);

}