Computer Notes - Inheritance in Class

8/3/2019 Computer Notes - Inheritance in Class

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InheritanceInheritance

http://ecomputernotes.com


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Inheritance in ClassesInheritance in Classes If a class B inherits from class A, then B contains allIf a class B inherits from class A, then B contains all

the characteristics (information structure andthe characteristics (information structure andbehavior) of class Abehavior) of class A

The parent class is calledThe parent class is called basebase class and the childclass and the childclass is calledclass is called derivedderivedclassclass

Besides inherited characteristics, derived class mayBesides inherited characteristics, derived class may

have its own unique characteristicshave its own unique characteristics



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UML NotationUML Notation

Parent Class

Child Class

Base Class

Derived Class



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Inheritance in C++Inheritance in C++

There are three types of inheritance in C++There are three types of inheritance in C++

PublicPublic

PrivatePrivate

ProtectedProtected



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IS AIS ARelationshipRelationship

IS A relationship is modeled with the help of publicIS A relationship is modeled with the help of publicinheritanceinheritance

SyntaxSyntax

classclass ChildClassChildClass

: public: public BaseClassBaseClass{{

......

};};



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ExampleExample

class Person{class Person{

......

};};

class Student: public Person{class Student: public Person{

......};};



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Accessing MembersAccessing Members

Public members of base class become publicPublic members of base class become public

member of derived classmember of derived class

Private members of base class are notPrivate members of base class are notaccessible from outside of base class, even inaccessible from outside of base class, even in

the derived class (Information Hiding)the derived class (Information Hiding)



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ExampleExampleclass Person{class Person{

char *name;char *name;

int age;int age;

......

public:public:

const char *const char *GetNameGetName() const;() const;intint GetAgeGetAge() const;() const;

......

};};



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class Student: public Person{class Student: public Person{int semester;int semester;intint rollNorollNo;;

......public:public:

intint GetSemesterGetSemester() const;() const;

intint GetRollNoGetRollNo() const;() const;void Print() const;void Print() const;......

};};

ExampleExample



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ExampleExample

voidvoidStudent::PrintStudent::Print()(){{

coutcout


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ExampleExample

voidvoidStudent::PrintStudent::Print()()

{{

coutcout


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ExampleExampleint main(){int main(){

StudentStudent stdtstdt;;

stdt.semesterstdt.semester = 0;//error= 0;//error

stdt.namestdt.name = NULL; //error= NULL; //error

coutcout


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Allocation in MemoryAllocation in Memory

The object of derived class is represented inThe object of derived class is represented in

memory as followsmemory as follows

Data members ofbase class

Data members ofderived class

base member1

base member2...

derived member1derived member2

...


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Allocation in MemoryAllocation in Memory

Every object of derived class has anEvery object of derived class has an

anonymous object of base classanonymous object of base class



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ConstructorsConstructors

The anonymous object of base class must beThe anonymous object of base class must be

initialized using constructor of base classinitialized using constructor of base class

When a derived class object is created theWhen a derived class object is created theconstructor of base class is executed beforeconstructor of base class is executed before

the constructor of derived classthe constructor of derived class



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ConstructorsConstructors

Base class constructor

initializes the anonymous

object

Derived class constructor

initializes the derived class

object

base member1

base member2

...

derived member1derived member2

...



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class Parent{class Parent{public:public:

Parent(){Parent(){ coutcout


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ExampleExample

intintmain(){main(){

ChildChildcobjcobj;;

return 0;return 0;}}

Output:

Parent Constructor...Child Constructor...



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ConstructorConstructor

If default constructor of base class does notIf default constructor of base class does not

exist then the compiler will try to generate aexist then the compiler will try to generate a

default constructor for base class and executedefault constructor for base class and executeit before executing constructor of derivedit before executing constructor of derived

classclass



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ConstructorConstructor

If the user has given only an overloadedIf the user has given only an overloaded

constructor for base class, the compiler willconstructor for base class, the compiler will

not generate default constructor for base classnot generate default constructor for base class



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class Parent{class Parent{

public:public:

Parent(intParent(int i){}i){}};};

class Child : public Parent{class Child : public Parent{

public:public:Child(){}Child(){}

}} Child_ObjectChild_Object;; //ERROR//ERROR

ExampleExample



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Base Class InitializerBase Class Initializer

C++ has provided a mechanism to explicitlyC++ has provided a mechanism to explicitly

call a constructor of base class from derivedcall a constructor of base class from derived

classclass

The syntax is similar to member initializer andThe syntax is similar to member initializer andis referred as baseis referred as base--class initializationclass initialization



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class Parent{class Parent{

public:public:

Parent(intParent(int i){i){};};

};};

class Child : public Parent{class Child : public Parent{

public:public:

Child(intChild(int i):i): Parent(iParent(i))

{{}}

};};

ExampleExample



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Parent(){coutParent(){cout


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User can provide base class initializer andUser can provide base class initializer and

member initializer simultaneouslymember initializer simultaneously



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Parent(){Parent(){}}

};};class Child : public Parent{class Child : public Parent{int member;int member;

public:public:Child():member(0),Child():member(0), Parent()Parent(){{}}

};};

ExampleExample



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The base class initializer can be written afterThe base class initializer can be written after

member initializer for derived classmember initializer for derived class

The base class constructor is executed beforeThe base class constructor is executed beforethe initialization of data members of derivedthe initialization of data members of derived

class.class.



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Initializing MembersInitializing Members

Derived class can only initialize members ofDerived class can only initialize members of

base class using overloaded constructorsbase class using overloaded constructors

Derived class can not initialize the public dataDerived class can not initialize the public datamember of base class using member initializationmember of base class using member initialization

listlist



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ExampleExampleclass Person{class Person{

publicpublic::intint age;age;

char *name;char *name;......

public:public:

Person();Person();};};



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ExampleExampleclass Student: public Person{class Student: public Person{

private:private:

int semester;int semester;

......

public:public:

Student(intStudent(int a):a):age(aage(a))

{{ //error//error

}}

};};



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ReasonReasonIt will be an assignment not an initializationIt will be an assignment not an initialization


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DestructorsDestructors

Destructors are called in reverse order ofDestructors are called in reverse order of

constructor calledconstructor called

Derived class destructor is called before theDerived class destructor is called before the

base class destructor is calledbase class destructor is called



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Parent(){coutParent(){cout


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ExampleExample

Output:Output:

Parent ConstructorParent ConstructorChild ConstructorChild Constructor

Child DestructorChild DestructorParent DestructorParent Destructor


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Computer Notes - Inheritance in Class