inheritance by: er. gurpreet singh assistant professor department of information technology,...
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INHERITANCE By: Er. Gurpreet SinghBy: Er. Gurpreet Singh
Assistant ProfessorAssistant Professor Department of Information Technology, Department of Information Technology,
MIMIT MaloutMIMIT Malout
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Objective
On completion of this lecture, you will be able to:• Explore the importance of Inheritance.• Define derived classes.• Explain Protected visibility mode.• Explain various types of Inheritance• Distinguish between overriding and overloading.• Create objects of derived classes.• Concept of constructors in the derived classes.• Declare an object of a class in another class.
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INTRODUCTION
• Inheritance is a powerful feature of object-oriented programming. It is a process of creating a new class from existing class.
• The class from which we create a new class is called the base class(Super class or Parent class)
• The newly created class is known as Derived class also known as Sub Class or Child Class.
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Feature A
Feature A
Feature B
Feature C
Feature B
Base Class
Derived Class
INHERITANCE RELATIONSHIP
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Defining Derived Class• Whenever a derived class is defined, we have to specify its
relationship with the base class. The general form of specifying derived class:
Class derived_class_name: visibility_mode base_class_name{
------------// members of derived class------
};• The colon(:) symbol shows the relationship of a derived class to its
base class. The visibility mode may be private or public.
The default mode is private. 5
Public visibility modeClass d: public b{
-------- //members of derived class----
};
In this example d is derived class & b is base class visibility mode is public means features of base class are publically derived or publically inherited to class d. 6
Private visibility modeClass d: private b{
-------- //members of derived class----
};
In this example d is derived class & b is base class visibility mode is private means features of base class are privately derived or privately inherited to class d. 7
Remember • When base class is publically derived or publically
inherited , each public member of the base class becomes public member in the derived class. The private members of the base class are not inherited.
• When base class is privately derived or privately inherited , each public member of the base class becomes private member in the derived class. The private members of the base class are not inherited.
• In protected derivation, both the public & protected members of the base class become protected members of the derived class. When a protected member is inherited in public mode, it becomes protected in derived & when protected member is inherited in private mode it becomes private in the derived class.
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Effect of Inheritance on the visibility of members.
Private
Protected
Public
Private
Protected
Public
Not Inheritable
Class D: private BClass B
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Effect of Inheritance on the visibility of members.
Private
Protected
Public
Private
Protected
Public
Not Inheritable
Class D: public BClass B
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Effect of Inheritance on the visibility of members.
Private
Protected
Public
Private
Protected
Public
Not Inheritable
Class D: protected BClass B
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Review the access control to public, private & protected members of the class.
Access specifier
Accessible from own class
Accessible from derived
class
Accessible from objects outside class
Public Yes Yes Yes Protected Yes Yes No
Private Yes No No
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TYPES OF INHERITANCE
1. Single Inheritance 2. Multiple Inheritance3. Multilevel Inheritance4. Hierarchical Inheritance5. Hybrid Inheritance
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MULTILEVEL INHERITANCE
Base Class 1
Derived Class
Note: Intermediate class contains protected data members. Private will not work.
Intermediate class
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HIERARCHICAL INHERITANCE
Base Class
Derived Class 3
One Base More Derived
Derived Class 2Derived Class 1
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HYBRID INHERITANCE
Combination of two or more types of inheritance.(Here combination of Multilevel & Multiple inheritance.)
Base Class 1
Derived Class
Intermediate class
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student
address
private:char name[20];int rno;
public:void getstudent();void displaystudent();
private:char city[20];
public:void getaddress();void displayaddress();
SINGLE INHERITANCE
#include<iostream.h>#include<conio.h>#include<stdio.h>class student{private:char name[20];int rno;public: void getstudent(){cout<<”enter name of the student=”;cin>>name;cout<<”enter roll number of the student=”;cin>>rno;}void displaystudent(){cout<<”name of the student=”<<name;cout<<”\nroll number of the student=”<<rno;}};
class address : public student{private: char city[20];public:void getaddress(){getstudent();cout<<”\nenter city=”;cin>>city;}void displayaddress(){displaystudent();cout<<”\ncity=”<<city;}};
student address
private:char name[20];int rno;public:void getstudent();void displaystudent();
private:char city[20];public:void getaddress();void displayaddress();
MULTIPLE INHERITANCE
account
private:Int tfee,submit,balance;public:void getaccount();void displayaccount();
#include<iostream.h>#include<conio.h>#include<stdio.h>class student{private:char name[20];int rno;public: void getstudent(){cout<<”enter name of the student=”;cin>>name;cout<<”enter roll number of the student=”;cin>>rno;}void displaystudent(){cout<<”name of the student=”<<name;cout<<”\nroll number of the student=”<<rno;}};
class address {private: char city[20];public:void getaddress(){cout<<”\nenter city=”;cin>>city;}void displayaddress(){cout<<”\ncity=”<<city;}};
class account: public student, public address {private: int tfee,submit,balance;public:void getaccount(){getstudent();getaddress();cout<<“\nenter total fee=“;cin>>tfee;cout<<“\nenter submit fee=“ ;cin>>submit;}
void displayaccount(){displaystudent();displayaddress();cout<<”\ntotal fee=”<<tfee;cout<<”\nsubmit fee=”<<submit;balance=tfee-submit;cout<<“\nbalance fee=“<<balance; }};
Note: Intermediate class contains protected data members. Private will not work.
class result: public test{private:int total,avg;public:void getresult()void displayresult()
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MULTILEVEL INHERITANCE
Base Class 1
Derived Class
Intermediate class
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class student{private: char name[20];int rno;public:void getstudent()void displaystudent()
class test: public student{protected: int math,eng,sci;public:void gettest()void displaytest()
#include<iostream.h>#include<conio.h>#include<stdio.h>class student{private:char name[20];int rno;public: void getstudent(){cout<<”enter name of the student=”;cin>>name;cout<<”enter roll number of the student=”;cin>>rno;}void getstudent(){cout<<”name of the student=”<<name;cout<<”\nroll number of the student=”<<rno;}};
class test: public student{protected:int math,eng,sci;public:void gettest(){getstudent();cout<<”enter math marks=”;cin>>math;cout<<”enter english marks=”;cin>>eng;cout<<”enter science marks=”;cin>>sci;}void displaytest(){displaystudent();cout<<”\n math marks=”<<math;cout<<”\n english marks=”<<eng;cout<<”\nscience marks=”<<sci;}};
class result : public test{private: int total,avg;public:void getresult(){gettest();total=math+eng+sci;avg=total/3;} void displayaddress(){displaytest();cout<<”\nTotal Marks=”<<total;cout<<”\n Average marks=”<<avg;}};
void main(){class result r1;clrscr();r1.getresult();clrscr();r1.displayresult();getch();}
student Base Class
One Base More Derived
Derived Class 2Derived Class 1
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private:char name[20];int rno;public:void getstudent();void displaystudent();
class bsc: public student{private:int phy,chem,math;public:void getbsc()void displaybsc()
HIERARCHICAL INHERITANCE
class ba: public student{private: int hindi,punjabi;public:void getba()void displayba()
#include<iostream.h>#include<conio.h>#include<stdio.h>class student{private:char name[20];int rno;public: void getstudent(){cout<<”enter name of the student=”;cin>>name;cout<<”enter roll number of the student=”;cin>>rno;}void getstudent(){cout<<”name of the student=”<<name;cout<<”\nroll number of the student=”<<rno;}};
class bsc: public student{private:int phy,chem,math;public:void getbsc(){getstudent();cout<<”enter math marks=”;cin>>math;cout<<”enter physics marks=”;cin>>phy;cout<<”enter chemistry marks=”;cin>>chem;}void displaybsc(){displaystudent();cout<<”\n math marks=”<<math;cout<<”\n physics marks=”<<phy;cout<<”\n chemistry marks=”<<chem;}};
class ba: public student{private: int hindi,punjabi;public:void getba(){getstudent();cout<<”enter hindi marks=”;cin>>hindi;cout<<”enter punjabi marks=”;cin>>punjabi;} void displayba(){displaystudent();cout<<”\n hindi marks=”<<hindi;cout<<”\n punjabi marks=”<<punjabi;}};
void main(){class bsc b1;class ba b2;int choice;clrscr();cout<<”1. bsc 2. ba \n enter your stream=”;cin>>choice;if(choice==1){b1.getbsc();clrscr();b1.displaybsc();}else{b2.getba();clrscr();b2.displayba();}getch();}
HYBRID INHERITANCE
Combination of two or more types of inheritance.(Here combination of Multilevel & Multiple inheritance.)
Base Class 1
Derived Class
Intermediate class
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HYBRID INHERITANCEclass student{private: char name[20];int rno;public:void getstudent()void displaystudent()
class test: public student{protected: int math,eng,sci;public:void gettest()void displaytest()
class result: public test, public address{private:int total,avg;public:void getresult()void displayresult()
class address{private:char city[20];public:void getaddress();void displayaddress();
Abstract class:
A class which is not used to create objects is called abstract class.For exp student class is abstract class which is only used as a base class no object created.
SOME IMPORTANT TERMS RELATED WITH INHERITANCE
Constructors & Destructor based inheritance:
if both base class derived class have the default constructors, then the object of derived class first invokes base class constructorthen the derived class constructor.
The destructors are executed in reverse order i.e. the destructorof derived class is executed before the destructor of Its base class.
With overloading many function of the same name with different signature are created.
With overriding, the function in the derived class has the identical signature to the function in the base class.
With overriding, a derived class implements its own version of a base class function.
The derived class can selectively use some base class function as they are, and override others.
OVERRIDING VS OVERLOADING
Overloading..1.Same name but there are different definitions and parameters..2.Here, the definitions are extended.3.Seperate methods share the same name. 4.It is mainly for operators.5.It must have different method signatures.
Overriding.1.Here replacement of methods.2.It is used in inheritance.3.subclass methods replaces the super class.4.It is mainly for functions.5.It must have same signature
OVERRIDING VS OVERLOADING
class A{public :void display(){ cout<<”Class A \n”;}};
class B{ public :void display(){ cout <<”class B \n”;}};
AMBIGUITY (A Problem)
class D : public A, public B{ void display(){display(); //Ambiguity, which display() function is used.}}
In this case, an ambiguity arises. which display() function is used by the derived class when we inherit both classes A and B. We can solve this problem by specifying a class name with the scope resolution operation as shown below
class D : public A, public B{public :void display() //override display() of A and B{
B::display();}};
A class definition can contains objects of another class. This kind of relationship is called Containership or nesting of classes.
Inheritance and nesting of classes can serve the same purpose in some cases.
Our new program shows how to use nesting how to use nesting of classes to get the similar output.
CONTAINERSHIP OR NESTING OF CLASSES
#include<iostream.h>#include<iomanip.h>#include<conio.h>//Base classclass student{int roll;char name[25];public:void getstudent(){cout<<“Enter roll number“<<endl;cin>>roll;cout<<“Enter name of student”<<endl;cin>>name;}void displaystudent(){cout<<“Roll No : “<<roll <<endl;cout<<“Name :”<<name<<endl; }};
//Derived class
class test{Int sub1,sub2;student st; //containershippublic:void gettest();void displaytest();};
void test :: gettest(){st.getstudent(); //student class functioncout<<“Enter the marks of subject-1”<<endl;cin>>sub1;cout<<“Enter the marks of subject-2”<<endl;cin>>sub2;}
void test :: displaytest(){st.displaystudent(); //student class functioncout<<“Marks of Subject-1 : “<<sub1<<endl;cout<<“Marks of Subject-1 : “<<sub1<<endl;}
Output
Enter roll number 501Enter name of student sony Enter the marks of subject-1 89Enter the marks of subject-2 87
Roll No : 501Name : sonyMarks of subject -1 : 89Marks of subject -2 : 87
We see that the output st is created in the class test . The member functions of student are accessed through the object st. No class is inherited from another class.
SOME IMPORTANT QUESTIONS RELATED TO INHERITANCE FOR EXAMS.
Q1. Explain Inheritance & its types.
Q2. Differentiate Overloading & Overriding.
Q3. What is ambiguity how this problem can be solve?
Q4. What is abstract class?
Q5. Is nested class equal to inherited class?
Q6. Explain visibility modes & access specifications of inheritance.
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