Abstract class in C++ language

Abstract class in C++ language

In this tutorial, we will discuss the Oop concept of Abstract class in C++ language

An abstract class in C++ language, which is a class contain pure one or more(at least one) virtual function in a base class . A pure virtual function is a virtual member function, that noticeable as having no any implementation.

Virtual function 

virtual void functionName()=0;

virtual void sayHollow()=0;

Some important points about abstract class

• An abstract class must have at least one pure virtual(it can have one or more virtual function) function and it can have normal functions and variables.
• Abstract classes are mainly used to inherit properties or attributes to derived class so that its derived classes can use their interface.
• Classes inheriting an abstract class must implement all pure virtual functions or otherwise, they will become abstract too.
• We can’t declare an object of abstract class because it has partoal implementation of the method. When we create an object of abstract class, an error message would be displayed.

Example of abstract class in C++

class class_Name {
public:
//A pure virtual function is specified by placing "= 0" in its declaration as follows 
virtual display()=0; //pure virtual function
 //it has no definition
}

Explanation of abstraction in C++

Example given below

Example 1

class shape{//class ahape has a vertual function
virtual void draw()=0;  
//virtual function with no implementation

}
class circle{ //derived (1) class circle
void draw(){
// implementation of draw() function
}
class rectangle{ //derived (2) class rectangle
void draw(){
// implementation of draw() function
}

class square{ //derived (2) class squair
void draw(){
// implementation of draw() function
}

At the above example, shape is a base class. Draw() is a virtual function is inside the shape( base) class which has no implementation, but it is only definition. So class shape is a abstract class. function draw() is a pure virtual function.
Every derived class having implementation of draw() method

facts

A class is abstract if it has at least 
one pure virtual function

 

Program 1

When the above code is executed, It produces the following result

this is teacher class
this is principal class
this is school clark class
End the program

Example

Abstraction in Cpp using pointer

Program 2

When the above code is executed, It produces the following result

This is first derived class
This is second derived class
End the program

Related Links

Encapsulation in C++                                       Encapsulation in Java

Polymorphism in C++                                      Methodoverriding in Java

Method overloading in java                             Constructor overloading in Java

Exception Handling in Java                             Abstract class in Java

Method over riding in Python