Why we use abstract class

Why we use abstract class

An abstract class is used to define what is known as a base class. A base class is a class which has the most basic definition of a particular requirement.

Understand more we take an example

Suppose we have a two class Permanent_Employee and contractual_employee

And both class have name (firstName , lastName) , department, in traditional approach we create two class then In main  we call each class method

In above image we have seen that we have common method name and variable name to minimize the code we just write a class that have common method definition and variable name.

Now we have declared a class Employee as a base class

class Permanent_Employee and contractual_employee are child class, both class inherit base class Employee

Now base class have all method and property, we declare base class method as virtual then may be override in child class

See the code I will explain the problem in this code

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace DPSG_DACK

{

    public class Employee

    {

        static string EmpFName,  EmpLName, Department;

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public string department { get; set; }

        public string getName()

        {

            return this.FirstName + " " + this.LastName +" You are working with "+this.department+" department";

        }

        public virtual double calculateSalary()

        {

            throw new NotImplementedException();   

         }

    }

    public class Permanent_Employee:Employee

    {

        public int annualsalry { get; set; }

        public override double calculateSalary()

        {

            return this.annualsalry / 12;

        }

    }

    public class contractual_employee:Employee

    {

        public int perdayRate { get; set; }

        public int NoOfdays { get; set; }

      

        public override double calculateSalary()

        {

            return this.perdayRate * this.NoOfdays;

        }

    }

    class Program

    {

        public static void Main(string[] args)

        {

            Permanent_Employee PEmpObj = new Permanent_Employee()

            {

                FirstName = "shiv",

                LastName = "Kumar",

                department = "IT",

                annualsalry=400000

            };

            Console.WriteLine("Hi MR." + PEmpObj.getName());

            Console.WriteLine("You current Month salry = " + PEmpObj.calculateSalary());

            Console.WriteLine("=============================================================================");

            contractual_employee CempObj = new contractual_employee()

            {

                FirstName = "deepak",

                LastName = "Bhati",

                department = "HR",

                perdayRate = 200,

                NoOfdays=20

            };

            Console.WriteLine("Hi MR." + CempObj.getName());

            Console.WriteLine("You current Month salry = " + CempObj.calculateSalary());

            Console.ReadLine();

        }

    }

}

The above code working fine, but in this code user have rights to create the object of base class Employee and access the calculateSalary() method , if you see the code base class method throw an error

public virtual double calculateSalary()

        {

            throw new NotImplementedException();   

         }

            Employee objEmp = new Employee();

            objEmp.calculateSalary();

To avoid this, we use abstract class by the definition

“An Abstract class is never intended to be instantiated directly.”

  

public abstract class Employee

    {

        static string EmpFName,  EmpLName, Department;

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public string department { get; set; }

        public string getName()

        {

            return this.FirstName + " " + this.LastName +" You are working with "+this.department+" department";

        }

        public abstract double calculateSalary();

     

    }

==================================================

It means the place where we want, our base class method must define in the child class that inherit a base class, or

No one can create the object of base class method directly we use abstract classes

When don’t want the base class to be instantiated 

========================================================

“In Interface we can’t create a filed in base class ” that’s why we use abstract class for best result

Hope this article is use full for you J

Thanks

Shiv Kumar Rawat

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