---
title: "Abstract class in C#"  
description: "A Method without any method body is known as an abstract, what the method contain only declaration without any implementation & should be declare by o"  
author: "Anonymous User"  
published: 2016-05-05  
updated: 2018-03-27  
canonical: https://www.mindstick.com/articles/12035/abstract-class-in-c-sharp  
category: "c#"  
tags: ["c#", "oops", "abstract class"]  
reading_time: 2 minutes  

---

# Abstract class in C#

A Method without any method body is known as an [abstract](https://www.mindstick.com/interview/1411/what-is-an-abstract-schema), what the method contain only declaration without any implementation & should be declare by only the ‘abstract modifier’.

The class under which we define these abstract methods is an abstract class & should be declared by ‘abstract modifier’.

## The purpose of abstract class is to provide default functionality to its sub classes:

**\****1.** When a method is declared as abstract in the base class then every derived class of that class must provide its own definition for that method.

\
**2**. An abstract class can also contain methods with complete implementation, besides abstract methods.

**3.** When a class contains at least one abstract method, then the class must be declared as abstract class.

**4.** It is mandatory to override abstract method in the derived class.

**5.** When a class is declared as abstract class, then it is not possible to create an instance for that class. But it can be used as a parameter in a method.

**Example:**

\
**ShapeAbstract class**

```
using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks; namespace OopsConcepts{    public abstract class ShapeAbstract    {        abstract public  int area();    }}
```

**Square class**\

```
using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks; namespace OopsConcepts{    class Square:ShapeAbstract    {        int side = 0;        public Square(int n)        {            side = n;        }         public override int area()        {            return side * side;        }     }}
```

**AbstractTest class**\

```
using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks; namespace OopsConcepts{    class AbstractTest    {        static void Main(string[]args)        {           Square sq = new Square(12);            Console.WriteLine("Square : {0}", sq.area());        }    }} 
```

\

Output: Square : 144

---

Original Source: https://www.mindstick.com/articles/12035/abstract-class-in-c-sharp

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