Using Abstract Class In C#

Vithal Wadje

7y157.1k21100Article

C#Abstract ClassAbstractKeywordUse of Abstract Class

21 Comments

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Hemalatha Sunnapu8y ago
When to use abstract class and when to use interfaces?
- Hemalatha Sunnapu7y ago
  When We will get reply?????????
- Vithal Wadje7y ago
  Check my article list related to Oops , I have explained in details
Hemalatha Sunnapu8y ago
The same question i want to ask you
Ganapathi Raman8y ago
Nice explanation bro.. Thanks
Vithal Wadje12y ago
thanks vishajeet
Vishvajeet Pawar12y ago
Nice Article..Vithal...!!
Vithal Wadje13y ago
thank you charinda nanayakkara sir,it my pleasure
Vithal Wadje13y ago
Thank you sarath kumar sir
charinda nanayakkara13y ago
nice simple article.thanx.
sarath kumar13y ago
Hi thanks for your article .. But i am having doubt . How the abstract class will work in asp.net?? Whatever the class we can create object for that directly know.. Whether it will improve in performance???
- Vithal Wadje7y ago
  Check sample code
Vithal Wadje13y ago
Thank you akhil sir for reading my article, this is a very good question now i am preparing article on that since last few days once it complted i will personally inform you. if you have suggestion regarding my current artilce then contact me i will improve it
Akhil Mittal13y ago
When to use abstract class and when to use interfaces????
- Ankit Singh9y ago
  The class is created for the purpose of providing common fields and members to all subclasses then use abstract class
Vithal Wadje13y ago
adil sir ,refer examples from above
Adil Ansari13y ago
thanks for this article, but i am still confused that in scenario where i need "common fields and members to all sub-classes" i can just use the non abstract class instead of the abstract class and also if implementation of the some of the member in my class isn't possible, I can make them virtual in non abstract class and can overwrite it later on in sub-classes. So when, where and why we should use the Abstract class ?? Any clarification would be appreciated!
Vithal Wadje13y ago
ok sir,i will try to write as soon as possible
Rohatash Kumar13y ago
waiting ...Vithal
Vithal Wadje13y ago
yes Rohatash sir ,i will write a new article on it becaue it deep concept and in some cases Abstract Base Classes fail in versioning
Rohatash Kumar13y ago
Vithal. can you define versioning with abstract class?

How To Use An Abstract Class In C#

What is an abstract class in C#? This is one of the most frequently asked questions in .NET technical interviews. In this article, we will learn what an abstract class it, how to declare it, and how to use an abstract class in C#.

What is an abstract class?

An abstract class in C# provides a blueprint of what its derived classes must implement before they can use it. An abstract class contains abstract members including abstract methods, abstract properties, abstract indexers, and abstract events. All abstract members of a class must be implemented by its derived classes.

Here are the key characteristics of abstract classes,

An abstract class cannot be instantiated.
A class may inherit one abstract class only.
An abstract class may contain abstract methods, properties, and events.
An abstract class can’t be modified with the sealed class modifier.
A derived from an abstract class must implement all inherited abstract methods and accessors

How to declare abstract methods in C#

An abstract method is declared by using the abstract modifier in a method declaration to indicate that the method is an abstract method and does not contain implementation. An abstract method is implicitly a virtual method.

Abstract methods have no implementation, so the method definition is followed by a semicolon instead of a normal method block. Derived classes of the abstract class must implement all abstract methods. When an abstract class inherits a virtual method from a base class, the abstract class can override the virtual method with an abstract method.

public abstract void AMethod();

The implementation is provided by a method override, which is a member of a non-abstract class.

How to declare abstract properties in C#

An abstract property is declared by using the abstract modifier in a property declaration to indicate that the property is an abstract method and does not contain implementation.

How to declare an abstract class in C#?

The abstract keyword is used to create an abstract class. The class definition starts with the abstract keyword.

The following code example declares an abstract base class, Shape.

abstract public class Shape
{
}

The following code example declares an abstract base class, Shape, with an abstract method and an abstract property.

// Abstract class
abstract public class Shape
{
// Abstract properties
public abstract int Height { set; }
// Abstract method
public abstract int Area();
}

How to implement an abstract class in C#?

The following code implements the Shape abstract class by inheriting two classes, Rectangle and Square, from the class. Both derived classes must implement all abstract members. In our case, both classes implement Height property and Area method.

// Rectangle class
public class Rectangle : Shape
{
private int width;
private int height;
public Rectangle(int height)
{
this.height = height;
}
public override int Height { set => height = value; }
public int Width {set => width = value; }
public override int Area()
{
return this.height * this.width;
}
}
// Square class
public class Square : Shape
{
private int width = 0;
private int height;
public Square(int w)
{
this.width = w;
}
public override int Height { set => height = value; }
public override int Area()
{
return this.width * this.width;
}
}

Complete Code Example

The following code example is the complete console application written in .NET Core.

using System;
namespace Abstractsample
{
class Program
{
static void Main(string[] args)
{
Square sq = new Square(10);
Console.WriteLine($"Square area: {sq.Area()}");
Rectangle rect = new Rectangle(50);
rect.Width = 20;
Console.WriteLine($"Rectangle area: {rect.Area()}");
Console.ReadKey();
}
}
// Rectangle class
public class Rectangle : Shape
{
private int width;
private int height;
public Rectangle(int height)
{
this.height = height;
}
public override int Height { set => height = value; }
public int Width {set => width = value; }
public override int Area()
{
return this.height * this.width;
}
}
// Square class
public class Square : Shape
{
private int width = 0;
private int height;
public Square(int w)
{
this.width = w;
}
public override int Height { set => height = value; }
public override int Area()
{
return this.width * this.width;
}
}
// Abstract class
abstract public class Shape
{
// Abstract properties
public abstract int Height { set; }
// Abstract method
public abstract int Area();
}
}

Summary

In this article, I discussed what an abstract class is and how to implement an abstract class in C#.