C# Abstract Class in OOPS – Complete Guide

What is an Abstract Class in C#?

An Abstract Class in C# is a class that cannot be instantiated and may contain abstract methods (without implementation) and implemented methods. It is used as a base for other classes. Abstract classes often work together with Abstraction and Polymorphism in real-world applications.

public abstract class Shape
{
    public abstract void Draw();
    public void Display()
    {
        Console.WriteLine("This is a shape.");
    }
}
      

Why Abstract Class is Required?

• Provides base class for related classes
• Enforces implementation of abstract methods in derived classes
• Supports code reuse and maintains Encapsulation
• Helps maintain organized class hierarchy with Inheritance

When Should We Use Abstract Classes?

• When multiple related classes share behavior
• When some methods need different implementation in each derived class
• When we need base class with partial default behavior

Real Project Scenario – Shapes Example

public class Circle : Shape
{
    public override void Draw()
    {
        Console.WriteLine("Drawing Circle");
    }
}

Shape shape = new Circle();
shape.Draw();
shape.Display();
      

Advantages

• Code reuse and default behavior
• Enforces contract for derived classes
• Helps maintain organized hierarchy

Disadvantages

• Cannot be instantiated
• Limited multiple inheritance support
• May increase coupling

Key Differences Between Abstract Class and Interface

• Abstract class can have fields, constructors, and implemented methods; interface cannot (except default methods in C# 8+)
• Abstract class supports access modifiers; interface members are public by default
• Abstract class allows partial default behavior; interface is purely a contract
• A class can inherit only one abstract class; multiple interfaces can be implemented
• Abstract class is better for closely related classes; interface is better for unrelated classes

Frequently Asked Questions about Abstract Class in C# (Beginner Friendly)