Difference Between Abstract Class and Normal Class in C#

C# is an object-oriented programming language that provides a powerful class system, allowing developers to define behavior through classes, inheritance, and polymorphism. Among the various class types in C#, abstract classes and normal (concrete) classes are key concepts, each serving different purposes in application design and development.

Understanding the distinction between abstract class and normal class is essential for writing clean, maintainable, and scalable C# code.

What is a Normal Class in C#?

A normal class, often referred to as a concrete class, is a fully defined class that can be instantiated (i.e., you can create objects from it). It may include fields, methods, properties, constructors, and other members, all of which can have complete implementations.

✅ Characteristics

• It can be instantiated.
• Can have fully implemented methods.
• It can be sealed, inherited, or used as-is.
• Does not need to contain any abstract members.

🔧 Example

public class Car
{
    public void Start()
    {
        Console.WriteLine("Car started.");
    }
}

🧪 Usage

Car myCar = new Car();
myCar.Start();  // Output: Car started.

What is an Abstract Class in C#?

An abstract class is a class that cannot be instantiated directly and is intended to be used as a base class. It may contain:

• Abstract members (methods or properties without implementation).
• Non-abstract (fully implemented) members.

Abstract classes define a common interface or base functionality for derived classes, encouraging code reuse and enforcing certain behaviors in child classes.

✅ Characteristics

• Cannot be instantiated directly.
• Must be inherited to be used.
• May contain abstract methods (must be overridden in derived classes).
• May contain implemented methods as well.
• Used to define partial behavior and enforce structure.

🔧 Example

public abstract class Animal
{
    public abstract void MakeSound(); // No implementation here

    public void Eat()
    {
        Console.WriteLine("Eating food.");
    }
}

🧪 Derived Class Example

public class Dog : Animal
{
    public override void MakeSound()
    {
        Console.WriteLine("Bark");
    }
}

🧪 Usage

Dog dog = new Dog();
dog.MakeSound(); // Output: Bark
dog.Eat();       // Output: Eating food.

Key Differences: Abstract Class vs Normal Class

Feature	Abstract Class	Normal Class
Instantiation	Cannot be instantiated	Can be instantiated
Purpose	Acts as a base class for inheritance and enforces structure	Used to create fully defined, usable objects
Abstract Members	Can contain abstract members (methods or properties without implementation)	Cannot contain abstract members
Implementation	Can have both implemented and unimplemented (abstract) methods	Must have complete implementation for all members
Use Case	When you want to provide a base functionality and enforce implementation rules in derived classes	When you want to define complete behavior of an object
Inheritance	Meant to be inherited from	Can be inherited or used directly
Keyword	Declared using the abstract keyword	No special keyword required

When to Use Each?

Use Abstract Class When

• You have a base concept with some shared code and some behaviors that vary.
• You want to enforce a contract for derived classes.
• You don’t want to allow instantiation of the base class.

Use Normal Class When

• You need a fully functional class with no intention of enforcing structure on derived classes.
• You need to instantiate the class directly.
• You want a straightforward implementation of functionality.

Can an Abstract Class Have Constructors?

Yes. Abstract classes can have constructors, which are called when derived classes are instantiated. These constructors can be used to initialize state common to all derived types.

public abstract class Shape
{
    protected string Color;

    public Shape(string color)
    {
        Color = color;
    }
}

Real-Life Analogy

Think of an abstract class as a blueprint for a house – you can’t live in the blueprint, but you can create real houses from it by filling in the missing details.

A normal class is a fully built house ready to be used without needing additional work.

Criteria	Abstract Class	Normal Class
Can it be instantiated?	❌ No	✅ Yes
Can it have abstract methods?	✅ Yes	❌ No
Used for?	Inheritance, enforcing structure	Creating usable objects
Can it contain implemented methods?	✅ Yes	✅ Yes
Must override abstract members in the child class?	✅ Yes	❌ Not applicable

🧠 Conclusion

Choosing between an abstract class and a normal class depends on your software design. If you're creating a hierarchy of related objects with shared and enforced behavior, an abstract class is your go-to. If you just need a reusable object with complete functionality, a normal class works best.