What types of inheritance does .NET support?

.NET supports single, multilevel, hierarchical, and multiple inheritance through interfaces.

Can you use multiple base classes in .NET?

No, .NET does not allow multiple class inheritance but supports multiple interfaces.

Different Types of Inheritance in .NET

💡 Concept: Types of Inheritance in .NET

Inheritance is one of those "superpowers" of object-oriented programming. It’s how you teach a class to automatically pick up traits, behaviors, and rules from another class—just like kids inherit traits from their parents 👨‍👩‍👧. In .NET, inheritance comes in different flavors, each designed to help you reuse code and build cleaner, extensible systems.

📘 Quick Intro

At its core, inheritance is about sharing and extending behavior. Instead of rewriting the same logic in multiple places, you define it once in a base class and let child classes reuse or override it. .NET supports different types of inheritance so developers can model relationships the way real-world systems evolve — from simple single-level to more complex multi-level setups.

🧠 Analogy / Short Story

Imagine a car company. 🚗 - First, they create a basic Car model with common features (wheels, engine, brakes). - Then they roll out a SportsCar 🏎️ (inherits Car’s features but adds turbo). - They also release a Truck 🚚 (inherits Car’s features but adds load capacity). - Later, they design an ElectricTruck ⚡🚚 (inherits from Truck but changes the fuel system). Each new model doesn’t reinvent the wheel (literally) — it just extends what’s already there. That’s exactly how inheritance works in .NET: you build once, reuse everywhere, and evolve cleanly.

🔧 Technical Breakdown

Single Inheritance: One class inherits from one base class. Example: Dog : Animal.
Multilevel Inheritance: A chain of inheritance where each class builds on the previous. Example: Puppy : Dog : Animal.
Hierarchical Inheritance: Multiple classes share the same parent. Example: Cat : Animal, Dog : Animal, Bird : Animal.
Multiple Inheritance (via interfaces): .NET doesn’t allow multiple base classes (to avoid the “diamond problem”), but you can implement multiple interfaces. Example: FlyingCar : IVehicle, IAircraft.

🎯 Purpose & Use Cases

✅ Code reuse: Common logic (like logging, validation, or base properties) lives in one place and spreads naturally to child classes.
✅ Consistency: Define standard rules/behavior in a base class, so all child classes follow the same contract.
✅ Polymorphism & Extensibility: Allows writing flexible code that can work with multiple derived types interchangeably.
✅ Cleaner evolution: As your system grows, you extend existing functionality instead of duplicating it.

💻 Real Code Example

public class Animal {
    public void Eat() => Console.WriteLine("Eating...");
}

public class Dog : Animal {
    public void Bark() => Console.WriteLine("Barking...");
}

public class Puppy : Dog {
    public void Weep() => Console.WriteLine("Weeping...");
}

public interface IWalkable { void Walk(); }
public interface IRunable { void Run(); }

public class Person : IWalkable, IRunable {
    public void Walk() => Console.WriteLine("Walking");
    public void Run() => Console.WriteLine("Running");
}

❓ Interview Q&A

Q1: What is inheritance in .NET?
A: A mechanism to derive new classes from existing ones for code reuse.

Q2: Does .NET support multiple inheritance via classes?
A: No, but supports via interfaces.

Q3: What is hierarchical inheritance?
A: Multiple classes inherit from a single base class.

Q4: Why use interfaces for multiple inheritance?
A: Interfaces allow type abstraction and multiple inheritance.

Q5: Can a class inherit both class and interface?
A: Yes, single class + multiple interfaces.

Q6: Which inheritance supports polymorphism?
A: Single, multilevel and interface-based inheritance.

Q7: Is constructor inherited in C#?
A: No, constructors are not inherited.

Q8: Can base class methods be overridden?
A: Yes, if marked virtual or abstract.

Q9: How to prevent inheritance in C#?
A: Use sealed keyword.

Q10: Can interfaces have default implementations?
A: Yes, from C# 8.0 onwards.

📝 MCQs

Q1. Which type of inheritance is supported directly in C#?

Multiple Inheritance
Diamond Inheritance
Single Inheritance
Hybrid Inheritance

Q2. How can .NET achieve multiple inheritance?

Abstract Classes
Delegates
Using Interfaces
Partial Classes

Q3. What does 'sealed' keyword do?

Makes class abstract
Prevents a class from being inherited
Allows multiple inheritance
Disables constructors

Q4. Which inheritance allows a class to extend a class that’s already derived?

Single
Multilevel
Hierarchical
None

Q5. Can a class inherit from more than one base class in .NET?

Yes
No
Only abstract
Only sealed

Q6. What does interface inheritance enable?

Overriding
Constructors
Multiple inheritance
Method hiding

Q7. Which of these is an example of hierarchical inheritance?

Car inherits from Vehicle
Dog and Cat inherit from Animal
Puppy inherits from Dog
None

Q8. What cannot be inherited in C#?

Methods
Properties
Fields
Constructors

Q9. Which keyword is used to prevent method override?

const
readonly
sealed
abstract

Q10. Which of the following supports polymorphism in .NET?

Encapsulation
Overloading
Inheritance
Constructor chaining

💡 Bonus Insight

Although multiple inheritance through classes is not supported, interface-based inheritance provides a safe and powerful alternative without the diamond problem.