Are you preparing for a C# OOPs interview? Object-oriented programming (OOP) is at the core of C#, and interviewers often test your understanding of its principles, concepts, and real-world applications. In this guide, we’ve compiled 30+ essential C# OOPs interview questions and answers to help you tackle technical rounds with confidence.
Fun Fact: C# developers in India with 1 to 4 years of experience earn between ₹2 lakh and ₹12 lakh per year.
Basic C# OOPs Interview Questions
Here is a list of basic C Sharp OOPs interview questions and answers:
- What is the difference between a class and an object in C#?
A class is a blueprint that defines properties and behaviours, while an object is an instance of a class with its own values for those properties.
- What is inheritance in C#, and how does it promote code reusability?
Inheritance allows a child class to inherit methods and properties from a parent class, reducing redundant code and promoting reusability.
Example:
class Animal { public void Eat() { Console.WriteLine(“Eating”); } }
class Dog : Animal { public void Bark() { Console.WriteLine(“Barking”); } }
Here, Dog can use Eat() from Animal without redefining it.
- Can you explain polymorphism in C# with an example?
Polymorphism allows methods to behave differently based on the object that calls them.
- Method Overloading:
class MathOperations {
public int Add(int a, int b) => a + b;
public double Add(double a, double b) => a + b;
}
- Method Overriding:
class Parent { public virtual void Show() { Console.WriteLine(“Parent”); } }
class Child : Parent { public override void Show() { Console.WriteLine(“Child”); } }
- What is the difference between an abstract class and an interface in C#?
| Feature | Abstract Class | Interface |
| Definition | Can have both method definitions and implementations | Only method signatures, no implementations (until C# 8.0) |
| Multiple Inheritance | Cannot be inherited by multiple classes | Can be implemented by multiple classes |
| Fields and Properties | Can have fields, properties, and constructors | Cannot have instance fields (only static fields from C# 8.0) |
| Access Modifiers | Methods can have different access modifiers | All members are public by default |
OOPs Concepts C# Interview Questions
You might also be asked about OOPs concept in C# interview questions. Here are some common ones:
- What is encapsulation, and how is it implemented in C#?
This is one of the most important C# OOPs concepts interview questions.
Encapsulation means restricting direct access to object data and modifying it through methods. It is implemented using private fields with public properties:
class Person {
private string name;
public string Name {
get { return name; }
set { if (value.Length > 0) name = value; }
}
}
- How does abstraction differ from encapsulation in C#?
- Encapsulation hides internal state and allows controlled access through methods/properties.
- Abstraction hides complex implementation details and provides a simple interface (achieved via abstract classes or interfaces).
- What are access modifiers in C#, and how do they control access to class members?
Access modifiers define visibility of members:
- public (accessible everywhere)
- private (accessible only within the class)
- protected (accessible within the class and derived classes)
- internal (accessible within the same assembly)
- protected internal (accessible within the same assembly or derived classes)
- private protected (accessible within the same class or derived classes in the same assembly)
- What is the purpose of interfaces in C#, and how do they differ from abstract classes?
An interface defines only method signatures, while an abstract class can have both method signatures and implementations.
interface IAnimal { void Speak(); }
class Dog : IAnimal { public void Speak() { Console.WriteLine(“Bark”); } }
An interface allows multiple inheritance, unlike abstract classes.
C# Object Oriented Interview Questions for Freshers
Let’s go through some frequently-asked C# OOPs interview questions and answers for freshers:
- What is a constructor in C#, and how is it different from a method?
A constructor initializes an object when it is created. It has the same name as the class and does not return a value.
class Car {
public string Model;
public Car(string model) { Model = model; }
}
- Can you explain method overloading with an example in C#?
Method overloading allows multiple methods with the same name but different parameters.
class MathOps {
public int Multiply(int a, int b) => a * b;
public double Multiply(double a, double b) => a * b;
}
- What is method overriding, and how is it achieved in C#?
Method overriding allows a derived class to provide a different implementation for a method in the base class using the override keyword.
class Base { public virtual void Show() { Console.WriteLine(“Base”); } }
class Derived : Base { public override void Show() { Console.WriteLine(“Derived”); } }
- What is the significance of the ‘base’ keyword in C# inheritance?
The base keyword is used to call base class constructors or methods from a derived class.
class Parent { public Parent() { Console.WriteLine(“Parent Constructor”); } }
class Child : Parent { public Child() : base() { Console.WriteLine(“Child Constructor”); } }
C# OOPs Interview Questions for Experienced
If you are an experience candidate, you might come across such C# OOPs interview questions:
- How do you implement the singleton design pattern in C#?
The Singleton pattern restricts a class to only one instance and provides a global access point. A thread-safe implementation is crucial for multi-threaded environments.
public sealed class Singleton {
private static readonly Lazy<Singleton> instance = new(() => new Singleton());
private Singleton() { }
public static Singleton Instance => instance.Value;
}
- What is dependency injection, and how is it used in C# applications?
Dependency Injection (DI) allows passing dependencies into a class rather than creating them inside the class. It improves testability and maintainability.
Example using IoC Container (ASP.NET Core Recommended Approach):
interface ILogger { void Log(string message); }
class ConsoleLogger : ILogger { public void Log(string message) => Console.WriteLine(message); }
class Service {
private readonly ILogger _logger;
public Service(ILogger logger) { _logger = logger; }
public void Process() { _logger.Log(“Processing…”); }
}
// Registering Dependencies in IoC Container
var services = new ServiceCollection();
services.AddScoped<ILogger, ConsoleLogger>();
services.AddScoped<Service>();
// Resolving Dependencies
var provider = services.BuildServiceProvider();
var service = provider.GetRequiredService<Service>();
service.Process();
- Can you explain the SOLID principles and how they apply to C# OOP design?
- S: Single Responsibility – A class should have one responsibility.
- O: Open/Closed – Open for extension, closed for modification.
- L: Liskov Substitution – A derived class should be replaceable for its base class.
- I: Interface Segregation – Clients should not depend on unused interfaces.
- D: Dependency Inversion – Depend on abstractions, not concrete implementations.
- What are delegates in C#, and how are they used to implement event handling?
A delegate is a type that references a method.
delegate void MyDelegate(string message);
class Program {
static void PrintMessage(string msg) => Console.WriteLine(msg);
static void Main() {
MyDelegate del = PrintMessage;
del(“Hello, Delegates!”);
}
}
Delegates are widely used in events and callbacks in C#.
OOPs Interview Questions C# for 5 Years Experienced
These are some common C# Object Oriented interview questions for professionals with 5 years of experience:
- Implement a generic repository pattern in C#.
- Describe a challenging C# project you worked on and how you applied OOP principles to solve problems.
- How do you approach learning new technologies or frameworks in the context of C# development?
OOPs Interview Questions C# for 7 Years Experienced
Here are C# Object Oriented Programming interview questions for candidates with 7 years of experience:
- Design a C# application demonstrating the use of the factory design pattern.
- Can you discuss a time when you had to refactor existing C# code to improve performance or maintainability?
- How do you mentor junior developers in understanding and applying OOP concepts in C#?
C# OOPs Interview Questions for 10 Years Experienced
These interview questions on OOPs C# are commonly asked to senior-level candidates with around 10 years of experience:
- Architect a C# solution that utilizes microservices while adhering to OOP principles.
- Describe your experience in leading a team to develop a complex C# application using OOP methodologies.
- How do you handle conflicts within your development team, especially when deciding on design patterns or OOP approaches?
Advanced C# Object Oriented Programming Interview Questions
Here are some advanced C# OOPs interview questions and answers:
- What is reflection in C#, and how can it be used to inspect metadata at runtime?
Reflection allows runtime type inspection and dynamic method invocation. It’s used for accessing assembly metadata, inspecting types, and working with attributes.
Example:
Type type = typeof(MyClass);
foreach (var method in type.GetMethods()) {
Console.WriteLine(method.Name);
}
It’s commonly used in plugins, serializers, and testing frameworks.
- Can you explain covariance and contravariance in C# with respect to delegates and generics?
- Covariance (out) allows returning a more derived type.
- Contravariance (in) allows passing a more generic type.
Example:
Func<object> covariant = () => “Hello”; // Covariance
Action<string> contravariant = (string s) => Console.WriteLine(s); // Contravariance
Used in delegates and generics for flexibility.
OOPs Tricky Interview Questions C#
You might also come across tricky interview questions on OOPs C# like these:
- How does the ‘this’ keyword differ from the ‘base’ keyword in C#?
- this refers to the current instance of a class.
- base refers to the parent class and is used to call its methods or constructors.
Example:
class Parent { public void Show() { Console.WriteLine(“Parent”); } }
class Child : Parent {
public void Display() { base.Show(); } // Calls Parent’s method
}
- Can you explain the difference between ‘finalize’ and ‘dispose’ methods in C#?
- Finalize() is called by the garbage collector and cannot be explicitly invoked.
- Dispose() is manually called to release unmanaged resources.
Example:
class MyClass : IDisposable {
public void Dispose() { Console.WriteLine(“Resources released”); }
}
C# OOps Scenario Based Interview Questions
Here are some scenario-based OOPs interview questions C# with example:
- How would you design a plugin architecture in C# to allow for dynamic feature addition?
Plugins are loaded dynamically using Reflection and Interfaces.
Example:
Assembly assembly = Assembly.LoadFrom(“Plugin.dll”);
Type type = assembly.GetType(“PluginNamespace.PluginClass”);
object instance = Activator.CreateInstance(type);
Each plugin implements a common interface, allowing easy integration.
- How would you handle versioning in a C# application to maintain backward compatibility?
Versioning is critical to avoid breaking changes in applications, especially Web APIs.
- Use API Versioning in ASP.NET Core
[ApiVersion(“1.0”)]
[Route(“api/v{version:apiVersion}/[controller]”)]
public class UsersController : ControllerBase {
[HttpGet]
public IActionResult GetUsers() => Ok(new { Message = “Users v1” });
}
- Mark Deprecated Methods with [Obsolete]
[Obsolete(“Use NewMethod() instead”)]
public void OldMethod() { }
- Maintain Separate Versioned Classes
public interface IFeatureV1 { void Execute(); }
public class FeatureV1 : IFeatureV1 { public void Execute() => Console.WriteLine(“Feature V1”); }
public class FeatureV2 : IFeatureV1 { public void Execute() => Console.WriteLine(“Feature V2”); }
Wrapping Up
So, these are the top 30+ C# OOPs interview questions and answers to help you prepare effectively. Understanding these concepts will boost your confidence and improve your chances of success.Looking for C# OOPs jobs in India? Hirist is the perfect platform for tech professionals. Find top opportunities and take the next step in your career.
