What is Object-Oriented Programming in C# | FullStackPrep.Dev

Q: What is Object-Oriented Programming in C#?

OOP in C# is a programming model that organizes code around objects—encapsulated units of data and methods.

💡 Concept: Object-Oriented Programming (OOP)

Object-Oriented Programming (OOP) is a paradigm in C# that structures code around objects—self-contained units combining data and behavior. OOP helps organize large programs, promote reuse, and model real-world systems effectively.

📘 Quick Intro

OOP in C# focuses on designing software using classes and objects. It enables principles like encapsulation, inheritance, abstraction, and polymorphism—collectively called the four pillars of OOP.

🧠 Analogy

Imagine a car as an object. It has data (color, model) and behavior (drive, brake). You don't need to know how the engine works—just how to drive. OOP in C# works the same way: objects expose what they do and hide how they do it.

🔧 Technical Explanation

🔹 OOP encourages modularity by creating classes as blueprints and objects as instances.
🔹 Supports encapsulation to hide internal data and behavior using access modifiers.
🔹 Inheritance allows reuse of base class features in derived classes.
🔹 Polymorphism enables different implementations with a unified interface.
🔹 Abstraction separates interface from implementation for simplified interactions.

🎯 Use Cases

✔️ Designing reusable, maintainable components.
✔️ Modeling real-world entities (e.g., Users, Products).
✔️ Reducing code duplication through inheritance and interfaces.
✔️ Promoting team collaboration with clearly defined class responsibilities.

💻 Real Code Example

public class Animal
{
    public string Name { get; set; }

    public virtual void Speak()
    {
        Console.WriteLine("Animal speaks");
    }
}

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

❓ Interview Q&A

Q1: What is Object-Oriented Programming?
A: A design approach where software is built using objects that encapsulate data and behavior.

Q2: What are the four pillars of OOP?
A: Encapsulation, Inheritance, Abstraction, and Polymorphism.

Q3: What is encapsulation?
A: Hiding internal object data using access modifiers like private and public.

Q4: What is inheritance in C#?
A: It's a mechanism to derive new classes from existing ones.

Q5: Define abstraction in C#.
A: Showing essential features while hiding internal implementation.

Q6: What is polymorphism?
A: The ability for methods to behave differently based on the object type.

Q7: What is the base class for all types in C#?
A: System.Object

Q8: How does OOP promote reuse?
A: Through inheritance and modular class design.

Q9: Can C# classes implement multiple interfaces?
A: Yes, but can inherit only one class.

Q10: How do you achieve abstraction in C#?
A: Using abstract classes and interfaces.

📝 MCQs

Q1. What is the main principle behind OOP?

Flat functions
Global variables
Objects encapsulate data and behavior
Sequential programming

Q2. Which is NOT a pillar of OOP?

Encapsulation
Inheritance
Compilation
Abstraction

Q3. Which access modifier hides class data?

public
internal
private
protected

Q4. Can a class inherit multiple classes in C#?

Yes
No
Only sealed
If partial

Q5. What is used to achieve polymorphism?

sealed
readonly
virtual and override keywords
params

Q6. What is the purpose of an abstract class?

Used in static methods
Cannot be inherited
Provide a base with optional implementation
None

Q7. What is a real-world analogy for encapsulation?

Glass jar
Capsule hiding medicine
Open book
None

Q8. What is System.Object?

Static class
Base for interfaces
Root of all C# types
Only for collections

Q9. How does OOP help large teams?

Creates fewer files
Avoids testing
Encourages modular reusable code
Prevents bugs

Q10. What is true about classes?

They store only static data
They define object structure and behavior
They are obsolete
None of these

💡 Bonus Insight

Object-oriented programming provides the foundation for most modern applications and frameworks. Understanding how to structure code using classes, interfaces, and design principles is key to mastering C# development.

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What is Object-Oriented Programming?