What are the Four Pillars of OOP?
💡 Concept: Four Pillars of Object-Oriented Programming
The four pillars of OOP—Encapsulation, Inheritance, Abstraction, and Polymorphism—are core concepts that guide structured and maintainable code design in C#.
📘 Quick Intro
Each pillar serves a specific role in object-oriented design. Together, they promote modularity, reuse, abstraction of complexity, and flexibility in application development.
🧠 Analogy
Think of a car: the driver uses a steering wheel (abstraction), doesn’t see the engine working (encapsulation), multiple models use a base chassis (inheritance), and turning the wheel works for different brands (polymorphism). That’s OOP in action.
🔧 Technical Explanation
- Encapsulation: Bundles data and behavior in classes, hides implementation using access modifiers.
- Inheritance: Enables one class to inherit members from another, promoting code reuse.
- Abstraction: Shows essential behavior while hiding complex internals, often using interfaces or abstract classes.
- Polymorphism: Allows methods to behave differently depending on the object that calls them, using
virtual,override, or interfaces.
🎯 Use Cases
- 🔒 Encapsulation protects internal logic and ensures a clean API.
- ♻️ Inheritance enables reuse across similar components.
- 🎭 Abstraction simplifies complex systems for the end user.
- 🔁 Polymorphism enhances flexibility by supporting multiple behaviors with the same interface.
💻 Real Code Example
public abstract class Shape
{
public abstract double Area();
}
public class Circle : Shape
{
public double Radius { get; set; }
public override double Area() => Math.PI * Radius * Radius;
}
public class Square : Shape
{
public double Side { get; set; }
public override double Area() => Side * Side;
}
❓ Interview Q&A
Q1: What are the four pillars of OOP?
A: Encapsulation, Inheritance, Abstraction, and Polymorphism.
Q2: How does encapsulation improve code quality?
A: By hiding internal implementation details from external access.
Q3: What is the benefit of inheritance?
A: It allows code reuse and simplifies the creation of specialized classes.
Q4: How is abstraction implemented in C#?
A: Through abstract classes and interfaces.
Q5: What is polymorphism in C#?
A: It allows methods to perform different behaviors based on the object instance.
Q6: Is method overloading part of polymorphism?
A: Yes, it is one type known as compile-time polymorphism.
Q7: Can interfaces be used for abstraction?
A: Yes, they define a contract without implementation details.
Q8: Can a subclass override a non-virtual method?
A: No, only virtual or abstract methods can be overridden.
Q9: What is dynamic polymorphism?
A: Runtime method behavior determined using virtual and override.
Q10: What access modifier helps encapsulate data?
A: private hides data, public exposes it.
📝 MCQs
Q1. Which is NOT a pillar of OOP?
- Inheritance
- Abstraction
- Polymorphism
- Compilation
Q2. Which keyword enables runtime polymorphism?
- static
- sealed
- virtual
- readonly
Q3. Which pillar hides internal state?
- Polymorphism
- Inheritance
- Encapsulation
- None
Q4. Which enables a class to reuse another's members?
- Polymorphism
- Encapsulation
- Inheritance
- Abstraction
Q5. Which allows different behaviors using same method signature?
- Inheritance
- Polymorphism
- Interface
- Encapsulation
Q6. What implements abstraction in C#?
- Events
- Structs
- Abstract classes and interfaces
- Delegates
Q7. Which modifier prevents method overriding?
- abstract
- sealed
- readonly
- partial
Q8. Which pillar enhances code readability and reuse?
- Polymorphism
- Encapsulation
- Inheritance
- All
Q9. What is the default access modifier for class members?
- public
- protected
- internal
- private
Q10. How is method overloading achieved?
- Different names
- Same name, same signature
- Same name, different signatures
- Overriding
💡 Bonus Insight
Mastering the four OOP pillars sets the foundation for writing maintainable and scalable applications. They’re essential for real-world enterprise development, especially in C# and .NET.
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