📘 OOP Concepts in Java – Example Codes

A collection of beginner-to-advanced examples that demonstrate the core principles of Object-Oriented Programming (OOP) using Java.
This repository is designed to help students, beginners, and interview candidates understand, practice, and master OOP with small, practical code snippets.

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🎯 What You’ll Learn

• ✅ Classes & Objects
• ✅ Encapsulation
• ✅ Inheritance
• ✅ Polymorphism (Overloading & Overriding)
• ✅ Abstraction (Abstract classes & Interfaces)
• ✅ Composition, Aggregation & Association
• ✅ Static & Final usage
• ✅ Constructor Overloading
• ✅ Inner Classes
• ✅ Enums
• ✅ Interfaces & Multiple Inheritance
• ✅ Design Patterns (Singleton, Factory, Strategy, Observer)

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📂 Project Structure

oop-concepts-examples/
│
├── encapsulation/       # Getters/Setters, Private fields, Immutable classes
├── inheritance/         # Parent/Child classes, Super/Override
├── polymorphism/        # Overloading, Overriding, Interfaces
├── abstraction/         # Abstract classes & methods, Interfaces
├── composition/         # HAS-A relationships (Car → Engine)
├── association/         # Teacher–Student, Department–Professors
├── static-final/        # Static methods, Constants
├── constructors/        # Constructor overloading examples
├── inner-classes/       # Static & Non-static inner classes
├── enums/               # Day, OrderStatus enums
├── interfaces/          # Multiple inheritance with interfaces
└── design-patterns/     # Singleton, Factory, Strategy, Observer

🚀 Getting Started

1. Clone the repository

git clone https://github.com/nuwanthikaishani/oop-fundamentals-java
cd oop-fundamentals-java

2. Compile and Run

cd src/encapsulation
javac EncapsulationDemo.java
java EncapsulationDemo

🎓 Who Is This For?

• ✅ Students learning Java OOP for the first time
• ✅ QA Engineers preparing for coding interviews
• ✅ Anyone who wants a quick refresher on OOP principles