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🚀 Introduction
Object-Oriented Programming (OOP) is a programming paradigm based on the concept of "objects" — units that bundle data (fields) and behavior (methods) together.
Java is built around OOP. When you understand its four core principles, you write cleaner, modular, reusable, and scalable code.
🏛️ The 4 Core Principles of OOP
1️⃣ Encapsulation – “Wrap it up!”
Encapsulation is about hiding internal details of an object and exposing only what’s necessary.
📌 You achieve this using:
privatevariablespublicgetters and setters
✅ Example:
public class BankAccount {
private double balance;
public void deposit(double amount) {
if (amount > 0) balance += amount;
}
public double getBalance() {
return balance;
}
}
🔐 The internal state (balance) is protected and cannot be accessed or changed directly from outside.
2️⃣ Inheritance – “Pass it on!”
Inheritance allows a class (child) to inherit properties and methods from another class (parent).
📌 It promotes code reuse and hierarchical relationships.
✅ Example:
public class Animal {
void eat() {
System.out.println("This animal eats food.");
}
}
public class Dog extends Animal {
void bark() {
System.out.println("Dog barks.");
}
}
🧠 Dog inherits eat() from Animal.
3️⃣ Polymorphism – “One name, many forms!”
Polymorphism allows you to use one method in multiple ways.
It comes in two types:
a. Compile-Time (Method Overloading)
public class MathUtils {
int add(int a, int b) {
return a + b;
}
double add(double a, double b) {
return a + b;
}
}
📌 Same method name, different parameters.
b. Runtime (Method Overriding)
class Animal {
void sound() {
System.out.println("Animal makes sound");
}
}
class Cat extends Animal {
@Override
void sound() {
System.out.println("Cat meows");
}
}
📌 At runtime, the sound() method of Cat overrides Animal.
4️⃣ Abstraction – “Focus on what, not how!”
Abstraction hides unnecessary details and shows only essential features.
📌 In Java, we use:
abstractclassesinterfaces
✅ Example:
interface Vehicle {
void start();
}
class Car implements Vehicle {
public void start() {
System.out.println("Car starts with key.");
}
}
👁 You don’t care how the car starts — you only need to know that it can start.
🎯 Why OOP Matters?
| Benefit | Description |
|---|---|
| ✅ Modularity | Code is divided into logical objects |
| ✅ Reusability | Inheritance allows the reuse of common logic |
| ✅ Maintainability | Encapsulation protects data integrity |
| ✅ Flexibility | Polymorphism lets you swap implementations |
🧠 Final Thoughts
Object-Oriented Programming gives you the power to:
- Build real-world models in code
- Write clean, organized, and maintainable applications
- Apply SOLID principles and design patterns easily
💬 Mastering OOP is a superpower every Java developer must have!
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