Java OOPs Concepts

Object-Oriented Programming designs a program using classes and objects. Its four pillars make code modular, reusable and easier to maintain.

Concept	Idea	In Java
Encapsulation	Bundle data and methods; hide internal details	`private` fields + getters/setters
Inheritance	One class acquires properties of another	`extends`
Polymorphism	One action, many forms	Overloading and overriding
Abstraction	Show what, hide how	`abstract` classes, `interface`

Encapsulation Example

Java

class Account {
    private double balance;           // hidden

    public void deposit(double amt) {
        if (amt > 0) balance += amt;  // controlled access
    }
    public double getBalance() { return balance; }
}

public class Main {
    public static void main(String[] args) {
        Account acc = new Account();
        acc.deposit(1500);
        System.out.println("Balance: " + acc.getBalance());
    }
}

Balance: 1500.0

Abstraction Example

Java

abstract class Shape {
    abstract void draw();
}
class Circle extends Shape { void draw() { System.out.println("Drawing circle"); } }
class Square extends Shape { void draw() { System.out.println("Drawing square"); } }

Shape s1 = new Circle(); s1.draw();
Shape s2 = new Square(); s2.draw();

Drawing circle Drawing square

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