Tutorials/Java/Opps

Lesson

Introduction

Opps/Java

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Java OOP (Object-Oriented Programming) Introduction

What is OOP?

OOP = Object-Oriented Programming
A programming approach based on classes and objects
Used to model real-world entities

Class

A blueprint/template to create objects
Contains:
- Variables (data)
- Methods (functions)

plaintext

class Car {
    String color;
    int speed;

    void drive() {
        System.out.println("Car is running");
    }
}

Object

An instance of a class
Used to access class properties and methods

plaintext

Car c1 = new Car();
c1.color = "Red";
c1.drive();

Pillars of OOP

1. Encapsulation 🔒

Wrapping data + methods into a single unit
Use private variables + getters/setters

Data hiding
Secure code

java

class Student {
    private int marks;

    public void setMarks(int m) {
        marks = m;
    }

    public int getMarks() {
        return marks;
    }
}

2. Inheritance

One class inherits another class
Use extends keyword

Code reuse
Parent → Child relationship

java

class Animal {
    void eat() {
        System.out.println("Eating");
    }
}

class Dog extends Animal {
    void bark() {
        System.out.println("Barking");
    }
}

3. Polymorphism

One method, multiple forms

Types:

Method Overloading (compile-time)
Method Overriding (runtime)

java

class MathUtil {
    int add(int a, int b) {
        return a + b;
    }

    int add(int a, int b, int c) {
        return a + b + c;
    }
}

4. Abstraction

Hiding implementation details
Show only important features

Key Points:

Use abstract class or interface
Reduce complexity

java

abstract class Vehicle {
    abstract void start();
}

class Car extends Vehicle {
    void start() {
        System.out.println("Start with key");
    }
}

Advantages of OOP

✔ Code reusability
✔ Easy maintenance
✔ Data security
✔ Real-world modeling

Quick Short

Class → Blueprint
Object → Instance

Encapsulation → Data hiding
Inheritance → Code reuse
Polymorphism → Many forms
Abstraction → Hide details

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