Object-Oriented Programming (OOP) with Java

This repository is a beginner-friendly guide to object-oriented programming (OOP) using Java.

OOP is a way of organizing programs around objects. An object groups:

• State — the data it stores
• Behavior — the actions it can perform

For example, a Car object might store its color and speed, and provide methods such as accelerate() and brake().

A small Java example

class Car {
    private String color;

    Car(String color) {
        this.color = color;
    }

    void describe() {
        System.out.println("This car is " + color + ".");
    }
}

public class Main {
    public static void main(String[] args) {
        Car myCar = new Car("blue");
        myCar.describe();
    }
}

What is happening?

1. Car is a class: a blueprint for car objects.
2. color is a field: data stored by each car.
3. Car(String color) is a constructor: it sets up a new object.
4. describe() is a method: behavior the object provides.
5. new Car("blue") creates an object (also called an instance).

Learning path

Read the guides in this order:

1. Introduction to OOP
2. Encapsulation
3. Inheritance
4. Polymorphism
5. Abstraction
6. Composition

Why use OOP?

OOP can make larger programs easier to understand by keeping related data and behavior together. It can also help you reuse code and change one part of a program without rewriting everything.

OOP is a tool, not a rule, so you use it when objects make the problem clearer.

Running Java examples

Save an example in a file whose name matches its public class, then run:

javac Main.java
java Main

You need a Java Development Kit (JDK) installed. Java 17 or newer is a good choice for learning.