Classes, Objects & Attributes

A class is a blueprint. An object is one instance built from that blueprint.

Classes & Objects

A class is a blueprint. An object is one instance built from that blueprint.

Create object with new: Student s = new Student();

Real-life example: Class = cookie cutter shape. Object = each actual cookie you bake from that cutter.

Class and object

class Car {
    String brand;
    int year;
}

public class Main {
    public static void main(String[] args) {
        Car myCar = new Car();
        myCar.brand = "Toyota";
        myCar.year = 2024;
        System.out.println(myCar.brand);
    }
}

Attributes — fields of a class

Attributes (fields) store object state — name, age, balance. Each object has its own copy of instance fields.

Access with dot: object.fieldName. Initialize in constructor or at declaration.

Real-life example: Attributes are labels on a student ID card — name, roll number, photo — unique per student.

Instance attributes

class Book {
    String title = "Unknown";
    String author;
    double price;

    void showInfo() {
        System.out.println(title + " by " + author + " — ₹" + price);
    }
}