Object & Class in Java

Imagine you have a box. This box is special because it can hold different things like toys, books, or anything you like. In programming, we have something similar called a “class.”

What is a Class?

A class is like a blueprint or plan for creating objects. Imagine you have a blueprint for building a house. It tells you what the house should look like and what rooms it should have. Similarly, a class tells the computer what properties and actions an object should have when it’s created.

Structure of a Class

// Define a class
[access_modifier] class ClassName {
//Execution code like methods, fields, properties, constructor, etc.
}

What is an Object?

Now, imagine using that blueprint to create an actual car. That car you create is called an “object.”
An object is a real instance or copy of a class. It has unique properties (like the color of the car) and behaviors (like driving or stopping).

Structure of an Object
// Creating an object
ClassName objectName = new ClassName(parameters);

// Accessing fields
objectName.fieldName = value;

// Calling methods
objectName.methodName();

Example: Car Class and Objects

public class Car {
    public String color;
    public int speed;

    public void drive() {
        System.out.println(“The car is driving.”);
    }

    public void stop() {
        System.out.println(“The car has stopped.”);
    }

    public static void main(String[] args) {
        Car myCar = new Car();
        myCar.color = “Red”;
        myCar.speed = 60;

        Car anotherCar = new Car();
        anotherCar.color = “Blue”;
        anotherCar.speed = 50;

        myCar.drive();
        anotherCar.stop();
    }
}

Explanation

//Define a simple class for the Car
public class Car {
    // Properties (attributes) of the car
    public String color;
    public int speed;

    // Methods (actions) the car can do
    public void drive() {
        System.out.println(“The car is driving.”);
    }

    public void stop() {
        System.out.println(“The car has stopped.”);
    }

    public static void main(String[] args) {
        // Let’s create objects (instances) of the Car class:
        Car myCar = new Car(); // Creating a new car object
        myCar.color = “Red”; // Setting the color of the car
        myCar.speed = 60; // Setting the speed of the car

        Car anotherCar = new Car(); // Creating another car object
        anotherCar.color = “Blue”; // Setting color
        anotherCar.speed = 50; // Setting speed

        // Using the methods of the car objects
        myCar.drive(); // Output: The car is driving.
        anotherCar.stop(); // Output: The car has stopped.
    }
}

Tasks:
1. Create a class named Employee with the following properties:
○ String name
○ int id
○ double salary
Create an object of the Employee class in the main method. Assign values to the properties and print them to the console.
2. Create a class named Product with the following properties:
○ String productName
○ String category
○ double price
Create an object of the Product class in the main method. Assign values to the properties and print them to the console.
3. Create a class named Student with the following properties:
○ String name
○ int rollNumber
○ String course
Create an object of the Student class in the main method. Assign values to the properties and print them to the console.
4. Create a class named Car with the following properties:
○ String make
○ String model
○ int year
Create an object of the Car class in the main method. Assign values to the properties and print them to the console.
5. Create a class named Book with the following properties:
○ String title
○ String author
○ int pages
Create an object of the Book class in the main method. Assign values to the properties and print them to the console.