Advanced Coding & Software Engineering Program

Java Classes and Objects Tutorial for Beginners

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Last Updated on: 24th Oct 2025 13:18:00 PM

Welcome to this complete beginner-friendly tutorial on Classes and Objects in Java — the foundation of Object-Oriented Programming (OOP)!

This tutorial explains everything step-by-step with real-life analogies, clear code examples, and practical scenarios you can relate to. By the end, you’ll not only understand what classes and objects are, but also how to use them like a pro.

Let’s start!

 

What Are Classes and Objects?

Term	Definition	Real-Life Example
Class	A blueprint or template for creating objects. It defines properties and behaviors.	A car design on paper (Toyota Camry blueprint)
Object	An instance of a class. A real, usable thing created from the blueprint.	A real car built in the factory using that design

 

 "Think of it like this:

A class is like a recipe for chocolate cake.

An object is the actual cake you bake using that recipe."

 

1. Creating a Class in Java

 

Syntax of a Class

class ClassName {
    // Fields (data/variables)
    // Methods (behaviors/functions)
}

 

Real-Life Example: Mobile Phone

Let’s create a MobilePhone class.

class MobilePhone {
    // Fields (Properties/Attributes)
    String brand;
    String model;
    int storageGB;
    double price;
    boolean isOn;

    // Methods (Behaviors/Actions)
    void turnOn() {
        isOn = true;
        System.out.println(brand + " " + model + " is now ON.");
    }

    void turnOff() {
        isOn = false;
        System.out.println(brand + " " + model + " is now OFF.");
    }

    void makeCall(String contact) {
        if (isOn) {
            System.com.println("Calling " + contact + "...");
        } else {
            System.out.println("Phone is OFF. Cannot call.");
        }
    }

    void displayInfo() {
        System.out.println("Brand: " + brand);
        System.out.println("Model: " + model);
        System.out.println("Storage: " + storageGB + " GB");
        System.out.println("Price: $" + price);
        System.out.println("Status: " + (isOn ? "ON" : "OFF"));
    }
}

 

 

2. Creating Objects (Instances)

 

Syntax to Create an Object

ClassName objectName = new ClassName();

 

Creating Real Phones from the Blueprint

public class PhoneShop {
    public static void main(String[] args) {
        // Creating objects (real phones)
        MobilePhone phone1 = new MobilePhone();
        MobilePhone phone2 = new MobilePhone();

        // Setting values for phone1
        phone1.brand = "Samsung";
        phone1.model = "Galaxy S23";
        phone1.storageGB = 256;
        phone1.price = 899.99;
        phone1.isOn = false;

        // Setting values for phone2
        phone2.brand = "Apple";
        phone2.model = "iPhone 15";
        phone2.storageGB = 128;
        phone2.price = 1099.99;
        phone2.isOn = false;

        // Using the phones (calling methods)
        phone1.turnOn();
        phone1.makeCall("Mom");
        phone1.displayInfo();

        System.out.println(); // empty line

        phone2.turnOn();
        phone2.makeCall("Friend");
        phone2.displayInfo();

        phone1.turnOff();
    }
}

 

Output:

Samsung Galaxy S23 is now ON.
Calling Mom...
Brand: Samsung
Model: Galaxy S23
Storage: 256 GB
Price: $899.99
Status: ON

Apple iPhone 15 is now ON.
Calling Friend...
Brand: Apple
Model: iPhone 15
Storage: 128 GB
Price: $1099.99
Status: ON

Samsung Galaxy S23 is now OFF.

 

3. Key Concepts Explained

Concept	Explanation	Example
Fields	Variables inside a class that store data (like properties).	brand, price
Methods	Functions that define what the object can do.	turnOn(), makeCall()
Object	A real instance with its own data. Multiple objects can exist from one class.	phone1, phone2
this keyword	Refers to the current object. Used to avoid naming conflicts.	See below
new keyword	Allocates memory and creates a new object.	new MobilePhone()

 

4. Using this Keyword (Important!)

When field names and parameter names are the same, use this to refer to the current object’s field.

Improved Class with this

class MobilePhone {
    String brand;
    String model;
    int storageGB;
    double price;
    boolean isOn;

    // Constructor will be explained next
    MobilePhone(String brand, String model, int storageGB, double price) {
        this.brand = brand;        // this.brand = current object's brand
        this.model = model;
        this.storageGB = storageGB;
        this.price = price;
        this.isOn = false;
    }

    void turnOn() {
        this.isOn = true;
        System.out.println(this.brand + " " + this.model + " is ON.");
    }

    void displayInfo() {
        System.out.println("Phone: " + this.brand + " " + this.model);
    }
}

 

5. Summary Table

Feature	Class	Object
Definition	Blueprint / Template	Instance of the class
Memory	No memory allocated	Memory allocated when created
Creation	Defined using class keyword	Created using new keyword
Example	class Car {}	Car myCar = new Car();
Can it hold data?	Defines structure	Holds actual values
Real-Life	House design	Actual house built

 

6. Common Interview Questions

Question	Answer
Can we create an object without a class?	No. Class is required.
Can we have multiple objects of one class?	Yes! As many as needed.
What happens when new is used?	Memory is allocated, constructor is called.
Why use this?	To distinguish between field and parameter with same name.

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7. Practice Exercise (Try This!)

Create a Book class with:

• Fields: title, author, pages, isAvailable

• Constructor

• Methods: borrowBook(), returnBook(), showDetails()

Then create 2 book objects and test them.

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Final Words

You’ve now mastered:

• What classes and objects are

• How to create and use them

• Real-life examples (Phone, Student, Car, Book)

• Constructors, this, and multiple objects

 

OOP = Real World in Code

You’re now thinking like a Java developer!

 

Keep coding!
Next: Learn Encapsulation, Inheritance, and Polymorphism to level up! 

 

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