Classes and Objects in Java

Classes and objects in Java are the foundation of object-oriented programming (OOP). Every real-world Java application is built using classes and objects, making this one of the most important topics for Java beginners.

In this beginner-friendly tutorial, you will learn what a Java class is, what a Java object is, and how to create objects in multiple ways with simple real-world examples.

Class: A blueprint used to create objects.
Object: A real instance created from a class.

Real Life Analogy: Building Blueprint

Class = Blueprint

A building blueprint defines:

How many windows
How many floors
Type of materials
Layout

But a blueprint is not a building — it's only the plan.

Object = Real Building

Objects are real buildings that are built using the blueprint.

✔ Class = Blueprint, Object = Real Building

Java Class (Blueprint)

The Building class is like a blueprint:

Java Class (Blueprint)

class Building {
    int floors;
    String color;
    
    Building(int floors, String color) {
        this.floors = floors;
        this.color = color;
    }
}

Object = Real Building

Objects are created from the class using the new keyword.

objectExample.java

Building building1 = new Building(5, "Blue");
Building building2 = new Building(10, "White");

System.out.println("This building has " + building1.floors + " floors and is " + building1.color + ".");
System.out.println("This building has " + building2.floors + " floors and is " + building2.color + ".");

Output:

This building has 5 floors and is Blue.This building has 10 floors and is White.

Ways to Create Objects

There are four main ways to create objects in Java:

1. Using new keyword

Most common way

2. Using Reflection

Create objects dynamically

3. Using clone() method

Copy existing objects

4. Using Deserialization

Recreate from byte stream

1. Using new Keyword

Most common way to create an object.

Building building1 = new Building(5, "Blue");

2. Using Reflection

Create an object without using the new keyword, by asking Java to create it at runtime using the class name.

Useful for:

Frameworks (Spring, Hibernate)
Loading classes dynamically
Working with unknown classes at runtime

reflectionExample.java

Class<?> clazz = Class.forName("Building");
Building building = (Building) clazz.getDeclaredConstructor().newInstance();

Explanation:

Class.forName("Building") → loads the class using its name
getDeclaredConstructor().newInstance() → creates object
No new Building() used!

3. Using clone() Method

The clone() method creates a copy of an existing object instead of creating a new one manually.

Steps to Use clone():

Your class must implement Cloneable
You must override the clone() method
Then you can copy the object

cloneObjectExample.java

class Building implements Cloneable {
    int floors;
    String color;
    
    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

Building original = new Building(5, "Blue");
Building cloned = (Building) original.clone();

Output:

Original: 5, BlueClone: 5, Blue

4. Using Deserialization

Deserialization is a technique of reading an object from the saved state in a file. The object is recreated from a stored byte stream.

desenterlizationExample.java

ObjectInputStream in = new ObjectInputStream(new FileInputStream("building.ser"));
Building building = (Building) in.readObject();
in.close();

Output:

Building with 5 floors

Summary

Method	When to Use	Key Feature
new keyword	Standard object creation	Most common way
Reflection	Frameworks, dynamic loading	Runtime class loading
clone()	Copying existing objects	Creates duplicate
Deserialization	Loading saved objects	From byte stream

new keyword

When to Use:

Standard object creation

Key Feature:

Most common way

Reflection

When to Use:

Frameworks, dynamic loading

Key Feature:

Runtime class loading

clone()

When to Use:

Copying existing objects

Key Feature:

Creates duplicate

Deserialization

When to Use:

Loading saved objects

Key Feature:

From byte stream

Classes and Objects in Java – FAQ for Beginners

What is a class in Java?

A class in Java is a blueprint or template used to create objects. It defines properties (variables) and behaviors (methods).

What is an object in Java?

An object is a real instance of a class. It represents a real-world entity created from the class blueprint.

What is the difference between class and object in Java?

A class is a blueprint, while an object is a real instance created from that blueprint.

How many ways can we create objects in Java?

Objects in Java can be created using the new keyword, reflection, clone() method, and deserialization.