POJO in Java – What and Why?

In Java, POJO stands for Plain Old Java Object.

A POJO is a simple Java class that is not dependent on any special framework, API, or technology.

It is mainly used to store and manage data in a clean and organized way.

What is a POJO?

A POJO class usually contains:

• Private variables (fields)
• Getter and Setter methods
• Constructors
• Optional business methods

Example of a POJO Class

public class Student {

    private int id;
    private String name;

    // Default Constructor
    public Student() {
    }

    // Parameterized Constructor
    public Student(int id, String name) {
        this.id = id;
        this.name = name;
    }

    // Getter
    public int getId() {
        return id;
    }

    // Setter
    public void setId(int id) {
        this.id = id;
    }

    // Getter
    public String getName() {
        return name;
    }

    // Setter
    public void setName(String name) {
        this.name = name;
    }
}

This is called a POJO class because:

• It is a normal Java object
• No framework dependency
• Used mainly for storing data

Why Do We Use POJO?

1. To Store Data Properly

Instead of using many separate variables:

int id = 1;
String name = "Silambu";

We group them into one object:

Student s = new Student();

This makes code cleaner and easier to manage.

2. Improves Code Readability

POJO helps organize related data together.

Without POJO:

id, name, age, address

With POJO:

Student object

Easy to understand.

3. Reusability

One POJO class can be reused in:

• Controllers
• Services
• Database operations
• APIs
• JSON conversion

4. Easy Database Mapping

Frameworks like:

• Hibernate
• JPA
• Spring Boot

use POJO classes to map database tables into Java objects.

Example:

5. Easy JSON Conversion

POJO objects can easily convert to:

• JSON
• XML

Example:

{
  "id": 1,
  "name": "Silambu"
}

Real-Life Example

Think of a POJO like a student form.

A form contains:

• Name
• Age
• Roll Number

Similarly, a POJO stores related data together inside one class.

Important Characteristics of POJO

A POJO:

• Does not extend special classes
• Does not implement unnecessary interfaces
• Has private fields
• Uses getters/setters
• Is simple and independent

POJO vs Normal Variable

Normal Variables

String name;
int age;

Data is separate.

POJO

Student s;

All related data is grouped together.