Hibernate – Create POJO Classes

POJO stands for Plain Old Java Object. In simple terms, we use POJO to make a programming model for declaring object entities. The classes are simple to use and do not have any restrictions as compared to Java Beans. 

To read about POJO classes and Java Bean refer to the following article – POJO classes and Java Bean

POJO is handier as its best in readability and reusability. The only difference between java bean and POJO classes is POJOs don’t have any restrictions other than java but java beans have.

Properties of POJO classes

1. The POJO classes must be public so that we can use them outside the class.
2. POJO does not have any name convention for properties and methods. It’s just a java class consisting of some variables and getters-setters.
3. POJO classes are used in hibernate for mapping to database objects. That means all object entities we make in POJO classes will be reflected in a database object.
4. It should not extend classes, implement interfaces, or contain prespecified annotations. Also, it does not bound with any restrictions but strictly follows java language specifications.
5. In hibernate, POJOs also contain some annotations like @Entity, @Table, @id, etc for avoiding XML files for database objects.

Working with POJO classes 

POJO classes are used to encapsulate business logic and its members are treated as a database entity. The main motive of POJO classes is to define an object entity for hibernating.

Implementation: 

Let us make an employee POJO class

A. File: Employee.java

Java

// Java Program to Illustrate Employee Class
// POJO class

// Importing required classes
import java.io.*;

// Class
class Employee {

    // Private variables which are treated as an entity
    private int empid;
    private String name;
    private int age;

    // Getters and setters

    // Getter
    public int getEmpid() { return empid; }

    // Setter
    public void setEmpid(int empid) { this.empid = empid; }

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

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

    // Getter
    public int getAge() { return age; }

    // Setter
    public void setAge(int age) { this.age = age; }
}

Let’s make a POJO class method and use them to set and get the data.

B. File: MainClass.java

Java

// Importing required classes
import java.io.*;

// Main class
class MainClass {

    // Main driver method
    public static void main(String[] args)
    {

        // Making a POJO class method to
        // set and retrieve some values
        employee emp = new employee();

        // Setting the values with setters
        emp.setEmpid(123);
        emp.setName("Geek");
        emp.setAge(21);

        // Retrieving some values from getters
        System.out.println("The employee ID is "
                           + emp.getEmpid());
        System.out.println("The name of the employee is "
                           + emp.getName());
        System.out.println("The age of the employee is "
                           + emp.getAge());
    }
}

Output: