POJO vs Java Beans

POJO classes

POJO stands for Plain Old Java Object. It is an ordinary Java object, not bound by any special restriction other than those forced by the Java Language Specification and not requiring any class path. POJOs are used for increasing the readability and re-usability of a program. POJOs have gained most acceptance because they are easy to write and understand. They were introduced in EJB 3.0 by Sun microsystems.

A POJO should not:

  1. Extend prespecified classes, Ex: public class GFG extends javax.servlet.http.HttpServlet { … } is not a POJO class.
  2. Implement prespecified interfaces, Ex: public class Bar implements javax.ejb.EntityBean { … } is not a POJO class.
  3. Contain prespecified annotations, Ex: @javax.persistence.Entity public class Baz { … } is not a POJO class.

POJOs basically defines an entity. Like in you program, if you want a Employee class then you can create a POJO as follows:

filter_none

edit
close

play_arrow

link
brightness_4
code

// Employee POJO class to represent entity Employee
public class Employee
{
    // default field
    String name;
  
    // public field
    public String id;
  
    // private salary
    private double salary;
  
    //arg-constructor to initialize fields
    public Employee(String name, String id, 
                             double salary)
    {
        this.name = name;
        this.id = id;
        this.salary = salary;
    }
  
    // getter method for name
    public String getName()
    {
        return name;
    }
  
    // getter method for id
    public String getId()
    {
        return id;
    }
  
    // getter method for salary
    public Double getSalary()
    {
        return salary;
    }
}

chevron_right


The above example is a well defined example of POJO class. As you can see, there is no restriction on access-modifier of fields. They can be private, default, protected or public. It is also not necessary to include any constructor in it.



POJO is an object which encapsulates Business Logic. Following image shows a working example of POJO class. Controllers get interact with your business logic which in turn interact with POJO to access the database. In this example a database entity is represented by POJO. This POJO has the same members as database entity.
pojo_bean

Java Beans

Beans are special type of Pojos. There are some restrictions on POJO to be a bean.

  1. All JavaBeans are POJOs but not all POJOs are JavaBeans.
  2. Serializable i.e. they should implement Serializable interface. Still some POJOs who don’t implement Serializable interface are called POJOs beacause Serializable is a marker interface and therefore not of much burden.
  3. Fields should be private. This is to provide the complete control on fields.
  4. Fields should have getters or setters or both.
  5. A no-arg constructor should be there in a bean.
  6. Fields are accessed only by constructor or getter setters.

Getters and Setters have some special names depending on field name. For example, if field name is someProperty then its getter preferably will be:

public void getSomeProperty()
{
   return someProperty;
} 

and setter will be

public void setSomePRoperty(someProperty)
{
   this.someProperty=someProperty;
}

Visibility of getters and setters in generally public. Getters and setters provide the complete restriction on fields. e.g. consider below property,

Integer age;

If you set visibility of age to public, then any object can use this. Suppose you want that age can’t be 0. In that case you can’t have control. Any object can set it 0. But by using setter method, you have control. You can have a condition in your setter method. Similarly, for getter method if you want that if your age is 0 then it should return null, you can achieve this by using getter method as in following example:

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java program to illustrate JavaBeans
class Bean
{
    // private field property
    private Integer property;
    Bean()
    {
        // No-arg constructor
    }
  
    // setter method for property
    public void setProperty(Integer property)
    {
        if (property == 0)
        {
            // if property is 0 return
            return;
        }
        this.property=property;
    }
  
    // getter method for property
    public int getProperty()
    {
        if (property == 0)
        {
            // if property is 0 return null
            return null;
        }
        return property;
    }
}
  
// Class to test above bean
public class GFG
{
    public static void main(String[] args)
    {
        Bean bean = new Bean();
  
        bean.setProperty(0);
        System.out.println("After setting to 0: " +
                                 bean.getProperty());
  
        bean.setProperty(5);
        System.out.println("After setting to valid" +
                      " value: " + bean.getProperty());
    }
}

chevron_right


Output:-

After setting to 0: null
After setting to valid value: 5

POJO vs Java Bean

POJO Java Bean
It doesn’t have special restrictions other than those forced by Java language. It is a special POJO which have some restrictions.
It doesn’t provide much control on members. It provides complete control on members.
It can implement Serializable interface. It should implement serializable interface.
Fields can be accessed by their names. Fields are accessed only by getters and setters.
Fields can have any visiblity. Fields have only private visiblity.
There can be a no-arg constructor. It must have a no-arg constructor.
It is used when you don’t want to give restriction on your members and give user complete access of your entity It is used when you want to provide user your entity but only some part of your entity.

Conclusion

POJO classes and Beans both are used to define java objects to increase their readability and reusability. POJOs don’t have other restrictions while beans are special POJOs with some restrictions.

This article is contributed by Vishal Garg. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.



My Personal Notes arrow_drop_up

Improved By : rutvikatGFG, PHANIX



Article Tags :
Practice Tags :


1


Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.