[java] Difference between DTO, VO, POJO, JavaBeans?

Have seen some similar questions:

• What is the difference between a JavaBean and a POJO?
• What is the Difference Between POJO (Plain Old Java Object) and DTO (Data Transfer Object)?

Can you also please tell me the contexts in which they are used? Or the purpose of them?

POJO : It is a java file(class) which doesn't extend or implement any other java file(class).

Bean: It is a java file(class) in which all variables are private, methods are public and appropriate getters and setters are used for accessing variables.

Normal class: It is a java file(class) which may consist of public/private/default/protected variables and which may or may not extend or implement another java file(class).

• Value Object : Use when need to measure the objects' equality based on the objects' value.
• Data Transfer Object : Pass data with multiple attributes in one shot from client to server across layer, to avoid multiple calls to remote server.
• Plain Old Java Object : It's like simple class which properties, public no-arg constructor. As we declare for JPA entity.

difference-between-value-object-pattern-and-data-transfer-pattern

Java Beans are not the same thing as EJBs.

The JavaBeans specification in Java 1.0 was Sun's attempt to allow Java objects to be manipulated in an IDE that looked like VB. There were rules laid down for objects that qualified as "Java Beans":

1. Default constructor
2. Getters and setters for private data members that followed the proper naming convention
3. Serializable
4. Maybe others that I'm forgetting.

EJBs came later. They combine distributed components and a transactional model, running in a container that manages threads, pooling, life cycle, and provides services. They are a far cry from Java Beans.

DTOs came about in the Java context because people found out that the EJB 1.0 spec was too "chatty" with the database. Rather than make a roundtrip for every data element, people would package them into Java Beans in bulk and ship them around.

POJOs were a reaction against EJBs.

DTO vs VO

DTO - Data transfer objects are just data containers which are used to transport data between layers and tiers.

• It mainly contains attributes. You can even use public attributes without getters and setters.
• Data transfer objects do not contain any business logic.

Analogy:
Simple Registration form with attributes username, password and email id.

• When this form is submitted in RegistrationServlet file you will get all the attributes from view layer to business layer where you pass the attributes to java beans and then to the DAO or the persistence layer.
• DTO's helps in transporting the attributes from view layer to business layer and finally to the persistence layer.

DTO was mainly used to get data transported across the network efficiently, it may be even from JVM to another JVM.

DTOs are often java.io.Serializable - in order to transfer data across JVM.

VO - A Value Object [1][2] represents itself a fixed set of data and is similar to a Java enum. A Value Object's identity is based on their state rather than on their object identity and is immutable. A real world example would be Color.RED, Color.BLUE, SEX.FEMALE etc.

POJO vs JavaBeans

[1] The Java-Beanness of a POJO is that its private attributes are all accessed via public getters and setters that conform to the JavaBeans conventions. e.g.

    private String foo;
    public String getFoo(){...}
    public void setFoo(String foo){...}; 

[2] JavaBeans must implement Serializable and have a no-argument constructor, whereas in POJO does not have these restrictions.

Basically,

DTO: "Data transfer objects " can travel between seperate layers in software architecture.

VO: "Value objects " hold a object such as Integer,Money etc.

POJO: Plain Old Java Object which is not a special object.

Java Beans: requires a Java Class to be serializable, have a no-arg constructor and a getter and setter for each field

First Talk About

Normal Class - that's mean any class define that's a normally in java it's means you create different type of method properties etc.
Bean - Bean is nothing it's only a object of that particular class using this bean you can access your java class same as object..

and after that talk about last one POJO

POJO - POJO is that class which have no any services it's have only a default constructor and private property and those property for setting a value corresponding setter and getter methods. It's short form of Plain Java Object.