EJB OOAD??

[Ernest Lee]

in the book Mastering EJB II, it states that a OO system should contains 2 types of components.
1. Application logic component (action)
2. Persistant data component (data)
that really confuses me because in OO, aren't we suppose to have behavior+data in the same object? is that because of the fact that we are using EJB.. we have to separate them in Session bean and entity bean???
pls clarify.

[Ralf Allar]

Hi Ernest,
the separation between session and entity bean is no break with OO. Okay, let me explain it...
A session bean should represent the business logic, i.e. createEmployee, deleteEmployee, etc.
The entity bean represents the data. The employee itself. It's only methods should be the getter/setter ones.
So, the data is clearly and cleanly seperated from business logic and that's no affront to OOA/D.
Have fun,
Ralf

[Dave Landers]

An Entity bean can have behavior (business methods other than get/set), but they should be methods appropriate for a single Entity instance.
An Entity bean (in EJB 2.0) can also have Home methods that are appropriate for acting on Entities of that "type" (not instance-specific), but should generally not deal with entities of other types.
In a system, you are most likely dealing with several Entity (data) types. For example you may have Employee, Customer, Manager, Address, Product, etc. The Application Logic generally deals with multiple entities - actions, interactions, relationships, etc.
If you think about MVC, the entities are the Model (data), the session beans are usually used to implement a Controler, and the View is the user interface (whatever that is - outside EJB usually).