Use ActionForm to work on session data

In a Struts-based Web application, each ActionForm extends 
org.apache.struts.action.ActionForm. These ActionForms 
encapsulate page data and provide a validation framework to 
validate request parameters.

Most Web applications maintain data in session to make them 
available throughout the application. This best practice 
addresses this Web application feature. It allows methods 
toSession() and fromSession() to move session data to and 
from the form data. Thus, it addresses session data 
maintenance in a Web application.

To adhere to this practice, follow these steps:

Create an abstract class named BP3Form by extending 
org.apache.struts.action.ActionForm. 
In BP3Form, add methods with access modifiers as in public 
abstract void toSession(SessionData sessionData) and void 
fromSession(SessionData sessionData). 
In every ActionForm, extend BP3Form and implement the 
abstract methods in which the form data is transported to 
and from the session. 
The corresponding Action class may determine the order in 
which these methods are called. For example, you could 
invoke method toSession() on the ActionForm just before 
actionForward is determined.
When to use this practice

This practice is most useful when session data is 
maintained as a single object and/or every page manipulates 
or uses session data.

As far as my knowledge is concerned.ActionForm is super
class and the bean class is sub class of ActionForm.So in
the action class it is downcasting that is performed and
downcasting in java needs an explict casting.

Action Form is basically sub class of Action Form Class.
When we want to assign super class with subclass object type
casting is required.

ActionForm is a parent class for our userdefined formbean. 
Ex. MyBean,means which has to be extended the ActionForm.

when we try to assign a parent class into subclass we need 
downcasting.