Static method

One rule-of-thumb: ask yourself “does it make sense to call this method, even if no Obj has been constructed yet?” If so, it should definitely be static.

So in a class Car you might have a method double convertMpgToKpl(double mpg) which would be static, because one might want to know what 35mpg converts to, even if nobody has ever built a Car. But void setMileage(double mpg) (which sets the efficiency of one particular Car) can’t be static since it’s inconceivable to call the method before any Car has been constructed.

Choosing and developing a Session Bean

Use a session bean if:

  1. Only one client has access to bean at any given time
  2. State of bean is not persistent
  3. Bean represent a web service

Use a Stateful Session bean if:

  1. Bean state represent client interaction
  2. Bean needs to hold client data across interactions
  3. Bean acts as a client mediator to other beans
  4. Need thread-safe interactions

Session Bean cardinality(taken from DevelopIntelligence)

bean cardinality.PNG

From the diagram, you can see that Stateless and Singleton beans looks very similar when it comes to Client-bean instances, except that in singleton all the clients access single object while in Stateless some objects are uses by clients and returned back to pool.

Developing a Session Bean

Steps to create a session bean:

  1. Define business logic interface
  2. Annotate the business interface
  3. Create the session bean, implementing the interface
  4. Annotate class defining type
  5. Compile, deploy and debug as discussed above