Q 4) specification says Bean class should not define a constructor, because container uses a no-argument constructor to create bean instances, to create a pool when bean is deployed, if any constructor is defined, there should be a no-argument constructor to facilitate this activity. further as client does't instantiate bean class using a constructor, there is no use of defining a constructor.
Q 7) answer b is correct because, when finder method is called, a bean instance is pooled and populated with the data using the primary key. in this state its associated with the EJB remote stub, and ready to serve the client requests.
