2 simple eval/test questions 2003-07-31 - By Sam Fancourt
Back
Q1: The answer is B
- See the extracted text from the Java Tutorial pasted below (or read State
Management Modes in the book).
Q2: The answer is D
- A factory pattern is used to create objects, ie: (from the J2EE Tutorial
again): "the purpose of the home interface is to define the create methods
that a remote client may invoke."
You can also refer to the GoF definition of a Factory "Provide an interface
for creating families of related or dependant objects without specifying
their concrete classes"
Sam :-)
Stateful Session Beans
The state of an object consists of the values of its instance variables. In
a stateful
session bean, the instance variables represent the state of a unique
client-bean
session. Because the client interacts ("talks") with its bean, this state is
often
called the conversational state.
The state is retained for the duration of the client-bean session. If the
client
removes the bean or terminates, the session ends and the state disappears.
This
transient nature of the state is not a problem, however, because when the
conversation
between the client and the bean ends there is no need to retain the state.
Stateless Session Beans
A stateless session bean does not maintain a conversational state for a
particular
client. When a client invokes the method of a stateless bean, the bean's
instance
variables may contain a state, but only for the duration of the invocation.
When
the method is finished, the state is no longer retained. Except during
method
invocation, all instances of a stateless bean are equivalent, allowing the
EJB container
to assign an instance to any client.
Because stateless session beans can support multiple clients, they can offer
better
scalability for applications that require large numbers of clients.
Typically, an
application requires fewer stateless session beans than stateful session
beans to
support the same number of clients.
At times, the EJB container may write a stateful session bean to secondary
storage.
However, stateless session beans are never written to secondary storage.
Therefore, stateless beans may offer better performance than stateful beans.
-- --Original Message-- --
From: Ivy Se [mailto:ivy12see@(protected)]
Sent: Thursday, July 31, 2003 4:10
To: J2EEPATTERNS-INTEREST@(protected)
Subject: 2 simple eval/test questions
Hi guys,
I've got 2 simple self eval quesion which I'm not sure
of the answers. Can you guys help, please
Q1. Which statement is true about statefull session
beans, but is NOT true about stateless session beans
A. State can be cached but is not representative of
the client state
B. State can be cached but is representative of client
state
C. State is persistent
D. State is cached first, then persisted.
Q2. Which pattern is used by the Home interface of an
EJB
A. Proxy
B. Decorator
C. Mediator
D. Factory
=====
Thank you.
Ivy Se
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http://java.sun.com/blueprints/corej2eepatterns
Getting Started (Beta Version):
http://developer.java.sun.com/developer/technicalArticles/J2EE/patterns/
Get the book:
http://www.amazon.com/exec/obidos/ASIN/0130648841/corej2eepatte-20 (See http://tte-20.ora-code.com)
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