Com S 362 --- Object-Oriented Analysis and Design

       EXERCISE 18: GOF DESIGN PATTERNS: FACTORY AND SINGLETON
                 (File $Date: 2003/12/05 16:29:12 $)

The purpose of this exercise is for you to learn more about the
Factory and Singleton design patterns.

As with all exercises, this is to be done individually, not in teams.
And it is due the day this topic is planned to be discussed in class, unless
specified otherwise (see the syllabus at:
http://www.cs.iastate.edu/~cs362/syllabus.shtml). 

As with all exercises, you have two choices for doing the work. You
can either:

  - complete it as specified or
  - write down questions or problems that you had in trying to
    complete it.

If you write down questions or problems you have, these should be
detailed enough so that we can tell that you have read the materials
and thought about them.  (Don't just write: "I couldn't get it to
work; say what you tried and what you didn't understand.)  During the
class where this exercise is discussed, you should try to get help
with these by explaining what you did and what your problems or
confusions are.  Don't be shy; there will be other people with the
same problem, and everyone can learn by discussing these issues.

1. [Factory and Singleton]

Read Sections 23.3 and 23.4 of Larman's book "Applying UML and
Patterns: An Introduction to Object-Oriented Analysis and Design and
the Unified Process" (Second Edition, Prentice Hall PTR, Upper Saddle
River, NJ, 2001).

a. What problem does the factory design pattern solve?

b. Why is factory often combined with the singleton pattern?  How does
   that help?  Give an example.

c. Is there any place in your team's design where you do or could use
   the factory pattern?  If so, briefly describe it.  (Hint: think
   about any controllers or GUI elements if you can't think of other places.)

WHAT TO HAND IN

You should have at the beginning of class, written answers to the
above questions (or written out questions and problems you encountered
for each part).  Make sure your name is on these. Attach the
printouts, if any, requested above.

ADDITIONAL READINGS

If you have time, read the section on the Factory patterns (pp. 87ff
and 107ff) and the Singleton pattern (pp. 127ff) in Erich Gamma,
Richard Helm, Ralph Johnson, and John Vlissides's book "Design
Patterns: Elements of Reusable Object-Oriented Software"
(Addison-Wesley, Boston, MA, 1995).