Fall 2002 Programming Language Seminar: Aspect-Oriented Programming with AspectJ Back to main course page

Department of Computer Science

Homework 3: "Redesign" patterns

Goal: To design and implement a reusable design pattern in AspectJ
Due: Wednesday 02 October 2002 in class
Turn-in: during class and by email to mdeters@cse.wustl.edu (see below)

You should:

• Reconsider and redesign one of the Gang of Four design patterns (you will be assigned one to avoid two people covering the same one) with aspects in mind.
• Implement and test your design pattern. This includes writing one or more simple "clients" that make use of your design pattern.
• Identify:
  • Advantages or disadvantages in using AspectJ for this design pattern instead of plain Java
  • Advantages or disadvantages in using AspectJ for this design pattern instead of another non-aspect language (C++, or whatever you're familiar with)
  • Intermediate designs that you attempted but ultimately decided against (and why you made such a decision)
  • Difficulties in getting things to work
  • Any other experiential tidbits from completing this assignment
• When "redesigning" your design pattern, keep in mind the following general suggestions:
  • Attempt to increase the obliviousness of client objects of their role in the pattern.
  • Rather than studying the Gang of Four designs (UML diagrams, etc.) for places to inject aspects, go back to the original objective of the design pattern and think of crosscutting concerns in the big picture.
  • Don't try to shove everything into one aspect---if there are multiple, independent concerns, try to split them into separate aspects. Even concerns that aren't completely independent can often be cleanly separated. (As an example, "independent but cooperating" concerns fall into this category. A thread safety mechanism on top of another concern is one such example.)
  • Aim toward reusability of your pattern implementation.
  • Try to use abstract aspects and pointcuts where appropriate. Use the Subject/Observer example's "protocol" aspect (as discussed in class) for inspiration.
• You will lead a 10 (or so) minute discussion on October 2 (or the 9th if we run out of time on the 2nd).
• You are not required to prepare materials (presentation slides, demos, etc.) but may if you choose. Please be prepared to access your source code over the network and walk us through it. (I'll bring a network-ready laptop and projector.)
• Please turn in any source code, visual aids, and any other prepared materials to me by email. You are not required to write up answers to the above questions in the email to me, but you will include them in your class discussion.
• This assignment is intended to make you think about design and also write code. It may take some time to clearly identify aspects in your pattern, so please start thinking about this early and email me if you have any difficulties.

Please contact me at mdeters@cse.wustl.edu if you have problems with this assignment.

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