What s Extreme about XP?

What's Extreme about XP?

As explained in [Beck2000], XP takes good practices of professional software development to extreme levels. XP introduces a planned and coherent methodology without becoming overly dictatorial or secretarial. The four values of XP are given as communication, simplicity, feedback, and courage.

As we explain in this chapter, these values form the foundation of our approach. Thus, we think we're following the spirit of XP, although we're certainly not following every XP practice (testing, pair programming, planning game, and so on) [Hendrickson2000].

From these core XP values, five principles are given as fundamental to XP. Our approach uses each of these principles: rapid feedback, assume simplicity, incremental change, embracing change, and quality work.

Ten "less central principles" from [Beck2000] are given, of which we concentrate on the following four: teach learning; concrete experiments; open, honest communication; and local adaptation.

For example, as instructors, we often face a tension in developing good (often small) example programs for students. The tension arises because we want to develop simple, focused examples that teach a specific concept, yet we also want to show our students programs that are masterpieces of good design programs that are fully generic and robust, and exemplify the best practices of object-oriented design and programming.

XP advocates that we design the simplest possible solution that works well for the current set of requirements, not those that we imagine will exist in the future. This helps relieve some of the tension of designing overly generic or optimized programs when creating example code.

Additionally, with this new mind-set, we can now add new features to that example and show students how the code changes. In other words, we can give the students a peek into the process of creating programs. When we call this process refactoring, we can discuss a program's design in more concrete terms [Fowler2000B].

In this chapter, we report on three aspects of XP that we have employed very successfully. We have used XP in our introductory programming courses for majors, in advanced courses on object-oriented software design, and in programming courses for nonmajors. These three aspects are as follows:

• Pair (teacher/class) programming as part of lecture

• Small releases from student groups

• Refactoring to understand programming and design patterns