The geometry lab — an exercise

Last week I was traning a team on XP techniques. We tried the following exercise:

I want you people to build me a Swing application that computes the area of a square with a given side length.

I asked for an estimate. The devs were nervous, someone said “impossible!” :-) someone said 5 hours. I played the part of the project-manager-who-was-once-a-developer and said “come on, five hours?? I could do that in 10 minutes in my sleep. What’s so difficult about it”? Then I reasoned with them that if we keep our estimates too comfortable, our business opportunities may fly out of the window. They agreed on a 2 hours estimate.

They proceeded to implement the feature. The three devs rotated every 7 minutes. This was a good slot size; everyone was involved, even the junior one who is rarely given the keyboard. The feature was done in one and a half hour. Then I said

Cool. Now we need to compute the area of a triangle of a given base and height. How much time for this?

The devs estimated 1.5 hours. It was delivered on time. Now the fun part started. The team wrote the application in the “usual” way, by writing new code for the new window. No effort was spent, at this time, to reduce duplication. I pointed out that

We’re going to need to implement many more of these geometry formulae. Make it so that it is trivial to add others.

The team came up with a design where the Swing window object is generic and can be customized to support the input for any formula that requires a variable number of inputs with different names. They thought they could do it in 2 hours. It took 4. At some point we wasted a lot of time on Swing layouts, trying to fathom the mysteries of GroupLayout. I gave some help here. Then we were done! Stepping again in my role of customer I said

Very well. The next feature we need is to compute the area of a circle from the radius.

It was done in 10 minutes. The customer was very satisfied, and so were the devs.

What have we learned?

  • I have learned the power of letting the team come up with their own design. It’s difficult for me, an xp-trainer-who-was-once-a-developer, to give up giving guidance on design. But time and again, I have seen the damage of doing so: the team follows my design, gets bogged down, does not learn.
  • We have learned how hard it is to make the code easy to change. It would have been easy to declare we were “done” after the area of triangle was working. But we were not really “done” from the point of view of TDD. Remember, the cycle is red-green-REFACTOR, and by “refactor” what is really meant is “remove duplication”.
  • Once you get to clean, refactored code, the cost of changes drops. And it’s a pleasure to work with!
  • The decision to invest time in making the code generic might seem difficult. After all, you can get skilled at copy-pasting Swing code and writing many copies of the Swing form class. But then you are left with gobs of code. And good luck applying a different graphic layout to them all! My answer is that we should get skilled at writing flexible code. It took us 4 hours to make the code generic. Next time they have to do something similar, it will take less.

    Copying-and-pasting is a dead end; there is a limit at how skilled you can become at it, and there is certainly a big problem in the quality of the code you deliver. Learning to do good, clean, flexible code never ends. It’s a path where you can get to write better and better code. Which path would you rather be on?

Very cool, guys. This geometry app rocks!!

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