I’m helping out with a study group for “Head First Design Patterns,” which just finished chapter 6. On the whole, it’s a pretty good introduction to software design patterns — way more accessible than the seminal work by the Gang of Four; however, the examples sometimes make my head hurt. I can’t imagine what they’re doing to the heads of the beginners in the group. Coming up with decent examples is the hardest thing to do in expository writing, and I certainly give the authors an E for effort in creativity, but I wish they had been a little less concerned with making their examples “hip” and a little more concerned with making them appropriate.

To wit, the whole pizza store analogy in chapter 4 (to illustrate factory method and abstract factory) is flawed. For one thing, that’s just not the way you’d model a pizza business in any actual software that I can imagine. For another, the differences between a New York pizza factory and a Chicago pizza factory are too subtle/trivial to make for an effective illustration of why you would need to subclass anything (much less use a factory to manage the subclasses). A much better example, as everyone in my group agreed, would have been an application that needs to offer up a consistent set of functionality to users who are accessing it in wildly different ways: one’s in a web browser on a desktop, another is running a cell phone app, another is using a touch-tone phone, and yet another is using a voice-activated headset. All the client code knows is that, for example, it needs to ask a multiple-choice question and obtain the answer. It’s up to an abstract factory to provide the client with a set of classes that can do that, in the context of the selected user-interface, in whatever way is necessary.

To a lesser degree, the Starbucks coffee example at the beginning of the book suffers from the same too-hip-to-be-effective syndrome, although I do think that the remote-control example for the Command pattern in chapter six is dead on.

For any novice who is reading this book without the benefit of a study group, I highly suggest that you find at least one other programmer who is experienced in design patterns to explain why/if/how the examples are lacking.