If you build it they will come

Bill posted a comment to my last blog about seeing long methods and classes with too many responsibilities rather than the other way around. I posted a reply, but I though the reply was worth a short blog.

I like to keep a close eye on primitive instance variables, including Strings. When they start to look at all interesting, I make a class out of them. By interesting I mean that code starts to care about more than just the value. Perhaps decisions are being made, or they are used to influence other instance variables. Perhaps a groups of instance variables are palling around together. Those are all signs of a missing object. Even if it starts out as just a data object with a constructor and getters. Objects are like the Field of Dreams, if you build them, behavior will come.