class - Are static inner classes a good idea or poor design?

Question

I'm find I have several places that having public static inner classes designed that extend "helper" classes makes my code a lot more type safe and, in my opinion, readable. For example, imagine I have a "SearchCriteria" class. There are a lot of commonalities for the different things I search for (a search term and then a group of search term types, a date range, etc.) By extending it in a static inner class, I tightly couple the extension and the searchable class with the specific differences. This seems like a bad idea in theory (Tight Coupling Bad!) but the extension is specific to this searchable class (One Class, One Purpose).

My question is, in your experience, has the use of static inner classes (or whatever your language equivelent is) made your code more readable/maintainable or has this ended up biting you in the EOF?

Also, I'm not sure if this is community wiki material or not.

Answer 1

Sounds perfectly reasonable to me. By making it an inner class, you're making it easy to find and an obvious candidate for review when the searchable class changes.

Tight coupling is only bad when you couple things that don't really belong together just because one of them happens to call the other one. For classes that collaborate closely, e.g. when, as in your case, one of them exists to support the other, then it's called "cohesion", and it's a good thing.