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Despite many years in IT, I still struggle with OO design. One particular problem I seem to keep ending up with is large classes, often containing many hundreds of lines of code.
The OO world talks a lot about SRP, and I could argue that these large classes I end up with are each handling a single responsibility. The complex nature of the app (a scientific data processing system) means that one of these responsibilities requires an awful lot of code! E.g. a class might have a single public method
Calculate(), but there could be 15-20 or more private methods to support this operation.
Where possible I will extract methods into separate classes for re-usability, but often there is little or no scope for this. Part of me says I should split these large classes up purely to improve readibility (e.g. grouping similar methods into their own classes), but the times I've done this feels like a wasted exercise - all I've really done is spread the methods around, created more class dependencies, and made things a little more difficult for other devs to find stuff.
But then I read articles where developers talk about how all their classes are small enough to fit on the screen without scrolling, and I worry that I'm doing something wrong! In a previous job, I worked on a system where it had been OO'd to the extreme, and it was common to see classes containing just one method, often with no more than one or two lines of code. Personally I found this difficult to find my way around the code-base and to debug, and for this reason (and sheer number of classes) I could argue that it becomes more difficult to maintain - not the aim of good OO design. I guess it's down to personal taste.
So, is it acceptable to have large classes, or can you suggest other ways that I could deal with them?