Question

I have a large Shape class, instances of which can (should) be able to do lots of things. I have many “domain” shape classes which inherit from this class, but do not provide any different functionality other than drawing themselves.

I have tried subclassing the Shape class, but then all of the “domain” objects will still inherit this subclass.

How do I break up the class? (it is 300 text lines, C#)

Answer 1

A couple of ideas (more like heuristics):

1) Examine the fields of the class. If a group of fields is only used in a few methods, that might be a sign that that group of fields and the methods that use it might belong in another class.

2) Assuming a well-named class, compare the name of the class to what the class actually does. If you find methods that do things above and beyond what you’d expect from the class’ name, that might be a sign that those methods belong in a different class. For example, if your class represents a Customer but also opens, closes, and writes to a log file, break out the log file code into a Logger class. See also: Single Responsibility Principle (PDF) for some interesting ideas .

3) If some of the methods primarily call methods on one other class, that could be a sign that those methods should be moved to the class they’re frequently using (e.g. Feature Envy).

CAUTION: Like they say, breaking up is hard to do. If there is risk in breaking up the class, you may want to put some tests in place so that you know you’re not breaking anything as you refactor. Consider reading “Working Effectively with Legacy Code” and the “Refactoring” book.