Method refactoring

Question

How many lines of code can a method have with a good design before you need to make the design better?

Answer 1

Lines of code is an incomplete metric to use for refactoring. Cyclomatic Complexity should be used in conjuction with LOC as a decent gauge for when to refactor.

A decent guideline is

LOC > 80 || CC > 10 == "Time to refactor"

Chances are you will hit a Cyclomatic Complexity > 10 long before you ever reach 80 lines of code.

Of course there are a litany of other metrics to consider as well:

1. Afferent Coupling: How many methods depend on this method
2. Efferent Coupling: How many methods does this method rely on
3. No. of Parameters
4. No. of Varialbes used

You can go pretty in depth, but all this to say that determining when to refactor can't be decided with a blanket rule like "Thou shalt not have more than 40 lines in any method!"

Answer 2

There is no accepted rule. It should be as simple to read as possible. If that means taking 5 lines of a 10 line block and putting them in their own method, then so be it. But sometimes it can be fine to have 50-line methods. Just do what you think you'll understand best in 6 months time.