When is a class too long? [closed]

Question

When is a function too long? is a subset of this question, I think.

What are a few good metrics for determining that a class is too long?

I'm rerevising a set of code acceptance guidelines for a project with external contractors, and realized I haven't covered this in the past, but should cover this in the future.

Answer 1

When it has more than one responsibility.

Let me quote Robert C. Martin's Clean Code here:

The first rule of classes is that they should be small. The second rule of classes is that they should be smaller than that. ... With functions we measured size by counting physical lines. With classes we use a different measure. We count responsibilities. [Chapter 10, page 136]

Answer 2

Class fan-out complexity: The number of other classes a given class relies on. Also the square of this has been shown to indicate the amount of maintenence required in functional programs (on a file basis) at least.

Cyclomatic complexity: Checks cyclomatic complexity against a specified limit. The complexity is measured by the number of if, while, do, for, ?:, catch, switch, case statements, and operators && and || (plus one) in the body of a constructor, method, static initializer, or instance initializer. It is a measure of the minimum number of possible paths through the source and therefore the number of required tests. Generally 1-4 is considered good, 5-7 ok, 8-10 consider re-factoring, and 11+ re-factor now!