A class should be so small that anyone can easily understand it. If a method is not required to be understood in order to understand the class, then that method probably doesn’t belong in there and it’s not part of the responsibility of that class.
It is not a good idea to judge how big a class is based on the number of lines of code, however the following list can give you a rough estimate:
- Less than 100: Ideal
- 100 to 200: Ok
- 200 to 300: Warning
- 300+: The class is too big
Daniel Baharestani 