Is the Open Close Principle Up There Too?

The open close principle, no whic you mention, open for extension, but close for modification. You can always add as many sub classes of it as you want, but you should never be touching that original one. Herike: ideally we want to be able to add new functionality by extending the system, not modifying the existing code. How in all your career have you not had to modify the existing code? N i ans, lot.