剑花　烟雨

摘要： The Open-Closed Principle Calsses should be open for extension,but closed for modification. Our goal is to allow classes to be easily extended to incorperate new behavior without modifying exsiting code.Following the Open-Closed Principle usually introduces new levels of abstraction,which adds complexity to our code.You want to concentrate on those areas that are most likely to change in your designs and apply the principles there.Experience in designing OO systems and a matt 阅读全文