Which class design is better? [closed]

Answer 1

I don't think composition is always better than inheritance (just usually). If Employee and Member really are Users, and they are mutually exclusive, then the first design is better. Consider the scenario where you need to access the UserName of an Employee. Using the second design you would have:

myEmployee.UserInfo.UserName

which is bad (law of Demeter), so you would refactor to:

myEmployee.UserName

which requires a small method on Employee to delegate to the User object. All of which is avoided by the first design.

Answer 2

I don't like either one. What happens when someone is both a member and an employee?

Answer 3

Here's a scenario you should think about:

Composition (the 2nd example) is preferable if the same User can be both an Employee and a Member. Why? Because for two instances (Employee and Member) that represent the same User, if User data changes, you don't have to update it in two places. Only the User instance contains all the User information, and only it has to be updated. Since both Employee and Member classes contain the same User instance, they will automatically both contain the updated information.

Answer 4

Stating your requirement/spec might help arrive at the 'best design'.
Your question is too 'subject-to-reader-interpretation' at the moment.

Answer 5

The real questions are:

• What are the business rules and user stories behind a user?
• What are the business rules and user stories behind an employee?
• What are the business rules and user stories behind a member?

These can be three completely unrelated entities or not, and that will determine whether your first or second design will work, or if another completely different design is in order.