抽象还是虚拟方法？

Question

Whats recommended in an abstract class?

Have a virtual method returning null, or have an abstract method?

It is convenient and easy to have them returning null, as I don't have to do anything inheriting from the abstract class. But still, returning null is somewhat hard to understand if it is by purpose, error, or by design....

Are there any clear recommendations for this?

Answer 1

If returning null is a sensible and sane thing to do as a default behaviour (with supporting documentation), then perhaps virtual is fine. Likewise, if you can create a sensible default but just want to offer extensibility: virtual .

If the (concrete) class cannot function without a non-default implementation, then make it abstract . The casebook scenario here is Stream : without a sane implementation where would the bytes come from? (/go to).

Answer 2

如果我要求派生类提供功能，我有一个抽象方法，如果我不那么烦恼，我有一个返回null（或做一些默认操作）的虚方法。