Inherit from a class or an abstract class

Question

If you have several classes where you want them to inherit from a base class for common functionality, should you implement the base class using a class or an abstract class?

Answer 1

That depends, if you never want to be able to instantiate the base class then make it abstract. Otherwise leave it as a normal class.

Answer 2

If the base class ought not to be instantiated then make it an abstract class - if the base class needs to be instantiated then don't make it abstract.

In this example it makes sense to make the base class abstract as the base class does not have any concrete meaning:

abstract class WritingImplement {     public abstract void Write(); }  class Pencil : WritingImplement {     public override void Write() { } } 

However in this next example you can see how the base class does have concrete meaning:

class Dog {     public virtual void Bark() { } }  class GoldenRetriever : Dog {     public override void Bark() { } } 

It is all pretty subjective really - you ought to be able to make a pretty good judgment call based on the needs of your particular domain.