没有任何抽象方法的C＃中的抽象类

Question

Folks

I am surprised to see my code working, that I dont have any abstract method in abstract class. But as per rules we should have atleast one abstract method right ? :S

Answer 1

No, you don't need an abstract method in an abstract class.

The restrictions are:

• If a class has an abstract method, property, index, or event then the class must also be abstract.
• You can't instantiate an abstract class.

There is no requirement that abstract classes must have abstract methods.

Answer 2

No, this is entirely valid. Indeed, every static class in C# is actually an abstract and sealed class in .NET. (You can't declare an abstract class to be sealed with C# source code though.)

The C# 4 spec explicitly calls this out, in section 10.1.1.1 (abstract classes):

An abstract class is permitted (but not required) to contain abstract members.

It's certainly rare to have an abstract class with no abstract members, but it's not unheard of. (Don't forget that it's not just methods that can be abstract - you can have abstract events and properties, too.)

Answer 3

From MSDN - abstract (Emphasis added):

An abstract class may contain abstract methods and accessors.

Your abstract class can contain nothing but non-abstract methods, or it could be am empty class if you want. It gives you a base class that cannot be instantiated, which could be useful for plymorphism.

Answer 4

You don't need abstract methods to have an abstract class. Sometimes it's useful to just restrict a class from being instantiated, and designate it as a base to some inheritance hierarchy. All the methods can be defined in an abstract class.