没有抽象方法的抽象类

Question

借助C＃，可以定义不包含抽象方法的抽象类，那么将类定义为ABSTRACT有什么用？

Answer 1

an abstract class with properties can be used to represent a base class in inheritance. An abstract class can not be instantiated. that may fit well as we dont want to let otheres to create objects for our base class.

You can define abstract class to define the abstract nature of the object. Ex: Animal has Eyes. Dog can be inherited from Animal so that it will have Eyes. We may create a Dog object. But we don't want to create an Animal object.

from msdn ,

The purpose of an abstract class is to provide a common definition of a base class that multiple derived classes can share. For example, a class library may define an abstract class that is used as a parameter to many of its functions, and require programmers using that library to provide their own implementation of the class by creating a derived class.

Answer 2

With refrence to C#, it is possible to define abstract class containing no abstract methods

Yes, absolutely

then whats the use of defining class as ABSTRACT?

Mostly to communicate the fact the the class should be derived. A similar effect can be achieved by making the constructor protected: no one will be able to create an instance of the class without inheriting from it.

Answer 3

将类定义为抽象可防止直接实例化该类。

Answer 4

Basically, I use as a rule of thumb that you should always define classes abstract when they MUST be inherited to be instantiated. Because abstract classes themselves cannot.

For example. Say you have a Building class, which is abstract. It must then be instantiated through a derived class, for example, a Bank or House. The fact that there are no abstract methods in the Building class has nothing to do with it being abstract or not.

Answer 5

A simple rule is that make abstract classes (no matter it does or does not contain abstract methods) whenever u feel that this particular class does not make sens if it stands alone ...

Thus use abstract class when

• u do not allow the instantiation of the object of an abstract class as its too general for that purpose
• but at the same time allows you to give some concrete implementation of methods that can be inherited by other classes which is fruitful for your hierarchical structure that you have designed

Answer 6

您可以将一个类定义为抽象类，并且其中没有任何方法...但是，您将无法对其进行任何处理，因为它只能由其他类继承并且不能单独实例化。

Answer 7

1. You can not create an instance of abstract class.
2. The abstract keyword enables you to create classes and class members that are incomplete and must be implemented in a derived class.
3. The purpose of an abstract class is to provide a common definition of a base class that multiple derived classes can share.

Answer 8

An abstract class can contain abstract methods as well as normal (concrete methods).

The purpose of an abstract class is to be used as a base class that can be inherited by other classes. The advantage of doing this is that multiple child classes can take advantage of methods inside the base class(abstract class) without having to rewrite the same methods again.

Answer 9

You define a class abstract to preserve a possibility to define an abstract members.

It's true you can avoid do that, but in that case it just meaning less.

Other question like this can be done:

Why can I define some function virtual , even if noone will override it. ?

These are different concepts, for sure, but the idea of asking the question is the same.

Hope this helps.