31天重构指南之九：提取接口

现在让我们来看一个经常被忽略的重构，提取接口。但我们注意到超过一个的类要使用某一个类中方法的子集时，我们应该切断它们之间的依赖，让消费者（consumers)使用接口，这非常容易实现但却降低了代码的耦合性。

1: public class ClassRegistration

2: {

3:     public void Create()

4:     {

5:         // create registration code

6:     }

7: 

8:     public void Transfer()

9:     {

10:         // class transfer code

11:     }

12: 

13:     public decimal Total { get; private set; }

14: }

15: 

16: public class RegistrationProcessor

17: {

18:     public decimal ProcessRegistration(ClassRegistration registration)

19:     {

20:         registration.Create();

21:         return registration.Total;

22:     }

23: }

我们来对上面的代码进行重构，我们将ClassRegistration类中的Total属性、Create方法提取到接口中，这样ClassRegistration类的消费者就不用关心ClassRegistration的具体实现，

从而降低了代码的耦合性。下面是重构后的代码：

1: public interface IClassRegistration

2: {

3:     void Create();

4:     decimal Total { get; }

5: }

6: 

7: public class ClassRegistration : IClassRegistration

8: {

9:     public void Create()

10:     {

11:         // create registration code

12:     }

13: 

14:     public void Transfer()

15:     {

16:         // class transfer code

17:     }

18: 

19:     public decimal Total { get; private set; }

20: }

21: 

22: public class RegistrationProcessor

23: {

24:     public decimal ProcessRegistration(IClassRegistration registration)

25:     {

26:         registration.Create();

27:         return registration.Total;

28:     }

29: }

这个重构最早由Martin Fowler发表，你可以这里查看。

原文链接：http://www.lostechies.com/blogs/sean_chambers/archive/2009/08/07/refactoring-day-9-extract-interface.aspx

This refactoring was first published by Martin Fowler and can be found in his list of refactorings here.