31天重构指南之十四：分离职责

当一个类有许多职责时，将部分职责分离到独立的类中可以更好的遵守“类的单一职责原则”，使用“分享职责”这个重构非常简单，让我们来看下面的代码：

   1: public class Video

   2: {

   3:     public void PayFee(decimal fee)

   4:     {

   5:     }

   6:  

   7:     public void RentVideo(Video video, Customer customer)

   8:     {

   9:         customer.Videos.Add(video);

  10:     }

  11:  

  12:     public decimal CalculateBalance(Customer customer)

  13:     {

  14:         return customer.LateFees.Sum();

  15:     }

  16: }

  17:  

  18: public class Customer

  19: {

  20:     public IList<decimal> LateFees { get; set; }

  21:     public IList<Video> Videos { get; set; }

  22: }

我们可以看到Video类有两个职责，一个是处理video rental，另一个是计算每个客户的总租金。我们可以将这两个职责分离到两个独立类中，重构后的代码如下所示：

   1: public class Video

   2: {

   3:     public void RentVideo(Video video, Customer customer)

   4:     {

   5:         customer.Videos.Add(video);

   6:     }

   7: }

   8:  

   9: public class Customer

  10: {

  11:     public IList<decimal> LateFees { get; set; }

  12:     public IList<Video> Videos { get; set; }

  13:  

  14:     public void PayFee(decimal fee)

  15:     {

  16:     }

  17:  

  18:     public decimal CalculateBalance(Customer customer)

  19:     {

  20:         return customer.LateFees.Sum();

  21:     }

  22: }

原文链接：http://www.lostechies.com/blogs/sean_chambers/archive/2009/08/14/refactoring-day-14-break-responsibilities.aspx