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重构第四天 : 用多态替换条件语句（if else & switch)

2014-06-30 14:30  yanqinqiang  阅读(2428)  评论(0)  编辑  收藏  举报

面相对象的一个核心基础就是多态，当你要根据对象类型的不同要做不同的操作的时候，一个好的办法就是采用多态，把算法封装到子类当中去。

重构前代码：

 1 public abstract class Customer
 2 {
 3 }
 4   
 5 public class Employee : Customer
 6 {
 7 }
 8   
 9 public class NonEmployee : Customer
10 {
11 }
12   
13 public class OrderProcessor
14 {
15      public decimal ProcessOrder(Customer customer, IEnumerable<Product> products)
16      {
17          // do some processing of order
18          decimal orderTotal = products.Sum(p => p.Price);
19   
20          Type customerType = customer.GetType();
21          if (customerType == typeof(Employee))
22          {
23              orderTotal -= orderTotal * 0.15m;
24          }
25          else if (customerType == typeof(NonEmployee))
26          {
27              orderTotal -= orderTotal * 0.05m;
28          }
29   
30          return orderTotal;
31      }
32 }

重构后的代码：

 1 public abstract class Customer
 2   {
 3       public abstract decimal DiscountPercentage { get; }
 4   }
 5    
 6   public class Employee : Customer
 7   {
 8       public override decimal DiscountPercentage
 9       {
10           get { return 0.15m; }
11       }
12   }
13    
14   public class NonEmployee : Customer
15   {
16       public override decimal DiscountPercentage
17       {
18           get { return 0.05m; }
19       }
20   }
21    
22   public class OrderProcessor
23   {
24       public decimal ProcessOrder(Customer customer, IEnumerable<Product> products)
25       {
26           // do some processing of order
27           decimal orderTotal = products.Sum(p => p.Price);
28    
29           orderTotal -= orderTotal * customer.DiscountPercentage;
30    
31           return orderTotal;
32       }
33   }