重构第四天 : 用多态替换条件语句（if else & switch)

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   }