31天重构指南之十：提取方法
现在让我们来看提取方法这个重构，这是一个简单却又好处多多的重构，首先，它通过提供有意义的方法名会使代码更具可读性；其次见名知义的方法名减少了维护人员的工作量；最后它更好的可读性减少了对代码的臆断，从而降低了代码的错误率。让我们来看下面的待重构代码：
1: public class Receipt
2: {
3: private IList<decimal> Discounts { get; set; }
4: private IList<decimal> ItemTotals { get; set; }
5:
6: public decimal CalculateGrandTotal()
7: {
8: decimal subTotal = 0m;
9: foreach (decimal itemTotal in ItemTotals)
10: subTotal += itemTotal;
11:
12: if (Discounts.Count > 0)
13: {
14: foreach (decimal discount in Discounts)
15: subTotal -= discount;
16: }
17:
18: decimal tax = subTotal * 0.065m;
19:
20: subTotal += tax;
21:
22: return subTotal;
23: }
24: }
我们注意到上面的CalculateGrandTotal做了三件事，首先计算了subTotal，然后减去discount，最后计算tax。与其让程序员穿越整个代码去了解CalculateGrandTotal方法的功能，
不如我们将上述三个独立的任务分配到独立方法中来提CalculateGrandTotal方法的可读性。下面是重构后的代码：
1: public class Receipt
2: {
3: private IList<decimal> Discounts { get; set; }
4: private IList<decimal> ItemTotals { get; set; }
5:
6: public decimal CalculateGrandTotal()
7: {
8: decimal subTotal = CalculateSubTotal();
9:
10: subTotal = CalculateDiscounts(subTotal);
11:
12: subTotal = CalculateTax(subTotal);
13:
14: return subTotal;
15: }
16:
17: private decimal CalculateTax(decimal subTotal)
18: {
19: decimal tax = subTotal * 0.065m;
20:
21: subTotal += tax;
22: return subTotal;
23: }
24:
25: private decimal CalculateDiscounts(decimal subTotal)
26: {
27: if (Discounts.Count > 0)
28: {
29: foreach (decimal discount in Discounts)
30: subTotal -= discount;
31: }
32: return subTotal;
33: }
34:
35: private decimal CalculateSubTotal()
36: {
37: decimal subTotal = 0m;
38: foreach (decimal itemTotal in ItemTotals)
39: subTotal += itemTotal;
40: return subTotal;
41: }
42: }
这个重构来自于Martin Fowler，你可以在这里查看。