这篇文章要说的重构来自于Martin Fowlwrs的重构列表，你可以在这里查看原始描述
这是一个不常用的重构。当你发现一个方法中存在过多的局部变量时，你可以通过使用“提取方法对象”重构来引入一些方法，每个方法完成任务的一个步骤，这样可以使得程序更具有可读性。
1: public class OrderLineItem
2: {
3: public decimal Price { get; private set; }
4: }
5:
6: public class Order
7: {
8: private IList<OrderLineItem> OrderLineItems { get; set; }
9: private IList<decimal> Discounts { get; set; }
10: private decimal Tax { get; set; }
11:
12: public decimal Calculate()
13: {
14: decimal subTotal = 0m;
15:
16: // Total up line items
17: foreach (OrderLineItem lineItem in OrderLineItems)
18: {
19: subTotal += lineItem.Price;
20: }
21:
22: // Subtract Discounts
23: foreach (decimal discount in Discounts)
24: subTotal -= discount;
25:
26: // Calculate Tax
27: decimal tax = subTotal * Tax;
28:
29: // Calculate GrandTotal
30: decimal grandTotal = subTotal + tax;
31:
32: return grandTotal;
33: }
34: }
下面是重构后的代码中，我们引入了OrderCalculator类，该类实现了所有的计算方法，Order类将自身传递给OrderCalculator类并调用Calculate方法完成计算。
1: public class OrderLineItem
2: {
3: public decimal Price { get; private set;}
4: }
5:
6: public class Order
7: {
8: public IEnumerable<OrderLineItem> OrderLineItems { get; private set;}
9: public IEnumerable<decimal> Discounts { get; private set; }
10: public decimal Tax { get; private set; }
11:
12: public decimal Calculate()
13: {
14: return new OrderCalculator(this).Calculate();
15: }
16: }
17:
18: public class OrderCalculator
19: {
20: private decimal SubTotal { get; set;}
21: private IEnumerable<OrderLineItem> OrderLineItems { get; set; }
22: private IEnumerable<decimal> Discounts { get; set; }
23: private decimal Tax { get; set; }
24:
25: public OrderCalculator(Order order)
26: {
27: OrderLineItems = order.OrderLineItems;
28: Discounts = order.Discounts;
29: Tax = order.Tax;
30: }
31:
32: public decimal Calculate()
33: {
34: CalculateSubTotal();
35:
36: SubtractDiscounts();
37:
38: CalculateTax();
39:
40: return SubTotal;
41: }
42:
43: private void CalculateSubTotal()
44: {
45: // Total up line items
46: foreach (OrderLineItem lineItem in OrderLineItems)
47: SubTotal += lineItem.Price;
48: }
49:
50: private void SubtractDiscounts()
51: {
52: // Subtract Discounts
53: foreach (decimal discount in Discounts)
54: SubTotal -= discount;
55: }
56:
57: private void CalculateTax()
58: {
59: // Calculate Tax
60: SubTotal += SubTotal * Tax;
61: }
62: }
PS:我个人不是很喜欢重构，我还是喜欢提取方法这个重构。