今天要说的重构没有明确的出处，分解方法是我给它起的名字，我相信肯定还有别人做过类似的重构但却叫别一个名字，如果你在看完本文后觉得还有比“分解方法”更好的名字，请通知我。
分解重构是元重构的一种，所做的事情就是不停的分解方法，直到将一个大方法分解为可读性更好的若干个小方法。本文一会要遇到的例子是虚构的，因为现实中AcceptPayment方法不会做这么多的事情。
下面我们通过几次分解将AcceptPayment分解成若干个小方法。
1: public class CashRegister
2: {
3: public CashRegister()
4: {
5: Tax = 0.06m;
6: }
7:
8: private decimal Tax { get; set; }
9:
10: public void AcceptPayment(Customer customer, IEnumerable<Product> products, decimal payment)
11: {
12: decimal subTotal = 0m;
13: foreach (Product product in products)
14: {
15: subTotal += product.Price;
16: }
17:
18: foreach(Product product in products)
19: {
20: subTotal -= product.AvailableDiscounts;
21: }
22:
23: decimal grandTotal = subTotal * Tax;
24:
25: customer.DeductFromAccountBalance(grandTotal);
26: }
27: }
28:
29: public class Customer
30: {
31: public void DeductFromAccountBalance(decimal amount)
32: {
33: // deduct from balance
34: }
35: }
36:
37: public class Product
38: {
39: public decimal Price { get; set; }
40: public decimal AvailableDiscounts { get; set; }
41: }
如你所看到的,AcceptPayment方法中许多代码可以提取到独立的方法中，所以我们应用“提取方法”重构将这些代码提取到独立的方法中，下面是提取后的代码：
1: public class CashRegister
2: {
3: public CashRegister()
4: {
5: Tax = 0.06m;
6: }
7:
8: private decimal Tax { get; set; }
9: private IEnumerable<Product> Products { get; set; }
10:
11: public void AcceptPayment(Customer customer, IEnumerable<Product> products, decimal payment)
12: {
13: decimal subTotal = CalculateSubtotal();
14:
15: subTotal = SubtractDiscounts(subTotal);
16:
17: decimal grandTotal = AddTax(subTotal);
18:
19: SubtractFromCustomerBalance(customer, grandTotal);
20: }
21:
22: private void SubtractFromCustomerBalance(Customer customer, decimal grandTotal)
23: {
24: customer.DeductFromAccountBalance(grandTotal);
25: }
26:
27: private decimal AddTax(decimal subTotal)
28: {
29: return subTotal * Tax;
30: }
31:
32: private decimal SubtractDiscounts(decimal subTotal)
33: {
34: foreach(Product product in Products)
35: {
36: subTotal -= product.AvailableDiscounts;
37: }
38: return subTotal;
39: }
40:
41: private decimal CalculateSubtotal()
42: {
43: decimal subTotal = 0m;
44: foreach (Product product in Products)
45: {
46: subTotal += product.Price;
47: }
48: return subTotal;
49: }
50: }
51:
52: public class Customer
53: {
54: public void DeductFromAccountBalance(decimal amount)
55: {
56: // deduct from balance
57: }
58: }
59:
60: public class Product
61: {
62: public decimal Price { get; set; }
63: public decimal AvailableDiscounts { get; set; }
64: }
PS：个人认为“分解方法”重构和“提取方法”重构好像是一个重构，只是名字不一样吗？