重构22-Break Method（重构方法）

这个重构是一种元重构（meta-refactoring），它只是不停地使用提取方法重构，直到将一个大的方法分解成若干个小的方法。下面的例子有点做作，AcceptPayment方法没有丰富的功能。因此为了使其更接近真实场景，我们只能假设该方法中包含了其他大量的辅助代码。 下面的AcceptPayment方法可以被划分为多个单独的方法。

public class CashRegister {    public CashRegister() {        Tax = 0.06d;}    private Double Tax;    public void AcceptPayment(Customer customer, List<Product> products,Double payment) {        Double subTotal = 0d;        for(Product product : products) {            subTotal += product.Price;}        for(Product product : products) {            subTotal -= product.AvailableDiscounts;}        Double grandTotal = subTotal * Tax;customer.DeductFromAccountBalance(grandTotal);}}public class Customer {    public void DeductFromAccountBalance(Double amount) {        // deduct from balance        }}public class Product {    public Double Price;    public Double AvailableDiscounts;}

如您所见，AcceptPayment方法包含多个功能，可以被分解为多个子方法。因此我们

多次使用提取方法重构，结果如下：

public class CashRegister {    public CashRegister() {        Tax = 0.06d;}    private Double Tax;    private List<Product> Products;    public void AcceptPayment(Customer customer, List<Product> products, Double payment) {        Double subTotal = CalculateSubtotal();subTotal = SubtractDiscounts(subTotal);Double grandTotal = AddTax(subTotal);SubtractFromCustomerBalance(customer, grandTotal);}    private void SubtractFromCustomerBalance(Customer customer, Double grandTotal) {        customer.DeductFromAccountBalance(grandTotal);}    private Double AddTax(Double subTotal) {        return subTotal * Tax;}    private Double SubtractDiscounts(Double subTotal) {        for(Product product : Products){            subTotal -= product.AvailableDiscounts;}        return subTotal;}    private Double CalculateSubtotal() {        Double subTotal = 0d;        for(Product product : Products){            subTotal += product.Price;}        return subTotal;}}public class Customer {    public void DeductFromAccountBalance(Double amount) {        // deduct from balance        }}public class Product {    public Double Price;    public Double AvailableDiscounts;}

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