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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重构22-Break Method（重构方法）

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