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;
}