把一个类的多个职责进行拆分，这贯彻了SOLID中的单一职责原则（SRP）。尽管对于如何划分“职责”经常存在争论，但应用这项重构还是十分简单的。我这里并不会回答划分职责的问题，只是演示一个结构清晰的示例，将类划分为多个负责具体职责的类。
public class Video {
public void PayFee(Double fee) {
}
public void RentVideo(Video video, Customer customer) {
customer.Videos.add(video);
}
public Double CalculateBalance(Customer customer) {
return customer.sum(customer.LateFees);
}
}
public class Customer {
public List<Double> LateFees;
public List<Video> Videos;
double sum(List<Double> LateFees){
double sum=0d;
for (Double d:LateFees){
sum=+d;
}
return sum;
}
}
如你所见，Video类包含两个职责，一个负责处理录像租赁，另一个负责管理管理用户的租赁总数。要分离
职责，我们可以将用户的逻辑转移到用户类中。
public class Video {
public void RentVideo(Video video, Customer customer) {
customer.Videos.add(video);
}
}
public class Customer {
public List<Double> LateFees;
public List<Video> Videos;
public void PayFee(Double fee){}
public Double CalculateBalance(Customer customer) {
return sum(customer.LateFees);
}
double sum(List<Double> LateFees) {
double sum = 0d;
for (Double d : LateFees) {
sum = +d;
}
return sum;
}
}
