《重构-改善既有代码的设计》-第1例：租赁影片（1）

前些天发现了一个巨牛的人工智能学习网站，通俗易懂，风趣幽默，忍不住分享一下给大家。点击跳转到教程。

买了《重构 - 改善既有代码的设计》一书，一直没有好好看，大致过了下也觉得只是有点点印象而已，最后还是决定把代码敲一次，记录一下这些学习过程。

第一例：租赁影片

程序说明：顾客租了哪些影片，租期多长，根据租赁时间和影片类型算出费用和积分。

1. 分解并重组statement()

原代码如下有3个类。

package bean;
/*** 租赁订单* @author Administrator*/
public class Rental {private Movie _movie ; // 影片private int _daysRented; // 租赁天数public Rental(Movie _movie, int _daysRented) {this._movie = _movie;this._daysRented = _daysRented;}public Movie getMovie() {return _movie;}public int getDaysRented() {return _daysRented;}}

package bean;/*** 影片* @author Administrator*/
public class Movie {public static final int CHILDRENS = 2;  // 儿童片public static final int REGULAR = 0; // 普通片public static final int NEW_RELEASE = 1; // 新片private String _title;private int _priceCode;public Movie(String _title, int _priceCode) {this._title = _title;this._priceCode = _priceCode;}public int getPriceCode() {return _priceCode;}public void setPriceCode(int _priceCode) {this._priceCode = _priceCode;}public String getTitle() {return _title;}}

package bean;import java.util.Enumeration;
import java.util.Vector;/*** 顾客* @author Administrator*/
public class Customer {private String _name; // 顾客名字private Vector _rentals = new Vector();  // 租赁订单数组public Customer(String name) {super();this._name = name;}public void addRental(Rental arg){_rentals.addElement(arg);}public String getName() {return _name;}/*** 生成订单* @return*/public String statement(){double totalAmount = 0; // 总租金 int frequentRenterPoints = 0; // 积分Enumeration rentals = _rentals.elements();String result = "Rental Record for "+ getName() + "\n";while( rentals.hasMoreElements()){double thisAmount = 0; // 租金Rental each = (Rental)rentals.nextElement();// 确定每种片子的租金switch(each.getMovie().getPriceCode()){case Movie.REGULAR:thisAmount += 2;if(each.getDaysRented() > 2 ){thisAmount += (each.getDaysRented() - 2) * 1.5;}break;case Movie.NEW_RELEASE:thisAmount += each.getDaysRented()*3;break;case Movie.CHILDRENS:thisAmount += 1.5;if(each.getDaysRented() > 3 ){thisAmount += (each.getDaysRented() - 3) * 1.5;}break;}// 增加积分frequentRenterPoints ++;// 新片+租赁时间达2天  积分+1 if(each.getMovie().getPriceCode() == Movie.NEW_RELEASE && each.getDaysRented() > 1){frequentRenterPoints ++;}// 本次租赁记录说明result += "\t"+each.getMovie().getTitle()+"\t"+ String.valueOf(thisAmount)+"\n";totalAmount += thislAmount;}// 页脚result +="Amount owed is "+ String.valueOf(totalAmount)+"\n";result +="You eared "+String.valueOf(frequentRenterPoints)+"frequent renter points";return result;}}

1.1 抽离switch 语句到独立方法

1.1.1 Customer类改为：

package bean;import java.util.Enumeration;
import java.util.Vector;/*** 顾客* @author Administrator*/
public class Customer {private String _name; // 顾客名字private Vector _rentals = new Vector();  // 租赁订单数组public Customer(String name) {super();this._name = name;}public void addRental(Rental arg){_rentals.addElement(arg);}public String getName() {return _name;}/*** 生成订单* @return*/public String statement(){double totalAmount = 0; // 总租金 int frequentRenterPoints = 0; // 积分Enumeration rentals = _rentals.elements();String result = "Rental Record for "+ getName() + "\n";while( rentals.hasMoreElements()){double thisAmount = 0; // 租金Rental each = (Rental)rentals.nextElement();thisAmount = amountFor(each); // 计算租金// 增加积分frequentRenterPoints ++; // 新片+租赁时间达2天  积分+1 if(each.getMovie().getPriceCode() == Movie.NEW_RELEASE && each.getDaysRented() > 1){frequentRenterPoints ++;}// 本次租赁记录说明result += "\t"+each.getMovie().getTitle()+"\t"+ String.valueOf(thisAmount)+"\n";totalAmount += thisAmount;}// 页脚result +="Amount owed is "+ String.valueOf(totalAmount)+"\n";result +="You eared "+String.valueOf(frequentRenterPoints)+"frequent renter points";return result;}// 计算租金private int amountFor(Rental each){int thisAmount = 0; // 租金// 确定每种片子的租金switch(each.getMovie().getPriceCode()){case Movie.REGULAR:thisAmount += 2;if(each.getDaysRented() > 2 ){thisAmount += (each.getDaysRented() - 2) * 1.5;}break;case Movie.NEW_RELEASE:thisAmount += each.getDaysRented()*3;break;case Movie.CHILDRENS:thisAmount += 1.5;if(each.getDaysRented() > 3 ){thisAmount += (each.getDaysRented() - 3) * 1.5;}break;}return thisAmount;}}

1.1.2 注意 amountFor 方法的返回类型应该是double类型：

Customer类改为：

package bean;import java.util.Enumeration;
import java.util.Vector;/*** 顾客* @author Administrator*/
public class Customer {private String _name; // 顾客名字private Vector _rentals = new Vector();  // 租赁订单数组public Customer(String name) {super();this._name = name;}public void addRental(Rental arg){_rentals.addElement(arg);}public String getName() {return _name;}/*** 生成订单* @return*/public String statement(){double totalAmount = 0; // 总租金 int frequentRenterPoints = 0; // 积分Enumeration rentals = _rentals.elements();String result = "Rental Record for "+ getName() + "\n";while( rentals.hasMoreElements()){double thisAmount = 0; // 租金Rental each = (Rental)rentals.nextElement();thisAmount = amountFor(each); // 计算租金// 增加积分frequentRenterPoints ++; // 新片+租赁时间达2天  积分+1 if(each.getMovie().getPriceCode() == Movie.NEW_RELEASE && each.getDaysRented() > 1){frequentRenterPoints ++;}// 本次租赁记录说明result += "\t"+each.getMovie().getTitle()+"\t"+ String.valueOf(thisAmount)+"\n";totalAmount += thisAmount;}// 页脚result +="Amount owed is "+ String.valueOf(totalAmount)+"\n";result +="You eared "+String.valueOf(frequentRenterPoints)+"frequent renter points";return result;}// 计算租金private double amountFor(Rental each){double thisAmount = 0; // 租金// 确定每种片子的租金switch(each.getMovie().getPriceCode()){case Movie.REGULAR:thisAmount += 2;if(each.getDaysRented() > 2 ){thisAmount += (each.getDaysRented() - 2) * 1.5;}break;case Movie.NEW_RELEASE:thisAmount += each.getDaysRented()*3;break;case Movie.CHILDRENS:thisAmount += 1.5;if(each.getDaysRented() > 3 ){thisAmount += (each.getDaysRented() - 3) * 1.5;}break;}return thisAmount;}}

1.3 变量名称应该见名知意：好的代码应该清楚的表达出自己的功能，变量名称是代码清晰的一个关键。

amountFor方法中局部变量 thisAmount , 参数each 要改名。

改变量名 , Customer类改为：

package bean;import java.util.Enumeration;
import java.util.Vector;/*** 顾客* @author Administrator*/
public class Customer {private String _name; // 顾客名字private Vector _rentals = new Vector();  // 租赁订单数组public Customer(String name) {super();this._name = name;}public void addRental(Rental arg){_rentals.addElement(arg);}public String getName() {return _name;}/*** 生成订单* @return*/public String statement(){double totalAmount = 0; // 总租金 int frequentRenterPoints = 0; // 积分Enumeration rentals = _rentals.elements();String result = "Rental Record for "+ getName() + "\n";while( rentals.hasMoreElements()){double thisAmount = 0; // 租金Rental each = (Rental)rentals.nextElement();thisAmount = amountFor(each); // 计算租金// 增加积分frequentRenterPoints ++; // 新片+租赁时间达2天  积分+1 if(each.getMovie().getPriceCode() == Movie.NEW_RELEASE && each.getDaysRented() > 1){frequentRenterPoints ++;}// 本次租赁记录说明result += "\t"+each.getMovie().getTitle()+"\t"+ String.valueOf(thisAmount)+"\n";totalAmount += thisAmount;}// 页脚result +="Amount owed is "+ String.valueOf(totalAmount)+"\n";result +="You eared "+String.valueOf(frequentRenterPoints)+"frequent renter points";return result;}// 计算租金private double amountFor(Rental aRental){double result = 0; // 租金// 确定每种片子的租金switch(aRental.getMovie().getPriceCode()){case Movie.REGULAR:result += 2;if(aRental.getDaysRented() > 2 ){result += (aRental.getDaysRented() - 2) * 1.5;}break;case Movie.NEW_RELEASE:result += aRental.getDaysRented()*3;break;case Movie.CHILDRENS:result += 1.5;if(aRental.getDaysRented() > 3 ){result += (aRental.getDaysRented() - 3) * 1.5;}break;}return result;}}

1.4 函数应该放在它所使用的数据所属的对象中，顾客租金的计算应该移动到Rental类中去。

Rental 类改为 : （计算租金方法去掉参数并改名）

package bean;
/*** 租赁订单* @author Administrator*/
public class Rental {private Movie _movie ; // 影片private int _daysRented; // 租赁天数public Rental(Movie _movie, int _daysRented) {this._movie = _movie;this._daysRented = _daysRented;}public Movie getMovie() {return _movie;}public int getDaysRented() {return _daysRented;}// 计算租金double getCharge(){double result = 0; // 租金// 确定每种片子的租金switch(getMovie().getPriceCode()){case Movie.REGULAR:result += 2;if(getDaysRented() > 2 ){result += (getDaysRented() - 2) * 1.5;}break;case Movie.NEW_RELEASE:result += getDaysRented()*3;break;case Movie.CHILDRENS:result += 1.5;if(getDaysRented() > 3 ){result += (getDaysRented() - 3) * 1.5;}break;}return result;}}

原顾客类中amountFor方法直接调用计算租金方法即可，Customer 类改为：

package bean;import java.util.Enumeration;
import java.util.Vector;/*** 顾客* @author Administrator*/
public class Customer {private String _name; // 顾客名字private Vector _rentals = new Vector();  // 租赁订单数组public Customer(String name) {super();this._name = name;}public void addRental(Rental arg){_rentals.addElement(arg);}public String getName() {return _name;}/*** 生成订单* @return*/public String statement(){double totalAmount = 0; // 总租金 int frequentRenterPoints = 0; // 积分Enumeration rentals = _rentals.elements();String result = "Rental Record for "+ getName() + "\n";while( rentals.hasMoreElements()){double thisAmount = 0; // 租金Rental each = (Rental)rentals.nextElement();thisAmount = amountFor(each); // 计算租金// 增加积分frequentRenterPoints ++; // 新片+租赁时间达2天  积分+1 if(each.getMovie().getPriceCode() == Movie.NEW_RELEASE && each.getDaysRented() > 1){frequentRenterPoints ++;}// 本次租赁记录说明result += "\t"+each.getMovie().getTitle()+"\t"+ String.valueOf(thisAmount)+"\n";totalAmount += thisAmount;}// 页脚result +="Amount owed is "+ String.valueOf(totalAmount)+"\n";result +="You eared "+String.valueOf(frequentRenterPoints)+"frequent renter points";return result;}// 计算租金private double amountFor(Rental aRental){return aRental.getCharge();}}

1.5 去掉旧函数amountFor，直接调用新函数getCharge。Customer类改为 :

package bean;import java.util.Enumeration;
import java.util.Vector;/*** 顾客* @author Administrator*/
public class Customer {private String _name; // 顾客名字private Vector _rentals = new Vector();  // 租赁订单数组public Customer(String name) {super();this._name = name;}public void addRental(Rental arg){_rentals.addElement(arg);}public String getName() {return _name;}/*** 生成订单* @return*/public String statement(){double totalAmount = 0; // 总租金 int frequentRenterPoints = 0; // 积分Enumeration rentals = _rentals.elements();String result = "Rental Record for "+ getName() + "\n";while( rentals.hasMoreElements()){double thisAmount = 0; // 租金Rental each = (Rental)rentals.nextElement();thisAmount = each.getCharge(); // 计算租金// 增加积分frequentRenterPoints ++; // 新片+租赁时间达2天  积分+1 if(each.getMovie().getPriceCode() == Movie.NEW_RELEASE && each.getDaysRented() > 1){frequentRenterPoints ++;}// 本次租赁记录说明result += "\t"+each.getMovie().getTitle()+"\t"+ String.valueOf(thisAmount)+"\n";totalAmount += thisAmount;}// 页脚result +="Amount owed is "+ String.valueOf(totalAmount)+"\n";result +="You eared "+String.valueOf(frequentRenterPoints)+"frequent renter points";return result;}}

1.6 尽量去掉临时变量，临时变量会导致大量参数的传递，没有必要。 thisAmount 是个多余的临时变量，直接去掉。

Customer 改为：

package bean;import java.util.Enumeration;
import java.util.Vector;/*** 顾客* @author Administrator*/
public class Customer {private String _name; // 顾客名字private Vector _rentals = new Vector();  // 租赁订单数组public Customer(String name) {super();this._name = name;}public void addRental(Rental arg){_rentals.addElement(arg);}public String getName() {return _name;}/*** 生成订单* @return*/public String statement(){double totalAmount = 0; // 总租金 int frequentRenterPoints = 0; // 积分Enumeration rentals = _rentals.elements();String result = "Rental Record for "+ getName() + "\n";while( rentals.hasMoreElements()){Rental each = (Rental)rentals.nextElement();// 增加积分frequentRenterPoints ++; // 新片+租赁时间达2天  积分+1 if(each.getMovie().getPriceCode() == Movie.NEW_RELEASE && each.getDaysRented() > 1){frequentRenterPoints ++;}// 本次租赁记录说明result += "\t"+each.getMovie().getTitle()+"\t"+ String.valueOf(each.getCharge())+"\n";totalAmount += each.getCharge();}// 页脚result +="Amount owed is "+ String.valueOf(totalAmount)+"\n";result +="You eared "+String.valueOf(frequentRenterPoints)+"frequent renter points";return result;}}

1.7 把积分计算方法放到Rental类中，写为常客积分计算方法（getFrequentRenterPoints），并改变Customer类中积分计算代码。

Rental类改为：

package bean;
/*** 租赁订单* @author Administrator*/
public class Rental {private Movie _movie ; // 影片private int _daysRented; // 租赁天数public Rental(Movie _movie, int _daysRented) {this._movie = _movie;this._daysRented = _daysRented;}public Movie getMovie() {return _movie;}public int getDaysRented() {return _daysRented;}// 计算租金double getCharge(){double result = 0; // 租金// 确定每种片子的租金switch(getMovie().getPriceCode()){case Movie.REGULAR:result += 2;if(getDaysRented() > 2 ){result += (getDaysRented() - 2) * 1.5;}break;case Movie.NEW_RELEASE:result += getDaysRented()*3;break;case Movie.CHILDRENS:result += 1.5;if(getDaysRented() > 3 ){result += (getDaysRented() - 3) * 1.5;}break;}return result;}// 常客积分计算int getFrequentRenterPoints(){// 增加积分int frequentRenterPoints =0;frequentRenterPoints++; // （新片+租赁时间达2天  积分+1 ）if(getMovie().getPriceCode() == Movie.NEW_RELEASE && getDaysRented() > 1){frequentRenterPoints ++;}return frequentRenterPoints;}}

Customer类中statement方法改为：

/*** 生成订单* @return*/public String statement(){double totalAmount = 0; // 总租金 int frequentRenterPoints = 0; // 积分Enumeration rentals = _rentals.elements();String result = "Rental Record for "+ getName() + "\n";while( rentals.hasMoreElements()){Rental each = (Rental)rentals.nextElement();// 积分frequentRenterPoints += each.getFrequentRenterPoints();// 本次租赁记录说明result += "\t"+each.getMovie().getTitle()+"\t"+ String.valueOf(each.getCharge())+"\n";totalAmount += each.getCharge();}// 页脚result +="Amount owed is "+ String.valueOf(totalAmount)+"\n";result +="You eared "+String.valueOf(frequentRenterPoints)+"frequent renter points";return result;}

1.8 去掉statement方法中的2个临时变量：totalAmount 和 frequentRenterPoints 。抽离出对应计算方法，并调用。

Customer 类改为：

package bean;import java.util.Enumeration;
import java.util.Vector;/*** 顾客* @author Administrator*/
public class Customer {private String _name; // 顾客名字private Vector _rentals = new Vector();  // 租赁订单数组public Customer(String name) {super();this._name = name;}public void addRental(Rental arg){_rentals.addElement(arg);}public String getName() {return _name;}/*** 生成订单* @return*/public String statement(){Enumeration rentals = _rentals.elements();String result = "Rental Record for "+ getName() + "\n";while( rentals.hasMoreElements()){Rental each = (Rental)rentals.nextElement();// 本次租赁记录说明result += "\t"+each.getMovie().getTitle()+"\t"+ String.valueOf(each.getCharge())+"\n";}// 页脚result +="Amount owed is "+ String.valueOf(getTotalCharge())+"\n";result +="You eared "+String.valueOf(getTotalFrequentRenterPoints())+"frequent renter points";return result;}// 计算总积分private int getTotalFrequentRenterPoints(){int result = 0;Enumeration rentals = _rentals.elements();while(rentals.hasMoreElements()){Rental each = (Rental)rentals.nextElement();result += each.getFrequentRenterPoints();}return result;}// 计算总租金private double getTotalCharge(){double result = 0;Enumeration rentals = _rentals.elements();while(rentals.hasMoreElements()){Rental each = (Rental)rentals.nextElement();result += each.getCharge();}return result;}}

本步改写作用说明：

这里虽然从1个循环变为3个，但是多了2个查询函数。

1) 使得Customer 类中的任何代码都可以调用这些查询函数。

2) 若系统其它部分需要这些信息，也可以轻松地将查询函数加入 Customer 类接口。而若没有这些查询波函数，其它函数就必须了解 Rental 类，并自行建立循环。

1.9 加功能：打印凭条。

statement 方法改为 htmlStatement ：

/*** 生成订单(打印凭条)* @return*/public String htmlStatement(){Enumeration rentals = _rentals.elements();String result = "<P><H1>Rentals for <EM> "+ getName() + "</EM></H1></P>\n";while( rentals.hasMoreElements()){Rental each = (Rental)rentals.nextElement();// 本次租赁记录说明result += each.getMovie().getTitle()+"："+ String.valueOf(each.getCharge())+"<BR>\n";}// 页脚result +="<P>You owe <EM>"+ String.valueOf(getTotalCharge())+"</EM></P>\n";result +="<P> on this rental you earned <EM> "+String.valueOf(getTotalFrequentRenterPoints())+"</EM> frequent renter points </P>";return result;}

未完，见：重构-改善既有代码的设计-第1例：租赁影片（2）

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