《重构-改善既有代码的设计》-第1例：租赁影片（1）

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）