《重构》第一章示例 — 体验重构的魔力 RefactorSample
一个月了，没有认真写博客，也没有认真学习，数据库的学习进度一直拖拖拉拉到现在也没有搞定，sad。。。
今天，看了一下《重构》的第一章，深深的被吸引了....
示例
情景：顾客租电影，电影分三种，儿童票，普通片，新片，儿童片2天以内1.5元，超过两天，每一天加收1.5元，普通片3天以内2元，超过两天，每一天加收2元，新片每天3元，每租一次电影积分加一，如果是新片，且租期超过2天，积分加二。
分析：
以面向对象的思想分析，涉及对象顾客，影片，外加一个租赁类作为顾客和影片的桥接
编写代码
影片类（Movie）：
public class Movie {
public static final int CHILDRENS = 0;
public static final int REGULARS = 1;
public static final int NEW_RELEASE = 2;
private String name;
private int movType;
public Movie(String name, int movType) {
this.name = name;
this.movType = movType;
}
name: set 和 get 方法
movType: set 和get 方法
}
为了节省篇幅，Movie类的name、movType的set和get就不贴了。
租赁类（Rental）：
public class Rental {
private Movie movie;
private int rentDays;
public Rental(Movie movie,int rentDays) {
this.movie = movie; this.rentDays = rentDays;
}
movie 和 rentDays的set和get方法
顾客类（Customer）：
public class Customer {
private String name;
private ArrayList<Rental> rentals = new ArrayList<Rental>();
public Customer(String name) {
this.name = name;
}
public void addRent(Rental r){
rentals.add(r);
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String statement() throws Exception {
String result = "Rental report for " + getName() + "\n";
double totalAmount = 0;
int frequent = 0;
for(Rental r : rentals){
double thisAmount = 0;
switch (r.getMovie().getMovType()){
case Movie.CHILDRENS :
thisAmount += (r.getRentDays()>2)?((r.getRentDays()-2)*1.5+1.5):1.5;
break;
case Movie.REGULARS:
thisAmount += (r.getRentDays()>3)?((r.getRentDays()-3)*2+2):2;
break;
case Movie.NEW_RELEASE:
thisAmount += r.getRentDays() * 3;
break;
default:throw new Exception("类型异常");
}
totalAmount += thisAmount;
frequent += (r.getMovie().getMovType()==Movie.NEW_RELEASE &&
r.getRentDays()>2)?2:1;
result+="\t" + r.getMovie().getName() + "\t" + String.valueOf(thisAmount) + "\n";
}
result += "Amount is " + String.valueOf(totalAmount) + "元\n";
result += "frequent is " + String.valueOf(frequent)+"分";
return result;
}
}
编写测试代码：
public class Test {
public static void main(String[] args) throws Exception {
Movie m1 = new Movie("葫芦娃",0);//儿童片
Movie m2 = new Movie("神雕侠侣",1);//普通片
Movie m3 = new Movie("何以笙箫默",2);//新片
Customer c = new Customer("朱小妹");
c.addRent(new Rental(m1,2));//1.5
c.addRent(new Rental(m2,2));//2
c.addRent(new Rental(m3,3));//9
System.out.println(c.statement());
}
}
以上代码完成了示例需求，但是代码写的...太烂了，我自己写绝对也是这个样子。。。代码烂，怎么办？重构！
第一步：一劳永逸 — 修改测试代码
为了方便测试，我们将打印结果作为一个字符串保存起来。
public class Test {
public static void main(String[] args) throws Exception {
Movie m1 = new Movie("葫芦娃",0);//儿童片
Movie m2 = new Movie("神雕侠侣",1);//普通片
Movie m3 = new Movie("何以笙箫默",2);//新片
Customer c = new Customer("朱小妹");
c.addRent(new Rental(m1,2));//1.5
c.addRent(new Rental(m2,2));//2
c.addRent(new Rental(m3,3));//9
String result = "Rental report for 朱小妹\n" +
"\t葫芦娃\t1.5\n" +
"\t神雕侠侣\t2.0\n" +
"\t何以笙箫默\t9.0\n" +
"Amount is 12.5元\n" +
"frequent is 4分";
System.out.println(c.statement().equals(result));
}
}
以后的测试结果，true就是修改正确，false就是修改失败。
第二步：一石二鸟 — 分解customer类statement方法
纵观所有代码，唯独customer类的statement代码最多，最乱，看着烦，看switch更烦，而switch的作用就是一个计算一个临时变量thisAmount的作用，而临时变量越多对一个程序来说就越容易出错，既然容易出错，totalAmount和frement有什么用，还占地方，留它们干嘛，拿走，单独封装。
更改后的customer类：
public class Customer {
private String name;
private ArrayList<Rental> rentals = new ArrayList<Rental>();
public Customer(String name) {
this.name = name;
}
public void addRent(Rental r){
rentals.add(r);
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String statement() throws Exception {
String result = "Rental report for " + getName() + "\n";
for (Rental r : rentals ) {
result += "\t" + r.getMovie().getName() + "\t" + String.valueOf(amountFor(r)) + "\n";
}
result += "Amount is " + String.valueOf(getTotalAmount()) + "元\n";
result += "frequent is " + String.valueOf(getTotalFrequent())+"分";
return result;
}
private double getTotalAmount() throws Exception {
double totalAmount = 0;
for(Rental r : rentals){
totalAmount += amountFor(r);
}
return totalAmount;
}
private int getTotalFrequent(){
int frequent = 0;
for(Rental r : rentals){
frequent += (r.getMovie().getMovType()==Movie.NEW_RELEASE &&
r.getRentDays()>2)?2:1;
}
return frequent;
}
private double amountFor(Rental r) throws Exception {
double thisAmount = 0;
switch (r.getMovie().getMovType()){
case Movie.CHILDRENS :
thisAmount += (r.getRentDays()>2)?((r.getRentDays()-2)*1.5+1.5):1.5;
break;
case Movie.REGULARS:
thisAmount += (r.getRentDays()>3)?((r.getRentDays()-3)*2+2):2;
break;
case Movie.NEW_RELEASE:
thisAmount += r.getRentDays() * 3;
break;
default:throw new Exception("类型异常");
}
return thisAmount;
}
}
这样statement方法庞大和临时变量多的问题都解决了，进行测试，true，修改正确
第三步：各回各家 — 做自己该干的事
重新审视一下customer类，你会发现它很多它不该干的事，switch计算单次租赁花费和积分这个事，应该电影类干吧，花多钱，得多少分，电影自身最清楚
问题还是存在switch身上，最好不要在另一个对象的属性基础上运用switch，如果非要使用，也应该是在对象自己的数据上使用，而不是在别人的数据上使用。
在rental类中增加getOneMoney方法和getOneFre方法，customer类删除amountFor方法，修改getTotalFrequent方法，switch搬家到Movie类中
更改后的customer类
只变动了getTotalFrequent方法for循环
public class Customer {
private String name;
private ArrayList<Rental> rentals = new ArrayList<Rental>();
public Customer(String name) {
this.name = name;
}
public void addRent(Rental r){
rentals.add(r);
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String statement() throws Exception {
String result = "Rental report for " + getName() + "\n";
for (Rental r : rentals ) {
result += "\t" + r.getMovie().getName() + "\t" + String.valueOf(r.getOne()) + "\n";
}
result += "Amount is " + String.valueOf(getTotalAmount()) + "元\n";
result += "frequent is " + String.valueOf(getTotalFrequent())+"分";
return result;
}
private double getTotalAmount() throws Exception {
double totalAmount = 0;
for(Rental r : rentals){
totalAmount += r.getOne();
}
return totalAmount;
}
private int getTotalFrequent(){
int frequent = 0;
for(Rental r : rentals){
frequent += r.getOneFre();
}
return frequent;
}
}
更改后的rental，起了一个桥梁作用
public class Rental {
private Movie movie;
private int rentDays;
public Rental(Movie movie,int rentDays) {
this.movie = movie; this.rentDays = rentDays;
}
public int getRentDays() {
return rentDays;
}
public void setRentDays(int rentDays) {
this.rentDays = rentDays;
}
public Movie getMovie() {
return movie;
}
public double getOne() throws Exception {
return getMovie().getMoney(rentDays) ;
}
public int getOneFre(){
return getMovie().getFrequent(rentDays);
}
public void setMovie(Movie movie) {
this.movie = movie;
}
}
更改后的movie类，终于开始做事了
/**
* Created by Kevy on 2015/1/21.
*/
/*编写电影类代码*/
public class Movie {
public static final int CHILDRENS = 0;
public static final int REGULARS = 1;
public static final int NEW_RELEASE = 2;
private String name;
private int movType;
public Movie(String name, int movType) {
this.name = name;
this.movType = movType;
}
public int getMovType() {
return movType;
}
public void setMovType(int movType) {
this.movType = movType;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getMoney(int RentDays) throws Exception {
double thisAmount = 0;
switch (getMovType()){
case Movie.CHILDRENS :
thisAmount += (RentDays>2)?((RentDays-2)*1.5+1.5):1.5;
break;
case Movie.REGULARS:
thisAmount += (RentDays>3)?((RentDays-3)*2+2):2;
break;
case Movie.NEW_RELEASE:
thisAmount += RentDays * 3;
break;
default:throw new Exception("类型异常");
}
return thisAmount ;
}
public int getFrequent(int RentDays){
return (getMovType()==NEW_RELEASE &&
RentDays>2)?2:1;
}
}
测试OK，没有问题。
第四步 利用多态
现在所有的类，都在干自己的事，movie类的getMoney方法的代码量看着还是不太好，既然是三种电影只是类型不同而已，那么久完全可以向上抽取使用抽象类。
public interface Type {
public int getType();
public double getMovMeony(int days);
}
public class ChildrenMov implements Type {
public int getType() {
return 0;
}
public double getMovMeony(int days) {
return (days>2)?((days-2)*1.5+1.5):1.5;
}
}
public class RegularMov implements Type {
public int getType() {
return 1;
}
public double getMovMeony(int days) {
return (days>3)?((days-3)*2+2):2;
}
}
public class NewMov implements Type {
public int getType() {
return 2;
}
public double getMovMeony(int days) {
return days * 3;
}
}
最终完整代码：
import java.util.ArrayList;
/**
* Created by Kevy on 2015/1/21.
*/
public class Customer {
private String name;
private ArrayList<Rental> rentals = new ArrayList<Rental>();
public Customer(String name) {
this.name = name;
}
public void addRent(Rental r){
rentals.add(r);
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String statement() throws Exception {
String result = "Rental report for " + getName() + "\n";
for (Rental r : rentals ) {
result += "\t" + r.getMovie().getName() + "\t" + String.valueOf(r.getOne()) + "\n";
}
result += "Amount is " + String.valueOf(getTotalAmount()) + "元\n";
result += "frequent is " + String.valueOf(getTotalFrequent())+"分";
return result;
}
private double getTotalAmount() throws Exception {
double totalAmount = 0;
for(Rental r : rentals){
totalAmount += r.getOne();
}
return totalAmount;
}
private int getTotalFrequent(){
int frequent = 0;
for(Rental r : rentals){
frequent += r.getOneFre();
}
return frequent;
}
}
/**
* Created by Kevy on 2015/1/21.
*/
public class Rental {
private Movie movie;
private int rentDays;
public Rental(Movie movie,int rentDays) {
this.movie = movie; this.rentDays = rentDays;
}
public int getRentDays() {
return rentDays;
}
public void setRentDays(int rentDays) {
this.rentDays = rentDays;
}
public Movie getMovie() {
return movie;
}
public double getOne() throws Exception {
return getMovie().getMoney(rentDays) ;
}
public int getOneFre(){
return getMovie().getFrequent(rentDays);
}
public void setMovie(Movie movie) {
this.movie = movie;
}
}
/**
* Created by Kevy on 2015/1/21.
*/
/*编写电影类代码*/
public class Movie {
public static final int CHILDRENS = 0;
public static final int REGULARS = 1;
public static final int NEW_RELEASE = 2;
private String name;
private Type t;
public Movie(String name, int movType) throws Exception {
this.name = name;
setT(movType);
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getMoney(int RentDays) {
return t.getMovMeony(RentDays);
}
public int getFrequent(int RentDays){
return (t.getType()==NEW_RELEASE &&
RentDays>2)?2:1;
}
public void setT(int d) throws Exception {
switch (d){
case CHILDRENS :t = new ChildrenMov();
break;
case REGULARS:t = new RegularMov();
break;
case NEW_RELEASE:t = new NewMov();
break;
default:throw new Exception("类型错误");
}
}
}
import sun.plugin2.message.ModalityChangeMessage;
/**
* Created by Kevy on 2015/1/21.
*/
/* 编写测试代码 */
public class Test {
public static void main(String[] args) throws Exception {
Movie m1 = new Movie("葫芦娃",0);//儿童片
Movie m2 = new Movie("神雕侠侣",1);//普通片
Movie m3 = new Movie("何以笙箫默",2);//新片
Customer c = new Customer("朱小妹");
c.addRent(new Rental(m1,2));//1.5
c.addRent(new Rental(m2,2));//2
c.addRent(new Rental(m3,3));//9
String result = "Rental report for 朱小妹\n" +
"\t葫芦娃\t1.5\n" +
"\t神雕侠侣\t2.0\n" +
"\t何以笙箫默\t9.0\n" +
"Amount is 12.5元\n" +
"frequent is 4分";
System.out.println(c.statement().equals(result));
}
}
至此，一个简单的代码重构示例，重构完毕
重构最大的启发就是：测试、小改、测试、小改....