菜鸟区域，老鸟绕路！
原代码，这是一个可以借阅影片的小程序，你可以想象成某个大型系统，我想代码应该都能很容易看懂：
using System;using System.Collections.Generic;using System.Linq;using System.Web;namespace Reconsitution{ public class Movie { /// <summary> /// 常规的 /// </summary> public const int Regular = 0; /// <summary> /// 新发布 /// </summary> public const int NewRelease = 1; /// <summary> /// 儿童版 /// </summary> public const int Childrens = 2; public string Title { get; private set; } public int PriceCode { get; set; } public Movie(string title, int priceCode) { Title = title; PriceCode = priceCode; } } public class Rental { public Movie @Movie { get; private set; } public int DaysRented { get; private set; } public Rental(Movie movie, int daysRented) { @Movie = movie; DaysRented = daysRented; } } public class Customer { public string Name { get; private set; } public List<Rental> Rentals { get { return _rentals; } } private readonly List<Rental> _rentals = new List<Rental>(); public Customer(string name) { Name = name; } public void AddRental(Rental rental) { _rentals.Add(rental); } public string Statement() { double totalAmount = 0; int frequentRenterPoints = 0; string result = "Rental Record for " + Name + "\n"; foreach (Rental rental in _rentals) { double thisAmount = 0; switch (rental.Movie.PriceCode) { case Movie.Regular: thisAmount += 2; if (rental.DaysRented > 2) thisAmount += (rental.DaysRented - 2)*1.5; break; case Movie.NewRelease: thisAmount += rental.DaysRented*3; break; case Movie.Childrens: thisAmount += 1.5; if (rental.DaysRented > 3) thisAmount += (rental.DaysRented - 3) * 1.5; break; } frequentRenterPoints ++; if ((rental.Movie.PriceCode == Movie.NewRelease) && rental.DaysRented > 1) frequentRenterPoints ++; result += "\t" + rental.Movie.Title + "\t" + thisAmount + "\n"; totalAmount += thisAmount; } result += "Amount owed is " + totalAmount + "\n"; result += "You earned " + frequentRenterPoints + " frequent renter points"; return result; } }}Customer customer = new Customer("Dennis Ding");customer.AddRental(new Rental(new Movie("Water World", Movie.Childrens), 5));customer.AddRental(new Rental(new Movie("Roman Holiday", Movie.Regular), 3));customer.AddRental(new Rental(new Movie("The First Blood", Movie.NewRelease), 6));TextBox1.Text = customer.Statement();一、拆解主体方法
简要预览代码，我们很直观的发现 Customer 中的方法 Statement 过长，不便于阅读，于是我们首先便考虑解体方法 Statement，我们可以这样考虑，为什么要重构，重构再于便于后期维护和功能拓展，对于Statement方法，生成一个文字版的影片借阅结果单，如果我们版本更新，要生成一个Html的结果单，或者直接返回数据Json，形成接口供第三方调用呢，我们不得不重新写一个叫HtmlStatement 或者 JsonStatement的方法，因为我们把细节到计算的整个生成逻辑多放在了这一个方法中了！这是一种很不合理的设计！
public string Statement(){ double totalAmount = 0; int frequentRenterPoints = 0; string result = "Rental Record for " + Name + "\n"; foreach (Rental rental in _rentals) { var thisAmount = AmountFor(rental); frequentRenterPoints ++; if ((rental.Movie.PriceCode == Movie.NewRelease) && rental.DaysRented > 1) frequentRenterPoints ++; result += "\t" + rental.Movie.Title + "\t" + thisAmount + "\n"; totalAmount += thisAmount; } result += "Amount owed is " + totalAmount + "\n"; result += "You earned " + frequentRenterPoints + " frequent renter points"; return result;}private static double AmountFor(Rental rental){ double thisAmount = 0; switch (rental.Movie.PriceCode) { case Movie.Regular: thisAmount += 2; if (rental.DaysRented > 2) thisAmount += (rental.DaysRented - 2)*1.5; break; case Movie.NewRelease: thisAmount += rental.DaysRented*3; break; case Movie.Childrens: thisAmount += 1.5; if (rental.DaysRented > 3) thisAmount += (rental.DaysRented - 3)*1.5; break; } return thisAmount;}这时候，我们发现，方法 AmountFor 并没有使用到和 Customer 相关的数据，但却放在 Customer 中，于是我们先考虑吧方法移到 Rental 中，
public class Rental { public Movie Movie { get; private set; } public int DaysRented { get; private set; } public Rental(Movie movie, int daysRented) { Movie = movie; DaysRented = daysRented; } public double AmountFor() { double thisAmount = 0; switch (this.Movie.PriceCode) { case Movie.Regular: thisAmount += 2; if (DaysRented > 2) thisAmount += (DaysRented - 2) * 1.5; break; case Movie.NewRelease: thisAmount += DaysRented * 3; break; case Movie.Childrens: thisAmount += 1.5; if (DaysRented > 3) thisAmount += (DaysRented - 3) * 1.5; break; } return thisAmount; } }原 Statement 方法变成 ：
public string Statement(){ double totalAmount = 0; int frequentRenterPoints = 0; string result = "Rental Record for " + Name + "\n"; foreach (Rental rental in _rentals) { var thisAmount = rental.AmountFor(); frequentRenterPoints ++; if ((rental.Movie.PriceCode == Movie.NewRelease) && rental.DaysRented > 1) frequentRenterPoints ++; result += "\t" + rental.Movie.Title + "\t" + thisAmount + "\n"; totalAmount += thisAmount; } result += "Amount owed is " + totalAmount + "\n"; result += "You earned " + frequentRenterPoints + " frequent renter points"; return result;}（为了让方法符合实际功能，我们可以把方法 AmountFor 命名为 GetCharge）
在方法Statement中，此时我们看到这样的代码
var thisAmount = rental.GetCharge();//……被省略的代码result += "\t" + rental.Movie.Title + "\t" + thisAmount + "\n";totalAmount += thisAmount;
由于 rental.GetCharge() 被使用两次，为了避免二次计算，代码中使用了一个临时变量 thisAmount，于是乎就产生了一个《重构与性能》的话题，这是一个很大的话题，所以我暂时也没深入学习，在重构中，我们可以去掉这样的临时变量（一两个不可怕，但是在一个项目中过度的临时变量使得代码无比混乱），实际上我们去掉这样的临时变量，可以尝试从 Rental 类中寻求优化方法。至于《重构与性能》后面介绍！
代码如下：
//……被省略的代码
result += "\t" + rental.Movie.Title + "\t" + rental.GetCharge() + "\n";
totalAmount += rental.GetCharge();
再往后，Statement方法中，有这样的代码：
frequentRenterPoints ++;if ((rental.Movie.PriceCode == Movie.NewRelease) && rental.DaysRented > 1) frequentRenterPoints ++;
frequentRenterPoints 是一个在方法中定义的临时变量（阿飘），这小部分代码的作用也不过是计算积分（现在的各种商店都有积分），这两句代码只是积分的计算方式，和实际生成逻辑没有关联，于是我们考虑把它拆出来。
public string Statement(){ double totalAmount = 0; int frequentRenterPoints = 0; string result = "Rental Record for " + Name + "\n"; foreach (Rental rental in _rentals) { frequentRenterPoints += GetFrequentRenterPoints(rental); result += "\t" + rental.Movie.Title + "\t" + rental.GetCharge() + "\n"; totalAmount += rental.GetCharge(); } result += "Amount owed is " + totalAmount + "\n"; result += "You earned " + frequentRenterPoints + " frequent renter points"; return result;}private int GetFrequentRenterPoints(Rental rental){ if ((rental.Movie.PriceCode == Movie.NewRelease) && rental.DaysRented > 1) return 2; return 1;}接下来，我们接着处理“阿飘”的问题，对于临时变量，能少用则少用，这是某某牛人给出的重构名言一则。
代码中 totalAmount 的计算可以单独封装为：
private double GetTotalAmount(){ return _rentals.Sum(rental => rental.GetCharge());}到此时，Statement方法已经比较简洁了，我们Copy再稍加修改就可以提供HtmlStatement和JsonStatement了，因为方法里面的计算逻辑已经被我们提取出来！
二、拆分后的方法调整
下一步，对于刚刚拆解的方法GetCharge，主体为一个switch，而switch却依赖对象 Movie的一个成员PriceCode，既然这样，为什么不把计算方式迁移到Movie类呢：
public double GetCharge(){ double thisAmount = 0; switch (this.Movie.PriceCode) { case Movie.Regular: thisAmount += 2; if (DaysRented > 2) thisAmount += (DaysRented - 2) * 1.5; break; case Movie.NewRelease: thisAmount += DaysRented * 3; break; case Movie.Childrens: thisAmount += 1.5; if (DaysRented > 3) thisAmount += (DaysRented - 3) * 1.5; break; } return thisAmount;}于是我们尝试在Movie中新建：
public double GetCharge(int daysRented) { double thisAmount = 0; switch (PriceCode) { case Movie.Regular: thisAmount += 2; if (daysRented > 2) thisAmount += (daysRented - 2) * 1.5; break; case Movie.NewRelease: thisAmount += daysRented * 3; break; case Movie.Childrens: thisAmount += 1.5; if (daysRented > 3) thisAmount += (daysRented - 3) * 1.5; break; } return thisAmount; }原方法则可用：
public double GetCharge(int daysRented) { return Movie.GetCharge(DaysRented); }然后看Customer中方法：
private int GetFrequentRenterPoints(Rental rental){ if ((rental.Movie.PriceCode == Movie.NewRelease) && rental.DaysRented > 1) return 2; return 1;}我们可以迁移到Rental中：
public int GetFrequentRenterPoints(){ if ((Movie.PriceCode == Movie.NewRelease) && DaysRented > 1) return 2; return 1;}接着发现和上面同样使用了Movie的成员，尝试移动到Movie中：
public int GetFrequentRenterPoints(int daysRented){ if ((PriceCode == Movie.NewRelease) && daysRented > 1) return 2; return 1;}Rental中可以这样：
public int GetFrequentRenterPoints(){ return Movie.GetFrequentRenterPoints(DaysRented);}和之前的GetTotalAmount方法一样，我们也可以有个GetTotalFrequentRenterPoints:
private double GetTotalFrequentRenterPoints(){ return _rentals.Sum(rental => rental.GetFrequentRenterPoints());}于是Statement就表示为：
public string Statement(){ string result = "Rental Record for " + Name + "\n"; foreach (Rental rental in _rentals) { result += "\t" + rental.Movie.Title + "\t" + rental.GetCharge() + "\n"; } result += "Amount owed is " + GetTotalAmount() + "\n"; result += "You earned " + GetTotalFrequentRenterPoints() + " frequent renter points"; return result;}三、大的变化——继承
例子中，我们的Movie类分成三个类型
/// <summary>/// 常规的/// </summary>public const int Regular = 0;/// <summary>/// 新发布/// </summary>public const int NewRelease = 1;/// <summary>/// 儿童版/// </summary>public const int Childrens = 2;
从而出现了方法 GetCharge 中计算的条件判断，当我们做同一件事使用不同的方式时候，我们想到了继承！对不同的电影类型，有不同的价格，我们认为价格是一个基类，每种电影的价格为子类，最终代码：
using System;using System.Collections.Generic;using System.Linq;using System.Web;namespace Reconsitution{ public class Movie { #region 常量电影分类 /// <summary> /// 常规的 /// </summary> public const int Regular = 0; /// <summary> /// 新发布 /// </summary> public const int NewRelease = 1; /// <summary> /// 儿童版 /// </summary> public const int Childrens = 2; #endregion public string Title { get; private set; } public int PriceCode { get { return _price.GetPriceCode(); } private set { switch (value) { case Regular: _price = new RegularPrice(); break; case Childrens: _price = new ChidrensPrice(); break; case NewRelease: _price = new NewReleasePrice(); break; default: throw new Exception("Incorrect Price Code!"); } } } private Price _price ; public Movie(string title, int priceCode) { Title = title; PriceCode = priceCode; } public double GetCharge(int daysRented) { return _price.GetCharge(daysRented); } public int GetFrequentRenterPoints(int daysRented) { return _price.GetFrequentRenterPoints(daysRented); } } #region 价格类Price public abstract class Price { public abstract int GetPriceCode(); public abstract double GetCharge(int daysRented); public abstract int GetFrequentRenterPoints(int daysRented); } public class ChidrensPrice : Price { public override int GetPriceCode() { return Movie.Childrens; } public override double GetCharge(int daysRented) { double thisAmount = 1.5; if (daysRented > 3) thisAmount += (daysRented - 3) * 1.5; return thisAmount; } public override int GetFrequentRenterPoints(int daysRented) { return 1; } } public class NewReleasePrice : Price { public override int GetPriceCode() { return Movie.NewRelease; } public override double GetCharge(int daysRented) { double thisAmount = daysRented * 3; return thisAmount; } public override int GetFrequentRenterPoints(int daysRented) { return (daysRented > 1) ? 2 : 1; } } public class RegularPrice : Price { public override int GetPriceCode() { return Movie.Regular; } public override double GetCharge(int daysRented) { double thisAmount = 2; if (daysRented > 2) thisAmount += (daysRented - 2) * 1.5; return thisAmount; } public override int GetFrequentRenterPoints(int daysRented) { return 1; } } #endregion public class Rental { public Movie Movie { get; private set; } public int DaysRented { get; private set; } public Rental(Movie movie, int daysRented) { Movie = movie; DaysRented = daysRented; } public double GetCharge() { return Movie.GetCharge(DaysRented); } public int GetFrequentRenterPoints() { return Movie.GetFrequentRenterPoints(DaysRented); } } public class Customer { public string Name { get; private set; } public List<Rental> Rentals { get { return _rentals; } } private readonly List<Rental> _rentals = new List<Rental>(); public Customer(string name) { Name = name; } public void AddRental(Rental rental) { _rentals.Add(rental); } private double GetTotalAmount() { return _rentals.Sum(rental => rental.GetCharge()); } private double GetTotalFrequentRenterPoints() { return _rentals.Sum(rental => rental.GetFrequentRenterPoints()); } public string Statement() { string result = "Rental Record for " + Name + "\n"; foreach (Rental rental in _rentals) { result += "\t" + rental.Movie.Title + "\t" + rental.GetCharge() + "\n"; } result += "Amount owed is " + GetTotalAmount() + "\n"; result += "You earned " + GetTotalFrequentRenterPoints() + " frequent renter points"; return result; } }}可能有人会问了， 为什么要这样做，是不是没有必要，我想你可以这样设想：正如之前提及的，对于同一一件事，如果使用的不同的方式去解决，就应该尝试通过继承分离出来，好处在于，如果我有新的电影分类出现，将只需要再继承一个Movie产生新的子类，就能解决问题，或者某类型电影价格、积分计算方式变动，我们也只用更改相应子类的计算方式，不影响整体方式！
原标题：重构一个小例子
关键词：
我知道了 