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002-重构入门案例

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摘要：重构入门案例

概述

示例：影片出租店应用程序，计算每一位顾客的消费金额并打印详单。操作者告诉程序：顾客租客哪些影片、租期多长，程序便根据租赁时间和影片类型计算出费用。

影片分为三类：普通片、儿童片、新片。除了计算费用还要为常客计算积分，积分会根据足片种类是否为新片而有不同。

Ver01 示例-简单逻辑思维，没有扩展

  1. 使用几个类表达上述
    • Movie(影片类)：数据类
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      public class Movie {
          public static final int CHILDRENS = 2; //儿童
          public static final int REGULAR = 0; //常客
          public static final int NEW_RELEASE = 1;// 新片
          private String _title;
          private int _priceCode;

          public Movie(String title, int priceCode) {
              _title = title;
              _priceCode = priceCode;
          }

          public int getPriceCode() {
              return _priceCode;
          }

          public String getTitle() {
              return _title;
          }

          public void setPriceCode(int priceCode) {
              _priceCode = priceCode;
          }
      }
    • Rental(租赁类) 表示某个顾客租了一部影片
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      public class Rental {
          private Movie _movie; // 影片
          private int _daysRented; // 租期

          public Rental(Movie movie, int daysRented) {
              _movie = movie;
              _daysRented = daysRented;
          }

          public int getDaysRented() {
              return _daysRented;
          }

          public Movie getMovie() {
              return _movie;
          }
      }
    • Customer(顾客) 数据以及相应的访问函数。
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      public class Customer {
          private String _name; // 姓名
          private Vector _rentals = new Vector(); // 租借记

          public Customer(String name) {
              _name = name;
          };

          public void addRental(Rental arg) {
              _rentals.addElement(arg);
          }

          public String getName() {
              return _name;
          }

          public String statement() {
              double totalAmount = 0; // 总消费金。
              int frequentRenterPoints = 0; // 常客积点
              Enumeration rentals = _rentals.elements();
              String result = "Rental Record for " + getName() + "\n";
              while (rentals.hasMoreElements()) {
                  double thisAmount = 0;
                  Rental each = (Rental) rentals.nextElement(); // 取得一笔租借记。
                  // determine amounts for each line
                  switch (each.getMovie().getPriceCode()) { // 取得影片出租价格
                      case Movie.REGULAR: // 普通片
                          thisAmount += 2;
                          if (each.getDaysRented() > 2)
                              thisAmount += (each.getDaysRented() - 2) * 1.5;
                          break;
                      case Movie.NEW_RELEASE: // 新片
                          thisAmount += each.getDaysRented() * 3;
                          break;
                      case Movie.CHILDRENS: // 儿童。
                          thisAmount += 1.5;
                          if (each.getDaysRented() > 3)
                              thisAmount += (each.getDaysRented() - 3) * 1.5;
                          break;
                  }
                  // add frequent renter points （累计常客积点。
                  frequentRenterPoints++;
                  // add bonus for a two day new release rental
                  if ((each.getMovie().getPriceCode() == Movie.NEW_RELEASE)
                          && each.getDaysRented() > 1)
                      frequentRenterPoints++;
                  // show figures for this rental（显示此笔租借记录）
                  result += "\t" + each.getMovie().getTitle() + "\t"
                          + String.valueOf(thisAmount) + "\n";
                  totalAmount += thisAmount;
              }
              // add footer lines（结尾打印）
              result += "Amount owed is " + String.valueOf(totalAmount) + "\n";
              result += "You earned " + String.valueOf(frequentRenterPoints)
                      + " frequent renter points";
              return result;
          }
      }
    • 单元测试
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      public class CustomerTest {
          @Test
          public void statement() {
              Customer customer = new Customer("John");
              String title = "Titanic";
              int priceCode = 2;
              int _daysRented = 7;
              Movie movie = new Movie(title, priceCode);
              Rental rental = new Rental(movie, _daysRented);
              customer.addRental(rental);
              String result = customer.statement();
              System.out.println(result);
          }
      }
  2. 说明
    单一逻辑，没有扩展性以及面向对象思维

Ver02 分解重组statement()

  1. 避免长函数、逻辑独立的抽成方法 
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    public class Customer {
        private String _name; // 姓名
        private Vector _rentals = new Vector(); // 租借记

        public Customer(String name) {
            _name = name;
        };

        public void addRental(Rental arg) {
            _rentals.addElement(arg);
        }

        public String getName() {
            return _name;
        }

        public String statement() {
            double totalAmount = 0; // 总消费金。
            int frequentRenterPoints = 0; // 常客积点
            Enumeration rentals = _rentals.elements();
            String result = "Rental Record for " + getName() + "\n";
            while (rentals.hasMoreElements()) {
                Rental each = (Rental) rentals.nextElement(); // 取得一笔租借记。
                double thisAmount = amountFor(each);
                // add frequent renter points （累计常客积点。
                frequentRenterPoints++;
                // add bonus for a two day new release rental
                if ((each.getMovie().getPriceCode() == Movie.NEW_RELEASE)
                        && each.getDaysRented() > 1)
                    frequentRenterPoints++;
                // show figures for this rental（显示此笔租借记录）
                result += "\t" + each.getMovie().getTitle() + "\t"
                        + String.valueOf(thisAmount) + "\n";
                totalAmount += thisAmount;
            }
            // add footer lines（结尾打印）
            result += "Amount owed is " + String.valueOf(totalAmount) + "\n";
            result += "You earned " + String.valueOf(frequentRenterPoints)
                    + " frequent renter points";
            return result;
        }

        private double amountFor(Rental rental) {
            double thisAmount = 0;
            // determine amounts for each line
            switch (rental.getMovie().getPriceCode()) { // 取得影片出租价格
                case Movie.REGULAR: // 普通片
                    thisAmount += 2;
                    if (rental.getDaysRented() > 2)
                        thisAmount += (rental.getDaysRented() - 2) * 1.5;
                    break;
                case Movie.NEW_RELEASE: // 新片
                    thisAmount += rental.getDaysRented() * 3;
                    break;
                case Movie.CHILDRENS: // 儿童。
                    thisAmount += 1.5;
                    if (rental.getDaysRented() > 3)
                        thisAmount += (rental.getDaysRented() - 3) * 1.5;
                    break;
            }
            return thisAmount;
        }
    }

Ver03 金额计算代码，迁移至Rental类

参看：github ver03

Ver04 同类聚合，单一原则

  1. Movie中放置与影片直接相关方法

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        public class Movie {
            public static final int CHILDRENS = 2;
            public static final int REGULAR = 0;
            public static final int NEW_RELEASE = 1;
            private String _title;
            private int _priceCode;
        
            public Movie(String title, int priceCode) {
                _title = title;
                _priceCode = priceCode;
            }
        
            public int getPriceCode() {
                return _priceCode;
            }
        
            public String getTitle() {
                return _title;
            }
        
            public void setPriceCode(int priceCode) {
                _priceCode = priceCode;
            }
        
            public double getCharge(int daysRented) {
                double result = 0;
                switch (getPriceCode()) {
                    case Movie.REGULAR:
                        result += 2;
                        if (daysRented > 2)
                            result += (daysRented - 2) * 1.5;
                        break;
                    case Movie.NEW_RELEASE:
                        result += daysRented * 3;
                        break;
                    case Movie.CHILDRENS:
                        result += 1.5;
                        if (daysRented > 3)
                            result += (daysRented - 3) * 1.5;
                        break;
                }
                return result;
            }
        
            public int getFrequentRenterPoints(int daysRented) {
                if ((getPriceCode() == Movie.NEW_RELEASE) && daysRented > 1)
                    return 2;
                else
                    return 1;
            }
        }
       ```   

    2. 租赁放置相关方法
       ```java
        public class Rental {
            private Movie _movie; // 影片
            private int _daysRented; // 租期
        
            public Rental(Movie movie, int daysRented) {
                _movie = movie;
                _daysRented = daysRented;
            }
        
            public int getDaysRented() {
                return _daysRented;
            }
        
            public Movie getMovie() {
                return _movie;
            }
        
            double getCharge() {
                return _movie.getCharge(_daysRented);
            }
        
            public int getFrequentRenterPoints() {
                return _movie.getFrequentRenterPoints(_daysRented);
            }
        }

  2. 顾客相关

    public class Customer {
    private String _name; // 姓名
    private Vector _rentals = new Vector(); // 租借记

    public Customer(String name) {
        _name = name;
    };

    public void addRental(Rental arg) {
        _rentals.addElement(arg);
    }

    public String getName() {
        return _name;
    }

    public String statement() {
        int frequentRenterPoints = 0;
        Enumeration rentals = _rentals.elements();
        String result = "Rental Record for " + getName() + "\n";
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            frequentRenterPoints += each.getFrequentRenterPoints();
            // show figures for this rental
            result += "\t" + each.getMovie().getTitle() + "\t"
                    + String.valueOf(each.getCharge()) + "\n";
        }
        // add footer lines
        result += "Amount owed is " + String.valueOf(getTotalCharge()) + "\n";
        result += "You earned " + String.valueOf(getTotalFrequentRenterPoints())
                + " frequent renter points";
        return result;
    }

    public String htmlStatement() {
        Enumeration rentals = _rentals.elements();
        String result = "<H1>Rentals for <EM>" + getName() + "</EM></ H1><P>\n";
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            // show figures for each rental
            result += each.getMovie().getTitle() + ": "
                    + String.valueOf(each.getCharge()) + "<BR>\n";
        }
        // add footer lines
        result += "<P>You owe <EM>" + String.valueOf(getTotalCharge())
                + "</EM><P>\n";
        result += "On this rental you earned <EM>"
                + String.valueOf(getTotalFrequentRenterPoints())
                + "</EM> frequent renter points<P>";
        return result;
    }

    // 译注：此即所谓query method
    private int getTotalFrequentRenterPoints() {
        int result = 0;
        Enumeration rentals = _rentals.elements();
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            result += each.getFrequentRenterPoints();
        }
        return result;
    }

    // 译注：此即所谓query method
    private double getTotalCharge() {
        double result = 0;
        Enumeration rentals = _rentals.elements();
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            result += each.getCharge();
        }
        return result;
    }

}

重新分析，抽象模型

  1. 抽象过程一、

    • 影片实体：抽象类Movie,子类：普通片、儿童片、新片.每个子类有各自计费方法实现。常见操作是抽象功能接口
      影片可能会根据不同的类型有不同的收费规则，所以影片可以根据类型有不同的子类，但是有个问题，影片如果换了类型，但是class是不能换的，所以可以考虑影片没有子类，但是影片包含一个Price的类，这个类可以根据不同类型有不同子类。Movie有一个Price类的引用，不同的类型对应不同的Price子类，调用Price类的方法来计算收费。

    参看：github ver03

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