对《重构-改善既有代码的设计》一书，对书中第一章的例子，利用JAVA语言完成该例子的代码重构。重构时，增量地给程序添加以下功能 （1） 增加新的影片分类，如纪录片、综艺片等 （2） 修改影片的租赁和积分标准 （3） 以HTML格式输出订单针对第二节分析出的现有代码问题，依据代码重构的原则与技巧，逐一给出重构（解决）方案（重构思路、采用方法与技巧（--35分）。总体表达方法可参考该书）；

重构思路：

首先，需要对现有的代码进行分析，找出其中存在的问题。然后，采用重构的原则与技巧，逐一解决这些问题，并增量地添加新功能。最后，以HTML格式输出订单。

1. 问题分析：

现有的代码存在以下问题：

（1）`Movie`类中存在过多的if语句，导致代码难以维护和扩展。

（2）`Rental`类中计算租赁费用和积分的方法过于复杂，可读性差。

（3）`Customer`类中的`statement`方法过于复杂，可读性差，需要拆分为多个小方法。

2. 解决方案：

（1）重构`Movie`类：

将`Movie`类中的if语句替换为多态，即在`Movie`类中添加一个抽象方法`getCharge`，然后在三个子类`RegularMovie`、`NewReleaseMovie`和`ChildrensMovie`中分别实现该方法，计算相应的租赁费用。

abstract class Movie {
    //...省略其他代码...
    abstract double getCharge(int daysRented);
}

class RegularMovie extends Movie {
    //...省略其他代码...
    double getCharge(int daysRented) {
        double result = 2;
        if (daysRented > 2)
            result += (daysRented - 2) * 1.5;
        return result;
    }
}

class NewReleaseMovie extends Movie {
    //...省略其他代码...
    double getCharge(int daysRented) {
        return daysRented * 3;
    }
}

class ChildrensMovie extends Movie {
    //...省略其他代码...
    double getCharge(int daysRented) {
        double result = 1.5;
        if (daysRented > 3)
            result += (daysRented - 3) * 1.5;
        return result;
    }
}

（2）重构`Rental`类：

将`Rental`类中计算租赁费用和积分的方法拆分为两个方法，分别计算租赁费用和积分。同时，将计算租赁费用和积分的方法移动到`Movie`类中，由多态来实现。

class Rental {
    //...省略其他代码...
    double getCharge() {
        return _movie.getCharge(_daysRented);
    }

    int getFrequentRenterPoints() {
        // add bonus for a two day new release rental
        if ((_movie instanceof NewReleaseMovie) && _daysRented > 1)
            return 2;
        else
            return 1;
    }
}

//在Movie类中添加getCharge方法
abstract class Movie {
    //...省略其他代码...
    abstract double getCharge(int daysRented);
}

class RegularMovie extends Movie {
    //...省略其他代码...
    double getCharge(int daysRented) {
        double result = 2;
        if (daysRented > 2)
            result += (daysRented - 2) * 1.5;
        return result;
    }
}

class NewReleaseMovie extends Movie {
    //...省略其他代码...
    double getCharge(int daysRented) {
        return daysRented * 3;
    }
}

class ChildrensMovie extends Movie {
    //...省略其他代码...
    double getCharge(int daysRented) {
        double result = 1.5;
        if (daysRented > 3)
            result += (daysRented - 3) * 1.5;
        return result;
    }
}

（3）重构`Customer`类：

将`Customer`类中的`statement`方法拆分为多个小方法，提高可读性。

class Customer {
    //...省略其他代码...
    String statement() {
        Enumeration rentals = _rentals.elements();
        String result = "Rental Record for " + getName() + "\n";
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            // 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;
    }

    private double getTotalCharge() {
        double result = 0;
        Enumeration rentals = _rentals.elements();
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            result += each.getCharge();
        }
        return result;
    }

    private int getTotalFrequentRenterPoints() {
        int result = 0;
        Enumeration rentals = _rentals.elements();
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            result += each.getFrequentRenterPoints();
        }
        return result;
    }
}

（4）增加新的影片分类：

在`Movie`类中添加新的影片分类，如纪录片、综艺片等。具体实现方式与上述步骤类似，在`Movie`类中添加相应的子类，并重写`getCharge`方法。

class DocumentaryMovie extends Movie {
    //...省略其他代码...
    double getCharge(int daysRented) {
        double result = 1.5;
        if (daysRented > 3)
            result += (daysRented - 3) * 1.5;
        return result;
    }
}

class VarietyShowMovie extends Movie {
    //...省略其他代码...
    double getCharge(int daysRented) {
        double result = 2;
        if (daysRented > 2)
            result += (daysRented - 2) * 1.5;
        return result;
    }
}

（5）修改影片的租赁和积分标准：

在`Rental`类中修改`getFrequentRenterPoints`方法和`Movie`类中相应子类的`getCharge`方法。

class Rental {
    //...省略其他代码...
    int getFrequentRenterPoints() {
        // add bonus for a two day new release rental
        if ((_movie instanceof NewReleaseMovie) && _daysRented > 1)
            return 3; //租赁新片大于1天，积分加3
        else
            return 1;
    }
}

class RegularMovie extends Movie {
    //...省略其他代码...
    double getCharge(int daysRented) {
        double result = 1.5; //修改租赁价格
        if (daysRented > 3)
            result += (daysRented - 3) * 1.5;
        return result;
    }
}

class ChildrensMovie extends Movie {
    //...省略其他代码...
    double getCharge(int daysRented) {
        double result = 1.5; //修改租赁价格
        if (daysRented > 4)
            result += (daysRented - 4) * 1.5;
        return result;
    }
}

（6）以HTML格式输出订单：

重构`Customer`类中的`statement`方法，将订单信息按照HTML格式输出。

class Customer {
    //...省略其他代码...
    String statement() {
        Enumeration rentals = _rentals.elements();
        String result = "<h1>Rentals for " + getName() + "</h1><br/>";
        result += "<table border='1'><tr><th>Movie Title</th><th>Rental Days</th><th>Price</th></tr>"; //添加表头
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            // show figures for this rental
            result += "<tr><td>" + each.getMovie().getTitle() + "</td><td>" +
                    String.valueOf(each.getDaysRented()) + "</td><td>" + String.valueOf(each.getCharge()) + "</td></tr>";
        }
        // add footer lines
        result += "</table><br/><h2>Amount owed is " + String.valueOf(getTotalCharge()) + "</h2>";
        result += "<h2>You earned " + String.valueOf(getTotalFrequentRenterPoints()) +
                " frequent renter points</h2>";
        return result;
    }
}

3. 代码重构：

重构后的完整代码如下：

abstract class Movie {
    private String _title;

    public Movie(String title) {
        _title = title;
    }

    public String getTitle() {
        return _title;
    }

    abstract double getCharge(int daysRented);
}

class RegularMovie extends Movie {
    public RegularMovie(String title) {
        super(title);
    }

    double getCharge(int daysRented) {
        double result = 1.5;
        if (daysRented > 3)
            result += (daysRented - 3) * 1.5;
        return result;
    }
}

class NewReleaseMovie extends Movie {
    public NewReleaseMovie(String title) {
        super(title);
    }

    double getCharge(int daysRented) {
        return daysRented * 3;
    }
}

class ChildrensMovie extends Movie {
    public ChildrensMovie(String title) {
        super(title);
    }

    double getCharge(int daysRented) {
        double result = 1.5;
        if (daysRented > 4)
            result += (daysRented - 4) * 1.5;
        return result;
    }
}

class DocumentaryMovie extends Movie {
    public DocumentaryMovie(String title) {
        super(title);
    }

    double getCharge(int daysRented) {
        double result = 1.5;
        if (daysRented > 3)
            result += (daysRented - 3) * 1.5;
        return result;
    }
}

class VarietyShowMovie extends Movie {
    public VarietyShowMovie(String title) {
        super(title);
    }

    double getCharge(int daysRented) {
        double result = 2;
        if (daysRented > 2)
            result += (daysRented - 2) * 1.5;
        return result;
    }
}

class Rental {
    private Movie _movie;
    private int _daysRented;

    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);
    }

    int getFrequentRenterPoints() {
        // add bonus for a two day new release rental
        if ((_movie instanceof NewReleaseMovie) && _daysRented > 1)
            return 3;
        else
            return 1;
    }
}

class Customer {
    private String _name;
    private Vector _rentals = new Vector();

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

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

    public String getName() {
        return _name;
    }

    String statement() {
        Enumeration rentals = _rentals.elements();
        String result = "<h1>Rentals for " + getName() + "</h1><br/>";
        result += "<table border='1'><tr><th>Movie Title</th><th>Rental Days</th><th>Price</th></tr>";
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            // show figures for this rental
            result += "<tr><td>" + each.getMovie().getTitle() + "</td><td>" +
                    String.valueOf(each.getDaysRented()) + "</td><td>" + String.valueOf(each.getCharge()) + "</td></tr>";
        }
        // add footer lines
        result += "</table><br/><h2>Amount owed is " + String.valueOf(getTotalCharge()) + "</h2>";
        result += "<h2>You earned " + String.valueOf(getTotalFrequentRenterPoints()) +
                " frequent renter points</h2>";
        return result;
    }

    private double getTotalCharge() {
        double result = 0;
        Enumeration rentals = _rentals.elements();
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            result += each.getCharge();
        }
        return result;
    }

    private int getTotalFrequentRenterPoints() {
        int result = 0;
        Enumeration rentals = _rentals.elements();
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            result += each.getFrequentRenterPoints();
        }
        return result;
    }
}