重构改善既有代码的设计（一）

来源：互联网发布：如何做淘宝直通车推广编辑：程序博客网时间：2024/05/29 21:28

买了一本《重构改善既有代码的设计》，感觉味道不错，逗比来晒晒。

初品重构实例，就遇到两个没用过的类Vector、Enumeration。在这里做个知识的补充，Vector和ArrayList都是继承自AbstractList，ArrayList会比Vector快，他是非同步的，如果设计涉及到多线程安全，还是用Vector比较好一些。Vector的相关使用方法参照API调用即可，下面来看Vector内部的一段代码：

 /**     * Returns an enumeration of the components of this vector. The     * returned {@code Enumeration} object will generate all items in     * this vector. The first item generated is the item at index {@code 0},     * then the item at index {@code 1}, and so on.     *     * @return  an enumeration of the components of this vector     * @see     Iterator     */    public Enumeration<E> elements() {        return new Enumeration<E>() {            int count = 0;            public boolean hasMoreElements() {                return count < elementCount;            }            public E nextElement() {                synchronized (Vector.this) {                    if (count < elementCount) {                        return elementData(count++);                    }                }                throw new NoSuchElementException("Vector Enumeration");            }        };    }

这里的Enumeration接口源码如下：

public interface Enumeration<E> {    /**     * Tests if this enumeration contains more elements.     *     * @return  <code>true</code> if and only if this enumeration object     *           contains at least one more element to provide;     *          <code>false</code> otherwise.     */    boolean hasMoreElements();    /**     * Returns the next element of this enumeration if this enumeration     * object has at least one more element to provide.     *     * @return     the next element of this enumeration.     * @exception  NoSuchElementException  if no more elements exist.     */    E nextElement();}

两个方法分别是：1.枚举对象中是否还含有元素，如果返回true，则表示还含有至少一个的元素。2.枚举对象还含有元素，该方法得到对象中的下一个元素。

现在来看看需求：影片出租店，计算每位顾客的消费金额和明细，操作者告诉顾客租了那些影片、租期、和根据租期影片类型计算出费用和积分，影片类型分为普通片、儿童片、新片。下面是重构前相关代码：

/** *电影 **/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) {        super();        this._title = _title;        this._priceCode = _priceCode;    }    public String getTitle() {        return _title;    }    public void setTitle(String _title) {        this._title = _title;    }    public int getPriceCode() {        return _priceCode;    }    public void setPriceCode(int _priceCode) {        this._priceCode = _priceCode;    }}

/** *租赁 **/public class Rental {    private Movie _movie;    private int _daysRented;    public Rental(Movie _movie, int _daysRented) {        super();        this._movie = _movie;        this._daysRented = _daysRented;    }    public Movie getMovie() {        return _movie;    }    public void setMovie(Movie _movie) {        this._movie = _movie;    }    public int getDaysRented() {        return _daysRented;    }    public void setDaysRented(int _daysRented) {        this._daysRented = _daysRented;    }}

/** * 顾客 **/public class Customer {    private String _name;    private Vector<Rental> _rentals = new Vector<>();    public Customer(String _name) {        super();        this._name = _name;    }    public void addRental(Rental arg){           _rentals.add(arg);    }    public String getName(){        return _name;    }    public String statement(){        double totalAmount=0;        int frequentRenterPoints=0;        Enumeration<Rental> rentals = _rentals.elements();        String result = "Rental Record for "+getName()+"\n";        while(rentals.hasMoreElements()){            double thisAmount=0;            Rental each = (Rental)rentals.nextElement();            switch (each.getMovie().getPriceCode()) {            case Movie.CHILDRENS:                thisAmount += 1.5;                if(each.getDaysRented()>3){                    thisAmount += (each.getDaysRented()-3)*1.5;                }                break;            case Movie.NEW_RELEASE:                thisAmount += each.getDaysRented()*3;                break;            case Movie.REGULAR:                thisAmount += 2;                if(each.getDaysRented()>2){                    thisAmount += (each.getDaysRented()-2)*1.5;                }                break;            default:                break;            }            frequentRenterPoints++;            if(each.getMovie().getPriceCode()==Movie.NEW_RELEASE && each.getDaysRented()>1)frequentRenterPoints++;            result += "\t"+each.getMovie().getTitle()+"\t"+String.valueOf(thisAmount)+"\n";            totalAmount +=thisAmount;        }        result += "Amount owed is " + String.valueOf(totalAmount) + "\n";        result += "You earned " + String.valueOf(frequentRenterPoints) + " frequent renter points ";        return result;    }}

下面是测试代码和结果：

public class Test {    public static void main(String[] args) {        Customer mCustomer=new Customer("Mery Jing");        mCustomer.addRental(new Rental(new Movie("烈日灼心", Movie.NEW_RELEASE), 5));        mCustomer.addRental(new Rental(new Movie("武动乾坤", Movie.CHILDRENS), 2));        mCustomer.addRental(new Rental(new Movie("无极天下", Movie.REGULAR), 1));        System.out.println(mCustomer.statement());    }}测试结果：Rental Record for Mery Jing    烈日灼心    15.0    武动乾坤    1.5    无极天下    2.0Amount owed is 18.5You earned 4 frequent renter points

当你发现自己的程序需要添加一个特性，而代码结构无法使你很容易的达成目的，这时候你就要先重构那个程序，重构的第一步永远都相同：搭建一个可靠地测试环境，并拥有检测自身的能力。就上面的代码来看statement（）方法内容过长，处理事情过多，代码块应该越小越好，一个方法一个功能，这样容易管理移动，下面开始第一次重构（Eclipse：alt+shift+M抽取方法快捷键）：

    double thisAmount=0;    Rental each = (Rental)rentals.nextElement();    thisAmount = amountFor(each, thisAmount);    frequentRenterPoints++;    //.............略.........................    /**     * 计算价格     * @param each     * @param result >变量的命名要具有可读性，要让人能轻易读懂，重命名快捷键（eclipse）：alt+shift+R     * @return result      */             private double amountFor(Rental each, double result) {        switch (each.getMovie().getPriceCode()) {        case Movie.CHILDRENS:            result += 1.5;            if(each.getDaysRented()>3){                result += (each.getDaysRented()-3)*1.5;            }            break;        case Movie.NEW_RELEASE:            result += each.getDaysRented()*3;            break;        case Movie.REGULAR:            result += 2;            if(each.getDaysRented()>2){                result += (each.getDaysRented()-2)*1.5;            }            break;        default:            break;        }        return result;    }

租赁影片计算价格并没有与顾客关联，而是用到了Rental ，根据面向对象的知识，这里把把该方法提取到Rental 类里面，并重命名为getCharge():

     double thisAmount=0;     Rental each = (Rental)rentals.nextElement();     thisAmount = each.getCharge();          frequentRenterPoints++;     //.............略.........................   /**     * 计算价格     * 变量的命名要具有可读性，要让人能轻易读懂，重命名快捷键（eclipse）：alt+shift+R     * @return result      */    public double getCharge() {        double result=0;        switch (getMovie().getPriceCode()) {        case Movie.CHILDRENS:            result += 1.5;            if(getDaysRented()>3){                result += (getDaysRented()-3)*1.5;            }            break;        case Movie.NEW_RELEASE:            result += getDaysRented()*3;            break;        case Movie.REGULAR:            result += 2;            if(getDaysRented()>2){                result += (getDaysRented()-2)*1.5;            }            break;        default:            break;        }        return result;    }

做完以上修改，回过头来再看statement（）方法，就会发现thisAmout都点点多余了，这里可以直接通过方法获取了，修改如下：

while(rentals.hasMoreElements()){            Rental each = (Rental)rentals.nextElement();            frequentRenterPoints++;            if(each.getMovie().getPriceCode()==Movie.NEW_RELEASE && each.getDaysRented()>1)frequentRenterPoints++;            result += "\t"+each.getMovie().getTitle()+"\t"+String.valueOf(each.getCharge())+"\n";            totalAmount +=each.getCharge();        }

对于积分的计算，也没有与顾客关联上，这一和计算价格同理，抽取方法到Rental，statement()方法字节调用即可。这里代码就不贴了，以上内容基本来自《重构改善既有代码的设计》，个别内容本人添加。虽然原书内容重构还在继续，本人已然明了。欲知该例子重构更多内容自己买书吧，逗比倍懒写不动啦啦。

0 0