java 代码重构-第一章(提炼代码)

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java

上篇文章说了,类做回自己的事

上一篇文章:java 代码重构-第一章(类自己该做自己的事)

下一篇文章:java 代码重构-第一章(去除临时变量)

提炼「常客积点计算」代码

下一步要对「常客积点计算」做类似处理。点数的计算视影片种类而有不同，不过不像收费规则有那么多变化。看来似乎有理由把积点计算责任放在Rental class 身上。首先我们需要针对「常客积点计算」这部分代码（以下粗体部分）运用 Extract Method 重构准则。

再一次我又要寻找局部变量。这里再一次用到了each ，而它可以被当作参数传入新函数中。另一个临时变量是frequentRenterPoints。本例中的它在被使用之前已经先有初值，但提炼出来的函数并没有读取该值，所以我们不需要将它当作参数传进去，只需对它执行「附添赋值动作」（appending assignment，operator+=）就行了。

我完成了函数的提炼，重新编译并测试；然后做一次搬移，再编译、再测试。重构时最好小步前进，如此一来犯错的几率最小。

好,下面来代码了 Customer

/**
 * 通计清单
 * 
 * @return
 */
public String statement() {
    double totalAmount = 0;// 合计
    int frequentRentePoints = 0;
    Enumerationenu_rentals = rentals.elements();
    String result = "Rental Record for " + this.getName() + " \n";
    while (enu_rentals.hasMoreElements()) {
        double thisAmount = 0;
        Rental each = enu_rentals.nextElement();

        thisAmount = each.getCharge();// 计算一笔租片费

        frequentRentePoints++;

        if ((each.getMovie().getPriceCode() == Movie.NEW_RELEASE) && each.getDaysRented() > 1) {
            frequentRentePoints++;
        }

        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(frequentRentePoints) + " frequent renter points";
    return result;
}

看到段代码吗?

frequentRentePoints++;

if ((each.getMovie().getPriceCode() == Movie.NEW_RELEASE) && each.getDaysRented() > 1) {
    frequentRentePoints++;
}

我们要把这段代码提炼出去,好,那么我们的代码变成这样
首先我们在Rental里添加方法

package com.mkfree.refactoring.shap1;

/**
 * 租凭
 * 
 * @author hk
 * 
 *         2012-12-25 下午10:57:00
 */
public class Rental {

    /**
     * 
     * @return
     */
    int getFrequentRenterPoints() {
        if ((getMovie().getPriceCode() == Movie.NEW_RELEASE) && getDaysRented() > 1)
            return 2;
        else
            return 1;
    }
}

然后在customer 里 Statment方法调用,看下面代码

/**
 * 通计清单
 * 
 * @return
 */
public String statement() {
    double totalAmount = 0;// 合计
    int frequentRentePoints = 0;
    Enumerationenu_rentals = rentals.elements();
    String result = "Rental Record for " + this.getName() + " \n";
    while (enu_rentals.hasMoreElements()) {
        double thisAmount = 0;
        Rental each = enu_rentals.nextElement();

        thisAmount = each.getCharge();// 计算一笔租片费

        /*
         * 刚刚把代码提炼,现在注释起来 frequentRentePoints++;
         * 
         * if ((each.getMovie().getPriceCode() == Movie.NEW_RELEASE) &&
         * each.getDaysRented() > 1) { frequentRentePoints++; }
         */

        frequentRentePoints += each.getFrequentRenterPoints();

        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(frequentRentePoints) + " frequent renter points";
    return result;
}

我利用重构前后的UML（Unified Modeling Language ，统一建模语言）图形（图1.4 至图1.7〕总结刚才所做的修改。

修改前的uml

修改后的um

那么最后的代码

Customer

package com.mkfree.refactoring.shap1;

import java.util.Enumeration;
import java.util.Vector;

/**
 * 顾客
 * 
 * @author hk
 * 
 *         2012-12-25 下午10:59:03
 */
public class Customer {

    private String name;
    private Vectorrentals = new Vector<>();

    public Customer(String name) {
        this.name = name;
    }

    /**
     * 添加
     * 
     * @param rental
     */
    public void addRentals(Rental rental) {
        rentals.add(rental);
    }

    public String getName() {
        return name;
    }

    /**
     * 通计清单
     * 
     * @return
     */
    public String statement() {
        double totalAmount = 0;// 合计
        int frequentRentePoints = 0;
        Enumerationenu_rentals = rentals.elements();
        String result = "Rental Record for " + this.getName() + " \n";
        while (enu_rentals.hasMoreElements()) {
            double thisAmount = 0;
            Rental each = enu_rentals.nextElement();

            thisAmount = each.getCharge();// 计算一笔租片费

            /*
             * 刚刚把代码提炼,现在注释起来 frequentRentePoints++;
             * 
             * if ((each.getMovie().getPriceCode() == Movie.NEW_RELEASE) &&
             * each.getDaysRented() > 1) { frequentRentePoints++; }
             */

            frequentRentePoints += each.getFrequentRenterPoints();

            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(frequentRentePoints) + " frequent renter points";
        return result;
    }

}

Rental 类

package com.mkfree.refactoring.shap1;

/**
 * 租凭
 * 
 * @author hk
 * 
 *         2012-12-25 下午10:57:00
 */
public class Rental {

    private Movie movie;
    private int daysRented;

    public Rental(Movie movie, int daysRented) {
        this.movie = movie;
        this.daysRented = daysRented;
    }

    public Movie getMovie() {
        return movie;
    }

    public int getDaysRented() {
        return daysRented;
    }

    double getCharge() {
        double result = 0;
        switch (getMovie().getPriceCode()) {
        case Movie.REGULAR:
            result += 2;
            if (getDaysRented() > 2)
                result += (getDaysRented() - 2) * 1.5;
            break;
        case Movie.NEW_RELEASE:
            result += getDaysRented() * 3;
            break;
        case Movie.CHILDRENS:
            result += 1.5;
            if (getDaysRented() > 3)
                result += (getDaysRented() - 3) * 1.5;
            break;
        }
        return result;
    }

    /**
     * 
     * @return
     */
    int getFrequentRenterPoints() {
        if ((getMovie().getPriceCode() == Movie.NEW_RELEASE) && getDaysRented() > 1)
            return 2;
        else
            return 1;
    }
}

Movie

package com.mkfree.refactoring.shap1;

/**
 * 电影类
 * @author hk
 *
 * 2012-12-25 下午10:55:14
 */
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 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;
    }

}

最后是调用的Client

package com.mkfree.refactoring.shap1;

import org.junit.Test;

public class Client {

    @Test
    public void testStatement() {

        Movie movie1 = new Movie();
        movie1.setTitle("少林足球");
        movie1.setPriceCode(1);
        Rental rental1 = new Rental(movie1, 2);

        Movie movie2 = new Movie();
        movie2.setTitle("大话西游");
        movie2.setPriceCode(2);
        Rental rental2 = new Rental(movie2, 3);

        Customer customer = new Customer("oyhk");
        customer.addRentals(rental1);
        customer.addRentals(rental2);
        String statement = customer.statement();
        System.out.println(statement);
    }
}

好了,代码提炼完了...你们有什么感觉...