[JAVA] 3. Java中的重构

Posted 2021-02-27 modai

1. 重构

为了让之前的贷款额度计算程序简化，使其更符合DRY的原则。

这里就将输入数字抽取为一个函数，然后将计算贷款抽取成一个函数。

import java.util.Scanner;

public class Main {
    private static double getNumber(String prompt, double min, double max,Scanner scanner) {
        double value = 0;
        while (true) {
            System.out.print(prompt + ‘:‘);
            value = scanner.nextFloat();
            if (value > min && value < max)
                break;
            System.out.println("数据应当在" + min + " " + max + "之间。");
        }
        return value;
    }

    private static double getMortgage(float principle, float interest, byte years) {
        final byte MONTH = 12;
        final byte PERCENT = 100;
        float monthlyInterest = interest / MONTH / PERCENT;
        short numberOfMonth = (short) (MONTH * years);
        double mortgage = principle
                * monthlyInterest * Math.pow(1 + monthlyInterest, numberOfMonth)
                / (Math.pow(1 + monthlyInterest, numberOfMonth) - 1);
        return mortgage;

    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        float principle = (float)getNumber("请输入本金",1000,1_000_000,scanner);
        float interest = (float)getNumber("请输入年利率",1,2,scanner);
        byte years = (byte)getNumber("请输入贷款年限",5,20,scanner);
        double mortgage = getMortgage(principle,interest,years);
        System.out.println("月供为："+mortgage);

    }
}

之后重构的时候，会遇到函数中的长两个在多个函数中出现的情况，这时，我们应该将这个常量，放在类内，作为类变量，当然注意函数为static，它也能读取static的常量。而后，会发现月份数和每月利率这两个数值也是重复的，但是这两个数值并不会在其他函数中变更，属于函数之间的独立项，所以虽然重复了，但是也可以不更改（当然想让其作为类内变量也可以，只不过最后类内变量会变得较多）。

这个在后面的面向对象的编程中，会有更好的解决方案。

2. 将还款之后的剩余款项（结余）打印出来

import java.util.Scanner;

public class Main {
    final static byte MONTH = 12;
    final static byte PERCENT = 100;

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        float principle = (float) getNumber("请输入本金", 1000, 1_000_000, scanner);
        float interest = (float) getNumber("请输入年利率", 1, 2, scanner);
        byte years = (byte) getNumber("请输入贷款年限", 5, 20, scanner);

        double mortgage = getMortgage(principle, interest, years);
        System.out.println();
        System.out.println(" 贷 款 ");
        System.out.println("-------");
        System.out.println("月供为：" + mortgage);

        System.out.println();
        System.out.println(" 结 余 ");
        System.out.println("-------");
        for (short month = 1; month <= years * MONTH; month++) {
            double balance = getBalance(principle,interest,years,month);
            System.out.println(month+"月之后的结余： "+balance);
        }
    }

    private static double getNumber(String prompt, double min, double max, Scanner scanner) {
        double value = 0;
        while (true) {
            System.out.print(prompt + ‘:‘);
            value = scanner.nextFloat();
            if (value > min && value < max)
                break;
            System.out.println("数据应当在" + min + " " + max + "之间。");
        }
        return value;
    }

    private static double getBalance(
            float principle,
            float interest,
            byte years,
            short numberOfPaymentsMade
    ) {
        float monthlyInterest = interest / MONTH / PERCENT;
        short numberOfMonth = (short) (MONTH * years);
        double balance = principle
                * (Math.pow(1 + monthlyInterest, numberOfMonth) - Math.pow(1 + monthlyInterest, numberOfPaymentsMade))
                / (Math.pow(1 + monthlyInterest, numberOfMonth) - 1);
        return balance;
    }

    private static double getMortgage(float principle, float interest, byte years) {
        float monthlyInterest = interest / MONTH / PERCENT;
        short numberOfMonth = (short) (MONTH * years);
        double mortgage = principle
                * monthlyInterest * Math.pow(1 + monthlyInterest, numberOfMonth)
                / (Math.pow(1 + monthlyInterest, numberOfMonth) - 1);
        return mortgage;

    }
}