java My Basic货币转换器程序输出错误

Question

因此，代码应该转换货币，但它没有正确地进行转换。我有一个变量k（克罗地亚库纳…1欧元=7.5库纳），它是1，例如，如果我想将1欧元转换成1美元，程序将金额（1）乘以7.5，那么我有库纳的欧元金额，这是可行的。但是，当我将结果（7.5）除以6.3（1美元等于6.3库纳）时，我得到了相同的数字

import java.util.Scanner;

public class Conv {
    private double rez;
    private double rez2;
    private double svota;
    Scanner ul = new Scanner(System.in);

    public void PretvorbaInKunu(double y) {
        System.out.print("Insert amomunt: ");
        svota = ul.nextDouble();
        rez2 = svota*y;

    }

    public void PR2(double x) {
        rez = getRez2() / x;
    }

    public double getRez() {
        return rez;
    }
    public double getRez2() {
        return rez2;
    }
    public double getSvota() {
        return svota;
    }

}
import java.util.Scanner;

//Currency Converter

public class Vjezbica {
    public static void main(String[] args) {
        double e = 7.5;
        double d = 6.3;
        double p = 9.5;
        double k = 1.0;
        Conv more = new Conv();
        Scanner in = new Scanner(System.in);

        System.out.print("\t\tCurrency converter\nIz (e,p,d,k) - ");
        String iz = in.next();
        switch(iz) {
        case "e":
            more.PretvorbaInKunu(e);
            break;
        case "d":
            more.PretvorbaInKunu(d);
            break;
        case "p":
            more.PretvorbaInKunu(p);
            break;
        case "k":
            more.PretvorbaInKunu(k);
            break;
        }
        System.out.println(more.getRez2());

        System.out.print(" To  ");
        String u = in.next();
        switch(u) {
        case "e":
            more.PR2(e);
        case "d":
            more.PR2(d);
        case "p":
            more.PR2(p);
        case "k":
            more.PR2(k);
        }
        System.out.println(more.getSvota() + " " + iz + " is " + more.getRez() + " " + u);
    }
}

Answer 1

首先，正如托拜厄斯已经指出的那样，错误在于缺少了“突破” 但代码中还有其他错误，例如扫描仪未关闭

我还建议提高代码质量。您可以编写一个只执行计算的枚举类型（无输入-输入应该分开）。然后，您可以使用不同的枚举构造函数轻松定义货币

上面还讨论了是否应该使用双精度或双精度十进制。BigDecimal是一种“昂贵”的类型。我想知道浮动是否还不够，因为货币值通常包含2位数的精度——如果你没有处理非常高的金额，32位浮动类型应该已经受到影响

我将其改写如下：

import java.util.Scanner;

//Currency Converter

public class Vjezbica {

    private static enum Currency {
        EURO(7.5), KUNA(1), DOLLAR(6.3), P(9.3);

        private double cr;

        Currency(double conversionRate) {
            this.cr = conversionRate;
        }

        // precision: 2digits
        public float fromKuna(double kuna) {
            return (int) (((kuna) / cr) * 100) / 100f;
        }

        public float toKuna(double foreignCurrency) {
            return (int) (((foreignCurrency) * cr) * 100) / 100f;
        }
    }

    private static Currency readCurrency() {
        Scanner in = new Scanner(System.in);
        System.out.print("\t\tCurrency converter\nIz (e,p,d,k) - ");
        String iz = in.next();
        in.close();

        switch (iz) { // no break required when returning directly
        case "e":
            return Currency.EURO;
        case "d":
            return Currency.DOLLAR;
        case "p":
            return Currency.P;
        case "k":
            return Currency.KUNA;
        default:
            throw new IllegalArgumentException("invalid input: " + iz);
        }
    }

    private static float readAmount() {
        Scanner ul = new Scanner(System.in);
        float svota = ul.nextFloat();
        ul.close();
        return svota;
    }

    public static void main(String[] args) {

        System.out.print(" From  ");
        Currency c1 = readCurrency();

        System.out.print("Insert amomunt: ");
        float svota = readAmount();

        float amountInKuna = c1.toKuna(svota);

        System.out.print(" To  ");
        Currency c2 = readCurrency();

        float amountInC2 = c2.fromKuna(amountInKuna);
        System.out.println(svota + " " + c1.toString() + " is " + amountInC2 + " " + c2.toString());

    }


}

未考虑：转换首先从X转换为Kuna，然后从Kuna转换为Y。在这两种转换中，我们都在执行不精确舍入（地板而不是正确舍入，地板两次而不是一次）

根据这个建议，如果你计算出一个精确的转换率，最终可以直接从X转换到Y，然后对最终结果进行一轮运算，那就更好了

Answer 2

问题在于你的第二个switch case语句：你需要在每个case的末尾加上一个break

如果像这样更改Vjezbica类，它应该可以工作：

import java.util.Scanner;

//Currency Converter

public class Vjezbica {

    public static void main(String[] args) {
        double e = 7.5;
        double d = 6.3;
        double p = 9.5;
        double k = 1.0;
        Conv more = new Conv();
        Scanner in = new Scanner(System.in);

        System.out.print("\t\tCurrency converter\nIz (e,p,d,k) - ");
        String iz = in.next();
        switch (iz) {
            case "e":
                more.PretvorbaInKunu(e);
                break;
            case "d":
                more.PretvorbaInKunu(d);
                break;
            case "p":
                more.PretvorbaInKunu(p);
                break;
            case "k":
                more.PretvorbaInKunu(k);
                break;
        }
        System.out.println(more.getRez2());

        System.out.print(" To  ");
        String u = in.next();
        switch (u) {
            case "e":
                more.PR2(e);
                break;//added break here
            case "d":
                more.PR2(d);
                break;//added break here
            case "p":
                more.PR2(p);
                break;//added break here
            case "k":
                more.PR2(k);
                break;//added break here
        }
        System.out.println(more.getSvota() + " " + iz + " is " + more.getRez() + " " + u);

        //you should also close the scanner at the end...
        in.close();
    }
}