Java - 将字符输入(表示罗马数字)转换为十进制等值

Question

正如标题所示，我正在使用方法编写一个简单的程序，该程序将罗马数字的字符输入在(“M”，“D”，“C”，“L”，“X”，“V”之间转换) ，“I”)然后打印十进制等值。

我已经编写了程序，但它将小数(int)转换为罗马数字

当修改程序以仅接受字符输入(“M”，“D”，“C”，“L”，“X”，“V”，“I”)然后输出十进制时，我收到错误char 无法转换为 int。

关于我如何改变这一点的任何建议。谢谢

import java.util.Scanner;

class RomanNumeral {
    public static String romanNumeralToInt(int romanNumeral) {
        String Numeral = "";
        int repeat;

        int value[] = {1000, 500, 100, 50, 10, 5, 1 };
        String symbol[] = {"M", "D", "C", "L", "X", "V", "I" };

        for(int x = 0; romanNumeral > 0; x++) {
            repeat = romanNumeral / value[x];

            for(int i = 1; i <= repeat; i++) {
                Numeral = Numeral + symbol[x];
            }

            romanNumeral = romanNumeral % value[x];
        }

        return Numeral;
    }

    public static void main(String args[]){
        Scanner input = new Scanner(System.in);

        final String INVALID = "Invalid number, try again!";

        final int VALIDATE_NUMBER_1 = 1;
        final int VALIDATE_NUMBER_5 = 5;
        final int VALIDATE_NUMBER_10 = 10;
        final int VALIDATE_NUMBER_50 = 50;
        final int VALIDATE_NUMBER_100 = 100;
        final int VALIDATE_NUMBER_500 = 500;
        final int VALIDATE_NUMBER_1000 = 1000;

        while (true) {
            System.out.print("Enter a number: ");
            int inputValue = input.nextInt();

            if (inputValue == VALIDATE_NUMBER_1) {
                System.out.println(VALIDATE_NUMBER_1 + " = " + romanNumeralToInt(1));
            }
            else if (inputValue == VALIDATE_NUMBER_5) {
                System.out.println(VALIDATE_NUMBER_5 + " = " + romanNumeralToInt(5));
            }
            else if (inputValue == VALIDATE_NUMBER_10) {
                System.out.println(VALIDATE_NUMBER_10 + " = " + romanNumeralToInt(10));
            }
            else if (inputValue == VALIDATE_NUMBER_50) {
                System.out.println(VALIDATE_NUMBER_50 + " = " + romanNumeralToInt(50));
            }
            else if (inputValue == VALIDATE_NUMBER_100) {
                System.out.println(VALIDATE_NUMBER_100 + " = " + romanNumeralToInt(100));
            }
             else if (inputValue == VALIDATE_NUMBER_500) {
                System.out.println(VALIDATE_NUMBER_500 + " = " + romanNumeralToInt(500));
            }
             else if (inputValue == VALIDATE_NUMBER_1000) {
                System.out.println(VALIDATE_NUMBER_1000 + " = " + romanNumeralToInt(1000));
            }
             else {
                 System.out.println(INVALID);
             }
        }

    }
}

更新按照帖子的建议修改了代码，但仍然存在错误，因为 String 无法转换为 Int。有什么建议。谢谢您

import java.util.Scanner;

class RomanTest {
        public static int romanNumeralToInt(char romanNumeral) {
        String Numeral = "";
        int repeat;

        int value[] = {1000, 500, 100, 50, 10, 5, 1 };
        char symbol[] = {'M', 'D', 'C', 'L', 'X', 'V', 'I' };

        for(char x = 0; romanNumeral > 0; x++) {
            repeat = romanNumeral / value[x];

            for(int i = 1; i <= repeat; i++) {
                Numeral = Numeral + symbol[x];
            }

            romanNumeral = romanNumeral % value[x];
        }

        return Numeral;
    }

    public static void main(String args[]){
        Scanner input = new Scanner(System.in);

        final String INVALID = "Invalid number, try again!";

        final char VALIDATE_CHAR_M = 'M';
        final char VALIDATE_CHAR_D = 'D';
        final char VALIDATE_CHAR_C = 'C';
        final char VALIDATE_CHAR_L = 'L';
        final char VALIDATE_CHAR_X = 'X';
        final char VALIDATE_CHAR_V = 'V';
        final char VALIDATE_CHAR_I = 'I';


        while (true) {
            System.out.print("Enter a number: ");
            char inputValue = input.nextLine().charAt(0);

            if (inputValue == VALIDATE_CHAR_M) {
                System.out.println(VALIDATE_CHAR_M + " = " + romanNumeralToInt('M'));
            }
            else if (inputValue == VALIDATE_CHAR_D) {
                System.out.println(VALIDATE_CHAR_D + " = " + romanNumeralToInt('D'));
            }
            else if (inputValue == VALIDATE_CHAR_C) {
                System.out.println(VALIDATE_CHAR_C + " = " + romanNumeralToInt('C'));
            }
            else if (inputValue == VALIDATE_CHAR_L) {
                System.out.println(VALIDATE_CHAR_L + " = " + romanNumeralToInt('L'));
            }
            else if (inputValue == VALIDATE_CHAR_X) {
                System.out.println(VALIDATE_CHAR_X + " = " + romanNumeralToInt('X'));
            }
             else if (inputValue == VALIDATE_CHAR_V) {
                System.out.println(VALIDATE_CHAR_V + " = " + romanNumeralToInt('V'));
            }
             else if (inputValue == VALIDATE_CHAR_I) {
                System.out.println(VALIDATE_CHAR_I + " = " + romanNumeralToInt('I'));
            }
             else {
                 System.out.println(INVALID);
             }
        }

    }
}

Answer 1

首先你要注意public static int romanNumeralToInt(char romanNumeral)它应该返回 int，但你返回 String Numeral = ""; - 它是 String，Java 因为 C# 是强类型语言，所以你必须返回 String。第二:以您正在做的方式连接字符串 for(int i = 1; i <= repeat; i++) {
Numeral = Numeral + symbol[x];
}不推荐(太慢，字符串是不可变的，因此在每次连接时都创建新字符串)。更好的方法是使用 StringBuilder。

我修改了你的代码并提供了类似的内容:

private String decimalToRoman(int number) {
    String[] romans = {"M", "CM", "D", "C", "XC", "L", "X", "IX", "V", "I"};
    int[] values = {1000, 900, 500, 100, 90, 50, 10, 9, 5, 1};
    StringBuilder builder = new StringBuilder();


    for (int i = 0; i < values.length; i++) {
        int times= number / values[i];

        if (times== 0) {
            continue;
        }

        if (times == 4 && i > 0) {
            builder.append(romans[i]);
            builder.append(romans[i - 1]);
        } else {
            for (int ii = 0; ii < times; ii ++) {
                builder.append(romans[i]);
            }
        }

        number = number % values[i];
    }
    return builder.toString();
}