Java 将罗马数字转换为阿拉伯语

我是Java新手，我需要编写一个程序，将罗马数字转换为阿拉伯数字

我不能使用某些函数，因为我不允许在给定代码的末尾更改参数。我需要做的一切，在公共静态无效的主要功能

我开始在谷歌上搜索并开始编码。从现在起，我只能将一个字母数字转换为X，I，V。。。阿拉伯数字，但我不能这样做，超过详细的数字席，CCC，IX，IV.…< / P> 有人能帮我吗？我对Java真的很陌生。这是我的第一种程序语言，我正在努力理解它

这是我的密码：

import java.util.Scanner;

class Roman {

    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        int[] numbers = {1000, 500, 100, 50, 10, 5, 1 };
        String symbols = "MDCLXVI";

        /*******************************************
         * Complete your program
         *******************************************/

        System.out.print("Enter a roman numeral");
         final int MAX = 3999;
            Scanner keyb = new Scanner(System.in);
            String roman = keyb.next();
            roman=roman.toUpperCase();

            if(roman.matches(".*[0-9].*") || !roman.matches("[M|D|C|L|X|V|I]*")){
                System.out.println("Impossible to convert. Wrong roman numeral");
            } 

            int i = 0; //position in the string romain
            int arabic = 0; // Arabic numeral equivalent of the part of the string that
                            // has been converted so far


            int number;
            while (i < roman.length()){

                char letter = roman.charAt(i); // letter at the current position in the string


                if (letter == 'I'){
                    number = 1;
                } else if (letter == 'V'){
                    number = 5;
                } else if (letter == 'X'){
                    number = 10;
                } else if (letter == 'L'){
                    number = 50;
                } else if (letter == 'C'){
                    number = 100;
                } else if (letter == 'D'){
                    number = 500;
                } else if (letter == 'M'){
                    number = 1000;
                } else {
                    number = -1;
                }

                i++; // Move on to next position in the string

                if (i==roman.length()){
                    // There is no letter in the string following the one we have just processed.
                    // So just add the number corresponding to the single letter to arabic.

                    arabic += number;

                } else {
                    // Look at the next letter in the string.  If it has a larger Roman numeral
                    // equivalent than number, then the two letters are counted together as
                    // a Roman numeral with value (nextNumber - number).


                    number = roman.charAt(i);
                    int nextNumber = number;
                    if(nextNumber > number){
                        // Combine the two letters to get one value, and move on to next position in string.
                        arabic += (nextNumber - number);
                        i++;

                    } else {
                        // Don't combine the letters.  Just add the value of the one letter onto the number.
                        arabic += number;

                    }
                }
                System.out.println(number);
            } // end while

        /*******************************************
         * Do not change after this line.
         *******************************************/
    }
}

---

以下是一种方法：

import java.util.Scanner;

class Roman {

    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        int[] numbers = { 1000, 500, 100, 50, 10, 5, 1 };
        String symbols = "MDCLXVI";

        /*******************************************
         * Complete your program
         *******************************************/

        System.out.print("Enter a roman numeral: ");
        final int MAX = 3999;
        Scanner keyb = new Scanner(System.in);
        String roman = keyb.next();
        keyb.close(); // don't want a resource leak

        roman = roman.toUpperCase();

        if (roman.matches(".*[0-9].*") || !roman.matches("[M|D|C|L|X|V|I]*")) {
            System.out.println("Impossible to convert. Wrong roman numeral");
        }

        int i = 0; // position in the Roman string

        int current = 0; // the current Roman numeral character to Arabic
                         // conversion

        int previous = 0; // start previous at zero, that way when
                          // current is greater than previous in the first
                          // run, nothing will be subtracted from current

        int arabic = 0; // Arabic numeral equivalent of the part of the string
                        // that has been converted so far

        while (i < roman.length()) {

            char letter = roman.charAt(i); // letter at the current position in
                                            // the string

            // switch statement is easier to read than if - else if - else
            switch (letter) {
            case ('I'):
                current = 1;
                break;
            case ('V'):
                current = 5;
                break;
            case ('X'):
                current = 10;
                break;
            case ('L'):
                current = 50;
                break;
            case ('C'):
                current = 100;
                break;
            case ('D'):
                current = 500;
                break;
            case ('M'):
                current = 1000;
                break;
            }


            if (current > previous) {
                // subtract previous * 2 because previous was added to arabic
                // once already
                arabic += current - (previous * 2);
            } else {
                // if current is less than or equal to previous then add it to
                // arabic
                arabic += current;
            }

            previous = current; // set previous equal to current to check
                                // for less-than on next iteration

            i += 1; // move on to next position in the string

        } // end while

        // print the Arabic conversion after the loop is done
        System.out.println("Arabic: " + arabic);

        /*******************************************
         * Do not change after this line.
         *******************************************/
    }
}

---

我建议对你的单个罗马数字进行枚举。这使得代码被很好地封装

public enum Roman {
    I(1), V(5), X(10), L(50), C(100), D(500), M(1000);
    private final int value;
    private Roman(int value) {
        this.value = value;
    }
    public int toInt() {
        return value;
    }
}

将单个罗马数字转换为整数变得很简单。例如：

Roman.valueOf("X").toInt();

唯一复杂的位是处理IX和XC类型的值。识别它们的简单方法是，它们是数字不按降序排列的唯一时间。检查此项可以作为方法添加到枚举本身以继续封装：

public enum Roman {
    public boolean shouldCombine(Roman next) {
        return this.value < next.value;
    }
    public int toInt(Roman next) {
        return next.value - this.value;
    }
}

现在把所有这些放在一起：

List<Roman> romans = new ArrayList<>();
input.chars().mapToObj(Character::valueOf)
    .map(Roman::valueOf).forEach(romans::add);
int value = 0;
while (!romans.isEmpty()) {
    Roman current = romans.remove(0);
    if (!romans.isEmpty() && current.shouldCombine(romans.get(0))
        value += current.toInt(romans.remove(0));
    else
        value += current.ToInt();
}

---

该代码的第一部分使用Java8特性将字符串转换为罗马数字。如果您觉得有点困惑，请告诉我，我将把它转换为传统的迭代。

这是正式语言的一个展望。解决此问题的唯一方法是将位置0与下一个字符进行比较。如果值小于，则从acccumulator中减去该值；如果>=，则添加该值

您最好使用switch语句，而不是if-else if-else语句。枚举的可能副本会更好，就像在sprinter answernice中一样，我有非常类似的实现。换一种方式也很有趣；

List<Roman> romans = new ArrayList<>();
input.chars().mapToObj(Character::valueOf)
    .map(Roman::valueOf).forEach(romans::add);
int value = 0;
while (!romans.isEmpty()) {
    Roman current = romans.remove(0);
    if (!romans.isEmpty() && current.shouldCombine(romans.get(0))
        value += current.toInt(romans.remove(0));
    else
        value += current.ToInt();
}