java - 如何重新提示允许用户继续转换值？

Question

我需要将数值转换为罗马数字，但遇到了一些麻烦。当我测试我的代码并且用户输入一个数字时，代码将其转换为罗马数字，但之后我无法再次出现提示；它会在输入错误的整数后重新提示，但在输入正确的整数后不会重新提示。我不知道如何做到这一点，以便用户可以继续转换值，直到他们选择 -1 退出。以下是我到目前为止所想到的。

import java.util.Scanner;

public class arabicToRoman {
static String a = "";

public static void main (String[] args){

    Scanner input = new Scanner(System.in);
    System.out.println("Enter a number between 1 and 3999 (-1 to quit): ");

    while (!input.hasNext("-1")) {
        String a = input.next(); 

    try {
        Integer number = Integer.parseInt(a); 

        if ((number <= 3999) && (number > 0)) {
            System.out.println(arabicToRoman(number)); 

        } else if (number > 3999) {
            System.out.println("Error: number must be between 1 and 3999");

        } else if (number == 0) {
            System.out.println("Error: The Romans did not have a way to represent negative numbers or zero.");

        } else {
            System.out.println("Error: The Romans did not have a way to represent negative numbers or zero.");

        }
    } catch (NumberFormatException e) {
        System.out.println("You did not enter a number!");
    }
}  
}

public static String arabicToRoman(int arabic) {    
    while (arabic >= 1000){
        a += "M";
        arabic -= 1000;
    }
    while (arabic >= 900){
        a += "CM";
        arabic -= 900;
    }
    while (arabic >= 500){
        a += "D";
        arabic -= 500;
    }
    while (arabic >= 400){
        a += "CD";
        arabic -= 400;
    }
    while (arabic >= 100){
        a += "C";
        arabic -= 100;
    }
    while (arabic >= 90){
        a += "XC";
        arabic -= 90;
    }
    while (arabic >= 50){
        a += "L";
        arabic -= 50;
    }
    while (arabic >= 40){
        a += "XL";
        arabic -= 40;
    }
    while (arabic >= 10){
        a += "X";
        arabic -= 10;
    }
    while (arabic >= 9){
        a += "IX";
        arabic -= 10;
    }
    while (arabic >= 5){
        a += "V";
        arabic -= 5;
    }
    while (arabic >= 4){
        a += "IV";
        arabic -= 4;
        }
    while (arabic >= 1){
        a += "I";
        arabic -= 1;
    }
    return a;
}
}

输入完后，似乎显示了结果，但之后没有任何提示，但用户可以输入其他内容，它会读取；如果是另一个数字，则结果将添加到之前的结果中。

Answer 1

由于return，您的代码无法正常工作((number <= 3999) && (number > 0)) 时调用的语句条件满足。这个return终止循环。

相反，您可能想调用方法 arabicToRoman(int arabic)并简单地打印出结果。

我还会考虑重组您的代码以使用 sentinel value在 while循环条件并编辑代码，以便在给出非数字答案时不会崩溃。正如您现在编写的代码一样，这样做会生成 java.util.InputMismatchException .

Scanner input = new Scanner(System.in);
System.out.println("Enter a number between 1 and 3999 (-1 to quit):");

while (!input.hasNext("-1")) {

    String a = input.next(); // gets the next item from the Scanner

    try {
        Integer number = Integer.parseInt(a); // tries to 'cast' the String to an Integer

        if ((number <= 3999) && (number > 0)) {
            System.out.println(arabicToRoman(number)); // prints out the result

        } else if (number > 3999) {
            System.out.println("Error: number must be between 1 and 3999");

        } else if (number == 0) {
            System.out.println("Error: The Romans did not have a way to represent negative numbers or zero.");

        } else {
            System.out.println("Error: The Romans did not have a way to represent negative numbers or zero.");

        }
    } catch (NumberFormatException e) {
        System.out.println("You did not enter a number!");
    }
}

编辑:修复串联问题

编写的程序将结果存储在 state variable 中通过对同样的调用持续存在。这就是为什么每次调用该方法时，它都会打印当前结果并附加到先前的结果。您想要编辑代码以不存储 a作为状态变量并返回 arabicToRoman(int arabic)方法无需改变现有数据。在方法内部声明变量将允许在方法终止时释放该变量。

要进行此修复:

首先，在类中的方法之外删除此行:

static String a = "";

然后，编辑您的 arabicToRoman(int arabic)方法看起来像这样:

public static String arabicToRoman(int arabic) {
    String a = ""; // note this String declaration at the start of the method

    while (arabic >= 1000) {
        a += "M";
        arabic -= 1000;
    }
    while (arabic >= 900) {
        a += "CM";
        arabic -= 900;
    }
    while (arabic >= 500) {
        a += "D";
        arabic -= 500;
    }
    while (arabic >= 400) {
        a += "CD";
        arabic -= 400;
    }
    while (arabic >= 100) {
        a += "C";
        arabic -= 100;
    }
    while (arabic >= 90) {
        a += "XC";
        arabic -= 90;
    }
    while (arabic >= 50) {
        a += "L";
        arabic -= 50;
    }
    while (arabic >= 40) {
        a += "XL";
        arabic -= 40;
    }
    while (arabic >= 10) {
        a += "X";
        arabic -= 10;
    }
    while (arabic >= 9) {
        a += "IX";
        arabic -= 10;
    }
    while (arabic >= 5) {
        a += "V";
        arabic -= 5;
    }
    while (arabic >= 4) {
        a += "IV";
        arabic -= 4;
    }
    while (arabic >= 1) {
        a += "I";
        arabic -= 1;
    }
    return a;
}

我再次对此进行了测试，并可以确认它会产生您所描述的正确行为。

为了清楚起见，this is what the final product should look like .