输入字符串而不是整数（Java）

Question

我是一个绝对的初学者，没有任何编程语言的经验。

我写了一个程序作为将阿拉伯数字转换成罗马数字的练习。它起作用了。然而，如果输入的是字符串而不是整数，我想添加一部分来处理这个问题。我不知道该怎么做。我试图使用try/catch，但我不知道如何正确使用它。现在程序要求我输入两次数字。怎么办？

以下是他的主要方法：

public static void main(String[] args) {

    int numArabic; 
    boolean validEntry;

    try {
            System.out.println("Enter an integer number between 1 and 3999!");
            Scanner scan = new Scanner(System.in); 
            numArabic = scan.nextInt();
            validEntry = true;
        } catch (InputMismatchException e) {
            System.out.println("Entered value is not an integer!");
        }

    System.out.println("Enter an integer number between 1 and 3999!");
    Scanner scan = new Scanner(System.in); 
    numArabic = scan.nextInt();                            

    if ((numArabic < 1) || (numArabic > 3999)) {
            System.out.println();
            System.out.print("Wrong number. ");
            System.out.print("Enter an integer number between 1 and 3999!");
            System.out.println();
            }
    else {
            String numRoman1 = toRomanOne(numArabic % 10);
            String numRoman2 = toRomanTwo(((numArabic / 10) % 10));
            String numRoman3 = toRomanThree(((numArabic / 100) % 10));
            String numRoman4 = toRomanFour(numArabic / 1000);
            System.out.print("The number " + numArabic + " is equal to: ");
            System.out.print(numRoman4+numRoman3+numRoman2+numRoman1 + ".");
    }
}

Answer 1

public static void main(String[] args) {

    int numArabic; 
    boolean validEntry = false;

    while (validEntry = false){
    try {

            System.out.println("Enter an integer number between 1 and 3999!");
            Scanner scan = new Scanner(System.in); 
            numArabic = scan.nextInt();
            validEntry = true;
        }

        catch (InputMismatchException e) {
            System.out.println("Entered value is not an integer!");
            validEntry = false;
        }
    }                 

    if ((numArabic < 1) || (numArabic > 3999)) {
            System.out.println();
            System.out.print("Wrong number. ");
            System.out.print("Enter an integer number between 1 and 3999!");
            System.out.println();
            }
    else {
            String numRoman1 = toRomanOne(numArabic % 10);
            String numRoman2 = toRomanTwo(((numArabic / 10) % 10));
            String numRoman3 = toRomanThree(((numArabic / 100) % 10));
            String numRoman4 = toRomanFour(numArabic / 1000);
            System.out.print("The number " + numArabic + " is equal to: ");
            System.out.print(numRoman4+numRoman3+numRoman2+numRoman1 + ".");
    }
}

Answer 2

您可以使用Scanner#hasNextInt（）方法来检查。

如果扫描仪输入中的下一个标记可以解释为int值，则此方法返回true。

if (scan.hasNextInt()) {
   // Do the process with Integer.
} else {
   // Do the process if it is not an Integer.
}

请注意，这将覆盖所有不是整数，而不仅仅是字符串。

Answer 3

您的控制机制是真实的，但只起作用一次。你必须把它放在一个循环中，这样它才能允许用户最后输入一个整数。

boolean validEntry;

do {
   try {
      System.out.println("Enter an integer number between 1 and 3999!");
      Scanner scan = new Scanner(System.in); 
      numArabic = scan.nextInt();
      validEntry = true;
   }
   catch (InputMismatchException e) {
      validEntry = false;
      System.out.println("Entered value is not an integer!");
   }
}
while(!validEntry);