java - 如果用户输入 String 而不是 Int，可能会出现异常

Question

我只是在玩 Java。我试图强制我的程序只接受 3 位数字。我相信我已经使用 while 循环成功完成了此操作(如果我错了，请纠正我)。但是，如果用户输入字符串，我该如何打印错误语句。例如:“abc”。

我的代码:

    import java.util.Scanner;
    public class DigitSum {

    public static void main(String[] args) {

    Scanner newScan = new Scanner(System.in);

        System.out.println("Enter a 3 digit number: ");
        int digit = newScan.nextInt();

        while(digit > 1000 || digit < 100)
            {           
             System.out.println("Error! Please enter a 3 digit number: ");
             digit = newScan.nextInt();
            }

        System.out.println(digit);
       }
    }

Answer 1

这个怎么样？

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

        System.out.println ("Enter a 3 digit number: ");
        String line = newScan.nextLine ();
        int digit;
        while (true) {
            if (line.length () == 3) {
                try {
                    digit = Integer.parseInt (line);
                    break;
                }
                catch (NumberFormatException e) {
                    // do nothing.
                }
            }

            System.out.println ("Error!(" + line + ") Please enter a 3 digit number: ");
            line = newScan.nextLine ();
        }

        System.out.println (digit);
    }
}

正则表达式版本:

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

        System.out.println ("Enter a 3 digit number: ");
        String line = newScan.nextLine ();
        int digit;

        while (true) {
            if (Pattern.matches ("\\d{3}+", line)) {
                digit = Integer.parseInt (line);
                break;
            }

            System.out.println ("Error!(" + line + ") Please enter a 3 digit number: ");
            line = newScan.nextLine ();
        }

        System.out.println (digit);
    }
}