Java InputMismatchException错误。 我将如何解决这个问题？

Question

It only appears when I enter 10 or more numbers that are 3's and 7's. It is coming from this method below, I tested it without this method. Here is the code

Scanner input = new Scanner(System.in);
    System.out.print("Enter a positive integer...");
    int num = input.nextInt();

    // Outputs
    System.out.println("Number of digits in number is " + numberDigits(num));
    System.out.println("Number begins with " + firstNum(num));
    System.out.println("Number ends with " + lastNum(num));
    System.out.println("Does number begin with 7? " + beginWith(num, 7));
    System.out.println("Does number begin with 3? " + beginWith(num, 3));
    System.out.println("Does number contain a 7? " + contains(num, 7));
    System.out.println("Does number contain a 3? " + contains(num, 3));
    System.out.println("Is the number divisible by 13? " + divTest(num, 13));
    System.out.println("Is the number divisible by 77? " + divTest(num, 77)); 
    System.out.println("How many times does 7 appear in the number? " + digitAppearances(num, 7));
    System.out.println("How many times does 3 appear in the number? " + digitAppearances(num, 3));

public static int digitAppearances(int num, int x) {

    // Check if num is 0
  if (num <= 0 ) {
    return 0;
  }

// Count number of times x appears
else if (num % 10 == x) {
    return 1 + digitAppearances(num / 10, x);
}
else {
    return digitAppearances(num / 10, x);
}
}

Answer 1

The Scanner is attempting to read an int with the nextInt method .

An invocation of this method of the form nextInt() behaves in exactly the same way as the invocation nextInt(radix) , where radix is the default radix of this scanner.

• nextInt(radix):

Throws:

InputMismatchException - if the next token does not match the Integer regular expression, or is out of range

If you enter a value larger than Integer.MAX_VALUE (about 2.1 billion, 10 digits), then you will get an InputMismatchException .

If you want to enter up to 19 digits, use nextLong .

If you want to enter an arbitrary number of digits, just call next , get the string, and validate that it only contains digits. You'll need to convert the character digits to a numeric type before further processing.