isDigit方法中的Character.isDigit参数和行不可用错误（说明）

Question

I'm currently working on a small project for an introductory java class. We're supposed to make a program which can take in an integer from the user and output the number of odds, evens, and zeroes present within the code. This seemed pretty easy to me, and I managed to implement the code, but a class mate, after I criticized his code for incorrectly following the prompt, noted that my code would crash if anything but digits was input.

Out of spite I've tried to go beyond the prompt and have the program output an error message if it encounters characters aside from digits (instead of having my compiler return an error). However I'm returning multiple errors within the Eclipse compiler when using the isDigit method in the Character class.

I don't know exactly what's causing this, and I feel I must be missing something crucial, but my teacher quite frankly isn't qualified enough to understand what's causing the error, and none of my classmates can seem to figure it out either.

package ppCH5;
import java.util.Scanner;

public class PP5_3
{
    public static void main(String[]args)
    {   
        int even = 0;
        int odd = 0;
        int zero = 0;
        int num = 0;
        int count = 0;

        boolean inputError = false;
        System.out.println("please provide some integer");
        Scanner scan = new Scanner(System.in);
        String numbers = scan.next();
        scan.close();
        Scanner intSeperate = new Scanner(numbers);
        intSeperate.useDelimiter("");

        while(intSeperate.hasNext())
        {
                if(Character.isDigit(numbers.charAt(count)))
                {
                    count++;
                    num = intSeperate.nextInt();
                    if((num % 2)==1)
                        odd++;
                    if((num % 2)==0)
                        if(num==0)
                            zero++;
                        else
                            even++;
                }
                else
                {
                    count++;
                    inputError = true;
            }
        }
        intSeperate.close();
        if(!inputError)
        {
            System.out.println("There are " + even + " even digits.\n" + odd     + " odd digits.\nAnd there are " + zero + " zeros in that integer.");
        }
        else
        {
            System.out.println("You have provided a disallowed input");
        }
    }
}

Any help would be appreciated, I'm currently at a loss.

Answer 1

When you enter a single non-digit character, say a , the else branch inside the while loop will get executed, incrementing count , right? And then the loop will start a new iteration, right?

In this new iteration, intSeparator.hasNext() still returns true. Why? Because the input a is never read by the scanner (unlike if you have entered a digit, intSeparator.nextInt would be called and would have consumed the input).

Now count is 1 and is an invalid index for the 1-character string. Therefore, numbers.charAt(count) throws an exception.

This can be avoided if you break; out of the loop immediately in the else block:

else
{
    inputError = true;
    break;
}

Also, don't close the scan scanner. scan is connected to the System.in stream. You didn't open that stream, so don't close it yourself.