Discussion on: Daily Challenge #292 - ISBN-10 Identifiers

public static boolean validISBN10(String s){
        int sum = 0;
        if(s.matches("[0-9]{9}[X0-9]{1}"))
        {
            for(int i = 0; i < s.length(); i++) {
                sum += s.charAt(i) == 'X' ? 10 * (i + 1) : Character.getNumericValue(s.charAt(i)) * (i + 1);
            }
            if(sum % 11 == 0) return true;
        }
        return false;
    }