public boolean onlyLettersOrDigits(final @NonNull CharSequence input,final int numCharsToCheck,final int start){
  if (start < 0 || start > input.length()) {
    return false;
  }
  for (int i=0; i < numCharsToCheck; i++) {
    int positionToCheck=start + i;
    if (positionToCheck >= input.length()) {
      return false;
    }
    char charToCheck=input.charAt(positionToCheck);
    if (!Character.isLetterOrDigit(charToCheck)) {
      return false;
    }
  }
  return true;
}

public boolean onlyLettersOrDigits ( final @ NonNull CharSequence input , final int numCharsToCheck , final int start ) { if ( start < 0 || start > input . length ( ) ) { return false ; } for ( int i = 0 ; i < numCharsToCheck ; i ++ ) { int positionToCheck = start + i ; if ( positionToCheck >= input . length ( ) ) { return false ; } char charToCheck = input . charAt ( positionToCheck ) ; if ( ! Character . isLetterOrDigit ( charToCheck ) ) { return false ; } } return true ; }
given a string and starting index , return true if the first " numcharstocheck " characters at the starting index are either a letter or a digit .
