code: public boolean onlyLettersOrDigits(final @NonNull CharSequence input, final int numCharsToCheck, final int start) {
  
          // Starting position must be within the input string
          if (start < 0 || start > input.length()) {
              return false;
          }
  
          // Check the first "numCharsToCheck" characters to ensure they are a letter or digit
          for (int i = 0; i < numCharsToCheck; i++) {
              int positionToCheck = start + i;
              // Return false if we would throw an Out-of-Bounds exception
              if (positionToCheck >= input.length()) {
                  return false;
              }
              // Return false early if current character is not a letter or digit
              char charToCheck = input.charAt(positionToCheck);
              if (!Character.isLetterOrDigit(charToCheck)) {
                  return false;
              }
          }
  
          // First "numCharsToCheck" characters are either letters or digits, so return true
          return true;
      }
docs: Given a string and starting index, return true if the first "numCharsToCheck" characters at
  the starting index are either a letter or a digit.
  
  @param input           a {@link CharSequence} to test
  @param numCharsToCheck number of characters to examine at starting position
  @param start           starting position within the input string
  
  @return true if the first "numCharsToCheck" at the starting index are either letters or digits