code: public static boolean isAlphanumeric(final String input) {
          for (int i = 0; i < input.length(); i++) {
              if (!Character.isLetterOrDigit(input.charAt(i))) return false;
          }
          return true;
      }
docs: Checks to see if a string entered is alpha numeric
  
  @param input The string to be tested
  @return True if the string is alpha numeric otherwise false