code: public static String join(String delimiter, Iterable<String> strings) {
      StringBuilder sb = new StringBuilder();
      for (String item : strings) {
        if (sb.length() > 0) sb.append(delimiter);
        sb.append(item);
      }
      return sb.toString();
    }
docs: Join the array with the given delimiter, and return it as a string.
  
  @param delimiter string to be used as a separator between array elements
  @param strings the strings to join
  @return a single string containing all elements in `strings` joined together