code: public static String join(Object array, char separator, Object... pieces) {
          StringBuilder sb = new StringBuilder();
          for (int i = 0, ii = Array.getLength(array); i < ii; ++i) {
              Object element = Array.get(array, i);
              sb.append(element != null ? element.toString() : "null").append(separator);
          }
          for (int i = 0; i < pieces.length; ++i) {
              sb.append(pieces[i] != null ? pieces[i].toString() : "null").append(separator);
          }
          if (sb.length() > 0) sb.setLength(sb.length()-1);
          return sb.toString();
      }
docs: Concatenates elements in an array into a single String, with elements separated by the given separator.
  
  @param array - an array
  @param separator - a separator character
  @return the string from joining elements in the array