code: public static <T> String argsToString(String separator, T... args) {
      StringBuilder sb = new StringBuilder();
      for (T s : args) {
        if (sb.length() != 0) {
          sb.append(separator);
        }
        sb.append(s);
      }
      return sb.toString();
    }
docs: Converts varargs of objects to a string.
  
  @param separator separator string
  @param args variable arguments
  @param <T> type of the objects
  @return concatenation of the string representation returned by Object#toString
  of the individual objects