code: public static String join(Collection<? extends Object> lst, String separator) {
          StringBuilder buf = new StringBuilder(lst.size() * 64);
          boolean first = true;
          for (Object value : lst) {
              if (first) first = false; else buf.append(separator);
              buf.append(value.toString());
          }
          return buf.toString();
      }
docs: Concatenates a list of objects using the given separator.
  @param lst           list of text strings
  @param separator     separator
  @return string