docs: public static <T> String join(Collection<T> col, String delim) {
      StringBuilder sb = new StringBuilder();
      Iterator<T> iter = col.iterator();
      if (iter.hasNext())
        sb.append(iter.next().toString());
      while (iter.hasNext()) {
        sb.append(delim);
        sb.append(iter.next().toString());
      }
      return sb.toString();
    }