code: public static String join(final String sep, final Iterable<String> strs) {
          final StringBuilder buf = new StringBuilder();
          String prefix = "";
          for (final String str : strs) {
              buf.append(prefix).append(str);
              prefix = sep;
          }
          return buf.toString();
      }
docs: Join the given strings, separated by the given separator.
  
  @param sep
  the separator
  @param strs
  the strings to join
  @return the joined string