code: public static String join(final Collection<String> seq, final String delimiter) {
      if (null == seq || seq.size() < 1) {
        return "";
      } else {
        StringBuilder aim = new StringBuilder();
        for (String one : seq) {
          if (null != delimiter && aim.length() > 0) {
            aim.append(delimiter);
          }
          aim.append(one);
        }
        return aim.toString();
      }
    }
docs: <p>
  join.
  </p>
  
  @param seq
  a {@link java.util.Collection} object.
  @param delimiter
  a {@link java.lang.String} object.
  @return a {@link java.lang.String} object.