code: public static String join(Collection<?> collection, String separator)
    {
      return StringUtils.join(collection, separator);
    }
docs: Join a collection or list of elements, using the separator provided.
  For example, this could be used to join a list of strings by a comma,
  i.e. ",".
  
  @param collection - Collection&gt;?&lt;
  @param separator - String
  @return String - The joined string