code: protected String concat(Set<String> set, String sep)
  	{
  		String s = "";
  
  		int i = set.size();
  		for (String ss : set)
  		{
  			s += ss;
  			if (--i > 0) s += sep;
  		}
  		return s;
  	}
docs: Converts the set of string to a single string.
  @param set the set
  @param sep separator string
  @return concatenated string