public static void main(String[] args) {

        Map<String, String> map = new TreeMap<String, String>();

        map.put("d", "ddddd");

        map.put("c", "ccccc");

        List<Map.Entry<String, String>> list = new ArrayList<Map.Entry<String, String>>(map.entrySet());

        Collections.sort(list, new Comparator<Map.Entry<String, String>>() {

            public int compare(Map.Entry<String, String> o1, Map.Entry<String, String> o2) {

                return o1.getKey().compareTo(o2.getKey());

            }

        });

        String string = String.valueOf(list.get(0)) + String.valueOf(list.get(1));

        System.out.println(string);

    }