Java文字列のソート

    public static void main(String[] args) {
        // write your code here

        String test = "jjjkkkffffggg";
        List<Character> list = new ArrayList<>();
        for (int i = 0; i < test.length(); i++) {
            list.add(test.charAt(i));
        }
        list.sort((a, b) -> {
            return b - a;
        });

        StringBuffer stringBuffer = new StringBuffer();
        for (Character character : list) {
            stringBuffer.append(character);
        }
        System.out.println(stringBuffer.toString());
    }