升序

Collections.sort(list, new Comparator<T>() {
    @Override
    public int compare(T o1,
                       T o2) {
        return o1.getXxx().compareTo(o2.getXxx());
    }
});

降序

Collections.sort(list, Collections.reverseOrder(new Comparator<T>() {
    @Override
    public int compare(T o1,
                       T o2) {
        return o1.getXxx().compareTo(o2.getXxx());
    }
}));