Evolve ....

Collections.sort(itemList, new Comparator<Item>() {
    @Override    public int compare(Item o1, Item o2) {
        return o1.getItemId().compareTo(o2.getItemId());    }
});

Collections.sort(itemList, (o1, o2) -> o1.getItemId().compareTo(o2.getItemId()));

Collections.sort(itemList, Comparator.comparing(Item::getItemId));