Sorting a list with stream.sorted() in Java

Use list.sort instead:

list.sort((o1, o2) -> o1.getItem().getValue().compareTo(o2.getItem().getValue()));

and make it more succinct using Comparator.comparing:

list.sort(Comparator.comparing(o -> o.getItem().getValue()));

After either of these, list itself will be sorted.

Your issue is that list.stream.sorted returns the sorted data, it doesn't sort in place as you're expecting.

This is not like Collections.sort() where the parameter reference gets sorted. In this case you just get a sorted stream that you need to collect and assign to another variable eventually:

List result = list.stream().sorted((o1, o2)->o1.getItem().getValue().
                                   compareTo(o2.getItem().getValue())).
                                   collect(Collectors.toList());

You've just missed to assign the result