Compare the writing of data in two list sets

List<String> newUsers = newTaskUsers.stream().map(it ->it.getUserWorkNumber()).collect(toList());
            List<String> oldUsers = oldTaskUsers.stream().map(it ->it.getUserWorkNumber()).collect(toList());
            if(oldUsers.containsAll(newUsers)){
                flag = false;
            }else{
                flag = true;
            }