// remove duplicates with HashSet
Set<Song> songSet = new HashSet<>(songList);
System.out.println("6: " + songSet);
// TreeSet, remove duplicates and keep it sorted
Set<Song> songTreeSet = new TreeSet<>(songList);
System.out.println("7: " + songTreeSet);
// TreeSet can accept Comparator, pass it in its constructor
Set<Song> songTreeSetComparator = new TreeSet<>((o1, o2) -> o1.getBpm() - o2.getBpm());
songTreeSetComparator.addAll(songList);
System.out.println("8: (sort by BPM)" + songTreeSetComparator);