创建只读集合

Collections.unmodifiableCollection(Arrays.asList(""));
Collections.unmodifiableList(Collections.singletonList(""));
Collections.unmodifiableMap(new HashMap<>(1 << 4));
Collections.unmodifiableSet(new HashSet<>());
Collections.unmodifiableNavigableMap(new TreeMap<>());
Collections.unmodifiableNavigableSet(new TreeSet<>());
Collections.unmodifiableSortedMap(new TreeMap<>());
Collections.unmodifiableSortedSet(new TreeSet<>());

List<Integer> list = List.of(1, 2, 3, 4, 5, 6);
Set<Integer> sets = Set.of(1, 2, 3, 4, 5, 6);
Map<Integer, Integer> maps = Map.of(1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6);
Map<Integer, Integer> entries = Map.ofEntries(Map.entry(1, 1),
        Map.entry(2, 2),
        Map.entry(3, 3),
        Map.entry(4, 4),
        Map.entry(5, 5),
        Map.entry(6, 6));