Function<Integer,Integer> f = x -> x * x;

List<String> names = List.of("a","b","c");
names.forEach(System.out::println);

Map<Integer, Long> freq = List.of(1,2,2,3,3,3)
    .stream()
    .collect(Collectors.groupingBy(x -> x, Collectors.counting()));

Optional<String> os = Optional.of("x");
String v = os.map(String::toUpperCase).orElse("NA");

LocalDateTime now = LocalDateTime.now();
ZonedDateTime z = now.atZone(ZoneId.of("UTC"));
Duration d = Duration.between(now, now.plusHours(5));