java.util

---

1. Creating an ArrayList

List<String> list = new ArrayList<>();
list.add("Hello");
list.add("World");

2. Creating a HashSet

Set<String> set = new HashSet<>();
set.add("Hello");
set.add("World");

3. Creating a HashMap

Map<String, String> map = new HashMap<>();
map.put("Hello", "World");

4. Iterating over a List

List<String> list = new ArrayList<>();
list.add("Hello");
list.add("World");

for (String str : list) {
  System.out.println(str);
}

5. Iterating over a Set

Set<String> set = new HashSet<>();
set.add("Hello");
set.add("World");

for (String str : set) {
  System.out.println(str);
}

6. Iterating over a Map

Map<String, String> map = new HashMap<>();
map.put("Hello", "World");

for (Map.Entry<String, String> entry : map.entrySet()) {
  System.out.println(entry.getKey() + " = " + entry.getValue());
}

7. Sorting a List

List<String> list = new ArrayList<>();
list.add("Hello");
list.add("World");

Collections.sort(list);

8. Searching for an Element in a List

List<String> list = new ArrayList<>();
list.add("Hello");
list.add("World");

int index = list.indexOf("Hello");

9. Removing an Element from a List

List<String> list = new ArrayList<>();
list.add("Hello");
list.add("World");

list.remove("Hello");

10. Checking if a List Contains an Element

List<String> list = new ArrayList<>();
list.add("Hello");
list.add("World");

boolean contains = list.contains("Hello");

11. Creating a Queue

Queue<String> queue = new LinkedList<>();
queue.offer("Hello");
queue.offer("World");

12. Removing an Element from a Queue

Queue<String> queue = new LinkedList<>();
queue.offer("Hello");
queue.offer("World");

String removed = queue.poll();

13. Creating a Stack

Stack<String> stack = new Stack<>();
stack.push("Hello");
stack.push("World");

14. Removing an Element from a Stack

Stack<String> stack = new Stack<>();
stack.push("Hello");
stack.push("World");

String popped = stack.pop();

15. Creating a TreeMap

Map<String, String> map = new TreeMap<>();
map.put("Hello", "World");

16. Creating a LinkedHashMap

Map<String, String> map = new LinkedHashMap<>();
map.put("Hello", "World");

17. Creating a WeakHashMap

Map<String, String> map = new WeakHashMap<>();
map.put("Hello", "World");

18. Creating a ConcurrentHashMap

Map<String, String> map = new ConcurrentHashMap<>();
map.put("Hello", "World");

19. Creating a CopyOnWriteArrayList

List<String> list = new CopyOnWriteArrayList<>();
list.add("Hello");
list.add("World");

20. Creating a CopyOnWriteArraySet

Set<String> set = new CopyOnWriteArraySet<>();
set.add("Hello");
set.add("World");

21. Creating a BlockingQueue

BlockingQueue<String> queue = new ArrayBlockingQueue<>(10);
queue.put("Hello");
queue.put("World");

22. Creating a SynchronousQueue

BlockingQueue<String> queue = new SynchronousQueue<>();
queue.put("Hello");

23. Creating a PriorityBlockingQueue

BlockingQueue<String> queue = new PriorityBlockingQueue<>();
queue.put("Hello");
queue.put("World");

24. Creating a Deque

Deque<String> deque = new ArrayDeque<>();
deque.addFirst("Hello");
deque.addLast("World");

25. Creating a NavigableSet

NavigableSet<String> set = new TreeSet<>();
set.add("Hello");
set.add("World");

26. Creating a SortedMap

SortedMap<String, String> map = new TreeMap<>();
map.put("Hello", "World");

27. Creating a HashSet using a Builder

Set<String> set = Set.of("Hello", "World");

28. Creating a HashMap using a Builder

Map<String, String> map = Map.of("Hello", "World");

29. Creating a List using a Builder

List<String> list = List.of("Hello", "World");

30. Creating a StringJoiner

StringJoiner joiner = new StringJoiner(", ");
joiner.add("Hello");
joiner.add("World");

31. Creating a Base64 Encoder

Base64.Encoder encoder = Base64.getEncoder();
String encoded = encoder.encodeToString("Hello World".getBytes());

32. Creating a Base64 Decoder

Base64.Decoder decoder = Base64.getDecoder();
String decoded = new String(decoder.decode(encoded));

33. Creating a UUID

UUID uuid = UUID.randomUUID();

34. Creating a Random Number Generator

Random random = new Random();
int randomNumber = random.nextInt();

35. Creating a Date

Date date = new Date();

36. Creating a Calendar

Calendar calendar = Calendar.getInstance();

37. Creating a NumberFormat

NumberFormat numberFormat = NumberFormat.getInstance();
String formattedNumber = numberFormat.format(12345.67);

38. Creating a DateFormat

SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
String formattedDate = dateFormat.format(new Date());

39. Creating a TimeZone

TimeZone timeZone = TimeZone.getTimeZone("America/New_York");

40. Creating a Locale

Locale locale = new Locale("en", "US");

41. Creating a ResourceBundle

ResourceBundle resourceBundle = ResourceBundle.getBundle("messages");

42. Creating a Properties

Properties properties = new Properties();
properties.put("name", "John Doe");

43. Creating a Preferences

Preferences preferences = Preferences.userRoot();
preferences.put("name", "John Doe");

44. Creating a Logger

Logger logger = Logger.getLogger("MyLogger");
logger.info("Hello World");

45. Creating a Formatter

Formatter formatter = new SimpleFormatter();
logger.setFormatter(formatter);

46. Creating a Handler

Handler handler = new ConsoleHandler();
logger.addHandler(handler);

47. Creating a Timer

Timer timer = new Timer();
timer.schedule(new MyTimerTask(), 1000, 1000);

48. Creating a TimerTask

TimerTask timerTask = new MyTimerTask();
timer.schedule(timerTask, 1000, 1000);

49. Creating a Thread

Thread thread = new Thread(new MyRunnable());
thread.start();

50. Creating a Runnable

Runnable runnable = new MyRunnable();
Thread thread = new Thread(runnable);
thread.start();