Java.util Package in Java

1. AbstractCollection: This class provides a skeletal implementation of the Collection interface, to minimize the effort required to implement this interface.

2. AbstractList: This class provides a skeletal implementation of the List interface to minimize the effort required to implement this interface backed by a “random access” data store (such as an array).

3. AbstractMap<K,V>: This class provides a skeletal implementation of the Map interface, to minimize the effort required to implement this interface.

4. AbstractMap.SimpleEntry<K,V>: An Entry maintaining a key and a value.

5. AbstractMap.SimpleImmutableEntry<K,V>: An Entry maintaining an immutable key and value.

6. AbstractQueue: This class provides skeletal implementations of some Queue operations.

7. AbstractSequentialList: This class provides a skeletal implementation of the List interface to minimize the effort required to implement this interface backed by a “sequential access” data store (such as a linked list).

8. AbstractSet: This class provides a skeletal implementation of the Set interface to minimize the effort required to implement this interface.
ArrayDeque: Resizable-array implementation of the Deque interface.

9. ArrayList: Resizable-array implementation of the List interface.

10. Arrays: This class contains various methods for manipulating arrays (such as sorting and searching).

11. BitSet: This class implements a vector of bits that grows as needed.
Calendar: The Calendar class is an abstract class that provides methods for converting between a specific instant in time and a set of calendar fields such as YEAR, MONTH, DAY_OF_MONTH, HOUR, and so on, and for manipulating the calendar fields, such as getting the date of the next week.

12. Collections: This class consists exclusively of static methods that operate on or return collections.
Currency: Represents a currency.

13. Date: The class Date represents a specific instant in time, with millisecond precision.

14. Dictionary<K,V>: The Dictionary class is the abstract parent of any class, such as Hashtable, which maps keys to values.

15. EnumMap,V>: A specialized Map implementation for use with enum type keys.

16. EnumSet: A specialized Set implementation for use with enum types.

17. EventListenerProxy: An abstract wrapper class for an EventListener class which associates a set of additional parameters with the listener.

18. EventObject: The root class from which all event state objects shall be derived.

19. FormattableFlags: FomattableFlags are passed to the Formattable.formatTo() method and modify the output format for Formattables.

20. Formatter: An interpreter for printf-style format strings.

21. GregorianCalendar: GregorianCalendar is a concrete subclass of Calendar and provides the standard calendar system used by most of the world.

22. HashMap<K,V>: Hash table based implementation of the Map interface.

23. HashSet: This class implements the Set interface, backed by a hash table (actually a HashMap instance).

24. Hashtable<K,V>: This class implements a hash table, which maps keys to values.

25. IdentityHashMap<K,V>: This class implements the Map interface with a hash table, using reference-equality in place of object-equality when comparing keys (and values).

26. LinkedHashMap<K,V>: Hash table and linked list implementation of the Map interface, with predictable iteration order.

27. LinkedHashSet: Hash table and linked list implementation of the Set interface, with predictable iteration order.

28. LinkedList: Doubly-linked list implementation of the List and Deque interfaces.

29. ListResourceBundle: ListResourceBundle is an abstract subclass of ResourceBundle that manages resources for a locale in a convenient and easy to use list.

30. Locale – Set 1, Set 2: A Locale object represents a specific geographical, political, or cultural region.

31. Locale.Builder: Builder is used to build instances of Locale from values configured by the setters.
Objects: This class consists of static utility methods for operating on objects.

32. Observable: This class represents an observable object, or “data” in the model-view paradigm.

33. PriorityQueue: An unbounded priority queue based on a priority heap.

34. Properties: The Properties class represents a persistent set of properties.

35. PropertyPermission: This class is for property permissions.

36. PropertyResourceBundle: PropertyResourceBundle is a concrete subclass of ResourceBundle that manages resources for a locale using a set of static strings from a property file.

37. Random: An instance of this class is used to generate a stream of pseudorandom numbers.

38. ResourceBundle: Resource bundles contain locale-specific objects.

39. ResourceBundle.Control: ResourceBundle.Control defines a set of callback methods that are invoked by the

40. ResourceBundle: getBundle factory methods during the bundle loading process.

41. Scanner: A simple text scanner which can parse primitive types and strings using regular expressions.

42. ServiceLoader: A simple service-provider loading facility.

43. SimpleTimeZone: SimpleTimeZone is a concrete subclass of TimeZone that represents a time zone for use with a Gregorian calendar.
Stack: The Stack class represents a last-in-first-out (LIFO) stack of objects.

44. StringTokenizer: The string tokenizer class allows an application to break a string into tokens.

45. Timer: A facility for threads to schedule tasks for future execution in a background thread.

46. TimerTask: A task that can be scheduled for one-time or repeated execution by a Timer.

47. TimeZone: TimeZone represents a time zone offset, and also figures out daylight savings.

48. TreeMap<K,V>: A Red-Black tree based NavigableMap implementation.

49. TreeSet: A NavigableSet implementation based on a TreeMap.

50. UUID: A class that represents an immutable universally unique identifier (UUID).

51. Vector: The Vector class implements a growable array of objects.

52. WeakHashMap<K,V>: Hash table based implementation of the Map interface, with weak keys.