The java.util package in Java is a part of the standard library that contains a large collection of utility classes and interfaces for various functionalities such as data structures, date and time, event model, and more.
- AbstractCollection: This class provides a skeletal implementation of the Collection interface, to minimize the effort required to implement this interface.
- 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).
- AbstractMap<K,V>: This class provides a skeletal implementation of the Map interface, to minimize the effort required to implement this interface.
- AbstractMap.SimpleEntry<K,V>: An Entry maintaining a key and a value.
- AbstractMap.SimpleImmutableEntry<K,V>: An Entry maintaining an immutable key and value.
- AbstractQueue: This class provides skeletal implementations of some Queue operations.
- 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).
- 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.
- ArrayList: Resizable-array implementation of the List interface.
- Arrays: This class contains various methods for manipulating arrays (such as sorting and searching).
- 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.
- Collections: This class consists exclusively of static methods that operate on or return collections.
- Currency: Represents a currency.
- Date: The class Date represents a specific instant in time, with millisecond precision.
- Dictionary<K,V>: The Dictionary class is the abstract parent of any class, such as Hashtable, which maps keys to values.
- EnumMap,V>: A specialized Map implementation for use with enum type keys.
- EnumSet: A specialized Set implementation for use with enum types.
- EventListenerProxy: An abstract wrapper class for an EventListener class which associates a set of additional parameters with the listener.
- EventObject: The root class from which all event state objects shall be derived.
- FormattableFlags: FomattableFlags are passed to the Formattable.formatTo() method and modify the output format for Formattables.
- Formatter: An interpreter for printf-style format strings.
- GregorianCalendar: GregorianCalendar is a concrete subclass of Calendar and provides the standard calendar system used by most of the world.
- HashMap<K,V>: Hash table based implementation of the Map interface.
- HashSet: This class implements the Set interface, backed by a hash table (actually a HashMap instance).
- Hashtable<K,V>: This class implements a hash table, which maps keys to values.
- 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).
- LinkedHashMap<K,V>: Hash table and linked list implementation of the Map interface, with predictable iteration order.
- LinkedHashSet: Hash table and linked list implementation of the Set interface, with predictable iteration order.
- LinkedList: Doubly-linked list implementation of the List and Deque interfaces.
- ListResourceBundle: ListResourceBundle is an abstract subclass of ResourceBundle that manages resources for a locale in a convenient and easy to use list.
- Locale – Set 1, Set 2: A Locale object represents a specific geographical, political, or cultural region.
- 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.
- Observable: This class represents an observable object, or “data” in the model-view paradigm.
- PriorityQueue: An unbounded priority queue based on a priority heap.
- Properties: The Properties class represents a persistent set of properties.
- PropertyPermission: This class is for property permissions.
- PropertyResourceBundle: PropertyResourceBundle is a concrete subclass of ResourceBundle that manages resources for a locale using a set of static strings from a property file.
- Random: An instance of this class is used to generate a stream of pseudorandom numbers.
- ResourceBundle: Resource bundles contain locale-specific objects.
- ResourceBundle.Control: ResourceBundle.Control defines a set of callback methods that are invoked by the ResourceBundle.getBundle factory methods during the bundle loading process.
- Scanner: A simple text scanner which can parse primitive types and strings using regular expressions.
- ServiceLoader: A simple service-provider loading facility.
- 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.
- StringTokenizer: The string tokenizer class allows an application to break a string into tokens.
- Timer: A facility for threads to schedule tasks for future execution in a background thread.
- TimerTask: A task that can be scheduled for one-time or repeated execution by a Timer.
- TimeZone: TimeZone represents a time zone offset, and also figures out daylight savings.
- TreeMap<K,V>: A Red-Black tree based NavigableMap implementation.
- TreeSet: A NavigableSet implementation based on a TreeMap.
- UUID: A class that represents an immutable universally unique identifier (UUID).
- Vector: The Vector class implements a growable array of objects.
- WeakHashMap<K,V>: Hash table based implementation of the Map interface, with weak keys.
