# Package java.util

Contains the collections framework, legacy collection classes, event model, date and time facilities, internationalization, and miscellaneous utility classes (a string tokenizer, a random-number generator, and a bit array).

See: Description

- Interface Summary
  Interface | Description
  --- | ---
  Collection<E> | The root interface in the collection hierarchy.
  Comparator<T> | A comparison function, which imposes a total ordering on some collection of objects.
  Deque<E> | A linear collection that supports element insertion and removal at both ends.
  Enumeration<E> | An object that implements the Enumeration interface generates a series of elements, one at a time.
  EventListener | A tagging interface that all event listener interfaces must extend.
  Formattable | The `Formattable` interface must be implemented by any class that needs to perform custom formatting using the `'s'` conversion specifier of `Formatter`.
  Iterator<E> | An iterator over a collection.
  List<E> | An ordered collection (also known as a sequence).
  ListIterator<E> | An iterator for lists that allows the programmer to traverse the list in either direction, modify the list during iteration, and obtain the iterator's current position in the list.
  Map<K,V> | An object that maps keys to values.
  Map.Entry<K,V> | A map entry (key-value pair).
  NavigableMap<K,V> | A `SortedMap` extended with navigation methods returning the closest matches for given search targets.
  NavigableSet<E> | A `SortedSet` extended with navigation methods reporting closest matches for given search targets.
  Observer | A class can implement the `Observer` interface when it wants to be informed of changes in observable objects.
  Queue<E> | A collection designed for holding elements prior to processing.
  RandomAccess | Marker interface used by `List` implementations to indicate that they support fast (generally constant time) random access.
  Set<E> | A collection that contains no duplicate elements.
  SortedMap<K,V> | A `Map` that further provides a total ordering on its keys.
  SortedSet<E> | A `Set` that further provides a total ordering on its elements.

- Class Summary
  Class | Description
  --- | ---
  AbstractCollection<E> | This class provides a skeletal implementation of the `Collection` interface, to minimize the effort required to implement this interface.
  AbstractList<E> | 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<E> | This class provides skeletal implementations of some `Queue` operations.
  AbstractSequentialList<E> | 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<E> | This class provides a skeletal implementation of the `Set` interface to minimize the effort required to implement this interface.
  ArrayDeque<E> | Resizable-array implementation of the `Deque` interface.
  ArrayList<E> | 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<K extends Enum<K>,V> | A specialized `Map` implementation for use with enum type keys.
  EnumSet<E extends Enum<E>> | 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<E> | This class implements the `Set` interface, backed by a hash table (actually a `HashMap` instance).
  Hashtable<K,V> | This class implements a hashtable, 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<E> | Hash table and linked list implementation of the `Set` interface, with predictable iteration order.
  LinkedList<E> | Linked list implementation of the `List` interface.
  ListResourceBundle | `ListResourceBundle` is an abstract subclass of `ResourceBundle` that manages resources for a locale in a convenient and easy to use list.
  Locale | A `Locale` object represents a specific geographical, political, or cultural region.
  Observable | This class represents an observable object, or "data" in the model-view paradigm.
  PriorityQueue<E> | 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<S> | 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<E> | 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<E> | A `NavigableSet` implementation based on a `TreeMap`.
  UUID | A class that represents an immutable universally unique identifier (UUID).
  Vector<E> | The `Vector` class implements a growable array of objects.
  WeakHashMap<K,V> | A hashtable-based `Map` implementation with weak keys.

- Enum Summary
  Enum | Description
  --- | ---
  Formatter.BigDecimalLayoutForm |

- Exception Summary
  Exception | Description
  --- | ---
  ConcurrentModificationException | This exception may be thrown by methods that have detected concurrent modification of an object when such modification is not permissible.
  DuplicateFormatFlagsException | Unchecked exception thrown when duplicate flags are provided in the format specifier.
  EmptyStackException | Thrown by methods in the `Stack` class to indicate that the stack is empty.
  FormatFlagsConversionMismatchException | Unchecked exception thrown when a conversion and flag are incompatible.
  FormatterClosedException | Unchecked exception thrown when the formatter has been closed.
  IllegalFormatCodePointException | Unchecked exception thrown when a character with an invalid Unicode code point as defined by `Character.isValidCodePoint(int)` is passed to the `Formatter`.
  IllegalFormatConversionException | Unchecked exception thrown when the argument corresponding to the format specifier is of an incompatible type.
  IllegalFormatException | Unchecked exception thrown when a format string contains an illegal syntax or a format specifier that is incompatible with the given arguments.
  IllegalFormatFlagsException | Unchecked exception thrown when an illegal combination flags is given.
  IllegalFormatPrecisionException | Unchecked exception thrown when the precision is a negative value other than `-1`, the conversion does not support a precision, or the value is otherwise unsupported.
  IllegalFormatWidthException | Unchecked exception thrown when the format width is a negative value other than `-1` or is otherwise unsupported.
  InputMismatchException | Thrown by a `Scanner` to indicate that the token retrieved does not match the pattern for the expected type, or that the token is out of range for the expected type.
  InvalidPropertiesFormatException | Thrown to indicate that an operation could not complete because the input did not conform to the appropriate XML document type for a collection of properties, as per the `Properties` specification.
  MissingFormatArgumentException | Unchecked exception thrown when there is a format specifier which does not have a corresponding argument or if an argument index refers to an argument that does not exist.
  MissingFormatWidthException | Unchecked exception thrown when the format width is required.
  MissingResourceException | Signals that a resource is missing.
  NoSuchElementException | Thrown by the `nextElement` method of an `Enumeration` to indicate that there are no more elements in the enumeration.
  TooManyListenersException | The `TooManyListenersException` Exception is used as part of the Java Event model to annotate and implement a unicast special case of a multicast Event Source.
  UnknownFormatConversionException | Unchecked exception thrown when an unknown conversion is given.
  UnknownFormatFlagsException | Unchecked exception thrown when an unknown flag is given.

- Error Summary
  Error | Description
  --- | ---
  ServiceConfigurationError | Error thrown when something goes wrong while loading a service provider.

## Package java.util Description

Contains the collections framework, legacy collection classes, event model, date and time facilities, internationalization, and miscellaneous utility classes (a string tokenizer, a random-number generator, and a bit array).

## Package Specification

- Collections Framework Overview
- Collections Framework Annotated Outline

## Related Documentation

For overviews, tutorials, examples, guides, and tool documentation, please see:

- Collections Framework Tutorial
- Collections Framework Design FAQ

Since:
  JDK1.0

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For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

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