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## 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
Collection | The root interface in the collection hierarchy.
Comparator | A comparison function, which imposes a total ordering on some collection of objects.
Enumeration | 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.
Iterator | An iterator over a collection.
List | An ordered collection (also known as a sequence).
ListIterator | 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 | An object that maps keys to values.
Map.Entry | A map entry (key-value pair).
Observer | A class can implement the `Observer` interface when it wants to be informed of changes in observable objects.
RandomAccess | Marker interface used by `List` implementations to indicate that they support fast (generally constant time) random access.
Set | A collection that contains no duplicate elements.
SortedMap | A map that further guarantees that it will be in ascending key order, sorted according to the natural ordering of its keys (see the `Comparable` interface), or by a comparator provided at sorted map creation time.
SortedSet | A set that further guarantees that its iterator will traverse the set in ascending element order, sorted according to the natural ordering of its elements (see Comparable), or by a Comparator provided at sorted set creation time.

Class Summary
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 | This class provides a skeletal implementation of the `Map` interface, to minimize the effort required to implement this interface.
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.
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 | `Calendar` is an abstract base class for converting between a `Date` object and a set of integer fields such as `YEAR`, `MONTH`, `DAY`, `HOUR`, and so on.
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 | The `Dictionary` class is the abstract parent of any class, such as `Hashtable`, which maps keys to values.
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.
GregorianCalendar | `GregorianCalendar` is a concrete subclass of `Calendar` and provides the standard calendar used by most of the world.
HashMap | 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 | This class implements a hashtable, which maps keys to values.
IdentityHashMap | This class implements the `Map` interface with a hash table, using reference-equality in place of object-equality when comparing keys (and values).
LinkedHashMap | 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 | 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.
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.
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 | Red-Black tree based implementation of the `SortedMap` interface.
TreeSet | This class implements the `Set` interface, backed by a `TreeMap` instance.
Vector | The `Vector` class implements a growable array of objects.
WeakHashMap | A hashtable-based `Map` implementation with weak keys.

Exception Summary
ConcurrentModificationException | This exception may be thrown by methods that have detected concurrent modification of an object when such modification is not permissible.
EmptyStackException | Thrown by methods in the `Stack` class to indicate that the stack is empty.
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.

## 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 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

Copyright 2002 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.