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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 2003 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.