# Package java.util

package java.util

- Related Packages
  Package
  Description
  java.util.concurrent
  java.util.function
  java.util.stream
- Class
  Description
  AbstractCollection<E>
  Class `AbstractCollection` is an abstract implementation of the `Collection` interface.
  AbstractList<E>
  `AbstractList` is an abstract implementation of the `List` interface, optimized for a backing store which supports random access.
  AbstractMap<K,V>
  This class is an abstract implementation of the `Map` interface.
  AbstractMap.SimpleEntry<K,V>
  A key-value mapping.
  AbstractMap.SimpleImmutableEntry<K,V>
  An immutable key-value mapping.
  AbstractQueue<E>
  AbstractQueue is an abstract class which implements some of the methods in `Queue`.
  AbstractSequentialList<E>
  AbstractSequentialList is an abstract implementation of the List interface.
  AbstractSet<E>
  An AbstractSet is an abstract implementation of the Set interface.
  ArrayDeque<E>
  An implementation of Deque, backed by an array.
  ArrayList<E>
  ArrayList is an implementation of `List`, backed by an array.
  Arrays
  `Arrays` contains static methods which operate on arrays.
  BitSet
  The `BitSet` class implements a bit field.
  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.
  Collection<E>
  `Collection` is the root of the collection hierarchy.
  Collections
  `Collections` contains static methods which operate on `Collection` classes.
  Comparator<T>
  A `Comparator` is used to compare two objects to determine their ordering with respect to each other.
  ConcurrentModificationException
  An `ConcurrentModificationException` is thrown when a Collection is modified and an existing iterator on the Collection is used to modify the Collection as well.
  Date
  The class Date represents a specific instant in time, with millisecond precision.
  Deque<E>
  A kind of collection that can insert or remove element at both ends("double ended queue").
  Dictionary<K,V>
  **Note: Do not use this class since it is obsolete.
  EmptyStackException
  Thrown by methods in the Stack class to indicate that the stack is empty.
  Enumeration<T>
  An object that implements the Enumeration interface generates a series of elements, one at a time.
  EventListener
  EventListener is the superclass of all event listener interfaces.
  EventListenerProxy
  This abstract class provides a simple wrapper for objects of type `EventListener`.
  HashMap<K,V>
  HashMap is an implementation of Map.
  HashSet<E>
  HashSet is an implementation of a Set.
  Hashtable<K,V>
  Hashtable associates keys with values.
  IdentityHashMap<K,V>
  IdentityHashMap is a variant on HashMap which tests equality by reference instead of equality by value.
  Iterator<E>
  An `Iterator` is used to sequence over a collection of objects.
  LinkedHashMap<K,V>
  LinkedHashMap is a variant of HashMap.
  LinkedHashSet<E>
  LinkedHashSet is a variant of HashSet.
  LinkedList<E>
  LinkedList is an implementation of List, backed by a linked list.
  List<E>
  A `List` is a collection which maintains an ordering for its elements.
  ListIterator<E>
  An ListIterator is used to sequence over a List of objects.
  Locale
  Map<K,V>
  A `Map` is a data structure consisting of a set of keys and values in which each key is mapped to a single value.
  Map.Entry<K,V>
  `Map.Entry` is a key/value mapping contained in a `Map`.
  NavigableMap<K,V>
  NavigableMap is a SortedMap with navigation methods answering the closest matches for specified item.
  NavigableSet<E>
  NavigableSet is a SortedSet with navigation methods answering the closest matches for specified item.
  NoSuchElementException
  Thrown by the nextElement method of an Enumeration to indicate that there are no more elements in the enumeration.
  Objects
  This is a compatibility class which supports the java.util.Objects API.
  Observable
  Observable is used to notify a group of Observer objects when a change occurs.
  Observer
  `Observer` is the interface to be implemented by objects that receive notification of updates on an `Observable` object.
  PriorityQueue<E>
  A PriorityQueue holds elements on a priority heap, which orders the elements according to their natural order or according to the comparator specified at construction time.
  Queue<E>
  This kind of collection provides advanced operations compared to basic collections, such as insertion, extraction, and inspection.
  Random
  An instance of this class is used to generate a stream of pseudorandom numbers.
  RandomAccess
  RandomAccess is implemented by `List` implementations that support fast (usually constant time) random access.
  Set<E>
  A `Set` is a data structure which does not allow duplicate elements.
  SortedMap<K,V>
  A map that has its keys ordered.
  SortedSet<E>
  SortedSet is a Set which iterates over its elements in a sorted order.
  Stack<E>
  `Stack` is a Last-In/First-Out(LIFO) data structure which represents a stack of objects.
  StringTokenizer
  The `StringTokenizer` class allows an application to break a string into tokens by performing code point comparison.
  Timer
  TimerTask
  TimeZone
  TimeZone represents a time zone offset, and also figures out daylight savings.
  TreeMap<K,V>
  TreeMap is an implementation of SortedMap.
  TreeSet<E>
  TreeSet is an implementation of SortedSet.
  Vector<E>
  Vector is a variable size contiguous indexable array of objects.