package

java.util

Contains the collection classes, and the date and time facilities.

Interfaces

Collection<E> Collection is the root of the collection hierarchy. 
Comparator<T> A Comparator is used to compare two objects to determine their ordering with respect to each other. 
Deque<E> A kind of collection that can insert or remove element at both ends("double ended queue"). 
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. 
Iterator<E> An Iterator is used to sequence over a collection of objects. 
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. 
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. 
Observer Observer is the interface to be implemented by objects that receive notification of updates on an Observable object. 
Queue<E> This kind of collection provides advanced operations compared to basic collections, such as insertion, extraction, and inspection. 
RandomAccess Marker interface used by List implementations to indicate that they support fast (generally 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. 

Classes

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 class for getting and setting dates using a set of integer fields such as YEAR, MONTH, DAY, and so on. 
Collections Collections contains static methods which operate on Collection classes. 
Date The class Date represents a specific instant in time, with millisecond precision. 
Dictionary<K, V> Note: Do not use this class since it is obsolete. 
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> This class implements a hashtable, which maps keys to values. 
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. 
Observable Observable is used to notify a group of Observer objects when a change occurs. 
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. 
Random An instance of this class is used to generate a stream of pseudorandom numbers. 
Stack<T> The Stack class represents a last-in-first-out (LIFO) stack of objects. 
StringTokenizer The StringTokenizer class allows an application to break a string into tokens by performing code point comparison. 
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> TreeMap is an implementation of SortedMap. 
TreeSet<E> TreeSet is an implementation of SortedSet. 
Vector<E> The Vector class implements a growable array of objects. 

Exceptions

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. 
EmptyStackException Thrown by methods in the Stack class to indicate that the stack is empty. 
NoSuchElementException Thrown by the nextElement method of an Enumeration to indicate that there are no more elements in the enumeration.