Module java.base

Package java.util

Contains the collections framework, some internationalization support classes, a service loader, properties, random number generation, string parsing and scanning classes, base64 encoding and decoding, a bit array, and several miscellaneous utility classes. This package also contains legacy collection classes and legacy date and time classes.

Java Collections Framework

For an overview, API outline, and design rationale, please see:

• Collections Framework Documentation

For a tutorial and programming guide with examples of use of the collections framework, please see:

• Collections Framework Tutorial

Since:

1.0

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	Deprecated. This interface has been deprecated.
PrimitiveIterator<T,T_CONS>	A base type for primitive specializations of Iterator.
PrimitiveIterator.OfDouble	An Iterator specialized for double values.
PrimitiveIterator.OfInt	An Iterator specialized for int values.
PrimitiveIterator.OfLong	An Iterator specialized for long values.
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.
ServiceLoader.Provider<S>	Represents a service provider located by ServiceLoader.
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.
Spliterator<T>	An object for traversing and partitioning elements of a source.
Spliterator.OfDouble	A Spliterator specialized for double values.
Spliterator.OfInt	A Spliterator specialized for int values.
Spliterator.OfLong	A Spliterator specialized for long values.
Spliterator.OfPrimitive<T,T_CONS,T_SPLITR extends Spliterator.OfPrimitive<T,T_CONS,T_SPLITR>>	A Spliterator specialized for primitive values.

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).
Base64	This class consists exclusively of static methods for obtaining encoders and decoders for the Base64 encoding scheme.
Base64.Decoder	This class implements a decoder for decoding byte data using the Base64 encoding scheme as specified in RFC 4648 and RFC 2045.
Base64.Encoder	This class implements an encoder for encoding byte data using the Base64 encoding scheme as specified in RFC 4648 and RFC 2045.
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.
Calendar.Builder	Calendar.Builder is used for creating a Calendar from various date-time parameters.
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.
DoubleSummaryStatistics	A state object for collecting statistics such as count, min, max, sum, and average.
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<T extends EventListener>	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	FormattableFlags 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 hash table, 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).
IntSummaryStatistics	A state object for collecting statistics such as count, min, max, sum, and average.
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>	Doubly-linked list implementation of the List and Deque interfaces.
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.
Locale.Builder	Builder is used to build instances of Locale from values configured by the setters.
Locale.LanguageRange	This class expresses a Language Range defined in RFC 4647 Matching of Language Tags.
LongSummaryStatistics	A state object for collecting statistics such as count, min, max, sum, and average.
Objects	This class consists of static utility methods for operating on objects, or checking certain conditions before operation.
Observable	Deprecated. This class and the Observer interface have been deprecated.
Optional<T>	A container object which may or may not contain a non-null value.
OptionalDouble	A container object which may or may not contain a double value.
OptionalInt	A container object which may or may not contain an int value.
OptionalLong	A container object which may or may not contain a long value.
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 facility to load implementations of a service.
SimpleTimeZone	SimpleTimeZone is a concrete subclass of TimeZone that represents a time zone for use with a Gregorian calendar.
Spliterators	Static classes and methods for operating on or creating instances of Spliterator and its primitive specializations Spliterator.OfInt, Spliterator.OfLong, and Spliterator.OfDouble.
Spliterators.AbstractDoubleSpliterator	An abstract Spliterator.OfDouble that implements trySplit to permit limited parallelism.
Spliterators.AbstractIntSpliterator	An abstract Spliterator.OfInt that implements trySplit to permit limited parallelism.
Spliterators.AbstractLongSpliterator	An abstract Spliterator.OfLong that implements trySplit to permit limited parallelism.
Spliterators.AbstractSpliterator<T>	An abstract Spliterator that implements trySplit to permit limited parallelism.
SplittableRandom	A generator of uniform pseudorandom values applicable for use in (among other contexts) isolated parallel computations that may generate subtasks.
Stack<E>	The Stack class represents a last-in-first-out (LIFO) stack of objects.
StringJoiner	StringJoiner is used to construct a sequence of characters separated by a delimiter and optionally starting with a supplied prefix and ending with a supplied suffix.
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>	Hash table based implementation of the Map interface, with weak keys.

Enum Summary

Enum	Description
Formatter.BigDecimalLayoutForm	Enum for BigDecimal formatting.
Locale.Category	Enum for locale categories.
Locale.FilteringMode	This enum provides constants to select a filtering mode for locale matching.
Locale.IsoCountryCode	Enum for specifying the type defined in ISO 3166.

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.
IllformedLocaleException	Thrown by methods in Locale and Locale.Builder to indicate that an argument is not a well-formed BCP 47 tag.
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 various accessor methods to indicate that the element being requested does not exist.
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 locating, loading, or instantiating a service provider.