Module java.base

Package java.util

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:

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

Since:
1.0
  • 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 unmodifiable Entry maintaining a key and a 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.
    Collection<E>
    The root interface in the collection hierarchy.
    Collections
    This class consists exclusively of static methods that operate on or return collections.
    Comparator<T>
    A comparison function, which imposes a total ordering on some collection of objects.
    ConcurrentModificationException
    This exception may be thrown by methods that have detected concurrent modification of an object when such modification is not permissible.
    Currency
    Represents a currency.
    Date
    The class Date represents a specific instant in time, with millisecond precision.
    Deque<E>
    A linear collection that supports element insertion and removal at both ends.
    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.
    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.
    Enumeration<E>
    An object that implements the Enumeration interface generates a series of elements, one at a time.
    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.
    EventListener
    A tagging interface that all event listener interfaces must extend.
    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.
    FormatFlagsConversionMismatchException
    Unchecked exception thrown when a conversion and flag are incompatible.
    FormatProcessorPREVIEW
    Preview.
    This StringTemplate.ProcessorPREVIEW constructs a String result using Formatter specifications and values found in the StringTemplatePREVIEW.
    Formattable
    The Formattable interface must be implemented by any class that needs to perform custom formatting using the 's' conversion specifier of Formatter.
    FormattableFlags
    FormattableFlags are passed to the Formattable.formatTo() method and modify the output format for Formattables.
    Formatter
    An interpreter for printf-style format strings.
    Formatter.BigDecimalLayoutForm
    Enum for BigDecimal formatting.
    FormatterClosedException
    Unchecked exception thrown when the formatter has been closed.
    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.
    HexFormat
    HexFormat converts between bytes and chars and hex-encoded strings which may include additional formatting markup such as prefixes, suffixes, and delimiters.
    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).
    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.
    IntSummaryStatistics
    A state object for collecting statistics such as count, min, max, sum, and average.
    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.
    Iterator<E>
    An iterator over a collection.
    LinkedHashMap<K,V>
    Hash table and linked list implementation of the Map interface, with well-defined encounter order.
    LinkedHashSet<E>
    Hash table and linked list implementation of the Set interface, with well-defined encounter order.
    LinkedList<E>
    Doubly-linked list implementation of the List and Deque interfaces.
    List<E>
    An ordered collection, where the user has precise control over where in the list each element is inserted.
    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.
    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.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.
    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.
    Map<K,V>
    An object that maps keys to values.
    Map.Entry<K,V>
    A map entry (key-value pair).
    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.
    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.
    NoSuchElementException
    Thrown by various accessor methods to indicate that the element being requested does not exist.
    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.
    Observer
    Deprecated.
    This interface has 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.
    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.
    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.
    Queue<E>
    A collection designed for holding elements prior to processing.
    Random
    An instance of this class is used to generate a stream of pseudorandom numbers; its period is only 248.
    RandomAccess
    Marker interface used by List implementations to indicate that they support fast (generally constant time) random access.
    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.
    SequencedCollection<E>
    A collection that has a well-defined encounter order, that supports operations at both ends, and that is reversible.
    SequencedMap<K,V>
    A Map that has a well-defined encounter order, that supports operations at both ends, and that is reversible.
    SequencedSet<E>
    A collection that is both a SequencedCollection and a Set.
    ServiceConfigurationError
    Error thrown when something goes wrong while locating, loading, or instantiating a service provider.
    ServiceLoader<S>
    A facility to load implementations of a service.
    ServiceLoader.Provider<S>
    Represents a service provider located by ServiceLoader.
    Set<E>
    A collection that contains no duplicate elements.
    SimpleTimeZone
    SimpleTimeZone is a concrete subclass of TimeZone that represents a time zone for use with a Gregorian calendar.
    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.
    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 (with period 264) 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.
    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.
    TreeMap<K,V>
    A Red-Black tree based NavigableMap implementation.
    TreeSet<E>
    A NavigableSet implementation based on a TreeMap.
    UnknownFormatConversionException
    Unchecked exception thrown when an unknown conversion is given.
    UnknownFormatFlagsException
    Unchecked exception thrown when an unknown flag is given.
    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.