# java.util # java.util ## Interfaces |-----------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | [Collection](https://developer.android.com/reference/kotlin/java/util/Collection) | The root interface in the*collection hierarchy*. | | [Comparator](https://developer.android.com/reference/kotlin/java/util/Comparator) | A comparison function, which imposes a*total ordering*on some collection of objects. | | [Deque](https://developer.android.com/reference/kotlin/java/util/Deque) | A linear collection that supports element insertion and removal at both ends. | | [Enumeration](https://developer.android.com/reference/kotlin/java/util/Enumeration) | An object that implements the Enumeration interface generates a series of elements, one at a time. | | [EventListener](https://developer.android.com/reference/kotlin/java/util/EventListener) | A tagging interface that all event listener interfaces must extend. | | [Formattable](https://developer.android.com/reference/kotlin/java/util/Formattable) | The`Formattable`interface must be implemented by any class that needs to perform custom formatting using the`'s'`conversion specifier of[java.util.Formatter](https://developer.android.com/reference/kotlin/java/util/Formatter). | | [Iterator](https://developer.android.com/reference/kotlin/java/util/Iterator) | An iterator over a collection. | | [List](https://developer.android.com/reference/kotlin/java/util/List) | An ordered collection, where the user has precise control over where in the list each element is inserted. | | [ListIterator](https://developer.android.com/reference/kotlin/java/util/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](https://developer.android.com/reference/kotlin/java/util/Map) | An object that maps keys to values. | | [NavigableMap](https://developer.android.com/reference/kotlin/java/util/NavigableMap) | A[SortedMap](https://developer.android.com/reference/kotlin/java/util/SortedMap)extended with navigation methods returning the closest matches for given search targets. | | [NavigableSet](https://developer.android.com/reference/kotlin/java/util/NavigableSet) | A[SortedSet](https://developer.android.com/reference/kotlin/java/util/SortedSet)extended with navigation methods reporting closest matches for given search targets. | | [Observer](https://developer.android.com/reference/kotlin/java/util/Observer) | A class can implement the`Observer`interface when it wants to be informed of changes in observable objects. | | [PrimitiveIterator](https://developer.android.com/reference/kotlin/java/util/PrimitiveIterator) | A base type for primitive specializations of`Iterator`. | | [Queue](https://developer.android.com/reference/kotlin/java/util/Queue) | A collection designed for holding elements prior to processing. | | [RandomAccess](https://developer.android.com/reference/kotlin/java/util/RandomAccess) | Marker interface used by`List`implementations to indicate that they support fast (generally constant time) random access. | | [SequencedCollection](https://developer.android.com/reference/kotlin/java/util/SequencedCollection) | A collection that has a well-defined encounter order, that supports operations at both ends, and that is reversible. | | [SequencedMap](https://developer.android.com/reference/kotlin/java/util/SequencedMap) | A Map that has a well-defined encounter order, that supports operations at both ends, and that is reversible. | | [SequencedSet](https://developer.android.com/reference/kotlin/java/util/SequencedSet) | A collection that is both a[SequencedCollection](https://developer.android.com/reference/kotlin/java/util/SequencedCollection)and a[Set](https://developer.android.com/reference/kotlin/java/util/Set). | | [Provider](https://developer.android.com/reference/kotlin/java/util/ServiceLoader.Provider) | Represents a service provider located by`ServiceLoader`. | | [Set](https://developer.android.com/reference/kotlin/java/util/Set) | A collection that contains no duplicate elements. | | [SortedMap](https://developer.android.com/reference/kotlin/java/util/SortedMap) | A[Map](https://developer.android.com/reference/kotlin/java/util/Map)that further provides a*total ordering*on its keys. | | [SortedSet](https://developer.android.com/reference/kotlin/java/util/SortedSet) | A[Set](https://developer.android.com/reference/kotlin/java/util/Set)that further provides a*total ordering*on its elements. | | [Spliterator](https://developer.android.com/reference/kotlin/java/util/Spliterator) | An object for traversing and partitioning elements of a source. | ## Classes |-------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | [AbstractCollection](https://developer.android.com/reference/kotlin/java/util/AbstractCollection) | This class provides a skeletal implementation of the`Collection`interface, to minimize the effort required to implement this interface. | | [AbstractList](https://developer.android.com/reference/kotlin/java/util/AbstractList) | This class provides a skeletal implementation of the[List](https://developer.android.com/reference/kotlin/java/util/List)interface to minimize the effort required to implement this interface backed by a "random access" data store (such as an array). | | [AbstractMap](https://developer.android.com/reference/kotlin/java/util/AbstractMap) | This class provides a skeletal implementation of the`Map`interface, to minimize the effort required to implement this interface. | | [AbstractQueue](https://developer.android.com/reference/kotlin/java/util/AbstractQueue) | This class provides skeletal implementations of some[Queue](https://developer.android.com/reference/kotlin/java/util/Queue)operations. | | [AbstractSequentialList](https://developer.android.com/reference/kotlin/java/util/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](https://developer.android.com/reference/kotlin/java/util/AbstractSet) | This class provides a skeletal implementation of the`Set`interface to minimize the effort required to implement this interface. | | [ArrayDeque](https://developer.android.com/reference/kotlin/java/util/ArrayDeque) | Resizable-array implementation of the[Deque](https://developer.android.com/reference/kotlin/java/util/Deque)interface. | | [ArrayList](https://developer.android.com/reference/kotlin/java/util/ArrayList) | Resizable-array implementation of the`List`interface. | | [Arrays](https://developer.android.com/reference/kotlin/java/util/Arrays) | This class contains various methods for manipulating arrays (such as sorting and searching). | | [Base64](https://developer.android.com/reference/kotlin/java/util/Base64) | This class consists exclusively of static methods for obtaining encoders and decoders for the Base64 encoding scheme. | | [BitSet](https://developer.android.com/reference/kotlin/java/util/BitSet) | This class implements a vector of bits that grows as needed. | | [Calendar](https://developer.android.com/reference/kotlin/java/util/Calendar) | The class is an abstract class that provides methods for converting between a specific instant in time and a set of[calendar fields](https://developer.android.com/reference/kotlin/java/util/Calendar#fields:kotlin.IntArray)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. | | [Collections](https://developer.android.com/reference/kotlin/java/util/Collections) | This class consists exclusively of static methods that operate on or return collections. | | [Currency](https://developer.android.com/reference/kotlin/java/util/Currency) | Represents a currency. | | [Date](https://developer.android.com/reference/kotlin/java/util/Date) | The class`Date`represents a specific instant in time, with millisecond precision. | | [Dictionary](https://developer.android.com/reference/kotlin/java/util/Dictionary) | The`Dictionary`class is the abstract parent of any class, such as`Hashtable`, which maps keys to values. | | [DoubleSummaryStatistics](https://developer.android.com/reference/kotlin/java/util/DoubleSummaryStatistics) | A state object for collecting statistics such as count, min, max, sum, and average. | | [EnumMap](https://developer.android.com/reference/kotlin/java/util/EnumMap) | A specialized[Map](https://developer.android.com/reference/kotlin/java/util/Map)implementation for use with enum type keys. | | [EnumSet](https://developer.android.com/reference/kotlin/java/util/EnumSet) | A specialized[Set](https://developer.android.com/reference/kotlin/java/util/Set)implementation for use with enum types. | | [EventListenerProxy](https://developer.android.com/reference/kotlin/java/util/EventListenerProxy) | An abstract wrapper class for an`EventListener`class which associates a set of additional parameters with the listener. | | [EventObject](https://developer.android.com/reference/kotlin/java/util/EventObject) | The root class from which all event state objects shall be derived. | | [FormattableFlags](https://developer.android.com/reference/kotlin/java/util/FormattableFlags) | FormattableFlags are passed to the[Formattable.formatTo()](https://developer.android.com/reference/kotlin/java/util/Formattable#formatTo(java.util.Formatter,%20kotlin.Int,%20kotlin.Int,%20kotlin.Int))method and modify the output format for[Formattables](https://developer.android.com/reference/kotlin/java/util/Formattable). | | [Formatter](https://developer.android.com/reference/kotlin/java/util/Formatter) | An interpreter for printf-style format strings. | | [GregorianCalendar](https://developer.android.com/reference/kotlin/java/util/GregorianCalendar) | `GregorianCalendar`is a concrete subclass of`Calendar`and provides the standard calendar system used by most of the world. | | [HashMap](https://developer.android.com/reference/kotlin/java/util/HashMap) | Hash table based implementation of the`Map`interface. | | [HashSet](https://developer.android.com/reference/kotlin/java/util/HashSet) | This class implements the`Set`interface, backed by a hash table (actually a`HashMap`instance). | | [Hashtable](https://developer.android.com/reference/kotlin/java/util/Hashtable) | This class implements a hash table, which maps keys to values. | | [HexFormat](https://developer.android.com/reference/kotlin/java/util/HexFormat) | `HexFormat`converts between bytes and chars and hex-encoded strings which may include additional formatting markup such as prefixes, suffixes, and delimiters. | | [IdentityHashMap](https://developer.android.com/reference/kotlin/java/util/IdentityHashMap) | This class implements the`Map`interface with a hash table, using reference-equality in place of object-equality when comparing keys (and values). | | [IntSummaryStatistics](https://developer.android.com/reference/kotlin/java/util/IntSummaryStatistics) | A state object for collecting statistics such as count, min, max, sum, and average. | | [LinkedHashMap](https://developer.android.com/reference/kotlin/java/util/LinkedHashMap) | Hash table and linked list implementation of the`Map`interface, with well-defined encounter order. | | [LinkedHashSet](https://developer.android.com/reference/kotlin/java/util/LinkedHashSet) | Hash table and linked list implementation of the`Set`interface, with well-defined encounter order. | | [LinkedList](https://developer.android.com/reference/kotlin/java/util/LinkedList) | Doubly-linked list implementation of the`List`and`Deque`interfaces. | | [ListResourceBundle](https://developer.android.com/reference/kotlin/java/util/ListResourceBundle) | `ListResourceBundle`is an abstract subclass of`ResourceBundle`that manages resources for a locale in a convenient and easy to use list. | | [Locale](https://developer.android.com/reference/kotlin/java/util/Locale) | A object represents a specific geographical, political, or cultural region. | | [LongSummaryStatistics](https://developer.android.com/reference/kotlin/java/util/LongSummaryStatistics) | A state object for collecting statistics such as count, min, max, sum, and average. | | [Objects](https://developer.android.com/reference/kotlin/java/util/Objects) | This class consists of`static`utility methods for operating on objects, or checking certain conditions before operation. | | [Observable](https://developer.android.com/reference/kotlin/java/util/Observable) | This class represents an observable object, or "data" in the model-view paradigm. | | [Optional](https://developer.android.com/reference/kotlin/java/util/Optional) | A container object which may or may not contain a non-`null`value. | | [OptionalDouble](https://developer.android.com/reference/kotlin/java/util/OptionalDouble) | A container object which may or may not contain a`double`value. | | [OptionalInt](https://developer.android.com/reference/kotlin/java/util/OptionalInt) | A container object which may or may not contain an`int`value. | | [OptionalLong](https://developer.android.com/reference/kotlin/java/util/OptionalLong) | A container object which may or may not contain a`long`value. | | [PriorityQueue](https://developer.android.com/reference/kotlin/java/util/PriorityQueue) | An unbounded priority[queue](https://developer.android.com/reference/kotlin/java/util/Queue)based on a priority heap. | | [Properties](https://developer.android.com/reference/kotlin/java/util/Properties) | The`Properties`class represents a persistent set of properties. | | [PropertyPermission](https://developer.android.com/reference/kotlin/java/util/PropertyPermission) | Legacy security code; do not use. | | [PropertyResourceBundle](https://developer.android.com/reference/kotlin/java/util/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](https://developer.android.com/reference/kotlin/java/util/Random) | An instance of this class is used to generate a stream of pseudorandom numbers; its period is only 248. | | [ResourceBundle](https://developer.android.com/reference/kotlin/java/util/ResourceBundle) | Resource bundles contain locale-specific objects. | | [Scanner](https://developer.android.com/reference/kotlin/java/util/Scanner) | A simple text scanner which can parse primitive types and strings using regular expressions. | | [ServiceLoader](https://developer.android.com/reference/kotlin/java/util/ServiceLoader) | A facility to load implementations of a service. | | [SimpleTimeZone](https://developer.android.com/reference/kotlin/java/util/SimpleTimeZone) | `SimpleTimeZone`is a concrete subclass of`TimeZone`that represents a time zone for use with a Gregorian calendar. | | [Spliterators](https://developer.android.com/reference/kotlin/java/util/Spliterators) | Static classes and methods for operating on or creating instances of[Spliterator](https://developer.android.com/reference/kotlin/java/util/Spliterator)and its primitive specializations[Spliterator.OfInt](https://developer.android.com/reference/kotlin/java/util/Spliterator.OfInt),[Spliterator.OfLong](https://developer.android.com/reference/kotlin/java/util/Spliterator.OfLong), and[Spliterator.OfDouble](https://developer.android.com/reference/kotlin/java/util/Spliterator.OfDouble). | | [SplittableRandom](https://developer.android.com/reference/kotlin/java/util/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](https://developer.android.com/reference/kotlin/java/util/Stack) | The`Stack`class represents a last-in-first-out (LIFO) stack of objects. | | [StringJoiner](https://developer.android.com/reference/kotlin/java/util/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](https://developer.android.com/reference/kotlin/java/util/StringTokenizer) | The string tokenizer class allows an application to break a string into tokens. | | [Timer](https://developer.android.com/reference/kotlin/java/util/Timer) | A facility for threads to schedule tasks for future execution in a background thread. | | [TimerTask](https://developer.android.com/reference/kotlin/java/util/TimerTask) | A task that can be scheduled for one-time or repeated execution by a[Timer](https://developer.android.com/reference/kotlin/java/util/Timer). | | [TimeZone](https://developer.android.com/reference/kotlin/java/util/TimeZone) | represents a time zone offset, and also figures out daylight savings. | | [TreeMap](https://developer.android.com/reference/kotlin/java/util/TreeMap) | A Red-Black tree based[NavigableMap](https://developer.android.com/reference/kotlin/java/util/NavigableMap)implementation. | | [TreeSet](https://developer.android.com/reference/kotlin/java/util/TreeSet) | A[NavigableSet](https://developer.android.com/reference/kotlin/java/util/NavigableSet)implementation based on a[TreeMap](https://developer.android.com/reference/kotlin/java/util/TreeMap). | | [UUID](https://developer.android.com/reference/kotlin/java/util/UUID) | A class that represents an immutable universally unique identifier (UUID). | | [Vector](https://developer.android.com/reference/kotlin/java/util/Vector) | The`Vector`class implements a growable array of objects. | | [WeakHashMap](https://developer.android.com/reference/kotlin/java/util/WeakHashMap) | Hash table based implementation of the`Map`interface, with*weak keys*. | ## Exceptions |-------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | [ConcurrentModificationException](https://developer.android.com/reference/kotlin/java/util/ConcurrentModificationException) | This exception may be thrown by methods that have detected concurrent modification of an object when such modification is not permissible. | | [DuplicateFormatFlagsException](https://developer.android.com/reference/kotlin/java/util/DuplicateFormatFlagsException) | Unchecked exception thrown when duplicate flags are provided in the format specifier. | | [EmptyStackException](https://developer.android.com/reference/kotlin/java/util/EmptyStackException) | Thrown by methods in the`Stack`class to indicate that the stack is empty. | | [FormatFlagsConversionMismatchException](https://developer.android.com/reference/kotlin/java/util/FormatFlagsConversionMismatchException) | Unchecked exception thrown when a conversion and flag are incompatible. | | [FormatterClosedException](https://developer.android.com/reference/kotlin/java/util/FormatterClosedException) | Unchecked exception thrown when the formatter has been closed. | | [IllegalFormatCodePointException](https://developer.android.com/reference/kotlin/java/util/IllegalFormatCodePointException) | Unchecked exception thrown when a character with an invalid Unicode code point as defined by[Character.isValidCodePoint](https://developer.android.com/reference/kotlin/java/lang/Character.html#isValidCodePoint(kotlin.Int))is passed to the[Formatter](https://developer.android.com/reference/kotlin/java/util/Formatter). | | [IllegalFormatConversionException](https://developer.android.com/reference/kotlin/java/util/IllegalFormatConversionException) | Unchecked exception thrown when the argument corresponding to the format specifier is of an incompatible type. | | [IllegalFormatException](https://developer.android.com/reference/kotlin/java/util/IllegalFormatException) | Unchecked exception thrown when a format string contains an illegal syntax or a format specifier that is incompatible with the given arguments. | | [IllegalFormatFlagsException](https://developer.android.com/reference/kotlin/java/util/IllegalFormatFlagsException) | Unchecked exception thrown when an illegal combination flags is given. | | [IllegalFormatPrecisionException](https://developer.android.com/reference/kotlin/java/util/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](https://developer.android.com/reference/kotlin/java/util/IllegalFormatWidthException) | Unchecked exception thrown when the format width is a negative value other than`-1`or is otherwise unsupported. | | [IllformedLocaleException](https://developer.android.com/reference/kotlin/java/util/IllformedLocaleException) | Thrown by methods in[Locale](https://developer.android.com/reference/kotlin/java/util/Locale)and[Locale.Builder](https://developer.android.com/reference/kotlin/java/util/Locale.Builder)to indicate that an argument is not a well-formed BCP 47 tag. | | [InputMismatchException](https://developer.android.com/reference/kotlin/java/util/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](https://developer.android.com/reference/kotlin/java/util/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](https://developer.android.com/reference/kotlin/java/util/Properties)specification. | | [MissingFormatArgumentException](https://developer.android.com/reference/kotlin/java/util/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](https://developer.android.com/reference/kotlin/java/util/MissingFormatWidthException) | Unchecked exception thrown when the format width is required. | | [MissingResourceException](https://developer.android.com/reference/kotlin/java/util/MissingResourceException) | Signals that a resource is missing. | | [NoSuchElementException](https://developer.android.com/reference/kotlin/java/util/NoSuchElementException) | Thrown by various accessor methods to indicate that the element being requested does not exist. | | [ServiceConfigurationError](https://developer.android.com/reference/kotlin/java/util/ServiceConfigurationError) | Error thrown when something goes wrong while locating, loading, or instantiating a service provider. | | [TooManyListenersException](https://developer.android.com/reference/kotlin/java/util/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](https://developer.android.com/reference/kotlin/java/util/UnknownFormatConversionException) | Unchecked exception thrown when an unknown conversion is given. | | [UnknownFormatFlagsException](https://developer.android.com/reference/kotlin/java/util/UnknownFormatFlagsException) | Unchecked exception thrown when an unknown flag is given. |