Uses of Interface
java8.util.function.Function

Packages that use Function

Package	Description
java8.util	Provides some of the new java.util classes and implementations of static and default interface methods added in Java 8 and, in addition, the JEP 269: Convenience Factory Methods for Collections that were introduced in Java 9.
java8.util.concurrent	The Java 7 and Java 8 utility classes commonly used in concurrent programming.
java8.util.function	Functional interfaces provide target types for lambda expressions and method references.
java8.util.stream	Classes to support functional-style operations on streams of elements, such as map-reduce transformations on collections.

Uses of Function in java8.util

Methods in java8.util with parameters of type Function

Modifier and Type	Method and Description
static <T,U extends Comparable<? super U>> Comparator<T>	Comparators.comparing(Function<? super T,? extends U> keyExtractor) Accepts a function that extracts a Comparable sort key from a type T, and returns a Comparator<T> that compares by that sort key.
static <T,U> Comparator<T>	Comparators.comparing(Function<? super T,? extends U> keyExtractor, Comparator<? super U> keyComparator) Accepts a function that extracts a sort key from a type T, and returns a Comparator<T> that compares by that sort key using the specified Comparator.
static <K,V> V	Maps.computeIfAbsent(Map<K,V> map, K key, Function<? super K,? extends V> mappingFunction) If the specified key is not already associated with a value (or is mapped to null), attempts to compute its value using the given mapping function and enters it into the passed map unless null.
<U> Optional<U>	Optional.flatMap(Function<? super T,? extends Optional<? extends U>> mapper) If a value is present, returns the result of applying the given Optional-bearing mapping function to the value, otherwise returns an empty Optional.
<U> Optional<U>	Optional.map(Function<? super T,? extends U> mapper) If a value is present, returns an Optional describing (as if by Optional.ofNullable(T)) the result of applying the given mapping function to the value, otherwise returns an empty Optional.
static <T,U extends Comparable<? super U>> Comparator<T>	Comparators.thenComparing(Comparator<? super T> this_, Function<? super T,? extends U> keyExtractor) Returns a lexicographic-order comparator with a function that extracts a Comparable sort key.
static <T,U> Comparator<T>	Comparators.thenComparing(Comparator<? super T> this_, Function<? super T,? extends U> keyExtractor, Comparator<? super U> keyComparator) Returns a lexicographic-order comparator with a function that extracts a key to be compared with the given Comparator.

Uses of Function in java8.util.concurrent

Methods in java8.util.concurrent with parameters of type Function

Modifier and Type	Method and Description
static <K,V> V	ConcurrentMaps.computeIfAbsent(ConcurrentMap<K,V> map, K key, Function<? super K,? extends V> mappingFunction) If the specified key is not already associated with a value (or is mapped to null), attempts to compute its value using the given mapping function and enters it into the passed map unless null.

Uses of Function in java8.util.function

Subinterfaces of Function in java8.util.function

Modifier and Type	Interface and Description
interface	UnaryOperator<T> Represents an operation on a single operand that produces a result of the same type as its operand.

Methods in java8.util.function that return Function

Modifier and Type	Method and Description
static <R,T,V> Function<T,V>	Functions.andThen(Function<? super T,? extends R> this_, Function<? super R,? extends V> after) Returns a composed function that first applies the this_ function to its input, and then applies the after function to the result.
static <R,T,V> Function<V,R>	Functions.compose(Function<? super T,? extends R> this_, Function<? super V,? extends T> before) Returns a composed function that first applies the before function to its input, and then applies the this_ function to the result.
static <T> Function<T,T>	Functions.identity() Returns a function that always returns its input argument.

Methods in java8.util.function with parameters of type Function

Modifier and Type	Method and Description
static <R,T,U,V> BiFunction<T,U,V>	BiFunctions.andThen(BiFunction<? super T,? super U,? extends R> this_, Function<? super R,? extends V> after) Returns a composed function that first applies the this_ function to its inputs, and then applies the after function to the result.
static <R,T,V> Function<T,V>	Functions.andThen(Function<? super T,? extends R> this_, Function<? super R,? extends V> after) Returns a composed function that first applies the this_ function to its input, and then applies the after function to the result.
static <R,T,V> Function<T,V>	Functions.andThen(Function<? super T,? extends R> this_, Function<? super R,? extends V> after) Returns a composed function that first applies the this_ function to its input, and then applies the after function to the result.
static <R,T,V> Function<V,R>	Functions.compose(Function<? super T,? extends R> this_, Function<? super V,? extends T> before) Returns a composed function that first applies the before function to its input, and then applies the this_ function to the result.
static <R,T,V> Function<V,R>	Functions.compose(Function<? super T,? extends R> this_, Function<? super V,? extends T> before) Returns a composed function that first applies the before function to its input, and then applies the this_ function to the result.

Uses of Function in java8.util.stream

Methods in java8.util.stream that return Function

Modifier and Type	Method and Description
Function<A,R>	Collector.finisher() Perform the final transformation from the intermediate accumulation type A to the final result type R.

Methods in java8.util.stream with parameters of type Function

Modifier and Type	Method and Description
static <T,A,R,RR> Collector<T,A,RR>	Collectors.collectingAndThen(Collector<T,A,R> downstream, Function<R,RR> finisher) Adapts a Collector to perform an additional finishing transformation.
<R> Stream<R>	Stream.flatMap(Function<? super T,? extends Stream<? extends R>> mapper) Returns a stream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element.
static <T,U,A,R> Collector<T,?,R>	Collectors.flatMapping(Function<? super T,? extends Stream<? extends U>> mapper, Collector<? super U,A,R> downstream) Adapts a Collector accepting elements of type U to one accepting elements of type T by applying a flat mapping function to each input element before accumulation.
DoubleStream	Stream.flatMapToDouble(Function<? super T,? extends DoubleStream> mapper) Returns an DoubleStream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element.
IntStream	Stream.flatMapToInt(Function<? super T,? extends IntStream> mapper) Returns an IntStream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element.
LongStream	Stream.flatMapToLong(Function<? super T,? extends LongStream> mapper) Returns an LongStream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element.
static <T,K> Collector<T,?,Map<K,List<T>>>	Collectors.groupingBy(Function<? super T,? extends K> classifier) Returns a Collector implementing a "group by" operation on input elements of type T, grouping elements according to a classification function, and returning the results in a Map.
static <T,K,A,D> Collector<T,?,Map<K,D>>	Collectors.groupingBy(Function<? super T,? extends K> classifier, Collector<? super T,A,D> downstream) Returns a Collector implementing a cascaded "group by" operation on input elements of type T, grouping elements according to a classification function, and then performing a reduction operation on the values associated with a given key using the specified downstream Collector.
static <T,K,D,A,M extends Map<K,D>> Collector<T,?,M>	Collectors.groupingBy(Function<? super T,? extends K> classifier, Supplier<M> mapFactory, Collector<? super T,A,D> downstream) Returns a Collector implementing a cascaded "group by" operation on input elements of type T, grouping elements according to a classification function, and then performing a reduction operation on the values associated with a given key using the specified downstream Collector.
static <T,K> Collector<T,?,ConcurrentMap<K,List<T>>>	Collectors.groupingByConcurrent(Function<? super T,? extends K> classifier) Returns a concurrent Collector implementing a "group by" operation on input elements of type T, grouping elements according to a classification function.
static <T,K,A,D> Collector<T,?,ConcurrentMap<K,D>>	Collectors.groupingByConcurrent(Function<? super T,? extends K> classifier, Collector<? super T,A,D> downstream) Returns a concurrent Collector implementing a cascaded "group by" operation on input elements of type T, grouping elements according to a classification function, and then performing a reduction operation on the values associated with a given key using the specified downstream Collector.
static <T,K,A,D,M extends ConcurrentMap<K,D>> Collector<T,?,M>	Collectors.groupingByConcurrent(Function<? super T,? extends K> classifier, Supplier<M> mapFactory, Collector<? super T,A,D> downstream) Returns a concurrent Collector implementing a cascaded "group by" operation on input elements of type T, grouping elements according to a classification function, and then performing a reduction operation on the values associated with a given key using the specified downstream Collector.
<R> Stream<R>	Stream.map(Function<? super T,? extends R> mapper) Returns a stream consisting of the results of applying the given function to the elements of this stream.
static <T,U,A,R> Collector<T,?,R>	Collectors.mapping(Function<? super T,? extends U> mapper, Collector<? super U,A,R> downstream) Adapts a Collector accepting elements of type U to one accepting elements of type T by applying a mapping function to each input element before accumulation.
static <T,A,R> Collector<T,A,R>	Collectors.of(Supplier<A> supplier, BiConsumer<A,T> accumulator, BinaryOperator<A> combiner, Function<A,R> finisher, Collector.Characteristics... characteristics) Returns a new Collector described by the given supplier, accumulator, combiner, and finisher functions.
static <T,U> Collector<T,?,U>	Collectors.reducing(U identity, Function<? super T,? extends U> mapper, BinaryOperator<U> op) Returns a Collector which performs a reduction of its input elements under a specified mapping function and BinaryOperator.
static <T,K,U> Collector<T,?,ConcurrentMap<K,U>>	Collectors.toConcurrentMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper) Returns a concurrent Collector that accumulates elements into a ConcurrentMap whose keys and values are the result of applying the provided mapping functions to the input elements.
static <T,K,U> Collector<T,?,ConcurrentMap<K,U>>	Collectors.toConcurrentMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper) Returns a concurrent Collector that accumulates elements into a ConcurrentMap whose keys and values are the result of applying the provided mapping functions to the input elements.
static <T,K,U> Collector<T,?,ConcurrentMap<K,U>>	Collectors.toConcurrentMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper, BinaryOperator<U> mergeFunction) Returns a concurrent Collector that accumulates elements into a ConcurrentMap whose keys and values are the result of applying the provided mapping functions to the input elements.
static <T,K,U> Collector<T,?,ConcurrentMap<K,U>>	Collectors.toConcurrentMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper, BinaryOperator<U> mergeFunction) Returns a concurrent Collector that accumulates elements into a ConcurrentMap whose keys and values are the result of applying the provided mapping functions to the input elements.
static <T,K,U,M extends ConcurrentMap<K,U>> Collector<T,?,M>	Collectors.toConcurrentMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper, BinaryOperator<U> mergeFunction, Supplier<M> mapFactory) Returns a concurrent Collector that accumulates elements into a ConcurrentMap whose keys and values are the result of applying the provided mapping functions to the input elements.
static <T,K,U,M extends ConcurrentMap<K,U>> Collector<T,?,M>	Collectors.toConcurrentMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper, BinaryOperator<U> mergeFunction, Supplier<M> mapFactory) Returns a concurrent Collector that accumulates elements into a ConcurrentMap whose keys and values are the result of applying the provided mapping functions to the input elements.
static <T,K,U> Collector<T,?,Map<K,U>>	Collectors.toMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper) Returns a Collector that accumulates elements into a Map whose keys and values are the result of applying the provided mapping functions to the input elements.
static <T,K,U> Collector<T,?,Map<K,U>>	Collectors.toMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper) Returns a Collector that accumulates elements into a Map whose keys and values are the result of applying the provided mapping functions to the input elements.
static <T,K,U> Collector<T,?,Map<K,U>>	Collectors.toMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper, BinaryOperator<U> mergeFunction) Returns a Collector that accumulates elements into a Map whose keys and values are the result of applying the provided mapping functions to the input elements.
static <T,K,U> Collector<T,?,Map<K,U>>	Collectors.toMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper, BinaryOperator<U> mergeFunction) Returns a Collector that accumulates elements into a Map whose keys and values are the result of applying the provided mapping functions to the input elements.
static <T,K,U,M extends Map<K,U>> Collector<T,?,M>	Collectors.toMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper, BinaryOperator<U> mergeFunction, Supplier<M> mapFactory) Returns a Collector that accumulates elements into a Map whose keys and values are the result of applying the provided mapping functions to the input elements.
static <T,K,U,M extends Map<K,U>> Collector<T,?,M>	Collectors.toMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper, BinaryOperator<U> mergeFunction, Supplier<M> mapFactory) Returns a Collector that accumulates elements into a Map whose keys and values are the result of applying the provided mapping functions to the input elements.
static <T,K,U> Collector<T,?,Map<K,U>>	Collectors.toUnmodifiableMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper) Returns a Collector that accumulates the input elements into an unmodifiable Map, whose keys and values are the result of applying the provided mapping functions to the input elements.
static <T,K,U> Collector<T,?,Map<K,U>>	Collectors.toUnmodifiableMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper) Returns a Collector that accumulates the input elements into an unmodifiable Map, whose keys and values are the result of applying the provided mapping functions to the input elements.
static <T,K,U> Collector<T,?,Map<K,U>>	Collectors.toUnmodifiableMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper, BinaryOperator<U> mergeFunction) Returns a Collector that accumulates the input elements into an unmodifiable Map, whose keys and values are the result of applying the provided mapping functions to the input elements.
static <T,K,U> Collector<T,?,Map<K,U>>	Collectors.toUnmodifiableMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper, BinaryOperator<U> mergeFunction) Returns a Collector that accumulates the input elements into an unmodifiable Map, whose keys and values are the result of applying the provided mapping functions to the input elements.