Uses of Interface java.util.function.Function (Java SE 9 & JDK 9 )

## Uses of Interface
java.util.function.Function

- Packages that use Function
  Package | Description
  --- | ---
  java.lang | Provides classes that are fundamental to the design of the Java programming language.
  java.security | Provides the classes and interfaces for the security framework.
  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.
  java.util.concurrent | Utility classes commonly useful in concurrent programming.
  java.util.function | Functional interfaces provide target types for lambda expressions and method references.
  java.util.logging | Provides the classes and interfaces of the Java™ 2 platform's core logging facilities.
  java.util.regex | Classes for matching character sequences against patterns specified by regular expressions.
  java.util.stream | Classes to support functional-style operations on streams of elements, such as map-reduce transformations on collections.
  jdk.incubator.http | High level HTTP and WebSocket API
  jdk.jshell | Provides interfaces for creating tools, such as a Read-Eval-Print Loop (REPL), which interactively evaluate "snippets" of Java programming language code.

- - ### Uses of Function in java.lang

    Methods in java.lang with parameters of type Function
    Modifier and Type | Method | Description
    --- | --- | ---
    `ModuleLayer` | ModuleLayer.`defineModules​(Configuration cf, Function<String,ClassLoader> clf)` | Creates a new module layer, with this layer as its parent, by defining the modules in the given `Configuration` to the Java virtual machine.
    `static ModuleLayer.Controller` | ModuleLayer.`defineModules​(Configuration cf, List<ModuleLayer> parentLayers, Function<String,ClassLoader> clf)` | Creates a new module layer by defining the modules in the given `Configuration` to the Java virtual machine.
    `<T> T` | StackWalker.`walk​(Function<? super Stream<StackWalker.StackFrame>,? extends T> function)` | Applies the given function to the stream of `StackFrame`s for the current thread, traversing from the top frame of the stack, which is the method calling this `walk` method.

  - ### Uses of Function in java.security

    Methods in java.security with parameters of type Function
    Modifier and Type | Method | Description
    --- | --- | ---
    `Object` | Provider.`computeIfAbsent​(Object key, Function<? super Object,? extends Object> 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 this map unless `null`.

  - ### Uses of Function in java.util

    Methods in java.util with parameters of type Function
    Modifier and Type | Method | Description
    --- | --- | ---
    `static <T,U extends Comparable<? super U>> Comparator<T>` | Comparator.`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>` | Comparator.`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`.
    `V` | HashMap.`computeIfAbsent​(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 this map unless `null`.
    `V` | Hashtable.`computeIfAbsent​(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 this map unless `null`.
    `default V` | Map.`computeIfAbsent​(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 this map unless `null`.
    `Object` | Properties.`computeIfAbsent​(Object key, Function<? super Object,?> mappingFunction)` |
    `<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`.
    `default <U extends Comparable<? super U>> Comparator<T>` | Comparator.`thenComparing​(Function<? super T,? extends U> keyExtractor)` | Returns a lexicographic-order comparator with a function that extracts a `Comparable` sort key.
    `default <U> Comparator<T>` | Comparator.`thenComparing​(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 java.util.concurrent

    Methods in java.util.concurrent with parameters of type Function
    Modifier and Type | Method | Description
    --- | --- | ---
    `<U> CompletableFuture<U>` | CompletableFuture.`applyToEither​(CompletionStage<? extends T> other, Function<? super T,U> fn)` |
    `<U> CompletionStage<U>` | CompletionStage.`applyToEither​(CompletionStage<? extends T> other, Function<? super T,U> fn)` | Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed with the corresponding result as argument to the supplied function.
    `<U> CompletableFuture<U>` | CompletableFuture.`applyToEitherAsync​(CompletionStage<? extends T> other, Function<? super T,U> fn)` |
    `<U> CompletableFuture<U>` | CompletableFuture.`applyToEitherAsync​(CompletionStage<? extends T> other, Function<? super T,U> fn, Executor executor)` |
    `<U> CompletionStage<U>` | CompletionStage.`applyToEitherAsync​(CompletionStage<? extends T> other, Function<? super T,U> fn)` | Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed using this stage's default asynchronous execution facility, with the corresponding result as argument to the supplied function.
    `<U> CompletionStage<U>` | CompletionStage.`applyToEitherAsync​(CompletionStage<? extends T> other, Function<? super T,U> fn, Executor executor)` | Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed using the supplied executor, with the corresponding result as argument to the supplied function.
    `V` | ConcurrentHashMap.`computeIfAbsent​(K key, Function<? super K,? extends V> mappingFunction)` | If the specified key is not already associated with a value, attempts to compute its value using the given mapping function and enters it into this map unless `null`.
    `default V` | ConcurrentMap.`computeIfAbsent​(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 this map unless `null`.
    `V` | ConcurrentSkipListMap.`computeIfAbsent​(K key, Function<? super K,? extends V> mappingFunction)` | If the specified key is not already associated with a value, attempts to compute its value using the given mapping function and enters it into this map unless `null`.
    `CompletableFuture<T>` | CompletableFuture.`exceptionally​(Function<Throwable,? extends T> fn)` | Returns a new CompletableFuture that is completed when this CompletableFuture completes, with the result of the given function of the exception triggering this CompletableFuture's completion when it completes exceptionally; otherwise, if this CompletableFuture completes normally, then the returned CompletableFuture also completes normally with the same value.
    `CompletionStage<T>` | CompletionStage.`exceptionally​(Function<Throwable,? extends T> fn)` | Returns a new CompletionStage that, when this stage completes exceptionally, is executed with this stage's exception as the argument to the supplied function.
    `<U> void` | ConcurrentHashMap.`forEachEntry​(long parallelismThreshold, Function<Map.Entry<K,V>,? extends U> transformer, Consumer<? super U> action)` | Performs the given action for each non-null transformation of each entry.
    `<U> void` | ConcurrentHashMap.`forEachKey​(long parallelismThreshold, Function<? super K,? extends U> transformer, Consumer<? super U> action)` | Performs the given action for each non-null transformation of each key.
    `<U> void` | ConcurrentHashMap.`forEachValue​(long parallelismThreshold, Function<? super V,? extends U> transformer, Consumer<? super U> action)` | Performs the given action for each non-null transformation of each value.
    `<U> U` | ConcurrentHashMap.`reduceEntries​(long parallelismThreshold, Function<Map.Entry<K,V>,? extends U> transformer, BiFunction<? super U,? super U,? extends U> reducer)` | Returns the result of accumulating the given transformation of all entries using the given reducer to combine values, or null if none.
    `<U> U` | ConcurrentHashMap.`reduceKeys​(long parallelismThreshold, Function<? super K,? extends U> transformer, BiFunction<? super U,? super U,? extends U> reducer)` | Returns the result of accumulating the given transformation of all keys using the given reducer to combine values, or null if none.
    `<U> U` | ConcurrentHashMap.`reduceValues​(long parallelismThreshold, Function<? super V,? extends U> transformer, BiFunction<? super U,? super U,? extends U> reducer)` | Returns the result of accumulating the given transformation of all values using the given reducer to combine values, or null if none.
    `<U> U` | ConcurrentHashMap.`searchEntries​(long parallelismThreshold, Function<Map.Entry<K,V>,? extends U> searchFunction)` | Returns a non-null result from applying the given search function on each entry, or null if none.
    `<U> U` | ConcurrentHashMap.`searchKeys​(long parallelismThreshold, Function<? super K,? extends U> searchFunction)` | Returns a non-null result from applying the given search function on each key, or null if none.
    `<U> U` | ConcurrentHashMap.`searchValues​(long parallelismThreshold, Function<? super V,? extends U> searchFunction)` | Returns a non-null result from applying the given search function on each value, or null if none.
    `<U> CompletableFuture<U>` | CompletableFuture.`thenApply​(Function<? super T,? extends U> fn)` |
    `<U> CompletionStage<U>` | CompletionStage.`thenApply​(Function<? super T,? extends U> fn)` | Returns a new CompletionStage that, when this stage completes normally, is executed with this stage's result as the argument to the supplied function.
    `<U> CompletableFuture<U>` | CompletableFuture.`thenApplyAsync​(Function<? super T,? extends U> fn)` |
    `<U> CompletableFuture<U>` | CompletableFuture.`thenApplyAsync​(Function<? super T,? extends U> fn, Executor executor)` |
    `<U> CompletionStage<U>` | CompletionStage.`thenApplyAsync​(Function<? super T,? extends U> fn)` | Returns a new CompletionStage that, when this stage completes normally, is executed using this stage's default asynchronous execution facility, with this stage's result as the argument to the supplied function.
    `<U> CompletionStage<U>` | CompletionStage.`thenApplyAsync​(Function<? super T,? extends U> fn, Executor executor)` | Returns a new CompletionStage that, when this stage completes normally, is executed using the supplied Executor, with this stage's result as the argument to the supplied function.
    `<U> CompletableFuture<U>` | CompletableFuture.`thenCompose​(Function<? super T,? extends CompletionStage<U>> fn)` |
    `<U> CompletionStage<U>` | CompletionStage.`thenCompose​(Function<? super T,? extends CompletionStage<U>> fn)` | Returns a new CompletionStage that is completed with the same value as the CompletionStage returned by the given function.
    `<U> CompletableFuture<U>` | CompletableFuture.`thenComposeAsync​(Function<? super T,? extends CompletionStage<U>> fn)` |
    `<U> CompletableFuture<U>` | CompletableFuture.`thenComposeAsync​(Function<? super T,? extends CompletionStage<U>> fn, Executor executor)` |
    `<U> CompletionStage<U>` | CompletionStage.`thenComposeAsync​(Function<? super T,? extends CompletionStage<U>> fn)` | Returns a new CompletionStage that is completed with the same value as the CompletionStage returned by the given function, executed using this stage's default asynchronous execution facility.
    `<U> CompletionStage<U>` | CompletionStage.`thenComposeAsync​(Function<? super T,? extends CompletionStage<U>> fn, Executor executor)` | Returns a new CompletionStage that is completed with the same value as the CompletionStage returned by the given function, executed using the supplied Executor.

  - ### Uses of Function in java.util.function

    Subinterfaces of Function in java.util.function
    Modifier and Type | Interface | Description
    --- | --- | ---
    `interface` | `UnaryOperator<T>` | Represents an operation on a single operand that produces a result of the same type as its operand.

    Methods in java.util.function that return Function
    Modifier and Type | Method | Description
    --- | --- | ---
    `default <V> Function<T,V>` | Function.`andThen​(Function<? super R,? extends V> after)` | Returns a composed function that first applies this function to its input, and then applies the `after` function to the result.
    `default <V> Function<V,R>` | Function.`compose​(Function<? super V,? extends T> before)` | Returns a composed function that first applies the `before` function to its input, and then applies this function to the result.
    `static <T> Function<T,T>` | Function.`identity​()` | Returns a function that always returns its input argument.

    Methods in java.util.function with parameters of type Function
    Modifier and Type | Method | Description
    --- | --- | ---
    `default <V> BiFunction<T,U,V>` | BiFunction.`andThen​(Function<? super R,? extends V> after)` | Returns a composed function that first applies this function to its input, and then applies the `after` function to the result.
    `default <V> Function<T,V>` | Function.`andThen​(Function<? super R,? extends V> after)` | Returns a composed function that first applies this function to its input, and then applies the `after` function to the result.
    `default <V> Function<V,R>` | Function.`compose​(Function<? super V,? extends T> before)` | Returns a composed function that first applies the `before` function to its input, and then applies this function to the result.

  - ### Uses of Function in java.util.logging

    Methods in java.util.logging with parameters of type Function
    Modifier and Type | Method | Description
    --- | --- | ---
    `void` | LogManager.`updateConfiguration​(InputStream ins, Function<String,BiFunction<String,String,String>> mapper)` | Updates the logging configuration.
    `void` | LogManager.`updateConfiguration​(Function<String,BiFunction<String,String,String>> mapper)` | Updates the logging configuration.

  - ### Uses of Function in java.util.regex

    Methods in java.util.regex with parameters of type Function
    Modifier and Type | Method | Description
    --- | --- | ---
    `String` | Matcher.`replaceAll​(Function<MatchResult,String> replacer)` | Replaces every subsequence of the input sequence that matches the pattern with the result of applying the given replacer function to the match result of this matcher corresponding to that subsequence.
    `String` | Matcher.`replaceFirst​(Function<MatchResult,String> replacer)` | Replaces the first subsequence of the input sequence that matches the pattern with the result of applying the given replacer function to the match result of this matcher corresponding to that subsequence.

  - ### Uses of Function in java.util.stream

    Methods in java.util.stream that return Function
    Modifier and Type | Method | Description
    --- | --- | ---
    `Function<A,R>` | Collector.`finisher​()` | Perform the final transformation from the intermediate accumulation type `A` to the final result type `R`.

    Methods in java.util.stream with parameters of type Function
    Modifier and Type | Method | 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,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,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> 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,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`.
    `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`.
    `<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>` | Collector.`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, 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> 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,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.

  - ### Uses of Function in jdk.incubator.http

    Methods in jdk.incubator.http with parameters of type Function
    Modifier and Type | Method | Description
    --- | --- | ---
    `static <V> HttpResponse.MultiProcessor<MultiMapResult<V>,V>` | HttpResponse.MultiProcessor.`asMap​(Function<HttpRequest,Optional<HttpResponse.BodyHandler<V>>> pushHandler)` | Returns a general purpose handler for multi responses.
    `static <V> HttpResponse.MultiProcessor<MultiMapResult<V>,V>` | HttpResponse.MultiProcessor.`asMap​(Function<HttpRequest,Optional<HttpResponse.BodyHandler<V>>> pushHandler, boolean completion)` | Returns a general purpose handler for multi responses.

  - ### Uses of Function in jdk.jshell

    Methods in jdk.jshell with parameters of type Function
    Modifier and Type | Method | Description
    --- | --- | ---
    `JShell.Builder` | JShell.Builder.`fileManager​(Function<StandardJavaFileManager,StandardJavaFileManager> mapping)` | Configure the `FileManager` to be used by compilation and source analysis.