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Java Uses of Interface java.util.function.Function（JDK8）

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Java™ Platform
Standard Ed. 8
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Uses of Interface
java.util.function.Function

  • Packages that use Function 
    Package Description
    java.security
    Provides the classes and interfaces for the security framework.
    java.util
    Contains the collections framework, legacy collection classes, event model, date and time facilities, internationalization, and miscellaneous utility classes (a string tokenizer, a random-number generator, and a bit array).
    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.stream
    Classes to support functional-style operations on streams of elements, such as map-reduce transformations on collections.

    • Uses of Function in java.security

      Methods in java.security with parameters of type Function 
      Modifier and Type Method and 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 and 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 Hashtable.computeIfAbsent(K key, Function<? super K,? extends V> mappingFunction) 
      V HashMap.computeIfAbsent(K key, Function<? super K,? extends V> mappingFunction) 
      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.
      <U> Optional<U> Optional.flatMap(Function<? super T,Optional<U>> mapper)
      If a value is present, apply the provided Optional-bearing mapping function to it, return that result, otherwise return an empty Optional.
      <U> Optional<U> Optional.map(Function<? super T,? extends U> mapper)
      If a value is present, apply the provided mapping function to it, and if the result is non-null, return an Optional describing the result.
      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 and 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> 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> 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, 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 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.
      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.
      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> 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> CompletableFuture<U> CompletableFuture.thenApplyAsync(Function<? super T,? extends U> fn, Executor executor) 
      <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, when this stage completes normally, is executed with this stage as the argument to the supplied function.
      <U> CompletableFuture<U> CompletableFuture.thenComposeAsync(Function<? super T,? extends CompletionStage<U>> fn) 
      <U> CompletionStage<U> CompletionStage.thenComposeAsync(Function<? super T,? extends CompletionStage<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 as the argument to the supplied function.
      <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, 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.

    • Uses of Function in java.util.function

      Subinterfaces of Function in java.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 java.util.function that return Function 
      Modifier and Type Method and 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 and 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> 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<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.stream

      Methods in java.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 java.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.
      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> 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)
      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> mapSupplier)
      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> mapSupplier)
      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> mapSupplier)
      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> mapSupplier)
      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.
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