Uses of Interface java.util.stream.Collector (Java Platform SE 8 )
Date: 2016-12-09

## Uses of Interface
java.util.stream.Collector

- Packages that use Collector
  Package | Description
  --- | ---
  java.util.stream | Classes to support functional-style operations on streams of elements, such as map-reduce transformations on collections.

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

    Methods in java.util.stream that return Collector
    Modifier and Type | Method and Description
    --- | ---
    `static <T> Collector<T,?,Double>` | Collectors.`averagingDouble(ToDoubleFunction<? super T> mapper)` Returns a `Collector` that produces the arithmetic mean of a double-valued function applied to the input elements.
    `static <T> Collector<T,?,Double>` | Collectors.`averagingInt(ToIntFunction<? super T> mapper)` Returns a `Collector` that produces the arithmetic mean of an integer-valued function applied to the input elements.
    `static <T> Collector<T,?,Double>` | Collectors.`averagingLong(ToLongFunction<? super T> mapper)` Returns a `Collector` that produces the arithmetic mean of a long-valued function applied to the input elements.
    `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.
    `static <T> Collector<T,?,Long>` | Collectors.`counting()` Returns a `Collector` accepting elements of type `T` that counts the number of input elements.
    `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`.
    `static Collector<CharSequence,?,String>` | Collectors.`joining()` Returns a `Collector` that concatenates the input elements into a `String`, in encounter order.
    `static Collector<CharSequence,?,String>` | Collectors.`joining(CharSequence delimiter)` Returns a `Collector` that concatenates the input elements, separated by the specified delimiter, in encounter order.
    `static Collector<CharSequence,?,String>` | Collectors.`joining(CharSequence delimiter, CharSequence prefix, CharSequence suffix)` Returns a `Collector` that concatenates the input elements, separated by the specified delimiter, with the specified prefix and suffix, in encounter order.
    `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> Collector<T,?,Optional<T>>` | Collectors.`maxBy(Comparator<? super T> comparator)` Returns a `Collector` that produces the maximal element according to a given `Comparator`, described as an `Optional<T>`.
    `static <T> Collector<T,?,Optional<T>>` | Collectors.`minBy(Comparator<? super T> comparator)` Returns a `Collector` that produces the minimal element according to a given `Comparator`, described as an `Optional<T>`.
    `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,R> Collector<T,R,R>` | Collector.`of(Supplier<R> supplier, BiConsumer<R,T> accumulator, BinaryOperator<R> combiner, Collector.Characteristics... characteristics)` Returns a new `Collector` described by the given `supplier`, `accumulator`, and `combiner` functions.
    `static <T> Collector<T,?,Map<Boolean,List<T>>>` | Collectors.`partitioningBy(Predicate<? super T> predicate)` Returns a `Collector` which partitions the input elements according to a `Predicate`, and organizes them into a `Map<Boolean, List<T>>`.
    `static <T,D,A> Collector<T,?,Map<Boolean,D>>` | Collectors.`partitioningBy(Predicate<? super T> predicate, Collector<? super T,A,D> downstream)` Returns a `Collector` which partitions the input elements according to a `Predicate`, reduces the values in each partition according to another `Collector`, and organizes them into a `Map<Boolean, D>` whose values are the result of the downstream reduction.
    `static <T> Collector<T,?,Optional<T>>` | Collectors.`reducing(BinaryOperator<T> op)` Returns a `Collector` which performs a reduction of its input elements under a specified `BinaryOperator`.
    `static <T> Collector<T,?,T>` | Collectors.`reducing(T identity, BinaryOperator<T> op)` Returns a `Collector` which performs a reduction of its input elements under a specified `BinaryOperator` using the provided identity.
    `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> Collector<T,?,DoubleSummaryStatistics>` | Collectors.`summarizingDouble(ToDoubleFunction<? super T> mapper)` Returns a `Collector` which applies an `double`-producing mapping function to each input element, and returns summary statistics for the resulting values.
    `static <T> Collector<T,?,IntSummaryStatistics>` | Collectors.`summarizingInt(ToIntFunction<? super T> mapper)` Returns a `Collector` which applies an `int`-producing mapping function to each input element, and returns summary statistics for the resulting values.
    `static <T> Collector<T,?,LongSummaryStatistics>` | Collectors.`summarizingLong(ToLongFunction<? super T> mapper)` Returns a `Collector` which applies an `long`-producing mapping function to each input element, and returns summary statistics for the resulting values.
    `static <T> Collector<T,?,Double>` | Collectors.`summingDouble(ToDoubleFunction<? super T> mapper)` Returns a `Collector` that produces the sum of a double-valued function applied to the input elements.
    `static <T> Collector<T,?,Integer>` | Collectors.`summingInt(ToIntFunction<? super T> mapper)` Returns a `Collector` that produces the sum of a integer-valued function applied to the input elements.
    `static <T> Collector<T,?,Long>` | Collectors.`summingLong(ToLongFunction<? super T> mapper)` Returns a `Collector` that produces the sum of a long-valued function applied to the input elements.
    `static <T,C extends Collection<T>> Collector<T,?,C>` | Collectors.`toCollection(Supplier<C> collectionFactory)` Returns a `Collector` that accumulates the input elements into a new `Collection`, in encounter order.
    `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> 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> Collector<T,?,List<T>>` | Collectors.`toList()` Returns a `Collector` that accumulates the input elements into a new `List`.
    `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> 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> Collector<T,?,Set<T>>` | Collectors.`toSet()` Returns a `Collector` that accumulates the input elements into a new `Set`.

    Methods in java.util.stream with parameters of type Collector
    Modifier and Type | Method and Description
    --- | ---
    `<R,A> R` | Stream.`collect(Collector<? super T,A,R> collector)` Performs a mutable reduction operation on the elements of this stream using a `Collector`.
    `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.
    `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,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`.
    `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,D,A> Collector<T,?,Map<Boolean,D>>` | Collectors.`partitioningBy(Predicate<? super T> predicate, Collector<? super T,A,D> downstream)` Returns a `Collector` which partitions the input elements according to a `Predicate`, reduces the values in each partition according to another `Collector`, and organizes them into a `Map<Boolean, D>` whose values are the result of the downstream reduction.

Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
Copyright © 1993, 2016, Oracle and/or its affiliates. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.