Returns a Gatherer that performs an ordered, reduction-like, transformation for scenarios where no combiner-function can be implemented, or for reductions which are intrinsically order-dependent.

// will contain: Optional["123456789"]
Optional<String> numberString =
    Stream.of(1,2,3,4,5,6,7,8,9)
          .gather(
              Gatherers.fold(() -> "", (string, number) -> string + number)
           )
          .findFirst();

Parameters

<T>

the type of elements the returned gatherer consumes

<R>

the type of elements the returned gatherer produces

initial:Supplier<R>

the identity value for the fold operation

folder:BiFunction<? super R, ? super T, ? extends R>

the folding function

Returns:Gatherer<T, ?, R>

a new Gatherer

Exceptions

NullPointerException:

if any of the parameters are null

See Also

java.util.stream.Stream#reduce(Object, BinaryOperator)

An operation which executes a function concurrently with a configured level of max concurrency, using virtual threads. This operation preserves the ordering of the stream.

Parameters

<T>

the type of input

<R>

the type of output

maxConcurrency:int

the maximum concurrency desired

mapper:Function<? super T, ? extends R>

a function to be executed concurrently

Returns:Gatherer<T, ?, R>

a new Gatherer

Exceptions

IllegalArgumentException:

if maxConcurrency is less than 1

NullPointerException:

if mapper is null

Returns a Gatherer that performs a Prefix Scan -- an incremental accumulation -- using the provided functions. Starting with an initial value obtained from the Supplier, each subsequent value is obtained by applying the BiFunction to the current value and the next input element, after which the resulting value is produced downstream.

Example:

// will contain: ["1", "12", "123", "1234", "12345", "123456", "1234567", "12345678", "123456789"]
List<String> numberStrings =
    Stream.of(1,2,3,4,5,6,7,8,9)
          .gather(
              Gatherers.scan(() -> "", (string, number) -> string + number)
           )
          .toList();

Parameters

<T>

the type of element which this gatherer consumes

<R>

the type of element which this gatherer produces

initial:Supplier<R>

the supplier of the initial value for the scanner

scanner:BiFunction<? super R, ? super T, ? extends R>

the function to apply for each element

Returns:Gatherer<T, ?, R>

a new Gatherer which performs a prefix scan

Exceptions

NullPointerException:

if any of the parameters are null

Returns a Gatherer that gathers elements into windows -- encounter-ordered groups of elements -- of a fixed size. If the stream is empty then no window will be produced. The last window may contain fewer elements than the supplied window size.

Example:

// will contain: [[1, 2, 3], [4, 5, 6], [7, 8]]
List<List<Integer>> windows =
    Stream.of(1,2,3,4,5,6,7,8).gather(Gatherers.windowFixed(3)).toList();

Parameters

<TR>

the type of elements the returned gatherer consumes and the contents of the windows it produces

windowSize:int

the size of the windows

Returns:Gatherer<TR, ?, List<TR>>

a new gatherer which groups elements into fixed-size windows

Exceptions

IllegalArgumentException:

when windowSize is less than 1

Returns a Gatherer that gathers elements into windows -- encounter-ordered groups of elements -- of a given size, where each subsequent window includes all elements of the previous window except for the least recent, and adds the next element in the stream. If the stream is empty then no window will be produced. If the size of the stream is smaller than the window size then only one window will be produced, containing all elements in the stream.

Example:

// will contain: [[1, 2], [2, 3], [3, 4], [4, 5], [5, 6], [6, 7], [7, 8]]
List<List<Integer>> windows2 =
    Stream.of(1,2,3,4,5,6,7,8).gather(Gatherers.windowSliding(2)).toList();

// will contain: [[1, 2, 3, 4, 5, 6], [2, 3, 4, 5, 6, 7], [3, 4, 5, 6, 7, 8]]
List<List<Integer>> windows6 =
    Stream.of(1,2,3,4,5,6,7,8).gather(Gatherers.windowSliding(6)).toList();

Parameters

<TR>

the type of elements the returned gatherer consumes and the contents of the windows it produces

windowSize:int

the size of the windows

Returns:Gatherer<TR, ?, List<TR>>

a new gatherer which groups elements into sliding windows

Exceptions

IllegalArgumentException:

when windowSize is less than 1