Summary: Methods | Inherited Methods

Gatherers

public final class Gatherers
extends Object

java.lang.Object
↳	java.util.stream.Gatherers

Implementations of Gatherer that provide useful intermediate operations, such as windowing functions, folding functions, transforming elements concurrently, etc.

Summary

Public methods
`static <T, R> Gatherer<T, ?, R>`	`fold(Supplier<R> initial, BiFunction<? super R, ? super T, ? extends R> folder)` 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.
`static <T, R> Gatherer<T, ?, R>`	`scan(Supplier<R> initial, BiFunction<? super R, ? super T, ? extends R> scanner)` Returns a Gatherer that performs a Prefix Scan -- an incremental accumulation -- using the provided functions.
`static <TR> Gatherer<TR, ?, List<TR>>`	`windowFixed(int windowSize)` Returns a Gatherer that gathers elements into windows -- encounter-ordered groups of elements -- of a fixed size.
`static <TR> Gatherer<TR, ?, List<TR>>`	`windowSliding(int windowSize)` 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.

Inherited methods

From class


        
          java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long timeoutMillis, int nanos)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait()` Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

Public methods

fold

Added in Android Baklava

public static Gatherer<T, ?, R> fold (Supplier<R> initial, 
                BiFunction<? super R, ? super T, ? extends R> folder)

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.

Implementation Requirements:

If no exceptions are thrown during processing, then this operation only ever produces a single element.
Example: lang=java : // 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
`initial`	`Supplier`: the identity value for the fold operation
`folder`	`BiFunction`: the folding function

Returns
`Gatherer<T, ?, R>`	a new Gatherer

Throws
`NullPointerException`	if any of the parameters are `null`

See also:

Stream.reduce(Object, BinaryOperator)

scan

Added in Android Baklava

public static Gatherer<T, ?, R> scan (Supplier<R> initial, 
                BiFunction<? super R, ? super T, ? extends R> scanner)

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: lang=java : // 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
`initial`	`Supplier`: the supplier of the initial value for the scanner
`scanner`	`BiFunction`: the function to apply for each element

Returns
`Gatherer<T, ?, R>`	a new Gatherer which performs a prefix scan

Throws
`NullPointerException`	if any of the parameters are `null`

windowFixed

Added in Android Baklava

public static Gatherer<TR, ?, List<TR>> windowFixed (int windowSize)

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: lang=java : // 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();

Implementation Requirements:

Each window produced is an unmodifiable List; calls to any mutator method will always cause UnsupportedOperationException to be thrown. There are no guarantees on the implementation type or serializability of the produced Lists.

API Note:

For efficiency reasons, windows may be allocated contiguously and eagerly. This means that choosing large window sizes for small streams may use excessive memory for the duration of evaluation of this operation.

Parameters
`windowSize`	`int`: the size of the windows

Returns
`Gatherer<TR, ?, List<TR>>`	a new gatherer which groups elements into fixed-size windows

Throws
`IllegalArgumentException`	when `windowSize` is less than 1

windowSliding

Added in Android Baklava

public static Gatherer<TR, ?, List<TR>> windowSliding (int windowSize)

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: lang=java : // 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();

Implementation Requirements:

Each window produced is an unmodifiable List; calls to any mutator method will always cause UnsupportedOperationException to be thrown. There are no guarantees on the implementation type or serializability of the produced Lists.

API Note:

For efficiency reasons, windows may be allocated contiguously and eagerly. This means that choosing large window sizes for small streams may use excessive memory for the duration of evaluation of this operation.

Parameters
`windowSize`	`int`: the size of the windows

Returns
`Gatherer<TR, ?, List<TR>>`	a new gatherer which groups elements into sliding windows

Throws
`IllegalArgumentException`	when windowSize is less than 1