Summary: Nested Classes | Constants | Methods

Spliterator

public interface Spliterator

java.util.Spliterator<T>

Known indirect subclasses

Spliterator.OfDouble, Spliterator.OfInt, Spliterator.OfLong, Spliterator.OfPrimitive<T, T_CONS, T_SPLITR extends OfPrimitive<T, T_CONS, T_SPLITR>>, Spliterators.AbstractDoubleSpliterator, Spliterators.AbstractIntSpliterator, Spliterators.AbstractLongSpliterator, Spliterators.AbstractSpliterator<T>

Spliterator.OfDouble	A Spliterator specialized for `double` values.
Spliterator.OfInt	A Spliterator specialized for `int` values.
Spliterator.OfLong	A Spliterator specialized for `long` values.
Spliterator.OfPrimitive<T, T_CONS, T_SPLITR extends OfPrimitive<T, T_CONS, T_SPLITR>>	A Spliterator specialized for primitive values.
Spliterators.AbstractDoubleSpliterator	An abstract `Spliterator.OfDouble` that implements `trySplit` to permit limited parallelism.
Spliterators.AbstractIntSpliterator	An abstract `Spliterator.OfInt` that implements `trySplit` to permit limited parallelism.
Spliterators.AbstractLongSpliterator	An abstract `Spliterator.OfLong` that implements `trySplit` to permit limited parallelism.
Spliterators.AbstractSpliterator<T>	An abstract `Spliterator` that implements `trySplit` to permit limited parallelism.

An object for traversing and partitioning elements of a source. The source of elements covered by a Spliterator could be, for example, an array, a Collection, an IO channel, or a generator function.

A Spliterator may traverse elements individually (tryAdvance()) or sequentially in bulk (forEachRemaining()).

A Spliterator may also partition off some of its elements (using trySplit()) as another Spliterator, to be used in possibly-parallel operations. Operations using a Spliterator that cannot split, or does so in a highly imbalanced or inefficient manner, are unlikely to benefit from parallelism. Traversal and splitting exhaust elements; each Spliterator is useful for only a single bulk computation.

A Spliterator also reports a set of characteristics() of its structure, source, and elements from among ORDERED, DISTINCT, SORTED, SIZED, NONNULL, IMMUTABLE, CONCURRENT, and SUBSIZED. These may be employed by Spliterator clients to control, specialize or simplify computation. For example, a Spliterator for a Collection would report SIZED, a Spliterator for a Set would report DISTINCT, and a Spliterator for a SortedSet would also report SORTED. Characteristics are reported as a simple unioned bit set. Some characteristics additionally constrain method behavior; for example if ORDERED, traversal methods must conform to their documented ordering. New characteristics may be defined in the future, so implementors should not assign meanings to unlisted values.

A Spliterator that does not report IMMUTABLE or CONCURRENT is expected to have a documented policy concerning: when the spliterator binds to the element source; and detection of structural interference of the element source detected after binding. A late-binding Spliterator binds to the source of elements at the point of first traversal, first split, or first query for estimated size, rather than at the time the Spliterator is created. A Spliterator that is not late-binding binds to the source of elements at the point of construction or first invocation of any method. Modifications made to the source prior to binding are reflected when the Spliterator is traversed. After binding a Spliterator should, on a best-effort basis, throw ConcurrentModificationException if structural interference is detected. Spliterators that do this are called fail-fast. The bulk traversal method (forEachRemaining()) of a Spliterator may optimize traversal and check for structural interference after all elements have been traversed, rather than checking per-element and failing immediately.

Spliterators can provide an estimate of the number of remaining elements via the estimateSize() method. Ideally, as reflected in characteristic SIZED, this value corresponds exactly to the number of elements that would be encountered in a successful traversal. However, even when not exactly known, an estimated value may still be useful to operations being performed on the source, such as helping to determine whether it is preferable to split further or traverse the remaining elements sequentially.

Despite their obvious utility in parallel algorithms, spliterators are not expected to be thread-safe; instead, implementations of parallel algorithms using spliterators should ensure that the spliterator is only used by one thread at a time. This is generally easy to attain via serial thread-confinement, which often is a natural consequence of typical parallel algorithms that work by recursive decomposition. A thread calling trySplit() may hand over the returned Spliterator to another thread, which in turn may traverse or further split that Spliterator. The behaviour of splitting and traversal is undefined if two or more threads operate concurrently on the same spliterator. If the original thread hands a spliterator off to another thread for processing, it is best if that handoff occurs before any elements are consumed with tryAdvance(), as certain guarantees (such as the accuracy of estimateSize() for SIZED spliterators) are only valid before traversal has begun.

Primitive subtype specializations of Spliterator are provided for int, long, and double values. The subtype default implementations of Spliterator.tryAdvance(java.util.function.Consumer) and Spliterator.forEachRemaining(java.util.function.Consumer) box primitive values to instances of their corresponding wrapper class. Such boxing may undermine any performance advantages gained by using the primitive specializations. To avoid boxing, the corresponding primitive-based methods should be used. For example, Spliterator.OfInt.tryAdvance(java.util.function.IntConsumer) and Spliterator.OfInt.forEachRemaining(java.util.function.IntConsumer) should be used in preference to Spliterator.OfInt.tryAdvance(java.util.function.Consumer) and Spliterator.OfInt.forEachRemaining(java.util.function.Consumer). Traversal of primitive values using boxing-based methods tryAdvance() and forEachRemaining() does not affect the order in which the values, transformed to boxed values, are encountered.

See also:

Collection

Summary

Nested classes
`interface`	`Spliterator.OfDouble` A Spliterator specialized for `double` values.
`interface`	`Spliterator.OfInt` A Spliterator specialized for `int` values.
`interface`	`Spliterator.OfLong` A Spliterator specialized for `long` values.
`interface`	`Spliterator.OfPrimitive<T, T_CONS, T_SPLITR extends OfPrimitive<T, T_CONS, T_SPLITR>>` A Spliterator specialized for primitive values.

Constants
`int`	`CONCURRENT` Characteristic value signifying that the element source may be safely concurrently modified (allowing additions, replacements, and/or removals) by multiple threads without external synchronization.
`int`	`DISTINCT` Characteristic value signifying that, for each pair of encountered elements `x, y`, `!x.equals(y)`.
`int`	`IMMUTABLE` Characteristic value signifying that the element source cannot be structurally modified; that is, elements cannot be added, replaced, or removed, so such changes cannot occur during traversal.
`int`	`NONNULL` Characteristic value signifying that the source guarantees that encountered elements will not be `null`.
`int`	`ORDERED` Characteristic value signifying that an encounter order is defined for elements.
`int`	`SIZED` Characteristic value signifying that the value returned from `estimateSize()` prior to traversal or splitting represents a finite size that, in the absence of structural source modification, represents an exact count of the number of elements that would be encountered by a complete traversal.
`int`	`SORTED` Characteristic value signifying that encounter order follows a defined sort order.
`int`	`SUBSIZED` Characteristic value signifying that all Spliterators resulting from `trySplit()` will be both `SIZED` and `SUBSIZED`.

Public methods
`abstract int`	`characteristics()` Returns a set of characteristics of this Spliterator and its elements.
`abstract long`	`estimateSize()` Returns an estimate of the number of elements that would be encountered by a `forEachRemaining(Consumer)` traversal, or returns `Long.MAX_VALUE` if infinite, unknown, or too expensive to compute.
`default void`	`forEachRemaining(Consumer<? super T> action)` Performs the given action for each remaining element, sequentially in the current thread, until all elements have been processed or the action throws an exception.
`default Comparator<? super T>`	`getComparator()` If this Spliterator's source is `SORTED` by a `Comparator`, returns that `Comparator`.
`default long`	`getExactSizeIfKnown()` Convenience method that returns `estimateSize()` if this Spliterator is `SIZED`, else `-1`.
`default boolean`	`hasCharacteristics(int characteristics)` Returns `true` if this Spliterator's `characteristics()` contain all of the given characteristics.
`abstract boolean`	`tryAdvance(Consumer<? super T> action)` If a remaining element exists: performs the given action on it, returning `true`; else returns `false`.
`abstract Spliterator<T>`	`trySplit()` If this spliterator can be partitioned, returns a Spliterator covering elements, that will, upon return from this method, not be covered by this Spliterator.

Spliterator

Summary

Nested classes

Constants

Public methods

Constants

CONCURRENT

DISTINCT

IMMUTABLE

NONNULL

ORDERED

SIZED

SORTED

SUBSIZED

Public methods

characteristics

API Note:

estimateSize

API Note:

forEachRemaining

Implementation Requirements:

getComparator

Implementation Requirements:

getExactSizeIfKnown

Implementation Requirements:

hasCharacteristics

Implementation Requirements:

tryAdvance

trySplit

API Note: