Module java.base
Package java.util

Class Spliterators.AbstractSpliterator<T>

java.lang.Object
java.util.Spliterators.AbstractSpliterator<T>
All Implemented Interfaces:
Spliterator<T>
Enclosing class:
Spliterators
public abstract static class Spliterators.AbstractSpliterator<T> extends Object implements Spliterator<T>
An abstract Spliterator that implements trySplit to permit limited parallelism.

An extending class need only implement tryAdvance. The extending class should override forEachRemaining if it can provide a more performant implementation.

API Note:
This class is a useful aid for creating a spliterator when it is not possible or difficult to efficiently partition elements in a manner allowing balanced parallel computation.

An alternative to using this class, that also permits limited parallelism, is to create a spliterator from an iterator (see Spliterators.spliterator(Iterator, long, int). Depending on the circumstances using an iterator may be easier or more convenient than extending this class, such as when there is already an iterator available to use.

Since:
1.8
See Also:
Spliterators.spliterator(Iterator, long, int)

  • Constructor Details

    • AbstractSpliterator

      protected AbstractSpliterator​(long est, int additionalCharacteristics)
      Creates a spliterator reporting the given estimated size and additionalCharacteristics.
      Parameters:
      est - the estimated size of this spliterator if known, otherwise Long.MAX_VALUE.
      additionalCharacteristics - properties of this spliterator's source or elements. If SIZED is reported then this spliterator will additionally report SUBSIZED.

  • Method Details

    • trySplit

      public 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.

      If this Spliterator is Spliterator.ORDERED, the returned Spliterator must cover a strict prefix of the elements.

      Unless this Spliterator covers an infinite number of elements, repeated calls to trySplit() must eventually return null. Upon non-null return:

      • the value reported for estimateSize() before splitting, must, after splitting, be greater than or equal to estimateSize() for this and the returned Spliterator; and
      • if this Spliterator is SUBSIZED, then estimateSize() for this spliterator before splitting must be equal to the sum of estimateSize() for this and the returned Spliterator after splitting.

      This method may return null for any reason, including emptiness, inability to split after traversal has commenced, data structure constraints, and efficiency considerations. This implementation permits limited parallelism.

      Specified by:
      trySplit in interface Spliterator<T>
      Returns:
      a Spliterator covering some portion of the elements, or null if this spliterator cannot be split

    • estimateSize

      public long estimateSize()
      Returns an estimate of the number of elements that would be encountered by a Spliterator.forEachRemaining(java.util.function.Consumer<? super T>) traversal, or returns Long.MAX_VALUE if infinite, unknown, or too expensive to compute.

      If this Spliterator is Spliterator.SIZED and has not yet been partially traversed or split, or this Spliterator is Spliterator.SUBSIZED and has not yet been partially traversed, this estimate must be an accurate count of elements that would be encountered by a complete traversal. Otherwise, this estimate may be arbitrarily inaccurate, but must decrease as specified across invocations of Spliterator.trySplit().

      Specified by:
      estimateSize in interface Spliterator<T>
      Implementation Requirements:
      This implementation returns the estimated size as reported when created and, if the estimate size is known, decreases in size when split.
      Returns:
      the estimated size, or Long.MAX_VALUE if infinite, unknown, or too expensive to compute.

    • characteristics

      public int characteristics()
      Returns a set of characteristics of this Spliterator and its elements. The result is represented as ORed values from Spliterator.ORDERED, Spliterator.DISTINCT, Spliterator.SORTED, Spliterator.SIZED, Spliterator.NONNULL, Spliterator.IMMUTABLE, Spliterator.CONCURRENT, Spliterator.SUBSIZED. Repeated calls to characteristics() on a given spliterator, prior to or in-between calls to trySplit, should always return the same result.

      If a Spliterator reports an inconsistent set of characteristics (either those returned from a single invocation or across multiple invocations), no guarantees can be made about any computation using this Spliterator.

      Specified by:
      characteristics in interface Spliterator<T>
      Implementation Requirements:
      This implementation returns the characteristics as reported when created.
      Returns:
      a representation of characteristics