java8.util

Class Spliterators.AbstractDoubleSpliterator

java.lang.Object

java8.util.Spliterators.AbstractDoubleSpliterator

All Implemented Interfaces:

Spliterator<Double>, Spliterator.OfDouble, Spliterator.OfPrimitive<Double,DoubleConsumer,Spliterator.OfDouble>

Enclosing class:

Spliterators

public abstract static class Spliterators.AbstractDoubleSpliterator
extends Object
implements Spliterator.OfDouble

An abstract Spliterator.OfDouble that implements trySplit to permit limited parallelism.

To implement a spliterator an extending class need only implement Spliterator.OfDouble.tryAdvance(java8.util.function.DoubleConsumer) tryAdvance}. The extending class should override Spliterator.OfDouble.forEachRemaining(java8.util.function.DoubleConsumer) forEach} 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(java8.util.PrimitiveIterator.OfDouble, long, int). Depending on the circumstances using an iterator may be easier or more convenient than extending this class. For example, if there is already an iterator available to use then there is no need to extend this class.

Since:

1.8

See Also:

Spliterators.spliterator(java8.util.PrimitiveIterator.OfDouble, long, int)

Nested Class Summary

Nested classes/interfaces inherited from interface java8.util.Spliterator

Spliterator.OfDouble, Spliterator.OfInt, Spliterator.OfLong, Spliterator.OfPrimitive<T,T_CONS,T_SPLITR extends Spliterator.OfPrimitive<T,T_CONS,T_SPLITR>>

Field Summary

Fields inherited from interface java8.util.Spliterator

CONCURRENT, DISTINCT, IMMUTABLE, NONNULL, ORDERED, SIZED, SORTED, SUBSIZED

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	AbstractDoubleSpliterator(long est, int additionalCharacteristics) Creates a spliterator reporting the given estimated size and characteristics.

Method Summary

Modifier and Type	Method and Description
int	characteristics() Returns a set of characteristics of this Spliterator and its elements.
long	estimateSize() Returns an estimate of the number of elements that would be encountered by a Spliterator.forEachRemaining(java8.util.function.Consumer<? super T>) traversal, or returns Long.MAX_VALUE if infinite, unknown, or too expensive to compute.
Spliterator.OfDouble	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.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java8.util.Spliterator.OfDouble

forEachRemaining, forEachRemaining, tryAdvance, tryAdvance

Methods inherited from interface java8.util.Spliterator

getComparator, getExactSizeIfKnown, hasCharacteristics

Constructor Detail

AbstractDoubleSpliterator

protected AbstractDoubleSpliterator(long est,
                                    int additionalCharacteristics)

Creates a spliterator reporting the given estimated size and characteristics.

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 Detail

trySplit

public Spliterator.OfDouble 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.

API Note:
An ideal trySplit method efficiently (without traversal) divides its elements exactly in half, allowing balanced parallel computation. Many departures from this ideal remain highly effective; for example, only approximately splitting an approximately balanced tree, or for a tree in which leaf nodes may contain either one or two elements, failing to further split these nodes. However, large deviations in balance and/or overly inefficient trySplit mechanics typically result in poor parallel performance. This implementation permits limited parallelism.

Specified by:

trySplit in interface Spliterator<Double>

Specified by:

trySplit in interface Spliterator.OfDouble

Specified by:

trySplit in interface Spliterator.OfPrimitive<Double,DoubleConsumer,Spliterator.OfDouble>

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(java8.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().

API Note:
Even an inexact estimate is often useful and inexpensive to compute. For example, a sub-spliterator of an approximately balanced binary tree may return a value that estimates the number of elements to be half of that of its parent; if the root Spliterator does not maintain an accurate count, it could estimate size to be the power of two corresponding to its maximum depth.

Implementation Requirements:
This implementation returns the estimated size as reported when created and, if the estimate size is known, decreases in size when split.

Specified by:

estimateSize in interface Spliterator<Double>

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.

API Note:
The characteristics of a given spliterator before splitting may differ from the characteristics after splitting. For specific examples see the characteristic values Spliterator.SIZED, Spliterator.SUBSIZED and Spliterator.CONCURRENT.

Implementation Requirements:
This implementation returns the characteristics as reported when created.

Specified by:

characteristics in interface Spliterator<Double>

Returns:

a representation of characteristics