public abstract static class Spliterators.AbstractSpliterator<T> extends java.lang.Object implements Spliterator<T>
Spliterator that implements trySplit to
permit limited parallelism.
An extending class need only
implement tryAdvance.
The extending class should override
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(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.
Spliterators.spliterator(Iterator, long, int)Spliterator.OfDouble, Spliterator.OfInt, Spliterator.OfLong, Spliterator.OfPrimitive<T,T_CONS,T_SPLITR extends Spliterator.OfPrimitive<T,T_CONS,T_SPLITR>>CONCURRENT, DISTINCT, IMMUTABLE, NONNULL, ORDERED, SIZED, SORTED, SUBSIZED| Modifier | Constructor and Description |
|---|---|
protected |
AbstractSpliterator(long est,
int additionalCharacteristics)
Creates a spliterator reporting the given estimated size and
additionalCharacteristics.
|
| 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<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.
|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, waitforEachRemaining, getComparator, getExactSizeIfKnown, hasCharacteristics, tryAdvanceprotected AbstractSpliterator(long est,
int additionalCharacteristics)
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.public Spliterator<T> trySplit()
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:
estimateSize() before splitting,
must, after splitting, be greater than or equal to estimateSize()
for this and the returned Spliterator; andSUBSIZED, 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.
trySplit in interface Spliterator<T>Spliterator covering some portion of the
elements, or null if this spliterator cannot be splitpublic long estimateSize()
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.
estimateSize in interface Spliterator<T>Long.MAX_VALUE if infinite,
unknown, or too expensive to compute.public int characteristics()
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.
characteristics in interface Spliterator<T>