I came to know while studying that Parallelism
is a main advantage of Spliterator
.
This may be a basic question but can anyone explain me the main differences between Iterator
and Spliterator
and give some examples?
The names are pretty much self-explanatory, to me. Spliterator
== Splittable Iterator : it can split some source, and it can iterate it too. It roughly has the same functionality as an Iterator
, but with the extra thing that it can potentially split into multiple pieces: this is what trySplit
is for. Splitting is needed for parallel processing.
An Iterator
always has an unknown size: you can traverse elements only via hasNext/next
; a Spliterator
can provide the size (thus improving other operations too internally); either an exact one via getExactSizeIfKnown
or a approximate via estimateSize
.
On the other hand, tryAdvance
is what hasNext/next
is from an Iterator
, but it's a single method, much easier to reason about, IMO. Related to this, is forEachRemaining
which in the default implementation delegates to tryAdvance
, but it does not have to always be like this (see ArrayList
for example).
A Spliterator also is a "smarter" Iterator, via its internal properties like DISTINCT
or SORTED
, etc (which you need to provide correctly when implementing your own Spliterator
). These flags are used internally to disable unnecessary operations; see for example this optimization:
someStream().map(x -> y).count();
Because size does not change in the case of the stream, the map
can be skipped entirely, since all we do is counting.
You can create a Spliterator around an Iterator if you need to, via:
Spliterators.spliteratorUnknownSize(yourIterator, properties)