How to return the next element from a spliterator in java

Question

I want to get the next element from a spliterator, not just "perform action" on the next element. For example by implementing the following method

<T> T getnext(Spliterator<T> s) {

}

All search results I found just said that tryAdvance() was like a combination of an iterators hasNext() and next(), except that is a BIG LIE because I can't get next element, just "perform action on next element".

Answer 1

You can wrap the item in a list and then return from that list:

    public static <T> T getNext(Spliterator<T> spliterator) {
        List<T> result = new ArrayList<>(1);

        if (spliterator.tryAdvance(result::add)) {
            return result.get(0);
        } else {
            return null;
        }
    }

To make it more obvious to the caller that this is an operation that may return null, consider returning Optional:

    public static <T> Optional<T> getNext(Spliterator<T> spliterator) {
        final List<T> result = new ArrayList<>(1);

        if (spliterator.tryAdvance(result::add)) {
            return Optional.of(result.get(0));
        } else {
            return Optional.empty();
        }
    }

Answer 2

There are no direct way but you can use :

<T> T getnext(Spliterator<T> s) {
    Stream<T> stream = StreamSupport.stream(s, false); // convert Spliterator to stream
    Iterable<T> iterable = stream::iterator; // then stream to Iterable
    return iterable.iterator().next(); // then you can get next element
 }

Or in one step like so :

 return StreamSupport.stream(s, false).iterator().next();

Or more simpler :

 return Spliterators.iterator(s).next();

Answer 3

transform spliterator to stream

<T> Optional<T> getnext(Spliterator<T> s) {
    return StreamSupport.stream(s, false).findFirst();
}

example

List<String> lst = List.of("a", "b");
Spliterator<String> spliterator = lst.spliterator();

System.out.println(getnext(spliterator)); //Optional[a]
System.out.println(getnext(spliterator)); //Optional[b]