static <A, B> Stream<Pair<A, B>> zip(Stream<A> as, Stream<B> bs)
{
Iterator<A> i=as.iterator();
return bs.filter(x->i.hasNext()).map(b->new Pair<>(i.next(), b));
}
This does not offer parallel execution but neither did the original zip implementation.
And as F. Böller has pointed out it doesn’t work if bs is infinite and as is not. For a solution which works for all possible combinations of infinite and finite streams, an intermediate Iterator which checks both sources within the hasNext method seems unavoidable¹:
static <A, B> Stream<Pair<A,B>> zip(Stream<A> as, Stream<B> bs) {
Iterator<A> i1 = as.iterator();
Iterator<B> i2 = bs.iterator();
Iterable<Pair<A,B>> i=()->new Iterator<Pair<A,B>>() {
public boolean hasNext() {
return i1.hasNext() && i2.hasNext();
}
public Pair<A,B> next() {
return new Pair<A,B>(i1.next(), i2.next());
}
};
return StreamSupport.stream(i.spliterator(), false);
}
If you want parallel capable zipping you should consider the source of the Stream. E.g. you can zip two ArrayLists (or any RandomAccessList) like
ArrayList<Foo> l1=new ArrayList<>();
ArrayList<Bar> l2=new ArrayList<>();
IntStream.range(0, Math.min(l1.size(), l2.size()))
.mapToObj(i->new Pair(l1.get(i), l2.get(i)))
. …
¹(unless you implement a Spliterator directly)
