How to interleave (merge) two Java 8 Streams?

Question

 Stream a = Stream.of(\"one\", \"three\", \"five\");
 Stream b = Stream.of(\"two\", \"four\", \"six\");

What do I need

Answer 1

This may not be a good answer because
(1) it collects to map, which you don't want to do I guess and
(2) it is not completely stateless as it uses AtomicIntegers.

Still adding it because
(1) it is readable and
(2) community can get an idea from this and try to improve it.

Stream a = Stream.of("one", "three", "five");
Stream b = Stream.of("two", "four", "six");

AtomicInteger i = new AtomicInteger(0);
AtomicInteger j = new AtomicInteger(1);

Stream.of(a.collect(Collectors.toMap(o -> i.addAndGet(2), Function.identity())),
        b.collect(Collectors.toMap(o -> j.addAndGet(2), Function.identity())))
        .flatMap(m -> m.entrySet().stream())
        .sorted(Comparator.comparing(Map.Entry::getKey))
        .forEach(e -> System.out.println(e.getValue())); // or collect

Output

one
two
three
four
five
six

@Holger's edit

Stream.concat(a.map(o -> new AbstractMap.SimpleEntry<>(i.addAndGet(2), o)),
        b.map(o -> new AbstractMap.SimpleEntry<>(j.addAndGet(2), o)))
        .sorted(Map.Entry.comparingByKey())
        .forEach(e -> System.out.println(e.getValue())); // or collect