AtomicInteger lettersCloseCount = new AtomicInteger();
    Stream<String> letters = Stream.of("a", "b", "c").onClose(lettersCloseCount::incrementAndGet);
    AtomicInteger numbersCloseCount = new AtomicInteger();
    Stream<Integer> numbers = Stream.of(1, 2, 3).onClose(numbersCloseCount::incrementAndGet);

    Stream<String> zipped = Streams.zip(letters, numbers, (a, b) -> a + ":" + b);

    zipped.close();