Working with Modern Stream Features

Stream.of(1, 2, 3, 4, 5)
    .<Integer>mapMulti((n, sink) -> {
        if (n % 2 == 0) {
            sink.accept(n);
            sink.accept(n * n);
        }
    })
    .forEach(System.out::println);    // 2, 4, 4, 16

record Stats(double avg, long count) {}
Stats s = numbers.stream().collect(
    Collectors.teeing(
        Collectors.averagingInt(Integer::intValue),
        Collectors.counting(),
        (avg, count) -> new Stats(avg, count)
    ));

Gatherer<Integer, ?, Integer> runningMax =
    Gatherer.ofSequential(
        () -> new int[]{ Integer.MIN_VALUE },
        (state, n, downstream) -> {
            state[0] = Math.max(state[0], n);
            return downstream.push(state[0]);
        }
    );

Stream.of(1,2,3,4,5,6,7)
    .gather(Gatherers.windowFixed(3))
    .forEach(System.out::println);
// [1,2,3], [4,5,6], [7]