Rx Observable that doesn't start publishing until it has a subscriber. Observers that subscribe after the first subscriber only see items that are emitted after they have subscribed.

gistfile1.java

public class Temp {
	public static final ScheduledExecutorService s = Executors.newScheduledThreadPool(1);

	public static void main(String[] args) throws InterruptedException {
		final ConnectableObservable<Long> source = Observable.create(new OnSubscribe<Long>() {
			@Override
			public void call(final Subscriber<? super Long> t1) {
				final AtomicInteger n = new AtomicInteger(0);
				s.scheduleAtFixedRate(new Runnable() {

					@Override
					public void run() {
						t1.onNext((long)n.incrementAndGet());						
					}
				}, 1, 1, TimeUnit.SECONDS);
			}
		}).publish();

		Observable<Long> result = Observable.create(new OnSubscribe<Long>() {
			@Override
			public void call(Subscriber<? super Long> arg0) {
				source.subscribe(arg0);
				source.connect();
			}
		});

		result.subscribe(new Action1<Long>() {
			@Override
			public void call(Long t1) {
				System.out.println("A" + t1);
			}
		});

		Thread.sleep(3000);

		result.subscribe(new Action1<Long>() {
			@Override
			public void call(Long t1) {
				System.out.println("B" + t1);
			}
		});
	}
}