RxJava Scheduler to observe on main thread

Convert the Observable to a BlockingObservable via .toBlocking(); this gives you blocking methods to wait for completion, get one item, etc.

For RxJava2 use "blockingSubscribe()"

Flowable.fromArray(1, 2, 3)
                .subscribeOn(Schedulers.computation())
                .blockingSubscribe(integer -> {
                    System.out.println(Thread.currentThread().getName());
                });