ObserveOnObservable.java

        Observable.just("A", "BB", "CCC", "DDDD", "EEEEE", "FFFFFF") // UI
                .map(str -> str.length()) // UI
                .observeOn(Schedulers.computation()) //Changing the thread
                .map(length -> 2 * length)
                .subscribe(new Observer<Integer>() {
                    @Override
                    public void onSubscribe(Disposable d) {

                    }

                    @Override
                    public void onNext(Integer integer) {
                        System.out.println("2 * length of string: " + integer);
                    }

                    @Override
                    public void onError(Throwable e) {

                    }

                    @Override
                    public void onComplete() {

                    }
                });