MapObservable.java

   getOriginalObservable()
                .map(new Function<Integer, Integer>() {
                    @Override
                    public Integer apply(final Integer integer)  {
                        return (integer * 2);
                    }
                })
                .subscribeOn(Schedulers.io())
                .subscribe(new Observer<Integer>() {
                    @Override
                    public void onSubscribe(Disposable d) {

                    }

                    @Override
                    public void onNext(Integer integer) {
                        System.out.println("onNext: " + integer);
                    }

                    @Override
                    public void onError(Throwable e) {

                    }

                    @Override
                    public void onComplete() {

                    }
 });


private Observable<Integer> getOriginalObservable() {
        final List<Integer> integers = Arrays.asList(1, 2, 3, 4, 5, 6);

        return Observable
                .create(new ObservableOnSubscribe<Integer>() {
            @Override
            public void subscribe(ObservableEmitter<Integer> emitter) {
                for(Integer integer : integers) {

                    if (!emitter.isDisposed()) {
                        emitter.onNext(integer);
                    }
                }

                if(!emitter.isDisposed()) {
                    emitter.onComplete();
                }
            }

        });
    }