ScanObservable.java

        Observable.range(1, 10)
                .scan(new BiFunction<Integer, Integer, Integer>() {
                    @Override
                    public Integer apply(Integer integer, Integer integer2) {
                        return (integer + integer2);
                    }
                })
                .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() {

                    }
                });