CompletableObservable.java

        Completable.create(new CompletableOnSubscribe() {
            @Override
            public void subscribe(CompletableEmitter emitter) {
                Thread.sleep(1000);
                emitter.onComplete();
            }
        })
                .subscribeOn(Schedulers.io())
                .subscribe(new CompletableObserver() {
                    @Override
                    public void onSubscribe(Disposable d) {

                    }

                    @Override
                    public void onComplete() {
                        System.out.println("onComplete is called");
                    }

                    @Override
                    public void onError(Throwable e) {
                        System.out.println("onError is called" + e.getMessage());
                    }
                });