How to use observable and observer correctly with RxJava?

Firstly, thank you everyone for spending time helping me. I am not sure whether what I write the bellow code is correct or not. So if you do see any problem please let me know and maybe suggest some way to solve it.

So I want to apply rxjava in my 2 classes to present the observer and observable. So that whenever the currentPage in observable change by clicking a button in JavaFX, the observer will be notify and update. Despite the code run fine, I am not sure creating an observable variable every time is right or not? And also is the onComplete will un-subscribe or do some cleaning or not (I suspect that my code can have some leak memory). Since I cannot find any online resource that have a clear summarize/ explanation about this, I really need help from you guys. Thank you!

P/s: I am new to RxJava so please don't be harsh on me. Thank you!

So the PrimaryInfoModel is the observer:

public class PrimaryInfoModel {
    private int currentPage;
    private int currentCategory;

    public static Observer<Integer> getPageObserver() {
        return new Observer<>() {
            @Override
            public void onSubscribe(@NonNull Disposable d) {
                System.out.println("onSubscribe");
            }

            @Override
            public void onNext(@NonNull Integer integer) {
                System.out.println(integer); currentPage = integer;
            }

            @Override
            public void onError(@NonNull Throwable e) {
                System.out.println(e.getMessage());
            }

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

And the NavigationController is the obserable:

public class NavigationController implements Initializable {

    private int currentPage;
    private Observable<Integer> observable;

    public NavigationController() {
    }

    @FXML
    private Button page1, page2, page3, page4, page5, prevPage, nextPage;

    @Override
    public void initialize(URL url, ResourceBundle resourceBundle) {
        setCurrentButton();
    }

    @FXML
    private void setCurrentButton(MouseEvent event) {
        int oldPage = currentPage;
        cleanEffect();
        Object source = event.getSource();
        if (source == page1) {
            currentPage = 0;
        }
        if (source == page2) {
            currentPage = 1;
        }
        if (source == page3) {
            currentPage = 2;
        }
        if (source == page4) {
            currentPage = 3;
        }
        if (source == page5) {
            currentPage = 4;
        }
        if (oldPage != currentPage) {
            observable = getObservable();
            observable.observeOn(Schedulers.io()).subscribeOn(Schedulers.io()).subscribe(PrimaryInfoModel.getPageObserver());
        }
    }

    private Observable<Integer> getObservable() {
        return Observable.create(new ObservableOnSubscribe<Integer>() {
            @Override
            public void subscribe(@NonNull ObservableEmitter<Integer> emitter) throws Throwable {
                emitter.onNext(currentPage);
                emitter.onComplete();
            }
        });
    }
}