Question - Change Listener in RxJava

[bytecod3r]

I am very new to RxJava,

I just want to ask if RxJava has any alternative feature to JavafX Observable Change Listener. So I want to implement something like below with RxJava. I hope I am not wrong about Observable in RxJava and its similar to JavaFx..

ObservableList ov = new ....
ov .addListener(new ChangeListener<String>() {
        @Override
        public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
            if (!newValue.matches("\\d*")) {
                textField.setText(newValue.replaceAll("[^\\d]", ""));
            }

            if (newValue.isEmpty())
                textField.setText("0");

        }
    });

[akarnokd]

The closest thing would be to use PublishSubject and scan, possibly with distinctUntilChanged to filter out subsequent duplicates.

var subject = PublishSubject.create();

subject
.distinctUntilChanged()
.scan((prev, current) -> {
    // process change
    return current;
})
.subscribe(...);

subject.onNext("New value");
subject.onNext("New value2");

[bytecod3r]

Thanks,
Do you think RxJava is a good replacement for FXObservable? Does my question even make sense?

[akarnokd]

RxJava can do a lot more, but you'd need to bridge it back to JavaFX constructs. There is the https://github.com/ReactiveX/RxJavaFX project but I don't know where they are at the moment regarding version support.

[bytecod3r]

@akarnokd, Thanks for very quick responses.

I think I did not explain the issue well - I am using JavaFx in my java console app that has no GUI. Just because of the Property and addlistener of obervablelist. And I dont need JavaFX actually if I have a better way to fire a function when a change happens in a list,variabl, etc.

So I was searching for replacement of JavaFX Observable then I found your project.

So in conclusion, there is no UI exists, can I use FxJava to implement a change for a List and fire a function if a new value added or removed from the list from different thread? This is to achieve the same result as listString.Addlistener(() -> ...) in javafx. If I can find an alternative method then I can remove JavaFx completely from my console app.

Im not expert programmer so any other hint appreaciated.

[akarnokd]

You'd have to write such functionality on top of a data structure with the tools I mentioned above.

[bytecod3r]

Yes I tried that, but it does not replicate same functionality.

Currently what I have is a ObservableList<Test> testOV then attached a testOV.addlistener() to it to trigger a function when a changes happens, also testOV can list down the items that it stores.

By using the below, I can't list the items in the subject, or remove any item.

 PublishSubject<Test> subject = PublishSubject.create();

        subject
                .distinctUntilChanged()
                .subscribe(s -> System.out.println(s.getId()));


        subject.onNext(new TestBuilder().withId("1111").build());
        subject.onNext(new TestBuilder().withId("2222").build());

[akarnokd]

The subject is there for dispatching notifications, you'll still need a list to store the items.

Here is an example about listening to hashmap changes: https://stackoverflow.com/a/59834853/61158