RXjava implement an observable for an object update

Question

How can I add an observable to an Integer object, such that I get notified of every object update? In this case Integer number = 0; and I would like to get notified every time I add for example 1. Initially I just want to log the event. This is what I have so far, but I'm stuck.

code:

Subscriber<Integer> num = new Subscriber<Integer>() {
        @Override
        public void onNext(Integer num) { Log.d("RX", num.toString()); }

        @Override
        public void onError(Throwable e) { Log.d("RX", "error"); }

        @Override
        public void onCompleted() { Log.d("RX", "completed"); }
    };

    Observable.just(number)
            /*.doOnNext(new Action1<Integer>() {
                @Override
                public void call(Integer integer) {
                    Log.d("RX", "Updated integer" + integer.toString());
                }
            })*/
            /*.flatMap(new Func1<Integer, Observable<?>>() {
                @Override
                public Observable<?> call(Integer integer) {
                    Log.d("RX", "Updated integer" + integer.toString());
                    return Observable.just(number);
                }
            })*/
            .subscribe(num);

Answer 1

Without knowing exactly what you are trying to achieve it's hard to give the best answer but you could implement an ObservableInteger class along the lines of the following:

public class ObservableInteger {

    private Integer value;
    private PublishSubject<Integer> subject = PublishSubject.create();

    public Integer getValue() {
        return value;
    }

    public void setValue(Integer value) {
        this.value = value;
        subject.onNext(value);
    }

    public Observable<Integer> getObservable() {
        return subject.asObservable();
    }
}

Then you are able to subscribe to it:

    ObservableInteger obInt = new ObservableInteger();

    Subscription s = obInt
            .getObservable()
            .subscribe(
                    integer -> {
                        // each time a new value is set
                        // it will be emitted here
                    },
                    Throwable::printStackTrace
            );

Answer 2

I came across this post today and realized it is written for RxJava1. There are several changes in RxJava 2 . Some of them affecting the above sample. (.subscribe returns a Disposable https://github.com/ReactiveX/RxJava/wiki/What's-different-in-2.0#subscription and .asObservable() is now .hide() in RxJava 2.0 https://github.com/ReactiveX/RxJava/wiki/What's-different-in-2.0#instance-methods )

Here is the RxJava2 compatible solution of Jahnolds answer:

    public class ObservableInteger {

        private Integer value;
        private PublishSubject<Integer> subject = PublishSubject.create();

        public Integer getValue() {
            return value;
        }

        public void setValue(Integer value) {
            this.value = value;
            subject.onNext(value);
        }

        public Observable<Integer> getObservable() {
            return subject.hide();
        }
    }

and subscribe like so:

    ObservableInteger obInt = new ObservableInteger();

    Disposable d = obInt
            .getObservable()
            .subscribe(
                    integer -> {
                        // each time a new value is set
                        // it will be emitted here
                    },
                    Throwable::printStackTrace
            );