Julian Raj Manandhar Yes you are right. Btw I have another question.
Mert Şimşek

I’m new on RxJava too :) Follow the ReactiveX official document. ObserveOn operator affects the thread that the Observable will use below where that operator appears. Not sure if it works but could you try this:

Observable<RadioWrapper> radioListApi = apiSource.getRadioList()
.doOnNext(radioWrapper -> databaseSource.save(radioWrapper))