RXJava Observable emit items when subscribe with Observer as anonymous type ONLY - rx-java2

Question

When I create a new Observer as anonymous type It works Fine:
Observable<List<Post>> postsListObservable = mApplicationAPI.getPosts();
postsListObservable.
subscribeOn(Schedulers.io()).
observeOn(AndroidSchedulers.mainThread()).subscribe( new Observer<List<Post>>() {
#Override
public void onSubscribe(Disposable d) {
Log.i("ZOKa", "onSubscribe: ");
}
#Override
public void onNext(List<Post> posts) {
Log.i("ZOKa", "onNext: " + posts.size());
}
#Override
public void onError(Throwable e) {
Log.i("ZOKa", "onError: " + e.getMessage());
}
#Override
public void onComplete() {
Log.i("ZOKa", "onComplete: ");
}
});
When I create the Observer as a Dynamic Type it doesn't emit data
Observable<List<Post>> postsListObservable = mApplicationAPI.getPosts();
postsListObservable.
subscribeOn(Schedulers.io()).
observeOn(AndroidSchedulers.mainThread());
Observer<List<Post>> observer = new Observer<List<Post>>() {
#Override
public void onSubscribe(Disposable d) {
Log.i("ZOKa", "onSubscribe: ");
}
#Override
public void onNext(List<Post> posts) {
Log.i("ZOKa", "onNext: " + posts.size());
}
#Override
public void onError(Throwable e) {
Log.i("ZOKa", "onError: " + e.getMessage());
}
#Override
public void onComplete() {
Log.i("ZOKa", "onComplete: ");
}
};
postsListObservable.subscribe(observer);
Logcat for the first code snippet:
com.tripleService.basesetupfordi/I/ZOKa: onSubscribe:
com.tripleService.basesetupfordi/I/ZOKa: onNext: 100:
com.tripleService.basesetupfordi/I/ZOKa: onComplete:
Logcat for the second one:
com.tripleService.basesetupfordi/I/ZOKa: onError: null
So, What is the diff in between?

Answer 1

That's because Operators return new observables, but they don't modify the observable that they were called on. subscribeOn and observeOn in the second example has no impact on the postsListObservable and the observer.
Following should work:
Observable<List<Post>> postsListObservable = mApplicationAPI.getPosts();
Observable<List<Post>> postsListObservable2 = postsListObservable.
subscribeOn(Schedulers.io()).
observeOn(AndroidSchedulers.mainThread());
Observer<List<Post>> observer = new Observer<List<Post>>() {
...
};
postsListObservable2.subscribe(observer);
or
Observable<List<Post>> postsListObservable = mApplicationAPI.getPosts();
Observer<List<Post>> observer = new Observer<List<Post>>() {
...
};
postsListObservable.
subscribeOn(Schedulers.io()).
observeOn(AndroidSchedulers.mainThread()).subscribe(observer);