import io.reactivex.Observable;
import io.reactivex.Observer;
import io.reactivex.disposables.Disposable;

public class Launcher {

    public static void main(String[] args) {

        Observable<String> source =
                Observable.just("Alpha", "Beta", "Gamma", "Delta", "Epsilon");

        Observer<Integer> mySubscriber = new Observer<Integer>() {
            @Override
            public void onSubscribe(Disposable d) {

            }

            @Override
            public void onNext(Integer value) {
                System.out.println("RECEIVED: " + value);
            }

            @Override
            public void onError(Throwable e) {
                e.printStackTrace();
            }

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

        source.map(String::length)
                .filter(i -> i >= 5)
                .subscribe(mySubscriber);
    }
}