techindepth

Observable.from(letters)
  .defaultIfEmpty("Observable is empty")
  .first()
  .subscribe(s -> result += s);
  
assertTrue(result.equals("a"));

techindepth

Observable.empty()
  .defaultIfEmpty("Observable is empty")
  .subscribe(s -> result += s);
assertTrue(result.equals("Observable is empty"));

techindepth

Observable.from(numbers)
  .filter(i -> (i % 2 == 1))
  .subscribe(i -> result += i);
  
assertTrue(result.equals("13579"));

techindepth

Observable.from(numbers)
  .groupBy(i -> 0 == (i % 2) ? "EVEN" : "ODD")
  .subscribe(group ->
    group.subscribe((number) -> {
        if (group.getKey().toString().equals("EVEN")) {
            EVEN[0] += number;
        } else {
            ODD[0] += number;
        }
    })

techindepth

String[] letters = {"a", "b", "c"};
Observable.from(letters)
  .scan(new StringBuilder(), StringBuilder::append)
  .subscribe(total -> result += total.toString());
assertTrue(result.equals("aababc"));

techindepth

Observable<String> getTitle() {
    return Observable.from(titleList);
}
Observable.just("book1", "book2")
  .flatMap(s -> getTitle())
  .subscribe(l -> result += l);
 
assertTrue(result.equals("titletitle"));

techindepth

Observable.from(letters)
  .map(String::toUpperCase)
  .subscribe(letter -> result += letter);
assertTrue(result.equals("ABCDEFG"));

techindepth

Flowable<Integer> integerFlowable = Flowable.range(1,500000);

integerFlowable.reduce(new BiFunction<Integer, Integer, Integer>() {
    @Override
    public Integer apply(Integer integer, Integer integer2) throws Exception {
        return integer + integer2;
    }
});

Subscriber<Integer> integerSubscriber = new Subscriber<Integer>() {

techindepth

Observable<Integer> integerObservable = Observable.empty();

Completable completable = integerObservable.ignoreElements();


CompletableObserver completableObserver = new CompletableObserver() {
    @Override
    public void onSubscribe(Disposable d) {
        System.out.println("onSubscribe");
    }

techindepth

Observable<Integer> integerObservable = Observable.just(1, 2, 3, 4, 5);

Maybe<Integer> integerMaybe = integerObservable.reduce(new BiFunction<Integer, Integer, Integer>() {
    @Override
    public Integer apply(Integer integer, Integer integer2) throws Exception {
        if (integer > integer2)
            return integer;
        else
            return integer2;
    }