MaxObservable.java

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

        MathObservable
             .max(observable)
             .subscribe(new Observer<Integer>() {
                 @Override
                 public void onSubscribe(Disposable d) {

                 }

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

                 @Override
                 public void onError(Throwable e) {

                 }

                 @Override
                 public void onComplete() {

                 }
             });