DefaultIfEmptyObservable.java

        Observable.create(new ObservableOnSubscribe<Integer>() {
            @Override
            public void subscribe(ObservableEmitter<Integer> emitter) {
                int num = (int) (Math.random() * 10);
                if (num % 2 == 0) {
                    emitter.onNext(num);
                }
                emitter.onComplete();
            }
        })
                .defaultIfEmpty(-10)
                .subscribe(new Observer<Integer>() {
                    @Override
                    public void onSubscribe(Disposable d) {

                    }

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

                    @Override
                    public void onError(Throwable e) {

                    }

                    @Override
                    public void onComplete() {

                    }
                });