为什么 RxJava2 不向线程发送数据

Question

I have read the RxJava's doc. and try the demo below: The Output is d = [0]d = false

May I know the reason that: why the data does not emitter to the Observer

RxJava version: 2.2.6

        Observable.just("aa","bbb")
                .observeOn(Schedulers.newThread())
                .map(s -> {
                    System.out.println("s = [" + s + "]");
                    return s.toUpperCase();
                })
                .subscribeOn(Schedulers.single())
                .observeOn(Schedulers.io())
                .subscribe(new Observer<String>() {
                    @Override
                    public void onSubscribe(Disposable d) {
                        System.out.println("d = [" + d + "]"+"d = "+ d.isDisposed());
                    }

                    @Override
                    public void onNext(String s) {
                        System.out.println("s = [" + s + "]");
                    }

                    @Override
                    public void onError(Throwable e) {

                    }

                    @Override
                    public void onComplete() {

                    }
                });

Answer 1

With all the thread switches you have added to your subscription your subscription is not running on the main thread anymore. This also means that nothing is stopping the main thread anymore and you application quits before it could print the data you want.

For testing purposes you can add a Thread.sleep(1000); at the end of your main() method (where I suppose you have added this code). Then you will see the output from the System.out.println() statements. Other solutions are to not use subscribeOn() or observeOn() and stay on the current thread. Also, you can use blockingSubscribe() to wait for the subscription to finish before continuing on the main thread.