RXJava，如何异步执行两个可观察对象，在两个对象都完成后运行函数，并获取两个线程之间的时间差？

import io.reactivex.Observable;
import io.reactivex.schedulers.Schedulers;

public class Example {
    public static void main(String[] args) {
        long startTime = System.currentTimeMillis();

        Observable<Integer> observable1 = Observable.just(1, 2, 3)
                .subscribeOn(Schedulers.io())
                .doOnComplete(() -> System.out.println("Observable 1 completed"));

        Observable<Integer> observable2 = Observable.just(4, 5, 6)
                .subscribeOn(Schedulers.io())
                .doOnComplete(() -> System.out.println("Observable 2 completed"));

        Observable.zip(observable1, observable2, (result1, result2) -> {
            long endTime = System.currentTimeMillis();
            long timeDifference = endTime - startTime;
            System.out.println("Time difference: " + timeDifference + "ms");
            return result1 + result2;
        })
                .subscribeOn(Schedulers.io())
                .subscribe(result -> System.out.println("Result: " + result));

        // 等待异步操作完成
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}