如何在没有flatmap的情况下使用RxAndroid链接两个订阅？

Observable<Integer> observable1 = Observable.just(1, 2, 3);
Observable<String> observable2 = Observable.just("A", "B", "C");

Observable.zip(observable1, observable2, new BiFunction<Integer, String, String>() {
    @Override
    public String apply(Integer integer, String s) throws Exception {
        return integer + s;
    }
})
.subscribe(new Consumer<String>() {
    @Override
    public void accept(String s) throws Exception {
        // 处理配对后的数据
        Log.d(TAG, "onNext: " + s);
    }
});