Observable.zip example

MainActivity

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Observable.zip(
                getUserPhoto(),
                getUserMetadata(),
                (strings, strings2) -> {
                    ArrayList<String> stringsList = new ArrayList<>();
                    for(int i = 0; i < strings.size(); i++) {
                        stringsList.add(strings.get(i) + " | " + strings2.get(i));
                    }
                    return stringsList;
                })
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(photoWithData -> {
                    for(String s : photoWithData)
                        Log.e("tag", s);
                });
    }

    private Observable<ArrayList<String>> getUserPhoto() {
        ArrayList<String> strings = new ArrayList<>();
        strings.add("one");
        return Observable.fromArray(strings);
    }

    private Observable<ArrayList<String>> getUserMetadata() {
        ArrayList<String> strings = new ArrayList<>();
        strings.add("two");
        return Observable.fromArray(strings);
    }