v1.java

        Observable.just("[email protected]").flatMap(new Function<String, ObservableSource<String>>() {
            @Override
            public ObservableSource<String> apply(String s) throws Exception {
                // return Observable.concat(validateEmail(s), validateNonNull(s));



                return Observable.zip(validateEmail(s), validateNonNull(s), new BiFunction<String, String, String>() {
                    @Override
                    public String apply(String s, String s2) throws Exception {
                        return s;
                    }
                });
            }
        }).subscribe(new Observer<String>() {
            @Override
            public void onSubscribe(Disposable d) {

            }

            @Override
            public void onNext(String s) {

            }

            @Override
            public void onError(Throwable e) {

            }

            @Override
            public void onComplete() {

            }
        });

v2.java

        Observable.just(emailView, passwordView).flatMap(new Function<TextView, ObservableSource<DataValidator>>() {
            @Override
            public ObservableSource<DataValidator> apply(TextView textView) throws Exception {
                List<DataValidator> list = Arrays.asList(new DataValidator(), new DataValidator()); // TODO: ViewからValidatorを取得
                return Observable.fromIterable(list);
            }
        }).flatMap(new Function<DataValidator, ObservableSource<ValidateResult>>() {
            @Override
            public ObservableSource<ValidateResult> apply(DataValidator dataValidator) throws Exception {
                return Observable.just(dataValidator.validate());
            }
        }).subscribe(new Observer<ValidateResult>() {
            @Override
            public void onSubscribe(Disposable d) {

            }

            @Override
            public void onNext(ValidateResult validateResult) {

            }

            @Override
            public void onError(Throwable e) {

            }

            @Override
            public void onComplete() {

            }
        });

v3.java

        Observable.just(emailView, passwordView).flatMap(new Function<TextView, ObservableSource<DataValidator>>() {
            @Override
            public ObservableSource<DataValidator> apply(TextView textView) throws Exception {
                List<DataValidator> list = Arrays.asList(new DataValidator(), new DataValidator()); // TODO: ViewからValidatorを取得
                return Observable.fromIterable(list);
            }
        }).flatMap(new Function<DataValidator, ObservableSource<ValidateResult>>() {
            @Override
            public ObservableSource<ValidateResult> apply(DataValidator dataValidator) throws Exception {
                return dataValidator.validate();
            }
        }).subscribe(new Observer<ValidateResult>() {
            @Override
            public void onSubscribe(Disposable d) {

            }

            @Override
            public void onNext(ValidateResult validateResult) {

            }

            @Override
            public void onError(Throwable e) {

            }

            @Override
            public void onComplete() {

            }
        });