Upstream - the upstream value typeDownstream - the downstream value type@FunctionalInterface public interface ObservableTransformer<Upstream,Downstream>
Observables.| Modifier and Type | Method and Description | 
|---|---|
| @NonNull ObservableSource<Downstream> | apply(@NonNull Observable<Upstream> upstream)Applies a function to the upstream  Observableand returns anObservableSourcewith
 optionally different element type. | 
@NonNull @NonNull ObservableSource<Downstream> apply(@NonNull @NonNull Observable<Upstream> upstream)
Observable and returns an ObservableSource with
 optionally different element type.upstream - the upstream Observable instanceObservableSource instance