See: Description
| Class | Description | 
|---|---|
| AsyncSubject<T> | Subject that publishes only the last item observed to each  Observeronce the sourceObservablehas completed. | 
| BehaviorSubject<T> | Subject that emits the most recent item it has observed and all subsequent observed items to each subscribed
  Observer. | 
| PublishSubject<T> | Subject that, once an  Observerhas subscribed, emits all subsequently observed items to the
 subscriber. | 
| ReplaySubject<T> | Subject that buffers all items it observes and replays them to any  Observerthat subscribes. | 
| SerializedSubject<T,R> | Wraps a  Subjectso that it is safe to call its variousonmethods from different threads. | 
| Subject<T,R> | Represents an object that is both an Observable and an Observer. | 
| TestSubject<T> | A variety of Subject that is useful for testing purposes. | 
| UnicastSubject<T> | A Subject variant which buffers events until a single Subscriber arrives and replays them to it
 and potentially switches to direct delivery once the Subscriber caught up and requested an unlimited
 amount. |