So far, we have been working with Observables, Subscriber, Observer, and Scheduler entities to create our RxJava functional processing lines. In this section, we will introduce the reader to a new kind of entity in the RxJava framework, the Subject. The Subject is a sort of adapter or bridge entity that acts as an Observable and Observer:
public abstract class Subject<T,R> extends Observable<R> implements Observer<T>
Since it can act as a Subscriber, it can subscribe to one or more Observables that emit Objects of the generic type T, and since it acts as an Observable, it can emit events of the generic type R and receive subscriptions from other Subscriber. Hence, it can emit events of the same type as received or emit a different type of event.
For example, the Subject<String, Integer> will receive events of type String and emit events of the type Integer.
The Subject could receive the events from the Observable...