What is the difference between an Observer and a Subscriber?
EDITED: with @Alrid’s comment tl;dr public abstract class Subscriber<T> implements Observer<T>, Subscription So a Subscriber is an implementation of the Observer, with additional semantics on subscription (it’s more about un-subscription). The code in your question just shows that it passes the Observer interface, instead of the implementation (usual programming practice). Also this code returns a … Read more