Multicasting also allows us to cache values that are shared across multiple Observers. This may sound surprising, but when you think about it long enough, you may realize this makes sense. If we are sharing data across multiple Observers, it makes sense that any caching feature would be shared across Observers too. Replaying and caching data is a multicasting activity, and we will explore how to do it safely and efficiently with RxJava.
The replay() operator is a powerful way to hold onto previous emissions within a certain scope and re-emit them when a new Observer comes in. It will return a ConnectableObservable that will both multicast emissions as well as emit previous emissions defined in a scope. Previous emissions it caches will fire immediately to a new Observer so it is caught up, and then it will fire current emissions from that point forward.
Let's start with a replay() with no arguments. This will replay all previous emissions to tardy Observers,...