Observables

As we discussed earlier, in reactive programming, Observable has an underlying computation that produces values that can be consumed by a consumer (Observer). The most important thing here is that the consumer (Observer) doesn't pull values here; rather, Observable pushes the values to the consumer. So, we can say that an Observable interface is a push-based, composable Iterator that emits its items through a series of operators to the final Observer, which finally consumes the items. Let's now break these things down sequentially to understand it better:

• Observer subscribes to Observable
• Observable starts emitting the items that it has in it
• Observer reacts to whatever item the Observable emits

So, let's delve into how Observable works through its events/methods, namely onNext, onComplete, and onError.

How Observable works

As we stated earlier, an Observable value has the following three most important events/methods:

• onNext: The Observable interface passes all the items one by one...