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 value to the consumer. So, we may say, an Observable 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 things sequentially to understand it better:

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

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