Stream subscriber

A subscriber is used to listen to events generated by a publisher. When a subscriber registers to a publisher, it receives events in the following order:

As a result, the subscriber has the following interface to handle all of these events:

public interface Subscriber<T> {
    public void onSubscribe(Subscription s);
    public void onNext(T t);
    public void onError(Throwable t);
    public void onComplete();
}

Let's cover each of these methods in detail, as follows:

• onSubscribe(Subscription s): As soon as a publisher has received a subscriber, it generates a subscription event. The generated subscription event is then received in the specified method.
• onNext (T): All data events generated by a publisher are received by the subscriber in the specified method. A publisher may or may not publish a data event before closing the stream.
• onCompletion(): This refers to the completion event, which must be handled by a subscriber. Once a completion event is received, the subscription is considered void.
• onError(): This refers to the error event, which must be handled by a subscriber. An error can occur at any moment—while building a subscription or while generating the next data event. In any case, the publisher must send the error event. Once the event is received, the subscription is considered void.