The stream is a sequence of ongoing events one after another, which is ordered in time. The stream has a normal value and an error in case of something going wrong; it can have a completion state and, if everything goes well, the stream completes normally.
As the stream is ongoing events, these events trigger asynchronously, and upon the triggering of each event, one callback method will be executed. The one who listens to the event is called as subscriber and the process as subscribing to the events. The stream under observation can be denoted as subject or observable.
The Reactive stream is not a very old concept. In 2013, engineers from Netflix, TypeSafe, and Pivotal came together and started working on it. The streams used for Akka and Scala were difficult to grasp for business logic developments. The Rx-based approach came in discussion between Roland Kuhn and Erik Meijer, which was centric to the asynchronous approach, and the specification...