Observer is deprecated in Java 9. What should we use instead of it?

Question

Java 9 came out, and Observer has been deprecated. Why is that? Does it mean that we shouldn\'t implement observer pattern anymore?

It would be good to know what is

Answer 1

Why Observer is deprecated in Java 9?

Ans: The Observable class and the Observer interface have been deprecated in Java 9 because the event model supported by Observer and Observable is quite limited, the order of notifications delivered by Observable is unspecified, and state changes are not in one-for-one correspondence with notifications.

See Java doc https://docs.oracle.com/javase/9/docs/api/java/util/Observable.html

Alternate of Observer pattern?

There are many alternatives of Observer design pattern and Reactive Streams is one of them.

Reactive Streams or Flow API:

Flow is a class introduced in Java 9 and has 4 interrelated interfaces : Processor, Publisher, Subscriber and Subscription.

Flow.Processor : A component that acts as both a Subscriber and Publisher.

Flow.Publisher : A producer of items received by Subscribers.

Flow.Subscriber : A receiver of messages.

Flow.Subscription: Message control linking a Flow.Publisher and Flow.Subscriber.

See Java doc https://docs.oracle.com/javase/9/docs/api/java/util/concurrent/Flow.html