Java.util.concurrent.Flow will be introduced in JDK9. Flow is a standard for asynchronous stream processing and is discussed in Reactive Streams.
The Observer / Observable model has been available since JDK1.0, but with the introduction of Flow in JDK9, the following will be deprecated.
A sample program can be found in the Flow API documentation. It's not that complicated, but I'm going back and forth between three classes, so I wrote a sequence diagram.