title: Observer is deprecated in Java 9. What should we use instead of it?
body: <p>Java 9 came out, and <a href="https://docs.oracle.com/javase/9/docs/api/java/util/Observer.html" rel="noreferrer"><code>Observer</code></a> has been deprecated.
  Why is that? Does it mean that we shouldn't implement observer pattern anymore? </p>
  
  <p>It would be good to know what is a better alternative?</p>