Real World Java 9

How is Java 9 going to change the way developers work?


The feature we always hear about whenever Java 9 is in the news is Jigsaw, modularity. But this doesn’t scratch the same developer itch that Java 8’s lambdas and streams did, and we’re left with a vague sensation that the next version might not be that interesting.

Java 9 actually has a lot of great additions and changes to make development a bit nicer. These features can’t be lumped under an umbrella term like Java 8’s lambdas and streams, the changes are scattered throughout the APIs and language features that we regularly use.

In this presentation Trisha will show, via live coding:

  • How we can use the new Flow API to utilise Reactive Programming
  • How the improvements to the Streams API make it easier to control real-time streaming data
  • How to the Collections convenience methods simplify code

Along the way we’ll bump into other Java 9 features, including some of the additions to interfaces and changes to deprecation. We’ll see that once you start using Java 9, you can’t go back to Before.




The code for this presentation was originally created to demonstrate Java 8 code in Java 8 in Anger, take a look at the videos there to see more background on the application and how it used Java 8 Streams and Lambda Expressions for the core business logic. The code and the presentation evolved to include some Java 9 features.

I have another Java 9 talk based off this code, Anticipating Java 9 - Functionality and Tooling, which demos more individual Java 9 features and talks specifically about IntelliJ IDEA’s support for it.


  • The full application with all Java 9 code is currently under the working-system branch, the presentation builds off the code in start_point.
  • Original Java 8 code comes from, the master branch has the most up-to-date final working Java 8 application. JUnit 5 tests come from the junit-5 branch. Java 8 and 9 features live side-by-side in yow-brisbane. That app was built with Java build 9-ea+146, but does not work with build 9-ea+156

IntelliJ IDEA

The earlier version of this talk runs on IntelliJ IDEA 2017.1, which supports Jigsaw much better than earlier versions. However, I’m currently using 2017.2 EAP as later versions of Java 9 do not play nicely with earlier versions of IntelliJ. The current combo I have working is Java 9 build 9-ea+166 and IntelliJ IDEA Build #IU-172.2103.15.

Java 9


Migrating to Java 9 (and Jigsaw)

Reactive Programming and RxJava

Multi-Release JAR Files

Stack-Walking API

Process API