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:

  • What the Java Platform Module System is and how to make your code modular
  • The improvements to the Streams API that make it easier to control infinite streams
  • How 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 Optional, and a number of other small changes that make coding in Java a bit nicer than it was before.


These are all the available videos, with the most recent at the top. Usually, the more recent the talk the more polished, therefore usually they're better. With this talk, it's more a case of showcasing / focusing on different aspects in different versions.

This JetBrains webinar is the most up-to-date version of the talk, and includes more Java 9 features than any of the others, including a quick look at JShell. It has almost no content on Reactive Streams though, so check out one of the other videos if this is what you're interested in.

  • vJUG, September 2017. Lucky to have 90 minutes to cover the material.
  • GOTO Amsterdam. Less reactive streams, less Jigsaw, marginally more time for the "other" Java 9 features.
  • J on the Beach, Malaga. Pretty much the same as the DevoxxUK version.
  • DevoxxUK. More focus on Jigsaw / Java Modules.
  • QCon London. Much more focus on Reactive Streams: what they are, how they work, and how to migrate an app to use the Reactive Streams API.


These are the latest slides. For earlier versions, see Slideshare.


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.

Articles & More Detail

I've expanded upon the examples in this presentation in a couple of articles about adopting Java 9:


    The full application with all Java 9 code is currently under the
    working-system branch, the presentation builds off the code in _startpoint.
  • 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 earliest version of this talk runs on IntelliJ IDEA 2017.1, which supports Jigsaw much better than pre-2017 versions. However, I'm currently using 2017.3 EAP, as this has the best support for Java 9/JPMS and also a basic version of the Java Console. Read a summary of the Java 9 support in IntelliJ IDEA.

For a 5-minute version of IntelliJ IDEA's support for modularity, watch @jonnyzzz's demo during the JavaOne Keynote.

Java 9

Jigsaw / JPMS


Migrating to Java 9 (and Jigsaw)

Reactive Programming and RxJava

Multi-Release JAR Files

Stack-Walking API

Process API

JShell (the REPL)

HTML5 Javadoc



  • Trisha Gee

    Trisha is a software engineer, Java Champion and author. Trisha has developed Java applications for finance, manufacturing and non-profit organisations, and she's a lead developer advocate at Gradle.