More than three years after the release of Java 8, the next version is now just around the corner, with a tentative release date of September 21st, 2017. You may have heard about Java 9’s module system, but there’s even more to this new version. Here are nine exciting new features that will ship with Java 9.
Linking: When you have modules with explicit dependencies and a modularized JDK, new possibilities arise. Your application modules now state their dependencies on other application modules and on the modules it uses from the JDK. Why not use that information to create a minimal runtime environment containing just those modules necessary to run your application? That’s made possible with the new jlink tool in Java 9. Instead of shipping your app with a fully loaded JDK installation, you can create a minimal runtime image optimized for your application.
JShell: the interactive Java REPL: Many languages already feature an interactive Read-Eval-Print-Loop, and Java now joins this club. You can launch jshell from the console and directly start typing and executing Java code. The immediate feedback of jshell makes it a great tool to explore APIs and try out language features. Testing a Java regular expression is a great example of how jshell can make your life easier. The interactive shell also makes for a great teaching environment and productivity boost, which you can learn more about in this webinar. No longer do you have to explain what this `public static void main(String args)` nonsense is about when teaching people how to code Java.
Improved Javadoc: Sometimes it’s the little things that can make a big difference. Did you use Google all the time to find the right Javadoc pages, just like me? That’s no longer necessary. Javadoc now includes search right in the API documentation itself. As an added bonus, the Javadoc output is now HTML5 compliant. Also, you’ll notice that every Javadoc page includes information on which JDK module the class or interface comes from.
Collection factory methods: Often you want to create a collection (e.g., a List or Set) in your code and directly populate it with some elements. That leads to repetitive code where you instantiate the collection, followed by several `add` calls. With Java 9, several so-called collection factory methods have been added. Besides being shorter and nicer to read, these methods also relieve you from having to pick a specific collection implementation. In fact, the collection implementations returned from the factory methods are highly optimized for the number of elements you put in. That’s possible because they’re immutable: adding items to these collections after creation results in an `UnsupportedOperationException`.
Stream API improvements: The Streams API is arguably one of the best improvements to the Java standard library in a long time. It allows you to create declarative pipelines of transformations on collections. With Java 9, this only gets better. There are four new methods added to the Stream interface: dropWhile, takeWhile, ofNullable. Besides these additions on Stream itself, the integration between Optional and Stream has been improved. It’s now possible to turn an Optional object into a (possibly empty) Stream with the new `stream` method on Optional.