IntelliJ, Eclipse and Java 11

https://blog.jetbrains.com/idea/2018/06/java-11-in-intellij-idea-2018-2/

you must install IDEA 2018.2 or greater. 2018.1 will not work, it supports only Java 10. It's a 500 MB monster so be patient.

https://www.jetbrains.com/idea/download/ download 2018.3.5 here

then configure the platform JDK with your installed JDK 11 (of course you must have installed this JDK from Oracle or OpenJDK!), with ALT-SHIFT-CONTROL-S (project structure/SDKs)

then configure Java 11 level (File/Project Structure/Modules and File/Project Structure/Project)

also don't forget the bytecode level (File/Settings/Java Compiler):

If you get the "invalid source release: 11" , it's possible that you misconfigured the "platform JDK"




For Eclipse it's much easier: install Eclipse 2018-09 (4.9), then install this add-on:

https://marketplace.eclipse.org/content/java-11-support-eclipse-2018-09-49

make sure you configure the JDK in the "installed JRA" preferences tab,

and when you create a new project, select jdk11 and create the module-info by default.
All works fine.