You can use openHAB 2.4.0 with Java 11 today if you:
- don’t mind some harmless reflective access warnings at startup
- don’t use the MaryTTS voice addon (there are better voice add-ons anyway)
- don’t use Windows with bindings accessing serial ports (nrjavaserial)
- don’t use Jython
If you do run into some other new issue, please report it so we can keep track of it.
To keep things simple, it’s better to currently recommend everyone Java 8. We depend on the contributors/maintainers of these other projects to get these issues fixed.