The apple specific event handlers do not work with Java 9 anymore because Java 9 deprecated/removed the classes from package com.apple.eawt.*. See the following links for details:
People came up with workarounds, like Reflection, etc. but thats’s probably too complicated for the current state of this small project:
If you want to test a solution for that, feel free to check out the branch javastub-3.0 on my fork where I updated the JavaApplicationStub to the latest development version 3.0.0-BETA of universalJavaApplicationStub.