I know OP has probably figured it out or given up by now, but if any Mac users having trouble stumble upon this thread, just follow the instructions on https://smacpats.github.io/javauninstaller/ to get your launcher working.
Right click the jar file, then click open, and it will give you a prompt to open it. Double clicking it will not work.
If anybody has java issues and is on a mac, try following the instructions on https://smacpats.github.io/javauninstaller/