Then that is probably the problem. As I mentioned before, after upgrading to Mojave, I couldn't launch the jar with the desktoplauncher anymore (it worked fine under High Sierra). I fixed this by first removing everything Java and Oracle related. This was a bit of a hassle, as the components can be found in several subfolders of /Library and ~/Library, so Spotlight was next to useless as usual. Instead I used Easyfind, made by Devon technologies. Highly recommended. Then I installed the Zulu java 8 build of OpenJDK (made by Azul). Now the jar opens fine for me.