Unable to execute JAR file
In my case, I had a Netbeans app that I developed in Snow Leopard and was unable to open by double-clicking in High Sierra.

Instead of copying over just the app's .jar, I copied the dist directory that contained the app's .jar plus the library directory that contains 6 other .jar files that were added when I originally compiled the distribution version.

Double-clicking the app's .jar still didn't work, but I was able to launch "my_app.jar" from the terminal by cd-ing into the dist directory and using


  java -jar my_app.jar


(NB: I have the latest JDK installed.)