See issue #187 for the fix. This works on Java 9 and 10. I fixed my Mac launcher by going into the JD-GUI.app/Contents/MacOS folder and updating the Java call in the .sh file as follows (the two --add-opens lines): exec "$JAVACMD" -cp "${JVMClassPath}" -Xdock:icon="${ResourcesFolder}/${CFBundleIconFile}" -Xdock:name="${CFBundleName}" --add-opens java.base/jdk.internal.loader=ALL-UNNAMED --add-opens jdk.zipfs/jdk.nio.zipfs=ALL-UNNAMED ${JVMOptions:+$JVMOptions } ${JVMDefaultOptions:+$JVMDefaultOptions } ${JVMMainClass} ${JVMArguments:+ $JVMArguments}
OK so I solved this by specifying the version to run inside of the Info.plist file. To access that right click on the OSx JD-GUI icon and go to "Show Package Contents" then navigate into the "Contents" directory and open "Info.plist" inside of a text editor.
You want to look for the line that looks like:
<key>JVMVersion</key> <string>1.7+</string>
I believe the issue I was experiencing was caused by having Java 10 installed so the real issue may be that High Sierra is OK but Java 10 causes problems. To fix that I specified the Java 7 runtime in the Info.plist file by changing the above line to the following:
<key>JVMVersion</key> <string>1.7</string>
This allows me to run the JD-Gui from the osx .app wrapper as I did before my update.