The alternative is to check for the existence of Apple Java on the machine, and if present, append the ui.jar to the boot classpath. (It also seems like squirrel-sql.sh is doing macOS things outside of if $macosx blocks and probably should not.) This can be done in squirrel-sql.sh like so: . . . # Define mac-specific system properties if running on Mac OS X if $macosx; then APPLE_JAVA_UI="" [ -r /System/Library/Frameworks/JavaVM.framework/Classes/ui.jar ] && APPLE_JAVA_UI="-Xbootclasspath/a:/System/Library/Frameworks/JavaVM.framework/Classes/ui.jar"...
machos plugin fails on macOS without Apple Java
I have had it running fine on Java 9. Your problem is a bug in the squirrel-sql.sh which is fixed in the latest snapshot.