No. xdg-open is a command that opens the preferred handler for the specified file. So if you were to do this...
...your preferred text editor would open the file.
I don't know how to make this more clear really, but I'll give it a shot.
1. Open Terminal (can be named many different things, but mostly called just Terminal of some sort)
- if this doesn't work, you need to seek help in the MX Linux forum.
2. In the terminal type
xdg-open /tmp and press enter. /tmp is a directory, so the default handler of directories will be instructed to open it. In your case it seems likely that Thunar is the default handler.
- if this doesn't work, and you're sure you typed everything correctly, then you probably don't have xdg-open installed, and none of this will work for you. Your adventure ends here.
3. If step 2 worked, change your B4J code to run xdg-open as a shell command, together with the path to the dir that you want to open. In your example in the first post you seem to want to open the root dir (which is a bit weird, but sure, why not). In that case the command would be
xdg-open /.
Best of luck on your journey into Linux Land, it's a wild and very fun ride!