It would be great to be able to install java for Home Assistant OS, because it’s great to have an unattended system and your jar files in the config
You can use any runtime you want in an add-on.
There are already multiple that runs Java.
But he can at least draw the Java logo at add-on to know where Java is?
You choose that, when you create an add-on you decide everything about it.
The runtime, the image, the description, everything.
I’m waiting for an open protocol for HA to appear that will never become obsolete, and it will only have new features. This means that what is now will never become obsolete.