I’m going to recommend following the openHABian Manual instructions and let Thom do all the work for you. It was designed to work with the Raspberry Pi but it will work just fine on Ubuntu and it will take care of all the installation and configuration stuff for you so you can focus on learning OH itself.
http://docs.openhab.org/installation/openhabian.html#manual-setup
The real problem you have is OH doesn’t support running on 1.9 yet. The suggestion comes from awhile back there being some pretty significant problems running OH on openJDK. I beleive that may no longer be the case, though, as Dim said, Zulu is the recommended runtime I believe these days.