Unable to open .jar files with Java

You seem to be using a development version of java : Java 9 has not been released yet.

So, first of all, you should remove this version of java, and install the default one :

sudo apt-get remove openjdk-9-*
sudo apt-get install default-jre

Depending on your version of Ubuntu, it should be a version 7 or 8. If you're on a development version of Ubuntu, you might need to choose version 8 : sudo apt-get install openjdk-8-jre

Then you should be able to run Minecraft.

By the way, the simplest method to install it is to use the PPA instead of trying to run the .jar by hand :

sudo add-apt-repository ppa:minecraft-installer-peeps/minecraft-installer
sudo apt-get update
sudo apt-get install minecraft-installer