If for some reason you need Java (jre) from Sun (currently Oracle), because the openjdk doesn't work for you (if you want to share your desktop with BigBlueButton, for instance, that doesn't seem to like the openjdk, or IPA requiring it), you can add the proprietary java through external repositories.
For JRE 7-8-9 from Oracle, you can add the webupd8 repos (ppa:webupd8team/java ; it was added in a previous step through the proxy, etc), and install the installer package:
{CODE(colors="bash", wrap="1", caption="Command on a console")}
# Install Java 8
sudo apt-get install oracle-java8-installer
# Set the environments variables for Java 8
sudo apt-get install oracle-java8-set-default
{CODE}
Source:
* http://www.webupd8.org/2012/09/install-oracle-java-8-in-ubuntu-via-ppa.html
* http://www.webupd8.org/2014/03/oracle-java-8-stable-released-install.html
* https://launchpad.net/~webupd8team/+archive/ubuntu/java