I required a later version on Java that the one that came with Raspbian. This was required for OpenHAB. So how do you upgrade your version of Java? Run the following commands:
# sudo su
# echo "deb http://ppa.launchpad.net/webupd8team/java/ubuntu xenial main" | tee /etc/apt/sources.list.d/webupd8team-java.list
# echo "deb-src http://ppa.launchpad.net/webupd8team/java/ubuntu xenial main" | tee -a /etc/apt/sources.list.d/webupd8team-java.list
# apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys EEA14886
# apt-get install oracle-java8-installer
# exit