Editar /etc/apt/source.list y añadir
deb http://ppa.launchpad.net/webupd8team/java/ubuntu xenial main
deb-src http://ppa.launchpad.net/webupd8team/java/ubuntu xenial main
Ejecutar:
apt-key adv –keyserver hkp://keyserver.ubuntu.com:80 –recv-keys EEA14886
apt-get update
apt-get install oracle-java8-installer