From April 16, 2019 is not possible install Java8 on Ubuntu 16.04 or 18.04 from ppa repository.
Oracle Java (JDK) 8 Installer PPA (DISCONTINUED)
The Oracle JDK License has changed for releases starting April 16, 2019.
This means that now there is no easy way to install java on Ubuntu.
From April 16, 2019 is not possible install Java8 on Ubuntu 16.04 or 18.04 from ppa repository.
https://launchpad.net/~webupd8team/+archive/ubuntu/java
This means that now there is no easy way to install java on Ubuntu.