I tried to install java8 using the following commands:
sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java8-install
I just went through the same process and I fixed the problem by manually installing java 8 on my ubuntu 18.04 machine. Hopefully my answer will help you.
$mkdir /opt/jdk
.$tar -zxf jdk-8u5-linux-x64.tar.gz -C /opt/jdk
.Note: Each bullet point is one single command
update-alternatives --install /usr/bin/java java /opt/jdk/jdk1.8.0_/bin/java 100
update-alternatives --install /usr/bin/javac javac /opt/jdk/jdk1.8.0_/bin/javac 100
You can check the result by running java -version !
Before I started, I went through those steps as well in order to remove completely java from my system: https://askubuntu.com/questions/84483/how-to-completely-uninstall-java#185250
The source I used for the manual installation of JAVA was this article: https://www.digitalocean.com/community/tutorials/how-to-manually-install-oracle-java-on-a-debian-or-ubuntu-vps