install java 8:

add-apt-repository ppa:openjdk-r/ppa
apt-get update
apt-get install openjdk-8-jdk
java -version

terminal output java version 1.8

install jenkins:

wget -q -O - https://pkg.jenkins.io/debian/jenkins-ci.org.key | apt-key add -

echo deb http://pkg.jenkins-ci.org/debian binary/ > /etc/apt/sources.list.d/jenkins.list

apt-get update
apt-get install jenkins

(may need change port /etc/default/jenkins) with cloudflare open port then config it on web, 8080 port as default