wget -q -O - https://pkg.jenkins.io/debian/jenkins.io.key | sudo apt-key add -
sudo sh -c 'echo deb http://pkg.jenkins.io/debian-stable binary/ > /etc/apt/sources.list.d/jenkins.list'
sudo apt-get update
sudo apt-get install jenkins

$ apt-get install jenkins
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 jenkins : Depends: default-jre-headless (>= 2:1.8) but 2:1.7-52 is to be installed or
                java8-runtime-headless but it is not installable
E: Unable to correct problems, you have held broken packages.

$ apt install -t jessie-backports  openjdk-8-jre-headless ca-certificates-java

$ sudo /etc/init.d/jenkins start
[FAIL] Starting Jenkins Automation Server: jenkins failed!


$ tail -f /var/log/jenkins/jenkins.log
Jenkins requires Java8 or later, but you are running 1.7.0_151-b01
from /usr/lib/jvm/java-7-openjdk-amd64/jre
  java.lang.UnsupportedClassVersionError: 51.0
    at Main.main(Main.java:124)