sudo apt-get autoremove openjdk-7-jre
sudo apt-get purge openjdk*
java -version
sudo apt-get install software-properties-common
sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java8-installer
java -version
In Webupd8 ppa repository also providing a package to set environment variables, Install this package using following command.
$ sudo apt-get install oracle-java8-set-default