sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java8-installer
ref:
INSTALL ORACLE JAVA 8 IN UBUNTU VIA PPA REPOSITORY [JDK8]（http://www.webupd8.org/2012/09/install-oracle-java-8-in-ubuntu-via-ppa.html）
How To Install Java on Ubuntu with Apt-Get（https://www.digitalocean.com/community/tutorials/how-to-install-java-on-ubuntu-with-apt-get）