Java 8 is now available according to http://openjdk.java.net/projects/jdk8/, but http://openjdk.java.net/install/ does not yet mention how to install OpenJDK 8 (not Oracle Java) on Ubuntu 14.04 Long Term Support. (For 14.10 and later just run
apt-get install openjdk-8-jdk)
How and when can this be done?
(2017-08-08: The very short answer is: OpenJDK 8 as of 2017-08-08 is not officially available from the official repositories as an APT package for Ubuntu 14.04. See full summary in this answer)
Note: For now we will use Oracle Java – the optimal solution for me is, however, OpenJDK from the Ubuntu repositories, until Oracle Java is available directly and effortless from the Ubuntu repositories.