title: Downgrade java from version 8 to 7
body: <p>I have installed Java 1.8 from Oracle on Ubuntu because I though it would be best, newest version compatible with previous ones. But it is not.
  <code>javac</code> 1.8 produces bytecode runnable only on the java-8-oracle, scala does not run.</p>
  
  <p>Before upgrade I was using java-7-openjdk, everything was fine. While
  I can choose my older virtual machine using <code>sudo update-alternatives --config java</code>, but I also need to be able to choose older compiler.
  How can I do this?</p>