Heres the error:warning: current package is oracle-java8, but binary format already installed by openjdk-7. i used the purge command on openjdk before i tried to install Oracle Java 8 . now I'm at a loss.
First, reinstall openjdk. Then install Java 8. Then run
update-java-alternatives to select Java8. Finally, (optionally) try to remove openjdk. The cost of keeping the previous version (in disk space) is pretty low (because modern disks just keep getting bigger).
Once you have Java 8 installed, you need to set it as your JVM -
sudo update-java-alternatives -s java-8-oracle
Then you can verify that you have it selected correctly by