I still remember how *gruesome* it was to install or update Java on Ubuntu. I wrote it somewhere in earlier post. Fortunately now with Ubuntu 12.10, an easier method (a ready to execute script) is available:

First you need to remove openjdk for this run the following command from your terminal

sudo apt-get purge openjdk*

If you installed java 7 from any other PPA and you are having problem with java then you have to do following steps before installing the PPA menctioned here

sudo rm /var/lib/dpkg/info/oracle-java7-installer*
sudo apt-get purge oracle-java7-installer*
sudo rm /etc/apt/sources.list.d/*java*
sudo apt-get update

Install oracle java 7 in ubuntu 12.04
Open the terminal and run the following commands

sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java7-installer

http://www.ubuntugeek.com/how-to-install-oracle-java-7-in-ubuntu-12-04.html