Reposting this article verbatim from this source: http://www.ubuntugeek.com/how-to-install-oracle-java-7-in-ubuntu-12-04.html
Java is a programming language and computing platform first released by Sun Microsystems in 1995. It is the underlying technology that powers state-of-the-art programs including utilities, games, and business applications. Java runs on more than 850 million personal computers worldwide, and on billions of devices worldwide, including mobile and TV devices.
Preparing your system
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 13.04/12.10/12.04
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
You can check the java version by searching java in dashboard
