Ubuntu 12.04 Java install

First install python-software-properties:

sudo apt-get install python-software-properties

Next, remove openjdk package if installed:

sudo apt-get remove openjdk*

Now, add java repository by webupd8team:

sudo add-apt-repository ppa:webupd8team/java

And update your system:

sudo apt-get update

For installing Oracle Java 7 run:

sudo apt-get install oracle-java7-installer

For Oracle Java 6 run:

sudo apt-get install oracle-java6-installer

For Oracle Java 8 run:

sudo apt-get install oracle-java8-installer