Ubuntu : Install Sun java 6

Ubuntu has dropped including Sun/Oracle Java in its repository, and added OpenJDK. But, the former is more reliable than latter, and is also must for some applications.
Here is a way to add Sun java 6:

sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java6-installer

Possible error : "couldn't connect to host"

To make this version as default: here.

If you want to install java 7, instead of last command try

sudo apt-get install oracle-java7-installer

If you are under proxy network or seen a error like

Cannot add PPA: 'ppa:webupd8team/java'.
Please check that the PPA name or format is correct.

and if you are sure that the PPA is working, the try

sudo -E add-apt-repository ppa:webupd8team/java

and proceed with remaining commands.