sudo add-apt-repository ppa:webupd8team/java

sudo apt-get update

To install Oracle Java 8, run:

sudo apt-get install oracle-java8-installer

Change the number 8 to 6 (or 7) in the code to install Java 6 (or 7).

While installation, you’ll be asked to agree the license and then the installer start downloading Java file from oracle website and install it on your system.

To set the default Java, run:

sudo apt-get install oracle-java8-set-default

Also change number 8 to the Java version you want.