1
Open Terminal (Applications > Accessories > Terminal)

2
Next, type the following into the terminal: sudo apt-get install sun-java6-bin sun-java6-fonts sun-java6-jre sun-java6-plugin and press Enter

3
Wait until it loads entirely, then the terminal will change into an old-fashioned window with no mouse user interface. Use the down arrow to scroll down until you can't scroll further. Then press the right arrow and hit enter to accept the license agreement.

4
After accepting the license agreement, Java will download and it will ask you several questions about configuration which you should choose based on what you want.

Hope this helps.
Enjoy! - Nasty