As per the release note of Ubuntu 10.04 LTS, Ubuntu users can have Sun Java by executing the following piece of code on the command line.
sudo add-apt-repository "deb http://archive.canonical.com/ lucid partner" sudo apt-get update sudo apt-get install sun-java6-jre sun-java6-plugin sudo update-alternatives --config java
http://www.clickonf5.org/linux/how-install-sun-jav