Installing Java on Ubuntu 10.04

sudo apt-get install python-software-properties
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 sun-java6-fonts

If you want JDK for development, you should also do:

sudo apt-get install sun-java6-jdk