For Ubuntu 10.04 LTS all the sun-java6* packages, which were formerly found in the Multiverse section of Ubuntu repositories, have been removed from the repositories. We recommend that you use openjdk-6 instead. When you can not switch from the proprietary Sun JDK/JRE to OpenJDK, you can find sun-java6* packages in the Canonical Partner Repository. You can add this repository via command-line:
apt-repository “deb http://archive.canonical.com/ lucid partner”
or by manually adding the archive to your /etc/apt/sources.list with your favorite editor.