After Ubuntu’s decision to default to OpenJDK for 10.04 (which is a good decision, IMHO), Sun’s (but is it still Sun, or Oracle?) JAVA somewhat “disappeared” from Ubuntu (multiverse).
That being said, some people may still need features only available in Sun’s JRE/JDK, which might not yet have been Freed.
Actually, Ubuntu is still shipping it, but in its “partner” section. To add that section to your Sources and install Sun’s JDK (as an example), just:
sudo add-apt-repository "deb http://archive.canonical.com/ lucid partner" sudo apt-get update sudo apt-get install sun-java6-jdk
You might need to accept the license (press “tab”, “enter”, “tab” on “Yes” then “enter”).
You might also just want to install sun-java6-jre or sun-java6-plugin if you just want the (Mozilla) web browser plugin.
As a side note, remember to remove OpenJDK if you do not need it, or be prepared to encounter hard to diagnose problems sometime.
sudo apt-get remove openjdk-6-jdk openjdk-6-jre openjdk-6-jre-headless openjdk-6-jre-lib
Ubuntu 11.10: same operation. Just replace “lucid” por “oneiric”