Installing Sun JDK 6 in Ubuntu/Kubuntu Interpid

1. Open terminal
2. Type
sudo apt-get install sun-java6-jdk sun-java6-plugin
The installation downloads around 52 MB. A Operating System Distribution License (DLJ) agreement appear, read it till the end, press Tab and click OK buttion.

Usually, GCJ is installed in the system by default. So an alternative must be set for the Sun java, so that the java applications use the newly installed version during startup.

3. Type
sudo update-java-alternatives -s java-6-sun
4. Type
java --version
It will check which version is currently set as default.

Alternative to steps 3 & 4 the following step can be used:

5. Type
sudo update-alternatives --config java

and then select the number for sun java-6.

A detailed description can be found in kubuntu community docummentaion for java.