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Switching Java versions on a Debian/Ubuntu system

I recently found some issues with the openjdk Ubuntu/Debian default Java implementation. Specifically I had issues with their web start support (javaws). I found that the Sun implementation of Java did not have such a deficiency and the Sun implementation is available through the regular Ubuntu/Debian package sources. I installed the Sun implementation and wanted to switch the default Java to that version.

So what have I found out ?

When you want to switch to the Sun implementation:

sudo update-java-alternatives --set java-6-sun

When you want to go back to the openjdk implementation:

sudo update-java-alternatives --set java-6-openjdk

Notice that once you do any of the above you leave “auto” mode which means that new installation of Java implementation will not switch your default one. If that is what you want then ok. If not you can return to “auto” mode with:

sudo update-java-alternatives --auto

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Purging unneeded packages on a debian system

If you want to remove all packages which are in the “rc” state (means that the package was already removed but only it’s configuration remained) you can use the following command as administrator:

dpkg --purge `dpkg --list | grep "^rc" | tr -s " " | cut -d " " -f 2`

Take care to save configuration files that you need before issuing it.