twak@xxx:~$ cd /usr/lib/jvm
twak@xxx:/usr/lib/jvm$ sudo rm java-6-sun
twak@xxx:/usr/lib/jvm$ sudo ln -s jdk1.6.0_12/ java-6-sun
After and before:

I'm not sure this is the official way to switch jdk, but it works. Am getting fed up with netbeans niggles now....