Comment 2 for bug 669847

I'm fixing this problem. You must install the package sun-java6-jdk.

Add the Lucid source :
sudo add-apt-repository "deb http://archive.canonical.com/ lucid partner"

And :
sudo apt-get update
sudo apt-get install sun-java6-jdk

Modify the symbolic link default-java :
cd /usr/lib/jvm
rm default-java
ln -s java-6-sun default-java

After reboot, you must edit the configuration file of Netbeans in /etc/netbeans.conf
Add :
netbeans_jdkhome="/usr/lib/jvm/default-java"

I hope, I can resolve your problem ;)