If you change the jdk's dir path after Netbeans installation, the Netbeans will complains it cannot find the original jdk's path and ask if you'd like to use "default" jdk in a message box each time you start the program.
To disable the warning message box, just change the default jdk path to the new one Netbeans at "<netbeans_dir>/etc/netbeans.conf":
netbeans_jdkhome="E:\Java\jdk1.6"