As we know, when using netbeans, it will scan the project automaticly by itself, at this time, it will slow down the system. Also, when adding a file to the project folder (not via NetBeans but you do it in the folder), you have to close NetBeans to refresh the project files for the reason that you don't know when NetBeans will scan the project files!
So, we have to stop stop the NetBeans to scan the files automaticly, and add the "Refresh Folder" to the right-key menu. Here is the way to do it.
Go to Tools->Options->Miscellaneous->Files, un-check "Enable auto-scanning of sources".
then you will see the "Refresh Folder" item in the right-click menu.
Have fun with NetBeans!