2) The code you posted doesn't compile. Most of use don't use an IDE to create a GUI so we don't have access to the org.desktop.layout.GroupLayout class. So if you want us to run your code then you need to post executable code, which is why you create a SSCCE.
Finally, the error messages tells you the problem. You get a ClassCastException. It should also tell you the line that is causing the problem. It found a String, but your code is expecting something else. So either your data is wrong or the code is wrong.