but what I don't understand is that it seems that you already can use this combo box as you've written it. What additional functionality are you requiring? Also, this statement doesn't make much sense to me: "i can use this component directly to the JFrame". Do you mean so that you can add it to a NetBeans Swing app by drag and drop? If so, then say so.
Again, you need to clarify things greatly. I'm sorry if I'm frustrating you with this, but it's kind of frustrating me. You may wish to read this link:
How to ask questions the smart way
I know that the link has helped me greatly in formulating forum questions