Adding JPanel subclass to JFrame with GUI builder

[enkidu]

sorry not many explanation cause I HAVE made a thread before with long explanation and when I submit it the site tell I haven't login yet. so HOW COULD I make a thread if I weren't login yet? :argh:
Sorry Out Of Topic, this is it:

i have class

public class L extends JPanel

i want to show it in frame belong to class

public class F extends JFrame

have tried many ways no one worked :bowl:

what's wrong?
how to show it?