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Try it and see what happens.

Make sure the JPanel is given a size for the layout manager to use. Try using the set preferred size method.

Yes that was the code I was talking about. You need to read up on how to use layout managers.
A Visual Guide to Layout Managers (The Java™ Tutorials > Creating a GUI With JFC/Swing > Laying Out...

Check how you are using the layout manager. When add components to a container, the layout manger controls where the components go. For some layout mangers you need tell it where to put components by...