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In terms of Layout API, a JOptionPane is the same as a JPanel. I can, and have cut-and-pasted code generated by NetBeans for a JPanel into the code for classes that extend JOptionPane. I have never encountered an error due to the difference between classes. Of course, this is a very clumsy way to do layout. It would be far better to use the GUIBuilder on subclasses of JOptionPane directly, with a goal of supporting all Swing containers.