I have JPanels that can be embedded in JFrames or JInternalFrames--I don't know which when they are created.
But if I need to show dialogs or force the frame to be repacked as a result of a GUI event, I have to do it differently for each. 
The same goes for JApplet, I guess.
(Review ID: 39715)
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I have a static pack(Component comp) routine like:
	public static void pack(Component comp) {
		while (comp != null) {
			comp = comp.getParent();
			if (comp instanceof JInternalFrame) {
				((JInternalFrame) comp).pack();
				return;
			} else if (comp instanceof Window) {
				((Window) comp).pack();
				return;
			}
		}
		System.out.println("NO PARENT FOUND FOR "+comp);
	}
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This does not seem like a big deal to me, and definitely not worth adding an (immutable) interface.

 xxxxx@xxxxx  2000-02-29

Disagree with evaluation, It would allow code to abstract 
its container:
 public interface FrameFeatures {
  setTitle(..);
  setJMenuBar(..);
  ..
 }

This would be VERY useful for projects like PJE.

Changed my mind.  Whilst it would have been better from the outset, it is now impossible as JFrames fire 
events referring to Window, and JInternalFrame has no Window as a parent class.  They are too different.

Frimble (adapter) is the solution. - PJH