Compile and run the attached test case. The three buttons in the control frame cause a small 10 x 10 region in the center of the test bed frame to be redrawn by sending repaint() to either the content pane (drawn in red), or one of the two JComponents (drawn in blue and green) in the content pane. Clicking the "Repaint green component" button will show the region being invalidated.

I get the following output when I click the content pane, blue component, and green component buttons, respectively:

Command = content pane
Painting content pane
Painting green component
Painting blue component
Command = blue component
Painting blue component
Command = green component
Painting green component

Both the green component case and the content pane case are incorrect. Neither one should cause any paint()'ing to occur since the blue component is setOpaque(true) and it obscures both the green component and the content pane in this region.