Although... I was trying to find an example in my source code archive and only came up with examples like this. This was NOT implemented as an ANONYMOUS class because the constructor takes a parameter so it could be used in more than one place.
I might suggest a different approach. The problem with your approach is that if there was something beneath the circle you drew then that would be erased also. If you drew the circle on it's own buffered image and then have paint() display the combined buffer images then you could just remove the one BufferedImage or effectively use the alpha value and set the pixels to transparent.
Preferred size is the starting point for the size a layout manager will use if possible. This size may be reduced due to constraints placed by other components but should not be reduced below Minimum size.