I've compared the behavior of paintComponent() within JPanel to show that the background is being redrawn/repainted in addition to the circle despite there being no invocation of super.paintComponent().

According to Head First Java (Second Edition), omitting the invocation of super.paintComponent() should cause the circle to be drawn again WITHOUT the previous circle being removed. The book is assuming the reader is using Java 5 - has something changed since then that would cause this?

свернуть