question: public void update ( Graphics g , JComponent c ) { if ( c . isOpaque ( ) ) { g . setColor ( new ColorUIResource ( 251 , 248 , 241 ) ) ; g . fillRect ( 0 , 0 , c . getWidth ( ) , c . getHeight ( ) ) ; g . setColor ( new ColorUIResource ( 251 , 248 , 241 ) ) ; g . fillRect ( 0 , getRoundHeight ( ) , c . getWidth ( ) , c . getHeight ( ) - getRoundHeight ( ) ) ; } paint ( g , c ) ; }
target:  Overriden to paint the background of the component but keeping the rounded corners.