question: public static void clearRect ( Graphics2D g , Rectangle rect , Color background ) { if ( background != null ) { g . setColor ( background ) ; g . fillRect ( rect . x , rect . y , rect . width , rect . height ) ; } else { g . setComposite ( AlphaComposite . getInstance ( AlphaComposite . CLEAR , 0.0f ) ) ; g . fillRect ( rect . x , rect . y , rect . width , rect . height ) ; g . setComposite ( AlphaComposite . SrcOver ) ; } }
target:  Clears the given area of the specified graphics object with the given color or makes the region transparent.