If you check the JavaDoc for Swing/AWT, specifically the repaint method of the Component class (found here:
http://docs.oracle.com/javase/7/docs/api/java/awt/Component.html#repaint()[
^]), you will see that calling this method will tell Java to repaint the component at its next opportunity. Since a JFrame is a component, this method can also be called on your JFrame, or any other Swing component that extends Component (such as JPanel).