Java, A Beginner's Guide, 5th Edition, 5th Edition

Requesting Repainting

As a general rule, an AWT-based applet writes to its window only when its paint( ) method is called by the run-time system. This raises an interesting question: How can the applet itself cause its window to be updated when its information changes? For example, if an applet is displaying a moving banner, what mechanism does the applet use to update the window each time this banner scrolls? Remember that one of the fundamental architectural constraints imposed on an applet is that it must quickly return control to the Java run-time system. It cannot create a loop inside paint( ) that repeatedly scrolls the banner, for example. This would prevent control from passing back to the run-time system. Given this constraint, it may ...