Java Swing, 2nd Edition

Painting and Repainting

Repainting is a fundamental task for a graphical application, but one that is rarely explained in the detail you’d expect for something so central. This section is intended to give you a better feel for how painting and repainting via the repaint manager and JComponent work. You typically do not need to get involved with the RepaintManager class, and only the extremely brave override it. However, there are some instances in which a firm understanding of the repaint manager can help avoid confusion, and, starting with SDK 1.4, Swing provides a way for savvy code to take advantage of accelerated graphics hardware when it is available.

Swing Responsibilities

Recall that Swing uses lightweight components, which are drawn inside heavyweight top-level containers. Since the operating system has no knowledge of lightweight components (that’s what makes them lightweight), it can’t help coordinate their repainting. To continue the analogy first presented in the earlier lightweight and heavyweight discussion, Swing is responsible for painting and repainting everything inside its own easels. Swing delegates this duty to a RepaintManager class, which organizes and schedules repainting when told to do so.

The RepaintManager Class

The RepaintManager class is responsible for keeping track of the components (and the components’ parts) that have become dirty, which means that they need to be repainted. Note that the “dirty region” does not necessarily include the entire region ...