public void actionPerformed(ActionEvent event) {
Window window;
String msg;
if (model.isZoomUndoStackEmpty()) {
window = SwingUtilities.windowForComponent((JToolBar) toolbar);
msg = "Zoom Undo Stack is empty";
Dialogs.warn(window, msg);
} else model.zoomUndo();
// Set toolbar buttons to reflect status
if (toolbar != null) toolbar.resetZoomButtons();
if (Debug.isActive()) Debug.println("Action for Zoom Undo button.");
}
