The Undo Framework - The Definitive Guide to Java Swing - page 793

public void setPolygon(Polygon newValue) {
polygon = newValue;
repaint();
}
public Polygon getPolygon() {
Polygon returnValue;
if (polygon.npoints == 0) {
returnValue = new Polygon();
} else {
returnValue = new Polygon(
polygon.xpoints, polygon.ypoints, polygon.npoints);
}
return returnValue;
}
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawPolygon(polygon);
}
public static void main(String args[]) {
Runnable runner = new Runnable() {
public void run() {
JFrame frame = new JFrame("Drawing Sample2");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
UndoableDrawingPanel2 drawingPanel = new UndoableDrawingPanel2();
UndoManager manager = new UndoManager();
drawingPanel.addUndoableEditListener(manager);
JToolBar toolbar = new JToolBar();
JButton undoButton =
new JButton(UndoManagerHelper.getUndoAction(manager));
toolbar.add(undoButton);
JButton redoButton =
new JButton(UndoManagerHelper.getRedoAction(manager));
toolbar.add(redoButton);
frame.add(toolbar, BorderLayout.NORTH);
frame.add(drawingPanel, BorderLayout.CENTER);
frame.setSize(300, 150);
frame.setVisible(true);
}
};