The Undo Framework - The Definitive Guide to Java Swing - page 792

Listing 21-8. The Updated UndoableDrawingPanel2 Main Component
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.undo.*;
import java.awt.*;
import java.awt.event.*;
import java.util.Hashtable;
public class UndoableDrawingPanel2 extends JPanel implements StateEditable {
private static String POLYGON_KEY = "Polygon";
UndoableEditSupport undoableEditSupport = new UndoableEditSupport(this);
Polygon polygon = new Polygon();
public UndoableDrawingPanel2() {
MouseListener mouseListener = new MouseAdapter() {
public void mouseReleased(MouseEvent mouseEvent) {
StateEdit stateEdit = new StateEdit(UndoableDrawingPanel2.this);
polygon.addPoint(mouseEvent.getX(), mouseEvent.getY());
stateEdit.end();
undoableEditSupport.postEdit(stateEdit);
repaint();
}
};
addMouseListener(mouseListener);
}
public void addUndoableEditListener(
UndoableEditListener undoableEditListener) {
undoableEditSupport.addUndoableEditListener(undoableEditListener);
}
public void removeUndoableEditListener(
UndoableEditListener undoableEditListener) {
undoableEditSupport.removeUndoableEditListener(undoableEditListener);
}
public void storeState(Hashtable state) {
state.put(POLYGON_KEY, getPolygon());
}
public void restoreState(Hashtable state) {
Polygon polygon = (Polygon)state.get(POLYGON_KEY);
if (polygon != null) {
setPolygon(polygon);
}
}