实现Undo＆amp; Redo Java Blackboard Paint

Question

我有一块黑板，我可以在那里画拖鼠。 我正在尝试实现撤销和放大重做以删除/恢复绘制的最后一个坐标。 撤消＆amp;重做有效，但我的黑板不会自动刷新，我不得不再次拖动鼠标。

这是我的代码（太长了）：

public class ClientBlackboard extends JPanel implements KeyListener {

[...]

class mMotionListener implements MouseMotionListener { 
    public void mouseDragged(MouseEvent e) {            
        x = e.getX();
        y = e.getY();
        points.add(new PointerDraw(x, y));

        _changed = true;
        try {
            drawCurrentShape(_bufImage.createGraphics());
        } catch (Exception e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }
        repaint();
    } 
    public void mouseMoved(MouseEvent e) { }
}

// subscribe to mouse events
class mListener implements MouseListener { 
    // Required by interface, but not used
    public void mouseClicked(MouseEvent e) {} 
    public void mouseEntered(MouseEvent e) {} 
    public void mouseExited(MouseEvent e) {} 
    public void mousePressed(MouseEvent e) {} 
    public void mouseReleased(MouseEvent e) {
        if (!_changed)
            System.out.println("Error");
        else
            System.out.println("Changes saved");
    } 
}

// draw
@Override
public void paintComponent(Graphics g){
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D) g;
    if (_bufImage == null){
        int w = this.getWidth();
        int h = this.getHeight();
        _bufImage = (BufferedImage) this.createImage(w, h);
        Graphics2D gc = _bufImage.createGraphics();
        gc.setColor(COLOR_BACKGROUND);
        gc.fillRect(0,  0,  w,  h);
    }
    g2.drawImage(_bufImage, null, 0, 0);
    test = g2;
}   

private void drawCurrentShape(Graphics2D g2) throws Exception{
    g2.setColor(COLOR_FOREGROUND);
    if (!_flagUndo)
        g2.drawLine(x,  y,  x,  y);
    else{
        for (PointerDraw p : points){
            g2.drawLine(p.getStartXPoint(), p.getStartYPoint(), p.getStartXPoint(), p.getStartYPoint());
        }
        _flagUndo = false;
    }
}



// Shortcuts: ctrl-z and ctrl-y
public void keyReleased(KeyEvent e) { }
public void keyPressed(KeyEvent e) {
    if (e.isControlDown() && e.getKeyCode() == KeyEvent.VK_Z){          
        try {
            PointerDraw point = Connection.remote.readDrawFromDB(_counter++);
            System.out.println("COUNTER: " + _counter);
            System.out.println("UNDO: " + "X: " + point.getStartXPoint() + " Y: " + point.getStartYPoint());
            points.removeLast();
            getAllList();
            _bufImage = null;
            _flagUndo = true;
            repaint();
            test.drawImage(_bufImage,  null,  0,  0);
        } catch (NullPointerException exc){
            System.out.println("You can't undo again");
            _counter--;
        } catch (Exception exc) {
            // TODO Auto-generated catch block
            exc.printStackTrace();
        }
    }

    if (e.isControlDown() && e.getKeyCode() == KeyEvent.VK_Y){
        try {
            if (_counter > 0){
                PointerDraw point = Connection.remote.readDrawFromDB(_counter--);
                System.out.println("COUNTER: " + _counter);
                System.out.println("REDO: X: " + point.getStartXPoint() + " Y: " + point.getStartYPoint());
                points.add(new PointerDraw(point.getStartXPoint(), point.getStartYPoint()));
                getAllList();
                _bufImage = null;
                _flagUndo = true;
                for (PointerDraw p : points){
                    test.drawLine(p.getStartXPoint(), p.getStartYPoint(), p.getStartXPoint(), p.getStartYPoint());
                }
                repaint();
            }
        } catch(NullPointerException exc){
            System.out.println("You can't redo again");
            _counter++;
        } catch (Exception e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }
    }
}