如何实现命令模式我的代码

Question

尊敬的StackOverFlow社区，

我正在尝试重构我的简单绘画程序的实现。但是我确实有实现命令模式的问题。基本上，我希望每种“绘画模式”都有一个单独的命令类，该类正在实现一个接口。目前，我有3种绘制模式：矩形，椭圆形和涂鸦。 我真的很感谢收到的每一份帮助。 我将在下面提供代码。

我已经尝试使用三个Command类来实现它，在其中将gui赋予命令类。但不幸的是，我收到了很多异常：（。

class ShapeManager implements ItemListener {
    DrawGUIs gui;

    abstract class ShapeDrawer extends MouseAdapter implements MouseMotionListener {
        public void mouseMoved(MouseEvent e) {
            /* ignore */ }
    }

    // if this class is active, the mouse is interpreted as a pen
    class ScribbleDrawer extends ShapeDrawer {
        int lastx, lasty;

        public void mousePressed(MouseEvent e) {
            lastx = e.getX();
            lasty = e.getY();
        }

        public void mouseDragged(MouseEvent e) {
            Graphics g = gui.getGraphics();
            int x = e.getX(), y = e.getY();
            g.setColor(gui.color);
            g.setPaintMode();
            g.drawLine(lastx, lasty, x, y);
            lastx = x;
            lasty = y;
        }
    }

    // if this class is active, rectangles are drawn
    class RectangleDrawer extends ShapeDrawer  implements Drawable{
        int pressx, pressy;
        int lastx = -1, lasty = -1;

        // mouse pressed => fix first corner of rectangle
        public void mousePressed(MouseEvent e) {
            pressx = e.getX();
            pressy = e.getY();
        }

        // mouse released => fix second corner of rectangle
        // and draw the resulting shape
        public void mouseReleased(MouseEvent e) {
            Graphics g = gui.getGraphics();
            if (lastx != -1) {
                // first undraw a rubber rect
                g.setXORMode(gui.color);
                g.setColor(gui.getBackground());
                doDraw(pressx, pressy, lastx, lasty, g);
                lastx = -1;
                lasty = -1;
            }
            // these commands finish the rubberband mode
            g.setPaintMode();
            g.setColor(gui.color);
            // draw the finel rectangle
            doDraw(pressx, pressy, e.getX(), e.getY(), g);
        }

        // mouse released => temporarily set second corner of rectangle
        // draw the resulting shape in "rubber-band mode"
        public void mouseDragged(MouseEvent e) {
            Graphics g = gui.getGraphics();
            // these commands set the rubberband mode
            g.setXORMode(gui.color);
            g.setColor(gui.getBackground());
            if (lastx != -1) {
                // first undraw previous rubber rect
                doDraw(pressx, pressy, lastx, lasty, g);

            }
            lastx = e.getX();
            lasty = e.getY();
            // draw new rubber rect
            doDraw(pressx, pressy, lastx, lasty, g);
        }

        public void doDraw(int x0, int y0, int x1, int y1, Graphics g) {
            // calculate upperleft and width/height of rectangle
            int x = Math.min(x0, x1);
            int y = Math.min(y0, y1);
            int w = Math.abs(x1 - x0);
            int h = Math.abs(y1 - y0);
            // draw rectangle
            g.drawRect(x, y, w, h);
        }

        @Override
        public void draw(Graphics g) {
            // TODO Auto-generated method stub

        }
    }

    // if this class is active, ovals are drawn
    class OvalDrawer extends RectangleDrawer implements Drawable {
        public void doDraw(int x0, int y0, int x1, int y1, Graphics g) {
            int x = Math.min(x0, x1);
            int y = Math.min(y0, y1);
            int w = Math.abs(x1 - x0);
            int h = Math.abs(y1 - y0);
            // draw oval instead of rectangle
            g.drawOval(x, y, w, h);
        }
        @Override
        public void draw(Graphics g) {
            // TODO Auto-generated method stub

        }
    }

    ScribbleDrawer scribbleDrawer = new ScribbleDrawer();
    RectangleDrawer rectDrawer = new RectangleDrawer();
    OvalDrawer ovalDrawer = new OvalDrawer();
    ShapeDrawer currentDrawer;



    public ShapeManager(DrawGUIs itsGui) {
        gui = itsGui;
        // default: scribble mode
        currentDrawer = scribbleDrawer;
        // activate scribble drawer
        gui.addMouseListener(currentDrawer);
        gui.addMouseMotionListener(currentDrawer);
    }

    // reset the shape drawer
    public void setCurrentDrawer(ShapeDrawer l) {
        if (currentDrawer == l)
            return;

        // deactivate previous drawer
        gui.removeMouseListener(currentDrawer);
        gui.removeMouseMotionListener(currentDrawer);
        // activate new drawer
        currentDrawer = l;
        gui.addMouseListener(currentDrawer);
        gui.addMouseMotionListener(currentDrawer);
    }

    // user selected new shape => reset the shape mode
    public void itemStateChanged(ItemEvent e) {
        if (e.getItem().equals("Scribble")) {
            setCurrentDrawer(scribbleDrawer);
        } else if (e.getItem().equals("Rectangle")) {
            setCurrentDrawer(rectDrawer);
        } else if (e.getItem().equals("Oval")) {
            setCurrentDrawer(ovalDrawer);
        }
    }
}

预期结果是带有附加CommandQueue的实际功能，以启用撤消和重做操作。