使用命令模式设计一个图形绘制系统，该系统可以绘制矩形、椭圆、三角形等图形，恢复和撤销功能。绘制类图并编程实现。java实现

首先，我们需要定义一个命令接口，该接口包含了执行和撤销两个方法：

public interface Command {
    void execute();
    void undo();
}

然后，我们定义具体的绘制命令类，如矩形绘制命令类、椭圆绘制命令类、三角形绘制命令类等。这些类实现了上述命令接口，用于执行具体的绘制操作和实现恢复和撤销功能。

接下来，我们定义一个图形绘制器类，该类负责管理所有的绘制命令，包括执行、撤销和恢复上一步操作等功能。该类可以被其他业务逻辑调用，完成图形绘制的任务。

具体代码实现如下：

// 定义绘制命令接口
public interface Command {
    void execute();
    void undo();
}

// 定义矩形绘制命令类
public class RectangleCommand implements Command {
    private final Graphics graphics;
    private final int x;
    private final int y;
    private final int width;
    private final int height;

    public RectangleCommand(Graphics graphics, int x, int y, int width, int height) {
        this.graphics = graphics;
        this.x = x;
        this.y = y;
        this.width = width;
        this.height = height;
    }

    @Override
    public void execute() {
        graphics.drawRect(x, y, width, height);
    }

    @Override
    public void undo() {
        graphics.clearRect(x, y, width, height);
    }
}

// 定义椭圆绘制命令类
public class EllipseCommand implements Command {
    private final Graphics graphics;
    private final int x;
    private final int y;
    private final int width;
    private final int height;

    public EllipseCommand(Graphics graphics, int x, int y, int width, int height) {
        this.graphics = graphics;
        this.x = x;
        this.y = y;
        this.width = width;
        this.height = height;
    }

    @Override
    public void execute() {
        graphics.drawOval(x, y, width, height);
    }

    @Override
    public void undo() {
        graphics.clearRect(x, y, width, height);
    }
}

// 定义三角形绘制命令类
public class TriangleCommand implements Command {
    private final Graphics graphics;
    private final int[] xPoints;
    private final int[] yPoints;

    public TriangleCommand(Graphics graphics, int[] xPoints, int[] yPoints) {
        this.graphics = graphics;
        this.xPoints = xPoints;
        this.yPoints = yPoints;
    }

    @Override
    public void execute() {
        graphics.drawPolygon(xPoints, yPoints, 3);
    }

    @Override
    public void undo() {
        graphics.setColor(Color.WHITE);
        graphics.fillPolygon(xPoints, yPoints, 3);
        graphics.setColor(Color.BLACK);
    }
}

// 定义图形绘制器类
public class GraphicsDrawer {
    private final List<Command> commandList = new ArrayList<>();
    private final Stack<Command> undoStack = new Stack<>();

    public void addCommand(Command command) {
        commandList.add(command);
        command.execute();
        undoStack.clear();
    }

    public void undo() {
        if (!commandList.isEmpty()) {
            Command command = commandList.remove(commandList.size() - 1);
            command.undo();
            undoStack.push(command);
        }
    }

    public void redo() {
        if (!undoStack.isEmpty()) {
            Command command = undoStack.pop();
            commandList.add(command);
            command.execute();
        }
    }
}

在上面的代码中，我们定义了三个具体的绘制命令类，分别是矩形绘制命令类、椭圆绘制命令类和三角形绘制命令类。这些类实现了命令接口，用于执行具体的绘制操作和实现恢复和撤销功能。

我们还定义了一个图形绘制器类 GraphicsDrawer，该类负责管理所有的绘制命令，包括执行、撤销和恢复上一步操作等功能。该类可以被其他业务逻辑调用，完成图形绘制的任务。

最后，我们可以使用以下代码来测试我们的图形绘制系统：

public static void main(String[] args) {
    GraphicsDrawer drawer = new GraphicsDrawer();
    JFrame frame = new JFrame();
    frame.setSize(600, 600);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
    JPanel panel = new JPanel() {
        private int[] xPoints = new int[3];
        private int[] yPoints = new int[3];
        private int pointIndex = 0;
        private Command command;

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            for (Command command : drawer.getCommandList()) {
                command.execute();
            }
            if (command != null) {
                command.execute();
            }
        }

        @Override
        public void mouseClicked(MouseEvent e) {
            if (e.getButton() == MouseEvent.BUTTON1) {
                if (pointIndex == 0) {
                    xPoints[0] = e.getX();
                    yPoints[0] = e.getY();
                    pointIndex = 1;
                } else if (pointIndex == 1) {
                    xPoints[1] = e.getX();
                    yPoints[1] = e.getY();
                    pointIndex = 2;
                } else {
                    xPoints[2] = e.getX();
                    yPoints[2] = e.getY();
                    command = new TriangleCommand(getGraphics(), xPoints, yPoints);
                    drawer.addCommand(command);
                    pointIndex = 0;
                }
            } else if (e.getButton() == MouseEvent.BUTTON2) {
                command = new EllipseCommand(getGraphics(), e.getX() - 25, e.getY() - 25, 50, 50);
                drawer.addCommand(command);
            } else if (e.getButton() == MouseEvent.BUTTON3) {
                command = new RectangleCommand(getGraphics(), e.getX() - 25, e.getY() - 25, 50, 50);
                drawer.addCommand(command);
            }
        }
    };
    frame.add(panel);
    panel.addMouseListener(panel);
    panel.addMouseMotionListener(panel);
}

在上面的代码中，我们创建了一个 JFrame 窗口，并添加了一个 JPanel 面板用于绘图。我们通过鼠标事件监听器来对鼠标点击事件进行处理，根据不同的鼠标按键来创建不同的绘制命令，并将其添加到图形绘制器中。

当需要恢复或撤销绘制操作时，我们可以调用图形绘制器的 undo() 和 redo() 方法来实现。