public class JavaMain { public static void main(String[] args) { new MyWindow(); } } class MyWindow extends JFrame implements MouseListener, MouseMotionListener, ActionListener { //定义两个点 private Point oldPoint = null,newPoint = null; public MyWindow () { this.setSize(600,600); addMouseListener(this); addMouseMotionListener(this); this.setVisible(true); this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); } //画图 public void paint(Graphics g) { Graphics2D g2 = (Graphics2D) g; g2.setStroke(new BasicStroke(10.0f)); g2.setColor(Color.red); if(oldPoint!=null&&newPoint!=null) { g2.drawLine(oldPoint.x, oldPoint.y, newPoint.x, newPoint.y); oldPoint=newPoint; newPoint=null;//置为空，为了迎接下一个点的到来 } } //鼠标拖动事件 @Override public void mouseDragged(MouseEvent e) { if(oldPoint==null) { oldPoint=e.getPoint(); }else { newPoint=e.getPoint(); repaint();//生成新的点，通知系统去更新绘图 } } @Override public void mouseMoved(MouseEvent e) {} //鼠标单击事件 @Override public void mouseClicked(MouseEvent e) {} @Override public void mouseEntered(MouseEvent e) {} @Override public void mouseExited(MouseEvent e) {} @Override public void mousePressed(MouseEvent e) {} //鼠标释放事件，清空工作 @Override public void mouseReleased(MouseEvent e) { newPoint=null; oldPoint=null; } }设置清除画布按钮

您可以在 `MyWindow` 类中添加一个按钮，并为其添加一个 `ActionListener`，在按钮被点击时清除画布。代码示例如下：

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class MyWindow extends JFrame implements MouseListener, MouseMotionListener, ActionListener {
    private Point oldPoint = null, newPoint = null;
    private JButton clearButton; // 添加一个清除按钮

    public MyWindow() {
        this.setSize(600, 600);
        addMouseListener(this);
        addMouseMotionListener(this);

        // 初始化清除按钮
        clearButton = new JButton("清除画布");
        clearButton.addActionListener(this);
        JPanel buttonPanel = new JPanel();
        buttonPanel.add(clearButton);
        add(buttonPanel, BorderLayout.SOUTH);

        this.setVisible(true);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public void paint(Graphics g) {
        Graphics2D g2 = (Graphics2D) g;
        g2.setStroke(new BasicStroke(10.0f));
        g2.setColor(Color.red);
        if (oldPoint != null && newPoint != null) {
            g2.drawLine(oldPoint.x, oldPoint.y, newPoint.x, newPoint.y);
            oldPoint = newPoint;
            newPoint = null;
        }
    }

    @Override
    public void mouseDragged(MouseEvent e) {
        if (oldPoint == null) {
            oldPoint = e.getPoint();
        } else {
            newPoint = e.getPoint();
            repaint();
        }
    }

    @Override
    public void mouseMoved(MouseEvent e) {}

    @Override
    public void mouseClicked(MouseEvent e) {}

    @Override
    public void mouseEntered(MouseEvent e) {}

    @Override
    public void mouseExited(MouseEvent e) {}

    @Override
    public void mousePressed(MouseEvent e) {}

    @Override
    public void mouseReleased(MouseEvent e) {
        newPoint = null;
        oldPoint = null;
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == clearButton) {
            Graphics g = getGraphics();
            g.setColor(getBackground());
            g.fillRect(0, 0, getWidth(), getHeight());
        }
    }
}

在上面的代码中，我们添加了一个 `clearButton` 按钮，并在其上添加了一个 `ActionListener`。当按钮被点击时，会调用 `actionPerformed` 方法清除画布。在 `actionPerformed` 方法中，我们获取了 `MyWindow` 的 `Graphics` 对象，并使用 `fillRect` 方法覆盖整个画布。这样就达到了清除画布的效果。