java程序实现鼠标绘图

import java.awt.*;

import javax.swing.*;
class Gstudy extends JFrame{
    
    private int x1,y1,x2,y2;
    private newPanel panel=new newPanel();
    private JButton btn=new JButton("清除");
    public Gstudy()
    {
        setTitle("交互式绘图");
        setBounds(10,10,750,700);
        btn.addActionListener(new ClearList());
        panel.add(btn,BorderLayout.SOUTH);
        add(panel);
    }
    public static void main(String[] args)
    {
        Gstudy frm=new Gstudy();
        frm.setVisible(true);
        frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
    private class ClearList  implements ActionListener
    {
        @Override
        public void actionPerformed(ActionEvent e) {
            
            panel.paintComponent(panel.getGraphics());
        }
    }
    private class MyMouseList extends MouseAdapter
    {
        public void mousePressed(MouseEvent e)
        {
            x1=e.getX();
            y1=e.getY();
        }
    }
    private class MyMouseMotionList extends MouseMotionAdapter
    {
        public void mouseDragged(MouseEvent e)
        {
            x2=e.getX();
            y2=e.getY();
            Graphics g=panel.getGraphics();
            g.drawLine(x1, y1, x2, y2);
            x1=x2;
            y1=y2;
        }
    }
    private class newPanel extends JPanel
    {
        
        public newPanel()
        {
            this.addMouseMotionListener(new MyMouseMotionList());
            this.addMouseListener(new MyMouseList());
        }
        @Override
        protected void paintComponent(Graphics g) {
            // TODO Auto-generated method stub
            super.paintComponent(g);
        }
        
    }