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);
         }

     }