JAVA swing小问题

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

public class wp
{
public static void main(String[] args)
{
MyJFrame2 m=new MyJFrame2();
m.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
m.setVisible(true);
}
}
class MyJFrame2 extends JFrame
{
public MyJFrame2()
{
setTitle("JButton");
setSize(300,200);
MyPanel2 panel=new MyPanel2();
add(panel);
}
}
class MyPanel2 extends JPanel
{
public void paintComponent(Graphics g)
{
final Graphics2D g2=(Graphics2D)g;
final Rectangle2D rectangle=new Rectangle2D.Float(200.0f,300.0f,200.0f,300.0f);
JButton b=new JButton("圆");
add(b);
b.addActionListener(new
ActionListener()
{
public void actionPerformed(ActionEvent a)
{
g2.draw(rectangle);

JAVA swing小问题 java swing 的小问题 关于JAVA swing小问题！ java swing窗口问题 java swing的问题 java中SWING 问题 JAVA关于Swing的问题 java Swing中table问题 JAVA swing方面的问题 javax.swing.JPanel小问题