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

public class MyDJialog extends JDialog{
 public MyDJialog(JFrame ee) {
 super(ee,"这行文字在哪？",true);
 Container c=getContentPane();
 c.setBackground(Color.green);
 JLabel q=new JLabel("弹窗文字");
 q.setHorizontalAlignment(SwingConstants.CENTER);
 q.setFont(new Font("黑体",Font.BOLD,30));
 c.add(q);
 
 setBounds(100, 100, 200, 200);
 setVisible(true);
 }
 public static void main(String[] args) {
  JFrame j=new JFrame("这是父窗体");
  j.setBounds(300, 300, 400, 400);
  j.setVisible(true);
  Container c=j.getContentPane();
  JButton bt=new JButton("点我点我快点我");
  bt.setLayout(new FlowLayout());
  c.add(bt);
  j.setDefaultCloseOperation(EXIT_ON_CLOSE);
  bt.addActionListener(new ActionListener() {
  
   public void actionPerformed(ActionEvent e) {
    new MyDJialog(j);
   }
  });
 }
}

请问这个代码写出来后，整个父窗体变成一个按钮了，问题出在哪里？