添加的JLabel无法显示。该怎么解决

container.setLayout(null);  //把这句话删掉
------解决方案--------------------
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class MyJDialog extends JDialog { 
public MyJDialog(MyFrame frame) {

super(frame, "第一个JDialog窗体", true);
Container container = getContentPane();
container.add(new JLabel("这是一个对话框")); 
setBounds(120, 120, 100, 100); 
}
}
public class MyFrame extends JFrame { 
/**
	 *  
	 */
	private static final long serialVersionUID = 8904641527445622030L;

public static void main(String args[]) {
new MyFrame(); 
}

public MyFrame() {
Container container = getContentPane(); 
container.setLayout(null);

JButton bl = new JButton("弹出对话框"); 
bl.setBounds(10, 10, 100, 21);
bl.addActionListener(new ActionListener() { 
public void actionPerformed(ActionEvent e) {

new MyJDialog(MyFrame.this).setVisible(true);
}
});
container.add(bl); 
JLabel jl = new JLabel("这是一个JFrame窗体"); 
//jl.setHorizontalAlignment(SwingConstants.CENTER);
jl.setBounds(10,30,150,30);
container.add(jl);
container.setBackground(Color.white);
setSize(200, 200);
setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
setVisible(true);
}
}
好了，楼主给分