为何JLable显示不出来？求教

[jack54877012]

package SwingTest;

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingConstants;

public class SwingTest3 extends JFrame{
	public SwingTest3() {
		super();
		setBounds(100, 100, 330, 220);
		setTitle("JFrame");
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		Container container=getContentPane();
		container.setLayout(null);
		JLabel JL=new JLabel();
		JL.setText("JFrame窗口");
		container.add(JL,BorderLayout.NORTH);
		JButton JB=new JButton("弹出对话框");
//		JB.setSize(50,50);
		JB.setBounds(10,10,100,21);
		JB.setLocation(300, 300);
		JB.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
	//			new SwingTest2().setVisible(true);;
			}
		});
		container.add(JB);
	}
	public static void main(String[] args) {
		SwingTest3 st=new SwingTest3();
		st.setVisible(true);
	}
}

[自由自在_Yu]

JLabel JL=new JLabel(); JL.setText("JFrame窗口"); JL.setBounds(20,20,80,80);