很简单为啥什么 都不能显示呢

很简单为什么什么 都不能显示呢

Java code

import java.awt.Container;import java.awt.FlowLayout;import javax.swing.BoxLayout;import javax.swing.JFrame;import javax.swing.JLabel;import javax.swing.JPanel;import javax.swing.JTextField;public class LoginWin extends JPanel{           private JLabel lab;    private JTextField jf;    public LoginWin() {        super();        initGUI();    }    private void initGUI() {        setSize(200, 200);        jf = new JTextField();        lab = new JLabel();            this.setLayout(null);        lab.setBounds(30,30,120,30);        jf.setBounds(30,80,120,30);    }        public static void main(String args[]){        JFrame jff = new JFrame();        Container con = jff.getContentPane();        con.setLayout(new FlowLayout());        LoginWin lw = new LoginWin();        con.add(lw);        jff.setSize(300, 200);        jff.setVisible(true);    }}