Java GUI JLabel 和 JPanel 图片 和组件重叠问题

package ui;
import java.awt.AWTEvent;
import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BorderFactory;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
public class MainUi extends JPanel implements ActionListener
{
 protected JTextField id, psw;
 protected JButton ok, register, exit;
 protected JLabel idl, pswl, imgl;
 protected static JLabel imgpanel;
 protected ImageIcon image;
 public MainUi()
 {
  enableEvents(AWTEvent.WINDOW_EVENT_MASK);
  image = new ImageIcon("D://java/PZ/image/bg.jpg");
  imgpanel = new JLabel(image);
  
  id = new JTextField(60);
  id.setActionCommand("ID");
  idl = new JLabel("ID :");
  idl.setLabelFor(id);
  psw = new JTextField(60);
  psw.setActionCommand("password");
  pswl = new JLabel("PassWord: ");
  pswl.setLabelFor(psw);
  ok = new JButton("OK");
  register = new JButton("REGISTER");
  exit = new JButton("EXIT");
  JPanel login = new JPanel();
  GridBagLayout gridbag = new GridBagLayout();
  GridBagConstraints c = new GridBagConstraints();
  login.setLayout(gridbag);
//  imgl.setBounds(0, 0, imgIcon.getIconWidth(), imgIcon.getIconHeight());
//  login.setOpaque(false);
  JLabel[] labels = { idl, pswl };
  JTextField[] textFields = { id, psw };
  addLabelTextRows(labels, textFields, gridbag, login);
  c.gridw