JComponents没有出现有图片背景？

Question

JComponents没有出现有图片背景？

我的部件没出现。我该怎么解决这个问题？

代码：

import java.awt.*;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import java.awt.image.BufferedImage;
import java.io.File;import java.io.IOException;import javax.imageio.ImageIO;import javax.swing.*;public class login implements ActionListener{
    JTextField gusername;
    JTextField gpassword;
    static String username;
    static String password;

    void logini() throws IOException {
        JFrame window = new JFrame("Login");
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setSize(300, 250);
        window.setResizable(false);
        window.setVisible(true);

        JPanel mainp = new JPanel(new GridBagLayout());
        GridBagConstraints c = new GridBagConstraints();
        window.add(mainp);

        BufferedImage myPicture = ImageIO.read(new File("c:\\bgd.png"));
        JLabel picLabel = new JLabel(new ImageIcon( myPicture ));
        mainp.add(picLabel, c);

        c.gridx = 0;
        c.gridy = 1;
        gusername = new JTextField();
        gusername.setText("Username");
        mainp.add(gusername, c);

        c.gridx = 0;
        c.gridy = 2;
        gpassword = new JTextField();
        gpassword.setText(" password ");
        mainp.add(gpassword, c);

        c.gridx = 0;
        c.gridy = 3;
        JButton login = new JButton("Login");
        mainp.add(login, c);

        login.addActionListener(this);
        login.setActionCommand("ok");
    }

    public void actionPerformed(ActionEvent e) {
        if (e.getActionCommand().equalsIgnoreCase("ok")){
            try {
                this.username = (gusername.getText());
                this.password = (gpassword.getText());
                System.out.println("0");
            }
            catch(NumberFormatException ex){
                System.out.println("ERROR: Could not preform function: 7424");
            }
        }
    }}