JComponents在有图片背景时未显示出来？

我的组件没有显示出来。我该如何修复这个问题？

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");
            }
        }
    }
}

结果：