我是菜鸟，求大神帮忙给下面程序加个图片背景急！！！！求救！！！
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class jiance extends Frame implements ActionListener {

    TextField t1, t2, t3, t4;
    Button b1;
    Button b2;
    Button btnExit;

    public jiance()
    {
        
        super("登陆界面");
        Dimension d=Toolkit.getDefaultToolkit().getScreenSize();



        setLayout(new FlowLayout());
        t1 = new TextField(20);
        t1.setBackground(Color.white);
        
        t2 = new TextField(20);
        t2.setBackground(Color.white);
        

        b1 = new Button("登陆");
        b2=new Button("管理");
        btnExit = new Button("退出");
        
        add(new Label("用户名:"));
        add(t1);
        
            add(new Label("密码:"));
        add(t2);
        

        add(b1);
        add(b2);
        add(btnExit);
        
            addWindowListener(new WindowAdapter()
        {
            public void windowClosing(WindowEvent e)
            {
                System.exit(0);
            }
        }

    );
        
        b1.addActionListener(this);
        b2.addActionListener(this);
        btnExit.addActionListener(this);
               
        
        setVisible(true);

        setBounds(200, 200, 200, 300);
        validate();
    }

    public void actionPerformed(ActionEvent e)
    {
        if(e.getSource()==b1)
        {

        }
        if(e.getSource()==b2)
        {
            ;
        }
        if(e.getSource()==btnExit)
        {
            System.exit(0);
        }

    }

    public static void main(String args[]) {

        jiance j=new jiance();
        Dimension d=Toolkit.getDefaultToolkit().getScreenSize();
        j.setSize(d.width,d.height);
        j.setLocation(0,0);
        }
}

学了swing不知道怎么添加背景图片？