程序代码：

package import java.awt.Color;
import java.awt.Graphics;
import java.awt.Rectangle;

import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

/**

 * 登录界面

 *

 * @author Administrator

 *

 */
public class MainFrame extends JFrame {
    private JLabel jLabel1;
    private JLabel jLabel2;
    private JPanel jContentPane;

    public MainFrame() {
        init();
    }

    /**
     * 初始化窗体
     */
    private void init() {
        this.setSize(380, 286);
        this.add(getJContentPane());
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
        this.setLocationRelativeTo(null);
        this.setVisible(true);
    }

    private JPanel getJContentPane() {
        if (jContentPane == null) {
            jContentPane = new JPanel(){
                    ImageIcon img = new ImageIcon("QQ登录界面背景2.jpg");
                    // 绘制面板 组件图片
                    protected void paintComponent(Graphics g) {
                        g.drawImage(img.getImage(), 0, 0, this);
                    }
            };
        }
        return jContentPane;
    }

    /**
     * 程序入口
     *
     * @param args
     */
    public static void main(String[] args) {
        MainFrame m = new MainFrame();

    }
}