请教大虾们为什么一下的程序运行时老是报java.lang.NullPointerException的异常啊

package manpowersystem;import java.awt.BorderLayout;
import java.awt.Dimension;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JButton;
import java.awt.*;
import com.borland.jbcl.layout.XYLayout;
import com.borland.jbcl.layout.*;public class MainFrame extends JFrame {
    JPanel contentPane;
    XYLayout xYLayout1 = new XYLayout();
    ImageIcon fmImage=new ImageIcon(manpowersystem.MainFrame.class.getResource("Fengmian.jpg"));
    JButton jButton1 = new JButton();    public MainFrame() {
        try {
            setDefaultCloseOperation(EXIT_ON_CLOSE);
            jbInit();
        } catch (Exception exception) {
            exception.printStackTrace();
        }
    }    /**
     * Component initialization.
     *
     * @throws java.lang.Exception
     */
    private void jbInit() throws Exception {
        jButton1.setIcon(fmImage);
        contentPane = (JPanel) getContentPane();
        contentPane.setLayout(xYLayout1);
        this.getContentPane().setBackground(new Color(210, 138, 177));
        setSize(new Dimension(400, 300));
        setTitle("Frame Title");
        jButton1.setText("jButton1");
        contentPane.add(jButton1, new XYConstraints(0, 0, 288, 300));
    }
}
我想在那个jbutton上面加上一个图片作为背景可是为什么加不上去啊