java，以下的代码所打开的JFileChooser为什么不能决定过滤器呢？

import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.filechooser.FileNameExtensionFilter;

public class FileChooseDemo
{
JPanel panel ;
JFrame frame ;
JButton btn ;
int rs ;
public FileChooseDemo ()
{
frame = new JFrame () ;
panel = new JPanel () ;
btn = new JButton ("click") ;

    btn.addActionListener(new ActionListener () 
    {
        @Override
        public void actionPerformed(ActionEvent arg0) 
        {
            // TODO Auto-generated method stub
            JFileChooser jfc = new JFileChooser () ;
            rs = jfc.showOpenDialog(frame) ;
            FileNameExtensionFilter fnef = new FileNameExtensionFilter ("jpg,png","jpg","png") ;
            jfc.addChoosableFileFilter(fnef) ;
            if(rs == JFileChooser.APPROVE_OPTION)
            {
                System.out.println(jfc.getSelectedFile().getName()) ;
            }
        }
    });

    panel.add(btn) ;
    frame.add(panel) ;

    frame.setPreferredSize(new Dimension(100,100)) ;
    frame.pack() ;
    frame.setResizable(false) ;
    frame.setLocationRelativeTo(null) ;     
    frame.setVisible (true) ;
}
public static void main(String[] args) 
{
    // TODO Auto-generated method stub
    new FileChooseDemo () ;
}

}

只要加上包名即可运行。我的目的是，只能选择jpg和png的文件，但是用的那个过滤器并没有过滤的效果，这是为什么呢？

https://blog.csdn.net/lntswangxin/article/details/5990865