求组！setfileSystemView(filter)为什么会显示出错？

Question

import java.awt.*;
import java.io.*;
import javax.swing.*;

import java.awt.event.*;
public class ImagePanel extends JPanel{
private Image img;
private String imageFiles[];
private int current=0;
private int counts=0;
private File imageDir=null;
Toolkit
mytool=Toolkit.getDefaultToolkit();
public ImagePanel(){
imageDir=new File(".");
changDir(imageDir);
}
public void changDir(File imageDir){
current=0;
counts=0;
this.imageDir=imageDir;
String[] filenames=imageDir.list();
for(int i=0;i<filenames.length;i++){
if(filenames[i].toLowerCase().endsWith(".jpg")||filenames[i].toLowerCase().endsWith(".png"))counts++;
else filenames[i]=null;
}
imageFiles=new String[counts];
for(int i=0,j=0;i<filenames.length;i++){
if(filenames[i]!=null){
imageFiles[j]=imageDir.getAbsoluteFile()+"\"+filenames[i];
j++;
}
}
repaint();
}

public void changDir(File imageDir,File selectedFile){
    this.imageDir=imageDir;
    counts=0;
    current=0;
    String[] filenames=imageDir.list();
    String selectedfilename=selectedFile.getName();
    for(int i=0;i<filenames.length;i++){
        if(filenames[i].toLowerCase().endsWith(".jpg")||filenames[i].toLowerCase().endsWith(".png")){
            counts++;
            if(filenames[i].equals(selectedfilename))current=counts;
        }
        else {
            filenames[i]=null;
        }
    }
    System.out.println(filenames+","+filenames.length);
    System.out.println("counts="+counts);
    System.out.println(imageDir);
    imageFiles=new String[counts];
    for(int i=0,j=0;i<filenames.length;i++){
        if(filenames[i]!=null){
            imageFiles[j]=imageDir.getAbsoluteFile()+"\\"+filenames[i];
            j++;
        }
    }
    repaint();
}
public void paintComponent(Graphics g){
    super.paintComponent(g);
    if(counts==0){
    g.drawString("该目录没有图像文件", 20, 20);


    }else
    {
        img=mytool.getImage(imageFiles[current]);
        g.drawImage(img,0,0,getSize().width,getSize().height,this);
    }
}
public int getCurrent(){return current;}
public void setCurrent(int a){
    if(a>=0&&a<counts)current=a;
    else if(a<0)current=0;
    else current=counts-1;
}

}

import java.awt.*;
import java.io.*;
import javax.swing.*;
import javax.swing.filechooser.FileFilter;
import javax.swing.filechooser.FileSystemView;

import java.awt.event.*;
import java.awt.image.*;
public class ImageViewer1 extends JFrame{
private JButton selectdir,bt1,bt2;
private ImagePanel mv;
private ImageViewer1 outer=this;
public ImageViewer1(){
super("图像查看器");
bt1=new JButton("上一张");
bt2=new JButton("下一张");
selectdir=new JButton("目录");
mv=new ImagePanel();
Panel p1=new Panel();
p1.add(selectdir);
p1.add(bt1);
p1.add(bt2);
add(p1,BorderLayout.SOUTH);
add(mv,BorderLayout.CENTER);

    Mylistener ls=new Mylistener();
    selectdir.addActionListener(ls);
    bt2.addActionListener(ls);
    bt1.addActionListener(ls);

}

private class Mylistener implements ActionListener{
    public void actionPerformed(ActionEvent e){
        if(e.getSource()==bt1)
        {
            mv.setCurrent(mv.getCurrent()-1);
            mv.repaint();

        }else if(e.getSource()==bt2){
            mv.setCurrent(mv.getCurrent()+1);
            mv.repaint();
        }else
        {
            JFileChooser fileChooser=new JFileChooser();
            fileChooser.setFileSelectionMode(JFileChooser.FILES_AND_DIRECTORIES);
            ImageFilter filter=new ImageFilter();
            fileChooser.setFileSystemView(filter);//这里的后半setfileSystemView(filter)为什么会显示出错？
            int returnValue=fileChooser.showOpenDialog(outer);
            File selectedFile=null;
            if(returnValue==JFileChooser.APPROVE_OPTION){
                selectedFile=fileChooser.getSelectedFile();

            }if(selectedFile.isDirectory()){
                mv.changDir(selectedFile);
            }else{
                File parentdir=selectedFile.getParentFile();
                mv.changDir(parentdir,selectedFile);
            }
        }
    }
}
public static void main(String[] args){
    ImageViewer1 myapp=new ImageViewer1();
    myapp.setSize(800,600);
    myapp.setVisible(true);
    myapp.addWindowListener(new WindowDestroyer());
}

}

Answer 1

改成 setFileFilter同样出错