问FileFilter不起作用

EN

import java.io.File;
import javax.swing.filechooser.FileFilter;
import javax.swing.filechooser.FileNameExtensionFilter;

public class Test {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        File ordner = new File("C:/eclipse/");
        listDir(ordner);
    }

    public static void listDir(File dir) {      

        final String[] pics = {"gif","png"};

        FileFilter picsFilefilter = new FileFilter() {
            private final FileNameExtensionFilter filter =
                new FileNameExtensionFilter("Only pics", pics);
            public boolean accept(File file) {
                return filter.accept(file);
            }
            public String getDescription() {
                return null;
            }

        };

        File[] files = dir.listFiles(picsFilefilter); //here the error occures

        if (files != null) {
            for (int i = 0; i < files.length; i++) {

                    if (files[i].isDirectory()) {
                        System.out.println("(Ordner) ");
                        listDir(files[i]); // ruft sich selbst mit dem 
                            // Unterverzeichnis als Parameter auf
                        }
                    else {
                        System.out.println("(Datei) ");
                    }
                    System.out.println(files[i].getName()+"\n");

            }
        }
    }

}