文件过滤FilenameFilter,该怎么解决

import java.io.File;import java.io.FilenameFilter;import java.util.regex.*;import java.util.*;public class DirList {     public static void main(String[] args) {                        String filePath="d:\\";                String filterName=".java";                FilenameFilter ff = new DirFilter(filterName);                File f = new File(filePath);                    String[] list = f.list(ff);                      Arrays.sort(list,String.CASE_INSENSITIVE_ORDER);            for(String dirItem : list){                System.out.println(dirItem);            }     }     static  class DirFilter implements FilenameFilter{                  private Pattern pattern;         public DirFilter(String regex){             pattern = Pattern.compile(regex);         }         public boolean accept(File dirFile , String name){             return pattern.matcher(name).matches();         }              }}