java递归所有文件

import java.io.File;
public class Filep {
public static File f = new File("E:\\javatest");
public static File ff;
public static String findfile(File f){
if(f.list()==null) return null;
String[] str = f.list();
for(String ss: str)
{
System.out.println(f.getAbsolutePath()+"\\"+ss);
ff = new File(f.getAbsolutePath()+"\\"+ss);
findfile(ff);
}
return null;
}
public static void main(String argv[])
{
findfile(f);
}
}