public int compare(MyFile left, MyFile right) {
   if (left.isDirectory()) {
     if (right.isDirectory()) {
       return left.compareTo(right);
     }
     return -1;
   }
   return right.isDirectory() ? 1 : left.compareTo(right);
 }
 public int compare(MyFile left, MyFile right) {
   return left.compareTo(right);
 }