@Override
 public int compare(FolderInfo lhs, FolderInfo rhs) {
   if (lhs.getNumOfTracks() > rhs.getNumOfTracks()) {
     return -1;
   } else if (lhs.getNumOfTracks() < rhs.getNumOfTracks()) {
     return 1;
   } else {
     return 0;
   }
 }
 @Override
 public int compare(FolderInfo lhs, FolderInfo rhs) {
   first_l = lhs.getFolderName().charAt(0);
   first_r = rhs.getFolderName().charAt(0);
   if (StringHelper.checkType(first_l) == StringHelper.CharType.CHINESE) {
     first_l = StringHelper.getPinyinFirstLetter(first_l);
   }
   if (StringHelper.checkType(first_r) == StringHelper.CharType.CHINESE) {
     first_r = StringHelper.getPinyinFirstLetter(first_r);
   }
   if (first_l > first_r) {
     return 1;
   } else if (first_l < first_r) {
     return -1;
   } else {
     return 0;
   }
 }