public String get(int sheet, int RowIndex, int CellIndex) {
   if (FileType.getFileType() == 1) {
     // xls
     return excel_xls.get(sheet, RowIndex, CellIndex);
   } else if (FileType.getFileType() == 2) {
     // xlsx
     return excel_xlsx.get(sheet, RowIndex, CellIndex);
   }
   return "";
 }