@Override
 public void setValueAt(Object aValue, int rowIndex, int columnIndex) {
   super.setValueAt(aValue, rowIndex, columnIndex);
   StudentModel student = students.get(rowIndex);
   String val = (String) aValue;
   try {
     switch (Columns.values()[columnIndex]) {
       case SURNAME:
         student.setSurname(val);
         break;
       case GROUP:
         student.setGroup(Integer.parseInt(val));
         break;
       case MATAN:
         student.getMarks().set(0, Integer.parseInt(val));
         break;
       case GA:
         student.getMarks().set(1, Integer.parseInt(val));
         break;
       case PROGRAMMING:
         student.getMarks().set(2, Integer.parseInt(val));
         break;
     }
     changeRows();
   } catch (NumberFormatException e) {
   }
 }