public  void sortEmployees(String sortBy){
        if (sortBy.equals("id")) {
            Collections.sort(employees, new EmployeeIdComparator());
        } else if(sortBy.equals("name")) {
            Collections.sort(employees, new EmployeeNameComparator());
        } else if(sortBy.equals("surname")) {
            Collections.sort(employees, new EmployeeSurnameComparator());
        } else if(sortBy.equals("date")) {
            Collections.sort(employees, new EmployeeDateComparator());
        } else if(sortBy.equals("salary")) {
            Collections.sort(employees, new EmployeeSalaryComparator());
        }
    }