public Employee(string FirstName, string LastName, DateTime Birthday, string department)
{
this.FirstName = FirstName;
this.LastName = LastName;
this.Birthday = Birthday;
_department = DepartmentObj.Add(department);
}
private void Button_Click(object sender, RoutedEventArgs e)
{
DepartmentObj.Add(TextBox.Text);
TextBox.Clear();
}