Flutter OOP

main.dart

class Order {
  var _id;
  var _reference;
  var date;
  var name;
  var _vorname;

  Order(this._id, this._reference, {this.date});

  Order.name(this._id, this._reference, {this.name = 'x'});

  Order.vorname(this._id, this._reference, {vorname}) {
    _vorname = vorname;
  }

  getInfo() {
    return 'Your order information:'
        '\n-------------------------------'
        '\n  Id: $_id'
        '\n  Reference: $_reference'
        '\n  Date: $date'
        '\n  Name: $name'
        '\n  Vorname: $_vorname'
        '\n-------------------------------';
  }
}

void main() {
  // var order1 = new Order(1, 'ref1', date: new DateTime.now());

  var order1 = new Order(1, 'ref1', date: '2019-04-09');
  print(order1.getInfo());
  var order2 = new Order.name(1, 'ref1');
  print(order2.getInfo());
  var order3 = new Order.vorname(1, 'ref1', vorname: 'a');
  print(order3.getInfo());
}