//full constructor
public GSM(string model, string manufacturer, double? price, string owner, Display display, Battery battery)
{
this.Model = model;
this.Manufacturer = manufacturer;
this.Price = price;
this.Owner = owner;
this.Display = display;
this.Battery = battery;
}
//full constructor
public GSM(string model, string manufacturer, double?price, string owner, Display display, Battery battery)
{
this.Model = model;
this.Manufacturer = manufacturer;
this.Price = price;
this.Owner = owner;
this.Display = display;
this.Battery = battery;
}