public GSM(string model, string manufacturer, decimal? price, string owner, Battery battery, Display display)
{
this.Model = model;
this.Manufacturer = manufacturer;
this.Price = price;
this.Owner = owner;
this.battery = battery;
this.display = display;
}
public GSM(string model, string manufacturer, decimal? price, string owner, Display display)
: this(model, manufacturer, price, owner, null, display)
{
}