Shopping Cart

Checkout.java

while (!cart.isEmpty()) {
    shipping.ship(cart.takeNext(), ???);
}

Checkout2.java

while (!cart.isEmpty()) {
    Item currentItem = cart.takeNext(); 
    if(current.isDownloadable) {
       shipping.ship(currentItem, shipToEmailAddress);
    } else {
       shipping.ship(currentItem, shipToSurfaceAddress);
    }
}

Item.java

public interface Item {
    public boolean ship(Shipping shipper); 
}


public class DownloadableItem implements Item {
    public boolean ship(Shipping shipper) {
        shipper.ship(this, customer.getEmailAddress());
    }
}

public class SurfaceItem implements Item {
    public boolean ship(Shipping shipper) {
        shipper.ship(this, customer.getSurfaceAddress());
    }
}

Shipping.java

public class Shipping {
    public boolean ship(Item item, SurfaceAddress address) { ... }
    public boolean ship(Item item, EMailAddress address { ... }
}

ShoppingCart.java

public class ShoppingCart {
    private List<Item> cart = new ArrayList<Item>();
    public void add(Item item) { cart.add(item); }
    public Item takeNext() { return cart.remove(0);  }
    public boolean isEmpty() { return cart.isEmpty(); }
}