interface Item {
	public void accept(Visitor visitor);
	public double getPrice();
}
class Book(1) {
		private double price;
		public Book(double price) {
			(2);
		}
		public void accept(Visitor visitor) { //访问本元素
			(3);
		}
		public double getPrice() {
			return price;
		}
	}
	//其它物品类略
interface Visitor {
	public void visit(Book book);
	//其它物品的visit方法
}
class Cashier(4) {
	private double totalForCart;
	//访问Book类型对象的价格并累加
	(5) {
		//假设Book类型的物品价格超过10元打8折
		if(book.getPrice() < 10.0) {
			totalForCart += book.getPrice();
		}
		else totalForCart += book.getPrice() * 0.8;
	}
	//其它visit方法和折扣策略类似，此处略
	public double getTotal() {
		return totalForCart;
	}
}
class ShoppingCart {
	//normal shopping cart stuff
	private java.util.ArrayListitems = new java.util.ArrayList < > ();
	public double calculatePrice() {
		Cashier visitor = new Cashier();
		for(Item item: items) {
			(6);
		}
		double total = visitor.getTotal();
		return total;
	}
	public void add(Item e) {
		this.items.add(e);
	}
}