阅读以下说明和Java代码，填补代码中的空缺，将解答填入答题纸的对应栏内。
[说明]
在股票交易中，股票代理根据客户发出的股票操作指示进行股票的买卖操作。其类图如下图所示。相应的Java代码附后。
类图
[Java代码]
import
Java.util.ArrayList;
import
java.util.List;
ClaSS Stock{
private String
name;
private int
quantity;
public
Stock(String name,int quantity){
thiS.name=name;this.quantity=quantity;
}
public void buy(){
System.out.println("[买进]:"+name+",数量:"
+quantity);}
public void sell()
{System.out.println("[卖出]:"+name+",数量:"
+quantity);}
}
interface Order {
VOid execute();
}
class BuyStock
______ Order {
private Stock
Stock;
public
BuyStock(Stock stock){______=stock; }
public void
execute(){ stock.buy(); }
}
//类SellStock实现和BuyStock类似,略
clasS Broker{
private List＜Order＞orderList=new ArrayList＜Order＞();
Dublic void
takeOrder(______ Order){ orderList.add(order); }
public void
placeorders(){
for {______
order:orderList) {order.execute(); }
orderLiSt.clear();
}
}
public class
StockCommand {
public static void
main(String[]args){
Stock aStock:new
Stock("股票A",10);
Stock bStock=new
Stock("股票B",20);
Order
buyStockorder=new BuyStock(aStock);
Order
sellStockOrder=new SellSt0Ck(bStoCk);
Broker broker=new
Broker();
broker.takeOrder(buyStockorder);
broker.takeOrder(sellStockOrder);
broker.______;
}
}
