[Java程序7-21] import java.u61.*; public class SalesSystem { private ProductList catalog; private OrderList sales; private static PrintWriter stdOut = new PrintWriter(System.out, true); public void statistic() { for (Product product: (3) ) { iht number = 0; for (Order order: (4) ) {for ( (5) : order) { if (produet.equals(item.getProduct())) number += item. getQuantity(); }} stdOut.println(product .getCode() +" "+ product.getDescription() +" "+ number +" "+ number * product.getPrice()); } } //其余的方法末列出 }