问答题 [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: {{U}}(3) {{/U}}) { iht number = 0; for (Order order: {{U}}(4) {{/U}}) { for ( {{U}}(5) {{/U}}: 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 }