修改项目目录

src/chapter3/demo31/Book.java

@@ -0,0 +1,36 @@
+package chapter3.demo31;
+
+public class Book {
+    private final int id;       // 编号
+    private final String name;  // 书名
+    private final double price; // 价格
+    private final int storage;  // 库存
+
+    // 有参构造
+    public Book(int id, String name, double price, int storage) {
+        this.id = id;
+        this.name = name;
+        this.price = price;
+        this.storage = storage;
+    }
+
+    // 获取书号
+    public int getId() {
+        return id;
+    }
+
+    // 获取书名
+    public String getName() {
+        return name;
+    }
+
+    // 获取价格
+    public double getPrice() {
+        return price;
+    }
+
+    // 获取库存
+    public int getStorage() {
+        return storage;
+    }
+}

src/chapter3/demo31/Order.java

@@ -0,0 +1,43 @@
+package chapter3.demo31;
+
+public class Order {
+    private final String orderId;
+    private final OrderItem[] items;
+    private double total;
+
+    // 有参构造
+    public Order(String orderId) {
+        this.orderId = orderId;
+        this.items = new OrderItem[3];
+    }
+
+    // 获取订单号
+    public String getOrderId() {
+        return orderId;
+    }
+
+    // 获取订单列表
+    public OrderItem[] getItems() {
+        return items;
+    }
+
+    // 获取订单总额
+    public double getTotal() {
+        calTotal();
+        return total;
+    }
+
+    // 指定一个订单项
+    public void setItem(OrderItem item, int i) {
+        this.items[i] = item;
+    }
+
+    // 计算订单总额
+    public void calTotal() {
+        double total = 0;
+        for (OrderItem item : items) {
+            total += item.getNum() * item.getBook().getPrice();
+        }
+        this.total = total;
+    }
+}

src/chapter3/demo31/OrderItem.java

@@ -0,0 +1,22 @@
+package chapter3.demo31;
+
+public class OrderItem {
+    private final Book book;
+    private final int num;
+
+    // 有参构造方法
+    public OrderItem(Book book, int num) {
+        this.book = book;
+        this.num = num;
+    }
+
+    // 获取图书对象
+    public Book getBook() {
+        return book;
+    }
+
+    // 获取订购图书数量
+    public int getNum() {
+        return num;
+    }
+}

src/chapter3/demo31/PayBooks.java

@@ -0,0 +1,64 @@
+package chapter3.demo31;
+
+import java.util.Scanner;
+
+public class PayBooks {
+    public static void main(String[] args) {
+        Book[] books = new Book[3];
+        // 模拟从数据库中读取图书信息并输出
+        outBooks(books);
+        // 顾客购买图书
+        Order order = purchase(books);
+        // 输出订单信息
+        outOrder(order);
+    }
+
+    // 顾客购买图书
+    public static Order purchase(Book[] books) {
+        Order order = new Order("00001");
+        OrderItem item = null;
+        Scanner in = new Scanner(System.in);
+
+        for (int i = 0; i < 3; i++) {
+            System.out.println("请输入图书编号选择图书：");
+            int cno = in.nextInt();
+            System.out.println("请输入购买图书数量：");
+            int pnum = in.nextInt();
+            item = new OrderItem(books[cno - 1], pnum);
+            order.setItem(item, i);
+            System.out.println("请继续购买图书。");
+        }
+        in.close();
+        return order;
+    }
+
+    // 输出订单信息
+    public static void outOrder(Order order) {
+        System.out.println("\n===================图书订单===================");
+        System.out.println("图书订单号：" + order.getOrderId());
+        System.out.println("图书名称\t购买数量\t图书单价");
+        System.out.println("--------------------------------------");
+        OrderItem[] items = order.getItems();
+        for (OrderItem item : items) {
+            System.out.println(
+                    item.getBook().getName() + "\t" + item.getNum() + "\t" + item.getBook().getPrice());
+        }
+        System.out.println("---------------------------------------");
+        System.out.println("订单总额：\t\t" + order.getTotal());
+    }
+
+    // 模拟从数据库中读取图书信息并输出
+    public static void outBooks(Book[] books) {
+        books[0] = new Book(1, "Java教程", 30.6, 30);
+        books[1] = new Book(2, "JSP教程", 42.1, 40);
+        books[2] = new Book(3, "SSH架构", 47.3, 15);
+        System.out.println("===================图书列表===================");
+        System.out.println("图书编号\t图书名称\t\t图书单价\t库存数量");
+        System.out.println("---------------------------------------");
+        for (int i = 0; i < books.length; i++) {
+            System.out.println(
+                    i + 1 + "\t" + books[i].getName() + "\t" + books[i].getPrice() + "\t" + books[i].getStorage());
+        }
+        System.out.println("---------------------------------------");
+    }
+}