public class InsertDemo {

     public static void main(String[] args) {

         String nums = "123418447.6717";

         StringBuffer words = new StringBuffer(nums);

         //向字符串插入逗号

         int index = words.length();

         if (words.lastIndexOf(".")>0) {

             index = words.lastIndexOf(".");

         }

         for (int i = index-3; i >0; i=i-3) {

             words.insert(i, ',');

         }

         System.out.println(words);

     }

 }

 import java.util.Scanner;

 /**

  * 实现商品批发总金额的显示

  * @author Administrator

  *

  */

 public class Goods {

     //创建数组存放商品名及对应的价格

     String[] goods = new String[]{"电风扇","洗衣机","电视机","冰箱","空调机"};

     double[] price = new double[]{124.23,4500,8800.90,5000.88,4456,12000.46};

     //登陆验证

     private boolean login(String name, String pwd) {

         boolean flag = false;

         if (name.equals("TOM")&&pwd.equals("123")) {

             System.out.println("登陆成功！");

             flag  = true;

         }else{

             System.out.println("用户名和密码不匹配！");

         }

         return flag;

     }

     //打印商品信息

     private void show() {

         //1.使用Map集合保存

         //2.使用一般方法打印

         System.out.println("*************欢迎进入商品批发城*************");

         System.out.println("\t编号\t商品\t价格");

         for (int i = 0; i < goods.length; i++) {

             System.out.println("\t"+(i+1)+"\t"+goods[i]+"\t"+price[i]);

         }

         System.out.println("****************************************");

     }

     //计算订单总价

     private double calc(int goodId, int sum) {

         //根据商品编号查找商品信息

         int index = goodId-1;

         double sumPrice = -1;

         if (index>=0&&index < goods.length) {

             sumPrice = price[index]*sum;

         } else {

             System.out.println("您选择的商品不存在！");

         }

         return sumPrice;

     }

     //格式化输出金额

     private boolean change(int goodId, int sum) {

         //调用calc()方法获取商品金额

         double d = this.calc(goodId, sum);

         boolean flag = false;//商品不存在

         if (d==-1) {

             return flag;

         }

         StringBuffer price = new StringBuffer(String.valueOf(d));

         for (int i = price.indexOf(".")-3; i > 0; i = i-3) {

             price.insert(i, ',');

         }

         System.out.println("您需要付款："+price);

         return flag = true;

     }

     //测试

     public static void main(String[] args) {

         Goods g = new Goods();

         @SuppressWarnings("resource")

         Scanner input = new Scanner(System.in);

         boolean flag = false;

         do {

             /*用户登录*/

             System.out.print("请输入用户名：");

             String name = input.next();

             System.out.print("请输入密码：");

             String pwd = input.next();

             flag  = g.login(name, pwd);

         } while (!flag);

         //打印批发商品信息

         g.show();

         flag = false;

         do {

             //接收用户批发操作

             System.out.print("请输入您批发的商品编号：");

             int goodId = input.nextInt();

             System.out.print("请输入批发数量：");

             int sum = input.nextInt();

             //输出货款总额

             flag = g.change(goodId,sum);

         } while (!flag);

     }

 }