日前 做了个接口小练习：D:\Tomcat 6.0\webapps\lx\InterfaceTest\src\com\cstp下面有3个文件夹 dao、impl、test 里面各有一个java   文件分别是：GoodsDAO.java 代码为：
                                       package com.cstp.dao;

                                      public interface GoodsDAO 

                                     { 
                               public void buy(int count);
                                      }
                            GoodsDAOImpl.java 代码为：

                                    package com.cstp.impl;

                                    import com.cstp.dao.GoodsDAO;

                                    public class GoodsDAOImpl implements GoodsDAO 
                                        {

                           public void buy(int count) {//传入物品数量
                                              // TODO Auto-generated method stub
                      double price = 20;//物品单价
                System.out.println("总价："+20*count);

                               }

                                        }

                                     Test.java 代码为：


                                      package com.cstp.test;

                                      import com.cstp.impl.GoodsDAOImpl;

                                         public class Test {
                                public static void main(String args[]){
                        GoodsDAOImpl goods = new GoodsDAOImpl();
                           goods.buy(2);
                                          }
                                                   }

一  编译之后 报错： Test.java:3: 软件包 com.cstp.impl 不存在
                    import com.cstp.impl.GoodsDAOImpl;
                 要是把包路径全部去掉 并放在一个文件夹下 则可以执行
请问为什么  如何修改