一段简单的代码 却是我要努力去接受的

今天老师教了个知识点，还是有点晕了，三层架构都没搞怎么懂，不知道该如何是好，下面这是老师给我们的关于集合深入运用的代码，真不明白JAVA怎么比WINFORM这么难...希望自己选择的是对的把...

 

 //数据库的数据

use master
go
if exists(select * from sysdatabases where name='business')
drop database business
go
create database business
go
use business
go
create table productType
(
 tid int identity(1,1) primary key,
 tname varchar(30) not null,
 tpid int not null,
 remark varchar(50)
)
go

select * from producttype
go

--插入父类型数据
insert into producttype
values('裙子',0,'女人的曲线美')

insert into producttype
values('帽子',0,'装饰你的气质')

--插入各父类型的子类型数据
insert into producttype
values('牛仔裙',1,'野蛮个性')
insert into producttype
values('连衣裙',1,'诱惑指数极高')
insert into producttype
values('超短裙',1,'低头率不胜数计')

insert into producttype
values('鸭舌帽',5,'可爱型')
insert into producttype
values('草帽',5,'简单而不平凡')
insert into producttype
values('爵士帽',5,'成熟男人的选择')

insert into producttype
values('睡裙',1,'老公的最爱')

select * from producttype
go

--hash<parent,childs>
--
--hash<ProductType,ArrayList<ProductType>>

create table productinfo
(
 pid int identity(1,1) primary key,
 pname varchar(30) not null,
 ptype int references productType(tid),
 price money,
 pdesc varchar(100)
)
go

select * from productinfo
go

insert into productinfo
values('真维斯连衣裙',3,128.0,'高贵大方得体')

insert into productinfo
values('李宁运动帽',6,52.0,'运动无极限')

select * from producttype
select * from productinfo
go

--父类型的集合 ArrayList
select * from producttype where tpid=0

--子类型的集合 ArrayList
select * from producttype where tpid<>0

//JAVA代码

package test;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;

import com.xiaogang.dao.Dao;
import com.xiaogang.pojo.POJO;
import com.xiaogang.pojo.ProductType;
import com.xiaogang.type.dao.ProductTypeDao;

public class FixCollection {

 
 public static void main(String[] args) {
  Dao dao = new ProductTypeDao();
  
  List<POJO> parent = dao.query("select * from producttype where tpid=0");
  System.out.println(parent);
  
  List<POJO> childs = dao.query("select * from producttype where tpid<>0");
  System.out.println(childs);
  
  HashMap hm = new HashMap();
  
  Iterator itr = parent.iterator();
  while(itr.hasNext()){
   ProductType ptype = (ProductType)itr.next();
   ArrayList al = new ArrayList();
   
   Iterator ite = childs.iterator();
   while(ite.hasNext()){
    ProductType ctype = (ProductType)ite.next();
    if(ctype.getTypeParentId()==ptype.getTypeId()){
     al.add(ctype);
    }
   }
   hm.put(ptype, al);
  }
  
  
  //HashMap
  Iterator ita = hm.keySet().iterator();
  while(ita.hasNext()){
   ProductType key = (ProductType)ita.next();
   System.out.println(key.getTypeName());
   
   ArrayList al = (ArrayList)hm.get(key);
   Iterator itt = al.iterator();
   while(itt.hasNext()){
    ProductType value = (ProductType)itt.next();
    System.out.println("   "+value.getTypeName());
   }
   
  }

 }

}