Iterator中的next()

DBExchangeMoney类：
  1 package com.ch.test15;

 import java.sql.DriverManager;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;
 import java.sql.Timestamp;
 import java.util.ArrayList;
 import java.util.Date;
 import java.util.Iterator;

 import com.ch.test02.Person;

 /**
  * 交换A,B,C的金额
  * @author Administrator
  *
  */
 public class DBExchangeMoney {
     public static void main(String[] args) throws ClassNotFoundException, SQLException {
         //定义数据库驱动器
         String DRIVER = "com.mysql.jdbc.Driver";
         //加载数据库驱动器
         Class.forName(DRIVER);
         //定义数据库的链接
         String URL = "jdbc:mysql://192.168.1.20:3306/cuihao?useUnicode=true&characterEncoding=UTF-8";
         String Users = "root";
         String Passw = "root";
         java.sql.Connection con = null;
         try {
             con = DriverManager.getConnection(URL, Users, Passw);
             con.setAutoCommit(false);
         } catch (SQLException e) {
             e.printStackTrace();
         }
         //PreparedStatement prepStmt = null;
         Statement st = null;
         ResultSet rs = null;
         int tem = 0;
         ArrayList<MoneyDefine> list = new ArrayList<MoneyDefine>();
         try {
             //执行sql查询
             String selectStatement = "select * from Moneys";
             st = con.createStatement();
             rs = st.executeQuery(selectStatement);
             while (rs.next()) {
                 String id = rs.getString("id");
                 String name = rs.getString("pname");
                 int moneys = rs.getInt("prices");
                 String dates = rs.getString("dates");
                 MoneyDefine md = new MoneyDefine(id,name,moneys,dates);
                 list.add(md);
             }
             for(Iterator<MoneyDefine> iterator = list.iterator();iterator.hasNext();){
                 //错误的，next()在list内，跳到下一条的下一个位置
                 //System.out.println(iterator.next().getId() +iterator.next().getName() 
                    //                   +iterator.next().getMoneys() +iterator.next().getDates());
                 //用对象p接收
                 MoneyDefine p = iterator.next();
                 System.out.println("ID:" +p.getId() +" 姓名：" +p.getName()
                         +" 金额：" +p.getMoneys() +" 时间：" +p.getDates());
 //                System.out.println(p.getMoneys());
 //                System.out.println(p.getDates());
             }

             System.out.println("--------------------------");
             //two给one 1000; one给two 1000;
             //更新
             String exchangeMoney = "UPDATE Moneys SET prices=prices+1000 WHERE id=1";
             String exchangeMoney1 = "UPDATE Moneys SET prices=prices-1000 WHERE id=2";
             st = con.createStatement();
             tem = st.executeUpdate(exchangeMoney);
             tem = st.executeUpdate(exchangeMoney1);
             System.out.println("执行后:" +tem);
             //查询更新后的内容
             String selectStatement1 = "select * from Moneys";
             st = (Statement) con.createStatement();
             rs = st.executeQuery(selectStatement1);
             while (rs.next()) {
                 String id = rs.getString("id");
                 String name = rs.getString("pname");
                 String moneys = rs.getString("prices");
                 Date dates = rs.getTimestamp("dates");
                 System.out.print("ID:" +id);
                 System.out.print(" 姓名:" +name);
                 System.out.print(" 金额:" +moneys);
                 System.out.print(" 时间：" +dates);
                 System.out.println();
             }
             System.out.println("--------------------");
         } catch (SQLException e) {
             con.rollback();
             e.printStackTrace();
         }
         //关闭
         con.commit();
         rs.close();
         st.close();
         con.close();
     }
 }

MoneyDefine类：
 1 package com.ch.test15;

 import java.sql.Timestamp;
 import java.util.Date;

 public class MoneyDefine {

     public String id;
     public String name;
     public int moneys;
     public String dates;

     public MoneyDefine(String id, String name, int moneys, String dates){
         this.id = id;
         this.name = name;
         this.moneys = moneys;
         this.dates = dates;
     }
     public String getId() {
         return id;
     }
     public void setId(String id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public float getMoneys() {
         return moneys;
     }
     public void setMoneys(int moneys) {
         this.moneys = moneys;
     }
     public String getDates() {
         return dates;
     }
     public void setDates(String dates) {
         this.dates = dates;
     }

 }

DBExchangeMoney类中，将从数据库取出的元素放入ArrayList中，然后再从list里取出。
这时遇到问题，当用迭代取元素时

System.out.println(iterator.next().getId() +iterator.next().getName() +iterator.next().getMoneys() +iterator.next().getDates());

执行出行错误。

修改为：

 MoneyDefine p = iterator.next();
 System.out.println("ID:" +p.getId() +" 姓名：" +p.getName()+" 金额：" +p.getMoneys() +" 时间：" +p.getDates());

正确输出。

如果每次都调用iterator.next()，则第一次调用iterate.next()，指向List的第一行的getId()，即id=1，第二次调用iterate.next()，就会指向第二行的getName()，即name=two。第三次调用，就会报出异常。所以无法正常输出！

id	name	prices	dates
1	one	0	2015-04-15 11:10:34
2	two	1000	2015-04-15 11:10:40

当iterator.next()应该赋值给一个对象p，然后调用对象p来取值，这样p每次会从每行的首个元素开始迭代。

JDK API 1.6，关于Iterator中next()的说明：

next()

返回迭代的下一个元素。

返回：

迭代的下一个元素。

抛出：

NoSuchElementException - 没有元素可以迭代。