iterator方法和for方法 遍历数据库user表结果集ResultSet

package com.swift.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class DBUtil {
    
    public static Connection getConn() {
        Connection conn=null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        try {
            String url="jdbc:mysql://localhost:3306/sw_database";
            String user="root";
            String password="root";
            conn=DriverManager.getConnection(url, user, password);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return conn;
    }
    
    public static void closeAll(Connection conn,PreparedStatement ps,ResultSet rs) {
        
        if(conn!=null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if(ps!=null) {
            try {
                ps.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if(rs!=null) {
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

package com.swift.jdbc;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Iterator;
import java.util.LinkedList;

public class QueryAllInUser {
    
    public static void main(String[] args) {
        Connection conn=DBUtil.getConn();
        PreparedStatement ps=null;
        ResultSet rs=null;
        LinkedList<User> list = new LinkedList<User>();
        try {
            ps=conn.prepareStatement("select * from sw_user");
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        try {
            rs=ps.executeQuery();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        try {
            while(rs.next()) {
                int id=rs.getInt("id");
                String username=rs.getString("username");
                String password=rs.getString("password");
                User user=new User(id,username,password);
                list.add(user);
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        //方法一，使用for循环
        for(int i=0;i<list.size();i++) {
            System.out.println(list.get(i));
        }
        System.out.println();
        //方法二，使用增强的for，相当于foreach
        for(User user:list) {
            System.out.println(user.toString());
        }
        System.out.println();
        //方法三，使用while+iterator
        Iterator<User> it=list.iterator();
        while(it.hasNext()) {
            System.out.println(it.next());
        }
        System.out.println();
        //方法四，使用for+iterator
        for(Iterator<User> it1=list.iterator();it1.hasNext();) {
            System.out.println(it1.next());
        }
        
        
    }
}