Java连接MySQL数据库。编写一个应用程序，在主类Test_4类中，通过JDBC访问stu数据库，显示t_student表中的内容（表结构见表1），显示效果自己设计。

import java.sql.*;
import java.util.Scanner;
public class Test_4 {
    public static void main(String[] args) {
        // 1.加载JDBC驱动程序
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        // 2.创建数据库的链接
        try {
            System.out.println("连接数据库...");
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/stu", "root", "dai324542");
            // 3.执行SQL语句
            Statement sql = con.createStatement();// Statement接口
            ResultSet re = sql.executeQuery("select * from t_student");// executeQuery查询----ResultSet结果集
            // 4.接收并处理结果集
            System.out.println("    查询中.....");
            while (re.next()) {
                int id = re.getInt("id");
                String name = re.getString("name");
                String classes = re.getString("classes");
                // 输出数据
                System.out.println("学号: " + id);
                System.out.println("姓名: " + name);
                System.out.println("班级: " + classes);
                System.out.print("\n");
            }
            Scanner reader = new Scanner(System.in);
            System.out.println("please input id: ");
            int Id = reader.nextInt();
            ResultSet rs = sql.executeQuery("select * from t_student where id='" + Id + "'");
            if (rs.next()) {
                System.out.println("please input new name: ");
                String newname = reader.next();
                int n = sql.executeUpdate("update t_student set name='" + newname + "'where id='" + Id + "'");
                if (n > 0) {
                    System.out.println("success!");
                } else {
                    System.out.println("修改失败!");
                }
            } else {
                System.out.println("未查询到此id!");
            }
            // 5.断开连接，关闭数据库
            re.close();
            con.close();
        } catch (
        SQLException e) {
            e.printStackTrace();
        }
    }
}