java中操作mysql数据库(适合菜鸟入门看的)_开始寻找bug

一起无废话，看懂代码就行！

package baidu.com;

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

/**
 * 数据库CURD操作
 * @author Administrator
 *
 */
public class jdbcDemo {
	
	//数据库地址
	public final static String URL  = "jdbc:mysql://localhost:3306/jdbc?Unicode=true&characterEncoding=UTF-8";
	//数据库用户名
	public final static	String USER = "root";
	//数据库密码
	public final static String PWD  = "root";
	
	
	/**
	 * 掺入操作--C
	 */
	public static void insert(){
		try {
			//1、加载数据库驱动
			Class.forName("com.mysql.jdbc.Driver");
			
			//2、链接数据库
			Connection conn = DriverManager.getConnection(URL, USER, PWD);
			
			//3、构造SQL语句
			String sql = "insert into pre_user (username,password,age) VALUE ('王武',88888,40)";
			
			//4、构造Statement实例(发送sql语句的载体)
			Statement stat = conn.createStatement();
			
			//5、执行sql语句
			//除了读取的sql语句，其他sql语句都叫更新executeUpdate
			stat.executeUpdate(sql);
			
			//6、关闭链接/释放资源
			stat.close();
			conn.close();
			
			System.out.print("success!");
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		} catch (SQLException e) {
			e.printStackTrace();
		}
		
	}
	
	
	/**
	 * 更新操作
	 */
	public static void update(){
		
		try {
			//1、加载数据库驱动
			Class.forName("com.mysql.jdbc.Driver");
			
			//2、链接数据库
			Connection conn = DriverManager.getConnection(URL, USER, PWD);
			
			//3、构造SQL语句
			String sql = "update pre_user set age = 88 where id = 4";
			
			//4、构造Statement实例(发送sql语句的载体)
			Statement stat = conn.createStatement();
			
			//5、执行sql语句
			//除了读取的sql语句，其他sql语句都叫更新executeUpdate
			stat.executeUpdate(sql);
			
			//6、关闭链接/释放资源
			stat.close();
			conn.close();
			
			System.out.print("success!");
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		} catch (SQLException e) {
			e.printStackTrace();
		}
		
	}
	
	/**
	 * 删除操作
	 */
	public static void delete(){
		
		try {
			//1、加载数据库驱动
			Class.forName("com.mysql.jdbc.Driver");
			
			//2、链接数据库
			Connection conn = DriverManager.getConnection(URL, USER, PWD);
			
			//3、构造SQL语句
			String sql = "delete from  pre_user  where id = 4";
			
			//4、构造Statement实例(发送sql语句的载体)
			Statement stat = conn.createStatement();
			
			//5、执行sql语句
			//除了读取的sql语句，其他sql语句都叫更新executeUpdate
			stat.executeUpdate(sql);
			
			//6、关闭链接/释放资源
			stat.close();
			conn.close();
			
			System.out.print("success!");
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		} catch (SQLException e) {
			e.printStackTrace();
		}
		
	}
	
	
	/**
	 * 查询操作
	 */
	public static void query(){
		
		try {
			//1、加载数据库驱动
			Class.forName("com.mysql.jdbc.Driver");
			
			//2、链接数据库
			Connection conn = DriverManager.getConnection(URL, USER, PWD);
			
			//3、构造SQL语句
			String sql = "select id,username,age from pre_user";
			
			//4、构造Statement实例(发送sql语句的载体)
			Statement stat = conn.createStatement();
			
			//5、执行sql语句
			ResultSet rs = stat.executeQuery(sql);
			
			while (rs.next()) {
				int id = rs.getInt("id");
				String name = rs.getString("username");
				int age = rs.getInt("age");
				System.out.println("id = "+id+",username = "+name+",age ="+age);
			}
			//6、关闭链接/释放资源
			rs.close();
			stat.close();
			conn.close();
			
			System.out.print("success!");
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		} catch (SQLException e) {
			e.printStackTrace();
		}
		
	}
	
	/**
	 * 程序入口
	 * @param args
	 */
	public static void main(String[] args) {
		//insert();
		//update();
		//delete();
		query();
	}

}
package baidu.com;

import j