问题描述

帮帮忙，看看应该改哪里，谢谢

package javaJDBC;

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

/*

• //采用PreparedStatement添加数据
  */
  public class InsertTest02 {

  public static void main(String[] args) {
  Connection conn = null;
  PreparedStatement pstmt = null;
  try{
  //加载数据库驱动
  Class.forName("com.mysql.jdbc.Driver");
  //连接数据库
  String dbUrl = "jdbc:mysql://localhost:3306/student";
  String username = "root";
  String password = "mysql";
  //执行PreparedStatement语句，执行SQL
  String name = "莫燕";
  String number = "123456";
  String class1 = "1102";
  int score = 97;
  String sql = "insert into stu(name, number, class1, scoree) values (?, ?, ?, ?)";
  pstmt = conn.prepareStatement(sql);
  pstmt.setString(1, name);
  pstmt.setString(2, number);
  pstmt.setString(3, class1);
  pstmt.setInt(4, score);
  pstmt.executeUpdate();
  System.out.println("添加员工成功");
  }catch(ClassNotFoundException e){
  e.printStackTrace();
  }catch(SQLException e){
  e.printStackTrace();
  }finally{
  try{
  //关闭原则：从里到外
  if(pstmt != null)
  pstmt.close();
  if(conn != null)
  conn.close();
  }catch(SQLException e){
  e.printStackTrace();
  }

  }
  

  }

}
Exception in thread "main" java.lang.NullPointerException
at javaJDBC.InsertTest02.main(InsertTest02.java:29)

解决方案

 public static void main(String[] args) {
         Connection conn = null;
         PreparedStatement pstmt = null;
         try{
         //加载数据库驱动
        Class.forName("com.mysql.jdbc.Driver");
         //连接数据库
        String dbUrl = "jdbc:mysql://localhost:3306/student";
         String username = "root";
         String password = "mysql";
         //执行PreparedStatement语句，执行SQL
         String name = "莫燕";
        String number = "123456";
         String class1 = "1102";
         int score = 97;
         String sql = "insert into stu(name, number, class1, scoree) values (?, ?, ?, ?)";
         conn= DriverManager.getConnection(dbUrl, username, password);   ------少了这一句
         pstmt =conn.prepareStatement(sql);
         pstmt.setString(1, name);
         pstmt.setString(2, number);
         pstmt.setString(3, class1);
         pstmt.setInt(4, score);
         pstmt.executeUpdate();
         System.out.println("添加员工成功");
         }catch(ClassNotFoundException e){
         e.printStackTrace();
         }catch(SQLException e){
         e.printStackTrace();
         }finally{
         try{
         //关闭原则：从里到外
        if(pstmt != null)
         pstmt.close();
         if(conn != null)
         conn.close();
         }catch(SQLException e){
         e.printStackTrace();
         }
        }

        }

解决方案二：

String sql = "insert into stu(name, number, class1, scoree) values (?, ?, ?, ?)";

是不是错了