Explication détaillée de la façon dont Java implémente les opérations de base sur MySQL

package com.cn.edu;
import java.beans.Statement;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
public class helloworld {
  private Connection conn = null;
  PreparedStatement statement = null;
  // connect to MySQL
  void connSQL() {
    String url = "jdbc:mysql://localhost:3306/hello?characterEncoding=UTF-8";
    String username = "root";
    String password = "root"; // 加载驱动程序以连接数据库
    try {
      Class.forName("com.mysql.jdbc.Driver" );
      conn = DriverManager.getConnection( url,username, password );
      }
    //捕获加载驱动程序异常
     catch ( ClassNotFoundException cnfex ) {
       System.err.println(
       "装载 JDBC/ODBC 驱动程序失败。" );
       cnfex.printStackTrace();
     }
     //捕获连接数据库异常
     catch ( SQLException sqlex ) {
       System.err.println( "无法连接数据库" );
       sqlex.printStackTrace();
     }
  }
  // disconnect to MySQL
  void deconnSQL() {
    try {
      if (conn != null)
        conn.close();
    } catch (Exception e) {
      System.out.println("关闭数据库问题 ：");
      e.printStackTrace();
    }
  }
  // execute selection language
  ResultSet selectSQL(String sql) {
    ResultSet rs = null;
    try {
      statement = conn.prepareStatement(sql);
      rs = statement.executeQuery(sql);
    } catch (SQLException e) {
      e.printStackTrace();
    }
    return rs;
  }
  // execute insertion language
  boolean insertSQL(String sql) {
    try {
      statement = conn.prepareStatement(sql);
      statement.executeUpdate();
      return true;
    } catch (SQLException e) {
      System.out.println("插入数据库时出错：");
      e.printStackTrace();
    } catch (Exception e) {
      System.out.println("插入时出错：");
      e.printStackTrace();
    }
    return false;
  }
  //execute delete language
  boolean deleteSQL(String sql) {
    try {
      statement = conn.prepareStatement(sql);
      statement.executeUpdate();
      return true;
    } catch (SQLException e) {
      System.out.println("插入数据库时出错：");
      e.printStackTrace();
    } catch (Exception e) {
      System.out.println("插入时出错：");
      e.printStackTrace();
    }
    return false;
  }
  //execute update language
  boolean updateSQL(String sql) {
    try {
      statement = conn.prepareStatement(sql);
      statement.executeUpdate();
      return true;
    } catch (SQLException e) {
      System.out.println("插入数据库时出错：");
      e.printStackTrace();
    } catch (Exception e) {
      System.out.println("插入时出错：");
      e.printStackTrace();
    }
    return false;
  }
  // show data in ju_users
  void layoutStyle2(ResultSet rs) {
    System.out.println("-----------------");
    System.out.println("执行结果如下所示:");
    System.out.println("-----------------");
    System.out.println(" 用户ID" + "/t/t" + "淘宝ID" + "/t/t" + "用户名"+ "/t/t" + "密码");
    System.out.println("-----------------");
    try {
      while (rs.next()) {
        System.out.println(rs.getInt("ju_userID") + "/t/t"
            + rs.getString("taobaoID") + "/t/t"
            + rs.getString("ju_userName")
             + "/t/t"+ rs.getString("ju_userPWD"));
      }
    } catch (SQLException e) {
      System.out.println("显示时数据库出错。");
      e.printStackTrace();
    } catch (Exception e) {
      System.out.println("显示出错。");
      e.printStackTrace();
    }
  }
  public static void main(String args[]) {
    helloworld h = new helloworld();
    h.connSQL();
    String s = "select * from ju_users";
    String insert = "insert into ju_users(ju_userID,TaobaoID,ju_userName,ju_userPWD) values("+8329+","+34243+",'mm','789')";
    String update = "update ju_users set ju_userPWD =123 where ju_userName= 'mm'";
    String delete = "delete from ju_users where ju_userName= 'mm'";
    if (h.insertSQL(insert) == true) {
      System.out.println("insert successfully");
      ResultSet resultSet = h.selectSQL(s);
      h.layoutStyle2(resultSet);
    }
    if (h.updateSQL(update) == true) {
      System.out.println("update successfully");
      ResultSet resultSet = h.selectSQL(s);
      h.layoutStyle2(resultSet);
    }
    if (h.insertSQL(delete) == true) {
      System.out.println("delete successfully");
      ResultSet resultSet = h.selectSQL(s);
      h.layoutStyle2(resultSet);
    }
    h.deconnSQL();
  }
}