Question

我正在编写一个用户必须登录的程序。我已经一次又一次地查看了我的代码，但我一直得到“null”作为错误。这不仅适用于部分程序的登录，也适用于用户可以创建帐户的部分。基本上，无论我在哪里实现JDBC，都会弹出“null”错误。我该如何解决这个问题？

String user_name_check = user_name.getText().trim();
char[] pass = password_enter.getPassword();
String password_check = Arrays.toString(pass);
String query = "SELECT * FROM USER_INFO WHERE USERNAME = '" + user_name_check + "';";
try{
    rs = st.executeQuery(query);
    if(rs.next()){
        //changing the panel (start)
        if(password_check.equals(rs.getString("PASS"))){
            MAIN.removeAll();
            MAIN.add(news_feed);
            MAIN.repaint();
            MAIN.revalidate();
            //changing the panel (end)
            //giving values to class level field variables (start)
            username = user_name_check;
            firstname = rs.getString("FIRST_NAME");
            lastname = rs.getString("LAST_NAME");
            dob = rs.getString("DOB");
            gender = rs.getString("GENDER");
            bio = rs.getString("BIO");
            home_user_name.setText(username);
            set_dp(home_user_dp, username);
        }
    }
    else sign_in_message.setVisible(true);
}

catch(Exception e){
    System.out.println(e.getMessage() + " @jButton2ActionPerformed SIGN IN");
}

错误：null @ jButton2ActionPerformed SIGN IN

修改

这是JDBC连接方法：

     public void JDBC_Connect(){
    try{
        Class.forName("com.mysql.jdbc.Driver");
        con = DriverManager.getConnection("jdbc:mysql://localhost/socialnetwork", "root", "mukundrox");
        st = con.createStatement();
    }
    catch(Exception e){
        System.out.println(e.getMessage() + " @JDBC_connect");
    }
}

我一直在JDBC中得到null错误。我如何解决它？

0 个答案: