'MySQL error Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException

This is my register page:

enter image description here

Registration was working before adding Email checker functionality. This function for check did someone used this email on database.

This is my code:

try {
    Class.forName("com.mysql.jdbc.Driver");
    sqlConn = DriverManager.getConnection(connect, username, password);
    if (check_email(u.getEmail())) {
        Class.forName("com.mysql.jdbc.Driver");
        sqlConn = DriverManager.getConnection(connect, username, password);
        String query = "insert into users_table (Name_surname,E_mail,Age,Profession,Student,Password)"
                            + " values (?,?,?,?,?,?)";
        pst = sqlConn.prepareStatement(query);

        pst.setString(1, u.getName_surname());
        pst.setString(2, u.getEmail());
        pst.setInt(3, u.getAge());
        pst.setString(4, u.getProffesion());
        pst.setString(5, u.getStudent());
        pst.setString(6, u.getPassword());
        pst.executeUpdate();
        JOptionPane.showMessageDialog(null, "You signed up");

    } else {
        JOptionPane.showMessageDialog(null, "You have already account");
    }
} catch (ClassNotFoundException | SQLException ex) {
    Logger.getLogger(Register.class.getName()).log(Level.SEVERE, null, ex);
}


public boolean check_email(String username) throws SQLException, ClassNotFoundException {
    Class.forName("com.mysql.jdbc.Driver");
    sqlConn = DriverManager.getConnection(connect, username, password);
    boolean e_mail = true;
    String query = "Select * from users.users_table where E_mail = ?";
    try {
        pst = sqlConn.prepareStatement(query);
        pst.setString(1, j_register_mail.getText());
        rs = pst.executeQuery();
        if (rs.next()) {
            e_mail = false;
        }
    } catch (SQLException ex) {
        Logger.getLogger(Register.class.getName()).log(Level.SEVERE, null, ex);
    }
    return e_mail;

This is my database:

enter image description here

enter image description here

I got this error:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at JFrame.Proje.Register.check_email(Register.java:462)
at JFrame.Proje.Register.register_btActionPerformed(Register.java:430)
at JFrame.Proje.Register.access$400(Register.java:30)
at JFrame.Proje.Register$5.actionPerformed(Register.java:334)
javamysqlswing


Solution 1:[1]

Within the method check_email you are connecting to the database using username and password.

But you do have a local variable/parameter with the same name username which prevents getConnection from seeing/using the correct global username.

And why create a new DB-connection within the check_email-method instead of passing the connection as a parameter to the method or using a class-variable for the connection?

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 Matthias Radde

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