Statement stmt problems netbeans

I'am working on this source code :

public class AuthentificationClient extends javax.swing.JFrame {

  connexion maconn; 
  Statement stmt1;  

    public AuthentificationClient() {
        initComponents();
    }

    private void numcompteActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
    }                                         

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        Bienvenue ret = new  Bienvenue  () ;
        ret.setVisible(true);
        this.dispose();
    }                                        

    private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        String requete ="Select * from Compte where numcompte='"+numcompte.getText()+"' and codec = '"+Arrays.toString(code.getPassword())+"'";
        try {
            Statement stmt1 = maconn.Obtenirconnexion().createStatement();
            ResultSet rs= stmt1.executeQuery(requete);
        } catch (SQLException ex) {
            Logger.getLogger(AuthentificationPharmacien.class.getName()).log(Level.SEVERE, null, ex);
        }
        OpClient oc = new  OpClient  () ;
        oc.setVisible(true);
        this.dispose();
    }                                        

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new AuthentificationClient().setVisible(true);
            }
        });
    }

There is no error but when I execute, it doesn't work correctly! This is the error message that I receive :

The variable maconn is never assigned, at least in the code you have provided, so you may be calling a method on a null object.

1. Use PreparedStatement instead of Statement to avoid SQL Injection attack as well to simplify your code e.g. you won't need to enclose string literals within ' ' when you use PreparedStatement.

2. Perform null check on an object (e.g. maconn) before accessing any member (method/variable) using it.

   Do it as follows:

   String requete ="Select * from Compte where numcompte = ? and codec = ?";
   PreparedStatement pstmt;
   ResultSet rs;
   try {
       if(maconn!=null && maconn.Obtenirconnexion()!=null) {
           pstmt = maconn.Obtenirconnexion().prepareStatement(requete);
           pstmt.setString(1, numcompte.getText());
           pstmt.setString(2, Arrays.toString(code.getPassword()));
           rs = pstmt.executeQuery(requete);
           //...
       }
   }