public void login () {
        PreparedStatement st=null;
        ResultSet result=null;

        Connection conn=ConnexioDB.getConnexion();

        try{
            st=conn.prepareStatement("SELECT * FROM users WHERE USERNAME=? AND PASSWORD=?");
            st.setString(1,textfield.getText());
            if(checkBox.isSelected()) {
                st.setString(2, passwordField.getText());
            }else {
                st.setString(2,passwordField.getText());
            }

            result=st.executeQuery();

            if(result.next()){
                Alert alert=new Alert(Alert.AlertType.CONFIRMATION,"Login successfully",ButtonType.OK);
                alert.show();
            }
            else {
                Alert alert =new Alert(Alert.AlertType.WARNING,"Login errore // Password o username false",ButtonType.PREVIOUS);
                alert.show();
            }
        }catch (Exception e){
            throw new RuntimeException(e);
        }
    }