Undefined is_user_logged_in() error with Plugin Query code

require_once( wp_normalize_path(ABSPATH).'wp-load.php');

class Your_Plugin_Class {
    private  $is_user_logged_in;

    add_action('init', function(){
        $this-> is_user_logged_in = is_user_logged_in();
        echo 'is_user_logged_in'.$this->is_user_logged_in;
    });

    add_filter('woocommerce_billing_fields-2',array( $this, 'add_billing_field' ));

   }

    public function add_billing_field( $fields = array() ) {
        if ( $this->is_user_logged_in  ){
            echo 'add_billing_field'.$this->is_user_logged_in;
            return $fields;
        }else{
            echo 'add_billing_field'.$this->is_user_logged_in;
        }
    }
}