private function validate()
    {
        if (!class_exists($this->class)) {
            throw new \RuntimeException(sprintf('Class %s does not exist, is this the correct namespace?', $this->class));
        }
        if (!in_array($this->method, get_class_methods($this->class))) {
            throw new \RuntimeException(sprintf('The method "%s" does not exist in "%s" class.', $this->method, $this->class));
        }
    }