public function getSubClasses($class)
    {
        $class = $this->normalize($class);
        if ($this->classExists($class)) {
            return $this->getSubclassOfClass($class);
        } elseif ($this->interfaceExists($class)) {
            return $this->getSubclassOfInterface($class);
        } else {
            throw new ClassNotExistException($class);
        }
    }