[工厂类](%E8%AE%BE%E8%AE%A1%E6%A8%A1%E5%BC%8F/%E5%8E%9F%E5%AF%B9%E8%B1%A1%E5%AE%9E%E7%8E%B0%E5%B7%A5%E5%8E%82%E7%B1%BB.md) [单例模式](%E8%AE%BE%E8%AE%A1%E6%A8%A1%E5%BC%8F/%E5%8D%95%E4%BE%8B%E6%A8%A1%E5%BC%8F.md)