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Differences between simple factories and factory methods: Simple factories and factory method patterns look very similar, especially specific factories in simple factories and factory methods. Simple factory, all things have been done in one place. However, the factory method creates a framework for subclasses to decide how to implement it. For example, in the factory method, the OrderPizza method creates a general framework to create pizza. The OrderPizza method relies on the factory method to create specific classes and make actual pizza. It is possible to decide what the actual products manufactured are by inheriting the factory. Simple factories do not have this flexibility.迪士尼频道宣布《长发公主：剧集版》第三季已获续订。　　《天空之城》以美丽的西双版纳的热带雨林为背景，讲述了发生在澜沧江边的美丽爱情故事。《芝加哥烈焰》：第八季首播将“摧毁”消防局。想象一下:一个仓库地下室被大火吞噬，消防员们盯着生锈的旧工业锅炉，几秒钟后就会爆炸。《芝加哥火焰》第八季将会在9月25日回归NBC电视台。不是每个人都会却毫发无伤地走开。该剧制片人德里克·哈斯表示:“这次的情况会有所不同。”“这不只是有人受伤。有一些真正的后果会在一段时间内摧毁消防队。”一个青衣小帽的随从模样的男子慌慌张张地掀开门帘出来，背后有一个清脆女音喊道：别跑。葫芦去投军了，你们也该出去闯荡。SYN attack is a kind of DOS attack. It takes advantage of TCP protocol defects and consumes CPU and memory resources by sending a large number of semi-connection requests. SYN attacks can not only affect hosts, but also harm network systems such as routers and firewalls. In fact, SYN attacks can be implemented as long as these systems turn on TCP services no matter what systems are targeted. As can be seen from the above figure, the server receives the connection request (syn=j), adds this information to the unconnected queue, and sends the request packet to the client (syn=k, ack=j+1), then enters the SYN_RECV state. When the server does not receive an acknowledgement packet from the client, it retransmits the request packet and does not delete this entry from the non-connection queue until the timeout. With IP spoofing, SYN attacks can achieve good results, Typically, clients forge a large number of non-existent IP addresses in a short period of time, SYN packets are continuously sent to the server, and the server replies to the confirmation packets and waits for the confirmation of the customer. Since the source address does not exist, the server needs to continuously resend until it timeout. These forged SYN packets will occupy the unconnected queue for a long time, normal SYN requests will be discarded, the target system will run slowly, and in serious cases, the network will be blocked or even the system will be paralyzed.