位于计算机网络体系结构的最上层，前面四层做的所有事情就是为了他服务，他也是设计和建立计算机网络的最终目的，通俗的讲，就是我们开发的应用软件，就处于这一层，

在计算机网络中实现通信必须依靠网络通信协议，目前广泛采用的是国际标准化组织（ISO）1997年提出的开放系统互联（Open System Interconnection，OSI）参考模型，习惯上称为ISO/OSI参考模型。

The Simple Factory、The Factory Method 、The Abstract Factory

HexoCommands clean Remove generated files and cache. config Get or set configurations. deploy Deploy your webs

The Singleton Pattern ensure a class has only one instance, and provides a global point of access to it.

The Adapter Pattern converts the interface of a class into another interface the clients expect. Adapter lets classes work together that couldn't otherwise because of incompatible interfaces.

The State Pattern allows an object to alter its behavior when its internal state changes. The object will appear to change its class.

Git is a free and open source distributed version control system designed to handle everything from small to very large projects with speed and efficiency.

public class Vector extends AbstractList implements List

The Facade Pattern provides a unified interface to a set of interfaces in subsystem. Facade defines a higher-level interface that makes the subsystem easier to use.

The Decorator Pattern attaches additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.

The Template Method Pattern defines the skeleton of an algorithm in a method, deferring some steps to subclasses. Template Method lets subclass redefine certain steps of an algorithm without changing the algorithm's structure.