最近在学习设计模式，每个模式都是前人经验的传承，是经过总结形成的一套某一类问题的一般性解决方案，说这些其实是有目的的，呵呵不跟大家卖关子了，言归正传，我是为了说接口的重要性的，我认为设计模式非常重要，所以其常用的就更重要了，最近学习设计模式的时候总是遇到接口，抽象类，这个模式是抽象类，那个模式是接口，弄的我迷迷糊糊的，决定认真研究一下，下面就跟大家分享一下我研究的结果吧，希望大家多提意见

什么是接口？

如何使用接口？

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace 用了抽象模式的数据访问程序{    class Program    {        static void Main(string[] args)        {            User user = new User();            Department dept = new Department();            //Ifactory factory =new SqlserverFactory();            IFactory factory = new AccessFactory();                        //此时已经与具体的数据库访问解除了依赖            IUser iu = factory.CreateUser();            iu.Insert(user);            iu.GetUser(1);            IDepartment id = factory.CreateDepartment();            id.Insert(dept);            id.GetDepartment(1);            Console.Read();        }    }    class User    {        private int id;        public int ID        {            get { return id; }            set { id = value; }        }    }    class Department    {        private int id;        public int ID        {            get { return id; }            set { id = value; }        }            }    //IDepartment接口，用于客户端访问，解除与具体数据库访问的耦合。    interface IDepartment    {        void Insert(Department department);        Department GetDepartment(int id);    }    //SqlserverDepartment类，用于访问SQL Server的Department    class SqlserverDepartment : IDepartment    {        public void Insert(Department department)        {            Console.WriteLine("在SQL Server 中给Department表增加一条记录");        }        public Department GetDepartment(int id)        {            Console.WriteLine("在SQL Server 中根据ID得到Department表一条记录");            return null;        }        }    //Access类，用于访问Access的Department    class AccessDepartment : IDepartment    {        public void Insert(Department department)        {            Console.WriteLine("在Access 中给Department表增加一条记录");        }        public Department GetDepartment(int id)        {            Console.WriteLine("在Access中根据ID得到Department表一条记录");            return null;        }    }    //IUser接口,用于客户端访问,解除与具体数据库访问的耦合    interface IUser    {        void Insert(User user);        User GetUser(int id);    }    //SqlserverUser类，用于访问SQL Server的User    class SqlserverUser : IUser   {        public void Insert(User user)        {            Console.WriteLine("在SQL Server 中给User表增加一条记录");        }        public User GetUser(int id)        {            Console.WriteLine("在SQL Server中根据ID得到User表一条记录");            return null;        }    }    //Access类，用于访问Access的User    class AccessUser : IUser    {        public void Insert(User user)        {            Console.WriteLine("在Access中给User表增加一条记录");        }        public User GetUser(int id)        {            Console.WriteLine("在Access中根据得到User表一条记录");            return null;        }    }    //IFactory 接口，定义一个创建访问Department表对象的抽象的工厂接口    interface IFactory    {        IUser CreateUser();        //增加的接口方法        IDepartment CreateDepartment();    }    //SqlServerFactory类，实现IFactory接口，实例化SqlserverUser和SqlserverDepartment    class SqlserverFactory : IFactory    {        public IUser CreateUser()        {            return new SqlserverUser();        }        public IDepartment CreateDepartment()        {            return new SqlserverDepartment();        }    }    //AccessFactory类，实现IFactory接口，实例化AccessUser和AccessDepartment    class AccessFactory : IFactory    {        public IUser CreateUser()        {            return new AccessUser();        }        public IDepartment CreateDepartment()        {            return new AccessDepartment();        }    }}

什么是抽象类？