专门定义一个类来负责创建其他类的实例，被创建的实例通常都具有共同的父类。简单工厂模式又称为静态工厂方法模式，属于类的创建型模式，通常它根据自变量的不同返回不同的类的实例。

namespace EFT
{
    //抽象电子付款类
    abstract class EFT
    {
        public abstract void process();
    }
    //具体子类，虚拟检查
    class VirtualCheck:EFT
    {
        public override void process()
        {
            Console.WriteLine("虚拟支票处理中");
        }
    }
    //具体子类，万事达卡
    class MasterCard:EFT
    {
        public override void process()
        {
            Console.WriteLine("万事达卡处理中");
        }
    }
    //简单工厂类
    class EFTFactory
    {
        public EFT createEFT(string type)
        {
            switch (type.ToLower())
            {
                case "virtualcheck":
                    return new VirtualCheck();
                case "mastercard":
                    return new MasterCard();
                default:
                    return null;
            }
        }
    }

    //客户应用测试
    class Client
    {
        [STAThread]
        static void Main(string[] args)
        {
            EFT eft;
            EFTFactory eftFactory = new EFTFactory();
            eft = eftFactory.createEFT("VirtualCheck");
            eft.process();
            eft = eftFactory.createEFT("mastercard");
            eft.process();
            Console.ReadLine();
        }
    }
}

 示例：学校登录系统
using System;

namespace SchoolSystem
{
    //Base Class 基类
    public class SchoolUser
    {
        public string FName;
        public string LName;
        public string UserType;
        public void Show()
        {
            Console.WriteLine("First Name: " + FName + "\n");
            Console.WriteLine("Last Name: " + LName + "\n");
            Console.WriteLine("User Type: " + UserType + "\n");
        }
    }
    //Derived Classes 派生类，校负责人
    public class SchoolPrincipal : SchoolUser
    {
        public SchoolPrincipal()
        {
            FName = "David";
            LName = "Smith";
            UserType = "Principal";
        }
    }
    //派生类，校教师
    public class SchoolTeacher : SchoolUser
    {
        public SchoolTeacher()
        {
            FName = "Patrecia";
            LName = "Terry";
            UserType = "Teacher";
        }
    }
    //简单工厂类
    public class SimpleFactory
    {
        public SchoolUser GetSchoolUser(string user, string password)
        {
            if (user == "Principal" && password == "Principal")
                return new SchoolPrincipal();
            if (user == "Teacher" && password == "Teacher")
                return new SchoolTeacher();
            return null;
        }
    }

    //客户应用
    class Client
    {
        [STAThread]
        static void Main(string[] args)
        {
            SimpleFactory sf = new SimpleFactory();
            SchoolUser su;
            su = sf.GetSchoolUser("Principal","Principal");
            Console.WriteLine("-------------------校长登录--------------------\n");
            su.Show();
            Console.WriteLine("-------------------教师登录--------------------\n");
            su = sf.GetSchoolUser("Teacher","Teacher");
            su.Show();
            Console.ReadLine();
        }
    }

}