Sealed seal type

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
#region Overview
//Using sealed in a class declaration prevents other classes from inheriting this class; using it in a method declaration The sealed modifier prevents extending classes from overriding this method.
//The sealed modifier is mainly used to prevent unintentional derivation, but it can also promote certain runtime optimizations. Specifically, since a sealed class will never have any derived classes, calls to virtual function members of instances of the sealed class can be converted to non-virtual calls for processing.

//密封类：//密封类在声明中使用sealed 修饰符，这样就可以防止该类被其它类继承。如果试图将一个密封类作为其它类的基类，C#将提示出错。理所当然，密封类不能同时又是抽象类，因为抽象总是希望被继承的。//在哪些场合下使用密封类呢？实际上，密封类中不可能有派生类。如果密封类实例中存在虚成员函数，该成员函数可以转化为非虚的，函数修饰符virtual 不再生效。#endregionnamespace Sealed密封类
{    class NOSealed
    {        public static void OO()
        {
            Console.WriteLine("没有使用密封");
        }
    }

    sealed class YESSealed
    {        public static void OO()
        {
            Console.WriteLine("使用了密封");
        }
    }    class MyClass : NOSealed //YESSealed 那就错了
    {        public new void OO()
        {
            Console.WriteLine("没有继承密封");
        }
    }    //密封类不可以被继承，可以被调用
    sealed class mysealed   //声明为密封类  
    {        public int x;        public int y;
    }    class Program
    {        static void Main(string[] args)
        {
            NOSealed.OO();
            MyClass M = new MyClass();
            M.OO();            //调用密封类
            YESSealed.OO();
            mysealed m = new mysealed();
            m.x = 100;
            m.y = 200;
            Console.WriteLine("x={0}, y = {1}", m.x, m.y);
            Console.ReadLine();

            Console.ReadKey();
        }
    }
}