静态成员

  class Program
    {
        static void Main(string[] args)
        {
           
            Pet[] pets = new Pet[] { new Dog("DD"), new Cat("CC") };//new Dog的时候执行了一次++Num
          
         
            Dog D = new Dog("DD1");//此对象的创建通过其类的构造函数执行了一次++Num
            Dog.ShowNum();//调用静态方法
            D.Lost();//
            Dog.ShowNum();
            Dog d0 = (Dog)pets[0];
            d0.Lost();
            Dog.ShowNum();

        }

    }
    abstract public class Pet//当包含抽象方法时，必须用abstract声明
    {
        protected string Name;//protected 保护级别，派生类可访问
        public Pet(string name)//基类的构造函数
        {
            Name = name;
        }
        public void PrintName()
        {
            Console.WriteLine("Print" + Name);
        }

      
        abstract public void Speak();
    }
    public class Dog : Pet
    {
        static int Num;
        static Dog()// 静态构造函数// 静态字段初始化
        {
            Num = 0;
        }
        public Dog(string name) : base(name)//构造函数//用关键字base调用了基类的构造函数
        {
            ++Num;
        }
        new public void PrintName()
        {
            Console.WriteLine("子打印" + base.Name);
        }
       
        sealed override public void Speak()
        {
            Console.WriteLine("子说" + Name);
        }
        static public void ShowNum()
        {
            Console.WriteLine("Dog‘s number = "+ Num);
        }
         public void Lost()
        {
            --Num;
            Console.WriteLine( Name+" is Lost!");
        }
    }