1、方法重寫  
  class Parent
    {
        public void m1()
        {
            m2();
        }
        public virtual void m2()
        {
            Console.WriteLine("I am Parent.");
        }
    }
    class Child : Parent
    {        
        public override void m2()
        {
            Console.WriteLine("I am Child.");
        }

    }
    class Program
    {
        static void Main(string[] args)
        {
            Parent parent = new Parent();
            parent.m1();        //I am parent
            parent.m2();        //I am parent

            Child child = new Child();
            child.m1();         //I am Child
            child.m2();         //I am child

            Parent parent2 = new Child();
            parent2.m1();       //I am Child
            parent2.m2();       //I am Child
        }
    }

 1     class Parent
 2     {
 3         public void m1()
 4         {
 5             m2();
 6         }
 7         public void m2()
 8         {
 9             Console.WriteLine("I'm parent");
10         }
11     }
12     class Child : Parent
13     {
14         public new void m2()
15         {
16             Console.WriteLine("I'm child");
17         }
18     }
19     
20    
21     class Program
22     {
23         
24         static void Main(string[] args)
25         {
26             Parent parent = new Parent();
27             parent.m1();    //I'm parent
28             parent.m2();    //I'm parent
29 
30             Child child = new Child();
31             child.m1();     //I'm parent
32             child.m2();     //I'm child
33 
34             Parent child2 = new Child();
35             child2.m1();    //I'm parent
36             child2.m2();    //I'm parent
37 
38         }   
39     }