接口IBaseA 、 IBaseB 和 IMyClass：

 interface IBaseA
    {
        void PrintBaseA();
    }

interface IBaseB
    {
        void PrintBaseB();
    }

 interface IMyClass
    {
        void PrintMyClass();
    }

实现IBaseA 、 IBaseB 和 IMyClass接口，继承类：

class BaseA : IBaseA 
    {
        public void PrintBaseA()
        {
            Console.WriteLine("This is PrintBaseA!");
        }
    }

 class BaseB : BaseA, IBaseB
    {
        public void PrintBaseB()
        {
            Console.WriteLine("This is PrintBaseB!");
        }
    }

 class MyClass : BaseB, IMyClass
    {
       public void PrintMyClass()
        {
            Console.WriteLine("This is PrintMyClass!");
        }
    }

Main

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace InterfaceIsAs
{
    //========================================================================
    //  クラス名 ： Program
    /// <summary>
    ///　Program
    /// </summary>
    /// <remarks>
    ///　查看带几个继承的类，使用强制转化的方式，
    ///　以及使用as转换, 并且练习is的类型判断
    /// </remarks>
    //========================================================================
    class InterfaceIsAs
    {
        //========================================================================
        //  メソッド名 ： Main
        /// <summary>
        ///　Main
        /// </summary>
        /// <remarks>
        ///　强制转化，查看其继承方式
        /// </remarks>
        //========================================================================
        static void Main(string[] args)
        {
            BaseA a1 = new BaseA();
            a1.PrintBaseA();

            BaseA a2 = new BaseB();
            a2.PrintBaseA();

            BaseA a3 = new MyClass();
            a3.PrintBaseA();

            BaseB b1 = new BaseB();
            b1.PrintBaseA();
            b1.PrintBaseB();

            BaseB b2 = new MyClass();
            b2.PrintBaseA();
            b2.PrintBaseB();

            MyClass mc1 = new MyClass();
            mc1.PrintBaseA();
            mc1.PrintBaseB();
            mc1.PrintMyClass();

            //TestBaseA
            TestBaseA(a1);
            TestBaseA(a2);
            TestBaseA(a3);
            Console.WriteLine();

            //TestBaseB
            TestBaseB(b1);
            TestBaseB(b2);
            Console.WriteLine();

            //TestMyClass
            TestMyClass(mc1);
            Console.WriteLine();

            Console.ReadKey();
        }

        //========================================================================
        //  メソッド名 ： TestBaseA
        /// <summary>
        ///　TestBaseA
        /// </summary>
        /// <param name="a">辅助变量</param>
        //========================================================================
        private static void TestBaseA(BaseA a)
        {
            /*
             * is: 检查对象是否与给定类型兼容，返回类型为bool(True or False)
             * 
             * as: 用于在兼容的引用类型之间之行转换。
             */
            if (a is IBaseA) 
            {
                IBaseA baseA = a as IBaseA;
                Console.WriteLine("baseA:{0}", baseA);
            }
            else
            {
                Console.WriteLine("Error!");
            }
        }

        //========================================================================
        //  メソッド名 ： TestBaseB
        /// <summary>
        ///　TestBaseB
        /// </summary>
        /// <param name="b">辅助变量</param>
        //========================================================================
        private static void TestBaseB(BaseB b)
        {
            if (b is IBaseB)
            {
                IBaseB baseB = b as IBaseB;
                Console.WriteLine("baseB:{0}", baseB);
            }
            else
            {
                Console.WriteLine("Error!");
            }
        }

        //========================================================================
        //  メソッド名 ： TestMyClass
        /// <summary>
        ///　TestMyClass
        /// </summary>
        /// <param name="mc">辅助变量</param>
        //========================================================================
        private static void TestMyClass(MyClass mc)
        {
            if (mc is IMyClass)
            {
                IMyClass myClass = mc as IMyClass;
                Console.WriteLine("myClass:{0}", myClass);
            }
            else
            {
                Console.WriteLine("Error!");
            }
        }
    }
}