CSharp: null object pattern in donet core 3

 

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/// <summary> /// 空对象模式  null object pattern /// geovin,Geovin Du eidt /// </summary> interface IVehicle {     void Travel(); } /// <summary> /// Bus class /// </summary> class Bus : IVehicle {       /// <summary>     ///     /// </summary>     public static int busCount = 0;     /// <summary>     ///     /// </summary>     public Bus()     {         busCount++;     }     /// <summary>     ///     /// </summary>     public void Travel()     {         Console.WriteLine("让我们乘公共汽车旅行吧.");     } } /// <summary> /// Train class /// </summary> class Train : IVehicle {       /// <summary>     ///     /// </summary>     public static int trainCount = 0;     /// <summary>     ///     /// </summary>     public Train()     {         trainCount++;     }     /// <summary>     ///     /// </summary>     public void Travel()     {         Console.WriteLine("让我们乘坐火车旅行吧.");     } } /// <summary> /// NullVehicle class /// </summary> class NullVehicle : IVehicle {       /// <summary>     ///     /// </summary>     private static readonly NullVehicle instance = new NullVehicle();     /// <summary>     ///     /// </summary>     private NullVehicle()     {         nullVehicleCount++;     }     /// <summary>     ///     /// </summary>     public static int nullVehicleCount;     /// <summary>     ///     /// </summary>     public static NullVehicle Instance     {         get         {             return instance;         }     }     /// <summary>     ///     /// </summary>     public void Travel()     {         //Do Nothing     } }

　　

 

调用：

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// 2//空对象模式                Console.WriteLine("***空对象模式 2 Null Object Pattern .***\n");                string duinput = String.Empty;                int dutotalObjects = 0;                  while (duinput != "exit")                {                    Console.WriteLine("输入您的选择(输入“a”代表公共汽车，输入“b”代表火车。输入“exit”退出应用程序 ");                    duinput = Console.ReadLine();                   GeovinDu.IVehicle duvehicle = null;                    switch (duinput)                    {                        case "a":                            duvehicle = new GeovinDu.Bus();                            break;                        case "b":                            duvehicle = new GeovinDu.Train();                            break;                        case "exit":                            Console.WriteLine("关闭应用程序.");                            duvehicle = NullVehicle.Instance;                            break;                        default:                            Console.WriteLine("请提供正确的输入(a/b/exit .)");                            duvehicle = NullVehicle.Instance;                            break;                    }                    dutotalObjects = GeovinDu.Bus.busCount + GeovinDu.Train.trainCount + NullVehicle.nullVehicleCount;                    //No need to do null check now.                    //if (vehicle != null)                    duvehicle.Travel();                    //}                    Console.WriteLine("系统中创建的对象总数 ={0}",                    dutotalObjects);                  }                  Console.ReadKey();

　　

输出：

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***空对象模式 2 Null Object Pattern .***   输入您的选择(输入“a”代表公共汽车，输入“b”代表火车。输入“exit”退出应用程序 a 让我们乘公共汽车旅行吧. 系统中创建的对象总数 =2 输入您的选择(输入“a”代表公共汽车，输入“b”代表火车。输入“exit”退出应用程序 b 让我们乘坐火车旅行吧. 系统中创建的对象总数 =3 输入您的选择(输入“a”代表公共汽车，输入“b”代表火车。输入“exit”退出应用程序 c 请提供正确的输入(a/b/exit .) 系统中创建的对象总数 =3 输入您的选择(输入“a”代表公共汽车，输入“b”代表火车。输入“exit”退出应用程序 a 让我们乘公共汽车旅行吧. 系统中创建的对象总数 =4 输入您的选择(输入“a”代表公共汽车，输入“b”代表火车。输入“exit”退出应用程序 a 让我们乘公共汽车旅行吧. 系统中创建的对象总数 =5 输入您的选择(输入“a”代表公共汽车，输入“b”代表火车。输入“exit”退出应用程序 b 让我们乘坐火车旅行吧. 系统中创建的对象总数 =6 输入您的选择(输入“a”代表公共汽车，输入“b”代表火车。输入“exit”退出应用程序