定義一個借口，接口封裝了矩形的長和寬，而且還包含一個自定義的方法以計算矩形的面積。然后定義一個類，繼承自該接口，在該類中實現接口中自定義方法。

 1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Text; 5  6 namespace Test06 7 { 8     interface ImyInterface 9     {10         /// <summary>11         /// 長12         /// </summary>13         int Width14         {15             get;16             set;17         }18         /// <summary>19         /// 寬20         /// </summary>21         int Height22         {23             get;24             set;25         }26         /// <summary>27         /// 計算矩形面積28         /// </summary>29         int Area();////////  int Area(int Width, int Height);  30     }31     class PRogram : ImyInterface//繼承自接口32     {33         private int width = 0;34         private int height = 0;35         /// <summary>36         /// 長37         /// </summary>38         public int Width39         {40             get41             {42                 return width;43             }44             set45             {46                 width = value;47             }48         }49         /// <summary>50         /// 寬51         /// </summary>52         public int Height53         {54             get55             {56                 return height;57             }58             set59             {60                 height = value;61             }62         }63         /// <summary>64         /// 計算矩形面積65         /// </summary>66         public int Area(int Width,int Height)67         {68             return Width * Height;69         }70         static void Main(string[] args)71         {72             Program program = new Program();//實例化Program類對象73             ImyInterface imyinterface = program;//使用派生類對象實例化接口ImyInterface74             imyinterface.Width = 5;//為派生類中的Width屬性賦值75             imyinterface.Height = 3;//為派生類中的Height屬性賦值76             Console.WriteLine("矩形的面積為：" + imyinterface.Area(3,5));77         }78     }79 }

下面是正確的：

 1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Text; 5  6 namespace Test06 7 { 8     interface ImyInterface 9     {10         /// <summary>11         /// 長12         /// </summary>13         int Width14         {15             get;16             set;17         }18         /// <summary>19         /// 寬20         /// </summary>21         int Height22         {23             get;24             set;25         }26         /// <summary>27         /// 計算矩形面積28         /// </summary>29         int Area();30     }31     class Program : ImyInterface//繼承自接口32     {33         int width = 0;34         int height = 0;35         /// <summary>36         /// 長37         /// </summary>38         public int Width39         {40             get41             {42                 return width;43             }44             set45             {46                 width = value;47             }48         }49         /// <summary>50         /// 寬51         /// </summary>52         public int Height53         {54             get55             {56                 return height;57             }58             set59             {60                 height = value;61             }62         }63         /// <summary>64         /// 計算矩形面積65         /// </summary>66         public int Area()67         {68             return Width * Height;69         }70         static void Main(string[] args)71         {72             Program program = new Program();//實例化Program類對象73             ImyInterface imyinterface = program;//使用派生類對象實例化接口ImyInterface74             imyinterface.Width = 5;//為派生類中的Width屬性賦值75             imyinterface.Height = 3;//為派生類中的Height屬性賦值76             Console.WriteLine("矩形的面積為：" + imyinterface.Area());77         }78     }79 }

 本題的關鍵出錯點是：在接口里聲明方法的時候的形式要與接口的實現里面方法的定義形式保持一致，否則會出現錯誤：“

錯誤 1 “Area”方法沒有任何重載采用“2”個參數”