接口里不能包括字段，构造函数，析构函数，静态成员或常量等，否则会导致错误

定义一个借口，接口封装了矩形的长和宽，而且还包含一个自定义的方法以计算矩形的面积。然后定义一个类，继承自该接口，在该类中实现接口中自定义方法。

 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         /// 长
12         /// </summary>
13         int Width
14         {
15             get;
16             set;
17         }
18         /// <summary>
19         /// 宽
20         /// </summary>
21         int Height
22         {
23             get;
24             set;
25         }
26         /// <summary>
27         /// 计算矩形面积
28         /// </summary>
29         int Area();
30     }
31     class Program : ImyInterface//继承自接口
32     {
33         private int width = 0;
34         private int height = 0;
35         /// <summary>
36         /// 长
37         /// </summary>
38         public int Width
39         {
40             get
41             {
42                 return width;
43             }
44             set
45             {
46                 width = value;
47             }
48         }
49         /// <summary>
50         /// 宽
51         /// </summary>
52         public int Height
53         {
54             get
55             {
56                 return height;
57             }
58             set
59             {
60                 height = value;
61             }
62         }
63         /// <summary>
64         /// 计算矩形面积
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();//实例化Program类对象
73             ImyInterface imyinterface = program;//使用派生类对象实例化接口ImyInterface
74             imyinterface.Width = 5;//为派生类中的Width属性赋值
75             imyinterface.Height = 3;//为派生类中的Height属性赋值
76             Console.WriteLine("矩形的面积为：" + imyinterface.Area(3,5));
77         }
78     }
79 }

下面是正确的：

 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         /// 长
12         /// </summary>
13         int Width
14         {
15             get;
16             set;
17         }
18         /// <summary>
19         /// 宽
20         /// </summary>
21         int Height
22         {
23             get;
24             set;
25         }
26         /// <summary>
27         /// 计算矩形面积
28         /// </summary>
29         int Area();
30     }
31     class Program : ImyInterface//继承自接口
32     {
33         int width = 0;
34         int height = 0;
35         /// <summary>
36         /// 长
37         /// </summary>
38         public int Width
39         {
40             get
41             {
42                 return width;
43             }
44             set
45             {
46                 width = value;
47             }
48         }
49         /// <summary>
50         /// 宽
51         /// </summary>
52         public int Height
53         {
54             get
55             {
56                 return height;
57             }
58             set
59             {
60                 height = value;
61             }
62         }
63         /// <summary>
64         /// 计算矩形面积
65         /// </summary>
66         public int Area()
67         {
68             return Width * Height;
69         }
70         static void Main(string[] args)
71         {
72             Program program = new Program();//实例化Program类对象
73             ImyInterface imyinterface = program;//使用派生类对象实例化接口ImyInterface
74             imyinterface.Width = 5;//为派生类中的Width属性赋值
75             imyinterface.Height = 3;//为派生类中的Height属性赋值
76             Console.WriteLine("矩形的面积为：" + imyinterface.Area());
77         }
78     }
79 }