命令式编程和声明式编程区别

  我是个新手，虽然在某个领域还算可以，但是在net，还算个新手。还需要向各位学习。

今天做了个例子，  是把相同地域的学生进行分组。想看看2种方式的区别，有很多不懂地方，还要向大侠请教。

有个方法是别人帮我编写的，还有些不懂。请教下。

实例代码 
  1  public class Student
  2     {
  3         public string Name { get; set; }
  4         public string City { get; set; }
  5     }
  6 
  7     /// <summary>
  8     /// 存放分组结果
  9     /// </summary>
 10      class StudentGroup
 11     {
 12         public string City;
 13         public List<Student> Students = new List<Student>();
 14     }
 15 
 16     class Program
 17     {
 18         /// <summary>
 19         /// 提取学生清单
 20         /// </summary>
 21         /// <returns></returns>
 22          static IEnumerable<Student> GetStudents()
 23         {
 24             List<Student> students = new List<Student>
 25             {
 26                new Student {Name="张三", City="北京"},
 27                new Student {Name="李四", City="上海"},
 28                new Student {Name="王五", City="北京"},
 29                new Student {Name="赵六", City="重庆"},
 30                new Student {Name="马七", City="北京"} ,
 31                 new Student {Name="牛八", City="上海"}
 32             };
 33             return students;
 34         }
 35         /// <summary>
 36         /// 按城市分组
 37         /// </summary>
 38         static void GroupStudentByCity()
 39         {
 40             var students = GetStudents();
 41             var results = new List<StudentGroup>();
 42 
 43             foreach (Student student in students)
 44             {
 45                 StudentGroup res = results.Find(item => item.City == student.City);
 46                 if (res != null)
 47                     res.Students.Add(student);
 48                 else
 49                 {
 50                     StudentGroup newRes = new StudentGroup() { City = student.City };
 51                     newRes.Students.Add(student);
 52                     results.Add(newRes);
 53                 }
 54             }
 55 
 56             PrintResult(results);
 57         }
 58 
 59         /// <summary>
 60         /// 输出结果
 61         /// </summary>
 62         /// <param name="Results"></param>
 63         static void PrintResult(IEnumerable<StudentGroup> Results)
 64         {
 65 
 66             foreach (StudentGroup res in Results)
 67             {
 68                 Console.WriteLine("============================");
 69                 Console.WriteLine("{0}的学生有{1}人：", res.City, res.Students.Count);
 70                 foreach (Student stu in res.Students)
 71                     Console.WriteLine(stu.Name);
 72                 Console.WriteLine();
 73             }
 74 
 75         }
 76 
 77         /// <summary>
 78         /// 对LINQ组进行处理
 79         /// </summary>
 80         /// <param name="group"></param>
 81         /// <returns></returns>
 82         static StudentGroup ProcessGroup(IGrouping<string, Student> group)
 83         {
 84             StudentGroup result = new StudentGroup { City = group.Key };
 85             foreach (Student stu in group)
 86                 result.Students.Add(stu);
 87             return result;
 88         }
 89 
 90         static void GroupStudentByCityUseLINQ()
 91         {
 92             var results = from student in GetStudents()
 93                           group student by student.City into grp
 94                           select ProcessGroup(grp);   --不太懂
 95 
 96             PrintResult(results);
 97 
 98 
 99         }
100 
101         static void Main(string[] args)
102         {
103             Console.WriteLine("使用命令式编程方式实现：\n");
104             GroupStudentByCity();
105 
106             Console.ForegroundColor = ConsoleColor.Yellow;
107             Console.WriteLine("\n使用声明式编程方式实现：\n");
108             GroupStudentByCityUseLINQ();
109             Console.ReadKey();
110         }
111     }

 写完这个程序，感觉用LINQ 确实带来很多方便。

posted @ 2011-04-20 17:27  高导  阅读(392)  评论(0)    收藏  举报