C#入门(03):泛型

C#提供5种泛型：类、结构、接口、委托和方法。在泛型类声明中，字符串由尖括号和T构成（也可以是其他标识符），在类声明的主体中，每一个T都会被编译器替换为实际类型。T被称为类型参数（type arguments），泛型类形如：

 

class MyGenericClass<t S>
{
  //...
 }</t>

 

1，下例是如果定义以及实现一个泛型类

 

using System;
 using System.Collections;
 using System.Text;

 namespace GenernicsDemo
{
   
    class Person<T, S>      // 泛型类
     {
        /// <summary>
        /// 1 类的定义：  T,S 作为属性,域的类型或者方法的参数类型
        /// 2 类的实例化：Person<string, int> me = new Person<string, int>("Wang Hongjian", 23); 或者Person<int, int> me2 = new Person<int, int>(1, 2);
        /// </summary>
         private T name;
        private S age;
   
        public Person(T name, S age)     /*构造*/
        {
            this.name = name;
            this.age = age;
        }
       
        public void Display<T>(T[] names) /*泛型方法*/
        {
            ///<summary>
            ///1 定义：
            ///2 实现： 实例名.Display<string>[string数组名]
            ///</summary>
             Console.WriteLine("Name is {0},and the age is {1}.", name, age);
            foreach (T _name in names)
            {
                Console.WriteLine("names are {0}", _name);
            }
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Person<string, int> me = new Person<string, int>("Wang Hongjian", 23); 
            string[] hobbies = new string[] { "music", "reading", "sports" };
            double[] moneys = new double[] { 12.34, 15.24, 78.34, 34.44 };

            me.Display<string>(hobbies);
            me.Display<double>(moneys);

            Person<int, int> me2 = new Person<int, int>(1, 2);
            me2.Display<string>(hobbies);
            Console.ReadKey();
        }
    }
}
 

 

2，下面是泛型接口的实现

 

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

namespace GenericInterface
{
    #region A generic interface
    public interface IBinaryOperations<T> where T : struct
    {
        T Add(T arg1, T arg2);
        T Subtract(T arg1, T arg2);
        T Multiply(T arg1, T arg2);
        T Divide(T arg1, T arg2);
    }
    #endregion

    #region Implementation of generic interface.
    public class BasicMath : IBinaryOperations<float>
    {
        public float Add(float arg1, float arg2)
        { return arg1 + arg2; }

        public float Subtract(float arg1, float arg2)
        { return arg1 - arg2; }

        public float Multiply(float arg1, float arg2)
        { return arg1 * arg2; }

        public float Divide(float arg1, float arg2)
        { return arg1 / arg2; }
    }
    #endregion

    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("***** Generic Interfaces *****\n");
            BasicMath m = new BasicMath();
            Console.WriteLine("1.98 + 1.3 = {0}", m.Add(1.98F, 1.3F));
            Console.ReadLine();
        }
    }
}

 

3，IEnumerable <T>的列子（阅读前请参阅xelement的文章）

 

using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 using System.Xml.Linq;
 using System.Collections;
 namespace Indexer
{
    class Program
    {
        static void Main(string[] args)
        {
            XElement xmlTree = new XElement("Root",
                                    new XElement("Child1", 1),
                                    new XElement("Child2", 8),
                                    new XElement("Child3", 3),
                                    new XElement("Child4", 4),
                                    new XElement("Child5", 5)
                                );

            Console.WriteLine(xmlTree);

            XElement xmlTreet = new XElement("Root",
             from elt in xmlTree.Elements()
             where ((int)elt >= 3 && (int)elt <= 5)
             select elt);
            //foreach (XElement el in xmlTree2)
             Console.WriteLine(xmlTreet);

            IEnumerable<XElement> elements =
                from el in xmlTree.Elements()
                where (int)el <= 3
                select el;
            foreach (XElement el in elements)
                Console.WriteLine(el);

            //the same, 因为xmlTree.Elements() 同样返回IEnumerable<XElement> 
             var a =
               from el in xmlTree.Elements()
               where (int)el <= 3
               select el;
            foreach (XElement el in a)
                Console.WriteLine(el);

        }
    }
}