c#索引器

经常见有这样的类：如aClass a = new Class();然后在程序里出现个a[i]="some string";感觉好奇怪：既然没有声明类数组却用[]索引，而且返回个string类型,在msdn2和google、baidu同学的帮助之下终于弄明白原来是c#的索引器，弄明白了原理之后自己写了个小示例程序。声明：程序完全自主编写，只要对大家有帮助，随便拷贝: )

using System ;
/// <summary>
/// 索引器示例
/// </summary>

class StringCollection  //建立一个字符串容器类
{
    readonly int _count;
    string[] str;
    public StringCollection(int count)
    {
        if (count > 1)
        {
            _count = count;
            str = new string[_count];
        }
    }
    public string this[int index]   //索引器
    {
        get
        {
            if (index >= 0 && index < _count)
                return str[index];
            else
                return "error index!";
        }
        set
        {
            if (index < 0 || index >= _count)
                throw new Exception("Out of Range!");
            else
                str[index] = value;
        }
    }
    static void Main()
    {
        StringCollection test = new StringCollection(5);
        test[0] = "Hello Word!";
        test[2] = "Hi China!";
        test[4] = "How do you do!";
        for (int i = 0; i < 6; i++)
            Console.WriteLine("String #{0} = {1}", i, test[i]);

        StringCollection[] a = new StringCollection[3]; //定义一个3维StringCollection
        for (int i =0;i<3;i++)
            for (int j = 0; j < 2; j++)
            {
                a[i] = new StringCollection(2); //对每一个StringCollection调用构造函数
                a[i][j] = i.ToString() + j.ToString();
                Console.WriteLine(a[i][j]);
            }
        Console.Read();
    }
}