索引器

 C#通过提供索引器（indexer），使得用户可以像处理数组一样对对象使用下标。索引器为我们提供了通过索引方式访问类的数据的方法。
例：

using System; 
namespace suoyinqi

{
    class Vector
    {
        private double x,y,z;
        public double this[int i]//定义索引器，使得可以使用数组的方式访问Vector的数据
        {
            get
            {
                switch(i)
                {
                    case 0:
                        return x;
                    case 1:
                        return y;
                    case 2:
                        return z;
                    default:
                        throw new IndexOutOfRangeException("访问下标超出范围！");//若访问下标超出范围，抛出异常
                }
            }
            set
            {
                switch(i)
                {
                    case 0:
                        x = value;
                        break;
                    case 1:
                        y = value;
                        break;
                    case 2:
                        z = value;
                        break;
                    default:
                        throw new IndexOutOfRangeException("访问下标超出范围！");//若访问下标超出范围，抛出异常
                }
            }
        }
    }
    public class Class1
    {
        [STAThread]
        public static void Main(string[] args)
        {
            Vector v = new Vector();
            v[0] = 4;
            v[1] = 5;
            v[2] = 6;
            Console.WriteLine("Vector.x = {0}",v[0]);
            Console.WriteLine("Vector.y = {0}",v[1]);
            Console.WriteLine("Vector.z = {0}",v[2]);
        }
    }
}