C# 索引 就是使对象可以像数组一样访问，并可以做出特殊的处理

    public class Point
    {
        private double x, y;
        public Point(double X, double Y)
        {
            x = X;
            y = Y;
        }
       
        public override string ToString()
        {
            return String.Format("X: {0} , Y: {1}", x, y);
        }
    }
    public class Points
    {
        Point[] points;
        public Points(Point[] Points)
        {
            points = Points;
        }
        public int PointNumber
        {
            get
            {
                return points.Length;
            }
        }
        
        public Point this[int Index]
        {
            get
            {
                return points[Index];
            }
        }
    }

    class IndexClass
    {
        public string this[int index]
        {
            get
            {
                switch (index)
                {
                    case 1:
                        return "一";
                    case 2:
                        return "二";
                    case 3:
                        return "三";
                    case 4:
                        return "四";
                    default:
                        return "unkonw number";
                }
            }
        }

        public string this[string str]
        {
            get
            {
                return str;
            }
        }

        public object this[object o]
        {
            get
            {
                return new object();//这个地方有点意思
            }
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            IndexClass ic = new IndexClass();
            Console.WriteLine(ic["字符串索引"]);

            Console.WriteLine(ic[4]);

            Console.WriteLine(ic[new object()].GetType());

            Point[] tmpPoints = new Point[10];
            for (int i = 0; i < tmpPoints.Length; i++)
            {
                tmpPoints[i] = new Point(i, Math.Sin(i));
            }

            Points tmpObj = new Points(tmpPoints);
            for (int i = 0; i < tmpObj.PointNumber; i++)
            {
                Console.WriteLine(tmpObj[i]);
            }

            Console.ReadKey();
        }
    }