对于一个类，如果定义后(记作对象a)，将另外一个对象b直接赋值（“a = b”）给它，则相当于将地址赋值给了这个对象。当另外一个对象b不再对这块地址应用时，a由于对这块地址仍在使用，这块地址的指向的栈空间仍然不被销毁。直道没有对象再对其引用，系统将按照回收机制对其进行回收。

Demo如下：

public class ObjectRef    {        public static void Demo_Main()        {            PointD a, b, c;            b = new PointD(100, 58);            a = b;            b = new PointD(200, 11);                       Console.WriteLine("a is now {0}, {1}", a.X, a.Y); // a is now 100, 58            c = new PointD(300, 22);            a = c;            c.X = 500;            Console.WriteLine("a is now {0}, {1}", a.X, a.Y); // a is now 500, 22        }    }    public class PointD    {        int x;        int y;        public int X        {            get { return x; }            set { x = value; }        }                public int Y        {            get { return y; }            set { y = value; }        }        public PointD(int x, int y)        {            this.x = x;            this.y = y;        }    }