using System;using System.Collections.Generic;using System.Text;using System.Collections; namespace __9{    class Program    {        static void Main(string[] args)        {            int a = 3;            testprimitive(a);            Console.WriteLine(a);              //3             ArrayList l = new ArrayList();            Console.WriteLine(l.Count);            //0                        textobjectlist(l);            Console.WriteLine(l.Count);        //?2            print(l);             Console.WriteLine("-------------");            ArrayList ll = new ArrayList();            ll.Add("major");            Console.WriteLine(ll.Count);           //1            print(ll);            Console.WriteLine("--------------");            textobjectlist2(ll);            Console.WriteLine(ll.Count);       //?1            print(ll);             Console.WriteLine("....---------------");                        string s = "jack";            teststring(s);            Console.WriteLine(s); //jack        }         private static void testprimitive(int a)        {            a *= 2;        }        private static void textobjectlist(ArrayList l)        {            l.Add("jumbo");            l.Add("jumbo2");        }        private static void textobjectlist2(ArrayList l)        {            l = null;                                            //l 指向null引用，以前的那个对象并没有变            //l.Add("a");            //l.Add("b");        }        private static void teststring(string s)        {            s = "john";        }         private static void print(ArrayList l)        {            foreach(string s in l)            {                Console.WriteLine(s);            }        }    }}  

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