static void Main(string[] args)

        {

            StringBuilder sb = new StringBuilder();

            Hello(sb);//StringBuilder做为方法参数使用时不需要赋值,其使用相当于 out str

            Console.WriteLine(sb.ToString());

            string str;

            World(out str);

            Console.WriteLine(str);

            Console.ReadKey();

        }

        public static void Hello(StringBuilder sb)

        {

            sb.Append("StringBuilder Hello World");

        }

        public static void World(out string str)

        {

            str = "string Hello World";

        }