LINQ 用法，返回结果不是在定义时取值，而是在调用时实时取值，有意思！

var names = new List<string> { "Nino o", "Alberto", "Juan", "Mike", "phi1" };
            var namesWithJ = from n in names
                             where n.StartsWith("J")
                             orderby n
                             select n;
            Console.WriteLine("First iteration");
            foreach (string name in namesWithJ)
            {
                Console.WriteLine(name);
            }
            Console.WriteLine();
            names.Add("John");
            names.Add("Jim");
            names.Add("Jack");
            names.Add("Denny");
            Console.WriteLine("second iteration");
            foreach (string name in namesWithJ)
            {
                Console.WriteLine(name);
            }

返回结果如下：

First iteration
Juan

second iteration
Jack
Jim
John
Juan

其他情况：

var names = new List<string> { "Nino o", "Alberto", "Juan", "Mike", "phi1" };
            var namesWithJ = (from n in names
                             where n.StartsWith("J")
                             orderby n
                             select n).ToList();
            Console.WriteLine("First iteration");
            foreach (string name in namesWithJ)
            {
                Console.WriteLine(name);
            }
            Console.WriteLine();
            names.Add("John");
            names.Add("Jim");
            names.Add("Jack");
            names.Add("Denny");
            Console.WriteLine("second iteration");
            foreach (string name in namesWithJ)
            {
                Console.WriteLine(name);
            }

返回结果如下：

First iteration
Juan

second iteration

Juan