Csharp+Asp.net系列教程（四）(1)[5]

                {
                 public static void test (object o)
                 {
                 class1 a;
                 class2 b;
                 if (o is class1)
                 {
                 console.writeline ("o is class1");
                 a = (class1)o;
                 // do something with a
                 }        
                 else if (o is class2)
                 {
                 console.writeline ("o is class2");
                 b = (class2)o;
                 // do something with b
                 }
                 else
                 {