class Student                                      
       {                 
         
       }//end Student
       public class GraduateStudent extends Student
       {                  
           public static void main(String[] args)         
           {  
               Student s = new GraduateStudent();           //
               GraduateStudent g = (GraduateStudent)s;      //
               GraduateStudent g = new Student();     //󣬲ݵ
               if(s instanceof GraduateStudent)       //жʵ֮
                    g = (GraduateStudent)s;
          }         
      }//end GraduateStudent
