1 /* 2 instancof 判断两个类之间是否有继承关系 3 Object->String 4 Object->Person->Teacher 5 Object->Person->Student 6 */ 7 Object s1 = new Student(); 8 System.out.println(s1 instanceof Object);//True 9 System.out.println(s1 instanceof Person);//True 10 System.out.println(s1 instanceof Student);//True 11 System.out.println(s1 instanceof Teacher);//False 12 System.out.println(s1 instanceof String);//False 13 Person s2 = new Student(); 14 System.out.println(s2 instanceof Object);//True 15 System.out.println(s2 instanceof Person);//True 16 System.out.println(s2 instanceof Student);//True 17 System.out.println(s2 instanceof Teacher);//False 18 //System.out.println(s2 instanceof String);//编译错误 19 Student s3 = new Student(); 20 System.out.println(s3 instanceof Object);//True 21 System.out.println(s3 instanceof Person);//True 22 System.out.println(s3 instanceof Student);//True 23 //System.out.println(s2 instanceof Teacher);//编译错误 24 //System.out.println(s2 instanceof String);//编译错误 25 26 public static void main(String[] args){ 27 Student s = new Student(); 28 s.student(); 29 Person p = s;//子转父 30 31 Person obj = new Student(); 32 ((Student)obj).student();//父转子 33 }