a intanceof A：判断a是否是类A的的一个实例，返回值为boolean
public class Person extends Object{}
public class Student extends Person{}
public class Graduate extends Person{}
public class Main { static void main(String[] args) { Person p = new Person(); Student s = Student(); Graduate g = Graduate(); System.out.println(p instanceof Person); System.out.println(s Person); System.out.println(g Person); } }
输出：
true
true
true
