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 {
public static void main(String[] args) {
Person p = new Person();
Student s = new Student();
Graduate g = new Graduate();
System.out.println(p instanceof Person);
System.out.println(s instanceof Person);
System.out.println(g instanceof Person);
}
}
输出：
true
true
true