Java instanceof 运算符

public class People {
}
public class Teacher extends People {
}
public class President extends Teacher {
}

 1 public final class Demo {
 2     public static void main(String[] args){
 3         People obj = new People();
 4         if(obj instanceof Object){
 5             System.out.println("我是一个对象");
 6         }
 7         if(obj instanceof People){
 8             System.out.println("我是一个人");
 9         }
10         if(obj instanceof Teacher){
11             System.out.println("我是一名教师");
12         }
13         if(obj instanceof President){
14             System.out.println("我是一名校长");
15         }
16 
17         System.out.println(" --------------------------------------------- ");
18 
19         obj = new Teacher();
20         if(obj instanceof Object){
21             System.out.println("我是一个对象");
22         }
23         if(obj instanceof People){
24             System.out.println("我是一个人");
25         }
26         if(obj instanceof Teacher){
27             System.out.println("我是一名教师");
28         }
29         if(obj instanceof President){
30             System.out.println("我是一名校长");
31         }
32     }
33 }