【Java学习笔记之二十三】instanceof运算符的用法小结

 1 class Person {  
 2 }
 3   
 4 class Student extends Person {  
 5 }
 6   
 7 class Postgraduate extends Student {  
 8 } 
 9  
10 class Animal {  
11 }
12   
13 public class Ex_instanceOf {  
14 public static void main(String[] args) {  
15    instanceofTest(new Student());  
16 }  

 1 public static void instanceofTest(Person p) {  
 2    // p 和 Animal类型不一样,彼此之间没有继承关系,编译会出错  
 3    // 提示错误:Incompatible conditional operand types Person and Animal  
 4    // if(p instanceof Animal){  
 5    // System.out.println("p是类Animal的实例");  
 6    // }  
 7    //下面代码的除了第一行都会输出  
 8    if (p instanceof Postgraduate) System.out.println("p是类Postgraduate的实例");  
 9    if (p instanceof Person) System.out.println("p是类Person的实例");  
10    if (p instanceof Student) System.out.println("p是类Student的实例");  
11    if (p instanceof Object) System.out.println("p是类Object的实例");  
12  
13 }  
14 } 

 1 interface A{  
 2       
 3 }  
 4 class B implements A{  
 5        
 6 }  
 7 class C extends B{  
 8        
 9 }  
10 public class Iinstanceof {  
11   
12     public static void main(String[] args) {  
13         A ab=new B();  
14         A ac=new C();  
15         B bc=new C();  
16         B bb=new B();  
17         C cc=new C();  
18         //对象实现一个接口，用这个对象和这个接口进行instanceof判断，都为true。  
19         System.out.println("ab instanceof A="+(ab instanceof A));  
20         System.out.println("ac instanceof A="+(ac instanceof A));  
21         System.out.println("bc instanceof A="+(bc instanceof A));  
22         System.out.println("bb instanceof A="+(bb instanceof A));  
23         System.out.println("cc instanceof A="+(cc instanceof A));  
24         //对象和父类进行instanceof判断，都为true  
25         System.out.println("ab instanceof B="+(ab instanceof B));  
26         System.out.println("ac instanceof B="+(ac instanceof B));  
27         System.out.println("bc instanceof B="+(bc instanceof B));  
28         System.out.println("bb instanceof B="+(bb instanceof B));  
29         System.out.println("cc instanceof B="+(cc instanceof B));  
30         //对象和他的子类进行instanceof判断为false  
31         System.out.println("ab instanceof C="+(ab instanceof C));  
32         System.out.println("ac instanceof C="+(ac instanceof C));  
33         System.out.println("bc instanceof C="+(bc instanceof C));  
34         System.out.println("bb instanceof C="+(bb instanceof C));  
35         System.out.println("cc instanceof C="+(cc instanceof C));  
36     }  
37 }  

 1 ab instanceof A=true
 2 ac instanceof A=true
 3 bc instanceof A=true
 4 bb instanceof A=true
 5 cc instanceof A=true
 6 ab instanceof B=true
 7 ac instanceof B=true
 8 bc instanceof B=true
 9 bb instanceof B=true
10 cc instanceof B=true
11 ab instanceof C=false
12 ac instanceof C=true
13 bc instanceof C=true
14 bb instanceof C=false
15 cc instanceof C=true