php中instanceof用法

<?php  
class User{  
	private $name="zhenlw"; 
	public function  getName(){  
		return "UserName is ".$this->name;  
}  
}  
class NormalUser extends User { 
	private $age = 99;  
	public function getAge(){  
		return "age is ".$this->age;  
 } 
 }  
 class UserAdmin{ //操作. 
	public static function  getUserInfo(User $user){
	if($user instanceof User){
		echo $user->getName();
	}elseif($user instanceof NormalUser){
		echo $user->getAge();
 } 
 }  
 } 
	$User = new User();  
	UserAdmin::getUserInfo($User); 
 ?>