如何在子类中访问可能的私有变量？

Question

我在oops中创建了一个程序，在那里发生了一个私有变量，在子类中访问它是如何可能的。代码输入以下..... 这里是我的代码，请帮助我如何在子类中使用私有变量，或者请确认此代码是否正确。

<?php
class student

{
    private $sname,$srollno; //private variable
    public function Getdata($name,$rollno){

        $this-> sname=$name;
        $this-> srollno=$rollno;
    }

    public function Showdata(){

        echo "Name :".$this-> sname."<br>";
        echo "Rollno:".$this-> srollno."<br>";
    }
}

    $obj1 = new student;
    $obj1-> Getdata("Sandeep","26");
    $obj1-> Showdata();


    $obj2 = new student;
    $obj2 -> Getdata("Vivek","45");
    $obj2 -> Showdata();





class teacher extends student
{
    //private $tname,$troll;

    public function teach(){
        $this-> sname="tillu"; //here access private variable
        $this-> srollno="12";
    }

    public function teachShow(){
        echo  "tname :".$this-> sname."<br>";
        echo "troll : ".$this-> srollno."<br>";
    }

}

$obj3 = new teacher;
$obj3-> teach();
$obj3-> teachShow();

?>