PHP - 访问类变量

how do i access a class variable in php ?

class Human 
{
    public $data = array(5,0,15,20,22,14,13,15,12,22,40,4); 

    public function test()
    {
      var_dump(json_encode($this->$data));
    }

}

Error :

(1/1) FatalThrowableError

Cannot access empty property

Remove the $:

var_dump(json_encode($this->data));