parent一般用来继承父类的构造方法

class Person
{
    private $name = 'KaiNan';

    public function __construct($name = 'MuMu')
    {
        $this->name = $name;
        echo "父类的构造方法<br>";
        echo $this->name,'<br>';
    }

}

class Stu extends Person
{
    protected $age = 22;

    public function __construct($name = 'HanBin', $age = '18')
    {
        parent::__construct($name);
        $this->age = $age;
        echo $this->age;
    }

}

$lucy = new Stu('XiaoPao',16);

/*
父类的构造方法
XiaoPao
16
*/