PHP 类的继承与方法重写

class Demo1
{

    private $name;
    public $age;
    protected $salary;
    const TXET_WORD='文本字';

    public function __construct($name,$age,$salary)
    {
        $this->name=$name;
        $this->age=$age;
        $this->salary=$salary;
    }

    public function __get($name)
    {
        if (isset($this->$name)) {
            return $this->$name;
        }
        return '非法属性';
    }
}
class Demo_one extends Demo1{
    private $sex;
    const  TXET_WORD = '超级文本字';
    public function __construct($name,$age,$salary,$sex='women')
    {
       parent::__construct($name,$age,$salary,$sex);
       $this->sex=$sex;
    }
    public function __get($name)
    {
       if (isset($this->$name)) {
            return $this->$name;
        }
        return '非法属性';
    }
}

$demo_one=new Demo_one('张三',80,6000);
echo $demo_one->age;
echo $demo_one->name;
echo $demo_one->salary;
echo Demo_one::TXET_WORD;
echo $demo_one->sex;