想想你的对象：

$employer = new Employer();
// You now have $employer object with the following properties:
// $employer->company_name;
// $employer->fname;
// $employer->sname;
 
$user = new User();
// You now have $user object with the following properties:
// $user->company_name;
 
$employer->company_name = "Company name is ";
// You now have $employer object with the following properties:
// $employer->company_name = 'Company name is ';
// $employer->fname;
// $employer->sname;
 
echo $user->company_name;
// You currently have $user object with the following properties:
// $user->company_name;  /* no value to echo! */

如果要使用继承的属性,它的工作方式更像：

class User{
    public $company_name;
 
    function PrintCompanyName(){
        echo 'My company name is ' . $this->company_name;
    }
}
 
class Employer extends User{
    public $fname;
    public $sname;
}
 
$employer = new Employer();
$employer->company_name = 'Rasta Pasta';
$employer->PrintCompanyName();  //echoes 'My company name is Rasta Pasta.'