Question

——-Now, another question, can anyone explain?

class DBFactory {  
                static function create(){  
                return new MysqlDB();  
        }  
    }  
class MysqlDB{ 
    function alo(){  
        echo 'ok';  
        }
}  
$db = DBFactory::create();  
$db->alo();  

—>Works

class DBFactory {  
                function create(){  
                return new MysqlDB();  
        }  
    }  
class MysqlDB{ 
    function alo(){  
        echo 'ok';  
        }
}  
$db = new DBFactory;  
$db->create();  
$db->alo();    

—>Not works

Answer 1

Because you’re returning a new MysqlDB instance, but are not saving the reference anywhere. DBFactory does not have an alo method. Compare:

$db = new DBFactory;  
$mysqlDb = $db->create();  
$mysqlDb->alo();