oop - Is it correct for an object to reject it self? -

i want parse several files formats. wondering if it's correct oop "take risk" create object nothing.

class parserfactory {     private fn;      public function parserfactory(fn)     {         this->fn = fn;     }     public function getparser()     {         = new formataparser(this->fn);         if ( a->isvalid() )         {             return( );         }         b = new formatbparser(this->fn);         // ... , on...     } }  class formataparser {     /*         object telling if able continue work...         **clean or dirty design ?**     */     public function isvalid()     {                     header = someconversionandreadingstuff();         if ( header != "formata" )         {             return(false)         }         return(true);     }     public function parse()     {         /*         parsing, using conversion stuff done in isvalid         */     } } 

thanks

edit
had answers. so, ok object check own validity. anyway, code un-oop because of procedural way select parser (format detection). improve this, better user factory pattern 1 (php code) :

class parser {     protected $raw;      public function setraw($raw)     {         $this->raw = $raw;     } }  class parsera extends parser {     public function __construct()     {         echo "parsera constructor\n";     }      public function isvalid()     {         if ( $this->raw == "a" )         {             return( true );         }         return(false);     } }  class parserb extends parser {     public function __construct()     {         echo "parserb constructor\n";     }     public function isvalid()     {         if ( $this->raw == "b" )         {             return( true );         }         return(false);     } }  class parserfactory {     static private $parserclasses = array();      public static function registerparser($parserclassname)     {         self::$parserclasses[] = $parserclassname;     }      public static function getparser($raw)     {         foreach( self::$parserclasses $parserclass )         {             $parser = new $parserclass();             $parser->setraw($raw);             if ( $parser->isvalid() )             {                 return( $parser );             }         }     } }  parserfactory::registerparser("parsera"); parserfactory::registerparser("parserb"); parserfactory::getparser("b"); 

a more common design

public function getparser() {     if (formataparser::isrecognizedheader(this->fn)     {         return new formataparser(this->fn);     }     if (formatbparser::isrecognizedheader(this->fn)     {         return new formatbparser(this->fn);     } } 

this uses class, not object method check header. obvious variation collect different parsers in list, instead of manually looping on them this. requires ability add classes (not objects) list.