public function addObserver(ObserverInterface $observerObject)
    {
        if (is_null($observerObject)) {
            throw new ObservableException('Given observer is null.', E_WARNING);
        } else {
            $this->getObserverSetObject()->add($observerObject);
        }
    }
public function addObserver(ObserverInterface $observerObject)
    {
        if (is_null($observerObject)) {
            throw new ObservableException('Given observer is null.', E_WARNING);
        } else {
            $this->getObserverSetObject()->add($observerObject);
        }
    }
public function addObserver ( ObserverInterface $ observerObject ) { if ( is_null ( $ observerObject ) ) { throw new ObservableException ( 'Given observer is null.' , E_WARNING ) ; } else { $ this -> getObserverSetObject ( ) -> add ( $ observerObject ) ; } }
add a observer to the observable

@param       ObserverInterface       $observerObject
@return      void
@throws      ObservableException
add a observer to the observable