public function getHash()
    {
        if (null === $this->hash) {
            $this->hash = $this->calculateHash();
        }

        return $this->hash;
    }
public function getHash()
    {
        if (null === $this->hash) {
            $this->hash = $this->calculateHash();
        }

        return $this->hash;
    }
public function getHash ( ) { if ( null === $ this -> hash ) { $ this -> hash = $ this -> calculateHash ( ) ; } return $ this -> hash ; }
Returns the hash of the form object, which should be calculated only once
for performance concerns.

@return string
Returns the hash of the form object which should be calculated only once for performance concerns .