private function print_heading() {
        $fontfamily = $this->pdf->getFontFamily();
        $fontstyle = $this->pdf->getFontStyle();
        $this->pdf->SetFont($fontfamily, 'B');
        $rowheight = 0;
        foreach ($this->columns as $columns) {
            $rowheight = max($rowheight, $this->pdf->getStringHeight($this->colwidth, $columns, false, true, '', 1));
        }

        $total = count($this->columns);
        $counter = 1;
        foreach ($this->columns as $columns) {
            $nextposition = ($counter == $total) ? 1 : 0;
            $this->pdf->Multicell($this->colwidth, $rowheight, $columns, 1, 'C', true, $nextposition);
            $counter++;
        }

        $this->pdf->SetFont($fontfamily, $fontstyle);
    }