}
    //next page
    public function next_page()
    {
        $this->page_str .= '下一页';
    }
    //go to page
    public function go_page()
    {
        $str = <<<EOT
<select>
\t<option>1</option>
\t<option>2</option>
\t<option>3</option>
</select>
EOT;
        $this->page_str .= $str;
    }
    //display()
    public function display_page()
    {
        //$this->page_str .= '';
        echo $this->page_str;
    }
}
//test
$p = new Page();
$p->pre_page();
$p->next_page();
$p->go_page();
$p->display_page();