mysqli,Fatal error

<?php

//mysql数据库类-mysqli版

//2014/6/13

class  mysqlidb{

     public $dbhost;

     public $dbuser;

     public $dbpasswd;

     public $dbname;

     public $dbport;

     public $dbobject;



     public function __contruct($host,$user,$pwd,$dbname,$port=3306){

         $this->dbhost = $host;

         $this->dbuser = $user;

         $this->dbpasswd = $pwd;

         $this->dbname = $dbname;

         $this->dbport = $port;

         

         $this->dbobject = new mysqli($this->dbhost,$this->dbuser,$this->dbpasswd,$this->dbname,$this->dbport);

           if ( $this->dbobject -> connect_error ) {

         die( 'Connect Error ('  .  $this->dbobject -> connect_errno  .  ') '

             .  $this->dbobject -> connect_error );

         }



     }



     public function executesql($sql,$param=array()){

         $dbstmt = $this->dbobject->prepare($sql);

         if(!empty($param)){

           foreach($param as $k => $v){

                $dbstmt -> bind_param($k,$v);

           }

         }

         $dbstmt -> execute();

         $dbresult = $dbstmt -> get_result();

         return  $dbresult->fetch_array();

     

     }



}



$db = new mysqlidb('127.0.0.1','root','','mysql');

$sql = 'select * from User';

$dbrs = $db->executesql($sql);





//Fatal error: Call to a member function prepare() on a non-object in C:\xampp\htdocs\tonglei\mysqli\demo2.php on line 28