登录脚本不起作用

以下是完整的脚本：

connection.php

class Connection{
    public function dbConnect(){
    return new PDO("mysql:host=localhost; dbname=test", "root", "");        
    }   
}

user.php

include_one（'connection.php'）；

class User{
  private $db;
  public function __constructor(){
    $this->db = new Connection();
    $this->db = $this->db->dbConnect();
  }
  public function Login($name, $pass){
    if(!empty($name) && !empty($pass)){
        $st = $this->db->prepare("SELECT * FROM users WHERE name =? and pass =?");
        $st->bindParam(1, $name);
        $st->bindParam(2, $pass);
        $st->execute();     
        if($st->rowCount() == 1){
            echo "User verified. Access granted";   
        }else{
            echo "Incorrect";   
        }
    }else{
        echo "Please enter name and password";  
    }
  }
}    

index.php

include_once('User.php');
if(isset($_POST['submit'])){
$name = $_POST['user'];
$pass = $_POST['pass'];
$object = new User();
$object->Login($name, $pass);   
}

但当我尝试时，会出现以下错误：

致命错误：在第16行的中，对C:''wamp''www''tests''User.php中的非对象调用成员函数prepare（）

第16行：$st=$this->db->prepare（"SELECT*FROM users WHERE name=？and pass=？"）；