构造属性为null

<?php 
    class user { 
     public $connection; 
     public $host; 
     public $username; 
     public $password; 
     public $database; 
     public $port; 

     public function __constructor() { 
      $this->host  = "localhost"; 
      $this->username = "root"; 
      $this->password = "Password"; 
      $this->database = "database"; 
      $this->port  = "port"; 

      // Create connection 
      $this->connection = new mysqli($this->host, $this->username, $this->password, $this->database, $this->port); 

      // Check connection 
      if ($this->connection->connect_error) 
      { 
       echo "Failed to connect to MySQL: " . $this->connection->connect_error; 
      } 
     } 

     public function save ($data) {    
      $prop = strval($data['prop']); 

      $sql = "INSERT INTO user (prop) 
        VALUES ('" .$prop. "')"; 

      if (!mysqli_query($this->connection, $sql)) 
      { 
       die('Error: ' . mysqli_error($this->connection)); 
      } 
      echo "1 record added"; 

      mysqli_close($this->connection); 
     } 
    } 
?>

当运行代码以上得到以下警告：构造属性为null