class poo php

<?php

#class.connection.php
class Connection{
public $server;
public $user;   
public $pass;   
public $db;   
public $sql;

public function __Construct($a,$b,$c,$d){
$this->server=$a;
$this->user=$b;
$this->pass=$c;
$this->db=$d;   
}   
public function Connect(){
return mysqli_connect($this->server,$this->user,$this->pass,$this->db);     
}
public function Query(){
$a=mysqli_query($this->Connect(),$this->sql) or die ("Error");   
return $a;
}
public function Total(){
return mysqli_num_rows($this->Query());
}
public function Fetch(){
return mysqli_fetch_assoc($this->Query());   
}     
}
$conn=new Connection("localhost","root","usbw","sistema"); //Criação do objeto
//Agora vamos aceder ao objeto
$conn->sql="SELECT * FROM users";
$f=$conn->Fetch();
echo $f['username'];

?>