<?php
class A {
    public $a = "a";
    private $b = "b";

    public function getB() {
        return $this->b;
    }
}
$obj = new A();
$mt = microtime();
$a = $obj->a;
echo microtime() - $mt . "<br />";
$mt = microtime();
$b = $obj->getB();
echo microtime() - $mt . "<br />";