<?php

class A {
    private $data;

    public function setData($value)
    {
        $this->data = $value;
    }
}

$a = new A;
$a->setData('hello world');
#echo $a->data; //error

$reflector = new ReflectionClass('A');
$properties = $reflector->getProperties();

foreach ($properties as $property) {
    $property->setAccessible(true);
    echo $property->getValue($a) . PHP_EOL; // hello world
    #$property->setAccessible(false);
    #echo $property->getValue($a) . PHP_EOL; // error
}