PHP input json_decode empty what's wrong?

Question

PHP

This code works great:

$json = json_decode(file_get_contents('php://input'));
var_export($json);

But it’s worth adding it to the class:
then the output is empty, if everything is fine without json_decode, I broke my whole head, I don’t understand what kind of bug this is

class name{
 public function __construct()
{
$json = json_decode(file_get_contents('php://input'));
var_export($json);
}

Forgot to specify php version 7.0

Answer 1

Should the class call itself?