PHP 비교 객체

<?php
class test1{
   private $x;
   private $y;
   function __construct($arg1, $arg2){
      $this->x=$arg1;
      $this->y=$arg2;
   }
}
class test2{
   private $x;
   private $y;
   function __construct($arg1, $arg2){
      $this->x=$arg1;
      $this->y=$arg2;
   }
}
?>

$a=new test1(10,20);
$b=new test1(10,20);
echo "two objects of same class";
echo "using == operator : ";
var_dump($a==$b);
echo "using === operator : ";
var_dump($a===$b);

two objects of same class
using == operator : bool(true)
using === operator : bool(false)

$a=new test1(10,20);
$c=$a;
echo "two references of same object";
echo "using == operator : ";
var_dump($a==$c);
echo "using === operator : ";
var_dump($a===$c);

two references of same object
using == operator : bool(true)
using === operator : bool(true)

$a=new test1(10,20);
$d=new test2(10,20);
echo "two objects of different classes";
echo "using == operator : ";
var_dump($a==$d);
echo "using === operator : ";
var_dump($a===$d);