JSON to php object and array

<?php
class StudentInfo{
    public $name;
    public $age;
    private $mobileNum;
    public  function setMobileNum($mobileNum){
        $this->mobileNum=$mobileNum;
    }
    public function getMobileNum(){
        return $this->mobileNum; 
    }
}
$student = new StudentInfo();
$student -> name ="Tommy Jones";
$student -> age =45;
print_r($student);
$student->setMobileNum('11111111');
echo "<br>";
print_r($student);
$jsonEncoded=json_encode($student);
echo "<br>";
print_r($jsonEncoded);
$jsonDecoded=json_decode($jsonEncoded);
echo "<br>";
print_r($jsonDecoded);
$jsonDecodedArray=json_decode($jsonEncoded,true);
echo "<br>";
print_r($jsonDecodedArray);
?>

StudentInfo Object ( [name] => Tommy Jones [age] => 45 [mobileNum:StudentInfo:private] => )
StudentInfo Object ( [name] => Tommy Jones [age] => 45 [mobileNum:StudentInfo:private] => 11111111 )
{"name":"Tommy Jones","age":45}
stdClass Object ( [name] => Tommy Jones [age] => 45 )
Array ( [name] => Tommy Jones [age] => 45 )