Why is the property not available on the heir?

Question

PHP

Guys, help me understand. Why the heir does not see the variable "year".

class Class1{
  
  protected $year = 1;
  
  public function setYear($year){
    $this->year = $year;
  }
  
}

class Class2 extends Class1{
  
  public function getYear(){
    return $this->year;
  }
  
}

$class1 = new Class1();
$class1->setYear(2018);


$class2 = new Class2();
echo $class2->getYear(); //NULL

Answer 1

Strange, I can see everything, returns 1, as it should be.

Answer 2

Try rearranging PHP.