Parent Class | Child Class PHP

class A{
var $a;
public function example(){
$this->a = "I am from Class A";
echo $this->a;
}
}

class B extends A{
var $b;
public function example(){
$this->b="I am from class B";
echo $this->b;
echo "
";
parent::example();
}
}
$a = new A;
$a->example();
echo "\n\n\n";
$b= new B;
$b->example();
?>