The code should display recipe_1 and recipe_2. But somehow it doesn't.. Can someone review my code?

class Recipe // Creates Class Recipe { public $title; // Creates public property from class Recipe with a property named title with no default value. public $ingredients = array(); // Creates public array property from class Recipe named ingredients. public $instructions = array(); public $yield; public $tag = array(); public $source = "Alena Holligan "; // Creates public property from class Recipe named source with a default value "Alena Holligan".

public function displayRecipe()
{
    $this -> title . " by " . $this -> source;
}

}

$recipe_1 = new Recipe(); // Creates an object named recipe_1 $recipe_1 -> source = "Grandma Holligan "; // Sets the property of source to "Grandma Holligan". $recipe_1 -> title = "My first recipe";

$recipe_2 = new Recipe(); // Creates an object named recipe_2 $recipe_2 -> source = "Betty Crocker"; $recipe_2 -> title = "My second Recipe";

echo $recipe_1->displayRecipe(); echo $recipe_2 -> displayRecipe();