static void displayVendingMachineProducts(VendingMachine vendingMachine) {
        System.out.println("Product Options...");

        int option_num = 1;
        for(Product product : vendingMachine.getStocked_products()) {

            System.out.println("Product #" + option_num +
                    " " + product.getProductName() +
                    " price: " + product.getProductValue());

            option_num ++;
        }

    }