MAIN
public class Main {
    public static void main(String[] args) {
        Shop p = new Shop();
        Product prod = new Product();
        prod.name = "Кефир";
        prod.srok = 10;
        prod.price = 100;

        Product prod2 = new Product();
        prod2.name = "Кефир2";
        prod2.srok = 10;
        prod2.price = 200;

        Product prod3 = new Product();
        prod3.name = "Кефир3";
        prod3.srok = 10;
        prod3.price = 300;

        p.setProduct(prod,prod2,prod3);

        System.out.println(p.getSum());
    }
}


==============PRODUCT
import java.util.ArrayList;

public class Product {

    public String name;
    public double srok;
    public double price;

}

================SHOP
import java.util.ArrayList;

public class Shop {
    ArrayList list = new ArrayList();

    public void setProduct(Product prod, Product prod2, Product prod3) {
        list.add(prod);
        list.add(prod2);
        list.add(prod3);
    }

    public double getSum() {
        double sum = 0;
        for (int i = 0; i < list.size(); i++) {
            Product p = (Product) list.get(i);
            sum = sum + p.price;

        }
        return sum;
    }

}