Matching value from multiple ArrayList in Map - Java

Question

I have to display the greatest value of user cart, and his owner. I have 3 lists, i need to match productId from cartList to productId and price from categoryList + multiply by quantity in cartList, after the greatest sum is calculated i have to match right cart with userName to which this cart belongs. Do you have any ideas how to solve this?

List <UserIN> userList example output:

[UserIN{id=1, name=UserName{firstname='john', lastname='doe'}}, UserIN{id=2, name=UserName{firstname='david', lastname='morrison'}}]

List<SumUserCart> cartList example output:

[SumUserCart{userId=1, products=[ProductsCart{productId=1, quantity=4}, ProductsCart{productId=2, quantity=1}, ProductsCart{productId=3, quantity=6}]}, SumUserCart{userId=1, products=[ProductsCart{productId=2, quantity=4}, ProductsCart{productId=1, quantity=10}, ProductsCart{productId=5, quantity=2}]}]

List<ProductCategories> categoryList example output:

[ProductCategories{Category name='men's clothing', productID=1, price='109.95'}, ProductCategories{Category name='men's clothing', productID=2, price='22.3'}]

That's the way i got these values, its coming from JSON file, it works the same way with other lists:

List<SumUserCart> cartList = new ArrayList<>();
List<Cart> carts = mapper.readValue(data3, typeReference2);
      for (Cart c : carts) {
            cartList.add(new SumUserCart(c.getUserId(),c.getProducts()));
      }

UserIN class:

public class UserIN {
    int id;
    UserName name;


    @Override
    public String toString() {
        return "UserIN{" +
                "id=" + id +
                ", name=" + name +
                '}';
    }

    public UserIN(int id, UserName name) {
        this.id = id;
        this.name = name;
    }
    // getters & setters here
}

UserName class:

public class UserName {
    String firstname;
    String lastname;

    @Override
    public String toString() {
        return "UserName{" +
                "firstname='" + firstname + '\'' +
                ", lastname='" + lastname + '\'' +
                '}';
    }
    
    //getters & setters here
 
    public UserName() {}

    public UserName(String firstname, String lastname) {
        this.firstname = firstname;
        this.lastname = lastname;
    }
}

ProductCategories class:

public class ProductCategories {
        private String categoryName;
        private int productId;
        private double price;

        public ProductCategories(String categoryName, int productId, double price) {
            this.categoryName = categoryName;
            this.productId = productId;
            this.price = price;
        }

        @Override
        public String toString() {
            return "ProductCategories{" + "Category name='" + categoryName + '\'' + ", productID=" + productId + ", price='" + price + '\'' + '}';
        }
    
        //getters & setters here
}

SumUserCart class:

public class SumUserCart {
    int userId;
    ProductsCart[] products;

    public SumUserCart(int userId, ProductsCart[] products) {
        this.userId = userId;
        this.products = products;
    }

    @Override
    public String toString() {
        return "SumUserCart{" +
                "userId=" + userId +
                ", products=" + Arrays.toString(products) +
                '}';
    }

    public ProductsCart[] getProducts() {
        return products;
    }
 
   //getters & setters here
}

ProductCart class:

public class ProductsCart {
    int productId;
    int quantity;


    @Override
    public String toString() {
        return "ProductsCart{" +
                "productId=" + productId +
                ", quantity=" + quantity +
                '}';
    }

    public ProductsCart() {}

    public ProductsCart(int productId, int quantity) {
        this.productId = productId;
        this.quantity = quantity;
    }

    //getters & setters here
}