function 返回一个没有数据的 ArrayList

Question

been trying to add an object of a class to an ArralyList of objects when a user clicks a button in javaFx. I am trying to add an object of a class (Product) to an ArrayList shoppingList, which is an ArrayList of Products. when I test the ArrayList in the addToCart() function,everything is fine, but when the program goes back to main the ArrayList is empty of data

here is my main where I call the function

ArrayList<Product> shoppingList = new ArrayList<>();
    Button btnAddToCart = new Button("Add to cart");

  btnAddToCart.setOnAction(e->addToCart(productList,productBox,shoppingList));

here is the function

 public ArrayList<Product> addToCart(ArrayList<Product> productList, ChoiceBox productBox, ArrayList<Product> shoppingList) {



    for(int x =0 ; x<productList.size();x++)
    {
        if(productList.get(x).getProductDescribtion() == productBox.getValue())
        {
            Product inCartProduct = new Product(productList.get(x).getProductCategory(),productList.get(x).getProductDescribtion(),
                    productList.get(x).getItemNumber(),productList.get(x).getInStockQty(),productList.get(x).getProductPrice() );

            System.out.println("Cart in for loop :>"+inCartProduct.toString());

            shoppingList.add(inCartProduct);


        }
    }
    for(Product onePr : shoppingList)
    {
       // System.out.println("Here in the cart : ");
        System.out.println("Cart in button function :> "+onePr.toString());
      //  System.out.println("The size of the cart : "+shoppingList.size());
    }


    return  shoppingList;
}

Answer 1

For comparing values use .equals(...) instead of ==

if(productList.get(x).getProductDescribtion().equals(productBox.getValue()))

... instead of

if(productList.get(x).getProductDescribtion() == productBox.getValue())