如何从列表中删除特定条目

Question

这是我的java类的代码

 @RequestMapping(value = "/addToCart", method = RequestMethod.POST)
    public String addToCart(@ModelAttribute("cartPageFlag") ArrayList<Boolean> cartPageFlag, 
            @ModelAttribute("productData") ProductData productData,final Model model,HttpSession httpSession){
    List<ProductData> timepass = new ArrayList<>();
    List<ProductData> previousCart = new ArrayList<ProductData>();
    timepass.addAll(previousCart);

    if(previousCart != null)
            {   
            Iterator<ProductData> iterator =timepass.iterator();
            while(iterator.hasNext()){
                    ProductData data = iterator.next();
                    iterator.remove();
                }
             }
    return REDIRECT_PREFIX + "/restaurantMenu" ;
    }

我的问题是：     我听说如果我们想要从列表中删除特定条目，那么我们可以使用迭代器但是在尝试这样做时我会得到以下错误

HTTP Status 500 - Request processing failed; nested exception is java.lang.IllegalStateException

@RequestMapping(value = "/addToCart", method = RequestMethod.POST)

public String addToCart(@ModelAttribute("cartPageFlag") ArrayList<Boolean> cartPageFlag, 
        @ModelAttribute("productData") ProductData productData,final Model model,HttpSession httpSession){

    List<ProductData> updatedCart = new ArrayList<>();
    List<ProductData> timepass = new ArrayList<>();
    List<ProductData> previousCart = new ArrayList<ProductData>();
    StudentData studentData =(StudentData)httpSession.getAttribute("student");

    if(studentData==null){
        isUserLoggedIn = false;
        previousCart =  (List<ProductData>) httpSession.getAttribute("sessionCart");

        if (null != previousCart) {
            updatedCart.addAll(previousCart);
            timepass.addAll(previousCart);
        }

    }
    else {
            previousCart =  listofProducts.retrieveCartEntriesFromDb(studentData.getName());
         }

    if(previousCart != null)
    {   
    Iterator<ProductData> iterator =timepass.iterator();
    System.out.println(iterator);
        while(iterator.hasNext()){
            ProductData data = iterator.next();
            iterator.remove();
        }
    System.out.println(iterator);
    }
        if(previousCart !=null ){
          for (ProductData cartItem : previousCart) {
            if(productData.getProductName().equalsIgnoreCase(cartItem.getProductName())){
                int quantityOfItem = productData.getQuantity()+cartItem.getQuantity();
                productData.setQuantity(quantityOfItem);
                updatedCart.remove(cartItem);
              }
            }
          }

        updatedCart.add(productData);

    if(!isUserLoggedIn){
        httpSession.setAttribute("sessionCart", updatedCart);

    }
    else {
        for (ProductData cartEntryData : updatedCart) {
        listofProducts.insertCartEntriesIntoDb(studentData.getName(),cartEntryData.getProductName(),cartEntryData.getQuantity());
         }
    }
    return REDIRECT_PREFIX + "/restaurantMenu" ;
}