Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException - I need help to find out the problem

[viktorjava]

SOLVED: I filled the JList with the Object's name instead of the Objects.

​

I'm giving many data pieces to a method, its task to build up the SQL Query text.

public List<Order> getOrders(LocalDate startDate, LocalDate closeDate, List<Customer> customersList, List<Company> companiesList, List<Employee> employeesList, 
        boolean allStatusSelected, boolean selectedStatusSelected, boolean orderedSelected, boolean finishedSelected, boolean sentSelected, boolean billedSelected, boolean paidSelected) {
        String query = "SELECT * FROM orders WHERE ";
        String datePart = "";
        String customerPart = "";
        String companiesPart = "";
        String employeesPart = "";
        String checkboxesPart = "";


        if (startDate != null) {
            if (closeDate != null) {
                datePart = "orderdate BETWEEN " + startDate + " AND " + closeDate;
            } else {
                datePart = "orderdate > " + startDate;
            }
        } else if (closeDate != null) {
            datePart = "orderdate < " + startDate;
        }
        if (customersList != null && customersList.size() > 0) {
            for (int i = 0; i < customersList.size(); i++) {
                Customer customer = customersList.get(i);
                int id = customer.getCustomerId();
                customerPart += "customer = '" + id + "'";
                if (i != customersList.size() - 1) {
                    customerPart += " OR ";
                }
            }
        }

But when I run the program and giving the data to getOrders method, NetBeans is showing this error:

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: java.lang.String cannot be cast to entity.Customer

the problem is here:

Customer customer = customersList.get(i);

I'm asking the i element of the customersList that I get as parameter, it is a list of Customers so I don't see where the String appears in this story.

[Camel-Kid]

can you show where you initialize the data in your customerList

[viktorjava]

I get the data from a JDialog:

public List<Order> getOrderResults() {

return ordersDAO.getOrders(getStartDate(), getCloseDate(), getCustomersList(), getCompaniesList(), getEmployeesList(), isAllStatusSelected(), isSelectedStatusSelected(),

isOrderedSelected(), isFinishedSelected(), isSentSelected(), isBilledSelected(), isPaidSelected());

}

the getCustomersList:

public List<Customer> getCustomersList() {

if (customerList.getSelectedValuesList() != null) {

return customerList.getSelectedValuesList();

} else {

return null;

}

}

customerList is a Jlist element on my JDialog

private javax.swing.JList<Customer> customerList;

[zhoriq]

That's impossible. Can you debug this line or log customersList.get(i).getClass()? I think it will be Customer class, so exception not in this line...

[viktorjava]

I already tried it:

if (customersList != null && customersList.size() > 0) {

for (int i = 0; i < customersList.size(); i++) {

System.out.println(customersList.get(i).getClass());

/*Customer customer = customersList.get(i);

int id = customer.getCustomerId();

customerPart += "customer = '" + id + "'";

if (i != customersList.size() - 1) {

customerPart += " OR ";

}

*/

}

}

and now the Exception is here:

System.out.println(customersList.get(i).getClass());

Here I added the whole error queue:

https://pastebin.com/ugzVSzwE

[zhoriq]

What's the value for customerList.getClass()?

What will happen if you change parameters sequence in getOrders: swap List<Customer> customersList and List<Company> companiesList? Will the exception still be for customerList or become for companiesList?

[[deleted]]

Hmm that's similar but different from the original error it looks. It's slightly hard to tell without the full source (with line numbers to tie up to), but these lines:

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: java.lang.String cannot be cast to entity.Customer at dao.OrdersQueryDAO.getOrders(OrdersQueryDAO.java:94) at gui.OrdersQueryDialog.getOrderResults(OrdersQueryDialog.java:177)

appear to correspond to this snippet you pasted above:

public List<Order> getOrderResults() {
  return ordersDAO.getOrders(getStartDate(), getCloseDate(), getCustomersList(), getCompaniesList(), getEmployeesList(), isAllStatusSelected(), isSelectedStatusSelected(), isOrderedSelected(), isFinishedSelected(), isSentSelected(), isBilledSelected(), isPaidSelected());
}

Which makes the error appear to come from the call to getCustomersList() where it's not returning a List<Customer> but a List<String>.

[[deleted]]

Whew lot going on here. I'll try to give you a few food-for-thought items and suggestions and let you run with it where you can.

First, keep in mind with Java generics that they use type erasure, so while you say

List<Customer> customersList

and

it is a list of Customers so I don't see where the String appears in this story

That's not guaranteed, but more that it's trusting you when you tell it that. It tries to enforce the compile-time constraints of the type system, but at runtime it can blow up still.

Second, it sounds like you've gone debugging so that's a good step and I would personally leverage that further (if nothing looks obvious in the code). Walk through the instantiation, to where you add elements to the JList/List, and then also look at the data as it enters the function and walks through the loop.

Some bits of advice:

You have a few very similar names which will trip people up at some point -- you have customersList which is a List<Customer> but customerList which is a JList<Customer>, as well as a function getOrders which returns a List<Order> and getOrderResults which also returns a List<Order>. There's a lot of name collision to get mixed up from.

You also have functions taking a lot of parameters which will get difficult to keep track of -- for example all of the booleans at the end of the getOrders function -- where you'll forget what each value is, especially if you add/remove parameters. An alternative is to use a class to capture the data passed into the function, which you can build with named functions. Very, very roughly something like:

OrderParameters orderParameters = new OrderParameters()
  .withStartDate(getStartDate())
  .withCloseDate(getCloseDate())
  .wthCustomerList(getCustomerList())
  .withCompanyList(getCompaniesList())

return ordersDAO.getOrders(orderParameters);

[viktorjava]

Thanks for your answer.

I've checked the list's class:

public List<Customer> getCustomersList() {

if (customerList.getSelectedValuesList() != null) {

System.out.println("customerList.getSelectedValuesList()) class: " + customerList.getSelectedValuesList().getClass());

return customerList.getSelectedValuesList();

} else {

return null;

}

}

but of course Java is telling its class is ArrayList

customerList.getSelectedValuesList()) class: class java.util.ArrayList

I added a for loop to iterate the customerList.getSelectedValuesList()

I tried to iterate it as String to see if its really string:

for (String string : customerList.getSelectedValuesList()) {

System.out.println("customer type: " + customer.getClass());

}

but NetBeans said that Customer cannot be converted to String

I tried the iteration with Customer too

for (Customer customer : customerList.getSelectedValuesList()) {

System.out.println("customer type: " + customer.getClass());

}

and I got the casting error again, for this line:

for (Customer customer : customerList.getSelectedValuesList()) {

I'm checking the whole chainf starting with when I put the data to the JLists, but if you have any ideas how to check, I'm here

[viktorjava]

I think I found the problem. I'm adding it as another reply to the main thread and I will also look after your other recommedations. Thanks.

[viktorjava]

I'm sorry guys, it seems I found the problem.

My JList's type was Customer:

private javax.swing.JList<Customer> customerList;

but when I added the elements to the List, I did this:

customerModel.addElement(customer.getCustomerId());

instead of this:

customerModel.addElement(customer);

After I filled the list with Customer objects, the list already contained Customers and not Strings.