Java ClassCastException thrown when trying to iterate through the list

Question

My code fails with a ClassCastException while running. I've tried to debug but in vain. I have declared a Class Subject with fields and am trying to load objects of that class into a list. Below is the code. It fails at the line: List items = (List)(it.next()). Adding ? for generics does not help. I guess the object is cast, though there are no generics mentioned in the List declaration. Is there a basic concept that I'm missing here?

In the below method, I'm trying to encode the data into an xml file.

 private void encodeSection(PrintStream output, Indenter indenter,
                                   String name, List list) {
            String indent = indenter.makeString();

            output.println(indent + "<" + name + "s>");

            indenter.in();
            String indentNext = indenter.makeString();

            if (list == null) {
                // the match is any
                output.println(indentNext + "<Any" + name + "/>");
            } else {
                String nextIndent = indenter.makeString();

                Iterator it = list.iterator();
                indenter.in();

                while (it.hasNext()) {
                  List items = (List)(it.next());//-------------> Error occurs
                    output.println(indentNext + "<" + name + ">");

                    Iterator matchIterator = items.iterator();
                    while (matchIterator.hasNext()) {
                        TargetMatch tm = (TargetMatch)(matchIterator.next());
                        tm.encode(output, indenter);
                    }

                    output.println(indentNext + "</" + name + ">");
                }

                indenter.out();
            }

            indenter.out();
            output.println(indent + "</" + name + "s>");
        }

    }

Stack Trace:

Exception in thread "main" java.lang.ClassCastException: SubjectID_V cannot be cast to java.util.List
    at Target_V.encodeSection(Target_V.java:71)
    at Target_V.encode(Target_V.java:41)
at com.sun.xacml.AbstractPolicy.encodeCommonElements(Unknown Source)
    at com.sun.xacml.PolicySet.encode(Unknown Source)
    at PolicyFactory_V.main(PolicyFactory_V.java:56)

You haven't posted your whole code. Also your erros are most likely because you are trying to casting one type of collection into other, which is probably not allowed. What is the type of your SubjectID_V? — ha9u63a7
– ha9u63a7, Commented Nov 6, 2014 at 10:52
You're using a lot of raw types here. Please look up what generic types are and how do you use them in List and Iterator. — Tom
– Tom, Commented Nov 6, 2014 at 10:54

Eran · Accepted Answer · 2014-11-06 10:52:21Z

2

List items = (List)(it.next()) will only work if the List you are iterating over contains just elements of type List (i.e. instances of classes implementing the List interface).

Based on the error you got, you are trying to cast an instance of type SubjectID_V to a List. You should look at the code that initializes that list. Your error might be there.

Using generic Lists may have helped you to avoid this exception, since it would have prevented the code from passing compilation in the first place.

answered Nov 6, 2014 at 10:52

Eran

395k57 gold badges726 silver badges793 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Java ClassCastException thrown when trying to iterate through the list

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related