Java: Polymorphism and invoking methods

Question

Possible Duplicate:
Why we can't do List<Parent> mylist = ArrayList<child>();

I've a question on polymorphism and invoking methods.

My service layer signature is public void saveRules(String paramOne, String paramTwo, List<RuleDTO> rules)

My EvaluationRuleDTO extends from RuleDTO

So from my controller I attempt to perform the following:

service.saveRules(String paramOne, String paramTwo, List<EvaluationRuleDTO> rules).

But this is not allowed as it complains about List<EvaluationRuleDTO> rules not being List<RuleDTO> rules.

This does not make much sense to me. Is this a weakness in the Java language, or what concept am I missing here?

Thanks

If you read that link, it becomes clear that this is not a weakness in Java. — jahroy, Jul 23 '12 at 22:42

score 4 · Accepted Answer · edited May 23 '17 at 10:34

4

It is happening because the polymorphism is applied in the List type, not in its generics.

Edit 1: Michael posted a comment with a usefull link.

Edit 2: You can do (from Why we can't do List<Parent> mylist = ArrayList<child>();):

List<? extends RuleDTO> list = yourEvaluationRuleDTOList;

edited May 23 '17 at 10:34

Community

answered Jul 23 '12 at 22:33

davidbuzatto

OK, I get it now, makes sense. So what would be a good solution here to my problem? I think something using generics but I'm not 100% sure – DJ180 Jul 23 '12 at 22:47
@DJoyce: I complemented my post using the tip presented in the link. – davidbuzatto Jul 23 '12 at 22:50
Now I get this error: The method saveRules(String, String, List) is not applicable for the arguments (String, String, List) – DJ180 Jul 23 '12 at 22:59
Define your method like this and then use your original `List` parameter: `public void saveRules(String paramOne, String paramTwo, List rules)` – Anthony Accioly Jul 23 '12 at 23:04

1 Answers1