Getting exception while using the Generic Array?

Question

I was using the following code to create a generic array of lists to mix up different types of lists:

List<Integer>[] intLists = (List<Integer>[])new List[] {Arrays.asList(1)}; 
List<? extends Object>[] objectList = intLists;
objectList[0] = Arrays.asList(1.01);
int n = objectList[0].get(0); // class cast exception!

But it gave me a cast exception. How can I work around this?

do you understand what this line does List extends Object>[] objectList = intLists; ? You are still using a List — Balaji Krishnan, May 26 '17 at 13:49
That code can't give you a ClasscastException, since it doesn't compile. — JB Nizet, May 26 '17 at 13:52

score 1 · Accepted Answer · answered May 26 '17 at 14:07

I am not sure if this gives a compile error though it apparently is creating a raw array of lists and while storing it seems the compiler cannot detect that its an array of List (it cannot detect the type of list - so perhaps it just interprets it as a raw list) and hence does not throw an error and when you try and retrieve the element into an integer it fails while trying to cast a double into an int. This is not a correct usage.

I believe you can do (Integer) listArray[0].get(0) but it will cause precision loss post the floating point.

score 0 · Answer 2 · answered May 26 '17 at 13:54

0

The type of objectList[0].get(0); is Double so you have to convert it to an int. The following works:

int n = ((Double) objectList[0].get(0)).intValue();

But depending on you use case you code is not very good.

answered May 26 '17 at 13:54

mohe2015

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2
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score 0 · Answer 3 · answered May 26 '17 at 14:00

0

You're trying to store a double value in an integer variable. You can't do that. So just store it in a double instead:

        List<Integer>[] intLists = (List<Integer>[])new List[] {Arrays.asList(1)}; 
        List<? extends Object>[] objectList = intLists;
        objectList[0] = Arrays.asList(1.01);
        double n = (double) objectList[0].get(0); // Make it a double :)

answered May 26 '17 at 14:00

Eren

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3
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If there is a requirement that it be stored as an `int`, this does not answer the question. – bradimus May 26 '17 at 14:01

Getting exception while using the Generic Array?

3 Answers3