Casting ArrayList to a Long[] Array fails with method toArray()

Asked Nov 28 '19 at 21:48

Active Nov 28 '19 at 21:48

Viewed 42 times

The following code unexpectatly throws the error shown below.

public static Long[] factorize() {
        final ArrayList<Long> returnValue = new ArrayList<>();
        return (Long[]) returnValue.toArray();
}

java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.Long;
    at primes2019.Factorization.factorize(Factorization.java:69)
    at primes2019.Factorization.main(Factorization.java:13)

asked Nov 28 '19 at 21:48

HopefullyHelpful

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There is another `.toArray(...)` method overload that you should be using. One that includes a `Long[]` parameter. – Hovercraft Full Of Eels Nov 28 '19 at 21:50
Thanks for the lightning fast help. – HopefullyHelpful Nov 28 '19 at 21:51
You're welcome -- has your problem been solved? – Hovercraft Full Of Eels Nov 28 '19 at 21:55
Yeah, just needed to add 'returnValue.toArray(new Long[0])' and now it's a 'Long[]' instead of 'Object[]' – HopefullyHelpful Nov 28 '19 at 21:55
Good deal. Note for future reference -- searching on the error message: [java arraylist toarray classcastexception site:stackoverflow.com](https://www.google.com/search?q=java+arraylist+toarray+classcastexception+site:stackoverflow.com) brought me the duplicate quickly. A search like this is a good tool to have in your arsenal. – Hovercraft Full Of Eels Nov 28 '19 at 21:57
Yeah, when my first search didn't turn up something useful I concluded the error wasn't existing in this form on the site. Everyone searches differently^^. https://stackoverflow.com/questions/4510354/java-classcastexception-ljava-lang-long-cannot-be-cast-to-java-lang-long here is the thread I found first – HopefullyHelpful Nov 28 '19 at 21:59
Indeed, thanks for sharing that. Your search was a bit too specific it looks like – Hovercraft Full Of Eels Nov 28 '19 at 22:21

Casting ArrayList to a Long[] Array fails with method toArray()

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