Typecast a ArrayList.toArray() in Java to normal array

Question

I'm having some trouble to do the following:

int[] tmpIntList = (int[])MyArrayList.toArray(someValue);

MyArrayList contains only numbers. I get a typecast error since ArrayList only returns Object[] but why isnt it possible to turn it into a int[] ?

what do you need it for? Collections are best kept as Collection classes... unless there is a need to optimise, but then you have to be sure that you are not optimising prematurely (an ArrayList is almost as fast an an array) — Robert
– Robert, Commented May 20, 2010 at 11:05
Thats correct, but in this case I need to have a int[] to return for another function that only takes int[]. (not built by me) — Marthin
– Marthin, Commented May 20, 2010 at 11:36

Jon Skeet · Accepted Answer · 2010-05-20 10:54:01Z

4

An ArrayList can't contain int values, as it's backed by an Object[] (even when appropriately generic).

The closest you could come would be to have an Integer[] - which can't be cast to an int[]. You have to convert each element separately. I believe there are libraries which implement these conversions for all the primitive types.

Basically the problem is that Java generics don't support primitive types.

answered May 20, 2010 at 10:54

Jon Skeet

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Bozho · Accepted Answer · 2010-05-20 10:59:20Z

3

ArrayUtils.toPrimitive(..) will do the conversion between Integer[] and int[], if you really need it. (apache commons-lang)

So:

int[] tmpIntList = ArrayUtils.toPrimitive(MyArrayList.toArray(someValue));

answered May 20, 2010 at 10:59

Bozho

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ponzao Over a year ago

Upvoted for giving Commons Lang as a solution, it has a utility method for pretty much everything you can think of.

Parth · Accepted Answer · 2010-05-20 11:17:45Z

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Rather then including apache-commons for only this single method call, you can use Integer[] .

@Bozho , thanks mate for this suggestion.

answered May 20, 2010 at 11:17

Parth

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