c.toArray might (incorrectly) not return Object[] (see 6260652) (original) (raw)

David Holmes - Sun Microsystems David.Holmes at Sun.COM
Fri May 22 12:05:30 UTC 2009

Doug Lea said the following on 05/22/09 21:56:

Sorry; I should have been clearer about why c.toArray(new Object[c.size()]) is subtly wrong here. ArrayList.size must equal the number of elements, which might be different than the array size. If c's size shrinks at an inconvenient moment during the call, then we might think that the trailing null, that toArray(T[] a) is required to append if a is too big, is actually a (null) element of the collection.

Ah I see.

I'm thinking though that I'd find this hack more aesthetically pleasing:

static final Object[] ZERO_ARRAY = new Object[0]; ... elementData = c.toArray(ZERO_ARRAY);

this deals with the size issue, gets the right type and only creates one array (asuming the collection doesn't concurrently grow).

Cheers, David

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