Hi Chris, On Mon, 23 Nov 2009 12:06:18 +0000 (UTC) Chris Miller <chris.miller@kbcfp.com> wrote:
MB> But does it increase the size of a Coord? I admit to not having MB> actually measured the size but I've added a boolean to an object MB> that already contains a boolean. If the Java implementers are smart MB> they would be stored as single bits rather than bytes/shorts/words. MB> Perhaps someone who knows about this could comment.
I haven't looked at the code/patch in question, however in most/all the VMs I'm aware of a boolean will use 4 bytes (same as an int). Multiple booleans aren't packed, unless they're stored in an array (where they're packed one per byte). There's also the possibility of word alignment causing additional bytes to be wasted, but that depends on whether it's a 32 or 64 bit VM, and the number and types of other fields in the same class.
If you need to pack bits as tightly as possible there's java.util.BitSet, but that only starts to make sense if you have a large number of booleans. If you only have a few of them, custom bit manipulation would be required to mimise the memory impact.
java version "1.6.0_16" Java(TM) SE Runtime Environment (build 1.6.0_16-b01) Java HotSpot(TM) 64-Bit Server VM (build 14.2-b01, mixed mode) Just tried a quick test and on an Intel box I am seeing 1 byte per boolean, not 4. As the object sizes are rounded to multiples of 8, it looks like a case of buy one, and get 7 for free! Cheers, Mark