ArrayList size of elements

  • Thread starter Thread starter NoLongerMicah
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NoLongerMicah

Does anyone know how the ArrayList works in regards to sizing of
elements? What I mean is if you add 1,000 byte values to an
ArrayList does that mean that the ArrayList is then 1,000 bytes long
- or does it store each byte as a generic "object" - thus storing it
as a 4 bytes each??
 
NoLongerMicah said:
Does anyone know how the ArrayList works in regards to sizing of
elements? What I mean is if you add 1,000 byte values to an
ArrayList does that mean that the ArrayList is then 1,000 bytes long
- or does it store each byte as a generic "object" - thus storing it
as a 4 bytes each??
Click to expand...

Actually, you'd end up taking more than that - 4 bytes for the actual
value, 8 bytes (IIRC) object overhead, and 4 bytes for the reference in
the ArrayList. Basically, you don't want to be doing that...
 
To answer my own question - the byte value is "boxed" - therefore for
each byte you add an "object" and a "byte" to the heap (the "object"
is a reference to the "byte" value).

So an array instance of 1,000 "bytes" would occupy 5,000 bytes on the
heap.
 
Thanks for the clarification. I wasn't thinking - didn't realize that
they store the byte as a object as well as it's reference as an
object.
 
NoLongerMicah said:
To answer my own question - the byte value is "boxed" - therefore for
each byte you add an "object" and a "byte" to the heap (the "object"
is a reference to the "byte" value).

So an array instance of 1,000 "bytes" would occupy 5,000 bytes on the
heap.
Click to expand...

You're assuming that the cost of an object is 4 bytes, and that the
byte can be stored on its own - what makes you think that? Each object
has an 8 byte header, and I believe the data itself is stored in 4 byte
blocks, so 1000 boxed bytes would actually take 12K of heap. That's
consistent with a short test program, too.
 
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