Review Request: 7088913/7088952 : Additions to primitive wrappers (original) (raw)

David Holmes david.holmes at oracle.com
Thu Sep 22 10:04:23 UTC 2011

On 22/09/2011 7:40 PM, Ulf Zibis wrote:

Yep, not easy to make a right decision here.

One if the questions might be, if SIZE/BYTES are meant as resolution (2**SIZE = number of distinct values) or as memory usage. I would say: SIZE should be meant as resolution, but BYTES as memory usage. This would add additional value to the new introduced constant. So: Boolean.SIZE = 1 Boolean.BYTES = 4 (8 for 64-bit build)

I can support the SIZE == resolution position.

But BYTES can't mean "memory usage" as that is totally VM dependent and also has platform dependencies, and is not a constant as such due to the way different fields can be packed together.

The constants are Java language constants, not VM related, so I think that both SIZE and BYTES have to be resolution. Which still means to me that for boolean BYTES is ambiguous enough to be worth leaving out.

... At the VM level they map to ints. This is not always true. Arrays of byte are mapped to byte[] in VM. For boolean, it's theoretically possible to map a boolean[32] to one int.

According to the VM spec booleans map to ints (Ref 3.11.1). But the VM's native representation could use bit-fields for booleans.

For that matter I'm not sure the addition of BYTES is worth the effort. Yes or not, I'm unsure. My first feeling was, there must be some additional APIs to justify the change to a new release, here 8. ;-)

I'm tempted to make a tongue-in-cheek comment about adding lambdas, but I'll resist the temptation ;-)

But I think, it's reasonable to have a short cut when calculating the footprint of some data, instead repeating SIZE/Bytes.SIZE in code.

But given that you can't calculate "footprint" this way the point seems somewhat moot.

Cheers, David

hat

said, there should be a clear definition, if BYTES is meant as VM-memory-footprint or persistent-storage-footprint e.g. by serialization, or we should have three: MEMBYTES ARRAYMEMBYTES SERIALIZATIONBYTES

-Ulf

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