JOL misatributes array length as gap:

> [B object internals:
> OFF SZ TYPE DESCRIPTION VALUE
> 0 8 (object header: mark) N/A
> 8 4 (object header: class) N/A
> 12 4 (array length) N/A
> 12 4 (alignment/padding gap)
> 16 0 byte [B.<elements> N/A
> Instance size: 16 bytes
> Space losses: 4 bytes internal + 0 bytes external = 4 bytes total