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Re: number to byte[]

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On 10/17/2015 11:45 PM, Eric Sosman wrote:
> On 10/17/2015 5:03 PM, Askfor wrote:
>> On 10/17/2015 02:03 PM, Eric Sosman wrote:
>>> On 10/17/2015 4:02 AM, Askfor wrote:
>>>> I am trying to get 4 byte[] representation of an integer, which
>>>> might be
>>>> 32 bit long.
>>>>
>>>> Obviously, I could AND with 255 and take byteValue(), then shift 8
>>>> times
>>>> to the right and repeat the process 3 times. Is there any more elegant
>>>> way ?
>>>
>>>      I can't think of one, off-hand.
>>>
>>>      But *why* do you want this four-byte array?  Are you planning to
>>> write it to some output destination?  If so, perhaps you should use a
>>> DataOutputStream (or other DataOutput implementation) and call its
>>> writeInt() method.  Or, perhaps you should use an IntBuffer.  What
>>> are you trying to do?
>>>
>>
>> It is going to be a part of a data header, which needs to be of fixed
>> length. Also it will contain a value of an offset which cabn't be longer
>> than 32-bits. So, I don't care how big int actually is, as long as it is
>> big enough to hold 32 bit unsigned value.
>
>      It's probably simplest just to read and write the int directly,
> letting the stream (or buffer) take care of assembling and disassembling
> the bytes.  Classes that implement DataOutput and DataInput already have
> the necessary machinery, provided you want BigEndian byte order.  If you
> need LittleEndian, I think you can manage it with a Buffer.
>
>      (I didn't mention it before, but RandomAccessFile can also read and
> write BigEndian integers.)
>
>> I started with serialization, too, but I realized it won't work.
>
>      I didn't suggest serialization.  Perhaps you've confused DataOutput
> with ObjectOutput; they are not the same.
>

I understand that, but then I will have to what the int is 32 bit. I am 
not sure that int is 32-bit on all platforms and all VM's . I need 
exactly 4 bytes to be written and read. Endian-ness wouldn't matter if
I could only be sure that int is 32-bit always. Java tutorial at 
Oracle's site says that int is 32-bi 'by default', which I understand
as 'unless someone has different implementation'.

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number to byte[] Askfor <askfor@nowhere.net> - 2015-10-17 10:02 +0200
  Re: number to byte[] Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-10-17 08:03 -0400
    Re: number to byte[] Askfor <askfor@nowhere.net> - 2015-10-17 23:03 +0200
      Re: number to byte[] Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-10-17 17:45 -0400
        Re: number to byte[] Askfor <askfor@nowhere.net> - 2015-10-18 12:13 +0200
          Re: number to byte[] Askfor <askfor@nowhere.net> - 2015-10-18 12:44 +0200
            Re: number to byte[] Lew <lewbloch@gmail.com> - 2015-11-29 23:07 -0800
          Re: number to byte[] Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-10-18 08:40 -0400
      Re: number to byte[] Nigel Wade <nmw@ion.le.ac.uk> - 2015-10-19 10:43 +0100
        Re: number to byte[] Wayne <nospam@all.invalid> - 2015-10-20 00:45 -0400
        Re: number to byte[] Kevin McMurtrie <mcmurtrie@pixelmemory.us> - 2015-10-20 13:35 -0700
  Re: number to byte[] Lothar Kimmeringer <news200709@kimmeringer.de> - 2015-10-25 10:22 +0100

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