Appending byte[] to another byte[] array

[Bharat Bhushan]

Hi,

I need to generate random bytes for x number of times and keep appending it
to a bigger byte[] array. How can I do this ?

for (int lctr=0; lctr < main.Main.NoOfa ttributes(); lctr=lctr+1){

// This line below generates the random bits for a given length
byte[] intervals = RandomFunctions .makeRandomGene Bits(length);

biggerByteArray[] = biggerByteArray + intervals ; // this is the
idea...obviousl y this statement doesn't work for byte[]
}

Any help, pointers on web are appreciated.


Many Thanks,

- Bharat.

[Mr. J M Court]

Re: Appending byte[] to another byte[] array


"Bharat Bhushan" <bharatb@talk21 .com> wrote in message
news:xlMXa.3629 $dL4.183@news-binary.blueyond er.co.uk...[color=blue]
> Hi,
>
> I need to generate random bytes for x number of times and keep appending[/color]
it[color=blue]
> to a bigger byte[] array. How can I do this ?
>
> for (int lctr=0; lctr < main.Main.NoOfa ttributes(); lctr=lctr+1){
>
> // This line below generates the random bits for a given length
> byte[] intervals = RandomFunctions .makeRandomGene Bits(length);
>
> biggerByteArray[] = biggerByteArray + intervals ; // this is the
> idea...obviousl y this statement doesn't work for byte[]
> }
>
> Any help, pointers on web are appreciated.
>
>
> Many Thanks,
>
> - Bharat.
>
>[/color]

byte[] intervals = ...

byte[] biggerByteArray = ...

byte[] temp = new byte[intervals.lengt h + biggerByteArray .length];

for(int i=0; i< intervals.lengt h; i++) temp[i] = intervals[i];
for(int i=0; i< biggerByteArray .length; i++) temp[i + intervals.lengt h] =
biggerByteArray[i];

biggerByteArray = temp;

...but if you are doing this lots of times it is desperately inefficient.
Much better to copy into a byte[][] and then "flatten" to byte[] once you
know the size.

(i didnt bother compiling this so it may not work).

John.

[Rory Graves]

Re: Appending byte[] to another byte[] array

Mr. J M Court wrote:
[color=blue]
> "Bharat Bhushan" <bharatb@talk21 .com> wrote in message
> news:xlMXa.3629 $dL4.183@news-binary.blueyond er.co.uk...
>[color=green]
>>Hi,
>>
>>I need to generate random bytes for x number of times and keep appending[/color]
>
> it
>[color=green]
>>to a bigger byte[] array. How can I do this ?
>>
>>for (int lctr=0; lctr < main.Main.NoOfa ttributes(); lctr=lctr+1){
>>
>> // This line below generates the random bits for a given length
>> byte[] intervals = RandomFunctions .makeRandomGene Bits(length);
>>
>> biggerByteArray[] = biggerByteArray + intervals ; // this is the
>>idea...obviou sly this statement doesn't work for byte[]
>>}
>>
>>Any help, pointers on web are appreciated.
>>
>>
>>Many Thanks,
>>
>>- Bharat.
>>
>>[/color]
>
>
> byte[] intervals = ...
>
> byte[] biggerByteArray = ...
>
> byte[] temp = new byte[intervals.lengt h + biggerByteArray .length];
>[/color]

It would be better to use a System.arrayCop y for each of the arrays here:

System.arraycop y(intervals,0,t emp,0, intervals.lengt h);
System.arraycop y(biggerByteArr ay,0,temp,inter vals.length,
biggerByteArray .length);

biggerByteArray = temp;

The array copy does the same job as the for loops suggested, but is more
effecient.

Cheers

Rory

[color=blue]
> for(int i=0; i< intervals.lengt h; i++) temp[i] = intervals[i];
> for(int i=0; i< biggerByteArray .length; i++) temp[i + intervals.lengt h] =
> biggerByteArray[i];
>
> biggerByteArray = temp;
>
> ..but if you are doing this lots of times it is desperately inefficient.
> Much better to copy into a byte[][] and then "flatten" to byte[] once you
> know the size.
>
> (i didnt bother compiling this so it may not work).
>
> John.
>
>
>[/color]

[Chris]

Re: Appending byte[] to another byte[] array

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Bharat Bhushan wrote:
[color=blue]
> Hi,
>
> I need to generate random bytes for x number of times and keep
> appending it to a bigger byte[] array. How can I do this ?[/color]
[snip]

Hi,
I don't know about efficiency (John suggested using a byte[][] and
"flattening " it at the end, which is probably fairly efficient), but
for convenience, you could just create a ByteArrayOutput Stream, then
write each byte[] into it and convert it using toByteArray() at the
end. You have to catch IOExceptions, but, AFAIK, they're pretty much
"can't happen" with ByteArrayOutput Stream.
- --
Chris
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[Roedy Green]

Re: Appending byte[] to another byte[] array

On Tue, 5 Aug 2003 12:15:53 +0100, "Bharat Bhushan"
<bharatb@talk21 .com> wrote or quoted :
[color=blue]
>I need to generate random bytes for x number of times and keep appending it
>to a bigger byte[] array. How can I do this ?[/color]

see http://mindprod.com/jgloss/random.html

you can generate them a byte or int or long at a time and fill in your
array.

--
Canadian Mind Products, Roedy Green.
Coaching, problem solving, economical contract programming.
See http://mindprod.com/jgloss/jgloss.html for The Java Glossary.