array copy. Simple question.

Say we have:

byte buf1[] = {1, 2, 3..};
byte buf2[];

And I want to make buf2 a copy of buf1 istead to reference it.
What would buf2 = buf1 do?
How to copy from one array to another?

Thank you.

Roberto Gallo

Roberto Gallo wrote:

>
>
> Say we have:
>
> byte buf1[] = {1, 2, 3..};
> byte buf2[];

The naming convention in java prefers declaring arrays as such (notice the
position of the square braces):

byte[] buf1 = {1,2,3...};

>
> And I want to make buf2 a copy of buf1 istead to reference it.
> What would buf2 = buf1 do?

That would make buf2 just another reference to the same array buf1 is
referencing (remember, variables != objects, they are just references to an
object).

> How to copy from one array to another?
>
> Thank you.

- Iterate over the original array in a for loop, and fill the second one
with the values of the first.

- Use System.arrayCopy(), which is very fast, but as it is written in native
code, don't use it for small arrays (the overhead of calling a native
method doesn't make up for the extra speed of the actual copying of the
array).


--
Kind regards,
Christophe Vanfleteren

Christophe Vanfleteren

"Roberto Gallo" <> wrote in message
news:bv6dqm$3ff$...
>
>
> Say we have:
>
> byte buf1[] = {1, 2, 3..};
> byte buf2[];
>
> And I want to make buf2 a copy of buf1 istead to reference it.
> What would buf2 = buf1 do?
that just makes buf2 a reference to the original array
> How to copy from one array to another?
>
have a look at http://www.javapractices.com/Topic3.cjp
- it shows a number of ways including
cloning : int[] copy = (int[])aArray.clone();
using a system utility: System.arraycopy( aArray, 0, copy, 0,
aArray.length );
and a simple for loop

it also has a discussion on relative performance of the methods

> Thank you.
>
>

Pat Ryan

Roberto Gallo wrote:
> Say we have:
>
> byte buf1[] = {1, 2, 3..};
> byte buf2[];
>
> And I want to make buf2 a copy of buf1 istead to reference it.
> What would buf2 = buf1 do?

It would make the two references point to the same array (i.e., what you
don't want).

> How to copy from one array to another?

Here's one way:

buf2 = buf1.clone();

Here's another:

buf2 = new byte[buf1.length];
System.arraycopy(buf1, 0, buf2, 0, buf1.length);

--
www.designacourse.com
The Easiest Way to Train Anyone... Anywhere.

Chris Smith - Lead Software Developer/Technical Trainer
MindIQ Corporation

Chris Smith

"Roberto Gallo" <> wrote in message
news:bv6dqm$3ff$...
>
>
> Say we have:
>
> byte buf1[] = {1, 2, 3..};
> byte buf2[];
>
> And I want to make buf2 a copy of buf1 istead to reference it.
> What would buf2 = buf1 do?

This makes the variable buf2 refer to the same array object that buf1 refers
to.

> How to copy from one array to another?

buf2 = new byte [buf1.length];
buf2 = System.arraycopy (buf1, 0, buf2, 0, buf1.length);

Cheers,
Matt Humphrey http://www.iviz.com/

Matt Humphrey

"Chris Smith" <> wrote in message
news:...
> Roberto Gallo wrote:
> > Say we have:
> >
> > byte buf1[] = {1, 2, 3..};
> > byte buf2[];
> >
> > And I want to make buf2 a copy of buf1 istead to reference it.
> > What would buf2 = buf1 do?
>
> It would make the two references point to the same array (i.e., what you
> don't want).
>
> > How to copy from one array to another?
>
> Here's one way:
>
> buf2 = buf1.clone();


Except that you need to cast the result:

buf2 = (byte[])buf1.clone();
--
Dale King

Dale King

"Dale King" <kingd[at]tmicha[dot]net> wrote:
> Except that you need to cast the result:
>
> buf2 = (byte[])buf1.clone();

Right. Good catch!

--
www.designacourse.com
The Easiest Way to Train Anyone... Anywhere.

Chris Smith - Lead Software Developer/Technical Trainer
MindIQ Corporation

Chris Smith