help with temporay variables

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aDeamon - 23 May 2007 15:35 GMT

When I do this
char[][] board;
// here I have some code placing data into board

// later I do this in another method that takes the former board as a
input
char[][] tmpBoard = board;
for(Point p : HashSet<Point>) {
tmpBoard[p.x][p.y] = EMPTY;
}

For some reson both board AND tmpBoard has been changed and looks the
same. I would expect only tmpBoard to have changed - am I wrong?

/Sam

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Lew - 23 May 2007 15:59 GMT

> When I do this
> char[][] board;
[quoted text clipped - 9 lines]
> For some reson both board AND tmpBoard has been changed and looks the
> same. I would expect only tmpBoard to have changed - am I wrong?

Yes. Variables in Java (except primitives like int) are pointers to objects,
not objects themselves. tmpBoard and board both point to the same array;
you're not changing "tmpBoard", you're changing the object to which "tmpBoard"
points, which is the same as the object to which "board" points.

board --->{array in memory}
tmpBoard ---^

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Lew

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aDeamon - 23 May 2007 16:16 GMT

> > When I do this
> > char[][] board;
[quoted text clipped - 20 lines]
> --
> Lew

Tanks it help to create a new variable.

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aDeamon - 23 May 2007 16:17 GMT

> > When I do this
> > char[][] board;
[quoted text clipped - 20 lines]
> --
> Lew

Tanks it help to create a new variable.

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aDeamon - 23 May 2007 16:17 GMT

> > When I do this
> > char[][] board;
[quoted text clipped - 20 lines]
> --
> Lew

Thanks it help to create a new variable.

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Ian Shef - 14 Jun 2007 21:21 GMT

aDeamon <stud1980@hotmail.com> wrote in news:1179930938.868379.56420
@q69g2000hsb.googlegroups.com:

> When I do this
> char[][] board;
[quoted text clipped - 11 lines]
>
> /Sam

I don't see any other replies to this one, so I will take a shot at it.
You are wrong.

The line
tmpBoard = board
does NOT copy the contents of an array from one place to another.
'board' references (points to) an array, and now 'tmpBoard' references
(points to) the SAME array. Changes to one are changes to the other because
there is NO other, they reference the same thing.

You need to allocate an array for 'tmpBoard' and use loops to copy from
'board' to 'tmpBoard'. You could also use java.lang.System.arraycopy(...)
but it may not help much because your arrays have multiple dimensions.

Signature

Ian Shef 805/F6 * These are my personal opinions
Raytheon Company * and not those of my employer.
PO Box 11337 *
Tucson, AZ 85734-1337 *

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help with temporay variables

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