Hi all,

I'm having little problems here with a very simple function that stores coordinates in a global array. Everytime new coordinates are found, the old ones should be shifted towards the end of the array and the new coordinates should be stored in coords[0]. The problem is that if I store the new coordinates in [0], *every* member of the array gets reset to those new values. I figured out that the coords[0] = newcoords assignment probably passes a reference and not the actual values.

But *how* can I store an array of integers in another array without passing it by reference ? I'm pretty new to java and processing, so please forgive me if this question seems really stupid to you.

Any help is really appreciated !!

Thanks, David


The relevant code looks like this:

for (int i = 20; i>0; --i) {
 coords[i+1] = coords[i]
}
coords[0] = newcoords;

Where coords is a global array of int[20][20][2] and newcoords is int[20][2].

This behaviour can also be demostrated by this code:

int[][] globalvar = new int[2][2];

void setup() {
 noLoop();
}

void draw() {
 int[] localvar = new int[2];
 localvar[0] = 1;
 localvar[1] = 1;
 
 globalvar[0] = localvar; // Why is this passed as reference ?????
 globalvar[1][0] = 2;
 globalvar[1][1] = 2;
 println("before: " + globalvar[0][0] + " " + globalvar[1][0]);
 localvar[0] = 3;
 localvar[0] = 3;
 println("after: " + globalvar[0][0] + " " + globalvar[1][0]);
}  

output:

before: 1 2
after: 3 2

Damnit !
Hours of searching the web and trying out stupid stuff and in the end it was just my debug-routine that was wrong ! ;-)

So to sum up:
System.arraycopy(...) works quite fine for to copying multi-dimensional arrays around (by value and *not* by reference).

I'm going to bed now.

The final code then looks like this:

Code:

// populate the glob history
for (int i = histglobs-2; i>-1; --i) {
  System.arraycopy(globhist[i], 0, globhist[i+1], 0, maxglobs);
}
System.arraycopy(globcurr, 0, globhist[0], 0, maxglobs);