Hello, I'm new to processing, but have been using arduino for awhile now, but I can't understand what is wrong with this program.

the program is supposed to take a goal position, store it as 0, and take each position around it one number higher. like...
2123456
1012345
2123456
3234567
it stores obsticles as -2 and the unmapped areas as -1
heres the part of the code that has the problem.

void plot() {
 for (int i = 0; i < col; i++) {
   for (int j = 0; j < row; j++) {
     ways[i][j] = -1;
   }
 }
 refresh();
 ways[gx] [gy] = 0;
 for (int z = 0; ways[ox] [oy] == -1; z++) {
   for (int i = 0; i < col; i++) {
     for (int j = 0; j < row; j++) {
       if (ways[i] [j] == z) {
         if (ways[i-1] [j] == -1) {
           ways[i-1] [j] = z+1;
         }
         if (ways[i+1] [j] == -1) {
           ways[i+1] [j] = z+1;
         }
         if (ways[i] [j-1] == -1) {
           ways[i] [j-1] = z+1;
         }
         if (ways[i] [j+1] == -1) {
           ways[i] [j+1] = z+1;
         }
       }
     }
   }
 }
}


and the error...

Exception in thread "Animation Thread" java.lang.ArrayIndexOutOfBoundsException: 20
     at plotter.plot(plotter.java:61)
     at plotter.mouseReleased(plotter.java:44)
     at processing.core.PApplet.handleMouseEvent(PApplet.java:1611)
     at processing.core.PApplet.dequeueMouseEvents(PApplet.java:1544)
     at processing.core.PApplet.handleDraw(PApplet.java:1436)
     at processing.core.PApplet.run(PApplet.java:1327)
     at java.lang.Thread.run(Thread.java:619)

ox and oy is the x and y cordinates of the object that needs to move to the goal.  gx and gy is the x and y position of the goal.  thanks for the out of bounds comment.  I'll try that.