Create random circles in a grid

Processing Coding Questions
16

But how do I do that?
I have changed the field into an array.

int[][] field = new int[cols][rows];
void drawgrid() {
  for (int i = 0; i < field.length; i++) {
    for (int j = 0; j < field[i].length; j++) {

How do I make a black diver that moves inside the array/grid?
Should i use:
int[][] diver = new int[cols][rows]; ?
Or am I thinking wrong?

So I managed to make the diver set at the location of what I want using the same formula.

boolean[][] diver = new boolean[cols][rows];
void setdiver() {
  int i = 0;
  int j = 0;
  diver[i][j] = true;
  movementdiver(i);
}

However now that movementdiver is out of keypressed() how do I make it move?
I tried calling the function in setdiver as you can see however it does not respond to keypresses this way.

void movementdiver(int i) {
  if (key == CODED) {
    if (keyCode == DOWN) {
      i = i + 1;
    }
  }