Updating sand simulation in grid doesn't work - processing

Question

I want to make a falling sand simulation using cellular automata, but when I update it, nothing happens, and when I want to do a line of diffrent material using lineDrawing() this material appear in random cells. This is update code:
void update()
{
for (int i = verticalNumberOfCells - 1; i > 0; i--)
{
for (int j = 0; j < horizontalNumberOfCells; j++)
{
world[j][i].update(false);
}
}
for (int y = verticalNumberOfCells - 1; y > 0; y--)
{
for (int x = 0; x < horizontalNumberOfCells; x++)
{
if (world[x][y].hasMoved) continue;
if (world[x][y].state == 0 && world[x][y].state == 1) continue;
if (canMove(world[x][y].state, x, y + 1))
{
move(x, y, x, y + 1);
}
}
}
}
The auxiliary functions that I use to check if the contents of a cell can change and to change the contents of a cell look like this:
boolean canMove(int state, int positionX, int positionY)
{
if (positionX < 0 || positionX >= horizontalNumberOfCells || positionY < 0 || positionY >= verticalNumberOfCells) return false;
int otherSubstance = world[positionX][positionY].state;
if (state == 5) return (otherSubstance == 4);
if (otherSubstance == 0) return true;
if (state == 2 && otherSubstance == 3 && random(1f) < 0.5f) return true;
return false;
}
void move(int fromX, int fromY, int toX, int toY)
{
Cells otherSubstance = world[toX][toY];
world[toX][toY] = world[fromX][fromY];
world[fromX][fromY] = otherSubstance;
world[fromX][fromY].hasMoved = true;
world[toX][toY].hasMoved = true;
world[fromX][fromY].velocityX = 0;
world[fromX][fromY].velocityY = 0;
if (toX > fromX)
{
world[toX][toY].velocityX = 1;
} else if (toX < fromX)
{
world[toX][toY].velocityX = -1;
} else
{
world[toX][toY].velocityX = 0;
}
if (toY > fromY)
{
world[toX][toY].velocityY = 1;
} else if (toY < fromY)
{
world[toX][toY].velocityY = -1;
} else
{
world[toX][toY].velocityY = 0;
}
}

Answer 1

I was able to fix this problem. The thing was, copying a cell in the move function didn't work. Here is the wrong version of the code:
Cells otherSubstance = world[toX][toY];
world[toX][toY] = world[fromX][fromY];
world[fromX][fromY] = otherSubstance;
and here is right version of the code:
int oldState = world[toX][toY].state;
world[toX][toY].state = world[fromX][fromY].state;
world[fromX][fromY].state = oldState;