Java- basic graphics

private final static int pocetPoli = 10;


 private void naMalujCtverce(int pocetCtvercu) {
        int rozmer = getStrana() / pocetCtvercu;

        Graphics grafika = this.getGraphics();

        for (int i = 0; i <= rozmer * pocetCtvercu; i += rozmer) {
            for (int j = 0; j <= rozmer * pocetCtvercu; j += rozmer) {

                grafika.setColor(getBarva());
                grafika.fillRect(i, j, rozmer, rozmer);

                try {
                    Thread.sleep(100);
                } catch (InterruptedException ex) {
                    Thread.currentThread().interrupt();
                }
            }

        }

    }

    private int getStrana() {
        return Math.min(this.getWidth(), this.getHeight());
    }

    private Color getBarva() {
        Random rand = new Random();

        float r = rand.nextFloat();
        float g = rand.nextFloat();
        float b = rand.nextFloat();

        return new Color(r, g, b);
    }

    @Override
    public void paint(Graphics g) {
        super.paint(g); //To change body of generated methods, choose Tools | Templates.
        naMalujCtverce(pocetPoli);
    }