NEED JAVA GRAPHICS HELP

I have 3 classes and everything seems to be right but the program doesn't show anything!
WHen I compile it, a new 1000 x 700 panel is shown, but nothing is drawn on the screen!
(My paint method is render() )
Thanks for help! :)

Main class:

    public class Main extends Canvas implements Runnable {

        public static final int WIDTH = 1000, HEIGHT = 700;
        public static boolean running = false;
        public Thread gameThread;

        public int grassX = -2000, grassY = -1400;

        //private Object obj
        private Background bg;

        public void init()
        {
            //obj = new Object();
            //this.addKeyListener(obj);
            bg = new Background();

        }

        public synchronized void start()
        {
            if(running)return;
            running = true;
            gameThread = new Thread(this);
            gameThread.start();
        }

        public synchronized void stop()
        {
            if(!running)return;
            running = false;
            try {
                gameThread.join();
            } catch (InterruptedException e) {e.printStackTrace();}
        }

        public void run()
        {
            init();
            long lastTime = System.nanoTime();
            final double amountOfTicks = 60D;
            double ns = 1000000000 / amountOfTicks;
            double delta = 0;

            while(running)
            {
                long now = System.nanoTime();
                delta += (now - lastTime) / ns;
                lastTime = now;
                if(delta >= 1)
                {
                    tick();
                    //COUNTERS HERE

                    //COUNTERS END
                    delta--;
                }
                render();
            }
        }
        public void tick()
        {

        }

        public void render()
        {
            BufferStrategy bs = this.getBufferStrategy();
            if(bs == null)
            {
                createBufferStrategy(3);
                return;
            }

            Graphics g = bs.getDrawGraphics();
            //RENDER
            bg.render(g);
            //END RENDER
            g.dispose();
            bs.show();
        }

        public static void main(String[] args)
        {
            Main game = new Main();
            game.setPreferredSize(new Dimension(WIDTH, HEIGHT));
            game.setMaximumSize(new Dimension(WIDTH, HEIGHT));
            game.setMinimumSize(new Dimension(WIDTH, HEIGHT));

            JFrame frame = new JFrame("Game");
            frame.setSize(WIDTH, HEIGHT);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setResizable(false);
            frame.add(game);
            frame.setVisible(true);

            game.start();

        }

    }

Background class:

public class Background {

    public static int grassX = -2000, grassY = -1400;

    public void render(Graphics g)
    {
        Tiles.grass(g);
    }

}

Tiles Class:

public class Tiles {

    public static void grass(Graphics g)
    {
        while(Background.grassY <= 2800 + 700)
        {
            while(Background.grassX <= 5000)
            {
                g.setColor(new Color(0, 232, 0));
                g.fillRect(Background.grassX, Background.grassY, 10, 10);
                g.setColor(new Color(0, 128, 0));
                g.drawRect(Background.grassX, Background.grassY, 10, 10);
                Background.grassX += 10;
            }
            Background.grassY += 10;
        }
    }

}