public class Window {

    public static final int WIDTH = 307, HEIGHT = 630;
    private JFrame window;
    private Board board;

    public Window(){
        window = new JFrame("Tetris Game");
        window.setSize(WIDTH, HEIGHT);
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setResizable(false);
        window.setLocationRelativeTo(null);

        board = new Board();
        window.add(board);

        window.setVisible(true);
    }



    public static void main(String[] args) {
        new Window();
    }
}


public class Board extends JPanel {

    public Board(){

    }

   @Override
    public void paintComponents(Graphics g) {
       g.setColor(Color.RED);
       g.fillRect(0, 0, 300,600);
    }
}