public void paintComponent(Graphics g) { // Draws content in the panel
        // Prepare panel for drawing
        super.paintComponent(g);
        
        g.drawRect(10, 60, 30, 100);
        g.drawRect(10,  160,  100,  30);
        g.drawRect(110, 90, 30, 100);
        g.drawRect(40, 60, 100, 30);
    }