// See e575 The Quintessential Drawing Program
    public void paint(Graphics g) {
        Graphics2D g2d = (Graphics2D)g;
    
        // Draw background...
    
        // Set alpha.  0.0f is 100% transparent and 1.0f is 100% opaque.
        float alpha = .3f;
        g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, alpha));
    
        // Draw foreground...
    }