How to use an alpha channel or transparency?

Question

I'm trying to make a game and I want to have a background and on top of that sprites. But the sprites need to be transparant in some parts. I have tried with gif's and png's but nothing works. Can anybody help me?
this is my code, I don't use paint because I render actively in fullscreen exclusive mode
private void initResources() {
Image img;
gc = getGraphicsConfiguration();
try {
img = ImageIO.read( new File("c:\\test.png") );
sprite = gc.createCompatibleImage(100, 100, Transparency.TRANSLUCENT);
if ( img != null && sprite != null )
((Graphics2D)sprite.getGraphics()).drawImage( img, null, null );
catch ( IOException ioe ) {
System.err.println(ioe.toString());
private void renderFrame(Graphics2D g2) {
g2.setPaint( Color.BLACK );
g2.fillRect(0,0,800,600);
g2.drawImage( sprite, 0, 0, null );
g2.dispose();
}

Answer 1

Hm, seems like I found a partial solution myself using an AlphaComposite. Problem now is that it only works with gif's and not with a png.
private void renderFrame(Graphics2D g2) {
g2.setPaint( Color.BLACK );
g2.fillRect(0,0,800,600);
g2.setComposite( AlphaComposite.getInstance( AlphaComposite.SRC_OVER ) );
g2.drawImage( sprite, 0, 0, null );
g2.dispose();