help with image effects

hey

I have been searching the web for help on a quiet simple question, but I can’t find anything.
My problem is that I have a background-image and how I want to make a image over it with
some kind of see throu effect.
Hope somebody can help, and understands what I mean

some thing like:

Graphics2D g;

Composite old = g.getComposite();
g.setComposite(AlphaComposite.getInstance(0.5f, Alphacomposite.SRC_OVER);
//draw image
g.setComposite(old);

thanx alot it works