Transparent vs Opaque pixels

Hi Ranchers,

I read in this webpage that below two are differences between a light weight component / heavy weight component.

A lightweight component can have transparent pixels; a heavyweight is always opaque.
A lightweight component can appear to be non-rectangular because of its ability to set transparent areas; a heavyweight can only be rectangular.

Could you please share your thoughts on the texts in bold in the above quote.
1. What is a transparent pixel, how it will appear on the GUI screen.
2. What is opaque
3. What is the meaning of appearing non-rectangular and rectangular.

Thanks much!

Maybe this article on Painting will help you: http://java.sun.com/products/jfc/tsc/articles/painting/index.html

Thanks Rob Camick... that was really useful and what I was exactly looking for.

Is there a webpage that lists all such good articles by Sun? A navigation page that lists good articles such as like Heavyweight & lightweight and Painting Article will be good.

If you can choose the right keywords, Google usually finds what you were looking for. I haven't even bookmarked those pages, but I'm always able to find them when I need them.