A heavyweight component is one that is associated with its own native screen resource (commonly known as a peer). A lightweight component is one that "borrows" the screen resource of an ancestor (which means it has no native resource of its own -- so it's "lighter").

As we know the original AWT (1.0), used the underlying Window Tool Kit for UserInterface (i.e., native screen resource) where as subsequent versions and Swing components do not use the native resources. Each part of the Swing component is fully developed in Java and hence Swings components are light weight components.

I must say, it is all confusing since you get pages like Java Foundation Classes and then Painting in AWT and Swing which contradict on what is what!

Swing was developed based on the AWT architecture. A significant benefit of such layering was that it greatly facilitates porting AWT-component programs to Swing. In fact, because both the AWT and Swing component sets use the same AWT infrastructure, it is possible to mix both kinds of components in the same program.

But not exactly.