A lightweight component is one that subclasses java.awt.Component (or java.awt.Container) directly - implementing the look-and-feel of the component in Java rather than delegating the look-and-feel to a native peer. Lightweight components can be more efficient at utilizing system resource, they can be transparent, and they do not have to be rectangular (all of which are limitations when working with components that have a peer).
You can use JApplet to develop Applets in Swing. JApplet is a subclass of java.applet.Applet. [ January 30, 2007: Message edited by: Henrik Engert ]