In order to understand Swing, it is first necessary to understand the infrastructure upon which it is based, the Abstract Window Toolkit, or AWT.  Java took off faster than anyone could have imagined, and the most visible of the Java APIs was suddenly thrust into the limelight. Unfortunately, the original AWT was ill prepared for such a fate.

The original AWT was not designed to be anything akin to a high-powered user interface (UI) toolkit to be used by more than a half million developers,instead, it was aimed at supporting the development of simple user interfaces for simple applets. For example, the original AWT lacked a great many features that one would expect in an object-oriented UI toolkit: clipboards, printing support, and keyboard navigation, for example, were all conspicuously absent from the AWT. The original AWT did not even include such basic amenities as popup menus or scroll panes, two staples of modern user interface development.

In addition, the AWT's infrastructure was badly flawed. The AWT was fitted with an inheritance-based event model that scaled horribly and, even worse, a peer-based architecture that was destined to become the AWT's Achilles' heel.