Built on top of GWT’s intelligent compilation system is a cross-browser UI layer. The real magic here comes from implementing the UI elements in Java and then using a browser-specific implementation of the core DOM to build out the native browser elements as they’re needed by the higher-level Java layer. Whereas some Ajax libraries have a lot of focus on UI widgets, GWT is intended to provide a core of UI functionality that users and the community can build upon.
The GWT UI layer provides a wide variety of layout-related panels, data representation constructs such as Tree and Grid, a set of user input elements, and more. The 1.4 release of GWT began to expand the UI toolkit to include some new advanced elements, like a rich text editor and a suggest box. This release also started to include some great new optimized UI elements that draw from the power of the plugin-capable compiler, such as the ImageBundle.
p/s:- Some of the article is an excerpt taken from the book GWT In Practice written by Robert T. Cooper and Charlie E. Collins , published by Manning. Hope you guys enjoy reading it….