The Google Web Toolkit (GWT) is a toolkit to develop Ajax web application with Java. Once the Java code is finished, the GWT compiler translates the Java code into HTML and Javascript. The compiler creates browser specific HTML and JavaScript to support all the major browsers correctly. GWT supports a standard set of UI widgets, has build in support for the browser back button and a JUnit based test framework.

GWT provides two modes

GWT applications are described as so-called modules. A module "modulename" is described by a configuration file "modulename.gwt.xml". Each module can define one or more Entry point classes. An entry point in GWT is the starting point for a GWT application similar to the main method in a standard Java program.

The module is connected with an HTML page, which is called "host page". The code for a GWT web application executes within this HTML document. The HTML page can define "div" containers to which the GWT application can assign UI components. Alternatively the GWT UI components can be assigned to the body of the HTML page.

The look and feel of a GWT application can be customized via CSS files. Each widget in GWT can be given a div container by using the method setStyle(String s); We will see later how this is used.