Hosted versus Web Mode
While developing and debugging your application, you'll be using GWT in hosted mode. When in production however, your application will be running in web mode. Think of hosted mode as training wheels for your GWT program. It's a hybrid environment unique to GWT that lets you run and debug the real Java code, while still inside a browser.
The simplest way to launch hosted mode is to run the script file created by applicationCreator. In the example, we called the project "GWTFlow," so the script to run hosted mode is called "GWTFlow-shell." This brings up the GWT development shell, which then starts your program in hosted mode inside an embedded web browser. Or, using your IDE to start the shell, you can set breakpoints, examine variables, and single step through your application just like any other Java program. A good plug-in (such as GWT Designer for Eclipse) can make this task easier, along with providing extra benefits such as WYSIWYG user interface creation.