If you've visited the BlackBerry Developer website you may have noticed that there are two recommended approaches to developing applications for BlackBerry handhelds—Java Application Development and BlackBerry Web Development. This book is focused on the Java Application Development approach, which is the more versatile of the two, but the other can be very useful in the right situation.
• Java Application Development approach: This is the most powerful approach and it creates applications written in Java that are loaded onto and executed on a BlackBerry handheld. They will be the focus of this book and are one of the most common ways to deploy an application. Two different tools exist to support this approach—the BlackBerry Java Development Environment (JDE) and the BlackBerry JDE Component Plug-in for Eclipse. Both offer the ability to create full custom applications. The BlackBerry JDE is a custom application written in Java that can be used to develop applications. The latter leverages the Eclipse Integrated Development Environment (IDE), which is a common platform for Java developers.
• BlackBerry Web Development approach: It is the other approach that runs completely within the BlackBerry Browser application and can use various standards such as HTML and AJAX. Applications created using the BlackBerry Web Development approach are similar to more common web applications and generally require network connectivity to work. More powerful features, including native API calls, aren't allowed natively but can be made using BlackBerry Widgets. BlackBerry Widgets is a separate SDK for creating small applets that can be leveraged by web applications. Overall, this approach can be powerful but it requires network connectivity, which potentially means data charges and/or delays for network communication.
Source of Information : Packt - BlackBerry Java Application Development Beginners Guide 2010