When you design an application, you can use either a Mobile Information Device Profile (MIDP) user interface (UI) application programming interface (API) or a BlackBerry UI API. However, a MIDP UI API (javax.microedition.lcdui.*) and a BlackBerry UI API (net.rim.device.api.ui.*, net.rim.device.api.ui.container.*, net.rim.device.api.ui.component.*) cannot be used together.
While designing an application, you must decide whether you want to use the MIDP or BlackBerry UI structures. The BlackBerry UI APIs are more extensive and provide rich field and screen management capabilities. The MIDP UI APIs are generic and allow applications to run on all MIDP devices.