Java Reference
In-Depth Information
MIDP
CLDC/CDC
Symbian OS
Figure 2.1
Basic Java Micro Edition environment architecture
Figure 2.1 summarizes the architecture of the Java ME environment.
Note that Symbian OS is not a mandatory part of the Java ME environment,
but we will consider it to be so for the scope of this topic.
The MIDP application model defines what a MIDlet is, how it is
packaged, and how it should behave with respect to the sometimes
constrained resources of an MIDP device. MIDP provides an application
framework for mobile devices based on configurations such as CLDC and
CDC.
It also defines how multiple MIDlets can be packaged together as a
suite, using a single distribution file called a Java Archive (JAR). Each
MIDlet suite JAR file must be accompanied by a descriptor file called the
JAD file, which allows the Application Management Software (AMS) on
the device to identify what it is about to install.
2.2 Using MIDlets
AMIDlet is an application that executes under the MIDP. Unlike a desktop
Java application, a MIDlet does not have a
main
method; instead, every
such application must extend the
javax.microedition.midlet.
MIDlet
class and provide meaningful implementations for its lifecycle
methods. MIDlets are controlled and managed by the AMS, part of the
device's operating environment. They are initialized by the AMS and then
guided by it through the various changes of state of the application. We
look briefly at these states next.
2.2.1 MIDlet States
A state is designed to ensure that the behavior of an application is
consistent with the expectations of the end users and device manufacturer.
Initialization of the application should be short; it should be possible to
put an application in a non-active state; and it should also be possible to
