J2ME in a Nutshell

The MIDP Java Platform

The Java platform available to MIDlets is that provided by CLDC as described in Chapter 2, together with a collection of MIDP-specific packages arranged under the javax.microedition package hierarchy. The core libraries themselves are almost unaffected by the MIDP specification; the only change is the addition of the J2SE 1.3 timer facility in the java.util package, which will be covered in Section 3.5.4. The MIDP specification also places the following requirements on the core libraries:

• Like applets, MIDlets are managed in an execution environment that is slightly different from that of a Java application. As you’ll see shortly, the initial entry point to a MIDlet is not the main( ) method of its MIDlet class, and the MIDlet is not allowed to cause the termination of the Java VM. In order to enforce this restriction, the exit( ) methods in both the System and Runtime classes are required to throw a SecurityException if they are invoked.

• In addition to the system properties defined by CLDC, MIDP devices must set the microedition.locale property to reflect the locale in which the device is operating. The locale names are formed in a slightly different way from those used by J2SE, because the language and country components are separated by a hyphen instead of an underscore character. A typical value for this property would be en-US on a MIDP device, whereas a J2SE developer would expect the locale name in the form en_US. Since both MIDP and CLDC provide almost ...