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J2ME Gets Personal
Create applications using the new J2ME Personal Profile, and find out how it relates to MIDP, PersonalJava, and J2SE
by David Hemphill

Until recently, developing J2ME applications meant putting Java on a cell phone or a pager using the mobile information device profile (MIDP). Personal Profile, a new Java 2 Platform, Micro Edition (J2ME) profile, however, opens up J2ME to a broad spectrum of devices and markets including Pocket PCs and communicator-class devices such as the Nokia 9290, as well as Internet appliances such as screen phones and TV set top boxes. Although Personal Profile has its origins in PersonalJava, its feet are firmly planted in the J2ME architecture.

Let's see how the Personal Profile relates to PersonalJava, MIDP, and Java 2 Platform, Standard Edition (J2SE), and how you can use the APIs and create Personal Profile applications.

J2ME Fundamentals
PersonalJava was created a few years ago to support Java on Pocket PC and other handheld devices. It was based on a branch of the Java Development Kit (JDK) 1.1.8 code base, but did not evolve past this point—until now. Personal Profile is the successor to PersonalJava and is backward compatible with the PersonalJava 1.2a specification. Personal Profile, however, introduces much more than just a new and improved PersonalJava. Personal Profile is based on the broader J2ME architecture, which includes the ability to move code between more limited devices (such as a PalmOS device) and more powerful devices (such as a Pocket PC) with little or no modification. This is possible because J2ME defines a core set of APIs at a basic level and builds on them in what are referred to as configurations and profiles.

Figure 1. Connected Devices

Configurations are the most basic layer of J2ME and define the requirements of the virtual machine. Profiles extend the configurations to provide more specific functionality, such as data storage and user interface APIs. Currently, J2ME is composed of two configurations: the Connected Limited Device Configuration (CLDC) and the Connected Device Configuration (CDC). The CLDC caters to more limited devices, such as cell phones and pagers, while the CDC addresses the needs of more powerful devices such as Pocket PCs and TV set top boxes. In J2ME each configuration has its own specification. Figure 1 illustrates the relationship between the CLDC and CDC.