Java 2 Micro Edition (J2ME) A t the JavaOne Conference in June 1999, Sun Microsystems announced a new edition of the Java 2 platform: the Java 2 Micro Edition (J2ME). The purpose of the Micro Edition is to enable Java applications to run on the smallcomputing devices that we discussed in the first chapter. Although the J2ME announcement was interesting, what really caused a stir was the preliminary release of a new Java virtual machine (JVM) that could run simple Java programs on Palm devices. The initial frenzy …

Introducing the Micro Edition Sun Microsystems’ Web site describes J2ME this way: . . . Java 2 Platform, Micro Edition is a highly optimized Java runtime environment targeting a wide range of consumer products, including pagers, cellular phones, screen- phones, digital set-top boxes and car navigation systems. The key phrase from this description is “highly optimized Java runtime environment.” We must emphasize that J2ME does not define a new kind of Java but instead adapts Java for consumer products that incorporate or are based on some kind of small computing device. A Java application written for the Micro Edition will also work with the Standard Edition and even the Enterprise Edition, assuming the APIs it uses are available in each edition. There are constraints, but the architecture of Java never changes. Writing Java code that runs unchanged in all three editions is possible. Cross-edition portability is not normally a requirement, however, because what you are really interested in is cross-device portability. In other words, will the application work correctly on a specific set or family of devices? Let’s look at some of the key features of J2ME and see why the answer to this question is a simple but resounding yes. A New Virtual Machine The Java 2 Standard Edition (J2SE) platform currently supports two differentvirtual machines: the so-called classic virtual machine and the newer HotSpot virtual machine. Swapping out the classic virtual machine and replacing it with a HotSpot virtual machine gives J2SE programs an immediate and measurable performance boost without making any other changes to the runtime environment. If a new virtual machine can be designed from the ground up in order to boost performance, why not design a virtual machine to run in a constrained environment? That is exactly what J2ME does with the KVM, which is short for Kuaui VM (an early name). The KVM is a completely new implementation of a Java virtual machine, an implementation optimized for use on small devices. The KVM accepts the same set of bytecodes (with a few minor exceptions) and the same class-file format that the classic virtual machine does. We will discuss the KVM in greater detail shortly.

Download Java 2 Micro Edition (J2ME) Specifications.Pdf