(Post 18/10/2005)

Today’s world is a wireless world. Everywhere, these days, you are bound to see people using gizmos and gadgets that are getting smaller and smaller by the day. While even ordinary folks are quite at ease handling cellular phones and pagers, the upwardly mobile have more hi-tech gadgets like PDAs (Personal Digital Assitants), Palm Pilots and Smart Phones.

Sun Microsystems have come up with yet another ace in their sleeves: the J2ME technology, which is targeted towards programming wireless devices as mentioned above. Since these devices have limited resources such as memory limitations, screen and keypad limitations, the standard Java platform cannot be used to program such devices. This is the reason why J2ME was born.

Mobile Gadgets

So what exactly is this J2ME?

J2ME, which stands for Java 2 platform, MicroEdition, is a highly optimized Java runtime environment aimed towards wireless consumer products such as pagers, mobile phones, PDAs etc.

In theory, the J2ME technology consists of a virtual machine and a set of APIs (Application Program Interface) that provide runtime environment for consumer devices. In actuality, the J2ME platform supports two different virtual machines-the standard virtual machine for 32 bit architectures, and the KVM for 16 bit or 32 bit architectures with limited memory.

The KVM earlier stood for Kuaui Virtual Machine but was later changed to KiloByte Virtual Machine. Today, however, it is more popularly known as the K virtual machine.

KVM is a completely new implementation of a Java Virtual Machine.

What does J2ME consist of?

The J2ME technology comprises of two major components-Configurations and Profiles.

A configuration is composed of the basic J2ME runtime environment and a set of core classes that capture the essential capabilities of each kind of device. It is the configuration that will specify which features of the Java language and the JVM are supported by the implementation. Currently there are two standard J2ME configurations-

• Connected Limited Device Configuration (CLDC), which is designed for hand-held consumer devices such as cellular phones, pagers
• Connected Device Configuration (CDC) which is intended for devices that can be plugged into a wall such as Internet TVs.

CLDC uses KVM while CDC uses the standard or classic virtual machine.

Some of the features of a virtual machine supporting CLDC are summarized below.

• No floating point support
• No finalization
• Limited Error handling
• No JNI
• No user defined class loaders

Since the devices on which the CLDC Library APIs (Application Programming Interface) run are limited in nature, some Java functionality has been removed or modified from the specification.

Essentially the CLDC Library APIs consist of two basic categories-

• Classes which are a subset of J2SE APIs i.e those derived from JDK1.3
• Classes specific to CLDC i.e. javax.microedition packages

A profile is a set of APIs that reside on top of a configuration to provide domain specific capabilities. As of today, the MIDP (Mobile Information Device Profile) is the only implemented profile.

Using MIDP and the J2ME platform, we can build MIDlets (which are small applications written using the J2ME platform) that work on all devices supporting MIDP. Using MIDP it is possible to create form-based applications, which can access wireless data sources and perform data manipulation just as we used to in earlier Java applications.

Many people are under the wrong impression that J2ME is a competitor to WAP. Nothing could be more wrong. J2ME could be thought of as a complementary technology to WAP using which the wireless market can be further explored. Motorola and Nokia are some of the brands offering mobile handheld gadgets supporting the J2ME platform. The Nokia 9210 Communicator is one such device that offers J2ME support.

To conclude, J2ME is definitely a technology to look out for, especially since shortly in the future, embedded devices will be entering our lives in a huge scale.

by Mamta M (Aptech Technology Group)