BACKGROUND

Introduction to Java 2 Micro Edition

After introducing Java 2 Standard Edition (J2SE) and Java 2 Enterprise Edition (J2EE), Sun recently added the Java 2 Micro Edition (J2ME) (Sun Microsystems, 2002). J2ME is designed to run on consumer devices and electronic appliances, including wireless devices such as cell phones and Palm PDAs (Raju, 2000). J2ME provides a way to exploit the processing power on the mobile device better by running the code on the device itself. Therefore, it provides better network implementation, better graphical user interface, and local database management.

The J2ME defines the following set of tools and APIs that can be used with consumer devices:

1. Java virtual machine suitable for consumer devices

2. Libraries and APIs that are suitable for consumer devices

3. Tools for development, deployment, and device configuration

Figure 1: Java technology map

Devices implement a complete software stack , which usually consists of a configuration, a profile, and optional APIs. Current J2ME cell phones usually implement the software stack shown in Figure 2.

Figure 2: Example of J2ME stack

In the future, J2ME cell phones could implement the stack shown in Figure 3, which includes the Mobile Media API (MMAPI). The MMAPI enables playback and capture of audio and video multimedia data.

Figure 3: Example of future J2ME stack

The Java virtual machine for consumer devices is known as Kilo Virtual Machine (KVM), which is a complete Java runtime environment for small devices. KVM was designed to be small, with a static memory footprint of 40 ‚ 80 kilobytes. KVM is derived from a research system called Spotless at Sun Microsystems Laboratories.

J2ME Profiles and Configurations

J2ME is divided into configurations and profiles (Ashri et al., 2001). Configurations are specifications that detail a virtual machine and a base set of APIs that can be used with a certain class of device. A profile builds on a configuration but adds more specific APIs to make a complete environment for building applications. While a configuration describes a JVM and a basic set of APIs, it does not by itself specify enough detail to build complete applications.

Configurations

Mobile devices such as cell phones, pagers , organizers, etc., are diverse in form, functionality, and features. For these reasons, the J2ME supports minimal configurations of the Java Virtual Machine and APIs that capture the essential capabilities of each kind of device (Feng & Zhu, 2001). A J2ME configuration defines a set of horizontal APIs for a family of products that have similar requirements.

A configuration specifies:

1. the Java programming features supported,

2. the Java virtual machine features,

3. the Java libraries and APIs supported.

Currently, there is one standard configuration: the Connected Limited Device Configuration (CLDC).

Profiles

A profile is a set of vertical APIs that reside on top of a configuration to provide domain-specific capabilities. Currently, there is one profile defined and implemented, the Mobile Information Device Profile (MIDP; Sun Microsystems, 2001). Other profiles, which are in the works, include the PDA profile and the RMI profile.

Table 1 shows the current and anticipated configurations, profiles, and APIs.

Table 1: J2ME profiles and APIs

Configurations
JSR 30
JSR 139	CLDC 1.0	Connected, Limited Device Configuration
JSR 36	CLDC 1.1	Connected, Limited Device Configuration 1.1
Profiles	CDC	Connected Device Configuration
JSR 37
JSR 118	MIDP 1.0	Mobile Information Device Profile
JSR 75	MIDP 2.0	Mobile Information Device Profile 2.0
JSR 46	PDAP	PDA Profile
JSR 129	FP	Foundation Profile
JSR 62	PBP	Personal Basis Profile
JSR 134	PP	Personal Profile
APIs	‚	Game Profile
JSR 66
JSR 80	‚	RMI Optional Package
JSR 82	‚	Java USB API
JSR 120	‚	Java APIs for Bluetooth
JSR 135	‚	Wireless Messaging API
JSR 169	MMAPI	Mobile Media API
JSR 179	‚	JDBC Optional Package for CDC/FP
JSR 180	‚	Location API for J2ME
JSR 184	‚	SIP API for J2ME

Comparison With Other Technologies

Currently, there are two prevalent technologies for developing applications on cell phones:

1. SMS (Short Message Service)

2. Browser-based programming (WAP and NTT DoCoMo i-Mode)

Short Message Service (SMS)

Short Message Service allows users to send and receive text messages to and from cell phones. Originally offered in 1992, SMS initially experienced a slow adoption rate. However, since reaching the 20% market penetration rate, SMS usage has grown exponentially. The number of SMS messages has nearly doubled every half a year since 1998 (GSM Association, 2001a).

Each SMS message can contain up to 160 characters . The application is customizable using SIM toolkit technology and ideal for one-to-one or one-to-few information pushing. However, SMS is not ideal for implementing an enterprise application since it can only support simple applications. The application can only be equipped with very limited logic, mainly text processing, and does not cater to complex enterprise solutions. Also, the current messaging technology does not guarantee that the packet will arrive at a certain time. However, SMS messages are ideal for delivering small, periodic information such as stock quotes, weather info , advertising, etc.

Browser-based programming

WAP. Phone.com (now Open Wave), a merged venture with Software.com, first introduced WAP in 1995. WAP is an open standard that enables easy delivery of information and services to mobile users. WAP is intended to address the need to access the Internet from handheld devices such as cell phones and PDAs. It defines a set of standard components that enable communication between mobile terminals and network servers, including the WAP programming model. WAP has received wide support in the wireless industry.

NTT DoCoMo i-Mode. i-Mode was first introduced by NTT DoCoMo in Japan (Eurotechnology.com, 2002). This technology competes with WAP. It offers a similar mechanism to allow users to access the Internet from their wireless devices over a packet-switched network. The majority of i-Mode users are in Japan and other Asian countries .

Study of J2ME Versus WAP in Enterprise Application

J2ME and WAP are complementary technologies. J2ME is not going to replace the WAP and i-Mode technologies. Both the WAP technology and i-Mode technology are comparable to HTML and Web browsers on desktop computers, while J2ME is comparable to desktop Java applications. However, in the enterprise application situation, J2ME is found to be superior to WAP.

Limitations of Browser-Based Technology

WAP and i-Mode are limited in some ways, including:

• Network disconnections : Mobile device communication over wireless networks tends to suffer from greater occurrences of disconnections due to a variety of problems, such as limited cell coverage, loss of signal, limited battery life, etc. Current frameworks only provide partial support for disconnected operations.

• Constant airtime : WAP application requires constant airtime in order to operate . When combined with the previous point, this may cause disruptions in the application's usage. This constant airtime requirement is also economically inefficient.

• Lack of security : The infrastructure of WAP forces the information to be passed into a WAP Gateway before it is presented to a cell phone. Therefore, there is a security loophole in the architecture since the WAP Gateway is usually controlled by a third party (network carrier). In addition, security issues may arise during the translation of pages from the server to the WAP Gateway.

• Primitive user interface : The user interface for WAP-enabled sites is primitive when compared to traditional Web sites. Devices that might be capable of displaying richer graphical user interface (GUI) screens through higher screen resolution are not being exploited.

As the industry matures, users demand more secure wireless applications for mobile commerce transactions, more interactive applications such as video games , and more sophisticated applications for client/server enterprise applications (Kirkley, 2001).

Benefits of J2ME

J2ME has the following benefits:

• Local computing power : Browser-based applications can often be an adequate solution for constructing software for devices, allowing Web access with minimal configuration. However, it is more valuable to be able to exploit the device's resources more by executing code on the device's processor and using the device's memory to run the application locally.

• Multithreading : J2ME allows an application to use multithreading. This provides a mean for application developers to create a more complex logic.

• User personalization : Browser-based applications often lack the sophistication in user interface compared to applications that take greater advantage of local operating systems. This sophistication can be leveraged by J2ME with better manipulation of device-side services.

• Offline operation : J2ME provides a solution that can run on or off the network, something that a browser solution can do only in a very unsophisticated way with local browser page caching.

• Lower network usage and server load : In a WAP-based solution, the server is responsible for generating display markup. This requires a roundtrip every time the interface changes. In contrast, an MIDP client's interface is contained within the device, so it can operate even when disconnected.

• Security : J2ME offers an enhanced security model. It provides connection end-to-end from client device to company servers and does not require gateways such as in WAP.

• Connectivity with distributed system : J2ME provides a better way to talk to back-end systems. Applications written in J2ME are able to talk in XML, a language that is suitable for cross-platform and distributed system application.