Programming Wireless Devices with the Java2 Platform

2.2 Java 2 Platform, Micro Edition (J2ME)

Java™ 2 Platform, Micro Edition (henceforth referred to as Java 2 Micro Edition or J2ME) specifically addresses the large, rapidly growing consumer space, which covers a range of devices from tiny commodities, such as pagers, all the way up to the TV set-top box, an appliance almost as powerful as a desktop computer. Like the larger Java editions, Java 2 Micro Edition aims to maintain the qualities that Java technology has become known for, including built-in consistency across products, portability of code, safe network delivery, and upward scalability.

The high-level idea behind J2ME is to provide comprehensive application development platforms for creating dynamically extensible, networked devices and applications for the consumer and embedded market. J2ME enables device manufacturers, service providers, and content creators to capitalize on new market opportunities by developing and deploying compelling new applications and services to their customers worldwide. Furthermore, J2ME allows device manufacturers to open up their devices for widespread third-party application development and dynamically downloaded content without losing the security or the control of the underlying manufacturer-specific platform.

At a high level, J2ME is targeted at two broad categories of products:

• "High-end" consumer devices. In Figure 2.1, this category is represented by the grouping labeled CDC (Connected Device Configuration). Typical examples of devices in this category include TV set-top boxes, Internet TVs, Internet-enabled screenphones, high-end wireless communicators, and automobile entertainment/navigation systems. These devices have a large range of user interface capabilities, total memory budgets starting from about two to four megabytes, and persistent, high-bandwidth network connections, often using TCP/IP.

• "Low-end" consumer devices. In Figure 2.1, this category is represented by the grouping labeled CLDC (Connected, Limited Device Configuration). Cell phones, pagers, and personal organizers are examples of devices in this category. These devices have simple user interfaces (compared to desktop computer systems), minimum memory budgets starting from about 128?56 kilobytes, and low bandwidth, intermittent network connections. In this category of products, network communication is often not based on the TCP/IP protocol suite. Most of these devices are battery-operated.

The line between these two categories is fuzzy and becoming more so every day. As a result of the ongoing technological convergence in the computer, telecommunication, consumer electronics, and entertainment industries, there will be less technical distinction between general-purpose computers, personal communication devices, consumer electronics devices, and entertainment devices. Also, future devices are more likely to use wireless connectivity instead of traditional fixed or wired networks. In practice, the line between the two categories is defined more by the memory budget, bandwidth considerations, battery power consumption, and physical screen size of the device rather than by its specific functionality or type of connectivity.

Because of strict manufacturing cost constraints, the majority of high-volume wireless devices today, such as cell phones, belong to the low-end consumer device category. Therefore, this book focuses only on the CLDC and MIDP standards that were specifically designed for that category of products.