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To develop applications using wireless Java technology, you'll need to assimilate information from several fields. You'll need to understand something about wireless communications technology, the business of wireless communications, and a lot about the Java platform. Where should you begin? This page contains a high-level overview of wireless Java technology and many links to detailed information about specific subjects. Overview of Wireless Communications Wireless communications is a huge field, encompassing everything from radio and television broadcasting through pagers, mobile phones, and satellite communications. The field of mobile phones is expanding very fast at the same time that standards and protocols are being adopted, used, updated, and sometimes discarded. The other rapidly expanding part of the wireless world is that of wireless local area networks (LANs). Driven by widespread acceptance of the IEEE 802.11 standard, wireless local networking for computers and other devices is spreading rapidly. Although wireless may seem like a special case, it is actually more intuitive and more natural than wired networking. Some day soon the need to plug a laptop into a network physically will seem quaint and antiquated. The notion that you could walk into a room with your cell phone and have it unable to interact with other devices in the room will seem unbelievably primitive. The future will reveal that wired networks are the special case. Conceptually, wireless communications can be split into two types, local and wide area. A local device is similar to a key fob with a button that unlocks a car, a 900 MHz cordless phone, a radio control toy, or a Bluetooth network. All of these devices operate over short distances, typically just a few meters. Wide area wireless devices operate effectively over a much greater area. A pager or mobile phone is a good example; you can talk on your mobile phone to any other phone on the planet. These devices' greater range relies on a trick, however: a more elaborate land-based network. A mobile phone doesn't have that much more radio power than a radio control toy. What it does have is a network of carefully placed radio antennas (cell towers); the phone can continue to operate as long as it is within range of at least one tower. The mobile phone device receives service from a wireless carrier, a company that operates the land-based network. While a number of industry consortia and standard bodies, such as the International Telecommunication Union, are trying to define or foster the development of standards for the wireless world, today's wireless world is still fragmented and complex. If you buy a mobile phone in the U.S. today, it might run on Motorola's iDEN network or Sprint's PCS network. Take it overseas to Europe and you'll be out of luck--your phone will not work with Europe's GSM network, nor will it work with the PDC network or any of the other mobile networks that live in Japan. Overview of the Java Platform The Java Platform comprises three elements:
Taken together, the Java language, Java virtual machine1, and Java APIs compose the Java platform. Moreover, the Java platform is designed to encompass a wide range of computer hardware, everything from smart cards through enterprise servers. Therefore, the Java platform comes in three flavors:
To learn much more about Java technology or the Java platform, visit http://java.sun.com/:
The Java Community Process (JCP) Specifications for Java SE, Java EE, and Java ME are developed under the aegis of the Java Community Process (JCP). A specification begins life as a Java Specification Request (JSR). An expert group consisting of representatives from interested companies is formed to create the specification. The JSR then passes through various stages in the JCP before it is finished. Every JSR is assigned a number. Java ME specifications are commonly referred to by their JSR number. Overview of Java ME Unlike Java SE, Java ME is not a piece of software, nor is it a single specification. This difference can be confusing, even for developers who are already familiar with Java SE. Instead, Java ME is a platform, a collection of technologies and specifications that are designed for different parts of the small device market. Because Java ME spans such a variety of devices, it wouldn't make sense to try to create a one-size-fits-all solution. Java ME, therefore, is divided into configurations, profiles,and optional packages. 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 configuration, for example, might be designed for devices that have less than 512 KB of memory and an intermittent network connection. The virtual machine is either a full Java Virtual Machine1 (as described in the specification) or some subset of the full JVM1. The set of APIs is customarily a subset of the Java SE APIs. A profile builds on a configuration but adds more specific APIs to make a complete environment for building applications. While a configuration describes a JVM1 and a basic set of APIs, it does not by itself specify enough detail to enable you to build complete applications. Profiles usually include APIs for application life cycle, user interface, and persistent storage. An optional package provides functionality that may not be associated with a specific configuration or profile. One example of an optional package is the Bluetooth API (JSR 82), which provides a standardized API for using Bluetooth networking. This optional package could be implemented alongside virtually any combination of configurations and profiles. The Java ME Universe Today The current universe of configurations, profiles and optional packages is shown in the diagram below. The tables immediately following provide more details about the abbreviations in the figure.  Java ME Overview
As the diagram shows, Java ME has two main branches.The first is based on the Connected, Limited Device Configuration (CLDC). This configuration is for small wireless devices with intermittent network connections, like pagers, mobile phones, and Personal Digital Assistants (PDAs). The Mobile Information Device Profile (MIDP), which is based on CLDC, was the first finished profile and thus the first finished Java ME application environment. MIDP-compliant devices are widely available. The other major branch of the Java ME tree is based on the Connected Device Configuration (CDC).
This configuration is for larger devices (in terms of memory and processing power) with robust
network connections. Set-top boxes and internet appliances are good examples of CDC devices,
although high-end PDAs like the Sharp Zaurus also fit this configuration well. The Foundation
Profile extends CDC and serves as the basis for several other profiles. It provides fundamental
APIs gleaned from Java SE, including classes and interfaces from Optional packages bubble like a froth above the CLDC and CDC branches of Java ME. These provide all sorts of capabilities ranging from Bluetooth communication through web services and instant messaging. Look in the table for links to the specifications themselves. For a thorough look at Java ME, see: The world of wireless Java technology also includes Java Card, for smart cards. For more information on Java Card, see: About Stacks and JSR 185 Devices implement a complete software stack, which usually consists of a configuration, a profile, and optional APIs. First generation Java ME mobile phones usually implemented the following software stack:  Example Java ME Stack
Given the plethora of configurations, profiles, and especially optional packages, how does a developer know what to expect on a device? JSR 185, Java Technology for the Wireless Industry, addresses this question by assembling other building blocks into a complete application environment. JSR 185 mandates CLDC 1.0 or 1.1, MIDP 2.0, and WMA. Support for MMAPI is optional. This helps nail things down for developers; on a JTWI device, the developer has a clear understanding of what APIs will be available. The following figure shows a JSR 185 stack:  JSR 185 Stack
For more information on JSR 185, see: The Scope of Wireless Java Technology Wireless Java technology is the intersection of two vast worlds, wireless data communications and the Java platform. Wireless Java technology spans parts of Java Card, Java ME, Java SE, and Java EE. That said, some common misconceptions about wireless Java technology need clearing up:
For other perspectives on wireless Java technology, select:
Why Use the Java Platform for Wireless Development? The Java platform is an excellent choice for wireless development for many reasons. Here are three compelling advantages:
The Market for Wireless Services The market for wireless applications and services is huge. This market can be divided into two segments:
Where to Go Next Perhaps the best next step toward getting a good grip on wireless Java technology is to create some:
1 As used in this document, the terms "Java virtual machine" or "JVM" mean a virtual machine for the Java platform. |
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