J2ME is aimed squarely at consumer devices with limited horsepower. Many such devices (e.g., a mobile phone or pager) have no option to download and install software beyond what was configured during the manufacturing process. With the introduction of J2ME, "micro" devices no longer need to be "static" in nature. Not unlike a web browser downloading Java applets, an implementation of J2ME on a device affords the option to browse, download and install Java applications and content.
Small consumer electronics have a way of changing our lives. Mobile phones let us communicate when away from our home or office. Personal digital assistants (PDAs) let us access email, browse the internet and run applications of all shapes and forms. With the introduction of Java for such devices, we now have access to the features inherent to the Java language and platform. That is, a programming language that is easy to master, a runtime environment that provides a secure and portable platform and access to dynamic content, not to mention an estimated developer community of over 2 million people.
Although it would be nice to have the entire J2SE Application Programming Interface (API) available on a micro device, it's not realistic. For example, a mobile phone with its limited display cannot provide all the functionality available in the Abstract Window Toolkit, the first graphical user interface released with Java. The "Micro Edition" was introduced to address the special needs of consumer devices that are outside the scope of J2SE and J2EE.
The capabilities of devices within the "Micro Edition" may vary greatly. An Internet Screenphone (a hardware device designed to provide access to email, news, online banking, etc.) may have a much larger display than a pager. However, even devices that seem similar in size may vary greatly in their capabilities. A cell phone and PDA are both limited in physical size, yet a typical cell phone may have a display with a total resolution of 12,288 pixels (96 x 128), whereas a PDA resolution may start at 20,000 pixels and go up from there.
One Java platform will most definitely not fit all. To better understand how J2ME will accommodate a broad range of consumer electronics and embedded devices, we need to introduce two new concepts, configurations and profiles.