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Java Platform, Micro Edition

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Java platform editions

In computing, the Java Platform, Micro Edition or Java ME (previously known as Java 2 Platform, Micro Edition or J2ME) is a specification of a subset of the Java platform aimed at providing a certified collection of Java APIs for the development of software for small, resource-constrained devices such as cell phones, PDAs and set-top boxes.

Java ME was designed by Sun Microsystems and is a replacement for a similar technology, PersonalJava. Originally developed under the Java Community Process as JSR 68, the different flavors of Java ME have evolved in separate JSRs. Sun provides a reference implementation of the specification, but has tended not to provide free binary implementations of its Java ME runtime environment for mobile devices, rather relying on third parties to provide their own.

As of 22 December 2006, the J2ME source code is licensed under the GNU General Public License, and is released under the project name phoneME.[1]

Usage

Java ME has become a popular option for creating games for cell phones, as they can be emulated on a PC during the development stage and easily uploaded to the phone. This contrasts with the difficulty of developing, testing, and loading games for other special gaming platforms such as those made by Nintendo, Sony, and others, as expensive system-specific hardware and kits are required.

Configurations and Profiles

Java ME devices implement a profile. The most common of these are the Mobile Information Device Profile aimed at mobile devices, such as cell phones, and the Personal Profile aimed at consumer products and embedded devices like Set-top boxes and PDAs.

Profiles are subsets of configurations, of which there are currently two: the Connected Limited Device Configuration and the Connected Device Configuration.

Connected Limited Device Configuration

The Connected Limited Device Configuration (CLDC) contains a strict subset of the Java class libraries, and is the minimal needed for a Java virtual machine to operate. CLDC is basically used to classify myriad devices into a fixed configuration.

A configuration provides the most basic set of libraries and virtual-machine features that must be present in each implementation of a J2ME environment. When coupled with one or more profiles, the Connected Limited Device Configuration gives developers a solid Java platform for creating applications for consumer and embedded devices.

Mobile Information Device Profile

Designed for cell phones, the Mobile Information Device Profile boasts an LCD-oriented GUI API, and MIDP 2.0 includes a basic 2D gaming API. Applications written for this profile are called MIDlets. Almost all new cell phones come with a MIDP implementation, and it is now the de facto standard for downloadable cell phone games. However, many cellphones can run only those MIDlets that have been approved by the carrier, especially in North America.

JSR 271: Mobile Information Device Profile 3 will specify the 3rd generation Mobile Information Device Profile (MIDP3), expanding upon the functionality in all areas as well as improving interoperability across devices. A key design goal of MIDP3 will be backward compatibility with MIDP2 content.

Information Module Profile

The Information Module Profile (IMP) is a profile for embedded, "headless" devices such as vending machines, industrial embedded applications, security systems, and similar devices with either simple or no display and with some limited network connectivity.

Originally introduced by Siemens Mobile and Nokia as JSR-195, IMP 1.0 is a strict subset of MIDP 1.0 except that it doesn't include user interface APIs — in other words, it doesn't include support for the Java package javax.microedition.lcdui. JSR-228, also known as IMP-NG, is IMP's next generation that is based on MIDP 2.0, leveraging MIDP 2.0's new security and networking types and APIs, and other APIs such as PushRegistry and platformRequest(), but again it doesn't include UI APIs, nor the game API.

IMP applications are called IMlets, but in reality they are MIDlets. They subclass MIDlet, and follow the same packaging, deployment, security and life-cycle as MIDlets.

Connected Device Configuration

The Connected Device Configuration is a subset of Java SE, containing almost all the libraries that are not GUI related. It is richer than CLDC.

Foundation Profile

The Foundation Profile is a headless version of Java SE.

Personal Basis Profile

The Personal Basis Profile extends the Foundation Profile to include lightweight GUI support in the form of an AWT subset.

Personal Profile

The Personal Profile is an extension of the Personal Basis Profile, and includes a more comprehensive AWT subset and adds applet support.

Implementations

Sun provides a reference implementation of the specification.

In contrast to the numerous binary implementations of the Java Platform Sun provides on server and workstation machines, Sun does not usually provide binaries for platforms J2ME is targetted at. One notable omission is for Microsoft Windows Mobile (Pocket PC) based devices, despite an open letter campaign to Sun to release a rumoured complete project "Captain America" which is such an implementation.[2]

Operating systems targetting J2ME have been implemented by DoCoMo in the form of DoJa, and by SavaJe as SavaJe OS. The latter company was purchased by Sun in April 2007 and now forms the basis of Sun's JavaFX Mobile.

See also

Notes

  1. ^ See the phoneME (project page) for more information.
  2. ^ http://forum.java.sun.com/thread.jspa?threadID=408223

References

The Wikibook Programming has a page on the topic of: J2ME
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