(Redirected from J2ME)
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 Java ME 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,
Microsoft, and others, as expensive system-specific hardware and kits are required.
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 ''configuration''s, 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
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 targeted 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 targeting 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
★
BREW
★
JSR-82
★
Smartphone
★
Mobile development
★
Mobile games
★
Location-based game
★
International Mobile Gaming Awards
Notes
1. See the phoneME (project page) for more information.
2. http://forum.java.sun.com/thread.jspa?threadID=408223
References
★
JSR 232: Mobile Operational Management An advanced OSGi technology based platform for mobile computing
★
JSR 291: Dynamic Component Support for Java SE - Symmetric programming model for Java SE to Java ME JSR 232
External links
★
The Source for Java ME Developers (Java ME Homepage)
★
Open source Mobile & Embedded Community
★
JSR 68
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