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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.
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 phones. 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 has also been used at mobile banking services since 2006. Lack of security of the handsets and limited time, Java ME provides two factor authentication and one click access to the banks' servers. Simply after downloading the application it's being personolised with a symmetric activation key. This key provides second authentication factor of the end user. Java ME applications are also used as an one times password tools to access securely to any site.
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 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 Java ME Connected Device Configuration (CDC) profile. This profile is intended to be used by devices requiring a complete implementation of the Java virtual machine up to and including the entire Java Platform, Standard Edition API. Typical implementations will use some subset of that API set depending on the additional profiles supported. This document describes the facilities that the Foundation Profile provides to the device and other profiles that use it. This specification was developed under the Java Community Process.
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 the platforms J2ME targets. Creating J2ME jar files is done with solutions like learning mobile author to make create once publish many possible. 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.
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
Notes
- ^ http://forum.java.sun.com/thread.jspa?threadID=408223
References
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