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Java 2ME


Java 2MEJava Platform, Micro Edition or Java ME (formerly referred to as Java 2 Platform, Micro Edition or J2ME), is a collection of Java APIs for the development of software for resource constrained devices such as PDAs, cell phones and other consumer appliances. Java ME is formally a specification, although the term is frequently used to also refer to the runtime implementations of the specification. Java ME was developed under the Java Community Process as JSR 68. The evolution of the platform has abandoned the umbrella Java Specification Request in favor of separate JSRs for the different flavors of Java ME.

Java ME was designed by Sun Microsystems and is a replacement for a similar technology, PersonalJava. Note that Sun only provides a reference implementation and that most work targeting a non-Intel-based small device will require a vendor-supplied JVM to be available on the device.

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.

Sun Microsystems 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, in stark contrast to the numerous binary implementations it provides for the full Java platform standard on server and workstation machines. One of the notable omissions 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.

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.

A profile is a superset of a configuration, of which there are currently two: Connected Limited Device Configuration and Connected Device Configuration.

The 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.

Designed for cell phones, MIDP 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.

The Information Module Profile (IMP) is a Java ME 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.

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

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