Java Platform, Micro Edition

Java Platform, Micro Edition, or Java ME, is a Java platform designed for embedded systems (mobile devices are one kind of such systems). Target devices range from industrial controls to mobile phones (especially feature phones) and set-top boxes. Java ME was formerly known as Java 2 Platform, Micro Edition (J2ME).

Java ME was designed by Sun Microsystems, acquired by Oracle Corporation in 2010; the platform replaced 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.

As of 2008, all Java ME platforms are currently restricted to JRE 1.3 features and use that version of the class file format (internally known as version 47.0). Should Oracle ever declare a new round of Java ME configuration versions that support the later class file formats and language features, such as those corresponding to JRE 1.5 or 1.6 (notably, generics), it will entail extra work on the part of all platform vendors to update their JREs.

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 (CLDC) and the Connected Device Configuration (CDC).[1]

There are more than 2.1 billion Java ME enabled mobile phones and PDAs.[2] It is popular in sub $200 devices such as Nokia's Series 40. It was also used on the Bada operating system and on Symbian OS along with native software. Also, there are implementations for Windows CE, Windows Mobile, Maemo, MeeGo and Android available for separate download.[3][4]

Connected Limited Device Configuration

The Connected Limited Device Configuration (CLDC) contains a strict subset of the Java-class libraries, and is the minimum amount needed for a Java virtual machine to operate. CLDC is basically used for classifying 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. The configuration is designed for devices with 160KB to 512KB total memory, which has a minimum of 160KB of ROM and 32KB of RAM available for the Java platform.

Mobile Information Device Profile

Designed for mobile phones, the Mobile Information Device Profile includes a GUI, and a data storage 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 (Final release on 09 Dec, 2009) specified 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 is 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.

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 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. This is the platform that BD-J is built upon.

Implementations

Sun provides a reference implementation of these configurations and profiles for MIDP and CDC. Starting with the JavaME 3.0 SDK, a NetBeans-based IDE will support them in a single IDE.

In contrast to the numerous binary implementations of the Java Platform built by Sun for servers and workstations, Sun does not provide any binaries for the platforms of Java ME targets with the exception of an MIDP 1.0 JRE (JVM) for Palm OS.[5] Sun provides no J2ME JRE for the Microsoft Windows Mobile (Pocket PC) based devices, despite an open-letter campaign to Sun to release a rumored internal implementation of PersonalJava known by the code name "Captain America".[6] Third party implementations like JBlend and JBed are widely used by Windows Mobile vendors like HTC and Samsung.

Operating systems targeting Java ME 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. The company IS2T provides a Java ME virtual machine (MicroJvm) for any RTOS and even with no RTOS (then qualified as baremetal). When baremetal, the virtual machine is the OS/RTOS: the device boots in Java.[7]

MicroEmu provides an open source (LGPL) implementation of an MIDP emulator. This is a Java Applet-based emulator and can be embedded in web pages.

The open-source Mika VM aims to implement JavaME CDC/FP, but is not certified as such (certified implementations are required to charge royalties, which is impractical for an open-source project). Consequently, devices which use this implementation are not allowed to claim JavaME CDC compatibility.

The linux-based Android operating system uses a proprietary version of Java that is similar, but not identical to Java Me.[8]

JSRs (Java Specification Requests)

Foundation

JSR #NameDescription
68J2ME Platform Specification
30CLDC 1.x
37MIDP 1.0
118MIDP 2.x
139CLDC 1.1
271MIDP 3.0Java ME 3.4 and earlier only, Last Specification for Mobile Phones, Java Language features as Java SE 1.3
360 CLDC 8 New in Java ME 8
361 MEEP 8 New in Java ME 8, Language feature as Java SE 8, for Internet of Everything devices

Main extensions

JSR #NameDescriptionMSA
75File Connection and PIMFile system, contacts, calendar, to-doYes
82Bluetooth Yes
120Wireless Messaging API (WMA)
135Mobile Media API (MMAPI)Audio, video, multimediaYes
172Web Services Yes
177Security and Trust Services Yes
179Location API Yes
180SIP API Yes
184Mobile 3D GraphicsHigh level 3D graphicsYes
185Java Technology for the Wireless Industry (JTWI)General
205Wireless Messaging 2.0 (WMA)
211Content Handler API Yes
226Scalable 2D Vector Graphics API for J2ME Yes
228Information Module Profile - Next Generation
229Payment API Yes
234Advanced Multimedia Supplements (AMMS)MMAPI extensionsYes
238Mobile Internationalization API Yes
239Java Bindings for the OpenGL ES API
248Mobile Service Architecture Yes
253Mobile Telephony API
256Mobile Sensor API
257Contactless Communication API
258Mobile User Interface Customization API
272Mobile Broadcast Service API for Handheld Terminals
280XML API for Java ME
281IMS Services API
287Scalable 2D Vector Graphics API 2.0 for Java ME
293Location API 2.0
298Telematics API for Java ME
300DRM API for Java ME
325IMS Communication Enablers

Future

JSR #NameDescription
297Mobile 3D Graphics API (M3G) 2.0

ESR

The ESR consortium is devoted to Standards for embedded Java. Especially cost effective Standards. Typical applications domains are industrial control, machine-to-machine, medical, e-metering, home automation, consumer, human-to-machine-interface, ...

ESR #NameDescription
001B-ON (Beyond CLDC) B-ON serves as a very robust foundation for implementing embedded Java software. It specifies a reliable initialization phase of the Java device, and 3 kind of objects: immutable, immortal and regular (mortal) objects.
002MicroUIMicroUI defines an enhanced architecture to enable an open, third-party, application development environment for embedded HMI devices. Such devices typically have some form of display, some input sensors and potentially some sound rendering capabilities. This specification spans a potentially wide set of devices.
011MWTMWT defines three distinct roles: Widget Designers, Look and Feel Designers, and Application Designers. MWT allows a binary HMI application to run the same on all devices that provide a compliant MWT framework (embedded devices, cellphones, set-top box TV's, PC's, etc...) allowing for true consistency and ubiquity of applications across product lines (ME, SE, EE).
015ECLASSPATHECLASSPATH unifies CLDC, CDC, Foundation, SE, and EE execution environments with a set of around 300 classes API. Compiling against CLDC1.1/ECLASSPATH makes binary code portable across all Java execution environments.

See also

Notes

Bibliography

External links

Wikibooks has a book on the topic of: J2ME Programming
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