computer science

Java Platform, Micro Edition

Java Platform, Micro Edition is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Java Platform, Micro Edition rather than just read about it. In short: Java Platform, Micro Edition, often called simply Java ME or J2ME, is a computing platform for development and deployment of portable code for embedded and mobile devices (micro-controllers, sensors, gateways, mobile phones, personal digital assistants, TV set-top boxes, printers). A program created for the platform is called a MIDlet.

Key takeaways

Java Platform, Micro Edition belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Java Platform, Micro Edition to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Java Platform, Micro Edition from memory before moving on to harder problems.

Reference excerpt

Java Platform, Micro Edition, often called simply Java ME or J2ME, is a computing platform for development and deployment of portable code for embedded and mobile devices (micro-controllers, sensors, gateways, mobile phones, personal digital assistants, TV set-top boxes, printers). A program created for the platform is called a MIDlet. The platform uses the object-oriented Java programming language, and is part of the Java software-platform family. It was designed by Sun Microsystems (now Oracle Corporation) in 1999 under the name Java 2 Platform, Micro Edition. The earliest commercial Java ME software and supporting consumer hardware were released in 2001. MIDlets run inside a Java virtual machine understood by devices of various mobile manufacturers. This "write once, run anywhere" approach along with highly compressed file sizes made Java ME very popular for building simple mobile apps, most notably mobile games. As of 2013, there were more than three billion Java ME–enabled mobile phones in the market, but the platform was in continued decline by that time as feature phones had been overtaken by smartphones. Smartphones used dedicated hardware acceleration chips utilising APIs like OpenGL ES rather than relying on device CPU-based software rendering to handle graphics, which had mostly been the case on Java ME.

History Java 2 Platform Micro Edition (and the related K virtual machine) was announced on June 15, 1999. It would replace a similar technology, PersonalJava. The platform used to be popular in feature phones, such as Nokia's Series 40 models. Siemens SL45i in 2001 was the first that could run Java. It was also supported on the Bada operating system and on Symbian OS along with native software. Users of Windows CE, Windows Mobile, Maemo, MeeGo and Android could download Java ME for their respective environments ("proof-of-concept" for Android). Originally developed under the Java Community Process as JSR 68, the different flavors of Java ME have evolved in separate JSRs. 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). In 2008, Java ME platforms were restricted to JRE 1.3 features and use that version of the class file format (internally known as version 47.0).

Implementations

Oracle provides a reference implementation of the specification, and some configurations and profiles for MIDP and CDC. Starting with the JavaME 3.0 SDK, a NetBeans-based IDE supported them in a single IDE. In contrast to the numerous binary implementations of the Java Platform built by Sun for servers and workstations, Sun tended not to provide binaries for the platforms of Java ME targets, and instead relied on third parties to provide their own. The exception was an MIDP 1.0 JRE (JVM) for Palm OS. 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". Third party implementations are widely used by Windows Mobile vendors. At some point, Sun released a now-abandoned reference implementation under the name phoneME. 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 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 in intent, but very different in many ways from Java ME.

Emulators Sun Java Wireless Toolkit (WTK, for short) — is a proprietary Java ME emulator, originally provided by Sun Microsystems, and later by Oracle. MicroEmulator (MicroEMU, for short) — is an open-source Java ME emulator. J2ME Loader — an Open Source Android Java ME emulator. FreeJ2ME-plus — A fork of FreeJ2ME, a free, cross-platform J2ME emulator with support for Libretro and AWT frontends. There are other emulators, including emulators provided as part of development kits by phone manufacturers, such as Nokia, Sony-Ericsson, Siemens Mobile, etc.

CLDC (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. JSR 271: Mobile Information Device Profile 3 (Final release on Dec 9, 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.

… excerpt ends here. Continue reading the full article.

Illustrations

Java Platform, Micro Edition: MicroEmulator screenshot — MicroEmulator screenshot

Worked examples

Example 1 — a first encounter with Java Platform, Micro Edition

Start with the simplest possible case. Write down what Java Platform, Micro Edition claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Java Platform, Micro Edition before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Java Platform, Micro Edition ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Java Platform, Micro Edition

In research: Java Platform, Micro Edition appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Java Platform, Micro Edition in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Java Platform, Micro Edition is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computing platforms, Java (software platform), Java device platform, so understanding it makes those chapters shorter.
In everyday life: Look for Java Platform, Micro Edition outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Java Platform, Micro Edition in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Java Platform, Micro Edition means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Java Platform, Micro Edition out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Java Platform, Micro Edition in simple terms?

Why does Java Platform, Micro Edition matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Java Platform, Micro Edition?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Java Platform, Micro Edition.