Mobile Information Device Profile

Mobile Information Device Profile (MIDP), is a specification published for the use of Java on embedded devices such as cell phones and PDAs. MIDP is part of the Java Platform, Micro Edition (Java ME) framework. MIDP sits on top of a "configuration", such as the Connected Limited Device Configuration or Connected Device Configuration. MIDP was developed under the Java Community Process as JSR 37 (MIDP 1.0) and JSR 118 (MIDP 2.0). As of 2006, MIDP 3.0 is being developed under JSR 271. The firsts MIDP devices were models i80s and i50sx from Motorola, launched in April 2001.

Noteworthy Limitations

MIDP 1.0 could not query key status.
MIDP 1.0 has no active rendering APIs
MIDP 1.0 has no support for audio.
MIDP 1.0 only requires HTTP support.
The specifications are not always clear, leading to differences in implementations.

General APIs

The core APIs are defined by the underlying Configuration Connected Limited Device Configuration.

javax.microedition.io

Contains the Java ME-specific classes used for I/O operations.

javax.microedition.lcdui

Contains the Java ME-specific classes used for the GUI.

LCDUI has a simple screen based approach where a single Displayable is always active at a time in the application user interface. LCDUI API provides a small set of displayables common in mobile device user interfaces: List, Alert, TextBox, Form and Canvas. For all displayables the device MIDP implementation has control over the presentation and layout of the displayable. Canvas is a low-level graphics surface in which application is in full control what is rendered to it but also it in normal mode is often associated with some areas like title and indicators common in mobile device UIs. Canvas has also full-screen mode that allows to make full screen graphics. This is used nearly always in MIDP based games.

LCDUI also has quite unique approach of abstract operations, called Commands. The placement of commands added to a displayable is completely upto the device implementation of this toolkit. The application programmer uses API specified command types to indicate the usage or purpose of the command in application user interface. Common types are BACK, EXIT, ITEM, SCREEN. The idea of the command abstraction is to make applications more portable between various different mobile device. Application developers should use the types propertly to indicate the purpose of an operation and device implementation then places the operation to the common location for a given type in devices specific user interface style. This may be e.g. a specific key e.g. "a back navigation key" for BACK commands or button on screen.

The term LCDUI was actually a joke in JCP Expert Group that created it. It has not been opened up in the MIDP specifications but stands for Limited Capability Device User Interface. The joke was that no-one else really knows what it stands for. Then later the Programming Wireless Devices with the Jave 2 Platform, Micro Edition book gave this term out.

Other common definitions have appeared. "LCD UI" due to the fact that mobile phones normally use LCD displays; the API is not specifically tailored to this particular display technology. It is also said that "LCD UI" stands for Least Common Divisor due to the fact the specific UI has simplest possible design.

javax.microedition.rms

Provides a form of persistent storage for Java ME.

javax.microedition.midlet

Contains the base classes for Java ME applications.

Specialized APIs added in MIDP 2.0

MIDP 2.0 saw the introduction of gaming and multimedia APIs and some optional packages.

javax.microedition.media

Contains the base classes of the multimedia playback. These are approximately a subset of the JSR 135 Java Mobile Media API.

javax.microedition.lcdui.game

A gaming API aimed at simple 2D sprite based games.

javax.microedition.pki

Authenticate APIs for secure connections.

javax.microedition.messaging

Wireless messaging API (optional), sending SMS and MMS messages.

javax.microedition.pim

Personal information management API (optional), access the device's address book.

javax.microedition.io.file

File connection API (optional), access the device's file system.

Development Tools

There are several different ways to create MIDP applications: Code can be written in a plain text editor, or you can use a more advanced IDE such as NetBeans or Eclipse (with the appropriate plugins) which has a user interface for graphically laying out any forms you create, as well as providing many other advanced features not available in a simple text editor.

External links

The MIDP Specification
JSR 271 (MIDP 3.0)
JSR 271 collaboration page (MIDP 3.0)
JSR 118 (MIDP 2.0)
JSR 37 (MIDP 1.0)
A worldwide list of MIDP enabled phones
J2MEDeveloper.com
An Example Midlet (MIDP1.0+). MIDP applications can be downloaded directly to a MIDP enabled phone. This is an example of an established free one.
What's New in MIDP 2.0

Java device platform | Java specification requests

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