A MIDlet is a Java program for embedded devices, more specifically the J2ME virtual machine. Generally, these are games and applications that run on a cell phone. Java is an object-oriented programming language developed by James Gosling and colleagues at Sun Microsystems in the early 1990s. ... Java 2 Platform, Micro Edition, or J2ME, is a collection of Java APIs targeting embedded consumer products such as PDAs, cell phones and other consumer appliances. ... Motorola T2288 mobile phone A mobile phone is a portable electronic device which behaves as a normal telephone whilst being able to move over a wide area (compare cordless phone which acts as a telephone only within a limited range). ...

MIDlets will (should) run on any device that implements J2ME Mobile Information Device Profile. Like all Java programs, MIDlets are "compile once, run anywhere". To write a MIDlet, you can get Sun's Wireless Toolkit from the Java website, which is available on several platforms and is completely free. Mobile Information Device Profile, MIDP, is a specification put out by Sun Microsystems for the use of Java on embedded devices such as cell phones and PDAs. ...

A MIDlet has to fulfill the following requirements in order to run on a mobile phone:

• The main class needs to be a subclass of javax.microedition.midlet.MIDlet
• The MIDlet needs to be packed inside a .jar file (e.g. by using the jar-tool)
• The .jar file needs to be pre-verified by using a preverifier.

Hints for writing MIDlets:

• Handsets impose a limit on the .jar file size. Nokia series 40, arguably the most popular handsets for mobile gaming, has a .jar file size limit of 64kB. The MIDlet size can be reduced through application of programmatic and design optimization techniques ( J2ME Optimizations. J2ME Optimizations. URL accessed on Oct 10, 2005.) and the use of obfuscators, PNG optimizers, and J2ME optimizers.
• Heap sizes can be very small, around 200kb. Therefore, use as few objects as possible and delete references to them when they are no longer needed. Some image formats such as png will decompress to enormous sizes when loaded so don't keep too many of them. Catching OutOfMemoryErrors exceptions will normally not work.
• Programs can not expect more than 20kb persistent storage. Don't keep more than you need. (Newer phones support additional APIs for file storing)
• Keep in mind that a device can have very different screen dimensions, orientations and color depths. In other words, don't use absolute position.
• Not all devices have keypads or pointers. One should be able to use the program with both. Key layouts may vary too, so use Game Actions for up-down-left-right-action style events.
• Don't white list devices. If the program hasn't been tested on a specific device, assume it works. Never attempt to block the user from trying it.
• Use an obfuscator such as Proguard to compress the MIDlet size.

2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... Obfuscation refers to the concept of concealing the meaning of communication by making it more confusing and harder to interpret. ... A PNG image with an 8-bit transparency layer (top), overlayed onto a chequered background (bottom). ... Persistence is the term used in computer science to describe a capability used by a computer programmer to store data structures in non-volatile storage such as a file system or a relational database. ... A white list is a list of accepted items or persons in a set. ...

References

• J2ME Optimizations. J2ME Optimizations. URL accessed on Oct 10, 2005.(http://www.innaworks.com/mBooster-2-0-Doc-Ch3-1-Optimizations.html)

2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ...

External links

• Openwap: Open Source Midlets News and Software
• An Example Midlet. Thousands of Midlets are now available. This is an example of an established free one.