Mobile Java Standards

jesus_thats_gre

Hi

I have been trying to figure this out for a while. Why do java games and applications have to be designed for specific handsets and brands of handsets, i.e. why do some java games only work with Sharp handset and others will only work with nokia handsets..

I understand that in some cases this is a requirement due to the capabilities of some handsets when compared to others, i.e. connectibility and processing abilities. But surely applications can be designed to work with generic handsets. Does this happen?

The whole cross platform thing with Java is what is throwing me off here. In that Java applications can run on virtually any PC using JVM. I am correct in assuming the MIDP for handets etc is similar to the JVM used on computers? If not, what does it do and what relevence does the different versions have. One final question regarding MIDP, wil games designed for the GX10 using MIDP 1.0 work with the GX20 uising MIDP 2.0?

Thanls

soiaf

MIDP 1.0 is the basic standard used for Java appilcations and games for mobile phones. However it is quite restrictive in what it lets you do, especially when talking about games.
For example there is no sound support and no transparency support for graphics in MIDP 1.0

But it is possible to write a game that complies with the MIDP 1.0 standard, that should work on pretty much any Java enabled handset, but it won't be a particularly exciting looking/sounding game, though it may be addictive etc.

To make the games more interesting some of the phone manufacturers e.g. Nokia, decided to add 'support' APIs/libraries on their phones. So all the basic MIDP1.0 functionality would be supported, but they also allowed you to make extra calls, to provide, in the case of Nokia, simple sound support and better graphics handling (support transparency etc.).
Vodafone, as part of their live! development, came up with their own set of extra APIs, called VSCL, which they asked handset
manufacturers to support, this is what the Sharp supports.

With these extra libraries it is possible to produce far better looking and sounding games. But some games are designed using VSCL, and some games are designed with the Nokia extension APIs, and of course the phones don't support these 'competiting' libararies. Some games makers produce games compiled/built with both, and you just download the correct version for your phone. Obviously some games are made with only one in mind.

MIDP 2.0 supports a lot more features natively, e.g. multi-channel sound, sprites etc. so assuming a phone supports it, games should be a lot more handset-agnostic.

I don't know much about the Sharp GX-20, but MIDP2.0 compatiable phones should be able to play MIDP1.0 games, and being a Sharp phone I'm sure it will also support VSCL, so Sharp GX10 games should work on the GX20. I say should, but I don't have a GX20 so.....

flywheel

this might answer you first question:
http://www.eetimes.com/story/OEG20030616S0077

The problem lies with the initial set of application programming interfaces for Java on the cell phone.... MIDP 1.0 was "broad and shallow" and contained a host of options, said Tim Lindholm, chief technology officer for Sun's consumer mobile-systems group. Vendors wrote their own APIs and class libraries for a variety of required security, audio and other functions

there is a nice series of 5 articles taken from the O'Reilly's J2ME in a Nutshell book, starting here:
The Mobile Information Device Profile and MIDlets

that will intro you (or give you more details depending how far you read into it), although one of the nuggets is in the hardware requirements section... "This wide disparity in capability provides the developer who wants to write a fully portable MIDlet with some interesting challenges", there's one way of putting it

if you limit yourself to elements offered in the specification (therefore more widely supported) and don't need to tap into the full capabilities (of those offered by a higher end device) you can get a cross device app out there, e.g. ReqWireless WebViewer

but for apps like games developed where the likes of different displays (size/colour depth) or extensions you may want to use provided for by different vendor's APIs (fragmentation), etc., you will certainly run into "some interesting challenges" to roll the app out for different devices (portability)

you can read more about MIDP 2.0 and how JSR 185 tries to address issues like fragmentation and portability here:
http://wireless.java.sun.com/midp/articles/midp20/
http://wireless.java.sun.com/midp/articles/jtwi/

jesus_thats_gre

Thanks both of you.. Cleared a few things up.

I will check those links out and come back if I have any probs