[rfk-dev] RFK for J2ME-enabled phones
screwtape at froup.com
Mon Oct 18 08:15:44 CDT 2004
Last year I got a Nokia 3530 phone, one that lets me install Java
applets via HTTP. A few months after that I found a port of the J2ME
tools ('Java 2 Mobile Edition', I believe), and a little while after
that I was looking for a simple-ish program to write that would be kind
to my phone's diminutive processor and miniscule display, when suddenly
I remembered robotfindskitten.
I've got the latest version of the program temporarily online at:
The interesting files are:
- robotfindskitten.jar: The actual installable package.
- robotfindskitten.jad: A required metadata file
- robotfindskitten-src.tar.gz: A standard tarball of the sourcecode.
- test.html, me-applet.jar: View test.html in a Java-enabled browser
to play with RFK without having to find a Java-enabled phone.
NOTE: Both the 'jad' and 'jar' files contain references to the URL
containing the software. If the software is to be hosted somewhere
else, it might need to be recompiled, or at least tinkered with. See
'Notes on the build system' below.
- Contains all the NKIs from whatever the latest version of RFK was
when I wrote the Java version.
- Lets you save a game in progress and come back to it later.
- Sophisticated scrolling system lets robot search for kitten in an
arena larger than the screen.
- No 'You found kitten!' animation, but there is a cute hand-drawn
Notes on the source code:
- Arena.java represents the arena robot explores, and contains the
list of NKIs.
- ArenaDisplay.java takes the Arena and figures out how to draw it
nicely on a bitmap screen whose dimensions are not necessarily integer
multiples of the font size. It also contains the main RFK event
- Main.java contains all the menus and the state-saving.
Notes on the build system:
In order to build RFK for J2ME, you'll need a copy of Sun's J2ME SDK;
basically a simple emulator for testing and class-libraries to link
It's available for Windows, Linux and Solaris, with all sorts of spiffy
IDEs and such, but I was using the cheapskate Mac OS X port which just
supplies the bare minimum necessary. Accordingly, rfk uses the highly
complicated and eerily advanced 'GNU make' as its build engine. Folk
who posess sufficient make-fu will no doubt be able to divine all I
know about J2ME packaging from the included makefile, others will need
to read on.
First, a word about J2ME packaging: Each 'midlet' needs certain
associated metadata in order to run. This metadata appears in two
places - some of it appears in the 'robotfindskitten.jad' file that you
feed to your phone, which tells it the name of the application and
where to download the actual code, and some of it appears in
'MANIFEST.MF' in the .jar file. The source tarball includes a file
called 'manifest.mf' which contains the union of the two information
sets, this file is filtered to become both metadata files.
Specifically, to set the 'source URL', edit the line 'MIDlet-Jar-URL'
in 'manifest.in' and rebuild.
There are 'test' and 'install' targets - these most likely won't work
unless you happen to have things set up identically to me. 'make
localtest' is more likely to be useful. 'make clean' works as it
You'll need to have $MIDP_HOME in your environment, but installing the
J2ME SDK should take care of that anyway.
Notes on installing the thing into a phone:
Some phones won't install a midlet that's over 64k. RFK is currently
22k, and most of that is NKIs.
Phones are very, *very* picky about MIME types. I have the following
settings in my .htaccess:
AddType text/vnd.sun.j2me.app-descriptor JAD jad
AddType application/java-archive JAR jar
I'm subscribed to rfk-dev now, if anyone has any further queries or
suggestions or even just wants to say they've installed it on their
phone and it worked, I'd be interested to hear them.
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