The J2ME application I have been working on has been ready for testing for quite some time, but I didn’t want to get a new AT&T phone. For J2ME, you really need a GSM phone–I don’t think any of the older TDMA models support it. But the GSM network coverage doesn’t match the coverage of the TDMA network–especially out west (aside: isn’t that magnifying glass pretty cool?). So I put off buying a phone until my summer road tripping was done.
I’ve had a Nokia 6160 for almost 4 years. Even though friends mocked the size of it, it was a great phone–durable, good talk time. I thought I’d try another Nokia, and got one of the lower end GSM phones, the 6200. This supported J2ME, and weighed maybe half as much. I was all stoked to try the application on my brand new phone.
I started download the jad file, and was getting ‘File Too Large’ errors. A couple of searches later, I found Nokia’s developer device matrix which is much more useful than the User Guide or the customer facing description of phones. Whoops. Most of the Series 40 (read: affordable) Nokia devices only supported J2ME applications which were, when jarred up, less than 64K in size.
Our application, however, was about 78K. This highlights one of the differences between J2ME and J2SE/J2EE. When coding in the latter world, I was never concerned about code size–getting the job done quickly was paramount, and if I needed to use 13 libraries which bloated the final size of my application, I did. On a cell phone, however, there’s no appeal to adding memory or changing the JVM configuration to optimize memory use. If the Nokia phone only accepts jars of 64K or less, I had three options:
1. Write off the Nokia Series 40 platform. Ugh–I like Nokias, and other folks do too.
2. Do some kind of magic URL classloading. This seemed complicated and I wasn’t sure how to do it.
3. Decrease the size of the jar file.
Now, the 78K jar had already been run through an obfuscator. I wasn’t going to get any quick and easy gains from automated software. I posted a question on the JavaRanch J2ME forum and received some useful replies. Here’s the sequence I went through:
1. Original size of the application: 79884 bytes.
2. Removal of extra, unused classes: 79881. You can see that the obfuscator did a good job of winnowing out unused classes without my help.
3. Changed all the data objects (5-6 classes), which had been written in classic J2SE style with getters and setters for their properties, to have public variables instead: 79465
4. Combined 3 of the data object classes into one generic class: 78868
5. Combined 5 networking classes into 2: 74543
6. Removed all the logging statements: 66044. (Perl to the rescue–
$ perl -p -i -e 's!Log\.!//Log.!' `find . -name "*.java" -print |xargs grep -l 'Log\.'`)
7. Next, I played around with the jode obfuscator which Michael Yuan recommended. I was able to radically decrease the size of the jar file, but, unfortunately, that jar file didn’t work on the phone. I also got a ton of exceptions:
java.util.NoSuchElementException at jode.bytecode.BytecodeInfo$1.next(BytecodeInfo.java:123) at jode.obfuscator.modules.LocalOptimizer.calcLocalInfo(LocalOptimizer.java:370) at jode.obfuscator.modules.LocalOptimizer.transformCode(LocalOptimizer.java:916) at jode.obfuscator.MethodIdentifier.doTransformations(MethodIdentifier.java:175) at jode.obfuscator.ClassIdentifier.doTransformations(ClassIdentifier.java:659) at jode.obfuscator.PackageIdentifier.doTransformations(PackageIdentifier.java:320) at jode.obfuscator.PackageIdentifier.doTransformations(PackageIdentifier.java:322) at jode.obfuscator.PackageIdentifier.doTransformations(PackageIdentifier.java:322) at jode.obfuscator.PackageIdentifier.doTransformations(PackageIdentifier.java:322) at jode.obfuscator.ClassBundle.doTransformations(ClassBundle.java:421) at jode.obfuscator.ClassBundle.run(ClassBundle.java:526) at jode.obfuscator.Main.main(Main.java:189)
I'm sure I just didn't use it right, but the jar file size was so close to the limit that I abandoned jode.
8. Instead, I put all the classes in one file (perl to the rescue, again) and compiled that: 64057 bytes. The jar now downloads and works on my Nokia 6200 phone.
When I have to do this again, I'll definitely focus on condensing classes, basically replacing polymorphism with
if statements. After removing extraneous Strings and concatenating all your classes into one .java file (both of which are one time shots), condensing classes is the biggest bang for your buck.