I was a pretty poor CS student, in hindsight I'm surprised I got it to work.

I used j2me in the early 2000s to make a mobile app where people could find home data. My first startup experience. Learned a lot but didn't earn a lot.

Wrote a paper about MIDP here: https://www.mooreds.com/midp/midp.html . No idea if it is still relevant 20 years on.

I can still remember setting up palette swapping (inspired by retro consoles, but still a common contemporary idea e.g. on GBA) by loading the byte data of PNG resources into an array and locating and replacing the PLTE chunk before handing it off to the MIDP image loader. Always wondered if anyone else had picked up the trick. I can also remember people suggesting on Nokia in particular to just store raw bitmaps (since they'd be compressed in the JAR anyway) with their API and that this was saving tons of space for some people... later I found out that one of these reports came from someone who had started out with individual image files for 12x12 tiles that had a full 256-entry PLTE (i.e., more colour entries than pixels).

I also remember a device-specific bug where doing something like `x[y+1]`, where `y` was a static byte set to -1, would produce an `IndexOutOfBoundsError` claiming the index used was -256. I assume this was some threading issue in the Java implementation, where the value would be loaded into a register and then the sign-extension would somehow affect the register after the increment. I only ever reproduced it with static class members, I think (but it did also happen with shorts).

J2ME gets a lot of stick, but modern mobile has actually recreated almost all the same problems. The big one for apps was the out of the box UI components were awful and utterly inconsistent between manufacturers. Several of the above companies tackled this (think conceptually like Flutter), but the market wasn't ready largely because data plans were expensive.

For games though, honestly, J2ME was dreadful, but in non-obvious ways: the control interfaces were hopeless, and sound was basically a non starter. People would be willing to forgive a lot more had the controls and sound been decent. Then the graphics stuff was just inconsistent enough that too much time ended up focused on portability and not enough on if the game was actually as fun as it should be. A consequence of that is most of the best J2ME games were ports from other systems or shameless reskins of other things.

But there is something to be said about taking a tube/metro/bus and seeing people playing stuff you did and enjoying it, especially given back then it was impossible to know who the players really were since things were sold through the carriers.

Thanks Otto

The java ecosystem of those days had similar terms like the servlet (still surviving), applet & midlet. Is there a significance of the suffix "let" or somebody thought let's add "let" to everything.

One I noticed is j2me games often don't play music on the background and just resorts to sporadic sounds, any reason for that?

What's really cool about that emulator is the way its sound emulation works. Instead of emulating the Gameboy's synthesizer synchronously and outputting a PCM waveform to a buffer, which is probably impossible on J2ME due to hardware and platform constraints, it uses the phone's own MIDI (or square wave) synthesizer to play whatever the GameBoy synthesizer should be playing. This gives the video game music a very idiosyncratic sound when played back in MeBoy.

And of course a limited port of Worms Armageddon that has to be one of the games I sunk the most time on, seeing as I played several matches a day with my friends for an entire school year! Ahh I even scribbled a "campaign mode" on my math notebook during class instead of paying attention!

Tested of course on the latest SonyEricsson of the time!

Maybe i can dig that out again and run it somewhere.

It was fun to build small apps and felt like magic at the time.

Also, you can head to gopher://magical.fish, gopher://hngopher.com and gopher://sdf.org to get 'modern' services and news.