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Show HN: Awesome J2ME

79 points| catstor | 3 months ago |github.com

An awesome list about Java platform Micro edition(J2ME). Documentation, academic papers, tutorials, communities, IDEs, SDKs, emulators, apps, video games. J2ME is a Java specification designed for old keypad phones and PDAs. MIDP, which is built upon CLDC, is used to create Midlets, which have `.jad` or `.jar` extension, and run on platforms like old keypad phones, Symbian and PDAs. MIDP is supported till Java ME SDK 3.4.

55 comments

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yanslookup|3 months ago

The first thing I ever wrote that other people used was a j2me app freshman year in college. It was a power hour app that played a random simpsons .wav every minute.

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

embedding-shape|3 months ago

One of the very first "hacks" I did was finding instructions via a random WAP website on how to patch a J2ME game for some early phone that could run .jar games, in order to effectively crack it.

zahlman|3 months ago

> a power hour app

Pardon?

mooreds|3 months ago

Wow, brings back memories!

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.

catstor|3 months ago

I am glad it was helpful.

Thanks for the paper as well. It explains concepts very clearly with a real-life problem statement. Added it to Awesome J2ME.

zahlman|3 months ago

I did J2ME development in the 64KB JAR era.

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).

d9k|3 months ago

Mr. zahlman, can you please share the source code of "palette swapping by loading the byte data of PNG resources into an array and replacing the PLTE chunk before handing it to the MIDP image loader"?

foofoo12|3 months ago

Brings back memories but I can't say they are good. It was so limited that it was mostly frustration.

jeffbee|3 months ago

How limited could it have been? They were able to ship Google Maps Mobile with it.

micheljansen|3 months ago

Thanks for making me feel old! One of my first real jobs involved MIDP/J2ME development. I cannot say I loved the platform, but it somehow felt more magical back then to develop something and run it on a Nokia brick than (mobile) development of today.

fidotron|3 months ago

Wow this brings back a lot. I did J2ME at Macrospace/Glu, Masabi, Javaground and EA, and at one point near the end was simultaneously responsible for 128k jars of Tetris and 4GB apk + obb for Real Racing because that is how rapidly the field exploded. Absolute madness.

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.

stuff4ben|3 months ago

Startup I used to work at fueled Cingular's mobile storefront and distributed those J2ME games along with ringtones and graphics. Those were the days...

easyThrowaway|3 months ago

And yet there were still some amazing games that today would be considered on the same league of the "impossible ports" for the Nintendo Switch.

tauntz|3 months ago

Ha, nostalgic! Was part of a small 3 person team that built the Skype app for J2ME back in the day. Fun times.. :)

devsda|3 months ago

Ah, the good old days of browsing wap sites to download "apps". Installing some of them only to find that my budget phone doesn't support the j2me profile required to run them.

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.

kryptiskt|3 months ago

-let is a diminutive, signifying something small. Like in piglet or booklet.

flykespice|3 months ago

BTW there is J2ME Loader, a free j2me emulator for android devices available through PlayStore, it plays very nice (you can customize your keys too).

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

Randomno|3 months ago

One of the difficulties I had searching for J2ME resources is that the mobile equivalent of the JVM is called KVM (K virtual machine), so most of the search results are about Linux's Kernel-based virtual machine instead.

indigo945|3 months ago

MeBoy brings back some memories. I used it to catch so many Pokémon in middle school.

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.

anthk|3 months ago

I used to run MeBoy under Sony w200 phone. With some frameskip Zelda for the GB was somehow playable. Pokémon ran well enough OFC.

andrepd|3 months ago

Have very fond memories of playing J2ME games. Here's some off the top of my head: Zombie Infection (what a great game!), Galaxy on Fire, Sims, Age of Empires, Real Football, Orcs&Elves, Pokémon Crystal on an emulator...

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!

kitd|3 months ago

Memories! I built a race timing app in J2ME. A useful exercise in designing a good UX within a constrained environment. Nowadays we just throw browser bloat around without a care.

mghackerlady|3 months ago

Someone should make a 4G LTE/5G dumb phone capable of running J2ME. I'd buy it, my dumb phone doesn't even have snake on it lol

anthk|3 months ago

You can run it under Android, there's a J2ME emulator at https://f-droid.org. Being both platforms Java-like makes emulation much easier as you will find thousand of competent enough people and OFC it woudn't surprise me if Google made tons of similar functions to J2ME ones at Android in order to ease the transition from former developers.

tacker2000|3 months ago

I remember creating a J2ME game back at uni, where the theme was to pour a beer exactly right.

Tested of course on the latest SonyEricsson of the time!

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

froh42|3 months ago

What is the next thing coming up? "Awesome WAP"?

catstor|3 months ago

> What is the next thing coming up

Awesome Symbian!

https://github.com/hstsethi/awesome-symbian

While WAP was pretty good too, but I doubt there are enough resources on it to create a seperate list. Same goes for Blackberry, Palm OS and others.

anthk|3 months ago

Gemini (the protocol, no the Google hype) it's close to these contraints, and partially the old Gopher. There's even a Gopher client for J2ME, Pocket Gopher, patched at gopher://hoi.st

lormayna|3 months ago

One of my university projects was an encrypted message system via Bluetooth using J2ME. Never worked, but I learnt a lot of things :)

Raed667|3 months ago

Blast from the past ! I remember building my last J2ME project ~2012 and struggling to find a Nokia phone to test it

juancn|3 months ago

Gosh! The memories! No floating point!

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

anthk|3 months ago

gopher://hoi.st has Pocket Gopher, a J2ME gopher client.

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

catstor|3 months ago

Thanks. I have added the Github repo of it on Awesome J2ME, as Gopher links are not allowed by linter.

zerr|3 months ago

Would interesting to hear about J2ME gold rush. Any success (or fail) stories?

fidotron|3 months ago

It was really a euro thing. Think the whole Jamba/Jamster ecosystem (Crazy Frog) and the explosion that occurred with premium SMS and ringtones.

It was all about selling into carriers associated with that, and that was a recipe for pain. I don't believe anyone made a killing in J2ME directly (Gameloft gave the impression of making most money, not entirely undeservedly), and many absolutely struggled, but it did provide the crucible for a lot of what came later.

One of the more curious incidents that stayed with me related to the game "Fatal Force" which had a 64kb build that was incredibly tight. We were mystified to discover a Chinese pirate was distributing a Chinese build of the game, still within 64kb limits. He had decompiled it, reverse engineered it, added more compression so he could fit in localized assets, and released it. The last I heard on the subject there was an effort to pay him for it.

The other was when a game of a game show was advertised in Germany, during the game show, it would generate such a traffic spike that the servers selling the game got knocked out, leading to requiring outsourcing that function to a more scalable competitor, a lesson that was not forgotten for the next company.

invalidname|3 months ago

No LWUIT?

catstor|3 months ago

Thanks for pointing out the omission. I have added it. It certainly deserves it place there.

ptx|3 months ago

LWUIT wasn't particularly awesome, in my opinion. It was enormous and hideous and couldn't integrate with the native cut-and-paste functionality offered by some phones.

k4rnaj1k|3 months ago

Still remember installing those j2me games on my classmate's phones. It was a bit hard to figure out and find the right resolutions versions for each phones.