Music in Java apps?

Just curious, when MMF2 actually compiles it to JAR file, doesn't it compress wave or uncompressed files?

For the moment, OGG is not supported as a native format by Java. This could change in the future.
Samples are compressed (zipped) in the jar file

My 571 KB Java game turned into a monstrous 27 MB game when I tried to put in a 2:47 WAV file. I didn't really expect anything less though. Does Java itself support MP3?

Java only supports WAV. There are libraries that enable MP3 playback but we would have to review them first to make sure they are safe to include, we'd have to include it in the runtime only if it was being used to save space, etc... it's not a simple process and there are other priorities at the moment.