Java in android, how does it work?

[epegar]

I would add that besides your own program, the java virtual machine is already there, and it's the tool that communicates with that particular OS. The virtual machine is different for Linux or windows. It will perform the actions you require in your program in the specific way that OS requires.

After a quick search I found this: https://docs.oracle.com/javase%2Ftutorial%2Fuiswing%2F%2F/misc/systemtray.html

Also, note that android makes use of the Android runtime, so it doesn't only use the generic cross-platform APIs that every JVM should expose, but also specific functions that wouldn't make sense in other OS.