So my question is this:
Nowhere in my code do I specify where the data (that ends up in my TargetDataLine) is coming from. I've not specified that it should come from a mic, or line-in, or any other physical device. It just magically reads data from my mic.
I see that there are no sources!Source and Target lines are what the user uses to write and read data from the line (respectively)... For example, the port that's actually associated with the microphone will have zero source lines, because you're not allowed to write to the microphone...but it gets data from the microphone, behind the scenes.