Ummm... Hmm. I'm having difficulty finding it at the moment...
The examples came from the modes\java\libraries\minim\examples\BeatDetect\FrequencyEnergy\ BeatListener directory.
They all execture perfectly normal as long as I don't modify anything, so i assume the BeatDetect class exist somewhere, but I cannot find it. I ran a search and come across BeatDetect.java, but it opened with a different IDE so I'm thinking is not the one being referenced for this code.