I've found this site http://blog.iharder.net/2009/08/18/rxtx-java-6-and-librxtxserial-jnilib-on-intel-mac-os-x
which seems to provide good guidance & solution on how to install in Macintosh these 2 files required to communicate between arduino and Java via USB:
The author of this site provides a download of his own librxtxSerial.jnilib and you'll see on of his comments that he re-directs towards this other site http://rxtx.qbang.org/wiki/index.php/Download
to download RXTXcomm.jar
Long ago, I've developped a java application (let's call it zpe.jar) which successfully interfaces between my iMac (Tiger) and arduino mega.
A few days ago, I've bought a refurbished MacBook Air running with Snow Leopard but my zpe.jar will not launch if I'm using both RXTXcomm.jar and librxtxSerial.jnilib coming from my iMac (Tiger version).
Now i've successfully installed both RXTXcomm.jar and librxtxSerial.jnilib from the above site and my zpe.jar launches & displays correctly my java application with template, sliders,... it does show the USB adress of arduino mega but it will not transfer any data.
Hoping someone can help !