This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
Your SerPorttype is just an interface whose implementation is generated at runtime so the generated class could be implementing all sorts of interfaces.
Look up the proxy pattern (there are three types) to find out more about this use case.