[Click] need your help

[=?gb2312?B?bGl1emhhbl9obg==?=]

I am a beginner of click router. I want to ask a question ,could anyone help me?
How to add a output to an element? thank you 
When I implemented an click example udpgen.click , it works well. But when I add a Print() to demonstrate the generated package information,I get error:UDPGen has 0 output. How to deal with it?  Thank you very much.

the example is:
elementclass UDPGen {
  $device, $rate, $limit, $size,
  $seth, $sip, $sport, $deth, $dip, $dport |

  source :: FastUDPSource($rate, $limit, $size, $seth, $sip, $sport,
                                                $deth, $dip, $dport);
  pd :: PollDevice($device) -> ToHost;
  source -> td :: ToDevice($device);
}

// create a UDPGen

u :: UDPGen(eth1, 82000, 820000, 1500,
	    00:e0:29:05:e2:d4, 2.0.0.2, 1234,
	    00:c0:95:e2:09:14, 1.0.0.2, 1234);


-------------------------------------------------------------------------------------AOC(¹Ú½Ý)17´çÒº¾§16ms£¤2888 http://design.163.com/aocmonitor/index.html